MODELING AND SIMULATION OF SOLID-LIQUID EQUILIBRIUM BY … · 2018-07-10 · modeling and simulation of solid-liquid equilibrium by perturbed-chain statistical associating fluid theory

MODELING AND SIMULATION OF SOLID-LIQUID EQUILIBRIUM

BY PERTURBED-CHAIN STATISTICAL ASSOCIATING

FLUID THEORY

THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

MASTER OF TECHNOLOGY

In

CHEMICAL ENGINEERING

By

SUNIL KUMAR MAITY

UNDER THE GUIDANCE OF

Prof. Saibal Ganguly & Prof. Sirshendu De

DEPARTMENT OF CHEMICAL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR

INDIA

January 2003

Indian Institute of Technology

Kharagpur

India CERTIFICATE

________________________________________________________________________

This is to certify that SUNIL KUMAR MAITY, final year M.Tech student in the

Department of Chemical Engineering, Indian Institute of Technology, Kharagpur has carried

out his project work under our guidance during the academic session 2002-03, and herewith

submitted the thesis entitled “MODELING AND SIMULATION OF SOLID-LIQUID

EQUILIBRIUM BY PERTURBED-CHAIN STATISTICAL ASSOCIATING FLUID

THEORY”, in partial fulfillment of the requirements for the award of the degree of

“MASTER OF TECHNOLOGY” in “CHEMICAL ENGINEERING”.

Prof. S. Ganguly Prof. S. De

DEPARTMENT OF CHEMICAL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY

KHARAGPUR, INDIA

ACKNOWLEDGEMENTS

I express my deep sense of gratitude and indebtedness to Dr. S. GANGULY and Dr. S. DE, Associate Professor, Department of Chemical Engineering for their invaluable guidance, inspiration, and encouragement given to me at all stages of my M.Tech thesis work.

I am also indebted to Mr. K. Gayen, Mr. M. K. Purakait, and Mr. D. P. Chakraborty, for their encouragement and help given to me carrying out the study for the dissertation work in their company.

I also like to thank Mr. B. De and Mr. S. Bayen for their constant support to me at all stages of my work.

Finally, I thank one and all who directly or indirectly rendered their help for the successful completion of my project work.

I.I.T., Kharagpur (SUNIL KUMAR MAITY)

13/01/2003

CONTENTS

Page

Chapter-1 INTRODUCTION 1

Chapter-2 LITERATURE REVIEW 4

Chapter-3 MODELING OF SOLID-LIQUID EQUILIBRIUM 9

3.1 Theory of Solid-Liquid Equilibrium 10

3.2 Solid-Liquid Equilibrium Phase Diagram 13

Chapter-4 PERTURBED-CHAIN STATISTICAL ASSOCIATING FLUID THEORY EQUATION OF STATE

14

4.1 PC-SAFT Equation of State 15

4.2 Summary of Equation for Calculating Thermo-Physical Properties Using Perturbed Chain SAFT Equation of State

25

Chapter-5 REGRESSION ANALYSIS OF SOLUBILITY DATA 34

5.1 Solid-Liquid Equilibrium of n-Alkanes 35

5.2 Solid-Liquid Equilibrium of Aromatic Compounds 40

5.3 Effect of Pressure on Solid-Liquid Equilibrium 42

5.4 Effect of Solvent on Solid-Liquid Equilibrium 44

5.5 Effect of Molecular Weight and Melting Temperature on Solid-Liquid Equilibrium

44

5.6 Discussion 45

Chapter-6 SENSITIVITY STUDY FOR POLYETHYLENE

SYSTEM 46

6.1 Results of Sensitivity Study 47

6.2 Discussion 50

Chapter-7 RESULTS OF SOLUBILITY OF POLYETHYLENE 51

7.1 Experimental Determination of Solubility 53

7.2 Conclusions and Future Scope of Work 55

References 57

Nomenclature 58

Appendix A Derivation of the Pure-Solute F02l/F02

s 61

Appendix B Program of Solid-Liquid Equilibrium Calculation 64

List of Tables

Sl no. Name of Tables Page

4.1.1 Model constants for the integrals I1( ,m) and I2( ,m) of square-well chains used in 4.1.20 and 4.1.21.

21

5.1 PC-SAFT Parameters of Organic Solutes and Solvents 35

5.1.1 Experimental SLE Data for System n-Dodecane and n-Heptane

36

5.1.2 Experimental SLE Data for System n-Hexadecane and n-Heptane

37

5.1.3

Experimental SLE Data for System n-Octadecane and n-Heptane

37

5.1.4 Solid-Solid Transition and Melting Properties of Aromatic Compounds

38

5 .1.5 Solid-Solid Transition and Melting Properties of Normal Alkanes

38

5.1.6

Experimental SLE Data for System n-Dotriacontane and n-Heptane

39

5.2.1 Experimental SLE Data for System Biphenyl and Benzene 40

5.2.2

Experimental SLE Data for System ε-Caprolactone and Toluene

41

5.3.1 Experimental Data for System n-Octacosane and Decane 42

5.3.2 Correlation of Molar Volume (Cm3/Mol) and Temperature for n-Octacosane

43

5.3.3 Experimental Data for System n-Octacosane, P-Xylene, and n-Decane

43

6.1 PC-SAFT Parameters of Polyethylene 47

7.1

Experimental SLE Data for System Polyethylene and m-Xylene

52

7.1.1 Properties of Polyethylene 53

7.1.2

Experimental SLE Data for Grade1 Polyethylene in Xylene

53

7.1.3

Experimental SLE Data for Grade2 Polyethylene in Xylene

53

7.1.4 PC-SAFT Parameters of Xylenes 55

List of Figures

Sl no. List of figures Page

2.1 Schematic Diagram of PVT Cell Apparatus 6

2.2 The Schematic Diagram of the High-Pressure Optical Vessel with a Video Microscope

7

3.2.1 Solid Liquid Equilibrium Phase Diagram 13

5.1.1 SLE for System n-Dodecane + n-Heptane 36

5.1.2 SLE for System n-Hexadecane and n-Heptane 37 5.1.3 SLE for System n-Octadecane and n-Heptane 38 5.1.4 SLE for System n-Dotriacontane and n-Heptane 39 5.2.1 SLE for System Biphenyl and Benzene 40 5.2.2 SLE for System ε-Caprolactone fnd Toluene 41

5.3.1 Effect of Pressure on Binary SLE of System n-Octacosane and n-Decane for Different Composition.

42

5.3.2 Effect of Pressure on SLE of System n-Decane+P-Xylene + n- Octacosane

43

5.4.1 Effect of Solvent on SLE 44 5.5.1 Effect of Molecular Weight on SLE in n-Heptane 44

6.1.1 Effect of Pressure on Solubility of Polyethylene in m-Xylene

47

6.1.2 Effect of Crystallizability Fraction on Solubility of Polyethylene in M-Xylene

48

6.1.3 Effect of Melting Point on Solubility of Polyethylene in m-Xylene

48

6.1.4 Effect of Solvent on Solubility of Polyethylene in m-Xylene

49

6.1.5 Effect of Kij on Solubility of Polyethylene in m-Xylene 49

7.1 Solubility of Polyethylene in m-Xylene at One Bar Pressure and Prediction By PC-SAFT Model.

52

7.1.1 Solubility of Polyethylene (PE30398.9) in Xylene 54 7.1.2 Solubility of Polyethylene (PE32599.8) in Xylene 55

CHAPTER 1

INTRODUCTION

Chapter 1: Introduction

The study of solid–liquid equilibrium, SLE is of great technical interest for developing and designing separation processes, such as crystallization and fractionation. Crystallization processes are used for separation of mixtures. Knowledge of solid-liquid equilibrium behavior is also important for pipeline design where undesirable crystallization can cause safety problem. In oil production, solubility of normal-alkanes as well as other materials such as aromatics and naphthalene are important. But most of the studies deal with solubility mostly at atmospheric pressure. In the production of crude oil, pressure is generally elevated and precipitation can be a troublesome problem. So the study of solubility at elevated pressure has huge industrial importance. Linear polyethylene is composed of a distribution of n-alkanes of different molecular weight. Lower molecular weight oligomer fractions have reasonably high solubility in various solvents. The study of the solubility of low molecular weight alkanes in various solvents and in polymer themselves will lead to their partition coefficients when a polymer is in contact with any of the solvents. Partition coefficients are useful in predicting the maximum or equilibrium levels of migration of these low molecular weight components from the polymer into contacting solvents when estimating the migration from food packaging materials into food. Polyethylene coming out of the reactor is separated from the solvents in a flush drum. Then cooling and crystallization is used to purify it. So crystallization on the surface of heat exchanger and flush drum and clogging of pipeline due to crystallization are the typical industrial problem. In the polyethylene production, reactor is operated at very high pressure. So the study of solubility at high pressure is industrially very important. The solubility data for low molecular weight n-alkanes and aromatic compounds is enormous in this regard. Using these data parameters of different equation was determined and hence solubility was predicted. But solubility data for polymers such as polyethylene is scarce even in atmospheric pressure. Again considerable experimental effort is generally required to study the high-pressure phase equilibrium for polymer system. The equations that are used for predicting solubility of low molecular weight aromatic compounds are not always applicable to highly non-ideal mixtures such as high molecular weight chain like polymers.

Modeling and Simulation of Solid-Liquid Equilibrium 2

Chapter 1: Introduction

In this work, PC-SAFT equation of state is used to model solid- liquid equilibrium since it has wide applicability starting from low molecular weight organic compounds to high molecular weight polymer system, highly non-ideal system to associating compounds. PC-SAFT equation of state is used for predicting thermo physical properties and liquid-liquid, vapor-liquid equilibrium since last few years. This equation of state requires three pure component parameters: segment no (m), segment diameter (σ), and energy parameter (ε/K), and it has one adjustable solvent-solute binary interaction parameter. The simplest case of SLE is that of a pure crystalline totally crystallizable solute and liquid Solvent, where the solute has a finite solubility in the solvent, but the solvent solubility in the solid is zero (X2

S=0). In case of polyethylene, it is not a totally crystalline solute. Crystallinity fraction of polyethylene varies from 0.4 to 0.6. This model is applicable to both totally crystalline to partially crystalline solutes. Here a model has been developed based on PC-SAFT equation of state, which is applicable to homopolymer system. This model requires melting point, crystallinity fraction, no of repeating unit data of polymer. In this work this model is initially tested with literature solubility data of low molecular weight n-alkanes and aromatic compound both at atmospheric and elevated pressure for different solvent systems. Then sensitivity study is done for polyethylene system to understand the effects of different parameters on solubility. Lastly solubility study is done for different grades of polyethylene in xylene at atmospheric pressure. This data is used to determine the model parameters such as crystallinity fraction and adjustable solvent-solute binary interaction parameter (Kij).


CHAPTER 2

LITERATURE REVIEW

Chapter 2: Literature Review

This chapter deals with the solubility study by previous workers and their findings, experimental set up, and modeling. These are discussed one by one in subsequent paragraphs. • Cheng Pan, Maciej Radosj (3) developed a solid-liquid equilibrium (SLE) model based on copolymer SAFT (Statistical Associating Fluid Theory). Copolymer SAFT was derived from well known homopolymer version of SAFT. This equation of state is applicable to heterosegmented chains; chains composed of segments varying in size, energy, and hence connected with different kinds of bonds. Copolymer-SAFT is used to calculate fugacity coefficients of solutes in the liquid mixture. This equation of state is applicable to totally crystalline to partially crystalline solutes. Initially this model was regressed and tested on solubility data for naphthalene, n-alkanes, and polyethylene. Then the model was used in sensitivity study to understand the effects of crystallizability, melting point, molecular weight, and pressure on SLE of polyethylene in supercritical and sub critical propane. The results of their sensitivity analysis are as follows: With increase in pressure, solubility decreases at fixed temperature. With increase in crystallinity fraction (C), solubility decreases at fixed temperature and pressure. With increase in melting point, solubility decreases at fixed temperature and pressure. • Shu-Sing Chang, John R. Maurey, and Walter J. Pummer (7) determined the solubility and phase equilibrium of two n-alkanes namely n-Octadecane (C18) and n-dotriacontane (C32) in different solvent systems: n-heptane, ethanol, ethanol/water mixture, tributyrin, trioctanoin, and mixed triglycerides. Solubility was determined by visual observing the dissolution temperature of a mixture of solvent and solute of known composition. Magnetic stirrer enhanced the mixing. For lower solubility where visual method become impractical, 14C labeled tracers were used. With a sensitive liquid scintillation counter operating at 20-30 cpm background, it was possible to detect the presence of 10-10 g of the labeled alkanes in aliquots taken from the solution. Differential Scanning Calorimeter (DSC) measured heat of fusion and melting temperature of the two n-alkanes, required for modeling of SLE.



• Hyo-Guk Lee, Frank R. Groves, and Joanne M. Walcott (6) measured the effect of pressure on binary (SLE) for system: n-decane + n-octacosane (C28) and ternary SLE for systems: n-decane + p-xylene + n-octacosane (C28), and n-decane + p-xylene + phenanthrene mixtures. Their measurements correspond to 10 mole% solid content and pressure up to 200 bars.

Fig 2.1: Schematic diagram PVT cell apparatus. A, Ruska pump; B, pressure gauge; C, PVT cell; D, air bath; E, cathetometer; F, mercury reservoir; G, CO2 reservoir; H, Flash separator; I, wet test meter; TC, temperature controller; TI, temperature indicator. Pressure effect was measured by a Ruska Pressure-Volume-Temperature (PVT) cell, in which equilibrium condition was observed visually through the sight glass of the cell as shown in fig 2.1. The results of their study showed that solubility of n-octacosane in n-decane is decreased by around 40% as pressure is increased from atmospheric to 200 bars. The results were correlated by calculating activity coefficient of solute in liquid mixture from Flory-Huggins plus regular solution equation including a pressure correction term.



