Ionic Liquids: A New Chemical Platform for CO2 Separations · 2016-12-08 · 2 capture process to ionic liquid properties • Results of the sensitivity analysis will be used to guide

W. F. Schneider CCTR - 4 June 2009

Ionic Liquids: A New Chemical Platform for

CO2 Separations

Bill Schneider

Dept. of Chemical and Biomolecular Engineering

University of Notre Dame

[email protected]

Indiana CCTR Advisory Committee Meeting

Indiana University, Bloomington

June 4, 2009

mailto:[email protected]

Why CO2 capture and sequestration (CCS)?

• Energy consumption is projected to grow significantly in

the coming decades

• Coal will necessarily be a major component of the

energy equation

• CCS essential to mitigate deleterious increases in

atmospheric CO2 concentration


Current technology and challenges

• Existing drop-in technologies based on aqueous amine chemistry

• Short-comings including energy overhead, cost, corrosivity, NOx/SOx cross reactivity, H2O content, decomposition, …


HO

NH2

CO2HO

NH

O

O

HO

NH3+

H2O CO2 H+ HCO3-

2

Absorption isotherms


Langmuir (single site) absorption

A + CO2 (g) ↔ A⋅CO2 Keq(T)

xCO

2

KP

CO2

1 KPCO

2

, K eG / RT

CO2

CO2

A-CO2

A-CO2A

PCO2

xCO2

T

O2

N2

H2O

liquid

gas

Carrying capacity


Langmuir (single site) absorption

A + CO2 (g) ↔ A⋅CO2 Keq(T)

Absorption

Low T, low P

Desorption

High T, high P

Carrying capacity

Mol CO2/mol absorbent

Absorption optimization


K(T ) eG (T )/RT , G(T ) H (T )TS(T )

S

t

r

o

n

g

b

i

n

d

i

n

g

W

e

a

k

b

i

n

d

i

n

g

A CO

O

Background – What Are Ionic Liquids?

• Salts that are liquid at

ambient temperatures

• Huge diversity of

potential compounds

– Mix and match cations

and anions


Why investigate ionic liquids?

• IL properties favorable for CO2 capture

– Negligible volatility

– High intrinsic physical selectivity for CO2

• Can add chemical functionality

– Opportunity to “tune” properties

– Computational methods enable molecule “design”

– “Molecularomics”

• Potential for drop-in or unique process configurations

• Possible to achieve better performance than aqueous

amines


Gravimetric gas adsorption

• Mass vs. temperature and pressure


Gravimetric microbalance Magnetic Suspension

Balance

Physical solubility of CO2 in ILs

• ILs have high physical CO2 solubility

• Good selectivity over O2 and N2


Gravimetric solubility

1-n-hexyl-3,5-

dimethylpyridinum

bis(trifluoromethane-

sulfonyl)amide

Henry’s Law

Pa = Hxa

Predicting properties with computation


Findings from previous work

• Physical solubility: low enthalpy of absorption

– ~ 12 kJ/mol

– Very low regeneration energy and temperature, but…

– CO2 capacity too low ⇒ high circulation rates

– Desorption at too low pressure ⇒ high compression costs

• Increase capacity by adding chemical functionality

– Increases enthalpy of absorption / desorption and capacity

– Increases regeneration temperature and energy, but reduces

circulation rates


Task-specific ionic liquids (TSILs)

• Build on aqueous amine chemistry:

• Tether amines to ionic liquid:


NH22 +

O

C

ONH

CO-+ NH3

+1:2

O

1 atm CO2

Room temp.

In situ vibrational spectroscopy

N2

Vacuum

ThermocoupleP

I

R

Silicon

probe

CO2

P-controller

trap

vent

vent


Volumetric gas absoprtion


Purge

CO2

Syringe PumpReservoir

(<300 cm3)

Vacuum

Purge

Glass Tank

(150-200 cm3)

Purge

101.0121 g (T)

Balance

Pressure

SensorHeise

50 mbar

Pressure

Sensor Heise

1550 mbar

Four Channels

Temperatute Sensor

40.01 ºCCell

2

1 2 3 4

Oven

Extra Volumen

(150 cm3)

Magnetic

Stirrer

Glass

Vessel-Cell

Problems with conventional TSILs

• Liquid becomes quite viscous upon contact with CO2

• 2:1 mechanism is inefficient…1:1 mechanism possible?

• How to tune the chemistry?


