This document discusses carbon dioxide (CO2) capture from power plant flue gases. It begins by outlining the need to reduce CO2 emissions due to constraints on emissions and fossil fuel resources. It then discusses various CO2 capture technologies currently used or under development for post-combustion, pre-combustion, and oxy-fuel combustion processes. These include chemical absorption, adsorption, membranes, and cryogenic separation. The document also addresses the costs, challenges, and energy penalties associated with implementing CO2 capture at power plants.

1. Capture of CO2
Background and Future Prospects
Dr. I. M. Mishra
Pt. G. B. Pant Chair Professor of Environmental Pollution Abatement,
Professor of Chemical Engineering and
Dean Saharanpur Campus
Indian Institute of Technology, Roorkee
E-mail:- imishfch@iitr.ernet.in

2. Planetary Constraints
 Availability of non renewable carbon-based fossil fuels-coal,
petroleum oils, natural gas
 Accommodation of emissions/effluents/wastes - CO2 emissions
(global warming); river/ground water/air pollution, etc.
 The range of carbon-based fuels, the resource constraint is
flexible. Emission constraint is inflexible
 Which constraint will become active first?
 Economic system can deal with resource constraint

3.  Ostrich-like behaviour-no consequences: So
 Emission constraint will “bite” before the Resource constraint
- whereabouts of carbon-based fuels is known: therefore not
much problem to biosphere
- scarcity of ‘supply’ can be coped with; scarcity of
emission capacity (carrying capacity) will have global
impact: hence economic devices need to be developed
 ‘Carbon –Trading’ is one such device, no guarantee of it to be
effective
 Reduction of carbon intensity in diverse economies is a
engineering challenge

4. Human Contribution to Climate Change
 Global concentrations of GHG increased markedly as a result of
human activities.
 In 2005, CO2 conc. >> the natural range over the last 650,000
years.
 > 375ppm CO2 now ; GHG emission now >70% over that of
1970.
 India emits ~ 1.2 ton/person as against Qatar ~44.5
ton/person/year

5. Atmospheric concentration of CO2 (solid blue line, right scale) and three principal
ODS (dashed red line, left scale). The ODS are chlorofluorocarbons (CFCs) 11, 12,
and 113 and were weighted based on their ozone-depleting potential). (World
Resources Institute: World Resources 2002-2004, Earth trends Data,
Washington,2003)

6. (IPCC Report, 2007)

7. Changes in temperature, sea level and northern hemisphere
snow cover (IPCC Report, 2007)

8. Carbon Emission Per Capita and Per-unit GDP of Nations.
(Sikdar, 2007)

9. The 12 Principles of Engineering for Sustainable Development
1. look beyond your own locality and the immediate future
2. innovate and be creative
3. seek a balanced solution
4. seek engagement from all stakeholders
5. make sure you know the needs and wants
6. plan and manage effectively
7. give sustainability the benefit of any doubt
8. if polluters must pollute. . . then they must pay as well
9. adopt a holistic, ‘cradle-to-crematorium’ approach
10. do things right, having decided on the right thing to do
11. beware cost reductions that masquerade as value engineering
12. practice what you preach.

10. Beyond Adaptation to Climate Change
 Adaptation to climate change is necessary to address impacts
resulting from the warming which is already unavoidable due to
past emissions.
 However: Adaptation alone cannot cope with all the projected
impacts of climate change
 The costs of adaptation and impacts will increase as global
temperatures increase.
 Making development more sustainable can enhance both
mitigative and adaptive capacity, and reduce emissions and
vulnerability to climate change
(Pachauri, R.K., Final presentation of IPCC Report, 2007)
UNEP,24th Sept., 2007

11. Global measures for Green House Gas Mitigation
 Worldwide agreement that, steps are necessary to contain rising CO2
levels.
 Less agreement on how best to achieve this.
 Only 55 countries including Russia have signed the Kyoto Protocol
where industrial nations will be required to bring their emissions of
GHG down by 5.2% to pre 1990 levels in the next 8 years.
 US has not ratified Kyoto Protocol. Measures announced in US include:
* Release of vision 21 statement
*Release of carbon sequestration technology roadmap
*Funding of CO2 capture tech development
*Hydrogen fuelled car development