• Roland Witting, Dana Constantineseu, and Jurgen Gmchling (5) measured the solubility of ε-caprolactone by visual technique in the following solvent systems: benzene, toluene, cyclohexane, 1-propanol, methanol, water, and 2-pentanone. For the description of the activity coefficient the NRTL model was used. Using the experimental solubility data the interaction parameters of the NRTL model were evaluated. Also activity coefficient of the solutes were predicted using the group contribution method modified UNIFAC (Dortmund) using the available group interaction parameter of the “acyclic esters” group (COO). • Hyo-Guk Lee, Philip A. Schenewerk, and Joanne Walcott, and Frank R. Groves Jrs (12) studied the pressure effect on solubility for n-octacosane in a mixture of n-decane and carbon dioxide. Their measurement was based on PVT cell apparatus as described earlier. Using perturbed hard sphere chain equation of state with empirical mixing rule then they correlated the solubility data. • Y. Tanaka and M. Kawakami (11) measured high-pressure solid-liquid binary phase equilibrium for the following four systems: benzene +n-tetradecane, benzene +n-hexadecane, cyclohexane + n-tetradecane, cyclohexane + n-hexadecane. They measured saturation condition using high pressure optical vessel with the aid of a video microscope as shown below in Fig 2.2

Fig 2.2: The schematic diagram of the high-pressure optical vessel with a video microscope. A, high-pressure optical vessel; B, CCD camera probe; C, color monitor; D, thermocouple; E, thermostat; F, pressure transducer; G, pressure and temperature indicator; H, sample inlet; I, sample outlet; J, oil pump; K, pressure intensifier; L, exchange of oil path.



• In the late sixties, E. McLaughlin and H.A. Zainal (8,9) studied the solubility of a large no aromatic compounds such as biphenyl, o-, m-, p-terphenyl, naphthalene, anthracene etc in benzene and carbon tetrachloride solvent. • Joachim Gross and Gabriele Sadowski (4) developed Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state based on modified square well potential. It requires three pure components parameters: segment no., segment diameter, energy parameter. Also it uses one adjustable binary interaction parameter. It is widely applicable to non-spherical chain like molecules like polymer. This equation of state has capability of predicting pure and mixture density; excess enthalpy, entropy, free energy of mixtures; vapor-liquid, liquid-liquid and solid-liquid equilibrium; and vapor pressure.


CHAPTER 3

MODELING OF

SOLID-LIQUID EQUILIBRIUM

Chapter 3: Modeling of Solid-Liquid Equilibrium

3.1 Theory of Solid-Liquid Equilibrium

At equilibrium, the crystalline-solute fugacity in the liquid phase is equal to that in the solid phase:

fL2=fS

2 (3.1.1)

Where 2 means solute. Further, the solute fugacities in both liquid and solid phases are:

fL2= L

2xL2P (3.1.2)

fS2=fS

02 (3.1.3)

Where, as usual, the solid phase is assumed to be pure crystalline solute.

Substituting Eq. 3.1.2 and Eq. 3.1.3 into Eq. 3.1.1, we have

L2xL

2P=fS02 (3.1.4)

Let us divide both sides of Eq. 3.1.4 by f02L, which is the fugacity of pure sub cooled

liquid solute at constant T and P:

L2xL

2P/fL02=fS

02/fL02 (3.1.5)

Since f02L is the fugacity of pure liquid, x2

L = 1, so f02L can be expressed as

fL02= 0P (3.1.6)

Where 0 is the fugacity coefficient of pure sub-cooled liquid solute at constant T and P.

Next, let us substitute Eq. 3.1.6 into Eq. 3.1.5 and take the natural logarithm of both sides of Eq. 3.1.5:

(3.1.7)

The fugacity ratio of pure solute on the right hand side of Eq. 3.1.7, derived from a thermodynamic cycle given in Appendices “A” is as follows:



(3.1.8)

Where Psat is the solute saturated-vapor pressure at its melting temperature. v is the volume difference of liquid and solid solute defined as v=vL-vS.

The first three terms on the right-hand side of Eq. 3.1.8 are not of equal importance, as suggested by Prausnitz et al (13); the first term is dominant. The other two terms have opposite signs, and hence, have a tendency approximately to cancel each other. These two heat-capacity terms, therefore, are neglected. The last term in Eq. 3.1.8, accounts for the pressure effect. The pressure effects tend to be negligible at low pressures. At higher pressures, however, and in general for compressible solutions, the pressure effects can be significant. So, after neglecting the heat capacity effect, Eq. 3.1.8 becomes

(3.1.9)

Substituting Eq. 3.1.9 into Eq. 3.1.7, we get our working equation:

(3.1.10)

For low-pressure systems, the second term in the right side of Eq. 3.1.10 vanishes.

Eq. 3.1.10 is applicable to crystalline solutes, that is solutes with 100% crystallizability, such as pure normal alkanes and aromatic hydrocarbons. We extend this approach to crystallizable polymers, that is, macromolecular solutes with partial crystallizability that are usually referred to as semi-crystalline polymers; the amorphous polymers will have 0% crystallizability. We quantify crystallizability in terms of a crystallinity fraction c, where 0 c 1, assuming that the polymer contains c crystalline fraction and (1-c) amorphous fraction.

Following Harismiadis and Tassios (14), who assume that the log of the ratio of fugacities is proportional to c, we express the effective log of the ratio of fugacities as follows:




(3.1.11)

Where u is the number of ethyl units in the backbone.

The fugacity ratio of the crystal unit for the sub-cooled liquid and solid can be estimated as for the crystalline molecules, using Eq. 3.1.9, except the enthalpy of melting, Hm, is exchanged for Hu, and Psat is set equal to zero because Psat is very low for polymers:

(3.1.12)

Where Hu is the enthalpy of melting per mole of crystal unit. For the ethyl unit, Hu=8.22 kJ/mol, as reported by Van Krevelen (15). The polymer-volume change, v, is

determined from the densities of an amorphous polymer, a, and a crystalline polymer, c: v=1/ a-1/ c. For polyethylene, a=0.853 g/cm3 and c=1.004 g/cm3.

Combining Eq. 3.1.7, Eq. 3.1.11 and Eq. 3.1.12, we get

(3.1.13)

Where subscript p stands for polymer. The fugacity coefficients of polymer in solution, p

L and of pure-liquid polymer, p0 are calculated by PC-SAFT equation of state.

Solid crystalline normal alkanes such as n-dotriacontane exhibits a solid-solid (ss) phase transition a few degrees below its melting point. Such phase transition is typical of n-alkanes larger than n-C20; from a higher-temperature phase of a hexagonal geometry to more stable crystalline structures at lower temperatures. Furthermore, the two solid phases are in a state of thermodynamic equilibrium. Similar to the above approach, we include the effect of the ss phase transition as follows:

(3.1.14)


Where Tss is the ss transition temperature and Hss is the enthalpy of the ss transition.

3.2 Solid-Liquid Equilibrium Phase Diagram

SLE data in this work are presented in the form of temperature-solubility, T–x, phase diagrams. The solubility is defined as the equilibrium mole fraction (for small molecules) or weight fraction (for macromolecules) of the solid solute in solution.

C L T

A

LS

Wt or mole fraction (x) Fig 3.2.1: solid liquid equilibrium phase diagram Continuous SL curve (AC) divides T-X phase plain into two regions, a liquid region (L) at higher temperature and a solid-liquid (SL) region at lower temperature. In SL region two phases coexists, the crystalline solid and the liquid solution.


CHAPTER 4

PERTURBED-CHAIN STATISTICAL ASSOCIATING FLUID THEORY

EQUATION OF STATE

Chapter 4: PC-SAFT Equation of State

4.1 PC-SAFT EQUATION OF STATE

Introduction

For the correlation and prediction of phase equilibrium in macromolecular systems, the equations of state for chain molecules have been successfully used for more than two decades. In many recent investigations, non-spherical molecules are conceived to be chains comprised of freely jointed spherical segments. Several routes have been established to obtain descriptions for those chain fluids. One particularly successful equation of state concept for chain molecules is based on Wertheim's theory of associating fluids. Applying Wertheim's first-order perturbation theory (TPT1), Chapman et al. derived an equation of state for chain mixtures, known as the statistical associating fluid theory (SAFT). Initially the chain structure was not accounted for in the dispersion term of the SAFT equation, since a hard-sphere reference was used within the chain term; the dispersion contribution of each segment in a chain was assumed to be equal to a non-bonded spherical molecule of the same diameter. Numerous investigators have subsequently examined the use of a square-well reference and a Lennard¯Jones reference fluid in the chain-term, leading to equations of state for square-well chains and Lennard¯Jones chains, respectively. These expressions are lengthy, and thus many of the most commonly applied engineering equations of state still utilize square-well dispersion terms, which do not account for the connectivity of the segments.

PC-SAFT equation uses the same chain term and association term as the earlier SAFT equations. Because a hard chain fluid serves as a reference for perturbation theory, rather than the spherical molecules as in the SAFT modifications, the proposed model is referred to as perturbed-chain SAFT (PC-SAFT). This model is applicable to real chain molecules of any length, from spheres to polymers.

Molecular Model: Modified Square Well Potential

In the proposed equation molecules are conceived to be chains composed of spherical segments. Pair potential for the segments of a chain is given by modified square well potential as suggested by Chen and Kreglewski. ∝ r < (σ -s1)

U(r) = 3ε (σ -s1) ≤ r < σ (4.1.1)

-ε σ ≤ r < λσ

0.0 r ≥ λσ



Where

U(r) is pair potential, r is radial distance between two segments, σ is temp independent segment diameter, ε is the depth of potential well, λ is reduced well width. As suggested by Chen and Kreglewski a ratio of s1 /σ = 0.12 is assumed. Any specific interactions, like hydrogen bonding or dipole-dipole forces have been neglected. Contributions to the Helmholtz free energy due to such interactions may be implemented separately. According to this model, nonassociating molecules are characterized by three pure component parameters: the temp independent segment diameter, σ; the depth of potential, ε; and the no of segments per chain, m.

PC-SAFT Equation of state

The properties of the square-well chain fluid are calculated applying a perturbation theory; where the structure of the fluid system is assumed dominate by the repulsive interactions. According to the perturbation theories, the interaction of molecules can be divided into a repulsive part and a contribution due to the attractive part of the potential. To calculate the repulsive contribution, a reference fluid in which no attractions are present is defined. Attractive interactions are treated as a perturbation to the reference system.

In the frame work of Barker and Henderson’s perturbation theory a temperature dependent segment diameter, d(T) can be used to describe the soft repulsion of the molecules, where

d(T) = ∫ 0σ 1 – exp -U(r) /κT dr (4.1.2)

For the potential function used in Eq. 4.1.1, integration leads to the temperature dependent hard segment diameter, di (T) of component i, according to

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛−−=

kTd i

iiεσ 3exp12.01 (4.1.3)

The complete equation of state is given as an ideal gas contribution (id), a hard chain contribution (hc), and a perturbation contribution, which accounts for the attractive interactions (disp).



Z = Zid + Zhc + Zdisp (4.1.4)

Where Z is the compressibility factor, with Z=PV/(RT) and Zid =1.0, P is the pressure, V is the molar volume, R denotes the gas constant.

Hard Chain Reference Equation of State

Based on Wertheim’s first-order thermodynamic perturbation theory Chapman et al. developed an equation of state, which for homonuclear hard-sphere chains is given by

(4.1.5)

(4.1.6)

Where xi is the mole fraction of chains of component i, mi is the number of segments in a chain of component i, is the total number density of molecules, gii

hs is the radial pair distribution function for segments of component i in the hard sphere system, and superscript hs indicates quantities of the hard-sphere system. Expressions of Boublik and Mansoori et al. are used in Eq. 4.1.3 for mixtures of the hard-sphere reference system:

(4.1.7)

(4.1.8)

Where

(4.1.9)

And i is the segment diameter of component i.

Note that 3 is equal to the packing fraction , i.e., 3 = . The packing fraction represents a reduced segment density.

Perturbation Theory for Pure Chain Molecules

The basic idea of the perturbation approach is that the Helmholtz free energy of a system can be expressed as an expansion in inverse temperature around the free energy of a



reference system. The perturbation expansion is fast convergent and can be truncated after the second term, so that the perturbation contribution to the Helmholtz free energy of the system is given by

(4.1.10)

Where A1 and A2 are the first-and second-order perturbation terms.

The perturbation theory of Barker and Henderson was derived for spherical molecules. If square-well chains are to be treated within this theory, all intermolecular segment-

segment interactions between two molecules have to be considered. The appropriate equations become as

(4.1.11)

(4.1.12)

With

(4.1.13)

Where gαβhc (m; x, ) is the site-site radial distribution function of chains, which represents the radial distribution function for a segment of one chain and a segment of another chain separated by the radial distance χαβ= x. In Eq. 4.1.11 and Eq. 4.1.12 homonuclear chains are assumed, where any two segments and on different chains interact with the same depth of the pair potential, αβ = , and same well width, αβ = . Note, that in Eq. 4.1.11 and Eq. 4.1.12 already and N were introduced on a per-molecule basis, i.e. the relations s= ·m and Ns=Nm were applied, where s is the segment density ( s = Ns/ V), and Ns is the number of segments in the system. The perturbation expressions originally required segment-based quantities ( s and Ns); the conversion to molecular quantities ( and N) leads to a factor m on the right hand side of



Eq. 4.1.12. The superscript "hc" in Eq. 4.1.11, Eq. 4.1.12, and Eq. 4.1.13 indicates quantities of the hard-sphere chain reference fluid.

