THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC …ourspace.uregina.ca/bitstream/handle/10294/5312/Zoubeik_Mohame… · Mr. Mohamed Farag Zoubeik, candidate for the degree of Mater

i

THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC LIQUIDS FOR

CARBON DIOXIDE CAPTURE

A Thesis

Submitted to the Faculty of Graduate Studies and Research

In Partial Fulfillment of the Requirements

For the Degree of

Master of Applied Science

In

Industrial Systems Engineering

University of Regina

By

Mohamed Farag Zoubeik

Regina, Saskatchewan

July, 2013

Copyright 2013: M. Zoubeik

UNIVERSITY OF REGINA

FACULTY OF GRADUATE STUDIES AND RESEARCH

SUPERVISORY AND EXAMINING COMMITTEE

Mr. Mohamed Farag Zoubeik, candidate for the degree of Mater of Applied Science in Industrial Systems Engineering, has presented a thesis titled, Thermodynamic and Experimental Studies of ionic Liquids for Carbon Dioxide Capture, in an oral examination held on July 25, 2013. The following committee members have found the thesis acceptable in form and content, and that the candidate demonstrated satisfactory knowledge of the subject material. External Examiner: Dr. David deMontigny, Process Systems Engineering

Supervisor: Dr. Amr Henni, Industrial Systems Engineering

Committee Member: Dr. Mohamed Ismail, Industrial Systems Engineering

Committee Member: Dr. Mohamed El-Darieby, Software Systems Engineering

Chair of Defense: Dr. Lisa Watson, Faculty of Business Administration

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Abstract

One of the biggest environmental challenges of our generation is global warming.

Emission of carbon dioxide (CO2) is possibly the most significant greenhouse gas activity

implicated in climate change. As a result, the development of environmentally friendly,

energy efficient and economic capture technologies for CO2 from flue gas is becoming a

hot topic. There have been an evolution of ideas surrounding capture modalities for CO2;

however, none without drawbacks. Ionic Liquids (ILs) offer the potential for a cleaner

capture technology compared to current chemical solvents.

There is a gap in the industrial applied knowledge and data regarding

thermodynamic and physical properties of ionic liquids. The objective of this research

study is to investigate ionic liquids and their potential for CO2 capture at different

concentrations and temperatures. CO2 solubility was obtained using an Intelligent

Gravimetric Analyzer (IGA 003, Hiden Analytical) for the following seven ionic liquids:

1,2,3-Tris(diethylamino) cyclopropenylium dicyanamide, 1-Ethyl-3-methylimidazolium

L-(+)- lactate, 3-Methyl-1-propylpyridinium bis [(trifluoromethyl) sulfonyl]imide,

Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide, 1,2,3-

Tris(diethylamino)cyclopropenylium bis(trifluoromethanesulfonyl)imide, 1-(4-

Sulfobutyl) -3-methylimidazolium Bis(trifluoromethanesulfonyl)imide, 1-(4-Sulfobutyl)-

3-methylimidazolium hydrogen sulfate. Carbon dioxide solubility was obtained at

temperatures of 313.15, 323.15 and 333.15K over a pressure range from 100 mbar to

20,000 mbar. The thermodynamic models used to correlate the experimental CO2

solubility included equations of state, such as the Peng-Robinson (PR-EoS), Sove-

Redlich-Kwong (SRK) with quadratic mixing rules, and Non-Random Two-Liquid

ii

(NRTL) activity coefficient model. Binary interaction parameters were obtained for the

correlations. All models produced low values for their average absolute deviations,

implying they can satisfactorily describe the solubility of CO2 in ionic liquids. The

solubility of CO2 in all the ionic liquids under study, decreased with increasing

temperature and increased with increasing pressure. Carbon dioxide solubility decreased

in the following order: [TCD][TF2N] > [PMPY][TF2N] > [EMMP][TF2N] >

[emim][LACTATE] > [TCD][DCN] > [(CH2)4SO3HMIm][TF2N] >

[(CH2)4SO3HMIm] [HSO4]. The three ionic liquids, [TCD][TF2N], [PMPY][TF2N]

and [EMMP][TF2N], show promise with respect to CO2 absorption as they have a similar

solubility pattern to some ionic liquids published in the literature that are noted for their

high solubility, such as [hmim][TF2N], which are comparable in terms of their physical

absorption. Furthermore, Henry’s Law constants for CO2 were determined from the ionic

liquids. The enthalpies and entropies of absorption were also calculated.

iii

Acknowledgments

First and foremost, I would like to give thanks to the Al-mighty Allah for giving me the

opportunity to study in Canada and for providing my health and many blessings. Without

the blessings from Allah none of this would have been possible.

I would like to thank my supervisor, Dr. Amr Henni, for accepting me as a graduate

student and providing the opportunity to come to Saskatchewan. I would also like to

thank him for his support and guidance throughout my studies. My grateful thanks are

extended to Dr. David deMontigny, Dr. Mohamed Ismail, and Dr. Mohamed El-Darieby,

my thesis committee.

I would like to thank my colleagues, Thanawat Nonthanasin and Kazi Zamshad Sumon,

for their support and training throughout my whole research experience, their expertise

was invaluable.

Additionally, I would like to thank the support of the CBIE (Canadian Bureau of

International Education) and the Libyan government for their support and funding of my

studies.

In addition, I would like to thank my parents, my brothers and my sisters, for their

continued support and prayers throughout my studies abroad. I would also like to thank

Dr. Fauzi and Nazmia Ramadan, my in-laws, for their unwavering support and

continuous prayers for my success. I would also like to thank Ahmed Ramadan, my

brother, who helped me settle and make Regina my home.

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Dedication

Dedicated to my mum, Keria Abd Aslam and my wife, Dr. Eman Ramadan for their

support and love.

iii

Table of Content

ABSTRACT ··························································································· I

ACKNOWLEDGMENTS······································································· III

DEDICATION ···················································································· IV

TABLE OF CONTENT ········································································· III

TABLE OF FIGURES ········································································· VIII

TABLE OF TABLES ········································································· XVII

LIST OF SYMBOLS AND ABBREVIATIONS ······································· XXVI

1 CHAPTER ONE: INTRODUCTION AND BACKGROUND THEORY ··· 1

1.1 INTRODUCTION ············································································· 1

1.2 OBJECTIVE OF THIS RESEARCH UNDERTAKING ······································· 1

1.3 BACKGROUND ·············································································· 2

1.3.1 Sources Of CO2 Emissions ···························································· 2

1.4 CAPTURE OF CO2 ·········································································· 2

1.4.1 Capture Systems For CO2: Pre, Oxy, And Post-Combustion ···················· 2

1.5 IONIC LIQUID CAPTURE TECHNOLOGY ·················································· 4

1.5.1 What Are Ionic Liquids? ······························································ 4

1.5.2 Synthesis Of Ionic Liquids ···························································· 5

1.5.3 What Are The Categories Of Ionic Liquids? ······································· 6

1.6 HISTORY OF IONIC LIQUID USE FOR CO2 CAPTURE AND THE DEVELOPMENT OF

IONIC LIQUIDS ······················································································ 8

1.6.1 Before The Development Of Ionic Liquids ········································· 8

iv

1.6.2 History And New Developments Of Ionic Liquids ································ 8

1.7 THERMOPHYSICAL PROPERTIES OF IONIC LIQUIDS ··································· 10

1.7.1 Physical Properties Of Ionic Liquids ··············································· 10

1.8 CO2 SOLUBILITY IN IONIC LIQUIDS AND FACTORS THAT AFFECT SOLUBILITY ·· 13

1.9 NEW DEVELOPMENTS IN THE PURSUIT OF THE PERFECT IONIC LIQUID:

LITERATURE REVIEW ············································································· 19

1.10 OUTLINE OF THE CHAPTERS ···························································· 26

2 CHAPTER TWO: GENERAL METHODOLOGY, THEORY AND

EXPERIMENTAL DETAILS ·································································· 27

2.1 METHODS FOR GAS SOLUBILITY MEASUREMENTS ··································· 27

2.1.1 Pressure Drop Technique For Measuring CO2 Solubility ······················· 27

2.1.2 Stoichiometric Technique For Measuring CO2 Solubility ······················· 28

2.1.3 Gravimetric Method For Measuring CO2 Solubility ····························· 29

2.1.4 Gravimetric Method: Buoyancy Correction Factor ······························ 31

2.1.5 Calculation Of Buoyancy Correction Factor ······································ 32

2.2 THERMODYNAMIC PROPERTIES ························································· 34

2.2.1 Derivation For Henry’s Law Constants ············································ 34

2.2.2 Derivation For Enthalpy And Entropy Of Absorption ··························· 35

2.3 MATERIALS ················································································ 37

2.3.1 Ionic Liquids ··········································································· 37

2.3.2 Ionic Liquid Treatment And Equilibrium Time ··································· 39

2.3.3 Selection Of Ionic Liquids ··························································· 41

2.3.4 Gases ···················································································· 42

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2.4 GRAVIMETRIC MICROBALANCE ························································· 42

2.5 EXPERIMENTAL PROCEDURE ···························································· 44

2.6 SUMMARY OF EXPERIMENTAL PROCEDURES ········································· 45

2.7 ACCOUNTING FOR BUOYANCY ·························································· 48

2.8 ENSURING EQUILIBRIUM ································································· 48

2.9 ERROR ANALYSIS ········································································· 49

3 CHAPTER THREE: RESULTS AND DISSCUSION ·························· 50

3.1 DENSITY OF PURE IONIC LIQUIDS ······················································ 50

3.2 SOLUBILITY OF CARBON DIOXIDE ····················································· 53

3.2.1 Verification Of Measurements ······················································ 53

3.2.2 Experimental Isotherm CO2 Solubility ············································· 54

3.3 SOLUBILITY ISOTHERMS GRAPHS ······················································· 58

3.3.1 Solubility Of CO2 In [EMMP][TF2N] ············································· 58

3.3.2 Solubility Of CO2 In [TDC] [TF2N] ··············································· 59

3.3.3 Solubility Of Co2 In [PMPY] [TF2N] ·············································· 60

3.3.4 Solubility Of CO2 In [TDC] [DCN] ················································ 61

3.3.5 Solubility Of CO2 In [EMIM] [LACTATE] ······································· 62

3.3.6 Solubility Of CO2 In [(CH2)4SO3HMIm][TF2N] And

[(CH2)4SO3HMIm][HSO4] ································································· 63

3.4 RESULTS: EFFECTS OF CATION WITH [TF2N] ANION ······························· 64

3.4.1 Discussion: Effects Of Cation With [TF2N] Anion ······························ 65

3.5 RESULTS: EFFECTS OF ANION WITH [TDC] CATION ································ 66

3.5.1 Discussion Results: Effects Of Anion With [TDC] Cation ····················· 67

vi

3.6 RESULTS: COMPARISON OF THE [DCN] ANION WITH DIFFERENT CATIONS ····· 68

3.6.1 Discussion: Comparison Of The [DCN] Anion With Different Cations ······ 69

3.7 COMPARISON OF ALL THE IONIC LIQUIDS STUDIED ································· 70

3.8 COMPARISONS OF CURRENT WORK WITH PREVIOUSLY PUBLISHED WORK ······ 72

3.8.1 Effect Of Changing The Cation ····················································· 73

3.8.2 Effect Of Changing The Anion With An [Emim] Cation ······················· 79

3.9 COMPARING THE LITERATURE WITH [BMIM][AC] ··································· 80

3.10 COMPARISON OF AMMONIUM BASED IONIC LIQUID FROM THE LITERATURE AND

CURRENT WORK ·················································································· 81

3.11 COMPARING THE CURRENT WORK WITH RECENT RESULTS FROM AN AFFILIATED

GROUP ······························································································ 84

4 CHAPTER FOUR: MODELING ··················································· 96

4.1 THEORY OF THERMODYNAMIC PROPERTIES AND MODELING ······················ 96

4.1.1 Peng Robinson Eos ···································································· 97

4.1.2 Soave-Redlich-Kwong (The SRK With Quadratic Mixing Rules) ············· 98

4.1.3 NRTL Activity Coefficient Method ·············································· 100

4.2 THERMODYNAMIC MODELING ························································ 101

4.2.1 Critical Property Estimation ······················································· 101

4.2.2 Modified Lydersen‐Joback‐Reid Method ········································ 101

4.2.3 Calculated Density And Deviation %Δp From Experimental Density ······ 103

4.3 EQUATION OF STATE ·································································· 107

4.3.1 The Standard Peng-Robinson (PR-Eos) ·········································· 107

4.3.2 Modeling Graphs Using PR-Eos For All Ils ····································· 109

vii

4.3.3 The Soave-Redlich-Kwong (SRK) With Quadratic Mixing Rules ··········· 116

4.3.4 Modeling Graphs Using SRK -Eos For All Ils ·································· 117

4.3.5 Non-Random Two Liquid Segment Activity Coefficient (NRTL) ··········· 122

4.3.6 Modeling Graphs Using NRTL For All Ils ······································ 124

4.4 HENRY’S LAW CONSTANTS ··························································· 131

4.5 ENTHALPIES AND ENTROPIES OF ABSORPTION ····································· 133

5 CHAPTER FIVE: CONCLUSION ··············································· 134

REFERENCES ··················································································· 137

6 APPENDIX ············································································ 143

6.1 RAW DATA FOR GAS SOLUBILITY MEASUREMENTS USING THE GRAVIMETRIC

MICROBALANCE ················································································· 143

6.2 MODELING RESULTS ··································································· 158

6.3 HENRY’S LAW CONSTANTS AND ENTHALPIES AND ENTROPIES OF ABSORPTION

184

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Table of Figures

Figure 1.1: Block diagrams illustrating post-combustion, pre-combustion, and oxy-

combustion systems (Figueroa et al., 2007)........................................................................ 3

Figure 1.2: Common routes for the preparation of ionic liquids (Arshad, 2009). .............. 5

Figure 1.3: Common anions and cations that make up ionic liquids (Ramdin et al., 2012).

............................................................................................................................................. 7

Figure 1.4: The effect of an anion on viscosity for a common [bmim] cation (Ramdin et

al., 2012). .......................................................................................................................... 12

Figure 1.5: the effect of alkyl chain length on viscosity for all IL classes (Ramdin et al.,

2012). ................................................................................................................................ 12

Figure 1.6: The effect of changing the cation on CO2 solubility (Ramdin et al., 2012). .. 15

Figure 1.7: CO2 solubility in [bmim][PF6] at 283.15, 298.15, and 273.15 K (10, 25 and 50

C) (Anthony et al., 2002). ............................................................................................... 16

Figure 1.8: Effect of fluorination on CO2 solubility (Ramdin et al., 2012). ..................... 17

Figure 1.9: The effect of the alkyl chain length on CO2 solubility (Ramdin et al., 2012).19

Figure 1.10: Comparison of the solubility of CO2 in different ionic liquids at 313 K: (■)

THEAL; (●) [bmim][PF6]; (▲) [omim][PF6]; (▼) [Nbupy][BF4]; (♦) [emim][EtSO4]

(Yuan et al., 2007). ........................................................................................................... 24

Figure 2.1: Pressure drop technique for measuring CO2 solubility (Brennecke et al, 2008).

........................................................................................................................................... 28

Figure 2.2: Stoichiometric gas solubility apparatus (Brennecke et al., 2008). ................. 29

Figure 2.3: Schematic diagram of IGA003 gravimetric microbalance. Symbols: arrow B

indicates direction due to buoyancy on the sample side of the balance, arrow Wg

ix

indicates direction of weight due to gravity on the sample side of the balance, additional

symbols described in Table 1 (Shiflett and Yokozeki, 2005). .......................................... 30

Figure 2.4: IGA apparatus (http://www.zpph.com/userfiles/file/iga_series_brochure.pdf)

........................................................................................................................................... 31

Figure 2.5:[TDC] [DCN] equilibrium under 1000 millibars and 40

°C............................ 39

Figure 2.6: [EMIM] [LACTATE] equilibrium under 1000 millibars pressure at 40

°C. . 40

Figure 2.7: Gravimetric microbalance .............................................................................. 43

Figure 2.8: Schematic of the gravimetric microbalance ................................................... 44

Figure 2.9: Experimental procedure followed when using IGA ....................................... 45

Figure 2.10: [TDC] [TF2N] equilibrium providing at high pressure................................ 48

Figure 3.1: Liquid density of the studied ionic liquids at temperatures ranging from

278.15 K to 353.15 K. ....................................................................................................... 52

Figure 3.2: Solubility of CO2 in [bmim][PF6] at 323.15 K compared to the solubility data

result this work with previously published results : ● [bmim][PF6],green this work; ■

[bmim][PF6],red, (Shiflett, 2005); ▼[bmim][PF6],blue, (Anthony et al., 2002). ........... 53

Figure 3.3: Comparison of measured isothermal solubility data of CO2 in

[EMMP][TF2N] at 313.15, 323.15 and 333.15 K. ........................................................... 58

Figure 3.4: Comparison of measured isothermal solubility data of CO2 in [TDC][TF2N]

at 313.15, 323.15 and 333.15 K. ....................................................................................... 59

Figure 3.5: Comparison of measured isothermal solubility data of CO2 in [PMPY][TF2N]

at 313.15, 323.15 and 333.15 K. ....................................................................................... 60

Figure 3.6: Comparison of measured isothermal solubility data of CO2 in [TDC][DCN] at

313.15, 323.15 and 333.15 K. ........................................................................................... 61

x


[EMIM][LACTATE] at 313.15, 323.15 and 333.15 K. .................................................... 62


[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and

333.15 K. ........................................................................................................................... 63

Figure 3.9: Comparison of three ionic liquids with the same anion to illustrate the effect

of the cation at 313 K. ....................................................................................................... 64

Figure 3.10: Comparison of CO2 solubility of [TDC] with [TF2N] and [DCN] at 313.15

K ........................................................................................................................................ 67

Figure 3.11: Comparison of CO2 solubility of [TDC] with [bmim] cations with same

anion at 313.15 K. ............................................................................................................. 69

Figure 3.12: Comparison of measured isothermal solubility data of CO2 in different ionic

liquids at 313.15 K ............................................................................................................ 70

Figure 3.13: Comparison of [emim][Ac] and [emim][LACTATE] at 50°C. ................... 72

Figure 3.14: Comparison of CO2 solubility at 333.15 K with different cations paired with

the [TF2N] anion............................................................................................................... 74

Figure 3.15: Comparison of CO2 solubility at 60°C with different cations paired with the

[TF2N] anion at 333.15 K and about 12 to 14.97 bar. ...................................................... 75

Figure 3.16: Comparison of CO2 solubility in different ILs with the same anion at 323.15

K ........................................................................................................................................ 77

Figure 3.17: Comparison of changing the anion with limidazoloium cation ................... 79

Figure 3.18: Comparison between the solubility of CO2 in the studied ionic liquids and

published results in the literature at 323.15 K .................................................................. 81

xi


the published results in the literature at 323.15 K and high pressure from 1 to 120 bar. . 82

Figure 3.20: Comparison of CO2 solubility at 323.15 K .................................................. 86

Figure 3.21: Comparison of CO2 solubility at 323.15 K ................................................... 87

Figure 3.22: CO2 solubility comparing the ionic liquids used in this work with that of

Nonthanasin (2013) ........................................................................................................... 88

Figure 3.23: Comparison of the solubility of CO2 in the studied ionic liquids and the one

in the present research at 313.15 K. .................................................................................. 89

Figure 3.24: Comparison of the solubility of CO2 in the studied ionic liquids and Uygur,

2013 at 323.15 K. .............................................................................................................. 90

Figure 3.25: Comparison of the solubility of CO2 in the studied ionic liquids and the ones

in our group at 323.15 K. .................................................................................................. 91

Figure 3.26: CO2 solubility of different best ionic liquid in this work, (Ugyur, 2013) and

(Nonthanasin, 2013) at 323.15 K. ..................................................................................... 92

Figure 3.27: Summary of the CO2 solubilities in decreasing order from this work, (Ugyur,

2013) and (Nonthanasin, 2013) at 323.15 K at same pressure 19 bar. ............................. 94

Figure 4.1: P-x diagram of the system [EMMP][TF2N] and CO2 with isothermal data.

Symbols represent the experimental dotted line at 313.15 K; at 323.15 K; red and, at

333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at 313.15

K; blue, at 323.15 K; red and at 333.15 K; green. .......................................................... 109

Figure 4.2: P-x diagram of the system [PMPY][TF2N] and CO2 with isothermal data.

Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red and, at

xii


K; blue, at 323.15 K; red and at 333.15K; green. ........................................................... 110

Figure 4.3: P-x diagram of the system [TDC][TF2N] and CO2 with isothermal data.




Figure 4.4: P-x diagram of the system [TDC][DCN] and CO2 with isothermal data.




Figure 4.5: P-x diagram of the system [EMIM][LACTATE] and CO2 with isothermal

data. Symbols represent the experimental dotted line at 313.15 K; Blue at 323.15 K; red

and, at 333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at

313.15 K; blue, at 323.15 K; red and at 333.15K; green. ............................................... 113

Figure 4.6: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]] and CO2 with

isothermal data. Symbols represent the experimental dotted line at 313.15 K; Blue at

323.15 K; red. Solid lines represent the estimations by the standard PR-EoS: at 313.15 K;

blue, at 323.15 K; red. ..................................................................................................... 114

Figure 4.7: P-x diagram of the system [(CH2)4SO3HMIm][HSO4] and CO2 with



blue, at 323.15 K; red. ..................................................................................................... 115

xiii



333.15 K; green. Solid lines represent the estimations by the SRK with quadratic mixing

rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. ................................ 117



333.15 K, green. Solid lines represent the estimations by the SRK with quadratic mixing










Figure 4.12: P-x diagram of the system [EMIM][LCATATE] and CO2 with isothermal


and, at 333.15 K; green. Solid lines represent the estimations by the SRK with quadratic

mixing rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green. .................... 121



xiv

333.15 K; green. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at

323.15 K; red and at 333.15 K; green. ............................................................................ 124















and, at 333.15 K; green. Solid lines represent the estimations by NRTL: at 313.15 K;

blue, at 323.15 K; red and at 333.15 K; green. ............................................................... 128

Figure 4.18: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]and CO2 with


323.15 K; red. Solid lines represent the estimations by the NRTL: at 313.15 K; blue, at

323.15 K; red. ................................................................................................................. 129

xv

Figure 4.19: P-x diagram of the system [(CH2)4SO3HMIm][HSO4]and CO2 with



323.15 K; red. ................................................................................................................. 130

Figure 4.20: Henry’s law constants for CO2 in [EMMP][TF2N], [PMPY][TF2N],

[TDC][TF2N], [TDC][DCN], [EMIM][LACTATE], [(CH2)4SO3HMIm][TF2N] and

[(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and 333.15 K ....................................... 132

Figure 6.1: Determining the Henry’s law constant for CO2 in [bmim][PF6] ................. 185

Figure 6.2: Determining the enthalpy of absorption for CO2 in [bmim][PF6] ............... 185

Figure 6.3: Determining the entropy of absorption for CO2 in [bmim][PF6] ................. 186

Figure 6.4: Determining the Henry’s law constant for CO2 in [Emmp][TF2N] ............. 188

Figure 6.5: Determining the entropy of absorption for CO2 in [Emmp][TF2N] ............ 189

Figure 6.6: Determining the entropy of absorption for CO2 in [Emmp][TF2N] ............ 190

Figure 6.7: Determining the Henry’s law constant for CO2 in [PMPY][TF2N] ............ 192

Figure 6.8: Determining the enthalpy of absorption for CO2 in [PMPY][TF2N] .......... 193

Figure 6.9: Determining the entropy of absorption for CO2 in [PMPY][TF2N] ............ 194

Figure 6.10: Determining the Henry’s law constant for CO2 in [TDC][TF2N] ............. 196

Figure 6.11: Determining the enthalpy of absorption for CO2 in [TDC][TF2N] ........... 197

Figure 6.12: Determining the entropy of absorption for CO2 in [TDC][TF2N] ............. 197

Figure 6.13: Determining the Henry’s law constant for CO2 in [TDC][DCN] .............. 199

Figure 6.14: Determining the enthalpy of absorption for CO2 in [TDC][DCN] ............ 200

Figure 6.15: Determining the entropy of absorption for CO2 in [TDC][DCN] .............. 201

Figure 6.16: Determining the Henry’s law constant for CO2 in [EMIM][LACTATE] .. 203

xvi

Figure 6.17: Determining the enthalpy of absorption for CO2 in [EMIM][LACTATE] 203

Figure 6.18: Determining the entropy of absorption for CO2 in [EMIM][LACTATE] . 204

Figure 6.19: Determining the Henry’s law constant for CO2 in [(CH2)4SO3HMIm]

[HSO4] ............................................................................................................................ 206

Figure 6.20: Determining the enthalpy of absorption for CO2 in [(CH2)4SO3HMIm]

[HSO4] ............................................................................................................................ 207

Figure 6.21: Determining the entropy of absorption for CO2 in [(CH2)4SO3HMIm]

[HSO4] ............................................................................................................................ 208

Figure 6.22: Determining the Henry’s law constant for CO2 in

[(CH2)4SO3HMIm][TF2N] ........................................................................................... 210

Figure 6.23: Determining the enthalpy of absorption for CO2 in

[(CH2)4SO3HMIm][TF2N] ........................................................................................... 211

Figure 6.24: Determining the entropy of absorption for CO2 in

[(CH2)4SO3HMIm][TF2N] ........................................................................................... 212

xvii

Table of Tables

Table 2-1: Microbalance components for buoyancy correction ....................................... 33

Table 2-2: Ionic liquids studied with their short hand notation and structure. ................. 37

Table 2-3: Ionic liquids used and their specifications: ..................................................... 38

Table 2-4: Calculation of weight lost for each ionic liquid at 313.15K and the percent

impurity lost ...................................................................................................................... 46

Table 3-1: Experimental densities of pure ionic liquids measured at 1.01325 bar ........... 51

Table 3-2: Temperature-dependent density correlations for the ionic liquids .................. 52

Table 3-3: CO2 solubility for all ionic liquids that used in this experiment: (T,P X) data

for [TDC][DCN] (1) + CO2 at 313.15, 323.15 and 333.15 K. ......................................... 54


for [PMPY][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ..................................... 55


for [EMMP][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ..................................... 55


for [TDC][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ......................................... 56


for [EMIM][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K. ...................................... 56


for [[(CH2)4SO3HMIm][TF2N]] (1) + CO2 at 313.15, 323.15 and 333.15 K. ................ 57


for [(CH2)4SO3HMIm][HSO4] (1) + CO2 at 313.15, 323.15 and 333.15 K. .................. 57

Table 3-10: Numerical representation summary of the IL seen in Figure 3.14 ................ 75

xviii

Table 3-11: Comparison of [emim] cation with different anions. .................................... 80

Table 3-12: Summary of the CO2 solubilities in decreasing order from this work, Ugyur

(2013) and Nonthanasin (2013) at 323.15 K and same pressure 19 bar. .......................... 93

Table 4-1: Molecular weights, normal boiling temperatures, critical properties, and

acentric factors of ionic liquids ....................................................................................... 103

Table 4-2: Regressed and Experimental Density Data of [EMMP] [TF2N] by using

Modified Group Contribution Method............................................................................ 103

Table 4-3: Regressed and Experimental Density Data of [PMPY] [TF2N] by using


Table 4-4: Regressed and Experimental Density Data of [TDC] [TF2N] by using


Table 4-5: Regressed and Experimental Density Data of [EMIM] [LACTATE] by using


Table 4-6: Regressed and Experimental Density Data of [TDC] [DCN] by using Modified

Group Contribution Method ........................................................................................... 105

Table 4-7: Regressed and Experimental Density Data [(CH2)4SO3HMIm][TF2N] by

using Modified Group Contribution Method .................................................................. 106

Table 4-8: Regressed and Experimental Density Data [(CH2)4SO3HMIm][HSO4] ..... 106

Table 4-9: Average absolute deviation (AAD %) between experimental and estimated

values of pressure by the standard PR-EoS for the ionic liquids + CO2 system ............. 108

Table 4-10: Binary interaction parameters of the standard PR-EoS for the ionic liquids (1)

+ CO2 (2) system. ............................................................................................................ 108

xix


values of pressure by the SRK with quadratic mixing rules for the ionic liquids + CO2

system ............................................................................................................................. 116

Table 4-12: Binary interaction parameters of the SRK with quadratic mixing rules for the

ionic liquids (1) + CO2 (2) system .................................................................................. 117


values of pressure by the NRTL for the ionic liquids + CO2 system .............................. 122

Table 4-14: Binary interaction parameters of the NRTL for the ionic liquids (1) + CO2 (2)

system (α = 0.3) .............................................................................................................. 123

Table 4-15: Henry’s law constants and enthalpies and entropies of absorption for CO2 in

the studied ionic liquids .................................................................................................. 132

Table 6-1: Carbon dioxide in [Emmp][TF2N] at 313.15 K ........................................... 143

Table 6-2: Carbon dioxide in [Emmp][TF2N] at 323.15 K ............................................ 144

Table 6-3: Carbon dioxide in [Emmp][TF2N] at 333.15 K ............................................ 145

Table 6-4: Carbon dioxide in [Pmpy][TF2N] at 313.15 K ............................................. 146



Table 6-7: Carbon dioxide in [TDC][TF2N] at 313.15 K .............................................. 149



Table 6-10: Carbon dioxide in [EMIM][LACTATE] at 313.15 K ................................. 152



xx

Table 6-13: Carbon dioxide in [TDC][DCN] at 313.15 K.............................................. 154

Table 6-14: Carbon dioxide in [TDC][DCN] at 323.15 K.............................................. 155

Table 6-15: Carbon dioxide in [(CH2)4SO3HMIm][TF2N]at 313.15 K ....................... 155

Table 6-16: Carbon dioxide in [(CH2)4SO3HMIm][TF2N] at 323.15 K ...................... 156

Table 6-17: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K ....................... 156

Table 6-18: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K ....................... 157

Table 6-19: Modeling solubility using Peng-Robinson (PR-EoS) (P, X) data for

[EMMP][TF2N] (1) + CO2 (2) system at 313.15 K........................................................ 158






[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K ........................................................ 159




[PMPY][TF2N] (1) + CO2 (2) system at 333.15 K ......................................................... 160

Table 6-25: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][TF2N]

(1) + CO2 (2) system at 313.15 K. .................................................................................. 161


(1) + CO2 (2) system at 323.15 K ................................................................................... 161

xxi


(1) + CO2 (2) system at 333.15 K ................................................................................... 162

Table 6-28: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN

(1) + CO2 (2) system at 313.15 K ................................................................................... 163

Table 6-29: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN]

(1) + CO2 (2) system at 323.15 K. .................................................................................. 163


(1) + CO2 (2) system at 333.15 K ................................................................................... 164

Table 6-31: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for

[EMIM][LACTATE ](1) + CO2 (2) system at 313.15 K ................................................ 164






[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 313.15 K .................................... 165