12. Key Technologies to Reduce Emissions
Energy supply:
Efficiency; fuel switching; renewable (hydropower, solar, wind,
geothermal and bioenergy); combined heat and power; nuclear power;
early applications of CO2 capture and storage.
Transport :
More fuel efficient vehicles; hybrid vehicles; biofuels; modal shifts
from road transport to rail and public transport systems; cycling,
walking; land-use planning
Buildings :
Efficient lighting; efficient appliances and air-conditioning; improved
insulation; solar heating and cooling; alternatives for fluorinated gases
in insulation and appliances

13. Key Policies to Reduce Emissions
 Appropriate incentives for Development of technologies
 Effective carbon price signal to create incentives to invest
in low-GHG products, technologies and processes
 Appropriate energy infrastructure investment decisions,
which have long term effects on emissions.
 Changes in lifestyle and behavior
 Patterns, especially in building, transport and industrial
sectors
(IPCC Report,2007)

14. Pathways towards Stabilization of CO2 Level
Characteristics of Stabilization Scenarios
Stabilization
level (ppm
CO2-eq)
Global mean
temp.
increase at
equilibrium
(oC)
Year CO2
needs to
peak
Year CO2
emissions
back at 2000
level
Reduction in
2050 CO2
emissions
compared to
2000
445-490 2.0-2.4 2000-2015 2000-2030 -85 to -50
490-535 2.4-2.8 2000-2020 2000-2040 -60 to -30
535-590 2.8-3.2 2010-2030 2020-2060 -30 to +5
590-710 3.2-4.0 2020-2060 2050-2100 +10 to +60
710-855 4.0-4.9 2050-2080 +25 to +85
855-1130 4.9-6.1 2060-2090 +90 to +140
Mitigation efforts over the next two to three decades will have a large impact on
opportunities to achieve lower stabilization levels(IPCC Report,2007).

15. Typical Composition of Flue Gases
CO2 3-5% (NG fired)
11-14% coal fired
Oxygen 12-15% (NG fired)
3-4% coal fired
Water 4-5%
NOx 300-500 mg/Nm3
SOx 700-1200 mg/Nm3
SPM 130-150 mg/Nm3
Temperature 150 °C
Pressure atmospheric
Typical Flow 1.5 MMCM/hr for 210 MW
plant

16. Operational Constraints under which CO2 recovery process
must perform in Post Combustion CO2 Capture
 Low Pressure
 High temperature
 Presence of oxygen
 Presence of Sox, NOx
 Presence of Water Vapour
 Soot
 Fly ash
 SPM

17. Cost Associated with Implementation of CO2 Capture Technologies
 Substantial cost factor is associated with implementation of CO2
capture technology in power generation
 This cost varies with plant type-greater for gas- fired plant than coal
fired plant.
 Cost of electricity generation estimated to be 40% higher if current
technology for CO2 capture used in power plants
 Large scope for development of more efficient CO2 capture
technologies

18. CO2 capture options

19. Advantages and Disadvantages of capture options

20. CO2 Capture
Efficient CO2 removal processes
from flue gas
CO2 concentration: 3-14%
Capture important for
 C1 feedstock into industrially useful compounds
 Reduction in GH effects.
Most widely used processes for CO2 capture are:
 Chemical absorption by solvents (aqueous amines or
amine based solvents to form carbamates)/New
Solvents, Wet Absorption.
 Adsorption by adsorbent using PSA/TSA./Dry
Adsorption.
 Membrane separation.
 Cryogenic separation.