Besides an expression for the compressibility factor Zhc of the reference hard-sphere chain fluid, the perturbation theory of Barker and Henderson requires the site-site radial distribution function gαβhc (m; x, ) of the reference fluid. Chiew has derived equations for gαβhc (m; x, ) of chains from integral equation theory by applying the Percus¯Yevick closure and obtained an approximation for the average intermolecular radial distribution function gαβhc (m; x, ), given by

(4.1.14)

The position of segments and within the appropriate chains has considerable influence on the site¯site radial distribution function. It is important for example, whether

refers to a terminal segment (segment located at the end of a chain) or to a non-terminal segment. By means of the averaging (Eq. 4.1.14), the segments of chain molecules are non-distinguishable. They are characterized by an average intermolecular radial distribution function, which is also given on a segment¯segment basis.

In the formulation of the perturbation terms given above in Eq. 4.1.11 and Eq. 4.1.12, all segment¯segment interactions have to be considered individually. However, it is fair to introduce an averaging into the perturbation theory analogous to that proposed by Chiew, i.e., Eq 4.1.14. For a pure fluid of homonuclear chains, the perturbation terms become

(4.1.15)

(4.1.16)

Where for pure chain fluids the compressibility term can be obtained from Eq. 4.1.5 in the form



(4.1.17) A Simple Mathematical Representation of the Perturbation Terms

Since the integrations over reduced radius x in Eq. 4.1.15 and Eq. 4.1.16 have to be performed numerically, it is desirable to find a simple mathematical representation for those integrals. Let us therefore introduce the abbreviations

(4.1.18)

(4.1.19)

Although the average radial distribution function depends upon radius, density and segment number, the integrations over radius yields expressions I1( , m) and I2( , m) which are functions of density and segment number only. Gulati and Hall have taken advantage of that fact by representing I1( , m) as a simple power series in density for the case of a spherical square-well fluid (m=1) and of a square-well dimer fluid (m=2). Those authors have obtained values of the radial pair distribution function of monomers and dimers from molecular dynamics simulations and upon integration obtained I1( ,m=1) and I1( , m=2)-values. They have subsequently fit coefficients of a power series to both sets of I1-values over a range of densities (0.025 0.475) in order to obtain simple expressions for I1( , m=1) and I1( , m=2). Hino and Prausnitz have also used a power series in density to substitute I1( ,m) for the case of a spherical square-well fluid (m=1). They have obtained the power series coefficients by fitting an analytic expression for the integral in Eq. 4.1.18, which was derived by Chang and Sandler.

In the present study, it is aimed at a simple function which can represent I1( , m) in Eq. 4.1.19 for the entire range of segment numbers. As in the previous investigations, a power series in density is assumed, where the appropriate coefficients are now functions of the segment number. The integrals I1( , m) and I2( , m) can accurately be represented by a power series in density of sixth order:



(4.1.20)

Where ai(m) and bi(m) are coefficients of the power series in density. From Eq. 4.1.19, it becomes apparent that bi=(i+1)ai. However, this simple relation does not hold if more realistic pair potentials would be adopted.

Let us now concern with the dependence of the power series coefficients ai(m) and bi(m) on the segment number. Only the function ai(m) will be considered in the following paragraph; the function bi(m) can be treated analogously. First coefficients are regressed ( ai(m)) of the power series i

6ai· i to the integral in 4.1. for different segment numbers (m=1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10, 100, 1000)). It was found, that the dependence of each of the power series coefficients on segment number can accurately be described with a relation proposed by Liu and Hu.

Eq. 18

(4.1.21)

Table 4.1.1. Model constants for the integrals I1( , m) and I2( , m) of square-well chains used in Eq. 4.1.20 and Eq. 4.1.21.

i a0i a1i a2i

0 0.91056314452 -0.30840169183 -0.09061483510 1 0.63612814495 0.18605311592 0.45278428064 2 2.68613478914 -2.50300472587 0.59627007280 3 -26.5473624915 21.4197936297 -1.72418291312 4 97.7592087835 -65.2558853304 -4.13021125312 5 -159.591540866 83.3186804809 13.7766318697 6 91.2977740839 -33.7469229297 -8.67284703680

i b0i b1i b2i

0 0.72409469413 -0.57554980753 0.09768831158 1 2.23827918609 0.69950955214 -0.25575749816 2 -4.00258494846 3.89256733895 -9.15585615297 3 -21.0035768149 -17.2154716478 20.6420759744 4 26.8556413627 192.672264465 -38.8044300521 5 206.551338407 -161.826461649 93.6267740770 6 -355.602356122 -165.207693456 -29.6669055852

With Eq. (4.1.21), the model-constants a0i, a1i, and a2i (with i=0,...6) are introduced. The constants a0i can easily be obtained by setting a0i=ai(m=1).The model-constants a1i and a2i were obtained by fitting them to a matrix of I1(m, ) values, where ranges of =0,...0.6



and m=1,...1000 were chosen. All I1(m, ) values were calculated from Eq. 4.1.18 using the average radial distribution function proposed by Chiew. The values of the model-constants a0i, a1i, and a2i as well as b0i, b1i, and b2i are given in Table 4.1.1.

Using Eq. 4.1.20 and Eq. 4.1.21, the perturbation terms of first and second order can be rewritten to the simple form

(4.1.22)

(4.1.23)

The three pure-component parameters required by the equation of state are those which entirely characterize square-well chain molecules: the segment number, m; the segment diameter, ; and the depth of the pair potential, /k.

Extension to the Mixtures

A rigorous application of Barker and Henderson's perturbation theory to mixtures (within the above described formalism) requires expressions for the average radial pair distribution function gij

hc(mk , k; xij, ) of mixtures. These must be given for any pair of molecules i and j in the system of molecules with segment numbers mk and segment diameter k of all k components. O'Lenick and Chiew have derived a set of equations for the radial pair distribution function of mixtures; however, those equations are not given in analytical form.

Therefore, Van der Waals one fluid mixing rules are adopted here to extend the perturbation terms to mixtures

(4.1.24)

(4.1.25)

Conventional combining rules are employed to determine the parameters between a pair of unlike segments



(4.1.26) (4.1.27)

The one-fluid mixing concept of the compressibility term in Eq. 4.1.25 were applied, i.e., similarly to Eq. 4.1.17 it is

(4.1.28)

The approximation within the Van der Waals one-fluid mixing rule, that the radial pair distribution function can be averaged for reduced radii, is a widespread approach for mixtures of spherical molecules. Since the radial pair distribution function for chain molecules in the above formalism is given on a per-segment basis, the one-fluid mixing rule is also applicable to chain molecules. The terms I1( , ) and I2( , ) in Eq. 4.1.24 and Eq. 4.1.25 are then evaluated for the mean segment number of the mixture, which is given by Eq. 4.1.6.

The equation of state can be written in terms of the compressibility factor applying the relation

(4.1.29)

The compressibility factor is calculated as Z = Zhc + Zpert, where the perturbation contribution is given by

Zpert=Z1+Z2 (4.1.30)

and the perturbation terms of first-and second-order are given by

(4.1.31)

With



(4.1.32)

and

(4.1.33)

Where

(4.1.34)

and where C1 and C2 are abbreviations defined as

(4.1.35)

(4.1.36)



4.2 SUMMARY OF EQUATIONS FOR CALCULATING THERMO-PHYSICAL PROPERTIES USING PERTURBED-CHAIN SAFT EQUATION OF STATE This section provides a summary of equations for calculating thermo-physical properties using the perturbed-chain SAFT equation of state. The Helmboltz free energy

is the starting point in this paragraph, as all other properties can be obtained as derivatives of . In the following, a tilde

resAresA ( )~ will be used for reduced quantities, and

caret symbols will indicate molar quantities. The reduced Helmholtz free energy, for example, is given by

( )^

NkTAa

resres

=~

(4.2.1)

At the same time, one can write in terms of the molar quantity

RTaa

resres

~^

= (4.2.2)

Helmholtz Free Energy The residual Helmholtz free energy consists of the hard-chain reference contribution and dispersion.

