This document discusses various methods for capturing carbon dioxide (CO2) from industrial processes and power plant flue gases. It describes both established and developing absorption-based techniques using liquid solvents such as amines, ionic liquids, and hyperbranched polymers. While amine scrubbing is a mature process, opportunities exist to improve solvent capacity and reduce regeneration energy needs through new solvent formulations and process designs. Developing technologies like facilitated transport membranes and task-specific ionic liquids also aim to enhance CO2 capture efficiency. Fundamental research on reaction mechanisms and new candidate materials continues to inform the design of more effective and economical CO2 capture systems.

1. Toward Benign Process of CO2 Separation;
Facts and Opportunities
Lean
absorber
CO2<2%
Desorption
Absorption
Combustion
gas
CO2, H2O
CO2 rich
absorber
Kyung Hee University
Green Chemistry Research Group

2. Red Alert !!

3. CO2 Capture Technology in Industry1,
From Gas Sweetening to Global Warming Issues
Raw materials
Industrial separation
Industrial process
CO2 separation
Compression
CO2
Product
Post-combustion
combustion
CO2 separation
Pre-combustion
Gasification/reform
CO2
Heat & Power
Air
Fossil fuels,
biomass
Compression
H2 and CO2
separation
Compression
H2
Air/O2 + steam
Heat & Power
Other products
Compression
Oxyfuel
CO2
CO2
Air/O
Combustion2-steam
O2
O2 separation
Air
1. http://wcentral.blogspot.com/2007/05/overview-of-carbon-capture.html
Heat & power

4. Methods for CO2 Capture
Separating agent
Method
Chemical
absorption
Physical
absorption
Adsorption
Gas permeation
Cryogenic
distillation
Combination
Principle of
separation
CO2 solubility
CO2 reactivity
CO2-solid affinity
Diffusion through
membrane, pressure,
concentration gradient
Liquid
Water, methanol, DME, PEG,
NMP, PC
Reacting liquid
MEA, DEA, TEA, NaOH,
K2CO3
Solid adsorbent
Zeolite, Active carbon, alumina
silicates, hydrotalcites
Polymeric, ceramic, ion
transport, membrane
Liquefaction, distillation
Pressure swing
adsorption
Distillation tower
Pressure swing – solid
adsorbent

5. Physical Versus Chemical Absorption
Physical
Chemical
No chemical
interaction
Regeneration by &
ΔP or (limited) & ΔT
Chemical interaction
occurs
Regeneration by &
ΔT (req. high temp.)
& ΔP
MeOH, NMP, PEG,
PC, water,
tri-n-Bu Phosphate,
ILs
• Less energy usage
and less
maintenance
demand under
optimal condition
and process
• 1o, 2o, 3o amines
(MEA, DEA, MDEA)
• Alkali metal OH- or
CO32(NaOH, K2CO3)
• Concentration
limited by solubility
• Susceptible with
corrosion, reactivity
with oxidator &
contaminant
Chemical absorption using amine
indicating sharp rise in outlet
PCO2 when loading reaches
reaction stoichiometry
Non-functionalized ILs is good
candidates for physical CO2
absorption.
• Good at low inlet P CO2
• Loading limited by reaction stoichiometry
• Can reach very low outlet P CO2 (down to
ppm)
PCO2 above Liquid, atm
• Better at high inlet P CO2
• Loading proportional to PCO 2
• Cannot reach very low outlet P CO2 (0.1-2%)
MeOH, 0°C
20wt% DEA, 50 °C
CO2, vol/vol absorbent

6. Typical CO2 Capture Process from Industrial Process and Power Plant
Carbon dioxide absorption using amine solution
CO2 Off Gas
Condenser
Lean Gas
Separator
Drum
Lean Solvent
Absorber
Stripping
Column
Trim
Cooler
CO2-Rich Feed Gas
Rich Solution
• Many variations possible
• Physical absorbent may not require
extensive heat input for regeneration
• CO2 off-gas often at low pressure
• May require pre-compression,
depending on feed gas pressure
Interchanger
Reboiler
• Recovery from low pressure (~1 atm) flue
gas
• Low CO2 partial pressure (~1-1.5 psi)
• Oxygen containing gas (~2-5%)
• Hot flue gas ~400-800 oC
• May contain NOx, Hg, SO2, H2S, other sulfur
species and particulates

