This document discusses the use of ionic liquids for gas separation. It begins by defining ionic liquids as salts with melting points below 100°C that contain discrete ions. Ionic liquids have properties like negligible vapor pressure and high thermal stability that make them suitable for gas separation. The document then covers various types of ionic liquid membranes for gas separation and reviews previous research studying gas separations using these membranes. It provides examples of applications for ionic liquid membranes in high temperature gas separation and CO2 sequestration. However, the high cost of ionic liquids remains a key challenge.

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IONIC LIQUIDS FOR GAS
SEPARATION
ANIL VIBHUTE
15CH60R03

2. OUTLINE:
 What are Ionic Liquids.
 Role of Ionic Liquids in Gas separation.
 Types of Ionic Liquid Membranes.
 Review of research in this area.
 Case studies.
 Applications.
 Challenges and Opportunities.
 References 2

3. WHAT ARE IONIC LIQUIDS-
 Salts having melting points below 1000C and whose melts
contain discrete ions are called as Ionic liquids.
 1000 Ionic liquids have been commercialized out of 1014
ionic liquids.
Properties-
 Negligible Vapor Pressure.
 Thermally Stable above 1000C.
 High CO2/H2 selectivity.
 Tunable physicochemical properties.
 High hydrophobicity.
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4. CLASSES OF IONIC LIQUIDS
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5. SOME OF THE IONIC LIQUIDS
Sr.No. Name Abbreviation Compounds to
separate
1 1-ethyl-3-methyl-imidazolium
bis(trifluoromethyl-sulfonyl) imide
[emim][NTf2] N2,CO2,CH4
2 1,3-dimethylimidazolium bis(trifluoromethyl-
sulfonyl) imide
[dmim][NTf2] N2,H2,O2,CO
3 1-(3-aminopropyl)-3-methylimidazolium
bis(trifuoromethyl-sulfonyl) imide
[H2NC3H6mim][NTf2] H2,CO2
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6. ROLE OF IONIC LIQUIDS IN GAS SEPARATIONS?
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Comparison of solubility of gases in solvents (gm/ml)
A key feature of ionic liquids is that their physical
properties can be tailored by correct selection of cation,
anion and substituents.
Henry’sConstant

7. Types of Ionic Liquid Membranes-
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1) Emulsion Ionic Liquid Membranes:
Rarely gas separation. Mostly for extraction of liquids.
application of emulsion liquid membrane for extraction
benzimidazole by tri-n-octyl methyl ammonium chloride (ph1)
& HCL solution (ph2)
studied emulsification time ,speed ; carrier concen; agitation
speed…….

8. Separation efficiency
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Permeability = solubility * diffusivity
solubility study of the particular gases with respect to pressure
and temperature is done.
As pressure of gas , solubility of gases
but
temperature , solubility of gases
Conclusion :- this technique is more effective than L-L
extraction method .

9. 2) SUPPORTED IONIC LIQUID MEMBRANE
Two types of mechanisms
1)Solubility-diffusivity mechanism
solubility study of gases should be done.
While according to size of molecule, gas will diffuse into the
membrane.
2) facilitated transport of gases
With Complexing agent, complexing agent becomes carrier
for the gas through the membrane.
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10. REVIEW OF RESEARCH IN THIS AREA-
Michiaki Matsumoto et.al. in 2007 studied separation of
cyclohexane and benzene using ionic liquids based upon 1-alkyl-
3-methylimidazolium and quaternary ammonium salts.
 Separating problem have close boiling points.
 Energy intensive operations like azeotropic distillation or
extractive distillation.
 Through this innovation Michiaki et.al. suggested to use ionic
liquid based supported membranes for their separation. However
they are failed to give stability assurance for higher temperatures
for these particular membranes. 10

11. CO2/CH4 SEPARATION CASE STUDY
 For experiments, two ionic liquid membranes and polymeric
membrane are taken.
A] Polymeric Membrane:
Poly (vinylidene fluoride-co-hexa-fluoro-propylene)
B] Ionic Liquid Membranes:
1-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl)
imide ([hmim][Tf2N])
&
1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)
imide ([emim] [Tf2N]) 11