(4.2.3) disphcres

aaa~~~

+= Hard-Chain Reference Contribution

(4.2.4) ( ) (∑ −−=i

iihsiii

hshc

gmxama σ ln 11

~~~)

Where is the mean segment number in the mixture ~m

(4.2.5) ∑=i

iimxm_

The Helmholtz free energy of the hard-sphere fluid is given on a per-segment basis



( ) ( )( )

⎥⎥⎦

⎤

⎢⎢⎣

⎡−⎟⎟

⎠

⎞⎜⎜⎝

⎛−+

−+

−== 302

3

32

233

32

3

21

0

~1ln

1131 ζζ

ζζ

ζζζ

ζζζ

ζkTNAa

s

hshs

(4.2.6)

and the radial distribution function of the hard-sphere fluid is

( ) ( ) ( )33

22

2

23

2

3 12

13

11

ζζ

ζζ

ζ −⎟⎟⎠

⎞⎜⎜⎝

⎛

++

−⎟⎟⎠

⎞⎜⎜⎝

⎛

++

−=

ji

ji

ji

jihsij dd

dddd

ddg (4.2.7)

With nζ defined as

∑=i

niiin dmxρπζ

6 { }3,2,1,0∈n (4.2.8)

The temperature-dependent segment diameter of component is given by id i

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛−−=

kTd i

iiεσ 3exp12.01 (4.2.9)

Dispersion Contribution The dispersion contribution to the Helmholtz free energy is given by

( ) 32221

321

~,,2 σηπρσηπρ ∈−∈⎟

⎠⎞

⎜⎝⎛−=

−−

mmlCmmmladisp

(4.2.10)

Where an abbreviation is introduced for the compressibility expression, which is defined as

1C

( ) ( )( )[ ]

1

2

432

4

2

1

1

2121227201

1281

1

−−−

−

⎟⎟⎠

⎞⎜⎜⎝

⎛

−−−+−

⎟⎠⎞

⎜⎝⎛ −+

−−

+=

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

++=

ηηηηηη

ηηη mm

pZpZC

hchc

(4.2.11)

Another set of abbreviations

∑∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛∈=∈

i jij

ijjiji kT

mmxxm 332 σσ (4.2.12)



∑∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛∈=∈

i jij

ijjiji kT

mmxxm 32

322 σσ (4.2.13)

Conventional combining rules are employed to determine the parameters for a pair of unlike segments.

( )jiij σσσ +=21 (4.2.14)

( )ijjiij k−∈∈=∈ 1 (4.2.15)

The integrals of the perturbation theory are substituted by simple power series in density

(4.2.16) ∑ ⎟⎠⎞

⎜⎝⎛=⎟

⎠⎞

⎜⎝⎛

=

−− 6

0

11 ,

i

imimI ηη

(4.2.17) ∑ ⎟⎠⎞

⎜⎝⎛=⎟

⎠⎞

⎜⎝⎛

=

−− 6

02 ,

i

ii mbmI ηη

Where the coefficients and depend on the chain length according to ia ib

iliii am

m

m

mam

mama 20211

−

−

−

−

−

−− −−

+−

+=⎟⎠⎞

⎜⎝⎛ (4.2.18)

iiii bm

m

m

mbm

mbmb 210211

−

−

−

−

−

−− −−

+−

+=⎟⎠⎞

⎜⎝⎛ (4.2.19)

The universal model constants for are available in literature. iiiiii bbbaaa 210210 and,,,,, Density The density at a given system pressure sysp must be determined iteratively by adjusting

the reduced density η until sysp = sysp . A suitable staring value for a liquid phase is

;5.0=η for a vapor phase, . Values of 1010−=η 7405.0>η ( )[ ]23/.τ= are higher then the closest packing of segments and have no physical relevance. The number of molecules p is calculated from η through

1

36 −

⎟⎠⎞⎜

⎝⎛∑=

iiii dmxη

πρ (4.2.20)



The quantities nζ given in Eq 4.2.8 can now be calculated. For a converged value of η ,

we obtain the molar density , in units of , from ^

ρ 3kmol/m

⎟⎠⎞

⎜⎝⎛

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ Α= −

Α molkmol1010 3

30

10^

mN V

ρρ (4.2.21)

Where p is, according to Eq 4.2.20, given in units of 0

3Α and denotes Avogadro

123 mol10022.6 ×=ΑVN,s number.

Pressure Equations for the compressibility factor will be derived using the thermodynamic relation

1,

~

1

xT

res

aZ⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

+=η

η (4.2.22)

The pressure can be calculated in units of by applying the relation 2/ ma Ν=Ρ

30

1010⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ Α=Ρ

mZkTρ (4.2.23)

From Eqs (4.2.22) and (4.2.3), it is disphc ZZZ ++=1 (4.2.24) Hard-Chain Reference Contribution The residual hard-chain contribution to the compressibility factor is given by

( )( )ρ

ρ∂∂

∑ −−=−− hs

iihsii

iii

hshc ggmxZmZ 11 (4.2.25)

Where hsZ is the residual contribution of the hard-sphere fluid, given by

( ) ( ) ( )330

323

32

230

21

3

3

13

13

1 ζζζζζ

ζζζζ

ζζ

−

−+

−+

−=hsZ (4.2.26)



( ) ( ) ( )

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎟⎠

⎞⎜⎜⎝

⎛

+

+⎟⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎟⎠

⎞⎜⎜⎝

⎛

++

−=

∂∂

43

322

33

22

2

33

322

3

22

3

3

16

14

16

13

1

ζζζ

ζζ

ζζζ

ζζ

ζζρ

ji

ji

ji

jihsij

dddd

dddd

pg

(4.2.27)

and was given in Eq. 4.2.7. hsijg

Dispersion Contribution The dispersion contribution to the compressibility factor can be written as

( ) ( ) 32222

21

3212 σηηηπρσ

ηηπρ ∈⎥

⎦

⎤⎢⎣

⎡+

∂∂

−∈∂

∂−=

−

mICICmmIZ disp (4.2.28)

Where

( ) ( )∑ +⎟⎠⎞

⎜⎝⎛=

∂∂

=

−6

01

1 1j

jjmaI ηηη (4.2.29)

( ) ( )∑ +⎟⎠⎞

⎜⎝⎛=

∂∂

=

−6

01

2 1i

jjmbI ηηη (4.2.30)

and where is an abbreviation defined as 2C

( ) ( )( )[ ] ⎟⎟⎠

⎞⎜⎜⎝

⎛

−−+−+

⎟⎠⎞

⎜⎝⎛ −+

−++−

−=∂∂

=−−

3

23

5

221

12 21

404812211

8204ηηηηη

ηηη

ηmmC

CC (4.2.31)

Fugacity Coefficient The fugacity coefficient ( PTk , )ϕ is related to the residual chemical potential according to

( ) Z ln,ln k −=kT

Tresk υµϕ (4.2.32)

The chemical potential can be obtained from

( ) ( ) ∑⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

−⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

+−+==

−−− N

j

xuTj

res

j

xuTk

resresres

k

ijkijk

xax

xaZa

kTvT

1

,,,,

1,µ (4.2.33)



Where derivatives with respect to mole fraction are calculated regardless of the summation relation . For convenience, one can define abbreviations for

derivatives of Eq. 4.2.8 with respect to mole fraction.

∑ =1jj x

( )nkkxTk

nxkn dm

xkj

ρπζζρ

6/,.

, =⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

= { }3,2,1,0∈n (4.2.34)

Hard-Chain Reference Contribution

( )( )∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

+=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂ −

ixTk

hsiihs

iii

xTk

hshs

k

xTk

hc

kjkjkj

xggmx

xamam

xa

///

,,

11

,,

~~

,,

~

1ρ

ρρ

(4.2.35)

With

( )( ) ( ) ( )

( )( )

( ) ( ) ⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

−⎟⎟⎠

⎞⎜⎜⎝

⎛−+−⎟

⎟⎠

⎞⎜⎜⎝

⎛−

−

+−

−+

−+

−+

−

+

+−=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

3

,323

32

03,033

,3323,2

22

33

23

3,332

233

,222

23

,321

3

,212,1

0

~

0

,0

,,

~

11ln

23

1

13

1

3

1

31

3

1

/

ζζ

ζζ

ζζζζ

ζζζζζ

ζζ

ζζζ

ζζ

ζζ

ζ

ζζζζ

ζζζζ

ζζζ

xkxk

xkxk

xkxkxkxkxk

hsxk

xpTk

hs

axa

kj

(4.2.36)

( ) ( ) ( )

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎟⎠

⎞⎜⎜⎝

⎛

+

+⎟⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎟⎠

⎞⎜⎜⎝

⎛

++

−=⎟

⎟⎠

⎞⎜⎜⎝

⎛

∂

∂

43

,322

33

,22

2

33

,322

3

,22

3

,3

,,

1

6

1

4

1

6

1

3

1/

ζ

ζζ

ζ

ζζ

ζ

ζζ

ζ

ζ

ζ

ζ

xkxk

ji

ji

xkxk

ji

jixk

xpTk

hsij

dddd

dddd

xg

kj (4.2.37)



Dispersion Contribution

( )[ ]

( )⎭⎬⎫

⎩⎨⎧ ∈+∈⎥⎦

⎤⎢⎣⎡ ++

−∈+∈−=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

−−−

xkxkxkk

xkxk

xpTk

hs

mICmmICmICmICmp

mImIpxa

kj

32221

322,212,121

321

32.1

,,

~

2

/

σσπ

σσπ

(4.2.38)

With

( ) ∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛∈=∈

jkj

kjjjkxk kT

mxmm 332 2 σσ (4.2.39)

( ) ∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛∈=∈

jkj

kjjjkxk kT

mxmm 32

322 2 σσ (4.2.40)

( ) ( )( )[ ] ⎭⎬⎫

⎩⎨⎧

−−−+−

−−−

−= 2

32

4

221,32,1 21

21227201

28ηη

ηηηηηηηζ kkxkxk mmCCC (4.2.41)

(4.2.42) ∑ ⎥⎦⎤

⎢⎣⎡ +⎟

⎠⎞

⎜⎝⎛=

=

−−6

0,

1,3,1

i

ixi

ixkixk aimaI ηηζ

(4.2.43) ∑ ⎥⎦⎤

⎢⎣⎡ +⎟

⎠⎞

⎜⎝⎛=

=

−−6

0,

1,3,2

i

ixi

ixkixk bimbI ηηζ

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−+=

−−

−

−

−

ik

ik

xki amm

mam

ma 2212,43 (4.2.44)

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−+=

−−

−

−

−

ik

ik

xki bmm

mam

mb 2212,43 (4.2.45)

Enthalpy and Entropy

The molar enthalpy is obtained from a derivative of the Helmholtz free energy with respect to temperature, according to

res

h^



( )1

,

~^

−+⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

−= ZT

aTRTh

ixp

resres

(4.2.46)

Unlike the enthalpy of an ideal gas, witch is a function of temperature only; the entropy of a real gas is a function of both temperature and pressure (or density). Hence, the residual entropy in the variables and P T is different from the residual entropy for the specified conditions and u T . It is

( ) ( ) ( )ZR

TvsRTPs

resres

ln,,^

^+= (4.2.47)

All of the equations for are given in the variables v and res

a~

T , so that the residual entropy can be written as

( ) ( )ZT

aT

aTR

TPsres

xp

resres

i

ln,~

,

~^

+⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

+⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

−= (4.2.48)

The residual molar Gibbs free energy is defined as ( TPgres

,^

)

( )R

TPSRTh

RTg

resresres

,^^^

−= (4.2.49)

or simply as

( ) (ZZa )RTg res

res

ln1~

^

−−+= (4.2.50)

The temperature derivative of in Eqs 4.2.46 and 4.2.48 is again the sum of two contributions.

res

a~

iii xp

disp

xp

hc

xp

res

Ta

Ta

Ta

,

~

,

~

,

~

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

+⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂ (4.2.51)

With abbreviations for two temperature derivatives

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ ∈−−⎟

⎠⎞

⎜⎝⎛ ∈

=∂∂

=kTkTT

dd iii

iTi 3exp12.03 2, σ (4.2.52)

( )∑ −=∂∂

=i

niTiii

nTn dndmx

T1

,, 6ρπζζ { }3,2,1∈n (4.2.53)

The hard-chain contribution and the dispersion contribution can conveniently be written.



Hard-Chain Reference Contribution

( )( )i

ii

xp

hsii

i

hsiiii

xp

hs

xp

hc

Tg

gmxTam

Ta

,

1

,

~

,

~

1 ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

∑ −−⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂ −−

(4.2.54)

( )( ) ( ) ( )

( )( )

( ) ( ) ⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

−⎟⎟⎠

⎞⎜⎜⎝

⎛−+−⎟

⎟⎠

⎞⎜⎜⎝

⎛ −

−

−+

−+

−+

−

+

=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

3

,323

32

0333

,3323,2

22

33

23

3,332

233

,222

23

,321

3

,212,1

0,

~

11ln

23

1

13

1

3

1

31

3

1

ζζ

ζζ

ζζζ

ζζζζζ

ζζ

ζζζ

ζζ

ζζ

ζ

ζζζζ

ζζζζ

ζ TTT

TTTTT

xp

hs

i

Ta (4.2.55)

Equation 4.2.54 requires only the ii − pairs in temperature derivative of the radial pair distribution function . For simplicity, one can restrict oneself to the pairs in

Eq 4.2.7 by equating

hsijg ii −

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=ii

iii dd

ddd

21 (4.2.56)

The temperature derivative of the radial pair distribution function is then hsijg

( ) ( ) ( ) ( )

( ) ( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎠⎞

⎜⎝⎛+

−

⎟⎠⎞

⎜⎝⎛+⎟

⎟⎠

⎞⎜⎜⎝

⎛

−+

−⎟⎠⎞

⎜⎝⎛+

−⎟⎠⎞

⎜⎝⎛+

−=

∂∂

43

,322

33

,222

33

22

,33

,32

3

,22

3

2,2

3

,3

16

14

21

12

21

1

613

21

13

21

1

ζ

ζζ

ζ

ζζ

ζζ

ζ

ζζζ

ζ

ζζ

ζ

ζ

TTi

TiiTT

iTiT

hsii

d

ddddT

g

(4.2.57)

Dispersion Contribution

32221

212

1

3211

,

~

2

2

σπ

σπρ

∈⎥⎦⎤

⎢⎣⎡ −

∂∂

+∂∂

−∈⎟⎠⎞

⎜⎝⎛ −∂∂

−=⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

∂∂

−

mTIC

TICI

TCmp

mTI

TI

Ta

ixp

disp

(4.2.58)

With

∑ ⎟⎠⎞

⎜⎝⎛=

∂∂

=

−−6

0

1,3

1

i

iTi ima

TI

ηζ (4.2.59)

∑ ⎟⎠⎞

⎜⎝⎛=

∂∂

=

−−6

0

1,3

2

i

iTi imb

TI

ηζ (4.2.60)

2,31 C

TC

Tζ=∂∂

(4.2.61)


CHAPTER 5

REGRESSION ANALYSIS OF

SOLUBILITY DATA

Chapter 5: Regression Analysis of Solubility Data