7. CO2 Capture Through Facilitated Membrane; Tons of Works Awaiting 2
1.
2.
3.
4.
5.
Process is under rapid investigations & developments
Numerous absorbents & membranes are available
Novel processes are possible
Some problems persist (solutions may directly correspond to costs)
Model, reaction mechanism, and kinetics are available
Problems
Current status
Vapor invasion through
membrane pores at
high temp. (wetting)
1.
Non/less-volatile
liquids
Surface
modification
composite
2.
3.
Opportunities
2. separ & Puri Tech 41(2005)109
Durability & thermal
stability
1.
2.
1.
2.
3.
4.
5.
Fluorinated
polymers
Non-aggressive
liquids
Selectivity
1.
2.
Selective liquids
Composite
Introduction of less volatile absorbent
Combination of membrane-novel absorbent
Membrane modification
Hybrid absorbent
Module design

8. CO2 Capture Through Facilitated Membrane, State-of-the-art
N2
Carbon dioxide separation through water-swollen-gel membrane 3
CO2
Carrier
Carrier + CO2
CO2 transportation
Carrier
CO2 desorption
K2CO3 + complex agents
(cryptand, crown ether)
Liquid membrane
CO2 absorption
CO2
Feed gas (CO2/N2)
Water-swollen-gel membrane
Porous membrane
Support membrane
Permeate
Stability Vs Selectivity (25 oC)
Gas and vapor permeation through liquid membrane using ionic liquid 4
Feed gas
Hydrophilic micropor. membrane
Ionic Liquid (pmim)Iodide
Hydrophobic micropor. membrane
Permeate
Sandwiched IL facilitated transport
membrane
3. Energy Convers. Mgmt. 36 (1995) 419; 4. Transaction-MRSJ 29(2004)3299
Permeability comparison of several gases

9. Ionic Liquids, Novel CO2 Absorbents; Escape the Limits ?
Solvent volumetric CO2 load (60 oC)5
Henry’s law constants (bar) for several gases in various ILs.
Small Henry’s constant indicates high solubility7
Comparison with physical CO2 absorbents5
5. A.B. de Haan, TU Eindhoven; 6. G. Wytze Meindersma, Univ. of Twente
7. http://www.netl.doe.gov/technologies/carbon_seq/core_rd/breakthrough/42122.html
CO2/CH4 selectivity in specific-task ILs6

10. Anion and Cation Effects on the Solubility of CO2
70
O
[bmim][PF6]
60
[bmim][BF4]
F3C
[bmim][Tf2N]
50
[MeBu3N][Tf2N]
40
S
S
O
[MeBuPyrr][Tf2N]
N
O
Anion effect
Cation effect
10
0
Henry’s law constants (bar) for CO2 in various ILs
CF3
F
F
F
P
F
F
F
determining the
CO2 solubility3;
The anions
30
20
O
Fluorinated anions are excellent but
costly, sometimes not
environmentally friendly.
Some strategies in ILs for CO2 absorption8
Creating more free
volume (introducing
ether and long,
branched alkyl chain
on the cation
8. Journal of Physical Chemistry B 109 (2005) 6366
Incorporating with CO2phylic functional groups
(carbonyl, sulfonyl,
phosphate, amine
groups)
Controlling the viscosity
(using dicyanamide
anions, trialkylsulfonium
cation)

11. Ionic Liquids for CO2 Absorption
Classical ILs
Cations
Anions
R
N
N
R
N
R
R
Cl -, Br -, BF 4-, PF 6N(CN) 2-, SCN -,
R
R
N
P
R
R
Tf 2N (bis(trifluoromethanesulfonyl)aminde
(bis(trifluoromethanesulfonyl)imide) )
R
R
Task specific ILs (via carbamate formation)
O
H2 N
NH2
N
N
O
O-
H2N
R
O-
Amino acids
Problems
Current status
Anions play critical
role.
Expensive anions
(Fluorinated anions,
effective yet expensive)
Slow rate and low CO2
capacity (nonfluorinated anions)
Reduction of capacity
in the presence of
water or other
organics9
Amino acids anions
Task specific ILs
(amine or amino acids
groups)
Underdeveloped
Opportunities
9. J Phys Chem B 106(2002)7315
1.
2.
3.
4.
5.
Additive
Blending
Task specific ILs
High pressure CO2
Choline chloride anion exchange