[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 323.15 K .................................... 166


[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 313.15 K .................................... 166


[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 323.15 K .................................... 167

xxii

Table 6-38: Modeling solubility using SRK+ quadratic mixing rules (P, X) data for







[TDC][TF2N] (1) + CO2 (2) system at 313.15 K ........................................................... 169






[TDC][DCN] (1) + CO2 (2) system at 313.15 K ............................................................ 170


[TDC][DCN] (1) + CO2 (2) system at 323.15 K. ........................................................... 171


[TDC][DCN] (1) + CO2 (2) system at 333.15 K. ........................................................... 171


[EMIM][LACTATE] (1) + CO2 (2) system at 313.15 K. ............................................... 172


[EMIM][LACTATE] (1) + CO2 (2) system at 323.15 K. ............................................... 172

xxiii


[EMMP][LACTATE] (1) + CO2 (2) system at 333.15 K. .............................................. 173

Table 6-50: Modeling solubility using NRTL (P, X) data for [EMMP][TF2N] (1) + CO2

(2) system at 313.15 K. ................................................................................................... 173


(2) system at 323.15 K. ................................................................................................... 174


(2) system at 333.15 K. ................................................................................................... 174

Table 6-53: Modeling solubility using NRTL (P, X) data for [PMPY][TF2N] (1) + CO2

(2) system at 313.15 K. ................................................................................................... 175


(2) system at 323.15 K. ................................................................................................... 175


(2) system at 333.15 K. ................................................................................................... 176

Table 6-56: Modeling solubility using NRTL (P, X) data for [TDC][TF2N] (1) + CO2 (2)

system at 313.15 K. ......................................................................................................... 176


system at 323.15 K. ......................................................................................................... 177


system at 333.15 K. ......................................................................................................... 178

Table 6-59: Modeling solubility using NRTL (P, X) data for [TDC][DCN] (1) + CO2 (2)

system at 313.15 K. ......................................................................................................... 178

xxiv


system at 323.15 K. ......................................................................................................... 179


system at 333.15 K. ......................................................................................................... 179

Table 6-62: Modeling solubility using NRTL (P, X) data for [EMIM][LACTATE] (1) +

CO2 (2) system at 313.15 K. ........................................................................................... 180


CO2 (2) system at 323.15 K. ........................................................................................... 180


CO2 (2) system at 333.15 K. ........................................................................................... 181

Table 6-65: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][HSO4]

(1) + CO2 (2) system at 313.15 K. .................................................................................. 181


(1) + CO2 (2) system at 323.15 K. .................................................................................. 182

Table 6-67: Modeling solubility using NRTL (P, X) data for [(CH2)4SO3HMIm][TF2N]]

(1) + CO2 (2) system at 313.15 K. .................................................................................. 182


(1) + CO2 (2) system at 323.15 K. .................................................................................. 183

Table 6-69: Experimental fugacity of CO2 in [bmim][PF6] (Shiflett, 2005) at 283.15 K

......................................................................................................................................... 184


......................................................................................................................................... 184

Table 6-71: Experimental fugacity of CO2 in [Emmp][TF2N] at 313.15 And 323.15 K 187

xxv

Table 6-72: Experimental fugacity of CO2 in [Emmp][TF2N] at 333.15 K ................... 188

Table 6-73: Experimental fugacity of CO2 in [PMPY][TF2N] at 313.15 And 323.15 K191

Table 6-74: Experimental fugacity of CO2 in [PMPY][TF2N] at 333.15 K. ................. 192

Table 6-75: Experimental fugacity of CO2 in [TDC][TF2N] at 313.15 And 323.15 K .. 195

Table 6-76: Experimental fugacity of CO2 in [TDC][TF2N] at 333.15 K ..................... 196

Table 6-77: Experimental fugacity of CO2 in [TDC][DCN] at 313.15 And 323.15 K ... 198

Table 6-78: Experimental fugacity of CO2 in [TDC][DCN] at 333.15 K ...................... 199

Table 6-79: Experimental fugacity of CO2 in [EMIM][LACTATE] at 313.15 ,323.15 and

333.15 K .......................................................................................................................... 202

Table 6-80: Experimental fugacity of CO2 in [(CH2)4SO3HMIm] [HSO4] at 313.15 And

323.15 K .......................................................................................................................... 205

Table 6-81: Experimental fugacity of CO2 in [(CH2)4SO3HMIm][TF2N] at 313.15 And

323.15 K .......................................................................................................................... 209

xxvi

List of Symbols And Abbreviations

Abbreviations:

RTILs Room temperature ionic liquids

VLE Vapour-liquid equilibrium

LLE Liquid liquid Equilibrium

SRK Sove-Redlich-Kwong

PR Peng-Robinson

AAD Average absolute deviation

EoS Equation of state

NRTL Non-random two-liquid models

DMA Digital density meter

IGA Intelligent gravimetric analyzer

Greek symbols:

γi Activity coefficient

ρ Density (kg/m3)

∆ represents a change

ω Acentric factor

Subscripts:

1 Component 1

2 Component 2

i i-th component

j j-th component

xxvii

Symbols:

F Fugacity (bar)

H Henry’s constant (bar)

K Kelvin

M Molar mass (g/mole)

Pc Critical pressure (bar)

Zc Critical compressibility factor

Tc Critical temperature (K)

Vc Critical volume (cm3/mol)

Tb Boiling point temperature

R Universal gas constant (cm3.bar/mole .K)

x Mole fraction in liquid phase

∆h Enthalpies

∆s Entropies

Cb Buoyancy

1

1 Chapter One: Introduction And Background Theory

1.1 Introduction

One of the biggest environmental challenges of our generation is global warming.

Emission of carbon dioxide (CO2) is possibly the most significant greenhouse gas activity

implicated in climate change. As a result, the development of environmentally friendly,

energy efficient and economic capture technologies for CO2 is becoming a hot topic.

There has been an evolution of ideas surrounding capture modalities for CO2; however,

none without drawbacks. In the midst of the advances in promising technologies for CO2

capture, ionic liquids (IL) have been given much attention and are regarded as

prospective candidates (MacDowell et al., 2010; Blanchard et al., 1999; Wappel et al.,

2010).

1.2 Objective of This Research Undertaking

There is a gap in the industrial applied knowledge and data regarding the

thermodynamic and physical properties of ionic liquids. There is a need for translation of

this knowledge into large scale industrial applications using simulation models to predict

the behaviors of ionic liquids in industrial applications. The objective of this research

study is to investigate different ionic liquids and their potential capacity for CO2 capture

at different temperatures and pressures. In addition, we hope to find some features and

physical characteristics that would allow us to contribute some knowledge towards the

industrial application of ionic liquids for CO2 capture.

2

1.3 Background

1.3.1 Sources of CO2 Emissions

Human activities, especially activities aimed at energy production, are the principal

sources of CO2 emission, of which fossil fuel combustion comprises the vast majority.

Carbon dioxide is the main greenhouse gas with emissions increasing by 80% from 1970

to 2004 (Pachauri and Reisinger, 2007).

Other than fossil fuels, deforestation produces about 17% of the global emissions

which places it in third place as the largest source of greenhouse gas emissions (Eliasch,

2008). Other sources include the transportation industry and residential and commercial

buildings (Pachauri and Reisinger, 2007).

1.4 Capture of CO2

1.4.1 Capture systems for CO2: Pre, Oxy, and Post-combustion

There are various stages where CO2 can be captured. The research interest of this

project will focus mainly on natural gas sweetening but also, to a lesser extent, post-

combustion CO2 capture from flue gases. Industrial power plants use atmospheric air

which contains about 80% nitrogen from combustion which generates a flue gas at

atmospheric pressure with about 15% CO2 concentration (Figueroa et al., 2007). The

flue gas has a CO2 partial pressure of about 0.15 atm or less, making it technically

challenging to design an effective capture medium (Figueroa et al., 2007). However,

as previously stated, ionic liquids are showing great promise as an effective capture

medium. Their physical properties allow for good CO2 solubility even at low

pressures and the fact that they are stable at high temperatures removes the need to

3

cool the flue gas before CO2 recovery, decreasing operating expenses and energy

expenditures.

Figure 1.1: Block diagrams illustrating post-combustion, pre-combustion, and oxy-

combustion systems (Figueroa et al., 2007).

4

1.5 Ionic Liquid Capture Technology

1.5.1 What Are Ionic Liquids?

Ionic liquids are liquids which are made up of ions. The ions are of two types:

cations and anions. Ionic liquids are different than ionic solutions which are just solutions

of salts in a molecular solvent (Arshad, 2009). Ionic liquids which are liquid at room

temperature are called room temperature ionic liquids (RTIL) (Arshad, 2009). Ionic

liquids are sometimes called liquid organic salts, fused salts or molten salts which are

mainly found in older literature (Arshad, 2009).

The main feature defining the essence of ionic liquids is a melting point of 100ºC

which is made possible by the asymmetry of the cation used in the ionic liquid (Dzyuba

and Bartsch, 2002). On the other hand, the anion is responsible for many of the ionic

liquids’ key physical properties (Dzyuba and Bartsch, 2002). The physical properties of

ionic liquids (melting point, viscosity, density, solubility) can be altered with a specific

task in mind by mixing which cation, anion or substituent is used. Hence the name

“designer solvent” came about (Freemantle, 1998). Ionic liquids have many advantages

over molecular solvents such as very low vapor pressure and thermal stability over a wide

range of temperatures (Arshad, 2009). Ionic liquids are also non-flammable (Arshad,

2009). Ionic liquid fluids are an alternative to volatile conventional solvents and this

leads to a major decrease in the atmospheric release of volatile organic compounds which

are a major source of air pollution (Arshad, 2009). Thus, ionic liquids are a green

beacon of hope for environmentally clean industrial processing of natural and flue gases.

5

1.5.2 Synthesis of Ionic Liquids

The following figure outlines a summary of how a sample ionic liquid is

synthesized.

Figure 1.2: Common routes for the preparation of ionic liquids (Arshad, 2009).

6

1.5.3 What Are The Categories Of Ionic Liquids?

Ionic liquids, previously defined as stable molten salts, can be categorized into

three groups: First generation, second generation, and third generation ionic liquids

(Holbrey and Seddon, 1999).

First Generation: This group encompasses the original ionic liquids that were

pyridinium- and imidazolium-based chloroaluminate ionic liquids (Wilkes, 2002).

They react with water to form HCL and thus are not water stable. They have many

drawbacks which include their reactivity with water which leads to a loss of the ionic

liquid and the production of corrosive byproducts.

Second Generation: This group of ionic liquids was developed as moisture stable

ionic liquids which allowed for easier use and wider applications. It also solved the

issue of corrosive byproducts and loss of ionic liquid. This group includes the first

moisture stable imidazolium salts paired with BF4 and PF6 anions (Wilkes, 1992).

Third Generation: This group is the task specific group of ionic liquids. This new

emerging group of ionic liquids features a special ability, to be tailored based on the

attached functionalities for a specific function or task. This idea of designing ionic

liquids was first proposed by Bates et al. in 2001 (Bates et al., 2001).

The following figure is an example of commonly used anions and cations that

make up ionic liquids (Ramdin et al., 2012).

7

Figure 1.3: Common anions and cations that make up ionic liquids (Ramdin et al.,

2012).

8

1.6 History of Ionic Liquid Use for CO2 Capture And The Development Of Ionic

Liquids

1.6.1 Before The Development of Ionic Liquids

Chemical absorption of CO2 by a weakly basic solution of monoethanolamine

(MEA) is, historically, one of the most popular industrial process for CO2 capture

(Sánchez, 2008). MEA was developed over seventy years ago as a non-specific

solvent to remove acidic gases such as CO2 and H2S from natural gas streams

(Herzog, 1999). However, MEA use had some drawbacks. During the capture

process, the amine group in MEA is broken down (Strazisar et al., 2003). The

byproducts of MEA degradation decrease the efficiency of CO2 capture, leading to

corrosion of machinery and the loss of solvent (Strazisar et al., 2003). When

comparing ionic liquid use with MEA, the use of IL can reduce the energy losses by

16% and provide a 12% reduction in the equipment footprint (Zhang et al., 2012).

The industry sought out a better alternative to MEA that would not increase material

and waste disposal costs (Strazisar et al., 2003). An alternative method to MEA is the

use of chilled ammonia (Wang et al., 2010). Ammonia also has its own set of

drawbacks. The low temperatures needed to minimize solvent losses lead to increased

energy expenditures and higher operating costs (Wang et al., 2010). Hence, there was

a large need by industry to revolutionize CO2 capture modalities.

1.6.2 History and New Developments of Ionic Liquids

Carbon dioxide capture took on a new life with the development of ionic liquids

as a solvent medium for absorption. The extremely low vapor pressure of ionic

liquids makes them non-volatile which is a major advantage (Sánchez, 2008). The

9

new development this kind of solvent allows for decreased solvent losses and thus

lower operating costs and a cleaner gaseous product (Sánchez, 2008). There were

issues with reactivity with water when ionic liquids first came about. The pyridinium-

and imidazolium-based chloroaluminate ionic liquids predated the moisture stable

salts. The ILs reacted with water (Wilkes, 2002) and produced a corrosive byproduct

(HCL). Zaworotko first proposed the idea of developing water stable ionic liquids in

1990 (Wilkes, 2002). He wanted to develop ionic liquids with dialkylimidazolium

cations and water-stable anions (Wilkes, 2002). They were able to produce moisture

stable imidazolium salts paired with BF4 and PF6 anions (Wilkes, 1992).

A research group used room temperature ionic liquids (RTILs) for CO2 capture in

1999 (Blanchard et al., 1999). They determined CO2 is highly soluble in 1-butyl-3-

methylimidazolium hexafluorophosphate ([bmim][PF6]) ILwhich triggered the

potential for CO2 separation (Blanchard et al., 1999; Baltus et al., 2005). Another

research team created a model that would predict the thermodynamic interactions

between a gas and ionic liquid (Shiflett and Yokozeki, 2005). They wanted to develop

a thermodynamic model that would allow testing of gas solubility under a wider

range of pressures, temperatures and different ionic liquid compositions (Shiflett and

Yokozeki, 2005). Shiflett and Yokozeki examined CO2 solubility with l-n-butyl-3-

methylimidazolium hexafluorophosphate ([bmim][PF6]) and l-n-butyl-3-

methylimidazolium tetrafluoroborate ([bmim]-[BF4]) (Shiflett and Yokozeki, 2005).

They tested the solubility of CO2 from 283.15 to 348.15 K and for pressures up to 2.0

MPa (Shiflett and Yokozeki, 2005). Their proposed thermodynamic model was an

equation of state (EoS) (Shiflett and Yokozeki, 2005). Since then, the use of ionic

10

liquids has been spreading and research into this potentially lucrative idea has

skyrocketed.

1.7 Thermophysical Properties of Ionic Liquids

1.7.1 Physical Properties of Ionic Liquids

Melting Point: One of the notable features of ionic liquids is that they have

melting points below 100°C and most of them are liquid at room temperature

(Arshad, 2009). Cations and anions play a role in creating this low melting point

property (Arshad, 2009). The increase in anion size leads to a decrease in melting

point (Wasserscheid & Keim, 2000). Other features of the ionic liquid such as the

length of the alkyl chain length can have an effect on the melting point (Gordon et

al., 1998). The melting point of salts increased to some extent with increasing

alkyl chain length (Gordon et al., 1998). The type of cation base can also affect

the melting point where the pyridinium cation produces higher melting points

than imidazolium salts of equivalent alkyl chain length cations (Gordon et al.,

1998).

Density: Ionic liquids are denser than water with density readings ranging from 1 to

1.6 g/cm3 (Arshad, 2009). Their densities decrease with an increase in the length of

the alkyl chain attached to the cation (Arshad, 2009). Density also decreases with an

increase in temperature (Meindersma et al., 2007). The relationship between density

and temperature was further demonstrated by Kim et al. who examined the density of

the following ionic liquids and calculated the densities using the group contribution

equation of state: [bmim][PF6], [C6mim][PF6], [emim][BF4], [C6mim][BF4],

11

[emim][TF2N] and [C6mim][TF2N] (Kim et al., 2005). They examined the density

over a range of temperatures from 293 to 343 K (Kim et al., 2005). Their findings

show that an increase in the temperature and alkyl chain length of an ionic liquid

leads to a decrease in density (Kim et al., 2005).

Viscosity: One of the drawbacks of ionic liquids is an increase in viscosity when

exposed to carbon dioxide (Gutowski and Maginn, 2008). Extensive research has

focused exclusively on finding a solution to this problem. Ionic liquids, when

compared to other molecular solvents, are naturally more viscous (Arshad, 2009). The

viscosity of ionic liquids is measured by van der Waals forces and hydrogen bonding

which leads to the formation of salt bridges (Gurkan et al., 2010). Thus, attempts have

been made to limit the available hydrogen bonds in a given ionic liquid in order to

limit the rise in viscosity once it reacts with CO2 (Gutowski and Maginn, 2008). For

example, the viscosity of ionic liquids containing imidazolium-based cations is

determined by the alkyl chain length of the cation, as well as the nature of the anion

used (Arshad, 2009). Viscosity is also affected by the type of anion used in the ionic

liquid (Ramdin et al., 2012). The viscosity increases with the anion in the following

order: [DCN] < [TF2N] < [SCN] < [TfA] < [TfO] < [BF4] < [BETI] < [NO3] <

[MeSO4] < [PF6] < [Ac] (Ramdin et al., 2012). Thus, the research world has many

options for fine-tuning ionic liquids in order to minimize the rise in viscosity with

CO2 fixation. The following graph shows the effect of an anion on viscosity for a

common [bmim] cation (Ramdin et al., 2012).

12

Figure 1.4: The effect of an anion on viscosity for a common [bmim] cation (Ramdin et

al., 2012).

The following graph shows the effect of the alkyl chain length on viscosity for different

ionic liquids with a common bis[(trifluoromethyl)sulfonyl]imide [TF2N] anion (Ramdin

et al., 2012). Viscosity increases with increasing alkyl chain length for all IL classes

(Ramdin et al., 2012).

Figure 1.5: the effect of alkyl chain length on viscosity for all IL classes (Ramdin et al.,

2012).

13

Vapour Pressure: One of the key features that make the use of ionic liquids green is

their almost non-existent vapour pressure. They do not evaporate and thus no solvent

is lost from the reaction vessels and separation equipment, minimizing operational

costs (Bates et al., 2001). This is a refreshing contrast to the traditional volatile

compounds used by industry. It also decreases worker exposure thus it is also better

from an occupational health point of view.

Thermal Stability: Another key identifier of ionic liquids is the fact they remain

thermally stable at temperatures above 300°C (Bates et al., 2001).

1.8 CO2 Solubility in Ionic Liquids and Factors That Affect Solubility

As ionic liquids are becoming a viable option for CO2 capture from natural and

flue gases, improving the efficiency of CO2 solubility in the ionic liquid is vital. There

are many different factors that influence the solubility of CO2 in ionic liquids and a good

understanding of these parameters is necessary in order to design an ionic liquid that is

optimized for the function of CO2 separation. The factors playing a role in the solubility

of CO2 in ionic liquids include the type of anion and cation, the amount of fluorination of

the anion, the alkyl chain length, the molecular weight of the ionic liquid and much more.

The anion effect on CO2 solubility: When it comes to CO2 solubility, the anion plays

a primary role and the cation takes a “back seat”. Many attempts and experiments

have been performed to understand the exact mechanism explaining why some ionic

liquids have a higher solubility than others. For example, Cadena et al. examined CO2

solubility in imidazolium ionic liquids: 1-butyl-3-methylimidazolium

hexafluorophosphate ([bmim][PF6]), 1-butyl-2,3- dimethylimidazolium

14

hexafluorophosphate ([bmmim][PF6]), 1-butyl-3-methylimidazolium

tetrafluoroborate ([bmim][BF4]), 1-butyl-2,3-dimethyl imidazolium tetrafluoroborate

([bmmim][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

([emim][TF2N]) and 1-ethyl-2,3-dimethylimidazolium

bis(trifluoromethylsulfonyl)imide ([emmim][TF2N]) (Cadena et al., 2004). They

studied the CO2 solubility at 283.15, 298.15, and 273.15 K and pressures up to about

13 bar (Cadena et al., 2004). The anion had the greatest impact on the solubility of

CO2 and the cation played a secondary role (Cadena et al., 2004). They specifically

noted that the [TF2N] anion had the highest affinity for CO2, whereas the [BF4] or

[PF6] anions had a minor effect on CO2 solubility (Cadena et al., 2004). Ramdin et

al. observed the effect of many different anions when paired with a [bmim] cation at

333K where CO2 solubilities increase in the order of the following anions: [NO3] <

[SCN] < [MeSO4] < [BF4] < [DCN] < [PF6] < [TF2N] < [Methide] < [C7F15CO2]

(Ramdin et al., 2012). This trend was reproduced using the COSMO-RS model by

Maiti (Maiti, 2009) and Sistla and Khanna (2011).

The cation effect on CO2 solubility: It has been accepted that the cation plays a

secondary role in the solubility of CO2. Nonetheless, it still plays a role. Adding fluro

groups to the cation also improves CO2 solubility but to a lesser extent than if it were

added to the anion. The effect of changing the cation group is shown in the following

graph where cholinium, ammonium, imidazolium, pyridinium, pyrrolidinium, and

phosphonium cations were paired with the [TF2N] anion (Ramdin et al., 2012).

15

Figure 1.6: The effect of changing the cation on CO2 solubility (Ramdin et al., 2012).

Temperature effect on CO2 solubility: The general trend in the literature is that CO2

solubility ionic liquids decreases with increasing temperature. This is a problem when

considering the high temperatures of flue gases (Muldoon et al., 2007). The effect of

temperature on CO2 solubility is clearly seen by the following graph (Figure 1.8)

from Anthony et al. where the solubility of CO2 in [bmim][PF6], at three

temperatures of 283.15, 298.15, and 273.15 K with pressures of up to 13 bar,

decreased with increasing temperature (Anthony et al., 2002). This trend was also

seen by Aki et al. who examined the effect of temperature on the solubility of CO2 in

[bmim][TF2N] (Aki et al., 2004).

16

Figure 1.7: CO2 solubility in [bmim][PF6] at 283.15, 298.15, and 273.15 K (10, 25 and 50

C) (Anthony et al., 2002).

Pressure effect on CO2 solubility: A general trend seen in most ionic liquids is that

CO2 solubility increases with increasing pressure (Muldoon et al., 2007). This was

shown by Aki et al. who investigated CO2 solubility in [bmim][TF2N] with CO2

solubility increasing with increasing pressure, reaching over 0.7 mole fraction at 60

bar (Aki et al., 2004).

Fluorination effect on CO2 solubility: The general trend found by Muldoon et al.

was an increase in CO2 solubility with increased fluorination. They also found that

fluorination of the anion had a greater effect on the solubility than the fluorination of

the cation (Muldoon et al., 2007). Yunus et al. showed the effect of fluorination by

looking at the solubility of CO2 in [C4py][TF2N],[C4py][TfAc] and [C4py][Dca] at

298.15 K and pressures of up to 10 bar (Yunus et al., 2012). The solubility of CO2

increased as follows: [C4py][Dca] < [C4py][TfAc] < [C4py][TF2N] (Yunus et al.,

2012). From the results, the order of CO2 solubility follows the order of fluorination

17

in the anion (Yunus et al., 2012). This was also observed by Aki et al. when they

examined seven different ionic liquids which all had the same cation (1-butyl-3-

methylimidazolium ([bmim])) (Aki et al., 2004). They used seven different anions to

see what effect the anion would have on solubility. The anions were dicyanamide

([DCN]), nitrate ([NO3]), tetrafluoroborate ([BF4]), hexafluorophosphate ([PF6]),

bis(trifluoromethylsulfonyl)imide ([TF2N]), trifuoromethanesulfonate ([TfO]) and

tris(trifluoromethylsulfonyl)methide ([methide]) (Aki et al., 2004). Carbon dioxide

solubility increases as the number of fluoro groups in the anion increases, as seen in

the graph below. The solubility increases in the following anion order: [BF4] < [TfO]

< [TfA] < [PF6] < [TF2N] < [methide] < [C7F15CO2] < [eFAP] < [bFAP] (Ramdin

et al., 2012).

Figure 1.8: Effect of fluorination on CO2 solubility (Ramdin et al., 2012).

18

Thus, one can conclude [bFAP] would achieve the maximum rate of CO2 capture

among the seven ionic liquids.

Alkyl Chain lengths and the effect of CO2 solubility: For any given cation, CO2

solubility increases with increasing alkyl chain length on the cation (Muldoon et al.,

2007). Ramdin et al. examined the effect of alkyl chain lengths on CO2 solubility

(Ramdin et al., 2012). The following graph (Figure 1.10) shows the effect of

increasing alkyl chain length. All the ionic liquids are matched with a common

bis(trifluoromethylsulfonyl)amide [TF2N] anion (Ramdin et al., 2012), while the

alkyl chain length on the imidazolium cation is varied. As the alkyl chain becomes

longer the solubility increases in the following order: [omim] < [hmim] < [pmim] <

[bmim] < [emim] (Ramdin et al., 2012). Aki et al. also examined the role of alkyl

chain length on CO2 solubility while working with [bmim][TF2N],

[hmim][TF2N],and [omim][TF2N] (Aki et al., 2004). They found similar results

where the solubility increased with increasing alkyl chain length (Aki et al., 2004).

For example, at a pressure of 83.7 bar, the solubility increased from 0.72 mole

fraction for [hmim][TF2N] to 0.763 mole fraction for [omim][TF2N] (Aki et al.,

2004). Yunus et al. also examined the effect of the alkyl chain length by looking at

solubility in [C4py][TF2N], [C8py][TF2N] and [C12py][TF2N] at 298.15 K, 313.15

K and 333.15 K (Yunus et al., 2012). The CO2 solubility increased with increasing

alkyl chain length, for example, from 0.200 mol fraction of CO2 to 0.233 mol fraction

of CO2 at 298.15 K and 8 bar in the case of butyl (n = 4) and dodecyl (n =12) (Yunus

et al., 2012).

19

Figure 1.9: The effect of the alkyl chain length on CO2 solubility (Ramdin et al., 2012).

Molecular weight and the effect of CO2 solubility: Another factor that strongly

affects CO2 solubility is the molecular weight of the ionic liquid where CO2 solubility

increases with increasing molecular weight (Ramdin et al., 2012). Carbon dioxide

solubility increases with increasing IL molecular weight, molar volume, and free

volume (Ramdin et al., 2012).

1.9 New Developments in the Pursuit of the Perfect Ionic Liquid: Literature

Review

A main issue or factor that is usually a drawback for ionic liquid use in CO2 capture is the

increase in viscosity of the ionic liquid once it reacts with CO2. Thus, it has become a

race to find solutions or new ILs whose viscosity can be minimized. In addition, certain

modifications of the IL can be done to decrease the reactionary increase in viscosity such

20

as the addition of water. The addition of water to the IL is known to decrease the

solubility, slightly, however the decrease in viscosity is a tradeoff. For example, when

water is added to the IL [P66614][Pro] it showed a significant drop in viscosity which

decreased from 625 cP (0.1 wt% water) to 360 cP (4 wt% water) at 278 K with a small

change in CO2 capacity (Zhang et al., 2012). The slight decrease in CO2 solubility by

[P66614][Pro] appears at lower pressures, and even decreases to a smaller extent at high

pressures (Zhang et al., 2012).

A new approach in the pursuit of an IL with high a CO2 capture rate is the idea of

ring-opened heterocycles which are promising ionic liquids for gas separation and

capture. Mahurin et al. studied the following three ILs: [(N11)2CH][TF2N],

[(N111)2N][TF2N], [(N111)2N][C(CN)3] (Mahurin et al., 2012). The CO2 solubilities

for all three RTILs were nearly equivalent with values of 0.090, 0.099, and 0.095

mol/L∙atm (Mahurin et al., 2012). They are also comparable to the CO2 solubility of

[emim][TF2N] which has been reported to be 0.103 mol/L∙atm. However, only

[(N111)2N][C(CN)3] had a lower viscosity than [emim][TF2N] (Mahurin et al., 2012).

Another new ionic liquid, developed by Martinez et al, examined a new low-viscosity

and non-fluorinated ionic liquid, 1-hexyl-3-methylimidazolium tetracyanoborate

([hmim][TCB]) (Martinez et al., 2012). They were able to demonstrate the new ionic

liquid [hmim][TCB] harbors potential as it shows high CO2 solubility when compared to

the usual ionic liquids that are highly fluorinated. They studied the solubility of CO2 in

[hmim][TCB] within a range of 283.56 to 364.04 K and pressures up to 12.34 MPa. In

addition, it also shows great promise as it has a lower viscosity as well (Martinez et al.,

2012). They compared the solubilities of CO2 in [hmim][TCB] at 333 K to the

21

solubilities of CO2 at the same temperature in other ionic liquids sharing the same cation

i.e., 1-hexyl-3-methylimidazolium hexafluoroborate ([hmim][PF6]), 1-hexyl-3-

methylimidazolium tetrafluoroborate ([hmim][BF4]), 1-hexyl-3- methylimidazolium

bis(trifluoromethylsulfonyl)amide ([hmim][TF2N]), and 1-hexyl-3-methylimidazolium

tris(pentafluoroethyl)trifluorophosphate ([hmim][eFAP]) (Martinez et al., 2012). They

concluded that the new ionic liquid [hmim][TCB] had higher solubilties than expected

from the highly fluorinated ([hmim][eFAP]). The disadvantage of this high solubility and

high fluorination is high viscosity, where the viscosity of [hmim][TCB] is almost half of

[hmim][eFAP] which has a major implication with respect to commercial applicability

(Martinez et al., 2012). Another issue is the health implication of using fluorinated ionic

liquids. Iconic liquids, in general, are starting to lose their environmentally green title, as

more and more evidence reveals that ILs have some problems when it comes to

persistence in the environment due to their low degradation and high water solubility

features (Pham et al., 2010).

Lei et al. came up with the idea of mixing ILs as another approach to increase CO2

solubility (Lei et al., 2012). They examined the solubility of CO2 in pure ILs, i.e.,

[emim][BF4], [bmim][BF4], and [omim][TF2N], and in their binary mixtures, i.e.,

[emim][BF4],[omim][TF2N] and [bmim][BF4], [omim][TF2N] at 313.2 and 333.2 K and

pressures up to 6 MPa (Lei et al., 2012). In this experiment, the IL [omim][TF2N] was

selected because its CO2 solubility is higher in ILs with an anion such as [TF2N] which

contains a fluoroalkyl group, and an increase in the alkyl chain length on the cation also

increases the CO2 solubility. The ILs [emim][BF4] and [bmim][BF4] were selected

because they exhibit higher selectivity but lower solubility (Lei et al., 2012). The

22

solubility of CO2 in mixed ILs increases with increasing pressure at all temperatures, but

decreases with increasing temperature. The solubility of CO2 in mixed ILs increases with

increasing [omim][TF2N] content under the same temperature and pressure, and the

solubility of CO2 in the [emim][BF4],[omim][TF2N] mixed ILs is lower than in the

[bmim][BF4], [omim][TF2N] mixed ILs under the same [omim][TF2N] content,

temperature and pressure (Lei et al., 2012). Thus, experimentation with binary mixtures

of ionic liquids has the potential for improving CO2 capture.