Plenty of solubility data are available for low molecular weight pure crystalline n-alkanes and aromatic compounds in different solvent system. These experimental data are collected from different literature to show the suitability of the developed PC-SAFT model for low molecular weight system. PC-SAFT parameters of these solvents and solutes are shown in Table 5.1. Table 5.1 PC-SAFT Parameters of Organic Solutes and Solvents Hydrocarbon Segment no Segment Diameter Energy Parameter (m) (σ, 0A) (ε/κ, K)

Solutes n-dodecane(C12) 5.3060 3.8959 249.21 n-hexadecane(C16) 6.6485 3.9592 254.70 n-octadecane(C18) 7.3271 3.9668 256.20 n-octacosane(C28) 10.3622 4.0217 252.0 n-dotriacontane(C32) 11.835 4.0217 252.0 biphenyl 3.8877 3.8151 327.42 ε-caprolactone 2.8149 3.9902 255.05

Solvents n-pentane 2.6896 3.7729 231.20 n-heptane 3.4831 3.8049 238.40 n-decane 4.6627 3.8384 243.87 benzene 2.4653 3.6478 287.35 toluene 2.8149 3.7169 285.69 5.1: SOLID-LIQUID EQUILIBRIUM OF n-ALKANES Illustrated in Fig 5.1.1 and Fig 5.1.2 are solubility of n-dodecane and n-hexadecane in n-heptane solvent respectively, on the basis of experimental data taken from Hoerr, Harwood (3) as presented in tabular form in Table 5.1.1 & 5.1.2. These data fits very well with PC-SAFT model with Kij = 0.0. Fig 5.1.3 represents the solubility of n-octadecane in n-heptane solvent. Corresponding experimental data are taken from S. Chang, J. R. Maurey, and W. J. Pummer (7). These data fit very well with the model with only small Kij (= 0.0003).



Table 5.1.1 Experimental SLE Data (3) for System n-Dodecane (2) and n-Hexane (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.05 215.5 0.5 249 0.1 223 0.6 252.5 0.15 228 0.7 256 0.2 233 0.8 259 0.3 240 0.9 261.5 0.4 245.5 1.0 263.6

0.0 0.2 0.4 0.6 0.8 1.0210

220

230

240

250

260

Experimental (3)

PC-SAFT(Kij=0.0)

Tem

pera

ture

(K)

Weight Fraction of n-Dodecane

Fig 5.1.1:SLE for system n-dodecane (C12) + n-hexane at 1 bar



Table 5.1.2 Experimental SLE Data (3) for System n-Hexadecane (2) and n-Hexane (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.025 236 0.5 274.7 0.05 245 0.6 278.4 0.1 252 0.7 282 0.15 256 0.8 284.6 0.2 260 0.9 287.6 0.3 265.8 1.0 291.2 0.4 270

0.0 0.2 0.4 0.6 0.8 1.0

230

240

250

260

270

280

290

Experimental(3)

PC-SAFT(Kij=0.0)

Tem

pera

ture

(K)

Weight Fraction of n-Hexadecane

Fig 5.1.2: SLE for system n-hexadecane (C16) and n-hexane at 1 bar

Table 5.1.3 Experimental SLE Data (7) for System n-Octadecane (2) and n-Heptane (1) Wt Fraction (W2) T, K Wt. Fraction (W2) T, K 0.213 273 0.38 281.4 0.37 281 0.395 282



0.0 0.2 0.4 0.6 0.8 1.0

250

260

270

280

290

300

E xp erim en ta l (7)

P C -S AF T(K ij=0.0003)

Tem

pera

ture

(K)

W e ig h t F rac tion o f n -O ctad ecan e

Fig 5.1.3: SLE for system n-octadecane (C18) and n-heptane at 1 bar

For n-alkanes larger than C20 such as n-octacosane and n-dotriacontane exhibits solid-solid phase transition a few degree below it’s melting point as shown in Table 5.1.5. These compounds form a higher temperature hexagonal geometry to a more stable crystalline structure at lower temperature. Effect of phase transition is included by model equation 3.1.14. Table 5.1.4 Solid-Solid Transition and Melting Properties of Aromatic Compounds Hydrocarbon Mol. Weight Tm, K ∆Hm, J/Mol biphenyl 154.211 342.1 18732 ε-caprolactone 96 272.13 13821 Table 5 .1.5 Solid-Solid Transition and Melting Properties of Normal Alkanes Hydrocarbon Tss, K ∆Hss, J/mol Tm, K ∆Hm, J/mol n-dodecane (C12) 263.6 36977 n-hexadecane (C16) 291.2 53563 n-octadecane (C18) 301.1 59400 n-octacosane (C28) 331.2 35447 334.4 64658 n-dotriacontane (C32) 338.9 42700 342.1 76000



Experimental solubility data for system n-Dotriacontane in n-Heptane is taken from S. Chang, J. R. Maurey, and W. J. Pummer (7) as listed in Table 5.1.6. Comparison of these data with theoretical model is shown in Fig 5.1.4. Table 5.1.6 Experimental SLE Data (7) for System n-Dotriacontane (2) and n-Heptane (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.0491 302.9 0.332 319.4 0.0604 304.5 0.499 324.7 0.0976 308.1 0.666 329.3 0.201 314.0 0.802 333.9

0.0 0.2 0.4 0.6 0.8 1.0280

290

300

310

320

330

340

Experimental (7)

PC-SAFT(Kij=0.0004)

Tem

pera

ture

(K)

Weight Fraction of n-Dotriacontane

Fig 5.1.4: SLE for system n-dotriacontane (C32) and n-heptane at 1 bar



5.2: SOLID-LIQUID EQUILIBRIUM OF AROMATIC COMPOUNDS E. McLaughlin and H.A. Zainal (8) studied the solubility of biphenyl in benzene for higher mole fraction range as shown in Table 5.2.1. PC-SAFT model fits well with these data as shown in Fig 5.2.1. Table 5.2.1 Experimental SLE Data (8) for System Biphenyl (2) and Benzene (1) Mole Fraction (X2) T, K Mole Fraction (X2) T, K 0.5118 310 0.8195 332.2 0.6478 320.6 0.8916 336.2

0.0 0.2 0.4 0.6 0.8 1.0

240

250

260

270

280

290

300

310

320

330

340

Experimental(8)

PC-SAFT(Kij=0.0)

Tem

pera

ture

(K)

Mole Fraction of Biphenyl

Fig 5.2.1: SLE for system biphenyl and benzene at 1 bar

Illustrated in Table 5.2.2 are the saturation solubility data for system ε-caprolactone in toluene as taken from R. Witting, D. Constantineseu, and J. Gmchling (5). Corresponding figure and comparison with model predicted results are shown in Fig 5.2.2.



Table 5.2.2 Experimental SLE Data (5) for System ε-Caprolactone (2) and Toluene (1) Mole Fraction (X2) T, K Mole Fraction (X2) T, K 0.1009 210.83 0.5468 250.02 0.1486 218.64 0.5896 252.41 0.1942 223.74 0.6384 254.98 0.2472 229.07 0.6878 257.42 0.2981 233.61 0.7914 262.44 0.3501 237.57 0.8474 265.08 0.3975 240.92 0.8959 267.4 0.4518 244.43 0.9369 269.26 0.5039 247.63 1.0 272.18

0.0 0.2 0.4 0.6 0.8 1.0170

180

190

200

210

220

230

240

250

260

270

280

Experimental(5)

PC-SAFT(Kij=0.0)

Tem

pera

ture

(K)

Mole Fraction of Caprolactone

Fig 5.2.2: SLE for system ε-caprolactone and toluene at 1 bar



5.3: EFFECT OF PRESSURE ON SOLID-LIQUID EQUILIBRIUM H. G. Lee, F. R. Groves, and J. M. Walcott (6) measured the saturation condition for n-octacosane + n-decane and n-octacosane + p-xylene + n-decane for approximately 10 mole% solid content and pressure up to 200 bar. Their experimental data are shown in Table 5.3.1 & 5.3.3. These data are plotted along with the model prediction for both binary and ternary system as shown in Fig 5.3.1 & 5.3.2. Data fits well with model with negligible Kij. Table 5.3.1 Effect of Pressure on Binary SLE: Experimental Data (6) for System n-Octacosane (2) and Decane (1) (X2 represents Mole Fraction of n-Octacosane) X2 =0.06013 X2=0.08198 X2=0.1074 T, K P, Bar T, K P, Bar T, K P, Bar 307.2 1 310 1 312.5 2 308 45 310.3 18 312.7 11 308.9 77 311 46 313.5 45 309.7 110 312.2 97 314.4 89 310.4 143 313.4 155 315.3 126 311.6 189 314.4 195 316.3 169 312.5 224 314.7 212 317.4 216

308 310 312 314 316 3180

50

100

150

200

250

X2=0.06013X2=0.08198X2=0.1074

---open sym bol-PC-SAFT(K ij=0.0006)

--closed sym bol--Experim en tal(6)

Pres

sure

(Bar

)

Tem peratu re(K)

Fig 5.3.1: Effect of pressure on binary SLE of system n-octacosane (C28) and n-decane for different composition.



Correlations of solid and liquid molar volume with temperature for n-octacosane are listed in Table 5.3.2

Table 5.3.2 Correlation of Molar Volume (Cm3/Mol) and Temperature (K) for n-Octacosane Liquid molar volume, VL = 0.42203T + 365.588 Solid molar volume, VS = 0.11828T + 381.623 Table 5.3.3 Effect of Pressure on Ternary SLE: Experimental Data (6) for System n-Octacosane (3), P-Xylene (2) and n-Decane (1) (X1/X2 =2.0, X3 =0.09803) T, K P, Bar T, K P, Bar 310.5 1 313.3 126 311 23 314.6 194 311.6 45 315.3 218 312.3 83

310 311 312 313 314 315 316

0

50

100

150

200

250

Experimental (6)

PC-SAFT(Kij=-0.0004)

Pres

sure

(Bar

)

Temperature(K)

Fig 5.3.2: Effect of pressure on SLE of system n-decane (1)+p-xylene (2) + n-octacosane(3) (x1/x2=2.0,x3=0.09803)



5.4: EFFECT OF SOLVENT ON SOLID-LIQUID EQUILIBRIUM

0.0 0.2 0.4 0.6 0.8 1.0270

280

290

300

310

320

330

340

350

n-hep tane+n-octacosane(C28)n -pen tane+n-octacosane(C28)

Tem

pera

ture

(K)

Mole Fraction of n -O ctacosane

Fig 5.4.1: Effect of solvent on SLE 5.5: EFFECT OF MOLECULAR WEIGHT AND MELTING TEMPERATURE ON SOLID-LIQUID EQUILIBRIUM

0.0 0.2 0.4 0.6 0.8 1.0

200

220

240

260

280

300

320

340

n -d odecan e(C 12),(K ij=0.000) n -h exadecane(C 16),(K ij=0.000) n -d otriacon tane(C 32),(K ij=0.0004)

Tem

pera

ture

(K)

W eigh t F raction of Solu te

Fig 5.5.1: Effect of molecular weight on SLE in n-hexane



5.6 DISCUSSION Here some important conclusions are drawn regarding the results of low molecular weight organic compounds.

• As shown in Fig 5.1.1 to 5.1.3, PC-SAFT equation of state gives good agreement with the experimental results for n-alkanes. The requirement of adjustable binary interaction parameter (Kij) increases with increasing chain length for same solvent system.

• For aromatic compounds, model prediction matches very well with literature

experimental data even with Kij=0.0 as shown in Fig 5.2.1 and Fig 5.2.2. • Illustrated in Fig 5.3.1 and Fig 5.3.2 are the effects of pressure on solubility for

binary and ternary systems. These figures show that with increase in pressure solubility decreases. So for saturated system if we increase the pressure at fixed temperature some solid will crystallize. This necessitates the study of solubility at elevated pressure.

• Effect of solvent on solubility is small as shown in Fig 5.4.1. However with

increasing the boiling point of solvent solubility decreases for same solute. • With increasing molecular weight of solute, melting point increases and

consequently its solubility decreases for same solvent.


CHAPTER 6

SENSITIVITY STUDY FOR

POLYETHYLENE SYSTEM

Chapter 6: Sensitivity Study for polyethylene System

Initially PC-SAFT model is regressed and tested on the solubility data for n-alkanes, and aromatic compounds as discussed in chapter 5. Also in the same chapter effect of pressure, solvent, melting point, and molecular weight are discussed rigorously for low molecular weight organic compounds. In this chapter, sensitivity study is performed using the same model as used for low molecular weight system to understand the effects of crystallizability, melting temperature, solvent, adjustable binary interaction parameter (kij) and pressure on solid–liquid equilibrium of polyethylene in m-xylene as shown in the following figures. The PC-SAFT parameters of polyethylene used for this study is listed below in Table 6.1 Table 6.1 PC-SAFT Parameters of Polyethylene Polyethylene Segment No Segment Diameter Energy Parameter (m/M, mol/g) (σ, 0A) (ε/κ, K) LDPE 0.0263 4.0217 249.5 HDPE 0.0263 4.0217 252.0

6.1 RESULTS OF SENSITIVITY STUDY

0.0 0.2 0.4 0.6 0.8330

340

350

360

370

380

390

400

410

420

1.0 bar100 bar

--------Kij=0.0,Tm=415K, C=0.4

Tem

para

ture

(K)

Weight Fraction of Polyethylene(PE120K)

Fig 6.1.1: Effect of pressure on solubility of polyethylene in m-xylene



0.0 0.2 0.4 0.6 0.8 1.0

300

320

340

360

380

400

420

C=0.2C=0.4C=0.6

---------Kij=0.0,Tm=415K

Tem

pera

ture

(K)

W t. Fraction of Polyethylene(PE120K)

Fig 6.1.2: Effect of crystallizability fraction (C) on solubility of polyethylene in m-xylene at 1 bar