12. Task Specific ILs for CO2 Capture; Which All Good Things Put Together
2
NH2
C4H9
N
N
BF4-
H
N
C4H9
N
CO2
O
N
O
N
N
H3N
C4H9
2 BF4-
Carbamate formation as an intermediate 10,11
Slow progress due to some problems
Problems
Current status
Viscosity problems at
high CO2 loading
Expensive anions
(Fluorinated anions,
effective yet expensive)
Amine-tethered ILs
Carbamate formation,
intensive energy
regeneration
Underdeveloped
Alteration with DCA12
or ROSO3- anions
Underdeveloped
1.
Opportunities
2.
Hindered 1o or 3o
amine-tethered
groups
Anions
modification
10. J of American Chemical Society 124(2002)926; 11. Ind Eng Chem Res 45(2006)2875; 12. Chem Eng Res Des 85(2007)31

13. Poly(ionic liquid)s; Creative Effort13,14,15
*
*
*
n
*
*
*
n
*
*
n
n
x
*
*
1-x
O
x
*
*
1-x
O
O
O
O
O
O
BF4N
N
R
R
R
P[VBTMA][BF4]
BF4
-
N
O
O
n
N
N
R
n
O
P[VBBI][BF4]
P[MABI]BF4
P[VBTMA][BF4]-g-PEG
O
P[MATMA][BF4]-g-PEG
Brittle materials
Current status
O
N
R
Problems
BF4N
R
P[MATMA][BF4]
BF4-
BF4-
N
BF4-
R
R
O
O
Thermodynamics,
kinetics and
mechanism
Low efficiency
Grafting polymers
In progress, limited
results available
Underdeveloped
1.
Opportunities
13. Chem Commun (2005)3325; 14. Ind Eng Chem Res 46(2007)5397; 15. J Membrane Sci 281(2006)130
2.
ILs grafted onto
selective polymers
Specific
membrane

14. Hyperbranched Polymers16; What Else Can We Do ?
1. Chemistry & process are underdeveloped
2. Candidates for replacing ILs-based absorbents
3. Limited numbers of chemical are commercially available
Problems
Current status
Unknown chemical &
Physical properties
Synthesis
CO2 absorption
On progress1
Papers & patents
available
Underdeveloped
Opportunities
1.
2.
3.
4.
Taylor-made amines
High press. & high temp. applications
Fundamental researches
Hot flue gas treatment
16. http://www.3me.tudelft.nl/live/pagina.jsp?id=7990c6da-316f-444b-94aa-334c23d3353e&lang=en

15. Amine-Based CO2 Absorption Process
1.
2.
3.
4.
Problems
Current status
Process is well established
Over 400 papers and patents are available
Model, reaction mechanism, and kinetics are available
Potential for immediate applications
Limited capacity at
high pressure
Thermal instability,
volatility, & degradation
Energy intensive
regeneration and
recycle
3o amine, hindered
amines, or polyamines
Activated K2CO3, Poly
or 3o amines
3o or poly 3o amines
1.
2.
3.
Opportunities
4.
5.
6.
7.
17. Green Chem 9(2007)594; 18. Fluid Phase Equilib227(2005)197
Amines blending17
3o amine & K2CO3 activation18
Combination physical and amine-based
absorbents
Introduction of various unique amines
Effective stripping study, i.e. stationary
carbamate hydrolysis catalyst in the stripper
Facilitated transport membrane
Hot flue gas treatment

16. Some unique amines for CO2 absorption
Common well-established amines
H
N
NH2
HO
HO
MEA (1o amine)
N
OH
HO
OH
DEA (2o amine)
MDEA (3o amine)
Relatively new
H
N
H2N
OH
Piperazine (2o polyamine)
AMP (hindered 1o amine)
N
H
New introduction of unique amines
HN
H
N
OH
N
TBAE (hindered 2o amine)19
N
2
NH2
DMAPA (1o, 3o polyamine)
TMBPA (2o, 3o polyamine)20
H
N
N
N
H
NH2
N,N-Dimethyldipropylenetriamine (1 o, 2o, 3o, polyamine)
H2N
OH
AEEA (1o, 2o, polyamine)21
More than 30 unique amines are available commercially, many have not been explored !!
19. J Chem Eng Data 45(2000)1195; 20. J Thermal Anal Cal 65(2001)419; 21. Ind Eng Chem Res 46(2007)5803