In another paper, Manica et al. tested the solubility of seven different ionic liquids in

a range of pressures from 8 to 22 MPa at two different temperatures (Manica et al.,

2012). They explored the effect and role of cations while using the same anion for all

their ionic liquids. The anion they used was bis(trifluoromethylsulfonyl)imide,[TF2N].

They then paired the anion up with different cations such as 1-butyl-3-

methylimidazolium, [C4mim], 1-decyl-3-methyl imidazolium, [C10mim], 1-butyl-1-

methylpyrrolidinium, [Pyrr4,1], butyltrimethyl ammonium,[N4,1,1,1],

methyltrioctylammonium, [N1,8,8,8] and trihexyltetradecylphosphonium, [P6,6,6,14]

cations. Their results echoed the findings of almost all previous studies which are that the

solubility of CO2 in ILs might be improved by increasing the pressure, increasing alkyl

chain length in the cation, adding fluorination in ILs or by decreasing the temperature.

Althuluth et al. experimented with CO2 solubility in the following ionic liquid 1-

ethyl-3- methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([emim][FAP])

(Althuluth et al., 2012). They examined different solubilites across a range of

temperatures from 283.75 to 364.13 K and at pressures up to 10.4MPa (Althuluth et al.,

2012). The solubility of CO2 was determined by examining different bubble point

23

pressures with different concentrations of CO2 in the ionic liquid. The solubility of CO2

in [emim][FAP] decreases with increasing temperature (Althuluth et al., 2012). This is a

general trend found in the literature for many types of ionic liquids. Therefore, as

temperature increases there is a need to increase pressure to dissolve the same amount of

CO2 in the ionic liquid. They compared the solubility of CO2 in [emim][FAP] and found

it to be higher than all other ILs having the same cation having the following trend:

[emim][FAP] > [emim][TF2N] > [emim][EtSO4] = [emim][PF6] >[emim][BF4]

(Althuluth et al., 2012). This is most likely due to the presence of a large amount of

fluorine atoms in the anion, which result in an increase in CO2 solubility in the IL and it

has a higher stability to moisture and air compared to other fluorinated ionic liquids.

Therefore, it has potential for use as a solvent for gas separation and CO2 capture.

Studies published in the literature are in general agreement that CO2 solubility increases

as fluorination increases in the anion. Thus, fluorination content would be an important

factor to consider in the search for an ionic liquid.

Another new category of ionic liquids being explored are hydroxyl ammonium

ionic liquids (Yuan et al., 2007). Yuan et al. studied eight ionic liquids: 2-hydroxy

ethylammonium formate (HEF), 2-hydroxy ethylammonium acetate (HEA), 2-hydroxy

ethylammonium lactate (HEL), tri-(2-hydroxy ethyl)-ammonium acetate (THEAA), tri-

(2-hydroxy ethyl)-ammonium lactate (THEAL), 2-(2-hydroxy ethoxy)-ammonium

formate (HEAF), 2-(2-hydroxy ethoxy)-ammonium acetate (HEAA) and 2-(2-hydroxy

ethoxy)- ammonium lactate (HEAL) (Yuan et al., 2007). They examined their CO2

solubility at temperatures of 303 to 323K and pressures ranging from 0 to 11MPa (Yuan

et al., 2007). Carbon dioxide solubility in the eight hydroxyl ammonium ionic liquids

24

decreased in the following sequence: THEAL >HEAA>HEA> HEF > HEAL

>THEAA≈HEL > HEAF (Yuan et al., 2007). They also reported all eight ionic liquids

had a lower CO2 solubility than [bmim][PF6] (Yuan et al., 2007). The following graph

compares the eight ionic liquids investigated by Yuan et al. with others from the

literature.

Figure 1.10: Comparison of the solubility of CO2 in different ionic liquids at 313 K: (■)

THEAL; (●) [bmim][PF6]; (▲) [omim][PF6]; (▼) [Nbupy][BF4]; (♦) [emim][EtSO4]

(Yuan et al., 2007).

In another report Jalili et al. examined 1-Octyl-3-methylimidazolium

bis(trifluoromethyl) sulfonylimide ([C8mim][TF2N]) (Jalili et al., 2012). They

experimented with temperatures of 303.15, 313.15, 323.15, 333.15, 343.15, and 353.15 K

and pressures of up to 2MPa. Carbon dioxide solubility was increased by increasing the

number of carbons in the alkyl substituent of the methylimidazolium cation ring (Jalili et

al., 2012).

25

Another group examined pyridinium based ionic liquids and CO2 solubility.

Yunus et al. examined six different pyridinium based ionic liquids, 1-butylpyridinium

bis(trifluoromethyl sulfonyl)imide [C4py][TF2N], 1-octylpyridinium

bis(trifluoromethylsulfonyl) imide [C8py][TF2N], 1-decylpyridinium

bis(trifluoromethylsulfonyl)imide [C10py][TF2N], 1-dodecylpyridinium

bis(trifluoromethylsulfonyl)imide [C12py][TF2N], 1-butylpyridinium trifluoroacetate

[C4py][TfAc] and 1-butylpyridinium dicyanamide [C4py][Dca], at temperatures of

298.12, 313.12, and 333.15K (Yunus et al., 2012). There is little difference in solubility

when compared to the more expensive imidazolium cation. They also arrived at the same

conclusion as all other papers that solubility increases by increasing the alkyl chain of the

anion. They concluded the solubility of CO2 in this series of ionic liquids increases in the

following sequence: [C4py][TfAc] < [bmim][TFA] < [emim][TF2N] < [C4py][TF2N]

≈[bmim] [TF2N] < [hmim][TF2N] < [C8py][TF2N] < [C12py][TF2N] < [bmim][Ac]

(Yunus et al., 2012).

Based on reports in the literature, a good choice for an ionic liquid should contain

an imidazolium cation with a long alkyl chain such as [emim] and an anion with fluro

groups such as [bFAP]. Other groups of ionic liquids that should be considered are those

that are less expensive such as the ionic liquids with the pyridinium cation. The creation

of an ionic liquid with the aforementioned features and maximum molecular weight

should yield an IL with a high CO2 solubility. This was taken into consideration when

selecting the ionic liquids. The selection was based on attempting to provide novel work

and finding ionic liquids that were uncommon in the literature.

26

1.10 Outline of the Chapters

Chapter 2 will provide the steps taken for measuring gas solubilities and the theory

behind calculation of Henry’s law constants, enthalpies and entropies of absorption. It

will also cover the experimental details and the methodology used to obtain the CO2

solubility in the ionic liquids. It will also include a description of all the chemicals, gases

and apparatus used in this experimental study.

Chapter 3 will present the results obtained from CO2 solubility measurements in the

different ionic liquids investigated in this work. The chapter will include the solubility of

carbon dioxide in five ionic liquids and will perform a comparison of the ionic liquids to

research published in the literature and research performed by the Acid Gas Research Lab

(AGRL) affiliated with this research.

Chapter 4 will discuss the theory behind thermodynamic modeling and include a

description of the density calculations for the ionic liquids. It contains details on the

thermodynamic models used to correlate the experimental CO2 solubility including

equations of state, such as the (PR-EoS), Peng-Robinson, Soave-Redlich-Kwong (SRK),

and the Non-Random Two-Liquid (NRTL) activity coefficient model. Henry’s law

constants and enthalpies and entropies of absorption for CO2 in the ionic liquids are

discussed in this chapter.

27

2 Chapter Two: General Methodology, Theory And Experimental Details

This chapter will include the steps taken for measuring gas solubilities and

calculating Henry’s law constants, enthalpies and entropies of absorption. It will explore

the various methods used to measure gas solubilites including the gravimetric method

used in this study.

This chapter will also cover details of the various experiments conducted, and will

also include a description of all the chemicals, gases, and apparatus used for the solubility

measurements.

2.1 Methods for Gas Solubility Measurements

Gas solubility is influenced by many factors as is the accurate measurement of

solubility (Clever and Battino, 1975). The purity of the liquid sample will affect the gas

solubility measurements. The diligent control of the important parameters such as

temperature, pressure, volume and mass are all important for accurate gas solubility

measurements (Clever and Battino, 1975). There are different methods for gas solubility

measurements which include volumetric and pressure drop methods, the stoichiometric

technique and gravimetric method (Clever and Battino, 1975). The following section will

provide a brief description of the different gas solubility measurements.

2.1.1 Pressure Drop Technique for Measuring CO2 Solubility

The pressure drop method measures the pressure change when a known mass of

gas dissolves into a known mass of ionic liquid (Brennecke et al., 2008). Once the system

has reached equilibrium, the pressure change is used to reflect the amount of gas

28

dissolved into the liquid, from which the gas solubility can be extrapolated (Brennecke et

al., 2008).

Figure 2.1: Pressure drop technique for measuring CO2 solubility (Brennecke et al, 2008).

2.1.2 Stoichiometric Technique for Measuring CO2 Solubility

This method determines the solubility of a gas by determining the volume of a

cell, which contains the gas, and the volume of the vapour and liquid phases as they mix

and dissolve (Brennecke et al., 2008). This information is used to measure the number of

moles of gas remaining in the gas phase and thus the number of moles of gas dissolved in

29

the liquid are extrapolated, leading to the solubility measurement (Brennecke et al.,

2008).

Figure 2.2: Stoichiometric gas solubility apparatus (Brennecke et al., 2008).

2.1.3 Gravimetric Method for Measuring CO2 Solubility

The gravimetric method uses the concept of change in the weight of the sample

after absorption to assess the solubility. Due to the non-volatile nature of ionic liquids

30

and the lack of loss of ionic liquid due to evaporation, the weight of the sample is not

affected, and thus this method is commonly used.

This experiment utilized an IGA (Intelligent Gravimetric Analyzer) which utilizes

the gravimetric technique. It combines the computer control and measurements of weight

change, pressure and temperature to allow automatic configuration of gas adsorption-

desorption isotherms. The microbalance is made of an electrobalance with sample and

counterweight parts inside a stainless steel pressure-vessel as shown in the figure below

(Shiflett and Yokozeki, 2005).

Figure 2.3: Schematic diagram of IGA003 gravimetric microbalance. Symbols: arrow B

indicates direction due to buoyancy on the sample side of the balance, arrow Wg

indicates direction of weight due to gravity on the sample side of the balance, additional

symbols described in Table 1 (Shiflett and Yokozeki, 2005).

31

Figure 2.4: IGA apparatus (http://www.zpph.com/userfiles/file/iga_series_brochure.pdf)

2.1.4 Gravimetric Method: Buoyancy Correction Factor

The gravimetric method for gas solubility must be carefully corrected for a

number of forces. These include the buoyant forces, the aerodynamic drag forces due to

the flow of gases, the change in balance sensitivity due to changes in temperature and

pressure and volumetric changes due to sample expansion (Shiflett and Yokozeki, 2005).

The buoyancy effect on the absorbed mass was minimized by using a sample pan

and a counterweight container that were symmetrically configured with the exact same

stainless steel bucket. The buoyancy correction factor follows one of Archimedes’

principals which states there is an upward force placed on an object equivalent to the

mass of the fluid displaced (Shiflett and Yokozeki, 2005). The upward force (Cb) due to

buoyancy is calculated using equation 2.1 where the mass of displaced carbon dioxide is

equivalent to the volume of the submersed object 𝑉𝑖 multiplied by the carbon dioxide

http://www.zpph.com/userfiles/file/iga_series_brochure.pdf

32

density (𝑝𝑔) at a measured temperature and pressure and the local gravitational

acceleration (g) (Shiflett and Yokozeki, 2005).

2.1.5 Calculation of Buoyancy Correction Factor

Cb = Buoyancy = gVipg(T, P) = gmi

pipg(T, P) (2.1)

many important components for weighing the sample are needed in order to use

the IGA to determine the buoyancy correction. The difference between the weight of the

sample side (i) and that of the counterweight side (j) represents the weight measured by

the balance. The microbalance components, their weights and densities can be found in

Table 2.1. Also refer to Figure 1 for the schematic representation of the IGA apparatus.

The mass balance, shown in Figure 1, is mathematically represented by equation 2.2:

Reading =∑ 𝑚𝐼𝐿𝑆𝑖=1 − ∑ 𝑚𝑐𝑤𝑗𝑐𝑤𝑗− ∑

𝑚𝐼𝐿

𝑝𝑠𝑠𝑖=1 𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) +

∑𝑚𝑐𝑤

𝑝𝑐𝑤𝑐𝑤𝑗=1 𝑝𝑔𝑎𝑠 (𝑇𝐶𝑤𝑗

, 𝑃) + 𝑚𝐼𝐿 + 𝑚𝑎𝑏−𝑔𝑎𝑠-𝑚𝐼𝐿

𝑝𝐼𝐿(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿, 𝑃) −

𝑚𝑎𝑏−𝑔𝑎𝑠

𝑝𝑎𝑏−𝑔𝑎𝑠(𝑇𝐼𝐿)

−

𝐶𝑓(𝑇𝐼𝐿𝑃) (2.2)

The IGA is used to measure the mass difference between the sample side and

counterweight which includes the summation of all components as seen in equation 2.2.

The following symbols are defined for the aforementioned equation: The mass of

absorbed gas (mIL) and a correction factor (Cf) due to the sensitivity of the balance, s

and a represent the density of ionic liquids and gas at a sample temperature (Ts) and mIL

is the weight of the dry IL sample (Shiflett and Yokozeki, 2005). The density of the IL

33

sample must be accurately known in order to determine the aforementioned buoyancy

correction and was measured with the DMA 4500 density meter.

Table 2-1: Microbalance components for buoyancy correction

Object Description

Weight

(g)

Density

(g/cm3)

Temperature

(C)

S Dry sample: ionic liquid used 𝑚𝐼𝐿 s -

A Interacted gas: CO2 gas 𝑚𝑎𝑏−𝑔𝑎𝑠 a -

i1 Sample container 0.63275 7.393103 -

i2 Wire 0.06524 21 -

i3 Chain 0.3055 19.8 35

j1 Counterweight 0.81219 7.9 -

j2 Hook 0.00582 2.71 25

j3 Chain 0.239 19.8 35

In addition to accounting for buoyancy, a possible volume expansion can occur at high

temperatures which may be large enough to affect the buoyancy correlation (Shiflett and

Yokozeki, 2005). Therefore, the solubility calculation may be inaccurate if the buoyancy

due to sample expansivity is not taken into account. The volume of the ionic liquid and

the CO2 was ascertained with their weight and density using the following equations

(Shiflett and Yokozeki, 2005):

𝑉𝑚𝐼𝐿=

𝑀𝑊𝐼𝐿

𝑝𝐼𝐿 (2.3)

34

𝑉𝑚𝐺𝑎𝑠=

𝑀𝑊𝑔𝑎𝑠

𝑝𝑔𝑎𝑠 (2.4)

The average molar volume is obtained using the following equation:

𝑉𝑚𝑎𝑣(𝑇, 𝑃) = 𝑉𝑚𝐼𝐿

(1 − 𝑥) + 𝑉𝑚𝑔𝑎𝑠𝑥 (2.5)

The volume of the ionic liquid could be calculated using the average liquid volume, the

moles of ionic liquid, and moles of absorbed gas using the following equations:

V (T, P) =𝑉𝑚𝑎𝑣(𝑇, 𝑃)[(

𝑚𝐼𝐿

𝑀𝑊𝐼𝐿) + (


𝑀𝑊𝑔𝑎𝑠)] (2.6)

V(T, P)𝑝𝑔𝑎𝑠(𝑇, 𝑃) =𝑚𝐼𝐿

𝑝𝐼𝐿(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) +


𝑝𝑎𝑏−𝑔𝑎𝑠(𝑇𝐼𝐿)𝑝𝑔𝑎𝑠(𝑇𝐼𝐿,𝑃) (2.7)

2.2 Thermodynamic Properties

Once the gas solubilites are measured and calculated, some thermodynamic

properties can be derived such as Henry’s law constants and enthalpies and entropies of

absorption.

2.2.1 Derivation for Henry’s Law Constants

Henry’s law constants are proportionality constants that are used to relate the

partial pressure of a gas to the gas solubility in a liquid state at infinitely dilute conditions

(Prausnitz et al., 1999).

The Henry’s law constant is defined as:

𝐻𝑖(𝑇, 𝑃) = lim𝑥𝑖→0

𝑓𝑖𝐿

𝑥𝑖 (2.8)

where fi

L

is the fugacity of the gas dissolved in the liquid phase. Since the fugacity of the

gas in the liquid phase must be equal to the fugacity in the gas phase and approximate the

35

gas phase fugacity at the gas phase pressure, the following form of Henry’s law can be

obtained:

𝑃𝑖 = 𝐻𝑖(𝑇)𝑥𝑖 (2.9)

where Pi is the partial pressure of the gas. H

i(T) will have units of pressure and is

inversely proportional to the mole fraction of gas in the liquid.

The fugacity of the gas is the method used in this experiment to calculate Henry’s

law constant. The fugacity was estimated from the experimental solubility data, pressure

and appropriate mode in AspenPlus. Henry’s law constant is found by fitting the data to a

first or second order polynomial obtain a correlation coefficient of R2 > 0.999. The

limitation of the mole fraction of CO2, as it approaches zero, was used to obtain the

Henry’s law constant at each temperature.

Henry’s constant can also be obtained in a different manner as it is also directly

related to the infinite dilution activity coefficient and the vapor pressure of the gas. The

activity coefficient of the gas in the IL phase, γ1, can be determined directly by measuring

the mole fraction of gas dissolved in the IL as a function of the pressure of gas above the

IL solution.

2.2.2 Derivation for Enthalpy And Entropy Of Absorption

The examination of temperature effects on gas solubilities allows for the

derivation of the enthalpies and entropies of absorption. The bonds between the liquid

and dissolved gas reflect the enthalpy, whereas the entropy indicates the level of ordering

that takes place in the liquid/gas mixture (Hildebrand and Scott, 1962).

36

∆ℎ2 = ℎ2 − ℎ2𝑖𝑔

= 𝑅𝑇 (𝜕𝑙𝑛𝑥2

𝜕𝑙𝑛𝑇)

𝑃(

𝜕𝑙𝑛𝑎2

𝜕𝑙𝑛𝑥2)

𝑃,𝑇 (2.10)

∆𝑠2 = ��2 − 𝑠2𝑖𝑔

= 𝑅 (𝜕𝑙𝑛𝑥2

𝜕𝑙𝑛𝑇)

𝑃(

𝜕𝑙𝑛𝑎2

𝜕𝑙𝑛𝑥2)

𝑃,𝑇 (2.11)

where h1 and s1 are the partial molar enthalpy and entropy of the gas in solution, h1

ig

and

s1

ig

are the enthalpy and entropy of the pure gas in the ideal gas phase, and a1

is the

activity of the gas in the solution:

𝑎2 = 𝛾2 ∙ 𝑥2 (2.12)

The above equations can be rewritten as follows:

∆ℎ2 = 𝑅 (𝜕𝑙𝑛𝑃

𝜕(1/𝑇))

𝑥2

(2.13)

∆𝑠2 = −𝑅 (𝜕𝑙𝑛𝑃

𝜕𝑙𝑛𝑇)

𝑥2

(2.14)

The equations provide ∆h2 and ∆s2 at a specific mole fraction of CO2 in the ionic liquid

(x2). The equations can be simplified to:

∆ℎ2 = −𝑅 (𝜕𝑙𝑛𝑥2

𝜕(1/𝑇))

𝑃= 𝑅 (

𝜕𝑙𝑛𝐻2,1

𝜕(1/𝑇))

𝑃 (2.15)

∆𝑠2 = 𝑅 (𝜕𝑙𝑛𝑥2

𝜕𝑙𝑛𝑇)

𝑃= −𝑅 (

𝜕𝑙𝑛𝐻2,1

𝜕𝑙𝑛𝑇)

𝑃 (2.16)

The above equations provide ∆h2 and ∆s2 at infinite dilution. The equations will also give

the same ∆h2 and ∆s2 as the x2 becomes adequately small to exist in the infinite dilution

range.

37

2.3 Materials

2.3.1 Ionic Liquids

The seven different ionic liquids are listed in the following table.

Table 2-2: Ionic liquids studied with their short hand notation and structure.

Ionic liquid Shorthand Name Structures

1,2,3-

Tris(diethylamino)cyclopropenylium

dicyanamide

[TDC] [DCN]

1-Ethyl-3-methylimidazolium L-(+)-

lactate

[EMIM] [LACTATE]

3-methyl-1-propylpyridinium

bis[(trifluoromethyl)sulfonyl]imide

[PMPY] [TF2N]

Ethyldimethylpropylammonium

bis(trifluoromethylsulfonyl)imide

[EMMP] [TF2N]

1,2,3-

Tris(diethylamino)cyclopropenylium

bis(trifluoromethanesulfonyl)imide

[TDC] [TF2N]

1-(4-sulfobutyl)-3-

methylimidazolium

Bis(trifluoromethanesulfonyl)imide

[(CH2)4SO3HMIm][TF2N]

1-(4-sulfobutyl)-3-

methylimidazolium hydrogen sulfate

[(CH2)4SO3HMIm][HSO4]

The ionic liquids were purchased from Sigma Aldrich. The exception is

[PMPY][TF2N] which was obtained from ionic liquid Technology (io-li-tec , USA) and

http://www.sigmaaldrich.com/catalog/product/aldrich/669512?lang=en&region=CA


38

[(CH2)4SO3HMIm][HSO4] and [(CH2)4SO3HMIm][TF2N] were obtained from

solvionic.

Table 2-3: Ionic liquids used and their specifications:

Ionic liquid Source Molecular weight

1,2,3-Tris(diethylamino) cyclo

propenylium dicyanamide

Sigma Aldrich (purity of

97%)

3g purchased

Product #: 744018

Color: yellow

318.46

1-Ethyl-3-methylimidazolium L-(+)-

lactate


>95%)

5g purchased

Product #: 669512

CAS #: 878132-19-5

Color: light brown

200.23

3-Methyl-1-propylpyridinium

bis[(trifluoromethyl)sulfonyl]imide

io-li-tec: ionic liquid

technologies (purity of

99%)

3g purchased

416.40

Ethyldimethylpropylammonium

bis(trifluoromethylsulfonyl)imide


99%)

3g purchased

Impurities: ≤1.0%

water

Product #: 727989

CAS#: 258273-77-7

Color: colorless

396.37

1,2,3-Tris(diethylamino)cyclo

propenylium bis(trifluoromethane

sulfonyl)imide


97%)

3g purchased

532.56

1-(4-Sulfobutyl)-3-methylimidazolium

Bis(trifluoromethanesulfonyl)imide

Solvionic (purity of

98%)

10g purchased

Impurities: H2O <0.2%

Catalog#: ImSF1808c

Color: colorless

499.43

1-(4-Sulfobutyl)-3-methylimidazolium

hydrogen sulfate

Solvionic (purity of

98%)

10g purchased

Impurities: H20 <1%, Br

<0.3%, Cl <0.3%

Catalog #: ImSF1213c

Color: colorless

316.35

39

2.3.2 Ionic Liquid Treatment and Equilibrium Time

1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) with an assay

of ≥ 97.0% (HPLC) was measured at 82 g. This ionic liquid was used to validate the

results obtained from the system and machine.

1,2,3-Tris(diethylamino)cyclopropenylium dicyanamide ([TDC] [DCN]) was

used in gas solubility measurements and purchased from Sigma-Aldrich. It was dried

under vacuum at 75°C for more than 14 hours in all three experiments before carbon

dioxide was sent to the sample chamber. It took less than 120 minutes to reach

equilibrium under 1000 millibars pressure at 40

°C.

Figure 2.5:[TDC] [DCN] equilibrium under 1000 millibars and 40

°C

1-Ethyl-3-methylimidazolium L-(+)-lactate ([EMIM] [LACTATE]) was used in

gas solubility measurements and purchased from Sigma-Aldrich. It was dried under

vacuum at 75°C for more than 14 hours in all three experiments before carbon dioxide

40

was sent to the sample chamber. It took more than 350 minutes to reach equilibrium

under 1000 millibars pressure at 40

°C.

Figure 2.6: [EMIM] [LACTATE] equilibrium under 1000 millibars pressure at 40

°C.

3-methyl-1-propylpyridinium bis[(trifluoromethyl)sulfonyl]imide ([PMPY]

[TF2N]) was used in gas solubility measurements and purchased from io-li-tec: ionic

liquid technologies. It was dried under vacuum at 75°C for more than 14 hours in all

three experiments before carbon dioxide was sent to the sample chamber. It took less than

120 minutes to reach equilibrium under 1000 millibars pressure at 40

°C.

Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide ([EMMP]

[TF2N]) was used in gas solubility measurements and purchased from Sigma-Aldrich. It

was dried under vacuum at 75°C for more than 14 hours in all three experiments before

carbon dioxide was sent to the sample chamber. For each run, the temperature was set for

41

the isotherm. It took less than 120 minutes to reach equilibrium under 1000 millibars

pressure at 40

°C.

1,2,3-Tris(diethylamino)cyclopropenylium bis(trifluoromethanesulfonyl) imide

([TDC] [TF2N]) was used in gas solubility measurements and purchased from Sigma-

Aldrich. It was dried under vacuum at 75°C for more than 14 hours in all three

experiments before carbon dioxide was sent to the sample chamber. It took less than 120

minutes to reach equilibrium under 1000 millibars pressure at 40

°C.

1-(4-sulfobutyl)-3-methylimidazolium Bis(trifluoromethane sulfonyl)imide

([(CH2)4SO3HMIm] [TF2N]) was used in gas solubility measurements and purchased

from solvionic. It was dried under vacuum at 70°C for more than 14 hours in all three

experiments before carbon dioxide was sent to the sample chamber. It took less more

than 350 minutes to reach equilibrium under 1000 millibars pressure at 40

°C.

1-(4-Sulfobutyl)-3-methylimidazolium hydrogen sulfate

([(CH2)4SO3HMIm][HSO4]) was used in gas solubility measurements and purchased

from solvionic. It was dried under vacuum at 75°C for more than 14 hours in all three

experiments before carbon dioxide was sent to the sample chamber. It took less more

than 350 minutes to reach equilibrium under 1000 millibars pressure at 40

°C.

2.3.3 Selection of Ionic Liquids

Seven ionic liquids were chosen to investigate the CO2 solubility. After an

extensive literature review was performed, certain qualities and characteristics were

chosen as being important for maximizing solubility. Ionic liquids, which have not been

42

extensively published, were identified in order to contribute something new to the field of

CO2 capture with ionic liquids.

A search was performed for anions that were known to have high CO2 solubility

and, of course, bis(trifluoromethylsulfonyl) imide is well known in the literature for

having high CO2 solubility. Thus four of the ionic liquids chosen had this anion. [TF2N]

is known for its high CO2 solubility due to the high fluorination content of the anion.

[emim][LACTATE] was chosen due to the long alkyl chain of the cation when

compared to other imidazolium based cations such as [omim], [hmim], [pmim] or

[bmim]. The anion lactate was chosen as it was thought to be interesting to see the effect

of having an organic anion and to see its effect on CO2 capture.

A good variety of ionic liquids were needs and, thus, different cation bases were

chosen where [TDC] is a propenylium based cation, [PMPY] is a pyridinium based

cation, [EMMP] is an ammonium based cation, [emim] and [(CH2)4SO3HMIm] are

imidazolium based cations. This enables the study of the effect and role of the cation base

on CO2 solubility especially since the anion was identical for most of the ionic liquids.

2.3.4 Gases

Carbon dioxide was purchased from Praxair Inc. (Regina) with a mass purity of

99.99%.

2.4 Gravimetric Microbalance

Solubility was calculated using the Intelligent Gravimetric Analyzer (IGA 003)

from Hiden Analytical. This machine has been used by many researchers and a detailed

description of the apparatus can be found elsewhere (Moore, 2000).

43

Figure 2.7: Gravimetric microbalance

44

2.5 Experimental Procedure

A detailed schematic of the apparatus and its individual components is shown in the

figure below.

Figure 2.8: Schematic of the gravimetric microbalance

45

2.6 Summary of Experimental Procedures

Figure 2.9: Experimental procedure followed when using IGA

46

The microbalance consists of a weighing mechanism with a sample pan and

counterweight which have been symmetrically configured to minimize buoyancy effects.

The sample buckets are attached to the weighing mechanism by chains. The sample

buckets used in the experiments were stainless steel buckets.

The sample is loaded onto the sample bucket which is hung onto the chains and

then placed within the reactor vessel where it is tightly sealed. The sample weight varied

for each ionic liquid used in a range of 60-83 mg. With the aid of a coarse vacuum, the

sample was degassed with the help of a diaphragm pump where the reactor vessel

reached about 200 milibars. The sample is then heated up to about 75°C for a specified

period of time during which the sample weight decreases slowly. The drop in weight is

attributed to the removal of impurities such as water from the loading sample. The

percent weight drop was calculated for each treatment as percentage impurity lost for

each ionic liquid. See the table below:

Table 2-4: Calculation of weight lost for each ionic liquid at 313.15K and the percent

impurity lost

Ionic liquid Initial weight (mg) Dry weight (mg) % impurity lost

[TDC] [DCN]

63.003 62.845 0.25078

[EMIM] [LACTATE]

74.551 70.658 5.22125

[PMPY] [TF2N]

79.935 79.827 0.13498

[EMMP] [TF2N]

79.158 78.962 0.24761

[TDC] [TF2N]

86.735 86.591 0.16729

[(CH2)4SO3HMIm][TF2N] 83.247 64.028 23.0867

[(CH2)4SO3HMIm][HSO4] 74.015 67.627 8.62961

47

All ionic liquids had an acceptable percent impurity loss except

[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4]. These two hydrophobic

ionic liquids had more than the expected weight loss which might be due to their

absorption of water when exposed to ambient atmosphere and some acid evaporation

loss.

The sample temperature is set to the desired experimental temperature once the

weight of the sample reaches a stabilized state, the sample is deemed purified. The

absorption measurements are initiated by allowing the flow of carbon dioxide into the

chamber once the experimental temperature is stabilized.

The temperature of the reactor chamber was controlled during the experiment at

the desired experimental temperature using a water jacket and a constant-temperature

water bath. The sample temperature was monitored with a type K platinum thermocouple

placed inside the sample chamber and automatically maintained within 0.1 °C of the set

point. Once the desired temperature of the sample was reached, gas or vapor was

introduced into the sample chamber through a leak valve until a predetermined pressure

was reached. A pressure maximum of 19 bar was used in this experiment.