21. Emerging Technologies
1. Carbonate based system
K2CO3(K)/piperazine(Pz)/ (5 molar K/2.5 molar Pz), O2 is less
soluble in K/Pz
2. Aqueous NH3
(Ammonium carbonate + CO2 + H2O Ammonium bicarbonate)
Flue gas to be cooled to 16-260C to reduce ammonia emission
chilled NH3 process
3. Membrane
Zeolite membrane
4. Adsorbents
Supported Na2CO3, meso porous zeolites
5. Metal organic Framework (MoF)
6. Enzyme based system

23. CO2 Emissions from Fertilizer Industry
• Fertlizer industry consumes ~35% petroleum products; ~70%
natural gas; ~3-4% coal and ~30% of fuel in utilities ofthat in
the total industrial sector (2007).
• Average specific power consumption (SEC)/ ton of ammonia
is ~ 50, 840, 210, 1490 kWh from NG, naphtha, fuel oil, coal
as feed stock.
• Average SEC for ammonia to urea is ~ 55, 200, 80, 315
kWh/ton of urea for NG , Naphtha, fuel oil and coal

24. Urea demand ~35 M tons/year
Phosphate (P2O5) ~ 7 mt/year
CO2 emissions (t/t) for ammonia/urea production
Ammonia Urea
NG ~ 0.55 ~ 0.55
Naphtha ~ 1.10 ~ 0.95
Fuel Oil ~ 1.25 ~ 1.05
Coal ~ 4.4 ~ 2.95

25. CO2 capture schemes for fossil-fueled power plants
• In a global context, among all the industries emitting CO2, fossil-fueled power
plants generate the largest amount of CO2 emission and that accounts for about
33–40 percent of the total (Carapellucci and Milazzo, 2003; Stewart and Hessami,
2005).
• CO2 needs to be separated and captured from the flue gases of such point sources
before direct sequestration.
• For these power plants, CO2 separation and capture processes can be divided into
several scenarios: post-combustion processes for a tradition coal-fired power plant,
• pre-combustion processes for gasification or reforming and oxy-fuel processes.
• Oxyfuel combustion is sometimes referred to as oxy-firing or oxy-combustion.
• Newly emerged technologies, such as chemical-looping combustion (CLC),
significantly reduce the complexity of separating CO2 from a gas stream.

26. CATs Options
 Supercritical & Ultra –Supercritical Technologies
 Gas Turbine Combined Cycle
 Integrated Gasification Combined Cycle
 Oxy-fuel Combustion
 Increasing Efficiency of old power plants by
Renovation & Modernization(R&M)

27. Variation of CO2 Emission with Technology
Efficiency (%) Technology Specific CO2
emission
kg/KWh
46-58 NGCC 0.40-0.30
>50 IGCC + FC 0.65-0.60
45-49 IGCC 0.75-0.70
>41.5 USC 0.80-0.75
39.3-40.5 Supercritical 0.85-0.80
37.9-38.5 PC Subcritical 0.90-0.85

28. Pulverized coal combustion CO2 separation and capture process.
• First seperation of CO2 from NOx and SO2
• One way to do post-combustion capture is to use chemical
absorption, such as monoethanolamine (MEA) absorption. This
technique has been widely used in natural gas industry for over 60
years.
• Another advantage of this technique is it produces a relatively pure
CO2 stream.
• Although the size and cost of the required absorber would be
comparable to those of an SO2 scrubber, the absorber would
consume one-quarter to one-third of the total steam produced by
the plant, reducing its generating capacity by the same amount.
Also the footprint of the host plant is increased by 60% (Elwell and
Grant, 2006).
• An alternative post-combustion CO2 capture method is the use of
membrane gas separation technologies.

30. Pre Combustion CO2 Capture: Gasification CO2 separation and
capture process
• In this pre-combustion process, fuels are first converted into a mixture of CO2
and H2 through a reforming (natural gas) or gasification (coal) process and the
subsequent shift-reaction. CO2 can be separated from the conversion product
stream and H2 can then be burned in gas turbine or be used by fuel cell. Fig.3
shows this process flow (Feron and Hendriks, 2005).
• Gasification partially oxidizes coal to produce a gaseous fuel, which is essentially
a hydrogen and carbon monoxide mixture. When syngas is used to fuel a plant
similar to a traditional combined-cycle power plant, the process is referred to as
integrated gasification combined-cycle (IGCC).
• Several methods can be used to capture CO2. The leading option for CO2
capture is an absorption process, in which the solvent can be a chemical one, such
as MEA absorption process, or physical one, such as pressure swing adsorption
(PSA).
• Physical absorption is a mature technology and has been used in the Great Plains
Synfuels plant in North Dakota, U.S. for 20 years (Elwell and Grant, 2006).

