Kinetics of CO2 Absorption into
MEA-AMP Blended Solution
Roongrat Sakwattanapong
Adisorn Aroonwilas
Amornvadee Veawab
Faculty of Engineering
University of Regina
Saskatchewan, Canada
Presented at the Annual Research Review Meeting,
University of Texas at Austin, Jan 10-11, 2008
1
Outline

Introduction & Research Motivation

Research Objective

CO2 Absorption Experiments

Experimental Results and Discussion

Kinetic Model for MEA-AMP System

Conclusions

Acknowledgement
2
Introduction

CO2 capture technology  Reduction in GHG emissions

Low pressure flue gas
amines

Performance of CO2 absorption
o
 Chemical absorption into
Higher performance  [Smaller unit]  Lower cost
CO2
Treated Gas
Process Design
Liquid Solvent (Lean)
ABSORPTION
COLUMN
REGENERATION
COLUMN
Absorption solvents
Feed Gas
Liquid Solvent (Rich)
3
Introduction (Solvent Characteristics)
MEA
Absorption efficiency or rate
rCO2 = k2 [CO2][Amine]
DEA
k2 ~ 6000
k2 ~ 550
to 7500
to 1600
m3/kmol-s m3/kmol-s
MDEA
k2 ~ 5
m3/kmol-s
Heat of reaction (kJ/mol CO2)
85.6
76.3
60.9
Energy requirement for regeneration
(kJ/kg CO2)
High
Medium
Low
0.5
0.5
1.0
CO2 solubility
(mol CO2/mol Amine)
Blended-alkanolamines

Blended alkanolamines have been receiving a great deal of
interest.

Low energy requirement with acceptable absorption rate
4
Research Motivation

MDEA-based solvents  Low rate of CO2 absorption.

AMP can absorb CO2 with the similar capacity with MDEA but at a
much higher rate.

The knowledge of CO2 absorption kinetics for MEA-AMP is
minimum and limited.
Aroonwilas and Veawab, 2004. (Ind. Eng. Chem. Res.)
5
Research Objective

To measure kinetic rate of CO2 absorption into
aqueous MEA-AMP solution

To investigate the effects of process parameters on
the kinetic rate of the blend. (The parameters of
interest are temperature, total amine concentration,
and MEA-AMP mixing ratio.)

To understand the kinetic rate data using reaction
mechanism model
6
CO2 Absorption Experiment
Wetted Wall Column

Diameter
= 12 mm, OD (stainless steel)

Column height = up to 100 mm.

Temperature measurement at different locations
Wetted Wall Cell
Water Bath
Heat Exchanger
Feed Tank
Saturation Cell
Bubble Flow Meter
Equalizer
Gas out
Condenser
Gas in
Receiver
Gas Flow Meter
7
CO2 Absorption Experiment (cont’d)
8
System Verification

Measurement of diffusion coefficient for CO2-water
system

T = 298 – 325 K
2
2
2
 2044 
HCO2  2.8249  106 exp

 T 
2h  d 
 
tc 
3  VL 
2/3
 3 


 g 
1/ 3
109 DCO2 (m2/sec)
DCO 2

NCO HCO 2 tc 

2pCO 2
4
3
2
This study
Versteeg and van Swaaij, 1988
Nijsing et al., 1959
Yoon et al., 2003
Rowley et al., 1997
Perez and Sandall, 1973
Takahashi et al., 1982
Perry and Green, 1984
1
0
3.0
3.1
3.2
3.3
3.4
3.5
1000 K/T
9
System Verification (cont’d)

Measurement of reaction rate constant for CO2-MEA system

Temperature = 298 – 318 K (at Various liquid flow rates)