As the gas entered the chamber, the change in mass of the ionic liquid was

monitored by the computer program and increased with increasing gas absorption. When

the change in weight stabilized, the sample reached equilibrium providing the absorption

isotherm. This was repeated for the different pressures until the maximum pressure was

reached.

48

Figure 2.10: [TDC] [TF2N] equilibrium providing at high pressure.

2.7 Accounting for Buoyancy

When performing this type of experiments it is important to carefully account for

buoyancy effects in the system, even when a symmetric balance is used. An accurate

calculation of the buoyancy effect is especially important as the buoyancy is a large

percentage of the measured weight change. As mentioned earlier in the chapter, accurate

buoyancy calculations require knowledge of the volume of the balance components

(sample and counterweight buckets, counterweight, and hang-down chains), the volume

of the sample, and the density of the bulk gas phase. The volume of the balance

components is constant. The volume of the sample is calculated from the density.

The volume of the ionic liquid sample is found from its density, therefore, the

density of the IL sample must be accurately known. The density of each ionic liquid was

obtained using a digital density meter DMA 4500 (Anton Par).

2.8 Ensuring Equilibrium

Another important step in the experimental procedure is to allow adequate time

for the system to reach equilibrium. Depending on the viscosity of the ionic liquid,

equilibrium can vary and be a long process requiring patience. The weight change can be

49

monitored as a function of time using a microbalance for the measurements. One is able

to ascertain how much time is required to reach equilibrium when there is no longer a

significant change in mass. The equilibrium time for all samples in this work ranged from

120 to 240 min per point, depending on the ionic liquid, gas or vapor, and the sample

temperature.

2.9 Error Analysis

There are several sources of uncertainty in the microbalance experiments. The

uncertainties in measuring the pressure and mass are extremely small, about 0.06% and

0.0013%, respectively. Most of the source of error comes from the uncertainty

surrounding equilibrium. The uncertainty in the IL density measurements can also affect

the uncertainty in the solubility measurements.

50

3 CHAPTER THREE: RESULTS AND DISSCUSION

This chapter will look at the results obtained for CO2 solubility in the

experimental ionic liquids. The first section looks at the measured experimental density

for seven pure ionic liquids at different temperatures. The second section focuses on the

solubility of carbon dioxide in the seven ionic liquids. The following section will

compare the ionic liquids from this work to others published in the literature. Finally, it

will compare the solubility of CO2 to other ionic liquids recently studied by an affiliated

research group.

3.1 Density of Pure Ionic Liquids

The density of the seven ionic liquids was experimentally obtained using a digital

density meter DMA 4500 (Anton Par) at atmospheric pressure over a range of

temperatures from 278.15 to 353.15K. The results of the experimental density are shown

in Table 1. The graphical representation of the densities illustrate that the density

decreases with increasing temperature in a linear fashion with a correlation coefficient R2

> 0.999. The calculated (AADs) average absolute deviations between the experimental

data of [PMPY] Tf2N] , [EMMP][TF2N]

,[TDC][TF2N],[emim][LACTATE],[TDC][DCN], [(CH2)4SO3HMIm] [TF2N] and

[(CH2)4SO3HMIm][HSO4] are 0.06%, 0.06%, 0.17%, 0.029% and 0.059% ,0.09% and

0.14%, respectively.

In summary, the trend in the experimental density of decreasing order in the ionic

liquids are as follows: [(CH2)4SO3HMIm][TF2N] >[PMPY] Tf2N]

>[(CH2)4SO3HMIm][HSO4]> [EMMP][TF2N]

>[TDC][TF2N]>[emim][LACTATE]>[TDC][DCN]. This is shown in Figure 3.1 below.

51

Table 3-1: Experimental densities of pure ionic liquids measured at 1.01325 bar T (K) (g/cm3)

[TCD][CN] [PMPY ][TF2N] [EMMP][TF2N] [TCD][TF2N] [EMIM][LACTATE]

278.15 1.01638 1.46723 1.42002 -- 1.15745

283.15 1.01327 1.46243 1.41526 -- 1.15347

288.15 1.01014 1.45762 1.41060 -- 1.14977

293.15 1.00701 1.45281 1.40596 -- 1.14611

298.15 1.00391 1.44800 1.40126 1.27341 1.14246

303.15 1.00079 1.44328 1.39646 1.26905 1.13889

308.15 0.99770 1.43854 1.39181 1.26470 1.13543

313.15 0.99462 1.43381 1.38791 1.26036 1.13195

318.15 0.99155 1.42911 1.38336 1.25604 1.12851

323.15 0.98850 1.42443 1.37982 1.25173 1.12507

328.15 0.98546 1.41979 1.37540 1.24743 1.12167

333.15 0.98243 1.41516 1.37097 1.24316 1.11851

338.15 0.97941 1.40980 1.36649 1.23889 1.11798

343.15 0.97641 1.40596 1.36168 1.23464 1.11166

348.15 0.97340 1.40140 1.35766 1.23042 1.10839

353.15 0.97042 1.39685 1.35330 1.22619 1.10514

T (K) (g/cm3)

278.15 [(CH2)4SO3HMIm][TF2N]


283.15 1.59792 1.45030

288.15 1.59296 1.44702

293.15 1.58785 -

298.15 1.58258 1.43708

303.15 1.57787 1.43368

308.15 1.57318 -

313.15 1.56852 1.42676

318.15 1.56387 -

323.15 1.55923 1.42051

328.15 1.55460 -

333.15 1.55001 1.41428

338.15 1.54556 -

343.15 1.54112 1.40807

348.15 1.53668 -

353.15 1.53223 1.40180

52

T(K)

280 300 320 340 360

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4 [TDC ][DCN]

[PMPY] [TF2N]

[EMMP] [TF2N]

[TDC] [TF2N]

[EMIM][LACATATE]



Figure 3.1: Liquid density of the studied ionic liquids at temperatures ranging from

278.15 K to 353.15 K.

Table 3-2: Temperature-dependent density correlations for the ionic liquids

Ionic liquids Density (g/cm3) AAD (%)

[TCD][CN] (g/cm3) =1.10193-0.0006[T(C)] 0.05

[EMIM] [LATATE] (g/cm3) = 1.1601-0.0007[T(C)] 0.02

[TCD][ Tf2N] (g/cm3) = 1.2947-0.0009[T(C)] 0.17

[EMMP][TF2N] (g/cm3) = 1.4236-0.0009[T(C)] 0.06

[PMPY ][TF2N] (g/cm3) = 1.1416-0.0009* [T(C)] 0.06

[(CH2)4SO3HMIm][TF2N] (g/cm3) = 1.6016-0.0009* [T(C)] 0.09

[(CH2)4SO3HMIm][HSO4] (g/cm3) = 1.4533-0.0006* [T(C)] 0.14

53

3.2 Solubility of Carbon Dioxide

3.2.1 Verification of Measurements

The solubility of CO2 was corroborated with [bmim][PF6] at 323.15 K and

compared with previously published results in the literature as published by (Shiflett and

Yokozeki, 2005) and (Anthony et al., 2002) where the AADs of the measured and

reported solubilities at 323.15 K are 4 and 12 %, respectively. The results are shown in

Figure 2. The comparison shows better agreement with data published by Shiflett and

Yokozeki.

Mole fraction of co2 in [Bmim][PF6] (%)

0 5 10 15 20 25

Pre

ssure

(b

ar)

0

5

10

15

20

25

This work

Anthony et al. (2002)

Shiflett and Yokozeki (2005)

Figure 3.2: Solubility of CO2 in [bmim][PF6] at 323.15 K compared to the solubility data

result this work with previously published results : ● [bmim][PF6],green this work; ■

[bmim][PF6],red, (Shiflett, 2005); ▼[bmim][PF6],blue, (Anthony et al., 2002).

54

3.2.2 Experimental Isotherm CO2 Solubility

Previous investigations in the literature have shown that carbon dioxide is highly

soluble in imidazolium-based ionic liquids (Blanchard et al., 2001). In this work, carbon

dioxide was dissolved in a variety of ionic liquids with different cations and anions to

explain the factors governing the solubility in the ILs. Three ionic liquids with the same

anion (bis(trifluoromethylsulfonyl)imide) were used where the effect of the cation on

solubility was investigated. Two ionic liquids with the same cation (1,2,3-

Tris(diethylamino) cyclopropenylium) were investigated to explore the effects of

changing the anion. Two other ionic liquids with the same cation were investigated

[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4]. The following table shows

the solubility of CO2 in all the ionic liquids studied in this work at three temperatures.


for [TDC][DCN] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[TCD][DCN]

At 313.15 K At 323.15 K At 333.15 K

Pressure

(mbar)

Mole

Fraction of

CO2 (%)

Pressure

(mbar)

Mole

Fraction

of CO2

(%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

101.01 0.178 102.34 0.187 99.81 0.175

500.17 0.854 500.17 0.754 499.63 0.609

1001.02 1.65 997.41 1.45 999.15 1.25

2002.05 3.39 1998.31 2.99 2000.05 2.55

4000.11 6.74 4001.58 5.87 3998.11 5.02

7000.13 11.24 6996.13 9.77 6997.87 8.35

8998.73 14.11 9001.39 12.31 8999.13 10.52

9998.15 15.49 9997.49 13.57 10000.16 11.63

10998.79 16.87 11002.93 14.78 11000.52 12.65

12997.65 19.59 12996.72 17.27 12999.25 14.75

14992.51 22.17 14997.18 19.57 14997.31 16.78

17001.38 24.79 16998.04 21.85 17007.12 18.59

19006.65 27.20 19006.11 24.03

55


for [PMPY][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[PMPY][TF2N]

At 313.15 K At 323.15 K At 333.15 K

Pressure

(mbar)

Mole

Fraction of

CO2 (%)

Pressure

(mbar)

Mole

Fraction of

CO2 (%)

Pressure (mbar) Mole

Fraction of

CO2 (%)

99.01 0.238 96.34 0.229 99.67 0.219

500.03 1.09 499.49 0.928 499.89 0.744

1001.28 2.12 998.21 1.868 999.01 1.539

1999.24 4.31 1999.37 3.787 1999.78 3.204

3998.51 8.35 3998.51 7.249 3999.04 6.062

7000.13 13.73 7000.93 11.85 6996.93 10.04

8998.99 17.15 9000.33 14.70 9001.53 12.57

9999.76 18.77 9996.42 16.06 9999.62 13.75

10998.79 20.36 10999.06 17.48 10999.06 14.90

12997.92 23.46 13002.45 20.24 12997.25 17.25

14998.65 26.34 14997.71 22.82 15000.25 19.35

16998.18 29.03 17007.38 25.26 16995.37 21.43

18996.91 31.67 19008.11 27.66 18996.51 23.23


for [EMMP][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[EMMP][TF2N]

At 313.15 K At 323.15 K At 333.15 K

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

97.67 1.60 99.93 0.209 100.87 0.182

499.63 2.29 499.76 0.876 500.16 0.682

998.61 3.35 998.47 1.74 1000.48 1.44

1999.37 5.48 2000.71 3.63 1999.11 3.17

3998.51 9.41 4000.77 7.01 3998.24 6.00

6997.99 14.62 6997.73 11.44 7000.81 9.942

8998.32 17.79 8998.86 14.32 8999.66 12.32

9998.02 19.33 10003.51 15.70 9997.75 13.46

10999.59 20.86 11000.26 17.11 10998.79 14.59

12997.65 23.82 12997.78 19.69 12997.65 16.83

14999.31 26.57 15002.12 22.12 14998.78 18.98

16999.24 29.21 16995.77 24.48 16990.03 20.94

19000.11 31.66 18996.24 26.73 18997.04 22.80

56


for [TDC][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[TCD][TF2N]

At 313.15 K At 323.15 K At 333.15 K

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

97.54 0.28 101.41 0.25 101.27 0.23

498.96 1.30 500.83 1.05 500.03 0.91

998.88 2.50 998.88 2.09 997.41 1.88

2000.31 5.03 2000.44 4.37 1999.51 3.91

4001.57 9.74 3998.37 8.37 3998.23 7.41

6999.06 15.90 6998.67 13.73 6999.06 12.19

8999.26 19.70 8998.46 17.04 8998.19 15.19

9998.56 21.51 9998.69 18.66 9997.09 16.68

11000.79 23.31 10999.32 20.18 10999.73 18.10

12999.12 26.73 12999.25 23.17 12998.72 20.78

15000.52 30.00 14997.71 26.14 14998.78 23.38

16997.51 33.18 17005.38 28.81 16999.51 25.78

18996.77 36.01 18996.64 31.27 18997.84 28.17


for [EMIM][TF2N] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[EMIM][LACTATE]

At 313.15 K At 323.15 K At 333.15 K

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

Pressure

(mbar)

Mole Fraction

of CO2 (%)

998.88 8.70 999.01 7.14 499.63 4.30

2001.51 11.63 3997.83 13.00 998.48 5.97

3998.64 15.25 4998.73 14.29 1999.65 8.29

6999.46 18.90 6998.93 16.39 3996.24 11.24

8997.92 20.90 9997.75 19.07 6999.61 14.27

9998.29 21.84 9997.75 19.07 9000.73 15.95

10999.73 22.70 18998.37 24.99 9998.29 16.74

12997.12 24.23

14998.91 25.59

17000.58 27.08

18998.10 28.31

57


for [[(CH2)4SO3HMIm][TF2N]] (1) + CO2 at 313.15, 323.15 and 333.15 K.

[(CH2)4SO3HMIm][TF2N]]

313.15K 323.15K

Pressure

(mbar)

Mole Fraction of CO2

(%)

Pressure

(mbar)

Mole Fraction of CO2

(%)

97.67 0.13 98.21 0.16

499.63 0.13 500.29 0.62

998.61 0.73 999.68 1.22

8998.33 13.49 3998.37 5.57

9998.02 14.55 7000.53 9.09

10999.59 15.96 8999.13 11.59

12997.65 18.29 10001.09 12.58

14999.31 20.82 15002.38 18.26

16999.24 22.96

19000.11 25.38


for [(CH2)4SO3HMIm][HSO4] (1) + CO2 at 313.15, 323.15 and 333.15 K.


313.15K 323.15K

Pressure

(mbar)

Mole Fraction of

CO2 (%)

Pressure (mbar) Mole Fraction of CO2

(%)

99.27 0.076 101.01 0.056

498.43 0.17 499.77 0.12

998.88 0.30 9000.59 3.19

6999.33 2.53 9997.89 3.65

10999.73 4.82 10998.79 4.08

12997.12 5.52 12997.65 4.73

14999.98 5.48

16999.51 6.14

58

3.3 Solubility Isotherms Graphs

The following graphs will illustrate the CO2 solubility of the seven ionic liquids at

three different temperatures.

3.3.1 Solubility of CO2 in [EMMP][TF2N]

The following is a graphical representation of the CO2 solublities in

[EMMP][TF2N] at 313.15, 323.15 and 333.15K.

Mole fraction OF CO2 in [EMMP][Tf2N ](%)

0 5 10 15 20 25 30 35

Pre

ssure

(M

ba

r)

0

5000

10000

15000

20000

313.15 k

323.15 k

333.15 k


[EMMP][TF2N] at 313.15, 323.15 and 333.15 K.


59

3.3.2 Solubility of CO2 in [TDC] [TF2N]


[TDC][TF2N] at 313.15, 323.15 and 333.15K.

Mole Fraction of CO2 in [TDC][Tf2N] (%)

0 5 10 15 20 25 30 35 40

Pre

ssure

(M

ba

r)

0

5000

10000

15000

20000

313.15 K

323.15 K

333.15 K

Figure 3.4: Comparison of measured isothermal solubility data of CO2 in [TDC][TF2N]

at 313.15, 323.15 and 333.15 K.

60

3.3.3 Solubility of Co2 in [PMPY] [TF2N]


[PMPY][TF2N] at 313.15, 323.15 and 333.15K.

Mole fraction of CO2 in [pmpy ][Tf2N](%)

0 5 10 15 20 25 30 35

Pre

ssure

(M

ba

r)

0

5000

10000

15000

20000

313.5 k

323.15 k

333.15 k

Figure 3.5: Comparison of measured isothermal solubility data of CO2 in [PMPY][TF2N]

at 313.15, 323.15 and 333.15 K.


61

3.3.4 Solubility of CO2 in [TDC] [DCN]

The following is a graphical representation of the CO2 solublities in [TDC][DCN]

at 313.15, 323.15 and 333.15K.

Mole fraction of CO2 in [TDC] [DCN] (%)

0 5 10 15 20 25 30

Pre

ssure

(M

ba

r)

0

5000

10000

15000

20000

313.15 k

323.15 k

333.15 k

Figure 3.6: Comparison of measured isothermal solubility data of CO2 in [TDC][DCN] at

313.15, 323.15 and 333.15 K.

62

3.3.5 Solubility of CO2 in [EMIM] [LACTATE]


[EMIM][LACTATE] at 313.15, 323.15 and 333.15K.

Mole fraction of CO2 in [Emim][LACTATE] (%)

0 5 10 15 20 25 30

Pre

ssure

(M b

ar)

5000

10000

15000

20000

313.15 K

323.15 K

333.15 K


[EMIM][LACTATE] at 313.15, 323.15 and 333.15 K.

63

3.3.6 Solubility of CO2 in [(CH2)4SO3HMIm][TF2N] And


The following is a graphical representation of CO2 solublities in

[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15 and 323.15K.

Mole fraction of CO2 (%)

0 5 10 15 20 25 30

Pre

ssure

(M

ba

r)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[(CH2)4SO3HMIm][TF2N] at 313.15k

[(CH2)4SO3HMIm][TF2N] at 323.15k

[(CH2)4SO3HMIm][HSO4] at 313.15 k

[(CH2)4SO3HMIm][HSO4] at 323.15 k


[(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and

333.15 K.

64

3.4 Results: Effects of Cation With [TF2N] Anion

The effect of changing the cation on CO2 solubility was investigated using three

cations: 3-Methyl-1-propylpyridinium, ethyldimethylpropylammonium and 1,2,3-

tris(diethylamino)cyclopropenylium, all with the bis(trifluoromethylsulfonyl)imide anion.

The following graph illustrates the CO2 solubility of the four ionic liquids at

313.15 K.

Mole fraction of CO2 in ionic liquids (%)

0 10 20 30 40

Pre

ssu

re (

M b

ar)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000[[PMPY ][Tf2N]

[EMMP][Tf2N]

[TCD][Tf2N]


Figure 3.9: Comparison of three ionic liquids with the same anion to illustrate the effect

of the cation at 313 K.

65

3.4.1 Discussion: Effects of Cation With [TF2N] Anion

By examining the results of the aforementioned graphs, there are a few trends that can

be identified when comparing the same anion a changing cation. The first trend, as shown

in Figures 3.3-3.5 and 3.8 and in numerous previous findings, shows that the solubility of

CO2 in ionic liquids decreases with increasing temperature and increases with increasing

pressure. The second trend is the effect of changing the cation, as seen in Figure 3.9. In

this case, changing the cation on the IL has a significant effect on the CO2 solubility. It is

clear that the cation [TDC] provides a higher solubility when compared to the other three

cations. The solubility in decreasing order is as follows:

[TDC][TF2N]>[PMPY][TF2N]>=[EMMP][TF2N]> [(CH2)4SO3HMIm][TF2N]].

[TDC] cation contains multiple methyl groups distributed around the ring structure of the

cation which could be providing better free volume dynamics for CO2 to interact with this

ionic liquid as a whole. If the cation structure is examined closely, [TDC] has six methyl

groups hanging off the cation, [PMPY] has three methyl groups, [EMMP] has two methyl

groups and [(CH2)4SO3HMIm][TF2N] has three methyl groups. However, in [TDC] and

[PMPY], the methyl groups are organized around a core ring structure of the cation

perhaps enhancing their interaction with CO2 and providing a larger free volume unlike

[EMMP] which does not contain a ring structure. This may be similar to how the effect of

the alkyl chain length affects CO2 solubility where the increase in alkyl chain length leads

to decreased density of the ILs, and increased free volume within the longer chain of IL

(Muldoon et al., 2007).

66

This is further supported by the fact that [TDC] has the lowest density when

compared to [PMPY], [EMMP] and [(CH2)4SO3HMIm][TF2N]. Thus, it has the most

free volume among the three ILs giving it the highest solubility. Each of the cations has a

different base. For example, [TDC] is a propenylium based cation, [PMPY] is a

pyridinium based cation, [EMMP] is an ammonium based cation and

[(CH2)4SO3HMIm][TF2N] is an imidazolium based cation. The differences in cation

base can also be responsible for the differences in CO2 solubility. According to Sumon

and Henni (2011), cation alterations that decrease CO2 solubility include the addition of

the following groups: hydroxyl ([bmim][TF2N] > [OC2mim][TF2N]), phenyl

([hmim][TF2N] > [bnmim][TF2N]), and ether ([bepyrr]][TF2N] > [EtOEtpyrr]][TF2N])

(Sumon and Henni, 2011). Thus, one can see that modification of the cation can play a

minor role in effecting CO2 solubility. However, substantial changes are seen with anion

modification as seen in the next section.

3.5 Results: Effects of Anion With [TDC] Cation

The effect from changing the anion on CO2 solubility was investigated using two

different anions: bis(trifluoromethanesulfonyl)imide and dicyanamide, each with the

1,2,3-tris (diethyl amino) cyclopropenylium cation.

67


0 10 20 30 40

Pre

ssure

( M

ba

r)

0

5000

10000

15000

20000

[TDC][DCN]

[TDC][TF2N]

Figure 3.10: Comparison of CO2 solubility of [TDC] with [TF2N] and [DCN] at 313.15

K

3.5.1 Discussion Results: Effects of Anion With [TDC] Cation

In this section, the effects of changing the anion are explored. The

previous graph shows the CO2 solubility of two ionic liquids with the same cation [TDC]

but with two different anions, [TF2N] and [DCN]. The ionic liquid with the higher CO2

solubility possesses the fluorinated anion. [TDC] [TF2N] CO2 solubility is 0.3127 at

323.15K and 19 bar whereas [TDC][DCN] CO2 solubility is 0.2403 at 323.15 K and 19

bar. Thus, the fluorinated anion leads to about a 30% increase in solubility when

compared to the non-fluorinated anion. From the literature (Cadena et al., 2004), it is has

68

been shown time and time again that the nature of the anion has the greatest influence on

the solubility of CO2 and the bis(trifluoromethylsulfonyl)-imide anion [TF2N] has the

greatest affinity for CO2 (Cadena et al., 2004). This increase in CO2 solubility is, in part,

explained by the strong coulombic interactions responsible for the organization of the

liquid (Zhang et al., 2012). The high CO2 solubility, especially with the [TF2N] anion, is

attributable to the fluoroalkyl groups in [TF2N] which are known to be CO2-philic (Aki

et al., 2004). This may be the result of the favorable interactions between the negative

fluorine atoms of the anions and the positive charge on the carbon of carbon dioxide (Aki

et al., 2004; Schilderman et al., 2007). These are similar findings to Aki et al., when they

compared anions and found that [TF2N] has a higher CO2 solubility than the inorganic

anion of [DCN] (Aki et al., 2004). Hence, the anion has an influential role in determining

the CO2 solubility of an ionic liquid and [TDC][TF2N] has a higher solubility than

[TDC][DCN].

3.6 Results: Comparison of The [DCN] Anion With Different Cations

In this next section the ionic liquid [TDC][DCN] is compared with the experimental

results by Aki et al. on [bmim][DCN] and the effect of changing the cation with the same

anion (dicyanamide) is examined. A graphical comparison can be seen in the figure

below.

69

Mole Fraction of CO2 in ILs

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Pre

ssure

(ba

r)

0

20

40

60

80

100

[BMIM][DCN] (Aki et al. 2004)

[TDC][DCN](this work)

Figure 3.11: Comparison of CO2 solubility of [TDC] with [bmim] cations with same

anion at 313.15 K.

3.6.1 Discussion: Comparison of The [DCN] Anion With Different Cations

From the graph, [TDC] [DCN] has a better or comparable CO2 solubility to

[bmim][DCN] at low pressures. This trend could be due to the fact that [TDC] has more

methyl groups hanging off the cation compared to [bmim]. However, [bmim] has a

longer alkyl chain, perhaps giving it the higher solubility at higher pressures. When

comparing the two cations, one is a propenylium based cation and the other is a

imidazolium based cation. This too has a role in the reaction as imidazolium based ionic

liquids can have a higher solubility.


70

3.7 Comparison of All the Ionic liquids Studied


0 10 20 30 40 50

Pre

ssure

(M

ba

r)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[[PMPY][Tf2N]

[EMMP][Tf2N]

[TCD][Tf2N]


[TCD][DCN]

[EMIM][LACTATE]


Figure 3.12: Comparison of measured isothermal solubility data of CO2 in different ionic

liquids at 313.15 K

The ionic liquids are compared in the previous graph where the CO2 solubility

increases in all ILs with increasing pressure and decreases with increasing temperature.

The CO2 solubility in decreasing order is as follows:

[TCD][TF2N]>[PMPY][TF2N]>[EMMP][TF2N]>[emim][LACTATE]>[TCD][DCN]>

[(CH2)4SO3HMIm][TF2N]>[(CH2)4SO3HMIm][HSO4]. The following are the

solubilities obtained at 323.15K and 19 bar: [TCD][TF2N] =0.3127, [PMPY][TF2N] =

0.2765, [EMMP][TF2N]= 0.2672, [emim][LACTATE]= 0.2499, [TCD][DCN]= 0.2402.

The following are the solubilities obtained at 323.15K and 15 bar:

71

[(CH2)4SO3HMIm][TF2N]= 0.182 and [(CH2)4SO3HMIm][HSO4] =0.0548. As

expected, the ionic liquids with fluorinated anions have the highest solubility among the

studied ionic liquids. In addition to fluorination, the combined effect of fluorination and

the presence of S=O groups on the TF2N anion act synergistically to increase the CO2

solubility (Muldoon et al., 2007). It is suggested that the S=O group can increase CO2-

philicity of molecules due to Lewis base-Lewis acid interactions with the carbon atom of

CO2 (Muldoon et al., 2007). The effect of the TF2N anion on CO2 solubility is seen most

dramatically when comparing [(CH2)4SO3HMIm][TF2N] and [(CH2)4SO3HMIm]

[HSO4], where the addition of the fluorinated anion increases the solubility of CO2 by

more than three times that of the hydrogen sulfate anion. The hydrogen sulfate anions

also face another issue beyond low solubility, which is high viscosity. This has also been

reported by Riberio who found imidazolium ionic liquids with HSO4 have a high

viscosity which may be due to the anion-anion interactions (Ribeiro, 2012).

An interesting point to note is that at low pressures, of less than 10 bar, [emim]

[LACTATE] seems to have a higher CO2 solubility. For example, at about 323.15K and 7

bar [emim][LACTATE] has a solubility of 0.1639 whereas [TCD][TF2N] has a solubility

of 0.1373. This trend is seen until about 10 bar. This is similar to Shiflett’s ionic liquid

[emim][Ac] as seen in the graph below, which demonstrates high solubility at low

pressures and thus, [emim][LACTATE] has elements of a physical and chemical reaction

with CO2. As shown by Blath et al. IL with carboxylic anions such as [emim]

[pivalate],[emim][OAc] and [emim][benzoate] show chemoabsorption (Blath et al.,

2012). [LACTATE] contains a carbonyl group which is known to increase CO2 solubility

72

by providing the free electrons to the oxygen and allowing them to interact with the

Lewis acidic carbon of the CO2 (Muldoon et al., 2007).

Mole fraction of CO2

0.1 0.2 0.3 0.4 0.5

Pre

ssure

(b

ar)

0

2

4

6

8

10

12

14

16

18

20

[Emim][LACTATE] (this work)

[Emim][Ac] (Shiflett et al.2008)

Figure 3.13: Comparison of [emim][Ac] and [emim][LACTATE] at 50°C.

3.8 Comparisons of Current Work With Previously Published Work

A great deal of work has been spent on developing CO2 friendly ionic liquids to

increase the solubility of polar molecules in CO2. Some have used fluorination, others

have used nonfluorous methods to increase the CO2-philicity. Other methods used to

increase CO2 solubility are the addition of carbonyl groups and the branching of the alkyl

chain to allow for more free volume for CO2 interactions. These are more

environmentally friendly ways to increase CO2 solubility.

73

There are endless published papers exploring CO2 solubility in many different ionic

liquids. This section will explore a sample of what is currently in the literature and

compare it with the results obtained from this work. Some of the highlights from the

literature include the work by Shiflett et al. and their work with

[hmim][TF2N],[bmim][BF4] ,[bmim][PF6] and [bmim][Ac] (Shiflett and Yokozeki

2007; Shiflett and Yokozeki 2005). Others include the study of [emim][FAP] by

Althuluth et al. (Althuluth et al., 2012), the study of [emim][TF2N] from Schildermana et

al. (Schilderman et al., 2007) and many others.

3.8.1 Effect of Changing The Cation

Among this vast pool of CO2 solubility in different ionic liquids the effect

of the cation alkyl chain length for the imidazolium-based ionic liquids paired with the

[TF2N] anion ([omim][TF2N], [bmim][TF2N] from Aki et al. (Aki et al., 2004) and

[hmim][TF2N]) will be examined and compared with ionic liquids with the same anion:

[PMPY] [TF2N], [TDC] [TF2N], [EMMP][TF2N] and [(CH2)4SO3HMIm][TF2N] and

others such as [hmpy][TF2N],[C6H4F9mim][TF2N], [C8H4F13mim][TF2N] and

[Choline][TF2N] from Muldoon et al (Muldoon et al., 2007).

74

Mole fraction CO2 in ionic liquids

0.0 0.2 0.4 0.6 0.8

Pre

ssure

( b

ar)

0

20

40

60

80

100

[Choline][Tf2N] (Muldoon et al., 2007)

[[C8H4F13mim][Tf2N]( Muldoon et al.,2007)

[bmim][Tf2N] (Aki et al., 2004)

[Omim][Tf2N] (Aki et al .,2004)

[TDC][TF2N] (this work).

[EMMP][TF2N](this work).

[Pmpy][TF2N](this work).

[[C6H4F9mim][Tf2N] (Muldoon et al., (2007)).

[hmmim][Tf2N] (Aki et al.,(2004)).

Figure 3.14: Comparison of CO2 solubility at 333.15 K with different cations paired with

the [TF2N] anion.

75

Table 3-10: Numerical representation summary of the IL seen in Figure 3.14

Ionic liquid at 60 oC Highest Pressure Solubility

[Choline][TF2N] Muldoon et al. (2007) 12 bar 0.156

[bmim][TF2N] Aki et al. (2004) 13.6 bar 0.170

[hmmim][TF2N] Aki et al. (2004) 14.79 bar 0.199

[EMMP][TF2N](this work) 13 bar 0.201

[PMPY][TF2N] (this work) 13 bar 0.205

[C6H4F9mim][TF2N] Muldoon et al.

(2007) 13bar 0.221

[C8H4F13mim][TF2N] Muldoon et al.