31. Gasification CO2 separation and capture process.
Oxy-combustion CO2 separation and capture process.

32. Oxy-combustion CO2 separation and capture process.
In the oxy-firing process, pure O2 is separated from air and sent to energy
conversion unit and combines with partially recycled flue gas of concentrated
CO2 to keep the furnace temperature below the allowable point.
The combustion takes place in an environment of O2/CO2 mixture. The
resulting flue gas is high-purity CO2 stream(Feron and Hendriks, 2005).
The exhaust gas stream is free of nitrogen components.Particulates and sulfur
compounds are first removed from the exhaust stream using widely adopted
techniques. After SO2 removal, the exhaust gas stream is approximately 90%
CO2 by volume on a dry basis.
Further separation of CO2 is not necessary. CO2 can then be compressed for
storage or transportation.
The main advantage of this technology is the elimination of NOx control
equipment and the CO2 separation step.

33. Chemical-looping combustion process
Chemical-looping combustion (CLC) is a novel process with inherent CO2 capture.
It has also been called unmixed combustion since direct contact between fuel and
combustion air is avoided.
Instead, an oxygen carrier brings oxygen from air to fuel. Suitable oxygen carriers
are small particles of metal oxide such as Fe2O3, NiO, CuO or
Mn2O3.
A basic CLC system is shown in Fig.5 (Ryd´en and Lyngfelt, 2006).
CLC has several advantages compared with conventional combustion.
The exhaust gas stream from air reactor is harmless, consisting mainly of N2.
In a well-designed system, there should be no thermal formation of NOx since
the regeneration of oxygen carrier takes place without flame and at moderate
temperatures.
The exhaust gas from the fuel reactor consists of CO2 and H2O.
Separation of CO2 can be done by a condenser. This is the major advantage with
CLC which avoids the huge energy penalty necessary in traditional amine scrubbing
process to capture CO2.

34. Chemical-looping combustion process.
O2  2Me2MeO
1 1 1
   
         
   
2 2 2 n m C H n m MeO nCO mH O n m Me
2 2
2 2

35. Carbon fixation
 Forestation.
 Ocean fertilization.
 Photosynthesis process.
6CO2  6H2O(l) light  heat C6H12O6 (aq.)  6O2 (g)
 In-situ CO2 capture.
2 3 CaOCO CaCO
 Hydrate-based separations.

36. Mineral carbonation, natural or biomimetic
One of the major CO2 fixation process in nature is the chemical
weathering of rocks, such as silicates, containing calcium or
magnesium. The silicate rocks could be turned into carbonates by
reacting with CO2 following this mechanism:
 Mg , Ca  Si O  xCO  x  Mg , Ca  CO 
ySiO x y x  2 y
2 3 2 Mineral carbonation results in the storage of CO2 in solid form as a
stable, environmentally benign mineral carbonate. The energy state
of mineral carbonate is 60 to 180 kJ/mol lower than CO2, which is
400 kJ/mol lower than carbon (Maroto-Valera et al., 2005).

37. • Carbon separation technical options Capture of CO2 contributes 75 percent to the
overall CCS cost and CCS increases the electricity production cost
• by 50 percent (Feron and Hendriks, 2005).
• Although these numbers may vary with different CCS schemes, cutting
• the capture cost is the most important issue for the CCS process to be acceptable to the
energy industry.
• There are many options for CO2 separation and capture, and these include
• adsorption, absorption, membrane and biotechnology. The optimum CO2 capture
scheme could be determined by analyzing costs in the context of power generation.
• The absorption/stripping process, using amine solutions such as MEA, is a
commercialized technology used in natural gas industry for 60 years and is regarded as
the most mature process. The CO2 recovery rate is 98% for
• MEA (Yamasaki, 2003).
• The adsorption process is based on the same principle but using porous solid adsorbents
such as zeolites and activated carbon, and chemical reactions between the adsorbent and
CO2 may or may not occur during the separation process. Both pressure swing
adsorption and temperature swing processes are widely used.