MEA concentration = 1 – 4 kmol/m3
pCO 2
HCO 2 ,MEA
DCO 2 ,MEAk2,MEA MEA 
k2,MEA
 NCO ,MEAHCO ,MEA 
2
2




p
CO 2


2


1


 DCO ,MEA MEA  
2


20000
1 kmol/m3
1.5 kmol/m3
17500
2 kmol/m3
3 kmol/m3
15000
k2,MEA(kmol/m3-sec)
NCO 2 ,MEA 
4 kmol/m3
Hikita et al., 1997
Horng and Li, 2002
12500
Versteeg et al., 1996
10000
7500
5000
2500
3.1
3.15
3.2
3.25
1000/T (K)
3.3
3.35
3.4
10
System Verification (cont’d)

Measurement of reaction rate constant for CO2-AMP system

Temperature = 298 – 318 K (at Various liquid flow rates)

AMP concentration = 1 – 4 kmol/m3
2000
1 kmol/m3
1.5 kmol/m3
2 kmol/m3
1500
3 kmol/m3
k2,AMP (m3/kmol.s)
4 kmol/m3
Alper, 1990
Saha et al., 1995
1000
500
0
3.1
3.15
3.2
3.25
1000/T(K)
3.3
3.35
3.4
11
Test Condition for MEA-AMP Blend
Test Parameters
Condition
Molar mixing ratio

Temperature
Total amine
concentration
MEA : AMP
1 : 0 (xMEA = 1.0)
4 : 1 (xMEA = 0.8)
1 : 1 (xMEA = 0.5)
1 : 4 (xMEA = 0.2)
0 : 1 (xMEA = 0.0)
 298, 303, 308, 313, and 318 K

1.0 , 1.5, 2.0, 3.0, and 4.0 kmol/m3
12
Experimental Results

Overall rate constant (kOV)

Parametric effects on kOV (Temperature, Amine conc., MEA-AMP
mixing ratio)
NCO 2 ,Blend 
pCO 2
HCO 2 ,Blend
DCO 2 ,Blend kov
kov
 NCO ,Blend HCO ,Blend
2
2


pCO 2





2

1

 DCO ,Blend
2





Regression of diffusion coefficient and Henry’s constant for MEA-AMP blend.
HN2O-mixed (kPa.m 3/kmol)
DN2O-mixed (109 m 2/s)
2
7000
1.75
6500
6000
Reported data
Reported data
1.5
1.25
1
5500
5000
4500
0.75
Mandal et al., 2005
4000
Mandal et al., 2005
Li and Lai, 1995
Li and Lai, 1995
0.5
0.5
0.75
1
1.25
1.5
1.75
Corre lation from this s tudy
2
3500
3500
4000
4500 5000 5500 6000 6500
Corre lation from this s tudy
7000
13
Effect of Temperature
General representation
80000
1 kmol/m3
70000
1.5 kmol/m3
2 kmol/m3
60000
kOV (1/sec)

3 kmol/m3
4 kmol/m3
50000
40000
30000
20000
10000
0
3.1
3.15
3.2
3.25
3.3
3.35
3.4
1000/T (K)
MEA : AMP = 1 : 1
14
Effect of Temperature (cont’d)

Individual Mixing Ratio
0.0
0.2
Effect of Temperature at xMEA = 0.5
0.8
1.0
80000
1 1kmol/m3
kmol/m3
70000
2 2kmol/m3
kmol/m3
MEA : AMP ratio
4 : 1 (xMEA = 0.8)
1 : 1 (xMEA = 0.5)
1 : 4 (xMEA = 0.2)
0 : 1 (xMEA = 0.0)
60000
kOV (1/sec)
1 : 0 (xMEA = 1.0)
1.5
1.5kmol/m3
kmol/m3
3 3kmol/m3
kmol/m3
4 4kmol/m3
kmol/m3
50000
40000
30000
20000
20000
10000
10000
0
0
3.1
3.1
3.15
3.15
3.2
3.2
3.25
3.25
3.3
3.3
3.35
3.35
3.4
3.4
1000/T (K)
15
Effect of Amine Concentration
General representation
80000
[MEA]/[Total] = 1.0
70000
[MEA]/[Total] = 0.8
[MEA]/[Total] = 0.5
60000
[MEA]/[Total] = 0.2
[MEA]/[Total] = 0.0
50000
kOV (1/sec)