(2007) 13 bar 0.232

[TDC][TF2N] (this work) 13 bar 0.235

[omim][TF2N] Aki et al. (2004) 16.23 bar 0.2467

Figure 3.15: Comparison of CO2 solubility at 60°C with different cations paired with the

[TF2N] anion at 333.15 K and about 12 to 14.97 bar.

76

The cation can have an effect on CO2 solubility. There are many variations of

cations causing significant changes to CO2 solubility. The IL showing some promise

when it comes to CO2 solubility from this group of IL is [TDC][TF2N] which has the

highest solubility. [omim][TF2N] from Aki et al. (2004) comes very close in terms of

solubility where [omim][TF2N] has a solubility of 0.2467 at about 16 bar and

[TDC][TF2N] has a solubility of 0.2614 at about 15 bar. By changing the cation from

[omim] to [TDC] the CO2 solubility can increase by about 10%.

Some of other trends that can clearly be seen from the graphs are that cations with

more fluro groups have a higher solubility as seen when comparing

[C6H4F9mim][TF2N] with [C8H4F13mim][TF2N] and [hmim][TF2N].

[C8H4F13mim][TF2N] has a higher solubility than [C6H4F9mim][TF2N] for two

reasons. First, it has more fluro groups and has a longer alkyl chain, both of which have

been shown in the literature to increase CO2 solubility (Muldoon et al., 2007). The ILs

also have comparable CO2 solubility when compared to the three ILs.

[EMMP][TF2N],[PMPY][TF2N] and [TDC][TF2N] all had a slightly lower solubility at

high pressure but very comparable solubility to [C6H4F9mim][TF2N]. The structure of

the cations used in [EMMP][TF2N],[PMPY][TF2N] and [TDC][TF2N] perhaps cause

crowding of the anion and may minimize the free volume of the ionic liquid and interfere

with how CO2 reacts with the anion. Thus, one can conclude that fluorination of the

cation leads to increased CO2 solubility.

77

Mole fraction CO2 in ionc liquids

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

pres

sure

(bar

)

0

5

10

15

20[hmim][Tf2N] (Shiflett and Yokozki. 2007)

[hmpy][Tf2N] (Muldoon et al. 2007)

[bmim][Tf2N] (Anthony et al. 2005)

[TDC] [Tf2N] (this Work)

[Pmpy] [Tf2N] (this work)

[EMMP][Tf2N] (this Work)

Figure 3.16: Comparison of CO2 solubility in different ILs with the same anion at 323.15

K

Similar trends exist for CO2 solubility which increases with increasing pressure. In

Figure 3.16, the comparison of the benchmark that most IL will be compared to,

Shiflett’s [hmim][TF2N], is compared to other ionic liquids with the same anion but

different cations highlighting the effect of cation change. The [hmim][TF2N] CO2

solubility is comparable to [TDC][TF2N]. The effect of the alkyl chain can be seen when

comparing [bmim], [omim] and [hmim] from Figures 3.14 and 3.16, where the trend in

decreasing solubility is as follows: [hmim]>[omim]>[bmim]. Thus, reiterating what is

published in the literature, the increase in alkyl chain length of the cation leads to

increased CO2 solubility.

78

Comparing [TCD] [TF2N] with [hmim] [TF2N] from Figure 3.16, [hmim][TF2N]

does have a slightly lower molecular weight, but the alkyl chain is longer and perhaps

organized in a more linear fashion making it more effective for solubility. The effect of

the alkyl chain length in [hmim] [TF2N] is related to the hydrogen atom located at the C2

position on the imidazolium ring which has a large positive charge (Ramdin et al., 2012).

If this carbon is replaced by a methyl group it decreases the solubility (Ramdin et al.,

2012). Therefore, the position of this acidic hydrogen gives Shiflett’s IL the higher

solubility as also seen in another imidazolium cation such as bmim which has a longer

alkyl chain and is known for higher CO2 solubility. Also, when comparing the cations

paired with [TF2N], at low pressures there is very little difference between the

imidazolium and pyridinium cations as seen between [hmim] and[hmpy] when paired

with [TF2N] (Muldoon et al., 2007). Therefore, depending on the modifications

employed and used on the cation, CO2 solubility can be improved or decreased.

By examining Figures 3.14 and 3.16, some general trends can be seen. Other

comparisons with [hmim][TF2N] can be made with the change of the cation when

examining the [choline] cation. The [choline] cation lowered CO2 solubility compared to

the [hmim] cation, hydrogen bonding of the [TF2N] anion with the [choline] cation may

make the anion less available for interaction with CO2 (Muldoon et al., 2007). Also, when

comparing [choline] with the [TDC] cation from the current experiment, the CO2

solubility is higher in [TDC][TF2N] than in [choline][TF2N] for similar reasons.

The general conclusion from the aforementioned figures is that the cation in an ionic

liquid can play an important role in determining the CO2 solubility capabilities of an ionic

liquid where [TDC][TF2N] has good potential for CO2 solubility.

79

3.8.2 Effect of Changing The Anion With An [Emim] Cation

One of the imidazolium based cations used in the experimental measurements is

[emim] in the ionic liquid [emim][LACTATE]. This section will compare the effects of

changing the anion with research published in the literature such as [emim][TF2N]

(Schilderman et al., 2007) and [emim][FAP] (Althuluth et al., 2012).

Mole fraction of CO2 ionic liquid

0.1 0.2 0.3 0.4 0.5 0.6 0.7

Pre

ssure

(bar)

0

20

40

60

80

[emim][FAP] (Althuluth et al. 2012)

[emim][TF2N] (Schilderman et al. 2007)

[Emim][LACTATE ](this work)

Figure 3.17: Comparison of changing the anion with limidazoloium cation

The solubility of CO2 in [emim][FAP] is higher than in the other ILs with the same

cation following the trend: [emim][FAP]> [emim][TF2N] > [emim][LACTATE]. The

trend seen above is most likely due to the presence of a large amount of fluorine atoms in

the anion, which results in an increase in CO2 solubility of the IL (Althuluth et al., 2012).

The above trend holds true when examining CO2 solubility at high pressures.

However, for low pressure trends, CO2 solubility changes where [emim][LACTATE] has

higher solubility than [emim][FAP] and[emim][TF2N] as seen in the table below.

80

[emim][LACTATE] has a higher solubility than the popular anion of [TF2N] and is more

environmentally friendly due to the lack of fluoro groups.

Table 3-11: Comparison of [emim] cation with different anions.

Ionic liquid Pressure/ bar Mole fraction of CO2 in ILs

[emim][FAP] 5.80 0.1003

[emim][LACTATE] 6.99 0.1427

[emim][TF2N] 8.52 0.1230

3.9 Comparing The Literature With [Bmim][Ac]

The following is a graphical representation of Shiflett’s [bmim][Ac] which

is known for its very high CO2 solubility and a comparison with other measurements of

IL from the literature.

81

Mole fraction of CO2 (%)

0 5 10 15 20 25 30 35 40

Pre

ssure

(M b

ar)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[bmim][Ac] (Shiflett et al., 2008).

[bmim] [PF6] (Shiflett and Yokozeki 2005)

[(CH2)4SO3HMIm][TF2N] (this work)

[(CH2)4SO3HMIm][HSO4](this work)

[TCD][DCN] (this work )

[PMPY][Tf2N] (this work)

[EMMP][Tf2N] (this work)

[TCD][Tf2N] (this work)

[EMIM][LACTATE] (this work)


published results in the literature at 323.15 K

3.10 Comparison of Ammonium Based Ionic Liquid from the Literature and

Current Work

82


the published results in the literature at 323.15 K and high pressure from 1 to 120 bar.

The previous graph compares the ionic liquid which is an ammonium

based Ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide and compares it

with 2-hydroxy ethylammonium formate (HEF), 2-hydroxy ethylammonium acetate

83

(HEA), 2-hydroxy ethylammonium LACTATE (HEL), tri-(2-hydroxy ethyl)-ammonium

acetate (THEAA), tri-(2-hydroxy ethyl)-ammonium LACTATE (THEAL), 2-(2-hydroxy

ethoxy)-ammonium formate (HEAF), 2-(2-hydroxy ethoxy)-ammonium acetate (HEAA)

and 2-(2-hydroxy ethoxy)- ammonium LACTATE (HEAL) from Yuan et al. (2007). The

eight ionic liquids by Yuan et al. have a much lower CO2 solubility than [EMMP] [TF2N]

at low pressure which can be due to the fact the ionic liquid has a fluorinated anion.

However, two of the Yuan et al. ionic liquids HEAA and THEAL show high CO2

solubility at high pressure.

Most of the contributions have provided information regarding the physical

absorption of CO2 in ionic liquids. Despite the high physical CO2 absorption of the seven

investigated ionic liquids, the solubilities of CO2 in the studied ionic liquids are less than

in [bmim][Ac] as seen in Figure 3.18, which demonstrates unusual behavior in

comparison to other ionic liquids and it possesses the highest CO2 solubility. However,

there is a tradeoff. According to Shiflett et al., when examining [bmim][Ac] which is

known for its high CO2 solubility at low pressure it becomes clear that it must be reacting

with a different mechanism. The high solubility of CO2 in [bmim][Ac] is explained by a

chemical reaction that occurs between the two reactants that leads to the formation of an

intermediary product produced which is 1-butyl-3-methylimidazolium-2-carboxylate

(Cabaco et al., 2012). This carboxylation reaction is irreversible even at very high

temperatures (Cabaco et al., 2012). The carboxylation of the imidazolium ring is

followed by acetic acid formation (Cabaco et al., 2012). The reactions occur as the CO2

solubility approaches 0.35 mole fraction. At this point, a physical reaction occurs

resulting from the interaction of acetic acid molecules with acetate anions (Cabaco et al.,

84

2012). During this second phase, the CO2 reacts with the carboxylate molecule and the

aceteic acids that resulted from the initial chemical reaction. Thus, the chemical reaction

creates a unique environment for the second physical reactions that explain the unique

behavior and high solubility of CO2 in [bmim][Ac].

Figure 3.19 compares Shifflet’s [bmim][PF6] and the seven ionic liquids investigated

in this work. All the ionic liquids had a higher solubility than [bmim][PF6] except for

[(CH2)4SO3HMIm][HSO4]. This is most likely due to the fact

[(CH2)4SO3HMIm][HSO4] lacks a fluorinated anion. When compared to most of the

ionic liquids studied in this work, the anion [PF6] is a weaker CO2 absorbent when

compared to the popular [TF2N] anion which is known for its higher CO2 solubility

(Muldoon et al., 2007).

3.11 Comparing the Current Work With Recent Results From An Affiliated Group

The next section will look at comparing the results from Ugyur, 2013 and

Nonthanasin, 2013 and this work. The ionic liquids used by Ugyur are 1-butyl-3-

methylimidazolium trifluoromethanesulfonate ([bmim OTF]), 1-butyl-3-

methylimidazolium dibutyl phosphate [bmim DPH], 1,3-dimethoxyimidazolium

bis(trifluoromethyl-sulfonyl)imide ([(OMe)2Im-NTF2]), 1-butyl-1-methylpiperidinium

bis(trifluoromethylsulfonyl)imide ([1b1mp NTF2]), and 1,3-diethoxyimidazolium

bis(trifluoromethylsulfonyl)imide ([(OEt)2Im-NTF2]) .

The ionic liquids used by Nonthanasin were triethylsulfonium bis(trifluoromethyl

sulfonyl)imide ([S222][TF2N]), diethylmethyl(2-methoxyethyl)ammonium

bis(trifluoromethyl sulfonyl)imide ([deme][TF2N]), 1-propyl-3-methylimidazolium

85

bis(trifluoromethyl sulfonyl)imide ([pmim][TF2N]), 1-allyl-3-methylimidazolium

bis(trifluoromethyl sulfonyl)imide ([amim][TF2N]), and 1-butyl-4-methylpyridinium

tetrafluoroborate ([4mbp][BF4]). The measurements from the two groups provide

evidence that the ammonium-based ionic liquid [deme][TF2N] achieved the highest CO2

absorption among all the ionic liquids. However, when comparing the current work to the

results, the trend for CO2 solubility in decreasing order is as follows: [TDC] [TF2N] <

[deme][TF2N]< [(OEt)2Im-NTF2]< [PMPY] [TF2N]< [pmim][TF2N]< [1b1mp NTF2]

<[EMMP][TF2N]< [S222][TF2N] < [emim][LACTATE] < [(OMe)2Im-NTf2]<

[TDC][DCN] < [bmim DPH] < [bmim OTF] < [4mbp][BF4]. The following graph

illustrates all the ionic liquids used in this work and their solubilites at different pressures

and at 323.15 K.

86

Mole fraction CO2 in ionic liquid (%)

0 5 10 15 20 25 30 35

Pre

ssure

(M b

ar)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[(OMe)2Im-NTf2](Uygur 2013)

[bmim OTF](Uygur 2013)

[bmim OTF](Uygur 2013)

[(OEt)2Im-NTF2](Uygur 2013)

[bmim DPH](Uygur 2013)

[TCD][DCN] (this work)

[PMPY ][Tf2N] (this work)

[EMMP ][Tf2N] (this work)

[TCD][Tf2N] (this work)

[EMIM][LACTATE] (this work)

[deme][Tf2N] (Nonthanasin 2013)

[pmim][Tf2N] (Nonthanasin 2013)

[S222][Tf2N] (Nonthanasin 2013)

[amim][Tf2N] (Nonthanasin 2013)

[4mbp][BF4] ( Nonthanasin 2013)

Figure 3.20: Comparison of CO2 solubility at 323.15 K

87

Figure 3.21: Comparison of CO2 solubility at 323.15 K

88

0 10 20 30 40

Pre

ssure

(M

ba

r)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[S222][Tf2N](Nonthanasin 2013)

[deme][Tf2N](Nonthanasin 2013)

[pmim][Tf2N](Nonthanasin 2013)

[amim][Tf2N](Nonthanasin 2013)

[4mbp][BF4](Nonthanasin 2013)

[TCD][DCN](this work)

[Pmpy ][Tf2N](this work)

[EMMP][Tf2N](this work)

[TCD][Tf2N](this work)

[(CH2)4SO3HMIm][HSO4](this work)

[(CH2)4SO3HMIm][TFSI](this work)

[EMIM][LACTATE](this work)

(%) liquids ionicin CO ofFraction Mole 2

Figure 3.22: CO2 solubility comparing the ionic liquids used in this work with that of

Nonthanasin (2013)

89

0 10 20 30 40

Pre

ssure

( M

ba

r)

5000

10000

15000

20000

[Deme][Tf2N](Nonthanasin 2013)

[TDC][Tf2N] (this work)


Figure 3.23: Comparison of the solubility of CO2 in the studied ionic liquids and the one

in the present research at 313.15 K.

Two ionic liquids are compared with the same anion but different cation,

thus, allowing an examination of the cation effect as seen in Figure 3.23. It compares the

cation [deme] as reported by Nonthanasin (Nothanasin, 2013) and [TDC] as explored in

this current work. The solubility of CO2 in [TDC][TF2N] is higher than [deme][TF2N]

by about 12.5%.

90

0 5 10 15 20 25 30 35

Pre

ssure

(M

ba

r)

5000

10000

15000

20000

(OEt)2Im-NTF2] (Uygur (2013)

[TDC][Tf2N] (this work)


Figure 3.24: Comparison of the solubility of CO2 in the studied ionic liquids and Uygur,

2013 at 323.15 K.

In the previous graph, the effect of the cation is seen when comparing Uygur’s best

(Uygur, 2013) ionic liquid to [TCD][TF2N] from this work. It can be seen that for every

pressure [TCD][TF2N] has a higher CO2 solubility than [OEt)2lm-NTF2]. The solubility

of [TCD][TF2N] solubility is higher by 12% .

91

0 5 10 15 20 25 30

Pre

ssure

(M

ba

r)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

[deme][Tf2N] (Nonthanasin 2013)

[emmp][Tf2N] (this work)


Figure 3.25: Comparison of the solubility of CO2 in the studied ionic liquids and the ones

in our group at 323.15 K.

A comparison between Nothanasin’s best ionic liquid of [deme][TF2N] and

[Emmp][TF2N] is presented in the previous graph. There is a minor difference in the

composition of the ionic liquids where [deme][TF2N] has an extra methylene group

which has given the solubility a slight increase.

92

0 5 10 15 20 25 30 35

Pre

ssure

(M

ba

r)

5000

10000

15000

20000

[1b1mp NTF2] (Uygur 2013)

[(OEt)2Im-NTF2](Uygur 2013)

[PMPY ][Tf2N] (this work)

[TDC][Tf2N] (this work))

[deme][Tf2N](Nonthanasin 2013)

[pmim][Tf2N](Nonthanasin 2013)


Figure 3.26: CO2 solubility of different best ionic liquid in this work, (Ugyur, 2013) and

(Nonthanasin, 2013) at 323.15 K.

93

Table 3-12: Summary of the CO2 solubilities in decreasing order from this work, Ugyur

(2013) and Nonthanasin (2013) at 323.15 K and same pressure 19 bar.

Ionic liquid Bar Solubility

[TDC] [TF2N] (this work) 19 0.3127

[deme][TF2N] (Nonthanasin 2013) 19 0.2805

[(OEt)2Im][TF2N](Ugyur 2013) 19 0.2779

[PMPY] [TF2N] (this work) 19 0.2765

[pmim][TF2N] (Nonthanasin 2013) 19 0.2724

[1b1mp][TF2N](Ugyur 2013) 19 0.2719

[EMMP][TF2N] (this work) 19 0.2673

[S222][TF2N]( Nonthanasin 2013) 19 0.2637

[emim][LACTATE] (this work) 19 0.2499

[(OMe)2Im][TF2N] (Ugyur 2013) 19 0.2405

[TDC][DCN] (this work) 19 0.2403

[bmim ][DPH]( Ugyu 2013) 19 0.2395

[bmim][TfO] (Ugyur 2013) 19 0.2085

[4mbp][BF4] (Nonthanasin 2013) 19 0.1706

94

[TDC] [Tf2N] (this Work)

[deme][Tf2N] (Nonthanasin (2013))

[(OEt)2Im][Tf2N](Ugyur (2013))

[PMPY] [Tf2N] (this Work)

[pmim][Tf2N] (Nonthanasin (2013))

[1b1mp][Tf2N](Ugyur (2013))

[EMMP][Tf2N] (this Work)

[S222][Tf2N]( Nonthanasin (2013))

[emim][LACTATE] (this Work)

[(OMe)2Im][Tf2N] (Ugyur(2013))

[TDC][DCA] (this Work)

[bmim ][DPH]( Ugyu (2013))

[bmim][TfO] (Ugyur (2013))

[4mbp][BF4] Nonthanasin(2013)

Mo

le fra

ctio

n o

f co

2

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

P= 19 bar

Figure 3.27: Summary of the CO2 solubilities in decreasing order from this work, (Ugyur,

2013) and (Nonthanasin, 2013) at 323.15 K at same pressure 19 bar.

When comparing the work of the two groups with the results obtained from the

current study, the propenylium based cation (1,2,3-Tris(diethylamino)cyclopropenylium

bis(trifluoromethanesulfonyl)imide) reigned supreme with respect to CO2 solubility.

When comparing the best ionic liquids from Ugyur and Nonthanasin, all three

[deme][TF2N], [(OEt)2Im-NTF2] and [TDC][TF2N] have the same fluorinated anion,

thus the discrepancy in their solubility must be attributable to their cation. Ugyur’s best

ionic liquid [(OEt)2Im-NTF2] cation only has two methyl groups attached to their cation,

95

perhaps contributing to its low solubility. When examining other factors responsible for

increasing solubility, such as the molecular weight and alkyl chain length, the IL with the

higher molecular weight is [TDC] [TF2N] and it has multiple long alkyl chains on the

cation which are perhaps responsible for its higher solubility.

96

4 CHAPTER FOUR: MODELING

This chapter contains three sections. The first section will describe the theory

behind the thermodynamic modeling. The second section will describe the density

calculations of the ionic liquids and details on the thermodynamic models used to

correlate the experimental CO2 solubility including equations of state, such as the Peng-

Robinson (PR-EoS), the Redlich Kwong (SRK), and the Non-Random Two-Liquid

(NRTL) activity coefficient model. Henry’s law constants, enthalpies and entropies of

absorption for CO2 in different ionic liquids are discussed in the last section.

4.1 Theory of Thermodynamic Properties and Modeling

The estimation of physical properties of gases and liquids is an important component

in research and in attempts to advance the field of ionic liquid research. Just like a

structural engineer needs to know the properties of concrete and steel to design a

structurally sound bridge, a chemical engineer needs to know the properties of gases and

liquids in order to develop their desired or targeted liquid or gas for a specific function

such as CO2 capture. This need or ability to estimate the physical properties was

addressed with the development of equations of state. There are many different

estimation methods or models that one could use. Depending on the effects studied

(Liquid Liquid Equilibrium (LLE), Vapour Liquid Equilibrium (VLE) or both), a

particular model is used (González, 2011). Empirical methods such as NRTL are used in

order to correlate LLE in mixtures of ionic liquids (González, 2011). On the other hand,

to correlate VLE systems, more sophisticated equation-of-state models are employed.

The different methods explored in this section deal with the equation of state method

97

which includes the Peng Robinson (PR-EoS) and Soave-Redlich-Kwong (SRK with

Quadratic Mixing Rules) and the activity coefficient method which includes the NRTL.

4.1.1 Peng Robinson EoS

The first method that the data could be correlated with is the Peng-Robinson

equation of state (EoS). The equation was developed in 1976 (Peng and Robinson, 1976).

It is a cubic thermodynamic equation that aims to describe the state of a given substance

under a specific set of physical conditions (Anthony et al., 2002). It provides a

relationship between temperature, pressure and volume.

The equation for the Peng-Robinson model is (Peng and Robinson, 1976):

)()( bVbbVV

a

bV

RTP

mmmm

(4.1)

The mixture parameters in the ionic liquid phase are calculated from following

four mixing rules (Song et al., 2010):

bVbbVV

a

bV

RTP

ˆˆˆˆ

(4.2)

c

c

P

RTa

2

45724.0

(4.3)

c

c

P

RTb 07780.0

(4.4)

2/11 cTTm (4.5)

226992.054226.137464.0 m (4.6)

The Peng-Robinson equation of state was used to calculate the fugacity

coefficient of carbon dioxide:

98

(4.7)

Some advantages of this equation are the simplicity of its application. However,

one of the drawbacks of this EoS is the limited accuracy that it can provide the user. To

calculate the parameters of the PR-EoS, the critical temperature (Tc), critical pressure

(Pc), and the acentric factor (ω) of both components, and CO2 and ionic liquids are

needed. The values are obtained by estimation using the modified Lydersen-Joback-Reid

method which is explained later in this chapter.

4.1.2 Soave-Redlich-Kwong (The SRK with Quadratic Mixing Rules)

The second method used to correlate the data is the SRK method with quadratic

mixing rules. It’s another equation of state method which provides results that are

comparable to the Peng-Robinson equation. The SRK equation of state is based on the

Redlich-Kwong-Soave (RKS) equation. The SRK equation originated from the Redlich-

Kwong (RK) equation of state (Redlich and Kwong, 1949) and was further modified by

Soave (Soave, 1972).

The Soave-Redlick-Kwon equation is as follows:

𝑃 =𝑅𝑇

𝑉−𝑏−

𝑎(𝑇)

𝑉(𝑉+𝑏) (4.8)

Where the parameters for the SRK-Equation of state are found using:

ci

cii

ci

ciii

P

RTb

P

TRa 08664.0,42747.0

22

(4.9)

The equations are obtained by applying the critical constraint to the EoS under the

following conditions:

m

V

nVTi

i ZdVV

RT

n

P

RTj

ln1

ln

,,

99

𝛼𝑖(𝑇𝑐𝑖) = 1.0 (4.10)

The parameter αi is a temperature function developed by Soave (Soave, 1972) in the RK-

EoS to improve the correlation of the vapor pressure:

𝛼𝑖(𝑇) = [1 + 𝑚𝑖(1 − 𝑇𝑟𝑖0.5)]

2 (4.11)

The parameter mi is uses the concept of correlation with the acentric factor:

𝑚𝑖 = 0.48508 + 1.55171𝜔𝑖 − 0.15613𝜔𝑖2 (4.12)

For multicomponent equilibria, mixing rules and combining rules which relate the

properties of the pure components to the properties of the mixtures are applied. The

mixture parameters in the liquid phase are calculated from the quadratic mixing rules:

𝑎 = ∑ ∑ 𝑥𝑖𝑗𝑖 𝑥𝑗𝑎𝑖𝑗 (4.13)

𝑎𝑖𝑗 = (𝑎𝑖𝑎𝑗)0.5

(1 − 𝑘𝑖𝑗) (4.14)

𝑏 = ∑ ∑ 𝑥𝑖𝑗𝑖 𝑥𝑗𝑏𝑖𝑗 (4.15)

𝑏𝑖𝑗 =(𝑏𝑖+𝑏𝑗)

2(1 − 𝑙𝑖𝑗) (4.16)

where bii = bi and bjj = bj. kij and lij are binary interaction parameters.

The interaction parameters in SRK EoS, has a linear relationship with temperature:

𝑘𝑖𝑗 = 𝑘𝑖𝑗0 + 𝑘𝑖𝑗

1 𝑇

1000 (4.17)

𝑙𝑖𝑗 = 𝑙𝑖𝑗0 + 𝑙𝑖𝑗

1 𝑇

1000 (4.18)

where kij0, kij

1, lij0 and lij

1 are constant.

100

4.1.3 NRTL Activity Coefficient Method

The third method used to correlate the data is the activity coefficient method of

NRTL. The general nonrandom two-liquid (NRTL) equation can be used to correlate the

vapor-liquid equilibrium of IL containing systems. Using AspenPlus, NRTL generates

the liquid activity coefficients. The idea behind NRTL is based on the premise that each

liquid is made of two types of molecules surrounded by each other in a binary mixture

(Walas, 1985). The theory looks at the concentration around each type of molecule which

is different from the overall concentration and this difference is related to the difference

in interaction energy between molecules of the same type (Walas, 1985). It is this energy

difference that introduces the concept of non-randomness at the molecular level in NRTL

(Walas, 1985).

The activity coefficients, γi, were correlated by the following equations based on

the NRTL model (Wang et al., 2010):

𝑙𝑛𝛾1 = 𝑥22 [𝜏21 (

𝐺21

𝑥1+𝑥2𝐺21)

2

+ (𝜏12𝐺12

(𝑥2+𝑥1𝐺12)2)] (4.19)

𝑙𝑛𝛾2 = 𝑥12 [𝜏12 (

𝐺12

𝑥2+𝑥1𝐺12)

2

+ (𝜏21𝐺21

(𝑥1+𝑥2𝐺21)2)] (4.20)

where,

𝐺12 = exp (−∝12 𝜏12)

𝐺21 = exp (−∝12 𝜏21)

12 = (𝑔12 − 𝑔22)/𝑅𝑇

21 = (𝑔21 − 𝑔11)/𝑅𝑇

101

The parameters g12 and g21, are equivalent (g12 = g21). 12, 21 and α12 are three binary

parameters adjusted to the experimental solubility data of ionic liquids.

4.2 Thermodynamic Modeling

4.2.1 Critical Property Estimation

The critical data for the ionic liquid used in this experiment was obtained by the

group contribution using the Modified Lydersen-Joback-Reid method (Valderrama and

Sanga, 2008). It is believed that ionic liquids begin to decompose at low temperatures or

temperatures approaching the natural boiling point and, as a result, the critical values

can’t actually be measured (Valderrama and Sanga, 2008). Therefore, the Modified

Lydersen-Joback-Reid method is used to estimate the values of the critical properties. A

group contribution method is used to find the critical properties (Tc, Pc and Vc), the

normal boiling point temperature (Tb), the critical compressibility factor (Zc), the density

(ρ) and the acentric factor (ω) of ionic liquids (Valderrama and Sanga, 2008).

4.2.2 Modified Lydersen‐Joback‐Reid Method

This method provides a way to estimate the critical properties of ionic liquids by

Valderrama et al. This method combines the equation for critical pressure and volume

which is based on Lydersen’s work and the equations of Joback-Reid for the normal

boiling temperature and the critical temperature (Valderrama and Sanga, 2008). One of

the advantages of this method is that it provides more accuracy for estimating the critical

properties of molecules with high molecular mass (Valderrama and Sanga, 2008).

The following correlations for estimating critical properties and acentric factors

are used (Valderrama and Sanga, 2008):

102

Modified Group Contribution Method: (Valderrama and Sanga, 2008).

𝑇𝑏(𝐾) = 198.2 + ∑ 𝑛∆𝑇𝑏 (4.21)

𝑇𝑐(𝐾) =𝑇𝑏

𝐴+𝐵 ∑ 𝑛∆𝑇𝐶−(∑ 𝑛∆𝑇𝐶)2 (4.22)

𝑃𝑐(𝑏𝑎𝑟) =𝑀

𝐶+(∑ 𝑛∆𝑃𝐶)2 (4.23)

𝑉𝐶(𝑐𝑚3𝑚𝑜𝑙−1) = 𝐷 + ∑ 𝑛∆𝑉𝐶 (4.24)

ω=(𝑇𝑏−43)(𝑇𝑐−43)

(𝑇𝑐−𝑇𝑏)(0.7𝑇𝑐−43)log (

𝑃𝑐

𝑃𝑏) −

(𝑇𝑐−43)

(𝑇𝑐−𝑇𝑏)log (

𝑃𝑐

𝑃𝑏) + log (

𝑃𝑐

𝑃𝑏) − 1 (4.25)

zc =PCVC

RTC (4.26)

Constants:

A=0.5703, B=1.0121, C=0.2573, D=6.75,

A=a+(BM / Vc ), B=(c/Vc )+d/M)Vc1.0470 where a=0.34111, b=2.0773, c=0.5386,

d=0.0393, R =84.31 (bar cm3 /mole k), Pp.=1.01325

In the equations above, M is in g/mol, Tb and Tc are in K, Pc is in bar and Vc is in

(cm3/mol). Where the contributions are indicated as ∆𝑇𝑏, ∆𝑇𝑐 , ∆𝑃𝑐, and ∆𝑉𝑐. M is the

molecular weight of the component. The boiling point Tb also needs to be estimated first

for 𝑇𝑐.

The calculated critical properties, normal boiling temperatures, and acentric

factors of the ionic liquids are listed in the table below. The experimental densities were

compared with the calculated densities obtained using the modified group contribution

method. The predicted densities are within an acceptable range of error.

