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Design And Evaluation Of Ionic Liquids As Novel Absorbents

Carbon Sequestration
04/2008
Design anD evaluation of ionic liquiDs
as novel absorbents

CONTACTS
Background
Sean Plasynski
There is growing concern among climate scientists that the buildup of greenhouse
Sequestration Technology Manager
gases (GHG), particularly carbon dioxide (CO ), in the atmosphere is affecting
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National Energy Technology
the global climate in ways that could have serious consequences. One approach
Laboratory
to reducing GHG emissions is to scrub CO from the flue gas of power plants and
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626 Cochrans Mill Road
sequester it in geologic formations. Although it is technically feasible to remove
P.O. Box 10940
CO from flue gas, current processes are too expensive. New, less expensive
Pittsburgh, PA 15236
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processes are needed. This project is investigating the feasibility of using a novel
412-386-4867
class of compounds – ionic liquids – for the capture of CO from the flue gas from
sean.plasynski@netl.doe.gov
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coal and natural gas–fired power plants. The success of ionic liquids technology
will be based on increasing the knowledge base on the chemical characteristics
José Figueroa
of ionic liquids and on the competitiveness of processes which utilize ionic liquid
Project Manager
based absorbents for CO capture from flue gas streams compared to commercial
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National Energy Technology
amine-based technologies. The successful ionic liquid absorbent will have high CO 2
Laboratory
selectivity and capacity (i.e., a Henry’s law constant lower than 10 bar) with a low
626 Cochrans Mill Road
energy requirement for regeneration (i.e., an enthalpy of absorption less than
P.O. Box 10940
60 kJ/mol).
Pittsburgh, PA 15236-0940
412-386-4966
jose.figueroa@netl.doe.gov
Description
The fundamental factors influencing the absorption of CO and other gases present
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Edward Maginn
in flue gas streams will be determined, relevant thermo-physical and phase behavior
Principal Investigator
properties measured, and a preliminary process design for the use of ionic liquids in
182 Fitzpatrick Hall
an absorption separation system developed.
Dept. of Chem. & Biomolec. Eng.
University of Notre Dame
St. Joseph County, IN 46556
Primary Project Goal
574-631-5687
The primary goal of this project is to provide a comprehensive evaluation of the
ed@nd.edu
feasibility of using a novel class of compounds – ionic liquids – for the capture of
CO from the flue gas of coal and natural gas – fired power plants.
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Objectives
The objectives of the project are to:
• Produce a range of ionic liquid sorbents for further evaluation.
• Determine the fundamental factors influencing the absorption of CO and other
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gases present in flue gas streams.
PArTNErS
• Determine relevant thermo-physical and phase behavior properties.
University of Notre Dame
• Develop a preliminary process design that uses ionic liquids in an absorption
separation system.
PErFOrMANCE PEriOd
07/16/2004 to 07/15/2007

COST
Total Project Value
Model of CO absorption
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$434,076
by an ionic liquid.

The model shows that
dOE/Non-dOE Share
the anions are control ing
$434,076 / $0
absorption in ionic liquids.
The green units represent
anions and the grey units
represent cations.
AddrESS
National Energy
Technology Laboratory
1450 Queen Avenue SW
Albany, OR 97321-2198
541-967-5892
Benefits
2175 University Avenue South
Suite 201
If CO capture from flue gas is to become economically feasible, improved capture
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Fairbanks, AK 99709
processes are needed. The use of ionic liquids as CO absorbents holds promise for
907-452-2559
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reducing costs by developing a process with higher CO loading in the circulating
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liquid and lower heat requirements for regeneration. Both of these effects would
3610 Collins Ferry Road
P.O. Box 880
lower process costs.
Morgantown, WV 26507-0880
304-285-4764
Accomplishments
626 Cochrans Mill Road
Eleven ionic liquids have been synthesized or acquired. CO solubility has been
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P.O. Box 10940
measured for five of these compounds, with 1-n-hexyl-3-methylimidazolium tris
Pittsburgh, PA 15236-0940
(pentafluoroethyl) trifluorophosphate showing the best performance to date, having
412-386-4687
a Henry’s constant of 25 bar at 25 oC. By measuring the solubility of other gases
in these liquids, including oxygen, ethylene and ethane, it was found that CO is
One West Third Street,
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Suite 1400
significantly more soluble in these ionic liquids than any of these other gases, Figure
Tulsa, OK 74103-3519
1. Other physical properties, including viscosity and density, have been measured
918-699-2000
for these compounds. The viscosities vary widely at low temperature, but all fall to
reasonable values above 40 oC.
CuSTOMEr SErViCE
First principles quantum mechanics calculations have been conducted to understand
the nature of CO absorption in these liquids. The calculations have shown that CO
1-800-553-7681
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associates primarily with the anion, but that the anion primarily associates with the
cation. Thus, the CO interacts most strongly with the secondary negatively charged
WEbSiTE
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regions of the anion, suggesting that greater negative charge delocalization could
www.netl.doe.gov
lead to enhanced CO solubility. These concepts are being used to identify new
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targets for synthesis and testing.
Research has also demonstrated that SO is highly soluble in ionic liquids, being 8 to
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25 times more soluble than CO , depending upon pressure. NETL researchers have
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proven that ionic liquids can be used as the separating media in supported liquid
membranes to separate CO .
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Project332.indd