0.0 0.2 0.4 0.6 0.8 1.0340

350

360

370

380

390

400

410

420

430

440

Tm=415KTm=440K

-----1 bar,Kij=0.0,C=0.4

Tem

peta

ture

(K)

Wt. Fraction of Polyethylene(PE120K)

Fig 6.1.3: Effect of melting point (Tm) on solubility of polyethylene in m-xylene



0.0 0.2 0.4 0.6 0.8 1.0330

340

350

360

370

380

390

400

410

420

m -xylen ecycloh exan e

----1 b ar,K ij=0.0,Tm =415K ,C=0.4

Tem

pera

ture

(K)

W t. F raction of Polyeth ylen e(PE120K)

Fig 6.1.4: Effect of solvent on solubility of polyethylene in m-xylene

0.0 0.2 0.4 0.6 0.8 1.0330

340

350

360

370

380

390

400

410

420

kij=0.012 kij=0.01 kij=-0.0 kij=-0.008

---1bar,Tm=415K,C=0.4

Tem

pera

ture

(K)

Wt. Fraction of Polyethylene(PE120K)

Fig 6.1.5: Effect of Kij on solubility of polyethylene in m-xylene



6.2 DISCUSSION Here some important conclusions are drawn regarding the results of sensitivity study of polyethylene system. In all figures solubility represent the saturation solubility. Here the study is based on molecular weight of polyethylene of 120000. But the phase diagram can also be drawn for other molecular weights as well. Here intentionally the effect of molecular weight is not shown because with change in molecular weight other property of polyethylene will also change such as melting point, binary interaction parameter, enthalpy of fusion etc.

1. With increase in pressure, solubility decreases at fixed temperature as shown in Fig 6.1. But the effect of pressure on solubility is not much for only a small change in pressure. But enormous change in pressure will decrease solubility of polyethylene to a great extent sufficient to cause industrial problem like clogging of pipelines due to crystallization of polyethylene.

2. With increase in crystallizability fraction (C), solubility decreases at fixed temperature and pressure as shown in Fig 6.2. Here influence of crystallizability fraction on solubility is much.

3. With increase in melting point, solubility decreases at fixed temperature, pressure and other fixed properties as shown in Fig 6.3.

4. Effect of solvent on solubility of polyethylene is not much; rather effect of solvent can be neglected when all other properties are same for both solvents as shown in Fig 6.4.But binary interaction parameter will be different for different solvents even for same solute. Solubility of polyethylene will be different for different solvents if this effect is accounted.

5. With increase in binary interaction parameter, Kij (adjustable parameter of PC-SAFT EOS), solubility of polymer decreases at fixed temperature and pressure as shown in Fig 6.5. Here Kij influences much on solubility.

6. In all the figures, solute is totally soluble in the solvent at the melting point of solute. Extrapolation of the figures to the melting point gives the same result.

7. Sensitivity study for polyethylene system gives similar trend as it is seen for low molecular weight organic compounds.


CHAPTER 7

RESULTS OF SOLUBILITY OF POLYETHYLENE

Chapter 7: Results of Solubility of Polyethylene

Experimental solubility data for polyethylene system is limited. In the year 1946, Richards (3) studied the solubility of polyethylene (of molecular weight 17000 and melting point 387.5K) in m-xylene at atmospheric pressure. Their experimental data is tabulated in Table 7.1. Table 7.1 Experimental SLE Data (3) for System Polyethylene (2) and m-Xylene (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.012 345 0.53 371.75 0.03 349 0.7 377 0.1 354 1 387.5 0.32 363.75 Experimental data fits very well with PC-SAFT model with C = 0.8 as shown in Fig 7.1

0.0 0.2 0.4 0.6 0.8 1.0340

350

360

370

380

390

Experimental (3)

PC-SAFT (Kij=0.0055)

Tem

pera

ture

(K)

Wt. Fraction of Polyethylene

Fig 7.1: Solubility of polyethylene in m-xylene at 1 atmospheric pressure and prediction by PC-SAFT model



7.1 EXPERIMENTAL DETERMINATION OF SOLUBILITY Solubility of polyethylene in xylene is determined for two commercial grade samples at atmospheric pressure. SLE was measured by visual technique. Since there is no standard apparatus for measurement of solubility, two opening conical flux fitted with a condenser serves the purpose. Temperature is measured using resistance thermometer inserted through side opening of the conical flux. Measured amount of solvent and solute was taken in a conical flux and heated slowly with occasional manual shaking. The temperature at which all solutes disappear is the saturation solubility temperature. The properties of two samples are tabulated below in Table 7.1.1 Table 7.1.1 Properties of Polyethylene Sample Melting Point, K Molecular Weight, g/mol Grade1 405 30398.9 Grade2 410 32599.8 Experimental results of the study are shown below in Table 7.1.2 & Table 7.1.3 Table 7.1.2 Experimental SLE Data for Grade1 Polyethylene (2) in Xylene (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.019 360.3 0.1276 367.6 0.04623 362.1 0.173 369.2 0.0674 365.6 0.245 371.5 0.106 366.7 Table 7.1.3 Experimental SLE Data for Grade2 Polyethylene (2) in Xylene (1) Wt Fraction (W2) T, K Wt Fraction (W2) T, K 0.0198 377.9 0.209 386.2 0.046 380 0.3028 388.8 0.074 81.1 0.4032 392.2



0.101 82.5 0.504 394.7 Model prediction and comparison with experimental results are shown in subsequent figures. Crystallizability fractions (C) of the polyethylene samples are not known. So crystallizability fractions are determined from the model. It is found that for C = 0.8, model prediction fits very well with the experimental results for both grades of samples. Solubility measurement is done with xylene. But proportion of individual xylenes (o-, m-, and p-xylenes) is not known. So PC-SAFT parameters of solvent is not known though parameters of individual xylenes are available in literature. For simplicity parameters of m-xylene are used for modeling of solubility of polyethylene, since the parameters are close to one another. PC-SAFT parameters for polyethylene used for modeling are listed in Table 6.1. Parameters of xylenes are listed in Table 7.1.4.



0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40355

360

365

370

375

380

385

Experimental PC-SAFT

C=0.8, Kij=0.002,Tm=405K

Tem

pera

ture

(K)


Fig 7.1.1: Solubility of polyethylene (PE30398.9) in xylene at atmospheric pressure

Table 7.1.4 PC-SAFT Parameters of Xylenes Xylenes Segment No Segment Diameter Energy Parameter (m) (σ, 0A) (ε/κ, K) m-xylene 3.1861 3.7563 291.05 o-xylene 3.1362 3.7600 283.77 p-xylene 3.1723 3.7781 288.13



0.0 0.2 0.4 0.6370

380

390

400

410


C = 0.8, Tm= 410 K

ExperimentalPC-SAFT (Kij=0.0135)

Tem

pera

ture

(K)

Fig 7.1.2: Solubility of polyethylene (PE32599.8) in xylene at atmospheric pressure

7.2 CONCLUSIONS AND FUTURE SCOPE OF WORK

• From the previous figures it is clear that PC-SAFT model can be used to predict the solubility of polyethylene with negligible error if crystallizability fraction, melting point, and molecular weight of polyethylene are known and binary interaction parameter is adjusted accordingly to fit the experimental data of polyethylene-solvent system.



• Here crystallizability fraction is determined from the model. But if the values of the same are known or measured then from the model it is possible to determine correct value of binary interaction parameter. From this it is possible to correlate binary interaction parameter with molecular weight of polyethylene for same solvent system.

• In this work the study is only limited to single solvent. This study can be extended

to different solvents as well. In order to overcome modeling difficulty and to get parameters of the solvent, laboratory grade pure solvent is to be used for the experimental study.

• The study can be extended to large variety of laboratory grade polymers of

different molecular weight. Study can also be done with narrow molecular weight distribution polyethylene in order to correlate the properties of polyethylene with molecular weight.

• Also the solubility study can be extended to high pressure as well in order to get

idea about the pressure effect on solubility. Solubility of polymer under pressure is important industrially because most of the polymer is manufactured under high pressure.

• Melting temperature and its relation with pressure is important for the study of

solubility at high pressure. This can be measured by Differential Scanning Calorimeter (DSC).

• No. average and weight average molecular weight of polymer and its molecular

weight distribution is important in order to extend this model to that based on pseudocomponent approach.


REFERENCES

1. Chemical Engineering Thermodynamics By Sandlar.

2. Molecular Thermodynamics of Fluid Phase Eqiulibria, 2nd edition by J. M. Prausnitz.

3. Cheng Pan, Maciej Radosz, Fluid Phase Equilibria 155, (1999) 57-73

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Nomenclature

NOMENCLATURE C crystallizability f fugacity k Boltzmann’s constant, 1.38 ×10 -23 J/K N Avogadro’s number, 6.023 ×10-23 molecules/mol P sat saturated pressure of solute at melting temperature P pressure, bar PE polyethylene R gas constant SAFT statistical association fluid theory PC-SAFT perturbed-Chain statistical association fluid theory SLE solid–liquid equilibrium SL solid–liquid SS solid-solid T temperature, K u number of ethyl units in backbone X, x mole fraction Z compressibility factor ρ density, mol/ml ρa, ρc density of completely amorphous and completely crystalline, g / cm 3

φ fugacity coefficient φ0 fugacity coefficient of pure sub cooled liquid solute at given T and P ∆CP Cp

L - CpS the heat capacity change of solute, J /K

∆G molar Gibbs free energy change

∆H molar enthalpy change

∆HU enthalpy of melting per crystal unit, for ethyl unit, ∆HU =8.22 kJ / mol

∆S molar entropy change

∆v vL-vS volume change, cm3/mol

A Helmholtz free energy, J

1A Helmholtz free energy of first-order perturbation term, J


Nomenclature

2A Helmholtz free energy of second-order perturbation term, J

030201 ,, aaa model constants; defined in Eq. 4.2.18

( )ma j functions defined by Eqs 4.2.18 and 4.2.19

030201 ,, bbb model constants defined in Eq. 4.2.19

d temperature-dependent segment diameter, 0A

hcg average radial distribution function of hard-chain fluid hcg site-site radial distribution function of hard-chain fluid

21 , II abbreviations defined by Eqs. 4.2.16, 4.2.17

k Boltzmann constant, J/K

ijk binary interaction parameter

Κ factor, Κ iii xy /=Κ

m number of segments per chain −

m mean segment number in the system, defined in Eq. 4.2.5 M molar mass, g/mol N total number of molecules P pressure, Pa R gas constant, -1molJ 1−Κ r radial distance between two segments, A

1s constant defining the pair potential, defined in Eq.4.1.1, 0

T temperature, Κ ( )ru pair potential function, J, defined in Eq.4.1.1

υ molar volume, mol/m3

W weight fraction x reduced radial distance between two segments

ix mole fraction of component i

Z compressibility factor Greek Letters ∈ Depth of pair potential, J η packing fraction, nζη = , defined in Eqs.4.2.20 & 4.2.8

λ reduced well width of square-well potential


Nomenclature

p total number density of molecules, 30