39. Amine absorption process
• Natural gas industry uses MEA to absorb CO2 from natural gas. There are
commercial MEA absorption processes with which CO2 is removed from
combustion flue gas stream.
• MEA reacts with CO2 in the gas stream to form MEA carbamate. The
CO2-rich MEA solution is then sent to a stripper where it is reheated to
release
• almost pure CO2. The MEA solution is then recycled to the absorber
• This process is generally uneconomic as it requires large equipment size
and intensive energy input. It is widely known that the heat duty for
solvent regeneration can constitute up to 70% of the total operating costs
in a CO2 capture plant (Idem et al., 2006).

40. • Besides MEA, diethanolamine (DEA) and methyldiethanolamine (MDEA) are often used
as absorbents.
• The proposed mechanism of reactions between CO2 and amines are shown in Fig.6.
According to this mechanism, the majority of the CO2 captured will result in the
formation of bicarbonate in the liquid amine capture system.
• In aqueous media, there is a requirement of 2 mol-amine/mol-CO2 for the formation of
stable bicarbonate compounds resulting in the capture of CO2.
Proposed reaction sequence for the capture of carbon dioxide by liquid amine-based systems
(Gray et al., 2005).

41. Mixed amines have been reported to maximize the desirable qualities of the individual
amines.
The use of mixed amines is to have a solution consisting of tertiary and primary amines
or tertiary plus secondary amines that retains much of the reactivity of primary amines
or secondary amines at similar or reduced circulation rates but offers low regeneration
costs similar to those of tertiary amines.
Ammonium absorption process
This process uses aqueous ammonia as CO2 sorbent with the capability of
multi-component control.
Flue gas needs to be pretreated by oxidizing SO2 and NO to SO3 and NO2,
respectively. The flue gas then reacts with aqueous ammonia in a wet scrubber.
The regeneration of ammonium requires heat input to thermally decompose
ammonium bicarbonate and ammonium carbonate.
They estimated that this process saves energy up to 60 percent compared to
MEA process.
The major by-products from this process include ammonium sulfate,
ammonium nitrate, ammonium bicarbonate. Ammonium sulfate and ammonium
nitrate are well-known fertilizers.

42. Dual-alkali absorption approach
2 3 2 3 4 CO NaCl NH H O NaHCO NH Cl       
4  2 3 2 2
2NH Cl Ca OH 2NH CaCl 2H O
3 2 CaCO CaOCO
2 2 3 2 2NaCl  2CO CaO H O2NaHCO CaCl
      
 
CO NaCL HOCH CH CH NH H O NaHCO
HOCH CH CH NH HCL
2 2 2 3 2 3
 
2 2 3 .

43. Molecular sieve adsorbent
This technology is believed to be cost-effective and can be adapted to a
variety of carbon sequestration schemes (Stewart and Hessami, 2005).
There were many research activities aiming to improve the CO2 adsorption
by chemically treat the molecular sieve surface.
Adsorbents based on high surface area inorganic supports that incorporate
basic organic groups, usually amines, are of particular interest. The
interaction between the basic surface and acidic CO2 molecules is thought
to result in the formation of surface ammonium carbamate under anhydrous
conditions and in the form of ammonium bicarbonate and carbonate species
in the presence of water.
Similar to amine absorption process, the CO2 adsorption capacity is
0.5 mol CO2/mol surface-bound amine group without the presence of
water.

44. Surface reactions of amine groups with CO2

45. “Molecular basket” adsorbent for CO2 separation
This adsorbent is based on mesoporous molecular sieve of MCM-41 impregnated with
polyethylenimine (PEI). Fig.8 shows the structures
of MCM41 and PEI.
With the increase in PEI loading, the surface area, pore size and pore volume of the
loaded MCM-41 decrease.
When the loading is higher than 30wt.%, the mesoporous pores began to be filled with
PEI and the adsorbent shows a synergetic effect on the adsorption
of CO2 by PEI. At PEI loading of 50 wt.%, the highest CO2 adsorption capacity of 246
mg/g PEI is obtained, which is 30 times higher than that of MCM-41 and is about 23
times that of the pure PEI.
Chemical impregnation proved to be a better way to prepare the molecular basket.
This study also shows that this molecular basket can selectively capture CO2 for the
separation of CO2 from simulated flue gas, the separation of CO2 from natural gas-fired
and coal-fired boiler flue gas

46. Structures of MCM-41 and PEI (Song, 2006).
“Molecular basket” concept for highly-selective high-capacity CO2 adsorbent
(Song, 2006).