No CO2 17 mbar CO2

Fundamental chemical questions

• What functional groups should be used?– Mechanism

– Capacity

– Enthalpy

– Selectivity

– Rate

• Other questions– Viscosity

– Stability

– Cost

– Water solubility

– Corrosion

– Mass transport


W. F. Schneider UW-Madison - 31 Mar 2009

Electronic Structure Method History

1920’s Schrödinger Equation (HΨ = EΨ)“The underlying physical laws necessary for the mathematical theory of a

large part of physics and the whole of chemistry are thus completely known,

and the difficulty is only that the exact application of these laws leads to

equations much too complicated to be soluble.”Dirac, P. A. M. Proc. R. Soc. London, 1929,123, 714

1960’s Kohn-Sham Equation (Ts[ρ]-υNe[ρ]+υee[ρ]-υXC[ρ])ψi=εiψi

Electron density replaces wavefunction as fundamental variable. Can be

described in terms of an exact (unknown) effective one-electron equation

1998 Noble Prize in Chemistry (J. Pople and W. Kohn)“…for pioneering contributions in developing methods that can be used for

theoretical studies of the properties of molecules and the chemical processes

in which they are involved.”

today astounding advances in theory + algorithms + inexpensive computer power

make application to a wide range of practical problems a reality

methods now be adopted in many progressive engineering departments

144 processor Opteron 265

dual-core computer being

purchased by Maginn,

Schneider, and Stadtherr groups

W. F. Schneider UW-Madison - 31 Mar 2009

First Principles Simulations for Catalysis

Electronic Structure Simulation

Define composition and structure

Define computational model

Select solution algorithms

Structures and thermodynamics Reaction pathways and kinetics Reaction dynamics

Primary Outputs

Distribution of electrons

Optimized structures

Absolute energy

Derived Outputs

Spectroscopy (vibrational, electronic, …)

Thermodynamics (heat capacities, entropies, …)

Kinetics (activation energies, prefactors, …)

Dynamics

Tools: TST, statistical mechanics

Example

alumina

supercell

~70 atoms

First-principles methodology

• Screen intrinsic functional group-CO2 reactivity

• Contrast tethering strategies

• Hybrid-DFT calculations implemented in Gaussian– B3LYP/6-311++G(d,p)

– Harmonic frequency analysis

– Standard ZPE and gas-phase free energy analysis

• Systematic exploration over conformation space

• Boltzmann averaged reaction energies


++

N

O


Reliability of first-principles models

�Grxn(T = 298 K)RR’NH + H+ RR’NH2+

Experimental

values as

tabulated in NIST

webbook

B3LYP/6-311++G(d,p)

Combined protonation and carbamate formation

• Intrinsic CO2capture energetics integrate both reactions

• Combine reactions on single energy correlation plot

• Reaction energies largely uncorrelated

• Potentially independent tunability


0-5

-10-15

NH22 +

O

C

ONH

CO-+ NH3

+1:2

O

CO2 reaction stoichiometry in TSILs

• What effect does ion tethering have on energetics and

mechanism of amine-CO2 reaction?

• Might ion tethering favor more desirable reaction

pathways?


NH

COH

O

1:1

MEA vs. Cation- vs. Anion-Tethered Amines

• Local cation tethering favors 2:1 binding

• Local anion tethering disfavors 2:1 binding

• Tethering ion and tethering point as important as functional groups in controlling CO2 reactions

+

-

MEA:

Pyridinium

amine

cation:

Amino

acetate

anion:

+

1:1

-

0

+2

-4

0 -

+ …NH3+

-17

2:1

+17

--

+

-

+ …NH3+

+ …NH3+

Reaction energies in kcal/mol relative to MEA

+CO2

+CO2

+CO2

-H+

-H+

-H+


1:1 stoichiometry for anion-tethered IL?

• Synthesized anion-

tethered task-specific

ionic liquid

• Experimental isotherm

consistent with 1:1

reaction stoichiometry


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.00 0.05 0.10 0.15P (MPa)

Mo

l C

O2 / M

ol IL

(m

ol/m

ol)

22 °C (RTA)

40 °C (ITA)

40 °C (High Temperature Apparatus)

Logarítmica (22 °C (RTA))

Logarítmica (40 °C (High TemperatureApparatus))

Literature precedence for 1:1 reaction


> 0.5 CO2 mole fraction

consistent with 1:1 reaction

stoichiometry

P+H2N

CH

CH O-

O

Computational predictions of anion energies


high low

Computational predictions of physical properties

• Quantitative prediction of properties like viscosity

– Often easier to compute at extreme conditions than measure

– Fill in gaps for process modeling


Trimeric sensitivity analysis

• Process simulation was used to evaluate the sensitivity

of a representative 500 MW coal plant CO2 capture

process to ionic liquid properties

• Results of the sensitivity analysis will be used to guide

the development of next-generation ionic liquids

• Sensitivity variables

– Stoichiometry: ND proposed both 1:1 and 2:1 (IL:CO2)

stoichiometries; preliminary modeling to date assumed 1:1.