103

Table 4-1: Molecular weights, normal boiling temperatures, critical properties, and

acentric factors of ionic liquids

Ionic liquids MW

(g/mol) Tb (K) Tc (K)

Pc

(bar)

Vc

(cm3/mol)

ZC

[EMMP][TF2N] 396.37

715.4

1038.7

25.88

955.5

0.3334

0.2863

[PMPY][TF2N] 416.36

839.8

1234.2

27.55

964.7

0.3070

0.2591

[TDC][TF2N] 532.56

938.1

1255.7

18.03

1394.0

0.5876

0.2407

[TDC][DCN] 318.5

858.6

1073.7

16.15

1115.9

1.0726

0.2019

[EMIM][LACTATE] 200.23

693.4

912.7

28.24

620.1

0.9702

0.2260


499.43 1097.6 1612.8 32.7 1070.1 0.377

0.2615


316.4 1017.6 1433.0 25.88 744.8 0.8437

0.3602

4.2.3 Calculated Density and Deviation %Δp From Experimental Density

Table 4-2: Regressed and Experimental Density Data of [EMMP] [TF2N] by using

Modified Group Contribution Method

T(K) ρ(g/cm3)EXP ρ calc %Δρ

278.15 1.42002 1.38396 2.53953

AAD (%) = 1.18

283.15 1.41526 1.38362 2.23565

288.15 1.41060 1.38329 1.93667

293.15 1.40596 1.38295 1.63710

298.15 1.40126 1.38261 1.33109

303.15 1.39645 1.38227 1.01594

308.15 1.39181 1.38193 0.70978

313.15 1.38791 1.38159 0.45540

318.15 1.38336 1.38125 0.15221

323.15 1.37982 1.38092 0.07944

328.15 1.37540 1.38058 0.37645

333.15 1.37097 1.38024 0.67611

338.15 1.36649 1.37990 0.98142

343.15 1.36167 1.37956 1.31352

348.15 1.35766 1.37922 1.58834

353.15 1.35329 1.37889 1.89088

104

Table 4-3: Regressed and Experimental Density Data of [PMPY] [TF2N] by using


T(K) ρ(g/cm3)EXP ρcalc %Δρ

278.15 1.46723 1.43590 2.13552

AAD (% ) =1.23

283.15 1.46243 1.43560 1.83473

288.15 1.45762 1.43530 1.53107

293.15 1.45281 1.43500 1.22561

298.15 1.44803 1.43471 0.92017

303.15 1.44328 1.43441 0.61478

308.15 1.43854 1.43411 0.30806

313.15 1.43381 1.43381 0.00021

318.15 1.42911 1.43351 0.30777

323.15 1.42442 1.43321 0.61680

328.15 1.41979 1.43291 0.92438

333.15 1.41516 1.43262 1.23348

338.15 1.40980 1.43232 1.59719

343.15 1.40596 1.43202 1.85322

348.15 1.40140 1.43172 2.16355

353.15 1.39685 1.43142 2.47474

Table 4-4: Regressed and Experimental Density Data of [TDC] [TF2N] by using



298.15 1.27341 1.27021 0.25123

AAD (%) = 1.59

303.15 1.26905 1.26997 0.07251

308.15 1.26470 1.26973 0.39769

313.15 1.26036 1.26949 0.72405

318.15 1.25604 1.26925 1.05159

323.15 1.25173 1.26901 1.38031

328.15 1.24743 1.26877 1.71049

333.15 1.24316 1.26853 2.04048

338.15 1.23889 1.26829 2.37276

343.15 1.23464 1.26805 2.70567

348.15 1.23042 1.26780 3.03836

353.15 1.22619 1.26756 3.37419

105

Table 4-5: Regressed and Experimental Density Data of [EMIM] [LACTATE] by using


T(k) ρ(g/cm3)EXP Ρcalc %Δρ

278.15 1.15745 1.14355 1.20113

AAD (%)=1.5

283.15 1.15347 1.14355 0.86023

288.15 1.14977 1.14355 0.54120

293.15 1.14611 1.14355 0.22358

298.15 1.14246 1.14355 0.09519

303.15 1.13889 1.14355 0.40895

308.15 1.13543 1.14355 0.71493

313.15 1.13195 1.14355 1.02456

318.15 1.12851 1.14355 1.33251

323.15 1.12507 1.14355 1.64234

328.15 1.12167 1.14355 1.95044

333.15 1.11831 1.14355 2.25675

338.15 1.11498 1.14355 2.56215

343.15 1.11166 1.14355 2.86846

348.15 1.10839 1.14355 3.17194

353.15 1.10514 1.14355 3.47535

Table 4-6: Regressed and Experimental Density Data of [TDC] [DCN] by using Modified

Group Contribution Method


278.15 1.01638 0.99699 1.90802

AAD (%) = 1.26

283.15 1.01327 0.99698 1.60695

288.15 1.01014 0.99699 1.30207

293.15 1.00700 0.99699 0.99431

298.15 1.00391 0.99699 0.68958

303.15 1.00079 0.99699 0.37997

308.15 0.99770 0.99699 0.07144

313.15 0.99462 0.99699 0.23801

318.15 0.99155 0.99699 0.54836

323.15 0.98850 0.99699 0.85860

328.15 0.98546 0.99699 1.16973

333.15 0.98243 0.99699 1.48176

338.15 0.97941 0.99699 1.79468

343.15 0.97641 0.99699 2.10744

348.15 0.97340 0.99699 2.42318

353.15 0.97042 0.99699 2.73771

106

Table 4-7: Regressed and Experimental Density Data [(CH2)4SO3HMIm][TF2N] by

using Modified Group Contribution Method

T(k) ρ(g/cm3)EXP ρcalc %Δρ

278.15 1.59792 1.53372 4.01790

AAD (%)= 1.9

283.15 1.59296 1.53346 3.73500

288.15 1.58785 1.53321 3.44121

293.15 1.58258 1.53295 3.13573

298.15 1.57787 1.53270 2.86270

303.15 1.57318 1.53245 2.58927

308.15 1.56852 1.53219 2.31608

313.15 1.56387 1.53194 2.04188

318.15 1.55923 1.53168 1.76668

323.15 1.55460 1.53143 1.49047

328.15 1.55001 1.53117 1.21516

333.15 1.54556 1.53092 0.94718

338.15 1.54112 1.53067 0.67830

343.15 1.53668 1.53041 0.40787

348.15 1.53223 1.53016 0.13522

353.15 1.52782 1.52990 0.13640

Table 4-8: Regressed and Experimental Density Data [(CH2)4SO3HMIm][HSO4]

by Using Modified Group Contribution Method

T(k) ρ(g/cm3)EXP ρcalc %Δρ

278.15 1.45030 1.44305 0.50014

AAD (%)= 1.3

283.15 1.44702 1.44305 0.27460

298.15 1.43708 1.44305 0.41518

303.15 1.43368 1.44305 0.65332

313.15 1.42676 1.44305 1.14150

323.15 1.42051 1.44305 1.58651

333.15 1.41428 1.44305 2.03400

343.15 1.40807 1.44305 2.48400

353.15 1.40180 1.44305 2.94240

107

4.3 Equation of State

Many thermodynamic models have been proposed for modeling the phase behavior of

ionic liquids and CO2 systems. In this work, the data has been correlated with different

thermodynamic models. The experimental CO2 solubility data were correlated using the

equations of state including the standard Peng-Robinson (PR), SRK and NRTL.

4.3.1 The Standard Peng-Robinson (PR-EoS)

The Peng–Robinson EoS has been applied to model the solubilities of CO2 in

ionic liquids. Using the correlation with the standard PR-EoS, the binary interaction

parameters (k12) from 313.15 to 333.15 K for each system are given in table 4-10. The P-

x diagrams for each system are graphically presented for the experimental results and the

calculated results from the PR-EoS, as depicted in Figures 4.1-4.7. The results show an

absolute average deviation (AAD) between the model correlations and experimental data

which are between 0.07 and 3.3% for the ionic liquids as shown in Table 4-9 below and it

is concluded Peng–Robinson can satisfactorily describe the solubility of CO2 in the ionic

liquids.

The absolute average deviation is calculated using the following equation:

𝐴𝐴𝐷% =∑[𝐴𝐵𝑆(

𝐸𝑥𝑝−𝑅𝑒𝑔

𝐸𝑥𝑝)]

𝑁𝑃∗ 100% (4.27)

where, Exp and Reg are the experimental and regressed values for the partial pressures of

carbon dioxide above ionic liquids, and NP is the number of experimental data points.

Note the different behaviour of [EMIM][LACATE] and its high binary interaction

parameters. Even though the EoS could correlate the data well, using an EoS in this case

108

is not recommended as the interaction is more that just physical interaction as will be

discussed later.


values of pressure by the standard PR-EoS for the ionic liquids + CO2 system

Ionic liquids T (K)

313.15 323.15 333.15 Average

[EMMP][TF2N] 2.5 1.9 2.3 2.2

[PMPY][TF2N] 2.2 2.4 2.3 2.3

[TDC][TF2N] 3.3 3.1 3.1 3.1

[TDC][DCN] 1.9 1.9 2.4 2.0

[EMIM][LACTATE] 0.7 0.3 0.6 0.5

[(CH2)4SO3HMIm][TF2N]] 0.8 2.7 - 1.2

[(CH2)4SO3HMIm][HSO4] 2.3 0.7 - 1.4

Table 4-10: Binary interaction parameters of the standard PR-EoS for the ionic liquids (1)

+ CO2 (2) system.

Ionic liquids Binary interaction parameter T (K)

313.15 323.15 333.15

[EMMP][TF2N] k12 = -3.290+[0.009995T(K)] -0.180 -0.083 0.016

[PMPY][TF2N] k12=-0.3368+ [0.0008T(K)] -0.091 -0.077 -0.069

[TDC][TF2N] K12 = 0.01127]+[-0.0004 T(K) -0.120 -0.126 -0.130

[TDC][DCN] k12 = -0.0552+ [0.0000897T(K)] -0.081 -0.084 -0.085

[EMIM][LACATE] k12 = 29.8502+[-0.0908T(K)] 1.422 0.511 -0.396

[(CH2)4SO3HMIm][TF2N]] k12 = 1.65+[-0.005T(K)] -0.440 -0.096 -

[(CH2)4SO3HMIm][HSO4] k12 = -4.5+[0.12T(K)] -0.770 -0.644 -

109

4.3.2 Modeling Graphs Using PR-EoS for All ILs

The following section outlines the graphical representation for the modeling using

PR-EoS for all seven ionic liquids used in this study.


Symbols represent the experimental dotted line at 313.15 K; at 323.15 K; red and, at


K; blue, at 323.15 K; red and at 333.15 K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [EMMP][TF2N]

Experiment (313.15 K)

Estimation (313.15 K)





110




K; blue, at 323.15 K; red and at 333.15K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [PMPY][TF2N]







111





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [TDC][TF2N]







112





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [TDC][DCN]







113



and, at 333.15 K; green. Solid lines represent the estimations by the standard PR-EoS: at

313.15 K; blue, at 323.15 K; red and at 333.15K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [emim][LACTATE]







114

Figure 4.6: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]] and CO2 with



blue, at 323.15 K; red.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [(CH2)4SO3HMIm][TF2N]]





115

Figure 4.7: P-x diagram of the system [(CH2)4SO3HMIm][HSO4] and CO2 with



blue, at 323.15 K; red.

0

2

4

6

8

10

12

14

16

18

20

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [(CH2)4SO3HMIm][HSO4]





116

4.3.3 The Soave-Redlich-Kwong (SRK) with Quadratic Mixing Rules

The SRK has also been applied to model the solubilities of CO2 in ionic liquids.

The two binary interaction parameters (k12 and l12) in the mixing rules are optimized

using the experimental CO2 solubility data. Table 4-12 summarizes the binary interaction

parameters of the SRK with the quadratic mixing rules at three different temperatures for

each system. k12 and l12 are linear temperature-dependent functions. The P-x diagrams of

each system are graphically presented for the experimental results and the calculated

results from the standard SRK-EoS are depicted in Figures 4.8-4.12. Joback’s group

contribution method was used to estimate the critical temperature and pressure for the

ionic liquids, as well as the normal boiling temperature. The results show an absolute

average deviation (AADs) between the model correlations and experimental data between

0.6-2.9% for the ionic liquids as shown in the table below and it is concluded that SRK

can satisfactorily describe the solubility of CO2 in the ionic liquids.


values of pressure by the SRK with quadratic mixing rules for the ionic liquids + CO2

system

Ionic liquids T (K)

313.15 323.15 333.15 Average

[EMMP][TF2N] 1 0.8 0.7 0.8

[PMPY][TF2N] 0.7 0.7 1.2 0.8

[TDC][TF2N] 0.5 1.2 1.5 1.0

[TDC][DCN] 0.6 1.3 2.9 1.6

[EMIM][LACTATE] 0.8 0.7 1.3 0.9

117

Table 4-12: Binary interaction parameters of the SRK with quadratic mixing rules for the

ionic liquids (1) + CO2 (2) system

Ionic liquids Binary interaction parameters T (K)

313.15 323.15 333.15

[EMMP][TF2N] k12 = -0.1166+[-10.776×T(K)/1000] 0.224 0.138 0.031

l12 = 1.610+[-4.7689×T(K)/1000] 0.117 0.069 0.021

[PMPY][TF2N] k12 =-0.296499+[0.970593×T(K)/1000] 0.007 0.017 0.026

l12 =0.01745+[0.025733×T(K)/1000] 0.025 0.025 0.026

[TDC][TF2N] k12 = -0.2366+[0.3965×T(K)/1000] 0.025 0.025 0.026

l12 =-0.007571+[0.060035×T(K)/1000] 0.011 0.011 0.012

[TDC][DCN] k12 = -0.36817+[0.80691×T(K)/1000] -0.115 -0.107 -0.099

l12 = -0.07954+[0.0795201×T(K)/1000] 0.004 0.001 0.005

[EMIM][LACTATE] k12 = -4.749+[15×T(K)/1000] 0.052 0.097 0.214

l12 = -0.2919+[0.9775×T(K)/1000] 0.070 0.107 0.145

4.3.4 Modeling Graphs Using SRK -Eos for All Ils

The following section outlines the graphical representation of the models using

SRK-EoS for all seven ionic liquids used in this study.




rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)








118



333.15 K, green. Solid lines represent the estimations by the SRK with quadratic mixing


0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [PMPY][TF2N]







119





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Pre

ssu

re (

bar

)








120





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3

Pre

ssu

re (

bar

)








121

Figure 4.12: P-x diagram of the system [EMIM][LCATATE] and CO2 with isothermal


and, at 333.15 K; green. Solid lines represent the estimations by the SRK with quadratic

mixing rules: at 313.15 K; blue, at 323.15 K; red and at 333.15 K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [emim] [LACTATE]







122

4.3.5 Non-Random Two Liquid Segment Activity Coefficient (NRTL)

The NRTL has also been applied to the solubilities of CO2 in ionic liquids. Table

4-14 shows the binary interaction parameters adjusted to the experimental solubility data

of the ionic liquids, which are (g12-g22)/R and (g21-g11)/R. The binary parameters are

related to 12 and 21, respectively. The parameter is assumed to be a constant unique

value of 0.3 in order to obtain accurate results (Al-Rashed et al., 2012). The binary

interaction parameters for the NRTL model, which are (g12-g22)/R and (g21-g11)/R, can be

linearly correlated as a function of temperature. The P-x diagrams of each system are

graphically presented for the experimental results and the calculated results from the

NRTL model, as depicted in Figures 4-13 – 4.19. The results show an absolute average

deviation (AAD) between the model correlations and experimental data between 0.6-

0.93% for the ionic liquids as shown in a table below and it is concluded that NRTL can

satisfactorily describe the solubility of CO2 in the ionic liquids.


values of pressure by the NRTL for the ionic liquids + CO2 system

ionic liquids T (K)

313.15 323.15 333.15 Average

[EMMP][TF2N] 1 0.9 0.9 0.9

[PMPY][TF2N] 0.5 1 1.2 0.9

[TDC][TF2N] 0.5 0.6 1 0.7

[TDC][DCN] 0.4 0.4 1.1 0.6

[EMIM][LACTATE] 1.4 0.4 1.0 0.9

[(CH2)4SO3HMIm][TF2N]] 1.4 0.8 1.1

[(CH2)4SO3HMIm][HSO4] 1.2 1.1 1.1

123

Table 4-14: Binary interaction parameters of the NRTL for the ionic liquids (1) + CO2 (2)

system (α = 0.3)

Ionic liquids

Binary

interaction

parameters

T (K) Linear function

313.150 323.150 333.150

[EMMP] [TF2N] (g12-g22)/R 180.241 578.011 975.782

(g12-g22)/R = [39.77×T(K)]-

12275.9

(g21-g11)/R -350.066 -500.736 -651.407

(g21-g11)/R =

[-15.067×T(K)]+4368.18

[PMPY][TF2N] (g12-g22)/R -186.869 -152.945 -119.020

(g12-g22)/R =

[3.3424×T(K)]-1299.221

(g21-g11)/R -23.244 -73.629 -124.013

(g21-g11)/R =

[-5.03844×T(K)]+1554.54

[TDC][TF2N] (g12-g22)/R -585.138 -593.922 -602.707

(g12-g22)/R =

[-0.8785×T(K)]-310.05

(g21-g11)/R 579.540 522.560 465.580

(g21-g11)/R = [-5.698´T(K)]-

2363.86

[TDC][DCN] (g12-g22)/R -19.353 -24.221 -29.090

(g12-g22)/R =

[-0.4868×T(K)]+422.72

(g21-g11)/R -108.584 -120.303 -132.021

(g21-g11)/R =

[-1.1719×T(K)]+258.384

[EMIM]

[LACTATE]

(g12-g22)/R 498.377 500.793 503.209

(g12-g22)/R =

[0.2415×T(K)]+305.191

(g21-g11)/R -629.930 -578.333 -526.737

(g21-g11)/R =

[5.15963×T(K)]+3690.01

[(CH2)4SO3HMIm]

[TF2N]

(g12-g22)/R 1435.801 523.701 -

(g12-g22)/R =

[-91.2×T(K)]+3000

(g21-g11)/R -496.940 -629.901 -

(g21-g11)/R =

[-13.3×T(K)]+3690

[(CH2)4SO3HMIm]

[HSO4]

(g12-g22)/R -32.830 72.030

(g12-g22)/R = [68.66×T(K)]-

21534.8

(g21-g11)/R 653.800 -246.701

(g21-g11)/R =

[-31.88×T(K)]+10056.81

124

4.3.6 Modeling Graphs Using NRTL for All ILs

The following section outlines the graphical representation for the modeling using

NRTL for all seven ionic liquids.




323.15 K; red and at 333.15 K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)








125





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [Pmpy][TF2N]







126





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Pre

ssu

re (

bar

)








127





0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3

Pre

ssu

re (

bar

)








128



and, at 333.15 K; green. Solid lines represent the estimations by NRTL: at 313.15 K;

blue, at 323.15 K; red and at 333.15 K; green.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [Emim][LACTATE]







129

Figure 4.18: P-x diagram of the system [(CH2)4SO3HMIm][TF2N]and CO2 with



323.15 K; red.

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [(CH2)4SO3HMIm][TF2N]





130

Figure 4.19: P-x diagram of the system [(CH2)4SO3HMIm][HSO4]and CO2 with



323.15 K; red.

0

2

4

6

8

10

12

14

16

18

20

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Pre

ssu

re (

bar

)

Mole fraction of CO2 in [(CH2)4SO3HMIm][HSO4]





131

4.4 Henry’s Law Constants

It is well understood that Henry’s law constant reflects the linear relationship

between concentration and pressure, which can be calculated from the slope of the

experimental solubility data of a gas at low solute concentrations. In most cases,

isotherms are not linear over the range of pressures. Based on this theory, the

experimental CO2 solubility data was fitted with a second order polynomial and the

limiting slope was calculated as the pressure (or solubility) approached zero (Anthony,

2004). [emim][LACTATE] was an exception, where a first order polynomial using three

data points was used to obtain the slope and, thus, Henry’s Law constant. Aspen plus was

used to estimate the fugacity coefficients from the experimental solubility data of the

systems of the ionic liquids and CO2. The fugacity was obtained by multiplying the

experimental pressure, mole fraction of CO2 and fugacity coefficient. The graph of the

fugacity of CO2 versus the mole fraction of CO2 at each temperature is reported in the

Appendix.

Henry’s law constants for CO2 in the ionic liquids are listed in Table 4-15 for three

different temperatures. Henry’s Law constants are graphically represented for all

temperatures in Figure 4-20. From Table 4-15, the Henry’s Law Constant at 313.15 K is

lower than at 333.15 K which is true for all ionic liquids studied in this work. This

relationship reflects how solubility changes with temperature indicating an inverse

relationship between Henry’s Law constant and CO2 solubility for each ionic liquid. For

example, the ionic liquid with the lowest Henry’s law constant is [TDC][TF2N] which is

already shown to be the ionic liquid with the highest CO2 solubility in the results section.

132

Table 4-15: Henry’s law constants and enthalpies and entropies of absorption for CO2 in

the studied ionic liquids

[Emm

p][Tf2N]

[PMPY][Tf2N]

[TDC][Tf2N]

[TDC][DCN]

[EMIM ][LACTATE]



H (

ba

r)

0

50

100

150

200

250

300

350

313.15 k

323.15 k

333.15 k

Figure 4.20: Henry’s law constants for CO2 in [EMMP][TF2N], [PMPY][TF2N],

[TDC][TF2N], [TDC][DCN], [EMIM][LACTATE], [(CH2)4SO3HMIm][TF2N] and

[(CH2)4SO3HMIm][HSO4] at 313.15, 323.15 and 333.15 K

Ionic liquids H (bar)

∆h

(kJ/mol)

∆s (J/mol

K) 313.15

K

323.15

K

333.15

K

[Emmp][TF2N] 36.1 53.0 61.0 -22.8 -69.4

[PMPY][TF2N] 43.7 52.1 60.1 -13.8 -42.9

[TDC][TF2N] 37.2 43.4 49.3 -12.2 -37.8

[TDC][DCN] 57.2 66.3 77.3 -13.0 -40.4

[EMIM ][LACTATE] 46.2 54.4 64.8 -14.6 -45.7

[(CH2)4SO3HMIm][TF2N] 58.8 70.9 -15.7 -49.5

[(CH2)4SO3HMIm] [HSO4] 274 301.4 -8 -25.2

133

4.5 Enthalpies and Entropies of Absorption

The CO2 solubility in ionic liquids depends on many thermodynamic properties

including the enthalpies (∆h) and entropies (∆s) of absorption. The enthalpy represents

the strength of interaction between the liquid and gas, while the entropy represents the

level of ordering occurring in the ionic liquid/gas mixture (Anthony et al., 2005). The

enthalpy of absorption is derived from the slope of the plot between the natural logarithm

of the calculated Henry’s law constant and the reciprocal inverse temperature (1/T)

multiplied by the universal gas constant (8.314 J/mol K) (Anthony et al., 2005).

Whereas, the entropy of absorption is derived from the product of the universal gas

constant and the slope of the graph between the natural logarithm of the Henry’s law

constant and the natural logarithm of the temperature (Anthony et al., 2005). The

enthalpy and entropy values for CO2 in the studied ionic liquids are reported in Table 4-

15. The negative enthalpy values show that CO2 has a strong interaction with most of the

ionic liquids and perhaps the strongest interaction is seen with [emmp][TF2N] (Kurnia et

al., 2009). The negative values for entropy indicate a higher ordering degree as CO2

dissolves in the ionic liquids (Kurnia et al., 2009).

134

5 CHAPTER FIVE: CONCLUSION AND FUTURE WORK

In this research work, CO2 solubility was measured in seven different ionic

liquids. The seven ionic liquids studied were 1,2,3-Tris(diethylamino)cyclopropenylium

dicyanamide, 1-Ethyl-3-methylimidazolium L-(+)-lactate, 3-methyl-1-propylpyridinium

bis[(trifluoromethyl) sulfonyl]imide, Ethyldimethylpropylammonium bis(trifluoromethyl

sulfonyl)imide, 1,2,3-Tris(diethylamino)cyclopropenylium bis(trifluoromethane

sulfonyl)imide, 1-(4-Sulfobutyl)-3-methylimidazolium Bis(trifluoromethane

sulfonyl)imide, and 1-(4-Sulfobutyl)-3-methylimidazolium hydrogen sulfate.

The density of the seven ionic liquids was experimentally measured, using a

DMA 4500, at atmospheric pressure over a range of temperatures from 278.15 to 353.15

K. For all the ionic liquids studied in this work, the density decreases with increasing

temperature, and increases with decreasing temperature as a linear function. The trend in

the experimental density in decreasing order in the ionic liquids are as follows:

[(CH2)4SO3HMIm][TF2N] > [PMPY] Tf2N] > [(CH2)4SO3HMIm][HSO4] >

[EMMP][TF2N] > [TDC][TF2N] > [emim][LACTATE] >[TDC][DCN].

The solubility of the ionic liquids was calculated using the Intelligent Gravimetric

Analyzer (IGA 003) from Hiden Analytical at 313.15, 323.15 and 333.15 K and at

different pressures under 20 bar. The solubility of CO2 in ionic liquids decreases with

increasing temperature and increases with increasing pressure for all ionic liquids studied.

CO2 solubility decreased in the following order: [TCD][TF2N] > [PMPY][TF2N] >

[EMMP][TF2N] > [emim][LACTATE] > [TCD][DCN] > [(CH2)4SO3HMIm][TF2N] >

[(CH2)4SO3HMIm] [HSO4]. Three ionic liquids ([TCD][TF2N], [PMPY][TF2N],

135

[EMMP][TF2N]) show promise with respect to CO2 absorption as they have similar

solubility patterns to some of the ionic liquids published in the literature that are well

known for their higher CO2 solubility, such as [hmim][TF2N]. The physical solubility of

CO2 is comparable due to their high fluorination content. However, lower solubilties

were obtained in [TCD][TF2N], [PMPY][TF2N], [EMMP][TF2N] when compared with

[bmim][Ac]. [bmim][Ac]-CO2 displays strong chemical interaction and the formation of

chemical intermediary product responsible for its high CO2 solubility.

The most promising ionic liquid from the current research is [TCD][TF2N] which

is a propenylium based ionic liquid paired with an anion well-known for its high CO2

solubility. The effect of fluorination and presence of S=O groups on the TF2N anion act

synergistically to increase the CO2 solubility (Muldoon et al., 2007). The S=O group may

increase the CO2-philicity of molecules due to Lewis base-Lewis acid interactions with

the carbon atom from CO2 (Muldoon et al., 2007). However, the use of fluorinated ionic

liquids is not without its environmental and health drawbacks when used in high

concentrations.

[EMIM][LACATE] showed high capacity for CO2 but both the solubility curve

shape and the EoS modeling show that the interaction with CO2 is much more than just

simple absorption.

In addition to obtaining CO2 solubility, modeling was used to correlate the

experimental data for the binary systems of CO2 + ionic liquids. The thermodynamic

models used to correlate the experimental CO2 solubility included equations of state, such

as the Peng-Robinson (PR-EoS), SRK with quadratic mixing rules, and the Non-Random

136

Two-Liquid (NRTL) activity coefficient model. All models resulted in low percentages

of AAD reflecting that they can satisfactorily correlate the solubility of CO2 in the ionic

liquids. Furthermore, Henry’s Law constants for CO2 in the ionic liquids at the three

different temperatures, 313.15, 323.15 and 333.15 K, were determined. As the

temperature increased, the Henry’s Law constants decreased for all the investigated ionic

liquids.

Future Work

Further investigations of the seven ionic liquids studied at higher pressures would

be beneficial as it would have more industrial applicability in natural gas processing.

Future work might involve the investigation of other gases such as methane,

ethane, propane, sulfur dioxide, carbon monoxide and hydrogen. Furthermore,

modifications to the seven ionic liquids by the addition of functional groups or the

modification of alkyl chain lengths to allow them to become more biodegradable and thus

more environmentally friendly will be an important aspect of industrial application. There

is a need to reconcile the demand for high solubility and the maintenance of the “green”

solvent reputation that ionic liquids initially possessed.

137

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ionic liquids: overview and progress." Energy & Environmental Science, 5, 6668-6681,

2012.