12.  Ionic liquid concentration varying from 0 % to 80 % w/w is
composed with either polymeric membrane or taken
separately.
 The most important conclusion from this paper is
permeability study of CO2 by comparison between polymeric
membrane, composite with ionic liquid and purely ionic
liquid.
 Experiments proved that 𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑤𝑖𝑡ℎ 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 >
𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑤𝑖𝑡ℎ 𝐼𝑜𝑛𝑖𝑐 𝑙𝑖𝑞𝑢𝑖𝑑 >
𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑤𝑖𝑡ℎ 𝑃𝑜𝑙𝑦𝑚𝑒𝑟𝑖𝑐 𝑚𝑒𝑚𝑏𝑟𝑎𝑛𝑒
 Explanation behind this could be “formation of new pores for
transport of gases when polymer is composed with ionic
liquid.” 12

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Removal of Acidic Gases
Removal of acidic gases was also addressed by the research from
group of Park in 2009.
In this research they studied the permeability rates of three gases
namely CH4, H2S and CO2. This is rather very interesting topic for
research since selectivity of these two acidic gases were studied
using 1-butyl-3-methylimidazolium tetra fluoroborate as membrane
and support as PVDF (poly-vinylidene fluoride).
Selectivity comparison of H2S/CH4 and CO2/CH4 was a major key
output of the whole process. And it was found that selectivity in
case of former case was about five times more than latter one.

14. APPLICATIONS-
A] High Temperature gas separation:
 Ionic liquids possesses negligible vapor pressure and hence
high temperature separation is feasible.
 As an illustration, water gas shift reaction is equilibrium
limited and takes place at higher temperatures, it is challenge to
separate the CO and H2 gas at higher temperatures.
𝐶𝑂 + 𝐻2 𝑂 −−−−→ 𝐻2 + 𝐶𝑂2
 Myers et.al. fabricated their own facilitated ionic liquid
membranes used at higher temperatures. At low temperatures,
CO2-H2 has higher selectivity but at higher temperatures,
solubility ratio decreases for CO2-H2 .
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2] CO2 Sequestration:
Ionic liquids have very high affinity for CO2. Being a green-house
gas, CO2 can be separated out from flue gases using relatively
cheaper techniques such as ionic liquid membrane separation
technology.
3] Fuel Cell Membrane:
Since Ionic liquid possesses charge when it is molten state, it can be
used for manufacturing of fuel cell membrane.
Preparing ionic liquid as a membrane or incorporation of ionic
liquid into membranes makes them to act as fuel cell membrane

16. CHALLENGES AND OPPORTUNITIES
 Energy intensive operations like distillations can be replaced
with membrane separation techniques.
 Ionic liquids coming out to be the most efficient separation
media since they hardly have any vapor pressure, selection of
cation and anion can give very long range of properties.
 A very big problem is associated with them is their cost-
effectiveness. Ionic liquid can cost around ten times more than
what one can get by selling the product obtained after
purification. Cost of ionic liquids is by far the most challenging
issue related with ionic liquids as gas separation media.
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17. REFERENCES
Bakonyi, P.; Nemestothy, N.; Belafi-Bako, K. Biohydrogen
Purification by Membranes: An Overview on the Operational
Conditions Affecting the Performance of Non-Porous, Polymeric
and Ionic Liquid Based Gas Separation Membranes. Int. J.
Hydrogen Energy 2013, 38, 9673–9687.
Bara, J. E.; Gabriel, C. J.; Carlisle, T. K.; Camper, D. E.;
Finotello, A.; Gin, D. L.; Noble, R. D. Gas Separations in
Fluoroalkyl-Functionalized Room-Temperature Ionic Liquids
Using Supported Liquid Membranes. Chem. Eng. J. 2009, 147,
43–50.
Brennecke, J. F.; Maginn, E. J. Ionic Liquids: Innovative Fluids
for Chemical Processing. AIChE J. 2001, 47, 2384–2389.
 And more……
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