17. Amine-Based Reaction Mechanism22
Zwitterion mechanism
Less bulky 1o, 2o amine
CO2 + RNH2
RNH2+COO- + RNH2
k1
CO2 + 2RNH2
Zwitterion formation
RNHCOO- + RNH3+
Carbamate formation
RNHCOO- + RNH3+
k-1
kB
RNH2+COO-
Sum of reactions
1o hindered amine
k1
CO2 + R3NH2
R3NH2+COO- + H2O
k-1
kB
RN3H2+COO-
Zwitterion formation
HCO3- + R3NH3+
CO2 + R3NH2 + H2O
HCO3- + RNH3+
Sum of reactions
R3NHCOO- + H2O
HCO3- + R3NH2
Another possible rnx,
less stable carbamate hydrolysis

18. Amine-Based Reaction Mechanism
Thermolecular mechanism
Less bulky 1o, 2o amine
CO2 + RNH2 - B
RNHCOO- - BH+
Simultaneously
Base-catalyzed hydration mechanism
3o amine
R3N + H2O + CO2
k’
CO2 + R3N
R3NCOO- + H2O
22. Chem Eng Technol 30(2007)1467
k1
Carbamate formation
R3N+H + OH-
R3N + H2O
R3N+H + HCO3-
Amine dissociation in water
RN+COO-
Alternative route of 3o amine
k-1
R3N+H + HCO3-

19. Current Lab Progress
Test equipment
1.
2.
3.
4.
5.
Isochoric method, based on pressure-decay history (batch analysis)23.
Using virial gas relationship.
Rapid, easy and semi quantitative analysis.
Robust for physical solubility analysis.
Materials
Not optimized for kinetics study.
1. Monoethanolamine (MEA)
2. Methyldiethanolamine (MDEA)
3. Imidazole
4. 1-Methylimidazole
5. 2-Methylimidazole
6. 1,2-Dimethylimidazole
7. K2CO3
8. Guanidine carbonate
9. Sodium glycine
10. N,N-Dimethylethanolamine (DMEA)
11. 3,3-Diaminodipropylamine (DAP)
Screening apparatus set-up
23. Ind Eng Chem Res 43(2004)3049

20. Data Reduction
Isothermal box
P
CO 2 reservoir
Equilibrium
cell
n CO2 before rnx =
Pvreservoir
ZsRT
(Ptotal – Psoln vapor)vtotal
n CO2 after equilibrium =
ZsRT
n CO2 dissolved = n CO2 before rnx – n CO2 after equilibrium
α (Capacity) = nCO2 dissoleved/n absorbent
Where,
V total = V CO2 reservoir + V Equilibrium cell
P total = P CO2 + P soln vapor
P solution vapor is obtained prior to CO 2 introduction
Zs is obtained from the virial gas equation24
Z mixture is neglected24
P CO2 (KPa)
to vacuum pump
α (Capacity)
24. AIChE Journal 51(2005)2311