143

6 APPENDIX

6.1 Raw Data for Gas Solubility Measurements Using the Gravimetric

Microbalance

Table 6-1: Carbon dioxide in [Emmp][TF2N] at 313.15 K

%Mass = Asymptotic mass uptake as percentage of dry mass

P = Average pressure reading for isotherm point (millibars)

Sample T = Average sample temperature reading for isotherm point (°C)

%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[EMMP][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.18103 97.67 39.95 0.0041 0.2522 1.604

0.2597 499.63 39.96 0.0059 0.2522 2.286

0.3852 998.61 39.98 0.0087 0.2522 3.353

0.64326 1999.38 39.98 0.0146 0.2522 5.476

1.15361 3998.51 39.98 0.0262 0.2522 9.412

1.90065 6997.99 39.98 0.0432 0.2522 14.62

2.40342 8998.32 39.98 0.0546 0.2522 17.79

2.65967 9998.02 39.96 0.0604 0.2522 19.32

2.92619 10999.59 39.97 0.0664 0.2522 20.86

3.47239 12997.65 39.99 0.0789 0.2522 23.82

4.01696 14999.31 39.96 0.0912 0.2522 26.57

4.58222 16999.24 39.96 0.1041 0.2522 29.21

5.14261 19000.11 39.95 0.1169 0.2522 31.65

144





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[EMMP][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.0234 99.94 49.95 0.00053 0.2523 0.210

0.0981 499.77 49.95 0.00223 0.2523 0.880

0.1973 998.48 49.96 0.00448 0.2523 1.750

0.4179 2000.71 49.97 0.00949 0.2523 3.630

0.8369 4000.77 49.97 0.01902 0.2523 7.010

1.4348 6997.73 49.96 0.03261 0.2523 11.44

1.8553 8998.86 49.97 0.04216 0.2523 14.32

2.0673 10003.51 49.97 0.04697 0.2523 15.70

2.2926 11000.26 49.96 0.05209 0.2523 17.11

2.7229 12997.78 49.95 0.06187 0.2523 19.69

3.1538 15002.12 49.98 0.07166 0.2523 22.12

3.5990 16995.77 49.96 0.08177 0.2523 24.48

4.0505 18996.24 49.98 0.09203 0.2523 26.73

145





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[EMMP][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.0201 100.87 59.98 0.00046 0.2523 0.180

0.0762 500.17 59.93 0.00173 0.2523 0.680

0.1627 1000.48 59.98 0.00369 0.2523 1.440

0.3631 1999.11 59.98 0.00825 0.2523 3.170

0.7091 3998.24 59.98 0.01611 0.2523 6.000

1.2251 7000.81 59.99 0.02785 0.2523 9.940

1.5600 8999.66 59.99 0.03544 0.2523 12.32

1.7271 9997.76 59.97 0.03924 0.2523 13.46

1.8968 10998.79 59.98 0.04311 0.2523 14.59

2.2464 12997.65 59.97 0.05104 0.2523 16.83

2.6017 14998.78 59.99 0.05911 0.2523 18.98

2.9406 16990.03 60.00 0.06681 0.2523 20.94

3.2791 18997.04 60.02 0.07451 0.2523 22.80

146

Table 6-4: Carbon dioxide in [PMPY][TF2N] at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[PMPY][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.0252 99.01 39.97 0.00057 0.2402 0.240

0.1169 500.03 39.97 0.00266 0.2402 1.090

0.2289 1001.28 39.96 0.00520 0.2402 2.120

0.4763 1999.24 39.97 0.01080 0.2402 4.310

0.9629 3998.51 39.96 0.02190 0.2402 8.350

1.6826 7000.13 39.97 0.03820 0.2402 13.73

2.1876 8998.99 39.97 0.04970 0.2402 17.15

2.4419 9999.76 39.97 0.05540 0.2402 18.77

2.7025 10998.79 39.96 0.06140 0.2402 20.36

3.2392 12997.92 39.97 0.07360 0.2402 23.46

3.7789 14998.65 39.98 0.08590 0.2402 26.34

4.3237 16998.18 39.97 0.09820 0.2402 29.03

4.8991 18996.9 39.98 0.11130 0.2402 31.67

147





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[PMPY][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.000001 1.58 49.96 2.27E-8 0.2402 0.001

0.024223 96.33 49.97 0.00055 0.2402 0.230

0.099011 499.49 49.96 0.00225 0.2402 0.931

0.201272 998.21 49.97 0.00457 0.2402 1.871

0.416054 1999.37 49.95 0.00945 0.2402 3.791

0.82614 3998.51 49.96 0.01877 0.2402 7.251

1.420329 7000.93 49.96 0.03227 0.2402 11.85

1.821213 9000.33 49.97 0.04138 0.2402 14.70

2.02189 9996.42 49.97 0.04594 0.2402 16.06

2.239413 10999.06 49.98 0.05088 0.2402 17.48

2.682775 13002.45 50.01 0.06096 0.2402 20.24

3.125906 14997.71 49.97 0.07103 0.2402 22.82

3.571628 17007.38 49.99 0.08115 0.2402 25.26

4.04087 19008.11 49.97 0.09182 0.2402 27.66

148





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[PMPY][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.0232 99.67 59.99 0.00053 0.2402 0.221

0.0791 499.89 59.99 0.00180 0.2402 0.741

0.1652 999.01 59.99 0.00376 0.2402 1.540

0.3498 1999.78 59.99 0.00795 0.2402 3.201

0.6821 3999.04 60.01 0.01550 0.2402 6.060

1.1799 6996.93 59.97 0.02681 0.2402 10.04

1.5199 9001.53 60.01 0.03454 0.2402 12.57

1.6853 9999.63 59.99 0.03829 0.2402 13.75

1.8508 10999.06 59.96 0.04206 0.2402 14.90

2.2031 12997.25 60.02 0.05006 0.2402 17.25

2.5366 15000.25 60.01 0.05764 0.2402 19.35

2.8837 16995.37 59.96 0.06552 0.2402 21.43

3.1991 18996.5 60.02 0.07269 0.2402 23.23

149

Table 6-7: Carbon dioxide in [TDC][TF2N] at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[TDC][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.0235 97.53 39.96 0.00053 0.1878 0.280

0.1085 498.96 39.96 0.00247 0.1878 1.301

0.2118 998.88 39.97 0.00481 0.1878 2.501

0.4379 2000.31 39.97 0.00995 0.1878 5.030

0.8917 4001.57 39.98 0.02026 0.1878 9.740

1.5626 6999.06 39.97 0.03551 0.1878 15.90

2.0276 8999.26 39.98 0.04607 0.1878 19.70

2.2639 9998.56 39.98 0.05144 0.1878 21.50

2.5118 11000.79 39.98 0.05707 0.1878 23.31

3.0142 12999.12 39.98 0.06849 0.1878 26.73

3.5424 15000.52 39.98 0.08049 0.1878 30.00

4.1041 16997.51 39.95 0.09325 0.1878 33.18

4.6494 18996.77 39.98 0.10564 0.1878 36.01

150





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[TDC][TF2N]

XCO2 (Mole

Fraction of

CO2 %)

0.02103 101.407 49.96 0.00048 0.1878 0.250

0.087862 500.833 49.96 0.00199 0.1878 1.050

0.176067 998.88 49.95 0.00401 0.1878 2.090

0.377358 2000.445 49.97 0.00857 0.1878 4.371

0.754707 3998.372 49.96 0.01715 0.1878 8.370

1.315197 6998.665 49.95 0.02988 0.1878 13.73

1.697512 8998.46 49.94 0.03857 0.1878 17.04

1.896281 9998.691 49.97 0.04309 0.1878 18.66

2.089385 10999.32 49.94 0.04747 0.1878 20.18

2.49237 12999.25 49.96 0.05663 0.1878 23.17

2.925119 14997.71 49.94 0.06646 0.1878 26.14

3.344412 17005.38 50.02 0.07599 0.1878 28.81

3.760257 18996.64 49.97 0.08544 0.1878 31.27

151





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[TDC][TF2N]

XCO2 (Mole

Fraction of CO2

%)

0.0191 101.27 59.98 0.00043 0.1878 0.230

0.0752 500.03 59.98 0.00171 0.1878 0.901

0.1587 997.41 59.99 0.00361 0.1878 1.880

0.3365 1999.51 59.99 0.00764 0.1878 3.911

0.6611 3998.24 59.98 0.01502 0.1878 7.410

1.1467 6999.07 59.98 0.02605 0.1878 12.18

1.4798 8998.19 59.99 0.03362 0.1878 15.19

1.6546 9997.09 60.01 0.03759 0.1878 16.68

1.8258 10999.71 60.01 0.04148 0.1878 18.10

2.1678 12998.71 59.99 0.04925 0.1878 20.78

2.5216 14998.88 59.99 0.05729 0.1878 23.38

2.8702 16999.51 59.94 0.06521 0.1878 25.78

3.2407 18997.84 60.03 0.07363 0.1878 28.17

152

Table 6-10: Carbon dioxide in [EMIM][LACTATE] at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[EMIM][LACTATE]

XCO2 (Mole

Fraction of

CO2 %)

2.095 998.88 39.97 0.04760 0.4994 8.701

2.893 2001.51 39.97 0.06570 0.4994 11.63

3.954 3998.64 39.97 0.08980 0.4994 15.25

5.122 6999.47 39.96 0.11630 0.4994 18.90

5.806 8997.93 39.99 0.13190 0.4994 20.90

6.141 9998.29 39.98 0.13950 0.4994 21.84

6.45 10999.7 39.96 0.14670 0.4994 22.70

7.029 12997.1 39.95 0.15970 0.4994 24.23

7.557 14998.91 39.97 0.17170 0.4994 25.59

8.161 17000.58 39.98 0.18540 0.4994 27.08

8.681 18998.1 39.97 0.19720 0.4994 28.31

153





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[EMIM][LACTATE]

XCO2 (Mole

Fraction of

CO2 %)

1.6891 999.01 49.96 0.03830 0.4994 7.141

3.2837 3997.84 49.96 0.07460 0.4994 13.00

3.6651 4998.74 49.95 0.08320 0.4994 14.29

4.3075 6998.93 49.96 0.09780 0.4994 16.39

5.1784 9997.76 49.96 0.11760 0.4994 19.07

7.3238 18998.37 49.95 0.16640 0.4994 24.99





%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[EMIM][LACTATE]

XCO2 (Mole

Fraction of

CO2 %)

0.9867 499.63 59.99 0.02242 0.4994 4.301

1.3969 998.48 59.99 0.03174 0.4994 5.980

1.9871 1999.65 59.99 0.04515 0.4994 8.290

2.7824 3996.24 59.99 0.06322 0.4994 11.24

3.6581 6999.6 59.98 0.08312 0.4994 14.27

4.1699 9000.73 60.01 0.09475 0.4994 15.95

4.4184 9998.29 59.97 0.10040 0.4994 16.74

154

Table 6-13: Carbon dioxide in [TDC][DCN] at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[TDC][DCN]

XCO2 (Mole

Fraction of CO2

%)

0.0247 101.01 39.97 0.00056 0.3139 0.181

0.1191 500.16 39.97 0.00271 0.3139 0.850

0.2313 1001.01 39.97 0.00526 0.3139 1.650

0.4856 2002.04 39.96 0.01103 0.3139 3.391

0.9987 4000.11 39.97 0.02269 0.3139 6.740

1.7497 7000.13 39.96 0.03976 0.3139 11.24

2.2701 8998.73 39.97 0.05158 0.3139 14.11

2.5331 9998.15 39.96 0.05756 0.3139 15.49

2.8033 10998.79 39.97 0.06369 0.3139 16.87

3.3666 12997.65 39.97 0.07649 0.3139 19.59

3.9351 14992.51 39.96 0.08942 0.3139 22.17

4.5553 17001.38 39.97 0.10350 0.3139 24.79

5.1638 19006.65 39.96 0.11733 0.3139 27.20

155

Table 6-14: Carbon dioxide in [TDC][DCN] at 323.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF CO2 Mole of

[TDC][DCN]

XCO2 (Mole

Fraction of CO2

%)

0.0258 102.342 49.96 0.00059 0.3139 0.190

0.1051 500.165 49.95 0.00239 0.3139 0.750

0.2028 997.412 49.96 0.00461 0.3139 1.451

0.4261 1998.31 49.95 0.00969 0.3139 2.991

0.8615 4001.575 49.96 0.01958 0.3139 5.870

1.4967 6996.13 49.95 0.03401 0.3139 9.771

1.9394 9001.396 49.96 0.04407 0.3139 12.31

2.1686 9997.49 49.97 0.04928 0.3139 13.57

2.3958 11002.93 49.98 0.05444 0.3139 14.78

2.8849 12996.72 49.94 0.06555 0.3139 17.27

3.3630 14997.18 49.95 0.07642 0.3139 19.57

3.8636 16998.04 49.98 0.08779 0.3139 21.85

4.3705 19006.11 49.97 0.09931 0.3139 24.03

Table 6-15: Carbon dioxide in [(CH2)4SO3HMIm][TF2N]at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of

[(CH2)4SO3HMIm][TF2N

]

XCO2 (Mole

Fraction of

CO2 %)

0.0116 97.67 39.96 0.00026 0.2002 0.138

0.0116 499.63 39.96 0.00026 0.2002 0.138

0.0652 998.61 39.98 0.00148 0.2002 0.731

1.3739 8998.33 39.98 0.03122 0.2002 13.49

1.5006 9998.02 39.97 0.03410 0.2002 14.55

1.6729 10999.59 39.97 0.03801 0.2002 15.96

1.9731 12997.65 39.99 0.04483 0.2002 18.29

2.3172 14999.31 39.96 0.05265 0.2002 20.82

2.6264 16999.24 39.96 0.05968 0.2002 22.96

2.9968 19000.11 39.95 0.06809 0.2002 25.38

156

Table 6-16: Carbon dioxide in [(CH2)4SO3HMIm][TF2N] at 323.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole OF

CO2

Mole of


XCO2 (Mole

Fraction of

CO2 %)

0.0139 98.21 49.96 0.00032 0.2002 0.159

0.0551 500.29 49.96 0.00125 0.2002 0.621

0.1091 999.68 49.96 0.00248 0.2002 1.222

0.5198 3998.37 49.97 0.01181 0.2002 5.570

0.8809 7000.53 49.9 0.02002 0.2002 9.091

1.1557 8999.13 49.94 0.02626 0.2002 11.59

1.2679 10001.09 49.95 0.02881 0.2002 12.58

1.9681 15002.38 49.92 0.04472 0.2002 18.26

Table 6-17: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole

OF CO2

Mole of


XCO2 (Mole

Fraction of

CO2 %)

0.0106 99.27 39.96 0.00024 0.3161 0.076

0.0244 498.43 39.96 0.00055 0.3161 0.175

0.0413 998.88 39.98 0.00094 0.3161 0.296

0.3611 6999.33 39.98 0.00821 0.3161 2.530

0.7044 10999.73 39.96 0.01601 0.3161 4.819

0.8127 12997.12 39.97 0.01847 0.3161 5.519

157

Table 6-18: Carbon dioxide in [(CH2)4SO3HMIm][HSO4]at 313.15 K




%Mass Pressure

(M bar)

Sample-

T(°C)

Mole

OF CO2

Mole of


XCO2 (Mole

Fraction of

CO2 %)

0.0078 101.01 49.96 0.00017 0.3161 0.056

0.0161 499.77 49.95 0.00036 0.3161 0.116

0.4588 9000.60 49.94 0.01042 0.3161 3.192

0.5267 9997.89 49.95 0.01196 0.3161 3.648

0.5911 10998.79 49.97 0.01343 0.3161 4.076

0.6907 12997.65 49.96 0.01569 0.3161 4.730

0.8068 14999.98 49.96 0.01833 0.3161 5.482

0.9095 16999.51 49.95 0.02066 0.3161 6.137

158

6.2 Modeling Results


[EMMP][TF2N] (1) + CO2 (2) system at 313.15 K

Experimental pressure

(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09767 0.09958 0.016 0.016

0.49963 0.50056 0.023 0.023

0.99861 0.99498 0.034 0.034

1.99938 1.98415 0.055 0.055

3.99851 3.95448 0.094 0.095

6.99800 6.89461 0.146 0.149

8.99833 8.84299 0.178 0.182

9.99802 9.81225 0.193 0.197

10.99959 10.78082 0.209 0.213

12.99765 12.70273 0.238 0.245

14.99931 14.60915 0.266 0.274

16.99924 16.49649 0.292 0.302

19.00011 18.36211 0.317 0.328




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed XCO2

0.09994 0.10011 0.002 0.002

0.49977 0.49877 0.009 0.009

0.99848 0.99663 0.017 0.017

2.00071 1.99927 0.036 0.036

4.00077 3.99616 0.070 0.070

6.99773 6.97690 0.114 0.115

8.99886 8.96106 0.143 0.144

10.00350 9.95390 0.157 0.158

11.00026 10.93746 0.171 0.172

12.99778 12.89749 0.197 0.199

15.00212 14.85165 0.221 0.224

16.99577 16.77958 0.245 0.248

18.99624 18.69769 0.267 0.272

159




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10087 0.10233 0.002 0.002

0.50017 0.50442 0.007 0.007

1.00048 1.01065 0.014 0.014

1.99911 2.02460 0.032 0.031

3.99824 4.04747 0.060 0.059

7.00080 7.08150 0.099 0.098

8.99966 9.09472 0.123 0.122

9.99776 10.09713 0.135 0.133

10.99879 11.10143 0.146 0.144

12.99765 13.10089 0.168 0.167

14.99878 15.09343 0.190 0.189

16.99003 17.06199 0.209 0.208

18.99704 19.03147 0.228 0.227


[PMPY][TF2N] (1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09901 0.10206 0.002 0.002

0.50003 0.50608 0.011 0.011

1.00128 1.00664 0.021 0.021

1.99924 2.01784 0.043 0.042

3.99851 4.00901 0.083 0.083

7.00013 6.92609 0.137 0.138

8.99900 8.84470 0.171 0.174

9.99976 9.79322 0.188 0.192

10.99879 10.73520 0.204 0.209

12.99792 12.60515 0.235 0.243

14.99865 14.44223 0.263 0.275

16.99818 16.24426 0.290 0.305

18.99690 18.02759 0.317 0.335

160




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09634 0.10317 0.002 0.002

0.49950 0.50879 0.009 0.009

0.99821 1.01847 0.019 0.018

1.99938 2.04498 0.038 0.037

3.99851 4.05196 0.072 0.071

7.00093 6.98725 0.118 0.118

9.00033 8.90924 0.147 0.148

9.99642 9.85639 0.161 0.163

10.99906 10.81563 0.175 0.178

13.00245 12.71613 0.202 0.207

14.99771 14.57324 0.228 0.236

17.00738 16.41388 0.253 0.263

19.00811 18.22785 0.277 0.289




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09967 0.10940 0.002 0.002

0.49990 0.50484 0.007 0.007

0.99901 1.01692 0.015 0.015

1.99978 2.05342 0.032 0.031

3.99904 4.05638 0.061 0.059

6.99693 7.00682 0.100 0.100

9.00153 8.95586 0.126 0.126

9.99963 9.91029 0.138 0.139

10.99906 10.85807 0.149 0.151

12.99725 12.76183 0.172 0.176

15.00025 14.61691 0.194 0.199

16.99537 16.44949 0.214 0.222

18.99650 18.23384 0.232 0.243

161


(1) + CO2 (2) system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09754 0.10643 0.003 0.003

0.49896 0.52412 0.013 0.012

0.99888 1.03619 0.025 0.024

2.00031 2.08044 0.050 0.048

4.00158 4.12090 0.097 0.094

6.99907 7.05287 0.159 0.157

8.99926 8.96272 0.197 0.198

9.99856 9.90149 0.215 0.218

11.00079 10.84211 0.233 0.238

12.99912 12.68633 0.267 0.276

15.00052 14.50634 0.300 0.314

16.99751 16.30026 0.332 0.351

18.99677 18.03165 0.360 0.385


(1) + CO2 (2) system at 323.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10141 0.10936 0.003 0.002

0.50083 0.50859 0.011 0.010

0.99888 1.01267 0.021 0.020

2.00045 2.06102 0.044 0.042

3.99837 4.06515 0.084 0.081

6.99867 6.96919 0.137 0.138

8.99846 8.85891 0.170 0.173

9.99869 9.79880 0.187 0.191

10.99932 10.71688 0.202 0.208

12.99925 12.54493 0.232 0.242

14.99771 14.36318 0.261 0.276

17.00538 16.12872 0.288 0.307

18.99664 17.82853 0.313 0.337

162


(1) + CO2 (2) system at 333.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10127 0.10976 0.002 0.002

0.50003 0.49986 0.009 0.009

0.99741 1.01381 0.019 0.018

1.99951 2.05956 0.039 0.037

3.99824 4.04531 0.074 0.072

6.99907 6.93965 0.122 0.123

8.99819 8.83254 0.152 0.155

9.99709 9.77781 0.167 0.171

10.99973 10.70768 0.181 0.187

12.99872 12.53017 0.208 0.217

14.99878 14.33234 0.234 0.247

16.99951 16.08285 0.258 0.275

18.99784 17.83185 0.282 0.303

163

Table 6-28: Modeling solubility Peng-Robinson (PR-EoS) (P, X) data for [TDC][DCN

(1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10101 0.10524 0.002 0.002

0.50017 0.51260 0.009 0.008

1.00102 1.01519 0.017 0.016

2.00205 2.05070 0.034 0.033

4.00011 4.09396 0.067 0.065

7.00013 7.05023 0.112 0.111

8.99873 8.99090 0.141 0.141

9.99815 9.94783 0.155 0.156

10.99879 10.90524 0.169 0.171

12.99765 12.80587 0.196 0.201

14.99251 14.64214 0.221 0.229

17.00138 16.53758 0.248 0.259

19.00665 18.34682 0.272 0.287


(1) + CO2 (2) system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed XCO2

0.10234 0.11261 0.002 0.002

0.50017 0.51016 0.008 0.007

0.99741 1.00642 0.015 0.014

1.99831 2.03831 0.030 0.029

4.00158 4.05666 0.059 0.057

6.99613 6.97560 0.098 0.098

9.00140 8.91191 0.123 0.124

9.99749 9.87323 0.136 0.138

11.00293 10.82688 0.148 0.151

12.99672 12.73672 0.173 0.178

14.99718 14.59825 0.196 0.203

16.99804 16.44996 0.219 0.229

19.00611 18.26883 0.240 0.254

164


(1) + CO2 (2) system at 333.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed XCO2

0.09981 0.11068 0.002 0.001

0.49963 0.49071 0.006 0.006

0.99915 0.99040 0.013 0.012

2.00005 1.99762 0.026 0.025

3.99811 3.96963 0.050 0.050

6.99787 6.83641 0.084 0.085

8.99913 8.72683 0.105 0.108

10.00016 9.68440 0.116 0.120

11.00052 10.61143 0.127 0.132

12.99925 12.47901 0.148 0.155

14.99731 14.32065 0.168 0.177

17.00712 16.10056 0.186 0.199


[EMIM][LACTATE ](1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.99888 1.00400 0.087 0.087

2.00151 2.00536 0.116 0.116

3.99864 3.99817 0.152 0.152

6.99947 6.99723 0.189 0.189

8.99793 8.99817 0.209 0.209

9.99829 10.00055 0.218 0.218

10.99973 11.00407 0.227 0.227

12.99712 13.00496 0.242 0.242

14.99891 15.00777 0.256 0.256

17.00058 17.00506 0.271 0.271

18.99810 18.99065 0.283 0.283

165




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.99901 0.99436 0.071 0.071

3.99784 3.96857 0.130 0.130

4.99874 4.96472 0.143 0.143

6.99893 6.96169 0.164 0.164

9.99776 9.97154 0.191 0.190

18.99837 19.06563 0.250 0.250




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.499631 0.49406736 0.043 0.043

0.998479 0.98472573 0.060 0.060

1.999645 1.96934955 0.083 0.083

3.996237 3.93937429 0.112 0.112

6.9996 6.9271834 0.143 0.143

9.000729 8.9351463 0.159 0.159

9.998292 9.94119949 0.167 0.167


[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

bar

Experimental

XCO2

Regressed

XCO2

0.09930 0.09700 0.001 0.001

0.49800 0.48300 0.002 0.002

0.99900 0.96800 0.003 0.003

6.99933 6.83845 0.025 0.026

10.99973 10.80109 0.048 0.049

12.99712 12.76284 0.055 0.056

166


[(CH2)4SO3HMIm] [HSO4] (1) + CO2 (2) system at 323.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10101 0.09973 0.001 0.001

0.49977 0.48946 0.001 0.001

9.00060 8.99469 0.032 0.032

9.99789 10.00962 0.036 0.036

10.99879 11.02875 0.041 0.041

12.99765 13.05889 0.047 0.047

14.99998 15.09916 0.055 0.055

16.99951 17.13126 0.061 0.061


[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09770 0.09570 0.001 0.001

0.50000 0.48200 0.001 0.001

0.99900 0.97500 0.007 0.007

8.99833 8.99693 0.135 0.135

9.99802 10.00525 0.146 0.146

10.99959 11.01490 0.160 0.160

12.99765 13.02341 0.183 0.183

14.99931 15.02135 0.208 0.208

16.99924 16.99923 0.230 0.230

19.00011 18.94820 0.254 0.254

167


[(CH2)4SO3HMIm][TF2N] (1) + CO2 (2) system at 323.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09820 0.09541 0.002 0.002

0.50030 0.48558 0.006 0.006

0.99968 0.97209 0.012 0.012

3.99837 3.93657 0.056 0.056

7.00053 6.95401 0.091 0.091

8.99913 8.98610 0.116 0.116

10.00109 10.00859 0.126 0.126

15.00238 15.13018 0.183 0.183




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09901 0.09860 0.002 0.002

0.50003 0.49011 0.011 0.011

1.00128 0.97783 0.021 0.022

1.99924 1.97222 0.043 0.043

3.99851 3.96254 0.083 0.084

7.00013 6.94770 0.137 0.138

8.99900 8.95256 0.171 0.172

9.99976 9.95477 0.188 0.188

10.99879 10.95728 0.204 0.204

12.99792 12.96687 0.235 0.235

14.99865 14.96477 0.263 0.265

16.99818 16.94607 0.290 0.292

18.99690 18.92629 0.317 0.319

168




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09634 0.09956 0.002 0.002

0.49950 0.49191 0.009 0.009

0.99821 0.98738 0.019 0.019

1.99938 1.99332 0.038 0.038

3.99851 3.98852 0.072 0.072

7.00093 6.96853 0.118 0.118

9.00033 8.95683 0.147 0.147

9.99642 9.94676 0.161 0.161

10.99906 10.95642 0.175 0.175

13.00245 12.97565 0.202 0.203

14.99771 14.97248 0.228 0.229

17.00738 16.97209 0.253 0.254

19.00811 18.96375 0.277 0.278




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09967 0.10546 0.002 0.002

0.49990 0.48729 0.007 0.008

0.99901 0.98393 0.015 0.015

1.99978 1.99627 0.032 0.032

3.99904 3.97704 0.061 0.061

6.99693 6.95070 0.100 0.101

9.00153 8.94917 0.126 0.126

9.99963 9.93720 0.138 0.138

10.99906 10.92439 0.149 0.150

12.99725 12.92460 0.172 0.174

15.00025 14.89492 0.194 0.195

16.99537 16.86243 0.214 0.217

18.99650 18.79394 0.232 0.236

169


[TDC][TF2N] (1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09754 0.10087 0.003 0.003

0.49896 0.49958 0.013 0.013

0.99888 0.99212 0.025 0.025

2.00031 2.00585 0.050 0.049

4.00158 4.02804 0.097 0.095

6.99907 7.02282 0.159 0.157

8.99926 9.02306 0.197 0.196

9.99856 10.01970 0.215 0.215

11.00079 11.02599 0.233 0.234

12.99912 13.02242 0.267 0.270

15.00052 15.01990 0.300 0.305

16.99751 17.01238 0.332 0.339

18.99677 18.95906 0.360 0.371




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10141 0.10423 0.003 0.002

0.50083 0.48805 0.011 0.011

0.99888 0.97499 0.021 0.021

2.00045 1.99490 0.044 0.043

3.99837 3.98440 0.084 0.083

6.99867 6.94760 0.137 0.138

8.99846 8.92171 0.170 0.172

9.99869 9.91557 0.187 0.189

10.99932 10.89527 0.202 0.205

12.99925 12.86645 0.232 0.237

14.99771 14.85229 0.261 0.268

17.00538 16.80721 0.288 0.298

18.99664 18.71254 0.313 0.326

170




(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10127 0.10507 0.002 0.002

0.50003 0.48229 0.009 0.009

0.99741 0.97991 0.019 0.019

1.99951 2.00041 0.039 0.038

3.99824 3.97544 0.074 0.073

6.99907 6.92713 0.122 0.122

8.99819 8.89983 0.152 0.153

9.99709 9.89600 0.167 0.169

10.99973 10.88431 0.181 0.184

12.99872 12.84290 0.208 0.212

14.99878 14.80484 0.234 0.240

16.99951 16.73604 0.258 0.267

18.99784 18.68382 0.282 0.293


[TDC][DCN] (1) + CO2 (2) system at 313.15 K


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.101007 0.10228235 0.002 0.002

0.500165 0.49928649 0.009 0.008

1.001015 0.99089577 0.017 0.016

2.002047 2.00638799 0.034 0.033

4.000107 4.02863206 0.067 0.066

7.000133 6.99998381 0.112 0.112

8.998728 8.97632411 0.141 0.141

9.99815 9.95848094 0.155 0.156

10.99879 10.945548 0.169 0.170

12.99765 12.9184655 0.196 0.199

14.99251 14.844459 0.221 0.227

17.00138 16.8443045 0.248 0.256

19.00665 18.7732977 0.272 0.283

171


[TDC][DCN] (1) + CO2 (2) system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10101 0.10228 0.002 0.002

0.50017 0.49929 0.009 0.008

1.00102 0.99090 0.017 0.016

2.00205 2.00639 0.034 0.033

4.00011 4.02863 0.067 0.066

7.00013 6.99998 0.112 0.112

8.99873 8.97632 0.141 0.141

9.99815 9.95848 0.155 0.156

10.99879 10.94555 0.169 0.170

12.99765 12.91847 0.196 0.199

14.99251 14.84446 0.221 0.227

17.00138 16.84430 0.248 0.256

19.00665 18.77330 0.272 0.283


[TDC][DCN] (1) + CO2 (2) system at 333.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09981 0.10792 0.002 0.002

0.49963 0.48287 0.006 0.006

0.99915 0.97521 0.013 0.013

2.00005 1.97100 0.026 0.025

3.99811 3.93739 0.050 0.050

6.99787 6.83509 0.084 0.085

8.99913 8.76798 0.105 0.108

10.00016 9.75223 0.116 0.119

11.00052 10.71114 0.127 0.130

12.99925 12.65281 0.148 0.153

14.99731 14.58368 0.168 0.175

17.00712 16.46891 0.186 0.195

172


[EMIM][LACTATE] (1) + CO2 (2) system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.99888 1.03701 0.087 0.081

2.00151 2.01555 0.116 0.113

3.99864 3.96379 0.152 0.152

6.99947 6.91639 0.189 0.191

8.99793 8.90596 0.209 0.211

9.99829 9.90958 0.218 0.221

10.99973 10.91508 0.227 0.229

12.99712 12.92572 0.242 0.245

14.99891 14.94907 0.256 0.259

17.00058 17.00301 0.271 0.274

18.99810 19.04888 0.283 0.286


[EMIM][LACTATE] (1) + CO2 (2) system at 323.15 K.

Experimental Pressure

(bar)

Estimated Pressure

(bar)

Experimental

XCO2

Estimated

XCO2

0.99901 1.02239 0.071 0.068

3.99784 3.93048 0.130 0.132

4.99874 4.91197 0.143 0.145

6.99893 6.88044 0.164 0.167

9.99776 9.87166 0.191 0.194

9.99776 9.87138 0.191 0.194

18.99837 19.00585 0.250 0.251

173


[EMMP][LACTATE] (1) + CO2 (2) system at 333.15 K.