47. Adsorption by activated carbon
Anthracites are known to produce high surface area activated
carbon.
The highest CO2 adsorption capacity was 65.7 mg CO2/g
adsorbent for the
anthracite activated at 800°C for 2 h with a surface area of 540
m2/g.
The anthracite with the highest surface area of 1,071 m2/g only
had a CO2 adsorption capacity of 40 mg CO2/g adsorbent.
This could be explained by certain size pores being effective for
CO2 adsorption. Also the NH3 treatment and PEI impregnation
increased the CO2 capture capacity of the activated anthracites
at higher temperature, due to the introduction of alkaline
nitrogen groups on the surface.

48. CO2 adsorbents based on lithium compounds
Li2ZrO3 (s) CO2 Li2CO3 (s)  ZrO2 (s)
4 4 2 2 3 2 3 Li SiO CO Li SiO  Li CO

49. CO2 capture based on membrane separation
1. Polymeric membranes
2. Inorganic membranes
3. Carbon membranes
4. Alumina membranes
5. Silica membranes
6. Zeolite membranes
7. Facilitated transport membranes
8. Mixed-matrix and hybrid membranes
9. Facilitated transport membranes

50. Problems with Amines
 The uptake of water into the gas stream requires additional
drying process.
 The loss of volatile amines and the evaporation of water:
energy and cost intensive process.
 The desorption of CO2 by heating causes serious corrosion and
other operational difficulties with addition of costly zeolites
($80,000/ton)
 SO2, even though present in small amount (500-2500 ppm) in
the flue gas undergoes chemical reaction (irreversible) with
amines and causes solvent degradation, so reduction in
solvent’s capacity to capture CO2.
 Therefore with sulfur bearing fossil fuels, an additional pre
scrubbing of SO2 from the flue gas before using amine-based
scrubbers is necessary.

51. Problems with Membranes
 Although the membrane separation technology is immature
compared with the other processes, the membrane separation
process is considered to be one of the least energy-demanding
processes if membranes that could withstand the process
temperature and conditions are available.
 Membranes that could withstand high temperatures in the
order of 500–600 ◦C are rarely available. Also membranes
such as microporous silica membranes, even if they could be
processed with high CO2 separation factors at high
temperature, will definitely allow higher permeance of lighter
molecules such as hydrogen making selective separation of
CO2 practically impossible from (for e.g.) membrane reactor
environment where mostly H2 and CO2 are the conversion
products.

52. Current commercially available solvents for CO2 capture
systems (EPA, 2006)
Supplier solvent Solvent
Loss,
kg/ton of
CO2
Solvent
cost, $/kg
Solvent
Cost, $/ton
CO2
Steam,
kg/kg Co2
Non
Proprietary
MEA 1 to 3 1.25 1.20 to2.50 2.0
Fluor; US MEA +
inhibitors
2.0 1.50 2.30 2.3
KS-1, MHI Hindered
Amines
0.35 3.00 1.55 1.5

53. Problems with Lithium silicate based membranes
Li4SiO4, has enhanced ability to absorb CO2 at high temperature.
The absorption of CO2 took place because of a reaction to form
lithium carbonate and a solid oxide. Theoretically this reaction,
if proceeds to the end, should make SiO2 as in the reaction
Li4SiO4 + 2CO2→2Li2CO3 + SiO2.
Hence, the material should be capable of absorbing 73.5%
(by wt.) of CO2. However, in practice the solid product Li2SiO3,
which is formed as the reaction product between 1 mol of
Li4SiO4 and CO2 restricts the absorption. Hence the reaction
proceeds according to the equation
Li4SiO4 +CO2→Li2CO3 +Li2SiO3.
Consequently the total amount of CO2 absorbed is limited
to 36.7% (by wt.)
Similarly, Li2ZrO3 membrane, salt hydrates etc. are
having the same problems as like this Li4SiO4 (Lithium
arthosilicate) based membranes.