21. Total Equilibrium
Pressure (KPa)
Total Equilibrium Pressure (KPa)
Total Pressure equilibrium Vs CO2 capacity (30 mins capacity (30 mins run)
Total Pressure equilibrium Vs CO2 run)
80. 0
80.00
80. 0
Total Equilibrium
Pressure (KPa)
Total equilibrium pressure (KPa)
100.00
60. 0
60.00
60. 0
40. 0
40.00
0.00 5.00
5.00
0.00
10.00
10.00
5.00
10.00
0. 0
15.00
15.00
15.00
mole of CO2/2kg of absorbent
mole of CO / kg of absorbent
60.0
40. 040.0
20. 0
20.00
80.0
20. 020.0
0. 0
0. 0
20.00
0.0
20.00
20.00
0. 4
0.0 0.0
mole of CO2/ kg of absorbent
1mL MDEA + + 4mL H2O
1mL MDEA 4mL H2O
5mL 4.76%wt 2- methylimidazole/ H2O
5mL 4. 76%wt 2- methylimidazole/ H2O
5mL 4.76%wt imidazole/ H2O
5mL 4. 76%wt imidazole/ H2O
5mL 4.76%wt guanidine carbonate/ H2O
5mL 4. 76%wt guanidine carbonate/ H2O
5mL 4.76%wt DMEA/ H2O
5mL 4. 76%wt DMEA/ H2O
5mL 4.76%wt DAP
5mL 4. 76%wt DAP
2mL MDEA +2mL MDEA + 3mL H2O
3mL H2O
5mL 23.08%wt K2CO3/ H2O
5mL 23. 08%wt K2CO3/ H2O
5mL 23.08%wt K2CO3/ H2O K2CO3/ H2O
5mL 23.08%wt
5mL 4.76%wt Naglycine/ H2O
5mL 4.76%wt Naglycine/ H2O
5mL 4.76%wt Naglycine/ H2O
5mL 4.76%wt 1,2- dimethylimidazole/ H2O
5mL 4.76%wt 1,2- dimethylimidazole/ H2O 5mL 4.76%wt Naglycine/ H2O
5mL 4.76%wt MEA/ H2O MEA/ H2O
5mL 4.76%wt
5mL 4.76%wt MEA/ H2O
5mL 4.76%wt MEA/ H2O
5mL 4.76%wt DMEA/ H2O DMEA/ H2O
5mL 4.76%wt
1mL DMEA + + 4mL H2O
1mL DMEA 4mL H2O
4mL 4.76%wt DAP + 1 mL DMEA 1 mL DMEA
4mL 4.76%wt DAP +
1mL
5mL
5mL
5mL
1mL
5mL
2. 0
2.4 2.4
MDEA +1mL MDEA + 4mL H2O
4mL H2O
4.76%wt 2- methylimidazole/ H2O
5mL 4. 76%wt 2- methylimidazol
4.76%wt 1,2- dimethylimidazole/ H2O
5mL 4. 76%wt 1,2- dimethylimid
9.09%wt guan-09%wt guan- car/ H2O
5mL 9. car/ H2O
DMEA +1mL DMEA + 4mL H2O
4mL H2O
4.76%wt DAP 76%wt DAP
5mL 4.
Capacity (mol of CO2/mol absorbent) of various amines
CO
Loading (mol of CO2/kgSolubility (Validation of Experiments)
absorbent) of various amines
2
16
160
[emim]etOSO3
120
CO2 mole fraction (x1000)
140
PCO2 equilibrium (KPa)
1.6
0.0. 8
4
0.8
1.2.0
6
0.4
0.8 1.2 1.2 1.2 1.6
2.0
a (molmol absorbent)
a (mol CO2(mol2/CO2absorbent)
a / CO mol / mol absorbent)
Jones et al; J Chem Eng Data4(1959)85
Shen et al; J Chem Eng Data 37(1992)96
Song et al; J Chem Eng Data 41(1996)497
This work
100
80
60
40
20
0
[emim]etOSO3 + 7.0% w/w ZnBr2
[emim]etOSO3 + 7.0% w/w sugar
12
[bmim]BF4
8
4
0
0. 4
0.5
0. 6
Capacity (mol CO2/ mol of MEA)
0. 7
Experimental Validation of CO2 solubility test (15.3%wt. MEA)
30
50
70
90
110
Pequilibrium (KPa)
Effect of additive on the CO2 absorption capacity of simple ILs

22. Proposal & Schedule (3 years basis)
Year
Assigned Project
1
2
3
4
5
6
7
8
9
10
11
12
Rapid
screening
2008
Amine-based absorber
development using
commercially available
unique amines
New
reactor
design
Physical & chemical
properties
Thermodynamics &
kinetics studies
1st report
2nd report
Evaluation
3rd report
Synthesis of materials
2009
Introduction of novel
CO2 absorbents
Poly(amines)
ILs & Poly(ILs)
Characterization &
mechanism studies
CO2 absorption investigations
1st report
2010
CO2 separation using
facilitated transport
membrane
2nd report
Evaluation
3rd report
Membrane
selection & development
Transport & Kinetics Study
1st report
Thank You
2nd report
Evaluation
3rd report