/1 A

σ segment diameter, 0A

nζ abbreviation ( defined by Eq. 4.2.8, )3,...,0=n30 n

A

Superscripts calc calculated property crit critical property disp contribution due to dispersive attraction exp experimental property hc residual contribution of hard-chain system hs residual contribution of hard-sphere system id ideal gas contribution sat property at saturation condition L liquid phase ref reference res residual S solid phase i component I Subscripts 2 solute O2 pure solute i component i m melting condition p polymer ss solid–solid phase transition


Appendix A: Derivation of the Pure-Solute F02l/F02

s

APPENDIX A: DERIVATION OF THE PURE-SOLUTE F02L/F02

S

The fugacity ratio of pure solute is derived from a thermodynamic cycle. Similar to what Prausnitz et al did for the temperature effect, we generate a loop for both, temperature and pressure effects. The detailed derivations are shown below.

The molar Gibbs energy change for solute from state a to state f is related to the fugacities of solid and sub cooled liquid.

(A-1)

It is also related to the corresponding enthalpy and entropy changes by

G(a f)= H(a f)-T S(a f) (A-2)

For the enthalpy change from state a to state f, we have

H(a f)= H(a b)+ H(b c)+ H(c d)+H(d e)+ H(e f) (A-3)



s

Using the Maxwell relations,

(A-4)

Eq. A-3 can be rewritten in terms of the heat capacity, CP, and the enthalpy of melting, Hm, as follows:

(A-5)

For the entropy change from state a to state f, we have

S(a f)= S(a b)+ S(b c)+ S(c d)+S(d e)+ S(e f)

(A-6)

Using the Maxwell relations again,

(A-7)

We rewrite the entropy change given by Eq. A-6 as

(A-8)



s

Substituting Eq. A-5 and Eq. A-8 into Eq. A-2, we obtain

(A-9)

Where CP=CPL-CP

S, and v=vL-vS. Since pressure has little effect on v, v can be taken out of the integration directly.

Substituting Eq. A-9 into Eq. A-1, we get the fugacity ratio given in Eq. 3.1.8.


Appendix B: Program of Solid-Liquid Equilibrium Calculation

APPENDIX B: PROGRAM OF SOLID-LIQUID EQUILIBRIUM CALCULATION IMPLICIT NONE INTEGER nc, nph PARAMETER (nc=20,nph=2) INTEGER ncomp, nphas DOUBLE PRECISION t,p,densys(nph),x_sys(nc) DOUBLE PRECISION parame(nc,5),kij(nc,nc) DOUBLE PRECISION d_sta c-----local variables------------------------------------------------- INTEGER i,j,ph DOUBLE PRECISION phi(nc),phio ,tmax,z,phi2,r,tm,ts,hm,hs,alnx,x2 DOUBLE PRECISION xtrans(nc),dstart,parsys(nc,25),fugcoe(nc),den DOUBLE PRECISION paramel(nc,5),v,c,u,z1,mp,ms c--------------------------------------------------------------------- PARAMETER (r=8.314) c--------------------------------------------------------------------- OPEN (85,FILE='pe_et.inp') OPEN (86,FILE='output.txt') READ(85,*) Read(85,*)p READ(85,*) Read(85,*)t READ(85,*) Read(85,*)tmax READ(85,*) Read(85,*)tm READ(85,*) Read(85,*)ts READ(85,*) Read(85,*)hm READ(85,*) Read(85,*)hs READ(85,*) Read(85,*)c READ(85,*) Read(85,*)u READ(85,*) Read(85,*)z READ(85,*) Read(85,*)v READ(85,*) Read(85,*)mp READ(85,*) Read(85,*)ms



READ(85,*) do i=1,2 read(85,*)paramel(i,1),paramel(i,2),paramel(i,3) enddo close(85) p=p*1.0d5 10 ncomp=1 parame(1,1)= paramel(1,1) parame(1,2)= paramel(1,2) parame(1,3)= paramel(1,3) kij(1,1)=0.0 x_sys(ncomp)=1.0 d_sta=0.4 dstart = d_sta DO 11 i = 1,ncomp xtrans(i) = x_sys(i) parsys(i,1) = parame(i,1) parsys(i,2) = parame(i,2) parsys(i,3) = parame(i,3) 11 CONTINUE CALL PHIEOS (fugcoe,xtrans,t,p,parsys,kij,ncomp,dstart,den) phio=fugcoe(1) ncomp=2 do i=1,ncomp do j=1,ncomp if(i.eq.j)then kij(i,j)=0.0 else kij(i,j)=0.00 endif enddo enddo do i=1,ncomp parsys(i,1) = paramel(i,1) parsys(i,2) = paramel(i,2) parsys(i,3) = paramel(i,3) enddo 12 xtrans(1) = z xtrans(2) =1-z CALL PHIEOS (fugcoe,xtrans,t,p,parsys,kij,ncomp,dstart,den) phi2=fugcoe(1) alnx= -((hm/(r*tm))*((tm/t)-1.0)+(hs/(r*ts))*((ts/t)-1.0) 1 +v*p*1.0d-5/(82.03*t))*c*u -(phi2-phio) x2=exp(alnx) if(dabs(x2-z).lt.1.d-10)then



c conversion of mole fraction to weight fraction z1=z*mp/(z*mp+(1-z)*ms) write(86,*)z1,t else z=z-(z-x2)*0.008 go to 12 endif if(t.lt.tmax)then t=t+2.0 go to 10 else endif STOP END c********************************************************************* SUBROUTINE PHIEOS (phi,x,t,p,parame,kij,ncomp,densta,dense) IMPLICIT NONE c-----variables used in the parameter list of subroutine-------------- INTEGER nc PARAMETER (nc=20) INTEGER ncomp DOUBLE PRECISION phi(nc) DOUBLE PRECISION kij(nc,nc) DOUBLE PRECISION pges,pgesdz,gij(nc, nc) DOUBLE PRECISION fres DOUBLE PRECISION x(nc),t,p,parame(nc,25),mseg(nc) DOUBLE PRECISION densta,dense,dap_dx(nc,7),dbp_dx(nc,7) DOUBLE PRECISION order1,order2,apar(7),bpar(7) DOUBLE PRECISION A,B,C,D,AA,BB(nc),CC(nc),DD(nc),EFF(nc), & QQ(nc,nc),PIJK(nc,nc,nc) DOUBLE PRECISION PI, RGAS, NA, KBOL, TAU DOUBLE PRECISION uij(nc,nc),d00ij(nc,nc),d0(nc) c-----local variables------------------------------------------------- INTEGER i, k, m DOUBLE PRECISION zms, rho, m_mean, term1, term2 DOUBLE PRECISION mhs(nc), mdisp(nc), mcha(nc), mpart(nc), & myres(nc), myresq, lnphi(nc) DOUBLE PRECISION dgijdx(nc, nc, nc),ddendx(nc) DOUBLE PRECISION zres, zges DOUBLE PRECISION I1, I2, I1_dx, I2_dx, & ord1dx, ord2dx, ddrdx, & drdpkt, te1,te2,te3, dte1dx,dte2dx,dte3dx c------obtain parameters and density independent expressions---------- CALL PERTPAR (kij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK,



3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) c------density iteration---------------------------------------------- CALL DENSITR (pges,pgesdz,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) c-----residual Helmholtz free energy---------------------------------- CALL F_EOS (fres,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) zms = 1.d0 - dense rho = 6.d0 * dense / (PI*D) m_mean = A c-----compressibility factor z = p/(kT*rho)--------------------------- zges = (p * 1.d-30)/(KBOL*t*rho) zres = zges - 1.d0 c-----calcul. the derivatives of f to mole fraction x ( d(f)/d(x) )--- DO 1 k = 1,ncomp c-------d(f)/d(x) : hard sphere contribution-------------------------- term1 = DLOG(zms)*(-1.d0+3.d0*CC(k)**2.d0 -2.d0*CC(k)**3.d0) & + (3.d0*CC(k)**2.d0 - 3.d0*CC(k)**3.d0) & * dense / zms**2.d0 term2 = (3.d0*CC(k)+3.d0*EFF(k)-CC(k)**3.d0 + AA*DD(k))/zms & + dense*3.d0 * BB(k) / zms**2.d0 & + 2.d0 * CC(k)**3.d0 / zms**3.d0 mhs(k) = mseg(k)* (term1 + term2 * dense) c-------d(f)/d(x) : chain term---------------------------------------- c-------d(dense)/d(x)=ddendx(p,k) and d(gij)/d(x)-------------------- ddendx(k) = dense/D*mseg(k)*d0(k)**3.d0 DO 10 i = 1, ncomp dgijdx(i,i,k) = ((1.d0+ 3.d0*PIJK(i,i,k)) & /(zms**2.d0) + 2.d0*dense*QQ(i,i)* & (3.d0+2.d0*PIJK(i,i,k))/zms**3.d0+ & dense**2.d0*6.d0*QQ(i,i)**2.d0/ & zms**4.d0)*ddendx(k) 10 CONTINUE mcha(k) = 0.d0 DO 12 i = 1, ncomp mcha(k) = mcha(k) + x(i) * (1.d0-mseg(i)) & * (1.d0/gij(i,i)) * dgijdx(i,i,k) 12 CONTINUE mcha(k) = mcha(k)+( 1.d0-mseg(k))*DLOG(gij(k,k)) c-------d(f)/d(x) : dispersion contribution--------------------------- I1 = 0.d0



I2 = 0.d0 I1_dx = 0.d0 I2_dx = 0.d0 DO 14 m = 0,6 I1 = I1 + apar(m+1)*dense**DBLE(m) I2 = I2 + bpar(m+1)*dense**DBLE(m) I1_dx = I1_dx + apar(m+1)*DBLE(m)*dense**DBLE(m-1)*ddendx(k) & + dap_dx(k,m+1)*dense**DBLE(m) I2_dx = I2_dx + bpar(m+1)*DBLE(m)*dense**DBLE(m-1)*ddendx(k) & + dbp_dx(k,m+1)*dense**DBLE(m) 14 CONTINUE ord1dx = 0.d0 ord2dx = 0.d0 DO 16 i = 1,ncomp ord1dx= ord1dx & + 2.d0*mseg(k) *x(i)*mseg(i)*d00ij(i,k)**3.d0 *uij(i,k)/t ord2dx= ord2dx & + 2.d0*mseg(k) *x(i)*mseg(i)*d00ij(i,k)**3.d0*(uij(i,k)/t)**2.d0 16 CONTINUE te1 = zms**4.d0 *(2.d0-dense)**2.d0 te2 = zms**2.d0 * ( zms**2.d0*(2.d0-dense)**2.d0 & +dense*(-2.d0*dense**3.d0+12.d0*dense**2.d0 & -27.d0*dense+20.d0) ) te3 = dense* ( (2.d0-dense)**2.d0*(8.d0-2.d0*dense) & -zms**2.d0*(-2.d0*dense**3.d0 & +12.d0*dense**2.d0-27.d0*dense+20.d0) ) drdpkt = te1 / (te2 + m_mean*te3) dte1dx = ( - 4.d0*zms**3.d0 *(2.d0-dense)**2.d0 & - 2.d0*zms**4.d0 *(2.d0-dense) )*ddendx(k) dte2dx = dte1dx+ ( (3.d0*dense**2.d0 - 2.d0*2.d0*dense + 1.d0) & *(-2.d0*dense**3.d0+12.d0*dense**2.d0 & -27.d0*dense+20.d0) & + dense*zms**2.d0*(-6.d0*dense**2.d0 & +24.d0*dense -27.d0) )*ddendx(k) dte3dx = ddendx(k)* ( te3/dense & + dense*( -2.d0*(2.d0-dense)*(8.d0-2.d0*dense) & +(2.d0-dense)**2.d0*(-2.d0) & + 2.d0*zms*(-2.d0*dense**3.d0 & +12.d0*dense**2.d0-27.d0*dense+20.d0) & -zms**2.d0*(-6.d0*dense**2.d0 & +24.d0*dense -27.d0) ) ) ddrdx = ( dte1dx*(te2+m_mean*te3) & -te1*(dte2dx +(m_mean*dte3dx+mseg(k)*te3)) ) & / (te2 + m_mean*te3)**2.d0



mdisp(k)= -2.d0*PI*rho*(order1*I1_dx+ord1dx*I1) & - PI*rho*drdpkt*m_mean*(order2*I2_dx+ord2dx*I2) & - PI*rho*(drdpkt*mseg(k)+ddrdx*m_mean)*order2*I2 c-----d(f)/d(x) : summation of all contributions---------------------- mpart(k) = mhs(k) + mcha(k) + mdisp(k) 1 CONTINUE myresq = 0.d0 DO i = 1, ncomp myresq = myresq - x(i)* mpart(i) END DO myresq = myresq + fres + zres DO k = 1, ncomp myres(k) = myresq + mpart(k) lnphi(k) = myres(k) - DLOG(zges) phi(k) = lnphi(k) END DO RETURN END c******************************************************************** SUBROUTINE P_EOS (pges,pgesdz,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) IMPLICIT NONE c-----variables used in the parameter list of subroutine-------------- INTEGER nc PARAMETER (nc=20) INTEGER ncomp DOUBLE PRECISION pges,pgesdz,gij(nc, nc) DOUBLE PRECISION x(nc),t,p,parame(nc,25),mseg(nc) DOUBLE PRECISION densta,dense,dap_dx(nc,7),dbp_dx(nc,7) DOUBLE PRECISION order1,order2,apar(7),bpar(7) DOUBLE PRECISION A,B,C,D,AA,BB(nc),CC(nc),DD(nc),EFF(nc), & QQ(nc,nc),PIJK(nc,nc,nc) DOUBLE PRECISION PI, RGAS, NA, KBOL, TAU DOUBLE PRECISION uij(nc,nc),d00ij(nc,nc),d0(nc) c-----local variables------------------------------------------------- INTEGER i, j, m DOUBLE PRECISION rho,zms,m_mean,ddendv DOUBLE PRECISION term1,term2,term3 DOUBLE PRECISION phs,pdisp,pcha,pideal DOUBLE PRECISION dgijdz(nc,nc),dgijd2(nc,nc),zmsdz, & dvzdz,te1dz,te2dz, & te3dz,pdspdz,fdspdz,fdspd2,pchadz,fchdz,fchd2, & piddz,phsdz DOUBLE PRECISION I2, edI1dz, edI2dz, edI1d2, edI2d2,



& z00, z00_dz, z00_d2, z00_d3, & drdpkt, drdpdz, drdpd2 c------------------------------------------------------------------- rho = 6.d0 * dense / (PI*D) zms = 1.d0 - dense m_mean = A C-----gij , the derivative dgijdz=d(gij)/d(dense) ------------------ C-----and dgijd2 = dd(gij)/d(dense)**2 ----------------------------- DO 2 i = 1, ncomp j=i gij(i,j) = 1.d0/zms + 3.d0*QQ(i,j)*dense/zms**2.d0 & +2.d0*(QQ(i,j)*dense)**2.d0/zms**3.d0 dgijdz(i,j) = (1.d0+3.d0*QQ(i,j)) /zms**2.d0 & +dense*(6.d0*QQ(i,j)+4.d0*QQ(i,j)**2.d0)/zms**3.d0 & +dense**2.d0*(6.d0*QQ(i,j)**2.d0) /zms**4.d0 dgijd2(i,j) = 2.d0*qq(i,j)*(( 1.d0/qq(i,j) & + 6.d0+2.d0*qq(i,j))/zms**3.d0+ (9.d0*dense & + 12.d0*qq(i,j)*dense)/zms**4.d0 +(12.d0*qq(i,j) & * dense**2.D0)/ zms**5.d0) 2 CONTINUE c-----derivations of dense to volume (ddendv = -d(dense)/d(volume)--- ddendv = dense**2.d0 *6.d0/ PI /D c-----p : ideal gas contribution------------------------------------- pideal = rho c-----p : hard sphere contribution----------------------------------- term1 = (A-C**3.d0/D**2.d0) / zms term2 = (3.d0*B*C/D-C**3.d0/D**2.d0)/zms**2.d0 term3 = (2.d0*C**3.d0/D**2.d0)/zms**3.d0 phs = ddendv*(term1 + term2 + term3) c-----p : chain term------------------------------------------------- fchdz = 0.d0 DO 4 i= 1, ncomp fchdz= fchdz + (x(i)*(1.d0-mseg(i))) & * (1.d0/gij(i,i)) * dgijdz(i,i) 4 CONTINUE pcha = ddendv * fchdz c------p : dispersion contribution----------------------------------- c------edI1dz is equal to d(dense*I1)/d(dense)----------------------- c------edI2dz is equal to d(dense*I2)/d(dense)----------------------- I2 = 0.d0 edI1dz = 0.d0 edI2dz = 0.d0 DO 6 m=0,6 I2 = I2 + bpar(m+1)*dense**DBLE(m) edI1dz = edI1dz + apar(m+1)*DBLE(m+1)*dense**DBLE(m) edI2dz = edI2dz + bpar(m+1)*DBLE(m+1)*dense**DBLE(m)