– Enthalpy of reaction: ND proposed a range of (low-high) based

on molecular modeling.

– Loading (Keq): Sensitivity includes a range of CO2 loadings that

result from the above enthalpies of reaction.

– Water miscibility: Both partially- and fully-miscible systems are

included. Activities coefficients modeled with NRTL using

experimental data


Base case process modeling

• Conventional absorber / stripper configuration

– “Drop in” replacement for MEA

• Other configurations possible


Preliminary parasitic energy predictions

• Courtesy Kevin Fisher, Duane Myers, Katherine Searcy, Trimeric Corp.


58.749.3

62.3

45.3

9.0

4.9

46.5

29.5

23.6

0

20

40

60

80

100

120

140

160

40 50 60

Enthalpy of Reaction (kJ/gmole)

To

tal

Eq

uiv

ale

nt

Wo

rk (

MW

)

Compressor power

Pump power

Regeneration heat

Equivalent

Work for

Conventional

MEA System

(approx.)

Theoretical

Thermodynamic

Minimum

Energy (approx.)

low medium high

Ionic Liquids: Breakthrough Absorption

Technology for Post-Combustion CO2 CaptureNETL Project 43091

• Funding and cost share

– Total project: $3,550,718

– Federal portion: $2,447,138 (69%)

– Cost share: $1,103,580 (31%)

• Project performance dates: Mar 1, 2007-June 30, 2010

• Project participants

– Notre Dame (molecule design, thermodynamics, property measurement, synthesis, project management)

– Babcock and Wilcox (corrosion, design of lab scale unit)

– DTE (consultation, feasibility of process designs)

– Air Products (thermodynamics, process design, molecule design)

– EMD / Merck (synthesis, molecule design)

– Trimeric (process design and system analysis)


Competing separation technologies

• Alternative CO2 capture chemistries

– Chilled NH3

– Enzyme-based (carbozyme)

– Nanoengineered materials

– Electrochemical

– …

• Physical separation

– Membranes

– Molecular sieves

• Pre-combustion

– Coal gasification

– Oxyfuel


Carbon sequestration options

• Oil/gas wells

– Enhanced oil recovery

• Coal beds

– Methane recovery

• Saline aquifers

• Ocean floor

• Mineralization

• Industrial use

• Thermal/photolytic/electrolytic recovery

– CO2 CO, H2, CH3OH, …


Notre Dame Team

Current members

• Prof. Edward Maginn

• Prof. Joan Brennecke

• Prof. Bill Schneider

• Prof. Jindal Shah

• Dr. Erica Price

• Dr. Zulema Lopes-Castillo

• Dr. Tom Rosch

• Devan Kestal

• Burcu Gurkan

• Alexandre Chapeaux

• Elaine Mindrup

• Marcos Perez-Blanco

• Hao Wu

• Brett Goodrich

• Mandy Danser

• Lindsey Ficke

Alumni

• Prof. Wei Shi

• Prof. Juan de la Fuenta

• Prof. Jessica Anderson

• Dr. JaNeille Dixon

• Dr. Keith Gutowski

• Dr. Manish Kelkar


• CO2 capture from flue gas is viable but currently

expensive

• Alternative materials/chemistries/configurations hold the

promise of significant improvements over current

configurations

– Simulations can accelerate the discovery process

• Many fundamental and technical hurdles remain to be

overcome

+ CO2(g)NH2

TSIL

NH2

NHCO2−

NH3+

+

NH2

+ CO2(g)

NH-COOH NH-COO- NH3+

2 ΔGsolv

ΔGrxn ΔGrxn

ΔGsolv ΔGsolv

2

+

+

-

-

+

+

-

-

+ + +

K(T), k(T)

Conclusions


Documents

Ionic Liquids: A New Chemical Platform for CO2 Separations · 2016-12-08 · 2 capture process to ionic liquid properties • Results of the sensitivity analysis will be used to guide