(2) system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09767 0.09963 0.016 0.016

0.49963 0.50377 0.023 0.023

0.99861 1.00189 0.034 0.034

1.99938 1.99877 0.055 0.055

3.99851 3.99085 0.094 0.095

6.99800 6.98393 0.146 0.148

8.99833 8.98402 0.178 0.180

9.99802 9.98486 0.193 0.195

10.99959 10.98983 0.209 0.210

12.99765 12.99796 0.238 0.240

14.99931 15.00800 0.266 0.267

16.99924 17.02047 0.292 0.293

19.00011 19.03159 0.317 0.317


(bar)

Regressed pressure

(bar)

Experimental XCO2 Regressed

XCO2

0.49963 0.52689 0.043 0.039

0.99848 1.00516 0.060 0.058

1.99965 1.96479 0.083 0.084

3.99624 3.88872 0.112 0.117

6.99960 6.82345 0.143 0.148

9.00073 8.81065 0.159 0.164

9.99829 9.81011 0.167 0.172

174


(2) system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09994 0.10036 0.002 0.002

0.49977 0.49704 0.009 0.009

0.99848 0.99378 0.017 0.018

2.00071 2.00153 0.036 0.036

4.00077 4.01204 0.070 0.070

6.99773 7.02759 0.114 0.114

8.99886 9.05777 0.143 0.143

10.00350 10.07897 0.157 0.156

11.00026 11.09870 0.171 0.170

12.99778 13.13481 0.197 0.195

15.00212 15.18056 0.221 0.218

16.99577 17.21968 0.245 0.241

18.99624 19.26835 0.267 0.263


(2) system at 333.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10087 0.10314 0.002 0.002

0.50017 0.49603 0.007 0.007

1.00048 1.00389 0.014 0.014

1.99911 2.03943 0.032 0.031

3.99824 4.07331 0.060 0.059

7.00080 7.08208 0.099 0.099

8.99966 9.03449 0.123 0.123

9.99776 10.00770 0.135 0.135

10.99879 10.98871 0.146 0.147

12.99765 12.97248 0.168 0.169

14.99878 14.96758 0.190 0.191

16.99003 16.91492 0.209 0.212

18.99704 18.86689 0.228 0.231

175


(2) system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09901 0.10013 0.002 0.002

0.50003 0.49566 0.011 0.011

1.00128 0.98768 0.021 0.022

1.99924 1.99371 0.043 0.043

3.99851 4.00114 0.083 0.084

7.00013 7.00443 0.137 0.138

8.99900 9.02089 0.171 0.172

9.99976 10.02905 0.188 0.188

10.99879 11.03793 0.204 0.204

12.99792 13.06259 0.235 0.234

14.99865 15.08058 0.263 0.262

16.99818 17.08942 0.290 0.289

18.99690 19.10650 0.317 0.315


(2) system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09634 0.10181 0.002 0.002

0.49950 0.49450 0.009 0.009

0.99821 0.99389 0.019 0.019

1.99938 2.01055 0.038 0.038

3.99851 4.02212 0.072 0.072

7.00093 7.02486 0.118 0.119

9.00033 9.03162 0.147 0.147

9.99642 10.03180 0.161 0.161

10.99906 11.05373 0.175 0.175

13.00245 13.10004 0.202 0.201

14.99771 15.12767 0.228 0.227

17.00738 17.16469 0.253 0.250

19.00811 19.20190 0.277 0.274

176


(2) system at 333.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09967 0.10804 0.002 0.002

0.49990 0.48181 0.007 0.008

0.99901 0.97748 0.015 0.016

1.99978 1.99544 0.032 0.032

3.99904 3.97910 0.061 0.061

6.99693 6.97221 0.100 0.101

9.00153 8.99289 0.126 0.127

9.99963 9.99292 0.138 0.138

10.99906 10.99343 0.149 0.150

12.99725 13.02780 0.172 0.173

15.00025 15.03468 0.194 0.194

16.99537 17.04691 0.214 0.215

18.99650 19.02799 0.232 0.233


system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09754 0.09958 0.003 0.003

0.49896 0.49659 0.013 0.013

0.99888 0.98776 0.025 0.025

2.00031 1.99402 0.050 0.051

4.00158 4.00494 0.097 0.098

6.99907 6.99891 0.159 0.160

8.99926 9.00684 0.197 0.198

9.99856 10.01075 0.215 0.216

11.00079 11.02549 0.233 0.233

12.99912 13.04770 0.267 0.267

15.00052 15.08227 0.300 0.299

16.99751 17.12367 0.332 0.330

18.99677 19.14213 0.360 0.357

177


system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10141 0.10441 0.003 0.002

0.50083 0.49232 0.011 0.011

0.99888 0.98319 0.021 0.021

2.00045 2.00639 0.044 0.044

3.99837 4.00790 0.084 0.084

6.99867 6.99706 0.137 0.138

8.99846 8.99477 0.170 0.171

9.99869 10.00245 0.187 0.187

10.99932 10.99905 0.202 0.203

12.99925 13.00986 0.232 0.233

14.99771 15.04337 0.261 0.262

17.00538 17.06351 0.288 0.288

18.99664 19.04998 0.313 0.313

178


system at 333.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.101274 0.106270 0.002 0.002

0.50003 0.48993 0.009 0.009

0.99741 0.99455 0.019 0.019

1.99951 2.02760 0.039 0.039

3.99824 4.02947 0.074 0.074

6.99907 7.02489 0.122 0.122

8.99819 9.03144 0.152 0.152

9.99709 10.04628 0.167 0.167

10.99973 11.05552 0.181 0.181

12.99872 13.06241 0.208 0.208

14.99878 15.08227 0.234 0.233

16.99951 17.08431 0.258 0.257

18.99784 19.11571 0.282 0.281


system at 313.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.10101 0.10070 0.002 0.002

0.50017 0.49280 0.009 0.009

1.00102 0.98004 0.017 0.017

2.00205 1.98559 0.034 0.034

4.00011 3.99859 0.067 0.068

7.00013 6.98563 0.112 0.113

8.99873 8.98467 0.141 0.142

9.99815 9.98222 0.155 0.155

10.99879 10.98629 0.169 0.169

12.99765 12.99886 0.196 0.196

14.99251 14.97994 0.221 0.221

17.00138 17.03355 0.248 0.248

19.00665 19.03755 0.272 0.272

179


system at 323.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.10234 0.10817 0.002 0.002

0.50017 0.49706 0.008 0.008

0.99741 0.98454 0.015 0.015

1.99831 1.99938 0.030 0.030

4.00158 4.01648 0.059 0.059

6.99613 7.00454 0.098 0.098

9.00140 9.02261 0.123 0.123

9.99749 10.03367 0.136 0.135

11.00293 11.04614 0.148 0.147

12.99672 13.08526 0.173 0.172

14.99718 15.10811 0.196 0.194

16.99804 17.14448 0.219 0.217

19.00611 19.17591 0.240 0.238


system at 333.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.09981 0.10761 0.002 0.002

0.49963 0.48776 0.006 0.006

0.99915 0.98508 0.013 0.013

2.00005 1.99290 0.026 0.026

3.99811 3.99591 0.050 0.050

6.99787 6.97681 0.084 0.084

8.99913 8.97813 0.105 0.106

10.00016 9.99819 0.116 0.117

11.00052 10.99820 0.127 0.127

12.99925 13.02500 0.148 0.148

14.99731 15.05079 0.168 0.167

17.00712 17.04946 0.186 0.186

180


CO2 (2) system at 313.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.99888 1.00606 0.087 0.088

2.00151 2.00787 0.116 0.118

3.99864 3.98541 0.152 0.156

6.99947 6.92117 0.189 0.196

8.99793 8.86029 0.209 0.218

9.99829 9.82755 0.218 0.229

10.99973 10.79099 0.227 0.238

12.99712 12.69983 0.242 0.256

14.99891 14.59751 0.256 0.272

17.00058 16.50170 0.271 0.289

18.99810 18.37668 0.283 0.303




(bar)

Regressed pressure

(bar)


XCO2

0.99901 1.01588 0.071 0.070

3.99784 4.02771 0.130 0.130

4.99874 5.02405 0.143 0.143

6.99893 7.00084 0.164 0.166

9.99776 9.94214 0.191 0.194

9.99776 9.94173 0.191 0.195

18.99837 18.59349 0.250 0.261

181




(bar)

Regressed pressure

(bar)


XCO2

0.49963 0.51470 0.043 0.041

0.99848 1.02660 0.060 0.058

1.99965 2.05054 0.083 0.080

3.99624 4.07760 0.112 0.110

6.99960 7.09427 0.143 0.141

9.00073 9.08932 0.159 0.158

9.99829 10.07943 0.167 0.166


(1) + CO2 (2) system at 313.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.09927 0.09916 0.001 0.001

0.49843 0.49355 0.002 0.002

0.99888 0.98206 0.003 0.003

6.99933 6.89043 0.025 0.026

10.99973 10.86691 0.048 0.049

12.99712 12.78427 0.055 0.056

182


(1) + CO2 (2) system at 323.15 K.


(bar)

Regressed pressure

(bar)

Experimental

XCO2

Regressed

XCO2

0.10101 0.10168 0.001 0.001

0.49977 0.49744 0.001 0.001

9.00060 9.12862 0.032 0.031

9.99789 10.14726 0.036 0.036

10.99879 11.17349 0.041 0.040

12.99765 13.20047 0.047 0.047

14.99998 14.85900 0.055 0.055

16.99951 16.61619 0.061 0.062


(1) + CO2 (2) system at 313.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.09767 0.09654 0.001 0.001

0.49963 0.48601 0.001 0.001

0.99861 0.98337 0.007 0.007

8.99833 9.03503 0.135 0.134

9.99802 10.04034 0.146 0.145

10.99959 11.04883 0.160 0.160

12.99765 13.04819 0.183 0.184

14.99931 15.03621 0.208 0.210

16.99924 16.99647 0.230 0.232

19.00011 18.93043 0.254 0.257

183


(1) + CO2 (2) system at 323.15 K.


(bar)

Regressed pressure

(bar)


XCO2

0.09820 0.10444 0.002 0.001

0.50030 0.48503 0.006 0.006

0.99968 0.96419 0.012 0.012

3.99837 4.05167 0.056 0.054

7.00053 6.92634 0.091 0.091

8.99913 8.88707 0.116 0.117

10.00109 9.79430 0.126 0.129

15.00238 14.53338 0.183 0.190

184

6.3 Henry’s Law Constants and Enthalpies and Entropies of Absorption



T=50° C Experimental

pressure (bar)

Experimental

XCO2

Experimental

KVL

Experimental

fCO2

0.1020 0.0020 499.5911 0.1019

0.5026 0.0060 166.6216 0.5025

1.0020 0.0120 83.3221 1.0019

3.9961 0.0470 21.2759 3.9960

7.0004 0.0790 12.6580 7.0003

9.9979 0.1090 9.1742 9.9978

13.0023 0.1360 7.3529 13.0022

15.0027 0.1550 6.4516 15.0026

19.9978 0.1970 5.0761 19.9977

T =10° C Experimental

pressure (bar)

Experimental

XCO2

Experimental

KVL

Experimental

fCO2

0.0969 0.0040 249.9879 0.0969

0.5009 0.0160 62.4993 0.5009

1.0018 0.0290 34.4825 1.0018

3.9956 0.1020 9.8039 3.9956

6.9959 0.1670 5.9880 6.9959

9.9996 0.2240 4.4643 9.9996

13.0027 0.2840 3.5211 13.0027

14.9980 0.3090 3.2362 14.9980

19.9975 0.3790 2.6385 19.9975

185

Figure 6.1: Determining the Henry’s law constant for CO2 in [bmim][PF6]

Figure 6.2: Determining the enthalpy of absorption for CO2 in [bmim][PF6]

y = 52.409x2 + 32.415xR² = 0.9993

y = 108.13x2 + 80.248xR² = 1

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4

fCO

2

XCO2

Experiment AT 283.15 K

Experiment AT 323.15 K

Poly. (Experiment AT 283.15 K)

Poly. (Experiment AT 323.15 K)

y = -2000.2x + 10.568R² = 0.9981

0

1

2

3

4

5

6

0 0.001 0.002 0.003 0.004

lnH

1/T

Series1

Linear (Series1)

186

Figure 6.3: Determining the entropy of absorption for CO2 in [bmim][PF6]

y = 6.3705x - 32.448R² = 0.9953

0

1

2

3

4

5

6

5.6 5.65 5.7 5.75 5.8 5.85 5.9

lnH

1/T

Series1

Linear (Series1)

187

Table 6-71: Experimental fugacity of CO2 in [Emmp][TF2N] at 313.15 And 323.15 K

SRK

T-40°C Experimental pressure

(bar)

Experimental X

CO2

Experimental

KVL

Experimental

f CO2

1 0.0977 0.0160 62.3318 0.0977

2 0.4996 0.0229 43.7410 0.4996

3 0.9986 0.0335 29.8209 0.9986

4 1.9994 0.0548 18.2618 1.9994

5 3.9985 0.0941 10.6249 3.9985

6 6.9980 0.1462 6.8418 6.9980

7 8.9983 0.1779 5.6198 8.9983

8 9.9980 0.1932 5.1747 9.9980

9 10.9996 0.2086 4.7944 10.9996

10 12.9977 0.2382 4.1976 12.9976

11 14.9993 0.2657 3.7641 14.9993

12 16.9992 0.2921 3.4231 16.9992

13 19.0001 0.3165 3.1591 19.0001

T-50°C Experimental pressure

(bar)

Experimental X

CO2

Experimental

KVL

Experimental

f CO2

1 0.0999 0.0021 476.3272 0.0999

2 0.4998 0.0088 114.1091 0.4998

3 0.9985 0.0175 57.2834 0.9985

4 2.0007 0.0363 27.5720 2.0007

5 4.0008 0.0701 14.2661 4.0008

6 6.9977 0.1144 8.7382 6.9977

7 8.9989 0.1432 6.9844 8.9989

8 10.0035 0.1570 6.3709 10.0035

9 11.0003 0.1711 5.8430 11.0003

10 12.9978 0.1969 5.0777 12.9978

11 15.0021 0.2212 4.5206 15.0021

12 16.9958 0.2448 4.0851 16.9958

13 18.9962 0.2673 3.7411 18.9962

188

Table 6-72: Experimental fugacity of CO2 in [Emmp][TF2N] at 333.15 K

T-°60C Experimental pressure

(bar)

Experimental X

CO2

Experimental

KVL

Experimental

f CO2

1 0.1009 0.0018 550.8477 0.1009

2 0.5002 0.0068 146.6770 0.5002

3 1.0005 0.0144 69.2369 1.0005

4 1.9991 0.0317 31.5770 1.9991

5 3.9982 0.0600 16.6584 3.9982

6 7.0008 0.0994 10.0586 7.0008

7 8.9997 0.1232 8.1174 8.9997

8 9.9978 0.1346 7.4287 9.9978

9 10.9988 0.1459 6.8536 10.9988

10 12.9977 0.1683 5.9427 12.9976

11 14.9988 0.1898 5.2676 14.9988

12 16.9900 0.2094 4.7758 16.9900

13 18.9970 0.2280 4.3860 18.9970

Figure 6.4: Determining the Henry’s law constant for CO2 in [Emmp][TF2N]

y = 76.484x2 + 36.149x

R² = 0.9988

y = 67.055x2 + 53.034x

R² = 1

y = 96.599x2 + 61.048x

R² = 0.9999

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4

fCO

2

XCO2

at 313.15 K

at 323.15 K

at 333.15 K

189

Figure 6.5: Determining the entropy of absorption for CO2 in [Emmp][TF2N]

y = -2746x + 12.393

R² = 0.942

3.5

3.6

3.7

3.8

3.9

4

4.1

4.2

0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325

lnH

1/T

190

Figure 6.6: Determining the entropy of absorption for CO2 in [Emmp][TF2N]

y = 8.4849x - 45.134

R² = 0.9377

3.5

3.6

3.7

3.8

3.9

4

4.1

4.2

5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82

lnH

lnT

191

Table 6-73: Experimental fugacity of CO2 in [PMPY][TF2N] at 313.15 And 323.15 K

SRK

T-40°C Experimental pressure (bar) Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.0990 0.0024 420.9515 0.0990

2 0.5000 0.0109 91.4021 0.5000

3 1.0013 0.0212 47.1882 1.0013

4 1.9992 0.0431 23.1912 1.9992

5 3.9985 0.0835 11.9777 3.9985

6 7.0001 0.1373 7.2821 7.0001

7 8.9990 0.1715 5.8318 8.9990

8 9.9998 0.1877 5.3286 9.9998

9 10.9988 0.2036 4.9113 10.9988

10 12.9979 0.2346 4.2632 12.9979

11 14.9987 0.2634 3.7971 14.9987

12 16.9982 0.2903 3.4447 16.9982

13 18.9969 0.3167 3.1576 18.9969

T-50°C Experimental pressure (bar) Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.0963 0.0023 437.3694 0.0963

2 0.4995 0.0093 107.7576 0.4995

3 0.9982 0.0187 53.5169 0.9982

4 1.9994 0.0379 26.4058 1.9994

5 3.9985 0.0725 13.7947 3.9985

6 7.0009 0.1185 8.4421 7.0009

7 9.0003 0.1470 6.8039 9.0003

8 9.9964 0.1606 6.2279 9.9964

9 10.9991 0.1748 5.7201 10.9991

10 13.0025 0.2024 4.9400 13.0025

11 14.9977 0.2282 4.3815 14.9977

12 17.0074 0.2526 3.9595 17.0074

13 19.0081 0.2766 3.6158 19.0081

192

Table 6-74: Experimental fugacity of CO2 in [PMPY][TF2N] at 333.15 K.

T-

60°C

Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.0997 0.0022 456.9450 0.0997

2 0.4999 0.0074 134.4821 0.4999

3 0.9990 0.0154 64.9621 0.9990

4 1.9998 0.0320 31.2161 1.9998

5 3.9990 0.0606 16.4955 3.9990

6 6.9969 0.1004 9.9582 6.9969

7 9.0015 0.1257 7.9544 9.0015

8 9.9996 0.1375 7.2718 9.9996

9 10.9991 0.1490 6.7109 10.9991

10 12.9973 0.1725 5.7978 12.9973

11 15.0003 0.1935 5.1670 15.0002

12 16.9954 0.2143 4.6655 16.9954

13 18.9965 0.2323 4.3041 18.9965

Figure 6.7: Determining the Henry’s law constant for CO2 in [PMPY][TF2N]

y = 51.089x2 + 43.67x

R² = 1

y = 60.176x2 + 52.132x

R² = 1

y = 91.247x2 + 60.077x

R² = 0.9999

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4

fCO

2

XCO2

at 313.15

Kat 323.15

K

193

Figure 6.8: Determining the enthalpy of absorption for CO2 in [PMPY][TF2N]

y = -1665.2x + 9.0983

R² = 0.9979

3.75

3.8

3.85

3.9

3.95

4

4.05

4.1

4.15

0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325

lnH

1/T

194

Figure 6.9: Determining the entropy of absorption for CO2 in [PMPY][TF2N]

y = 5.1546x - 25.84

R² = 0.997

3.75

3.8

3.85

3.9

3.95

4

4.05

4.1

4.15

5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82

lnH

lnT

195

Table 6-75: Experimental fugacity of CO2 in [TDC][TF2N] at 313.15 And 323.15 K

SRK

T-

40°C


(bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.0975 0.0028 352.1008 0.0975

2 0.4990 0.0130 77.1127 0.4990

3 0.9989 0.0250 40.0136 0.9989

4 2.0003 0.0503 19.8701 2.0003

5 4.0016 0.0974 10.2671 4.0016

6 6.9991 0.1590 6.2884 6.9991

7 8.9993 0.1970 5.0756 8.9993

8 9.9986 0.2150 4.6502 9.9986

9 11.0008 0.2331 4.2900 11.0008

10 12.9991 0.2673 3.7416 12.9991

11 15.0005 0.3000 3.3329 15.0005

12 16.9975 0.3318 3.0135 16.9975

13 18.9968 0.3601 2.7774 18.9968

T-

50°C


(bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.1014 0.0025 393.9556 0.1014

2 0.5008 0.0105 95.0550 0.5008

3 0.9989 0.0209 47.9359 0.9989

4 2.0004 0.0437 22.8993 2.0004

5 3.9984 0.0837 11.9498 3.9984

6 6.9987 0.1373 7.2834 6.9987

7 8.9985 0.1704 5.8682 8.9985

8 9.9987 0.1866 5.3579 9.9987

9 10.9993 0.2018 4.9552 10.9993

10 12.9993 0.2317 4.3157 12.9993

11 14.9977 0.2614 3.8251 14.9977

12 17.0054 0.2881 3.4709 17.0054

13 18.9966 0.3127 3.1977 18.9966

196

Table 6-76: Experimental fugacity of CO2 in [TDC][TF2N] at 333.15 K

T-

60°C

Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.1013 0.0023 434.6161 0.1013

2 0.5000 0.0090 110.9151 0.5000

3 0.9974 0.0188 53.1021 0.9974

4 1.9995 0.0391 25.5595 1.9995

5 3.9982 0.0741 13.4999 3.9982

6 6.9991 0.1218 8.2068 6.9991

7 8.9982 0.1519 6.5845 8.9982

8 9.9971 0.1668 5.9945 9.9971

9 10.9997 0.1810 5.5261 10.9997

10 12.9987 0.2078 4.8121 12.9987

11 14.9988 0.2338 4.2773 14.9988

12 16.9995 0.2578 3.8792 16.9995

13 18.9978 0.2817 3.5500 18.9978

Figure 6.10: Determining the Henry’s law constant for CO2 in [TDC][TF2N]

y = 42.776x2 + 37.21x

R² = 1

y = 54.816x2 + 43.363x

R² = 1

y = 64.157x2 + 49.312x

R² = 1

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4

fCO

2

XCO2

at 313.15 K

at 323.15 K

at 333.15 K

197

Figure 6.11: Determining the enthalpy of absorption for CO2 in [TDC][TF2N]

Figure 6.12: Determining the entropy of absorption for CO2 in [TDC][TF2N]

y = -1469.7x + 8.3124

R² = 0.999

3.6

3.65

3.7

3.75

3.8

3.85

3.9

3.95

0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325

lnH

1/T

y = 4.55x - 22.528

R² = 0.9983

3.6

3.65

3.7

3.75

3.8

3.85

3.9

3.95

5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82

lnH

lnT

198

Table 6-77: Experimental fugacity of CO2 in [TDC][DCN] at 313.15 And 323.15 K

SRK

T-

40°C

Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.1010 0.0018 555.5556 0.1010

2 0.5002 0.0085 117.6471 0.5002

3 1.0010 0.0165 60.6061 1.0010

4 2.0020 0.0339 29.4985 2.0020

5 4.0001 0.0674 14.8368 4.0001

6 7.0001 0.1124 8.8968 7.0001

7 8.9987 0.1411 7.0872 8.9987

8 9.9982 0.1549 6.4558 9.9981

9 10.9988 0.1687 5.9277 10.9988

10 12.9977 0.1959 5.1046 12.9977

11 14.9925 0.2207 4.5310 14.9925

12 17.0014 0.2479 4.0339 17.0014

13 19.0067 0.2720 3.6765 19.0067

T-

50°C

Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.1023 0.0019 526.3158 0.1023

2 0.5002 0.0075 133.3333 0.5002

3 0.9974 0.0145 68.9655 0.9974

4 1.9983 0.0299 33.4448 1.9983

5 4.0016 0.0587 17.0358 4.0016

6 6.9961 0.0977 10.2354 6.9961

7 9.0014 0.1231 8.1235 9.0014

8 9.9975 0.1357 7.3692 9.9975

9 11.0029 0.1478 6.7659 11.0029

10 12.9967 0.1727 5.7904 12.9967

11 14.9972 0.1957 5.1099 14.9972

12 16.9980 0.2185 4.5767 16.9980

13 19.0061 0.2403 4.1615 19.0061

199

Table 6-78: Experimental fugacity of CO2 in [TDC][DCN] at 333.15 K

T-

60°C

Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

1 0.0998 0.0017 588.2353 0.0998

2 0.4996 0.0061 163.9344 0.4996

3 0.9991 0.0125 80.0000 0.9991

4 2.0000 0.0255 39.2157 2.0000

5 3.9981 0.0500 19.9920 3.9981

6 6.9979 0.0835 11.9760 6.9979

7 8.9991 0.1051 9.5147 8.9991

8 10.0002 0.1163 8.5985 10.0002

9 11.0005 0.1265 7.9051 11.0005

10 12.9993 0.1475 6.7797 12.9993

11 14.9973 0.1678 5.9595 14.9973

12 17.0071 0.1859 5.3792 17.0071

Figure 6.13: Determining the Henry’s law constant for CO2 in [TDC][DCN]

y = 46.706x2 + 57.221x

R² = 1

y = 52.848x2 + 66.34x

R² = 1

y = 74.724x2 + 77.303x

R² = 1

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3

fCO

2

XCO2

at 313.15 K

at 323.15 K

at 333.15 K

200

Figure 6.14: Determining the enthalpy of absorption for CO2 in [TDC][DCN]

y = -1568.4x + 9.0532

R² = 0.9992

4

4.05

4.1

4.15

4.2

4.25

4.3

4.35

4.4

0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325

lnH

1/T

201

Figure 6.15: Determining the entropy of absorption for CO2 in [TDC][DCN]

y = 4.8583x - 23.874

R² = 0.9997

4

4.05

4.1

4.15

4.2

4.25

4.3

4.35

4.4

5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82

lnH

lnT

202

Table 6-79: Experimental fugacity of CO2 in [EMIM][LACTATE] at 313.15 ,323.15 and

333.15 K

Peng- Robinson (PR-EoS)

T=40°C Experimental

pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

0.9989 0.0870 11.4940 0.9989

2.0015 0.1163 8.5972 2.0015

3.9986 0.1525 6.5587 3.9986

6.9995 0.1890 5.2908 6.9995

8.9979 0.2090 4.7858 8.9979

9.9983 0.2184 4.5787 9.9983

10.9997 0.2270 4.4055 10.9997

12.9971 0.2423 4.1269 12.9971

14.9989 0.2559 3.9084 14.9989

17.0006 0.2708 3.6932 17.0006

18.9981 0.2831 3.5320 18.9981


pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

0.9990 0.0714 14.0132 0.9990

3.9978 0.1300 7.6935 3.9978

4.9987 0.1429 6.9970 4.9987

6.9989 0.1639 6.1026 6.9989

9.9978 0.1907 5.2444 9.9978

18.9984 0.2499 4.0012 18.9984


pressure (bar)

Experimental

X CO2

Experimental

KVL

Experimental

f CO2

0.4996 0.0430 23.2743 0.4996

0.9985 0.0598 16.7345 0.9985

1.9996 0.0829 12.0611 1.9996

3.9962 0.1124 8.8995 3.9962

6.9996 0.1427 7.0084 6.9996

9.0007 0.1595 6.2709 9.0007

203

Figure 6.16: Determining the Henry’s law constant for CO2 in [EMIM][LACTATE]

Figure 6.17: Determining the enthalpy of absorption for CO2 in [EMIM][LACTATE]

y = 46.182x - 3.144

R² = 0.9835

y = 54.442x - 2.9155

R² = 0.9948

y = 64.838x - 2.816

R² = 0.9596

-5

0

5

10

15

20

0 0.05 0.1 0.15 0.2

fCO

2

XCO2

Series1

y = -644.06x + 6.3527

R² = 0.9722

4.28

4.3

4.32

4.34

4.36

4.38

4.4

4.42

4.44

0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325

lnH

1/T

204

Figure 6.18: Determining the entropy of absorption for CO2 in [EMIM][LACTATE]

y = 1.9915x - 7.148

R² = 0.9692

4.28

4.3

4.32

4.34

4.36

4.38

4.4

4.42

4.44

5.74 5.75 5.76 5.77 5.78 5.79 5.8 5.81 5.82

lnH

lnT

205

Table 6-80: Experimental fugacity of CO2 in [(CH2)4SO3HMIm] [HSO4] at 313.15 And

323.15 K

Peng-Robinson (PR-EoS)


pressure

(bar)

Experimental X

CO2

Experimental

KVL

Experimental

f CO2

0.0993 0.0008 1308.2550 0.0993

0.4984 0.0018 570.5489 0.4984

0.9989 0.0030 337.7090 0.9989

6.9993 0.0253 39.5220 6.9993

10.9997 0.0482 20.7501 10.9997

12.9971 0.0552 18.1189 12.9971


pressure

(bar)

Experimental X

CO2

Experimental

KVL

Experimental

f CO2

0.1010 0.0006 1784.1086 0.1010

0.4998 0.0012 864.9262 0.4998

9.0006 0.0319 31.3251 9.0006

9.9979 0.0365 27.4136 9.9979

10.9988 0.0408 24.5344 10.9988

12.9977 0.0473 21.1411 12.9976

15.0000 0.0548 18.2429 15.0000

16.9995 0.0614 16.2957 16.9995

206

Figure 6.19: Determining the Henry’s law constant for CO2 in [(CH2)4SO3HMIm]

[HSO4]

y = -1304.4x2 + 301.42xR² = 0.9973

y = 20.891x2 + 274xR² = 0.9994

-2

0

2

4

6

8

10

12

14

16

18

0 0.02 0.04 0.06 0.08

fCO

2

XCO2

313.15 K

323 K

Poly. (313.15 K)

Poly. (323 K)

207

Figure 6.20: Determining the enthalpy of absorption for CO2 in [(CH2)4SO3HMIm]

[HSO4]

y = -965.16x + 8.6952

R² = 1

5.6

5.62

5.64

5.66

5.68

5.7

5.72

0.00308 0.0031 0.00312 0.00314 0.00316 0.00318 0.0032

lnH

1/T

208

Figure 6.21: Determining the entropy of absorption for CO2 in [(CH2)4SO3HMIm]

[HSO4]

y = 3.0342x - 11.823

R² = 1

5.6

5.62

5.64

5.66

5.68

5.7

5.72

5.745 5.75 5.755 5.76 5.765 5.77 5.775 5.78

lnH

lnT

209

Table 6-81: Experimental fugacity of CO2 in [(CH2)4SO3HMIm][TF2N] at 313.15 And

323.15 K


pressure (bar)

Experimental

XCO2

Experimental

KVL

Experimental

fCO2

0.0977 0.0013 758.7253 0.0977

0.4996 0.0013 758.7253 0.4996

0.9986 0.0073 136.2212 0.9986

8.9983 0.1349 7.4138 8.9983

9.9980 0.1455 6.8725 9.9980

10.9996 0.1596 6.2675 10.9996

12.9977 0.1829 5.4662 12.9977

14.9993 0.2082 4.8028 14.9993

16.9992 0.2296 4.3552 16.9992

19.0001 0.2538 3.9405 19.0001


pressure (bar)

Experimental

XCO2

Experimental

KVL

Experimental

fCO2

0.0982 0.0016 634.5178 0.0982

0.5003 0.0062 161.0565 0.5003

0.9997 0.0122 81.8331 0.9997

3.9984 0.0557 17.9520 3.9984

7.0005 0.0909 11.0038 7.0005

8.9991 0.1159 8.6252 8.9991

10.0011 0.1258 7.9503 10.0011

15.0024 0.1826 5.4774 15.0024

210

Figure 6.22: Determining the Henry’s law constant for CO2 in


y = 61.723x2 + 59.4xR² = 0.9988

y = 63.12x2 + 70.781xR² = 0.9997

0

5

10

15

20

25

0 0.05 0.1 0.15 0.2 0.25 0.3

fCO

2

XCO2

313.15

323.15

Poly.(313.15)

Poly.(323.15)

211

Figure 6.23: Determining the enthalpy of absorption for CO2 in


y = -1773.9x + 9.749

R² = 1

4.06

4.08

4.1

4.12

4.14

4.16

4.18

4.2

4.22

4.24

4.26

4.28

0.00308 0.0031 0.00312 0.00314 0.00316 0.00318 0.0032

lnH

1/T

212

Figure 6.24: Determining the entropy of absorption for CO2 in


y = 5.5766x - 27.963

R² = 1

4.06

4.08

4.1

4.12

4.14

4.16

4.18

4.2

4.22

4.24

4.26

4.28

5.745 5.75 5.755 5.76 5.765 5.77 5.775 5.78

lnH

lnT

Documents

THERMODYNAMIC AND EXPERIMENTAL STUDIES OF IONIC …ourspace.uregina.ca/bitstream/handle/10294/5312/Zoubeik_Mohame… · Mr. Mohamed Farag Zoubeik, candidate for the degree of Mater