54. Ionic Liquid (ILs)
 ILs have high CO2 solubility.
 The activity of H-2 in the imidazolium ring responsible for
high CO2 solubility.
 Higher selectivity for CO2 than CH4, so can be used for CO2
removal from natural gas.
 Both imidazolium and phosphonium cation based ILs can be
used. Several types of anions can be used.
 Amine based anions have superior sorption characteristics.
 Solid porous support enhances CO2 solubility as the bulk
liquid resistance gets decreased.
 Upto 50 mole% of CO2 can be absorbed by IL.
 With 1% water, equimolar absorption of CO2 can be obtained.

55. Ionic Liquid Properties
 ILs can be tailored by choice of cation and anion
Properties can be varied by choice of anion, cation and
substituents
 ILs have negligible vapor pressures (“green” potential)
No contamination of IL into gas stream
No loss of IL from evaporation
 Good solvation properties
Has been shown to dissolve polars, non-polars, organic,
inorganic, aromatics
 Thermally stable
 Reusable/recyclable

56. Ionic Liquid with Silica
Results of absorption of CO2 by [P(C4)4][b-Ala]-SiO2,
[P(C4)4][Gly]-SiO2 and P(C4)4][Ala]-SiO2
Cycles of CO2 absorption of [P(C4)4][AA]-SiO2. □ =[P(C4)4][Gly]-SiO2,
О =[P(C4)4][Ala]-SiO2, and  =[P(C4)4][b-Ala]-SiO2.

57. Results of absorption of CO2 by [P(C4)4][b-Ala]-SiO2,
[P(C4)4][Gly]-SiO2 and P(C4)4][Ala]-SiO2
The results suggests that
CO2 absorption equilibrium can all be reached in less
than 100 min.
 The absorbed CO2 was released in a vacuum at room
temperature over several hours.
 Due to the large surface area of silica gel
(approximately 500 m2g-1), the absorption rate of CO2
was significantly increased.

58. Results of absorption of CO2 by [P(C4)4][Gly]-SiO2
with water (1% mass fraction)

59. Results of absorption of CO2 by [P(C4)4][Gly]-SiO2
with water (1% mass fraction)
Absorption of CO2 by using these ionic liquids with a small
amount of water (1%, mass fraction) was found
 The viscosity was low and the liquid was stirred with greater
ease at the beginning of the absorption, but the viscosity
gradually increased and finally became very high and the
transparent liquid became cloudy.
 [P(C4)4][Gly] with water can absorb almost 13 wt% of CO2,
which is close to the theoretical absorption capacity (13.52%,
based on a 1:1 mol ratio between the ionic liquid and CO2), in
200 mins.

60. Results of absorption of CO2 by [P(C4)4][Gly]-SiO2
with water (1% mass fraction)
 If more water is added, the ionic liquid saturates with
CO2 separates into a solid phase and a liquid phase.
 The residue liquid finally obtained, after drying in
vacuum at 353.15 K for 12 h, is more viscous than
pure [P(C4)4][Gly].

61. Mechanisms of Absorption
(Scheme 1) (Scheme 2).
 In the first mechanism (Scheme 1), CO2 attacks the free
electron pair of the N atom on the -NH2 group and forms a
hydrogen bond OH···N with the NH2 group of another AA.
 A second possibility is that one of the H atoms in the NH2
group is taken as a proton by the original CO2
- to form a
new CO2H group (Scheme 2).

62. Finally;
 The rates of CO2 absorption of the supported ionic liquids
were much higher than those of the viscous ionic liquids
themselves.
 The CO2 absorption of the ionic liquids supported on porous
SiO2 is fast and reversible with a capacity of 1CO2/2
[P(C4)4][AA].
 The proposed mechanism suggests that a CO2 molecule attacks
the N atom of the NHgroup and results in -NHCO2 2
formation, during which one H atom leaves and forms a new
COH with the NHCO- or the original COin the amino acid
22
2 anion.
 The CO2H group formed a hydrogen bond with the electron
pair of NH2 in another amino acid anion for which the N atom
was inert to reaction with CO2.
 In the presence of water (1%, mass), the [P(C4)4][AA] can
absorb an equimolar amount of CO2 by a different mechanism.

63. For your Patience