6 CONTINUE z00 = 1.d0 + m_mean*(4.d0*dense-2.d0*dense**2.d0)/ZMS**3.d0 & + (1.d0 - m_mean)*(5.d0*dense-2.d0*dense**2.d0) & /(ZMS*(2.d0-dense)) z00_dz = m_mean*(-2.d0*dense**2.d0+4.d0*dense+4.d0)/ZMS**4.d0 & + (1.d0 - m_mean)*(dense**2.d0-8.d0*dense+10.d0) & /(ZMS*(2.d0-dense))**2.d0 drdpkt = 1.d0/(Z00 + dense*Z00_dz) c--- z00_d2 = m_mean*(-4.d0*dense**2.d0+8.d0*dense+20.d0)/ZMS**5.d0 & + (1.d0 - m_mean) & *(-2.d0*dense**3.d0+24.d0*dense**2.d0-60.d0*dense+44.d0) & /(ZMS*(2.d0-dense))**3.d0 drdpdz = (-2.d0*z00_dz -z00_d2*dense)*drdpkt**2.d0 c be aware: rho=6.d0*dense/(PI*D) fdspdz = -2.d0*PI *6.d0/(PI*D) * edI1dz * order1 & -( PI *6.d0*dense/(PI*D) *drdpdz* m_mean *I2 *order2 & +PI *6.d0/(PI*D) *drdpkt* m_mean *edI2dz *order2 ) pdisp = ddendv* fdspdz c-----p summation, p is obtained in unit [Pa] ------------------------ pges = pideal+phs+ pdisp +pcha pges = pges * (KBOL*t) / 1.d-30 c-----calcul. the derivatives of P to dense-----[d(p)/d(dense)]------- c-----the derivatives are usefull for the density-iteration ---------- c-----using a gradient (Newton) algorithm----------------------------- c-----abbreviations--------------------------------------------------- zmsdz = -1.d0 dvzdz = 2.d0*dense*6.d0/pi/D c-----d(p)/d(dense) : ideal gas contribution-------------------------- piddz = 6.d0/(pi*d) c-----d(p)/d(dense) : hard sphere contribution------------------------ te1dz = (a-c**3.d0/d**2.d0)/(-zms**2.d0)* zmsdz te2dz = (3.d0*b*c/d - c**3.d0/d**2.d0) * 2.d0/(-zms**3.d0)*zmsdz te3dz = (2.d0 * c**3.d0 /d**2.d0) * (-3.d0)/zms**4.d0 * zmsdz phsdz = dvzdz*(term1+term2+term3) + ddendv*(te1dz+te2dz+te3dz) c-----d(p)/d(dense) : chain term-------------------------------------- fchd2 = 0.d0 DO 8 i= 1,ncomp fchd2 = fchd2 + ( x(i)*(1.d0-mseg(i))) & *(dgijd2(i,i)/gij(i,i)-dgijdz(i,i)**2.d0/ gij(i,i)**2.d0) 8 CONTINUE pchadz = ddendv*fchd2 + dvzdz*fchdz c-----d(p)/d(dense) : dispersion contribution------------------------- edI1d2 = 0.d0



edI2d2 = 0.d0 DO 10 m=0,6 edI1d2 = edI1d2 + apar(m+1)*DBLE(m+1)*DBLE(m)*dense**DBLE(m-1) edI2d2 = edI2d2 + bpar(m+1)*DBLE(m+1)*DBLE(m)*dense**DBLE(m-1) 10 CONTINUE z00_d3 = m_mean*12.d0*(-dense**2.d0+2.d0*dense+9.d0)/ZMS**6.d0 & + (1.d0-m_mean)* 6.d0 & *(dense**4.d0-16.d0*dense**3.d0+60.d0*dense**2.d0 & -88.d0*dense+46.d0) & /(ZMS*(2.d0-dense))**4.d0 drdpd2 = (-3.d0*z00_d2 -z00_d3*dense)*drdpkt**2.d0 & + 2.d0/drdpkt*(drdpdz)**2.d0 fdspd2 = - 2.d0*PI *6.d0/(PI*D) * edI1d2 * order1 & - PI*6.d0/(PI*D)*order2*m_mean* ( drdpd2 *I2*dense & +2.d0 *drdpdz *edI2dz & + drdpkt *edI2d2 ) pdspdz = dvzdz*fdspdz + ddendv*fdspd2 c-----total d(p)/d(dense) with unit [Pa] ----------------------------- pgesdz = (piddz+phsdz+pdspdz+pchadz) * (kbol*T)/1.d-30 RETURN END c******************************************************************** SUBROUTINE DENSITR (pges,pgesdz,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) IMPLICIT NONE c-----variables used in the parameter list of subroutine-------------- INTEGER nc PARAMETER (nc=20) INTEGER ncomp DOUBLE PRECISION pges,pgesdz,gij(nc, nc) DOUBLE PRECISION x(nc),t,p,parame(nc,25),mseg(nc) DOUBLE PRECISION densta,dense,dap_dx(nc,7),dbp_dx(nc,7) DOUBLE PRECISION order1,order2,apar(7),bpar(7) DOUBLE PRECISION A,B,C,D,AA,BB(nc),CC(nc),DD(nc),EFF(nc), & QQ(nc,nc),PIJK(nc,nc,nc) DOUBLE PRECISION PI, RGAS, NA, KBOL, TAU DOUBLE PRECISION uij(nc,nc),d00ij(nc,nc),d0(nc) c-----local variables------------------------------------------------- INTEGER i,start,max_i DOUBLE PRECISION x1,y1,dydx,acc_i c--------------------------------------------------------------------- acc_i = 1.d-10 max_i = 50



i = 0 x1 = densta 1 CONTINUE i=i+1 dense = x1 CALL P_EOS (pges,pgesdz,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) y1 = (pges / p ) - 1.d0 dydx = pgesdz/p x1 = x1 - y1/ dydx IF (x1.GT.0.9d0) x1 = 0.6d0 IF (x1.LE.0.d0) x1 = 1.d-10 start = 1 IF (DABS(y1).LT.acc_i) start = 0 IF (i.GT.max_i) THEN start = 0 write (*,*) 'density iteration failed' c stop ENDIF IF (start.EQ.1) GOTO 1 dense = x1 RETURN END c*********************************************************************** SUBROUTINE F_EOS (fres,gij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) IMPLICIT NONE c-----variables used in the parameter list of subroutine-------------- INTEGER nc PARAMETER (nc=20) INTEGER ncomp DOUBLE PRECISION fres,gij(nc,nc) DOUBLE PRECISION x(nc),t,p,parame(nc,25),mseg(nc) DOUBLE PRECISION densta,dense,dap_dx(nc,7),dbp_dx(nc,7) DOUBLE PRECISION order1,order2,apar(7),bpar(7) DOUBLE PRECISION A,B,C,D,AA,BB(nc),CC(nc),DD(nc),EFF(nc), & QQ(nc,nc),PIJK(nc,nc,nc) DOUBLE PRECISION PI, RGAS, NA, KBOL, TAU DOUBLE PRECISION uij(nc,nc),d00ij(nc,nc),d0(nc) c-----local variables------------------------------------------------- INTEGER i,m



DOUBLE PRECISION zms,rho,m_mean,term1,term2 DOUBLE PRECISION I1,I2,z00,z00_dz,drdpkt DOUBLE PRECISION fhs,fdisp,fcha c-----abbreviations--------------------------------------------------- zms = 1.d0 -dense rho = 6.d0*dense/(PI*D) m_mean = A c-----Helmh. free energy : hard sphere contribution------------------- term1 = -(A-C**3.d0/D**2.d0)*DLOG(zms) term2 =(C**3.d0/D**2.d0)/(zms**2.d0)+(3.d0*B*C/D*dense & -(C**3.d0/D**2.d0))/zms fhs = term1 + term2 c-----Helmh. free energy : chain term--------------------------------- fcha = 0.d0 DO i = 1,ncomp fcha = fcha + x(i) *(1.d0- mseg(i)) *DLOG(gij(i,i)) END DO c-----Helmh. free energy : dispersion contribution-------------------- I1 = 0.d0 I2 = 0.d0 DO m=0,6 I1 = I1 + apar(m+1)*dense**DBLE(m) I2 = I2 + bpar(m+1)*dense**DBLE(m) END DO Z00 = 1.d0 + m_mean*(4.d0*dense-2.d0*dense**2.d0)/(zms**3.d0) & + (1.d0 - m_mean)*(5.d0*dense-2.d0*dense**2.d0) & /(zms*(2.d0-dense)) z00_dz = m_mean*(-2.d0*dense**2.d0+4.d0*dense+4.d0)/zms**4.d0 & + (1.d0 - m_mean)*(dense**2.d0-8.d0*dense+10.d0) & /(zms*(2.d0-dense))**2.d0 drdpkt = 1.d0/(Z00 + dense*z00_dz) fdisp = -2.d0*PI*rho*I1*order1 - PI*rho*drdpkt*m_mean*I2*order2 c-----resid. Helmholtz free energy------------------------------------ fres = fhs + fcha + fdisp RETURN END c********************************************************************* SUBROUTINE PERTPAR (kij, 1 ncomp,x,t,p,parame,mseg,densta,dense,dap_dx,dbp_dx, 2 order1,order2,apar,bpar,A,B,C,D,AA,BB,CC,DD,EFF,QQ,PIJK, 3 PI,RGAS,NA,KBOL,TAU,d0,uij,d00ij) IMPLICIT NONE c-----variables used in the parameter list of subroutine-------------- INTEGER nc PARAMETER (nc=20)



INTEGER ncomp DOUBLE PRECISION kij(nc,nc) DOUBLE PRECISION x(nc),t,p,parame(nc,25),mseg(nc) DOUBLE PRECISION densta,dense,dap_dx(nc,7),dbp_dx(nc,7) DOUBLE PRECISION order1,order2,apar(7),bpar(7) DOUBLE PRECISION A,B,C,D,AA,BB(nc),CC(nc),DD(nc),EFF(nc), & QQ(nc,nc),PIJK(nc,nc,nc) DOUBLE PRECISION PI, RGAS, NA, KBOL, TAU DOUBLE PRECISION uij(nc,nc),d00ij(nc,nc),d0(nc) c-----local variables------------------------------------------------- INTEGER i,j,k,m DOUBLE PRECISION m_mean DOUBLE PRECISION ap(7,3),bp(7,3) DOUBLE PRECISION d00(nc),u0k(nc) c-----constants------------------------------------------------------- PI = 3.14159265359d0 RGAS = 8.31441d0 NA = 6.022045d23 KBOL = RGAS/NA TAU = PI/3.d0/DSQRT(2.d0) c-----dispersion term constants--------------------------------------- ap(1,1)= 0.91056314451539d0 ap(1,2)= -0.30840169182720d0 ap(1,3)= -0.09061483509767d0 ap(2,1)= 0.63612814494991d0 ap(2,2)= 0.18605311591713d0 ap(2,3)= 0.45278428063920d0 ap(3,1)= 2.68613478913903d0 ap(3,2)= -2.50300472586548d0 ap(3,3)= 0.59627007280101d0 ap(4,1)= -26.5473624914884d0 ap(4,2)= 21.4197936296668d0 ap(4,3)= -1.72418291311787d0 ap(5,1)= 97.7592087835073d0 ap(5,2)= -65.2558853303492d0 ap(5,3)= -4.13021125311661d0 ap(6,1)= -159.591540865600d0 ap(6,2)= 83.3186804808856d0 ap(6,3)= 13.7766318697211d0 ap(7,1)= 91.2977740839123d0 ap(7,2)= -33.7469229297323d0 ap(7,3)= -8.67284703679646d0 bp(1,1)= 0.72409469413165d0 bp(1,2)= -0.57554980753450d0 bp(1,3)= 0.09768831158356d0



bp(2,1)= 1.11913959304690d0 *2.d0 bp(2,2)= 0.34975477607218d0 *2.d0 bp(2,3)= -0.12787874908050d0 *2.d0 bp(3,1)= -1.33419498282114d0 *3.d0 bp(3,2)= 1.29752244631769d0 *3.d0 bp(3,3)= -3.05195205099107d0 *3.d0 bp(4,1)= -5.25089420371162d0 *4.d0 bp(4,2)= -4.30386791194303d0 *4.d0 bp(4,3)= 5.16051899359931d0 *4.d0 bp(5,1)= 5.37112827253230d0 *5.d0 bp(5,2)= 38.5344528930499d0 *5.d0 bp(5,3)= -7.76088601041257d0 *5.d0 bp(6,1)= 34.4252230677698d0 *6.d0 bp(6,2)= -26.9710769414608d0 *6.d0 bp(6,3)= 15.6044623461691d0 *6.d0 bp(7,1)= -50.8003365888685d0 *7.d0 bp(7,2)= -23.6010990650801d0 *7.d0 bp(7,3)= -4.23812936930675d0 *7.d0 c-----pure component parameters--------------------------------------- DO 1 i = 1,ncomp mseg(i) = parame(i,1) d00(i) = parame(i,2) u0k(i) = parame(i,3) parame(i,5) = 0.12d0 d0(i)= d00(i)*(1.d0-parame(i,5)*DEXP(-3.d0*parame(i,3)/t)) 1 CONTINUE c-----combination rules----------------------------------------------- DO 2 i = 1, ncomp DO 21 j = 1, ncomp d00ij(i,j)=0.5d0*( d00(i) + d00(j) ) uij(i,j)= (1.d0-kij(i,j))*(u0k(i)*u0k(j))**0.5d0 21 CONTINUE 2 CONTINUE c-----abbreviations--------------------------------------------------- A = 0.d0 B = 0.d0 C = 0.d0 D = 0.d0 DO i = 1,ncomp A = A + x(i) * mseg(i) B = B + x(i) * mseg(i) * d0(i) C = C + x(i) * mseg(i) * d0(i)**2.d0 D = D + x(i) * mseg(i) * d0(i)**3.d0 END DO AA = A DO 4 k = 1, ncomp



BB(k) = B*C / D**2.d0 * d0(k)**3.d0 CC(k) = C/D * d0(k) DD(k) = d0(k)**3.d0 / D EFF(k) = B/D * d0(k)**2.d0 DO 41 i = 1, ncomp QQ(k,i)= C/D * (d0(k)*d0(i)) / (d0(k) + d0(i)) DO 411 j=1, ncomp PIJK(i,j,k) = (d0(i)*d0(j))/(d0(i)+d0(j)) / d0(k) 411 CONTINUE 41 CONTINUE 4 CONTINUE c-----dispersion term parameters for chain molecules------------------ m_mean = A DO m=1,7 apar(m) = ap(m,1) + (1.d0-1.d0/m_mean)*ap(m,2) & + (1.d0-1.d0/m_mean)*(1.d0-2.d0/m_mean)*ap(m,3) bpar(m) = bp(m,1) + (1.d0-1.d0/m_mean)*bp(m,2) & + (1.d0-1.d0/m_mean)*(1.d0-2.d0/m_mean)*bp(m,3) END DO c-----derivatives of apar, bpar to mole fraction ( d(apar)/d(x) )----- DO k=1,ncomp DO m=1,7 dap_dx(k,m) = mseg(k)/m_mean**2.d0*ap(m,2) & +(3.d0*mseg(k)/m_mean**2.d0 & - 4.d0*mseg(k)/m_mean**3.d0)*ap(m,3) dbp_dx(k,m) = mseg(k)/m_mean**2.d0*bp(m,2) & +(3.d0*mseg(k)/m_mean**2.d0 & - 4.d0*mseg(k)/m_mean**3.d0)*bp(m,3) END DO END DO c-----van der Waals mixing rules for perturbation terms--------------- order1 = 0.d0 order2 = 0.d0 DO i = 1,ncomp DO j = 1,ncomp order1 = order1 + x(i)*x(j)* mseg(i)*mseg(j) & *d00ij(i,j)**3.d0 * uij(i,j)/t order2 = order2 + x(i)*x(j)* mseg(i)*mseg(j) & *d00ij(i,j)**3.d0 * (uij(i,j)/t)**2.d0 END DO END DO RETURN END


Appendix C: Saturation data Binary Systems (11):

Table 1:

Table 2:

Table 3:

Table 4:

Appendix D: Saturation data for CO2/n-decane/n-octacosane (12).

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