40000
30000
20000
10000
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Total Concentration (kmol/m3)
T = 318 K
16
Effect of Amine Concentration (cont’d)
Individual temperatures
Effect
Effectof
ofTotal
TotalConcentration
Concentrationatat308
298
303
318
313KK
80000
[MEA]/[Total]
[MEA]/[Total]==1.0
1.0
70000
[MEA]/[Total]
[MEA]/[Total]==0.8
0.8
[MEA]/[Total]
[MEA]/[Total]==0.5
0.5
60000
k (1/sec)
kOVOV(1/sec)

[MEA]/[Total]
[MEA]/[Total]==0.2
0.2
[MEA]/[Total]
[MEA]/[Total]==0.0
0.0
50000
40000
30000
20000
10000
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Total Concentration (kmol/m3)
17
Effect of Mixing Ratio

General Representation
Effect of Mixing Ratio at 318 K
80000
1 kmol/m3
70000
MEA : AMP ratio
1.5 kmol/m3
2 kmol/m3
60000
4 : 1 (xMEA = 0.8)
50000
1 : 1 (xMEA = 0.5)
1 : 4 (xMEA = 0.2)
0 : 1 (xMEA = 0.0)
kOV (1/sec)
1 : 0 (xMEA = 1.0)
3 kmol/m3
4 kmol/m3
40000
Without Synergy Effect
30000
20000
10000
0
0
AMP
0.2
0.4
0.6
[MEA]/[Total]
0.8
1
MEA
18
Effect of Mixing Ratio (cont’d)
Individual Temperatures
Effect
Effectof
ofMixing
MixingRatio
Ratioat
at298
318
303
308
313KK
60000
80000
11M
kmol/m3
1kmol/m3
kmol/m3
50000
70000
1.5
1.5
kmol/m3
kmol/m3
M
1.5
kmol/m3
22M
kmol/m3
2kmol/m3
kmol/m3
60000
33M
kmol/m3
3kmol/m3
kmol/m3
40000
kOV(1/sec)
(1/sec)
kOV

44M
kmol/m3
4kmol/m3
kmol/m3
50000
30000
40000
30000
20000
20000
10000
10000
00
0
0
Single
AMP
0.2
0.2
0.4
0.4
[MEA]/[Total]
0.6
0.6
[MEA]/[Total]
0.8
0.8
1
Single1
MEA
19
Kinetic Model for MEA-AMP System

Xiao et al. (2000) proposed a model based on a hybrid reaction
rate

Ali (2005) expressed the reaction rates of both AMP and MEA
based on the zwitterion mechanism (for low amine concentration)
k2
 RR'NH COO 
CO2  RR NH 
k
'
1

CO2-MEA System
rCO2 , MEA 
k 2, MEA CO2 MEA


1  k 1 
  k B  
B


B
RR'NH COO   B 

 BH   RR'NCOO
k

CO2-AMP System
rCO 2 ,AMP 
k2,AMP CO2 AMP 

k 1 
1 

  k B  
B


 Xiao, J., Li, C.W., and Li, M.H., “Kinetics of absorption of carbon dioxide into aqueous solutions of 2-amino-2-methyl-1-propanol +
monoethanolamine,” Chemical Engineering Science, 55(1), 161-175 (2000).
 Ali, S.H., “Kinetics of the Reaction of Carbon Dioxide with Blends of Amines in Aqueous Media Using the Stopped-Flow Technique,”
International Journal of Chemical Kinetics, 37(7), 391-405, July 2005.
20
Kinetic Model (cont’d)

Overall reaction of CO2-MEA-AMP System
rov k ov CO2   rCO 2 ,MEA  rCO 2 ,AMP  rCO
*

kOV  kOH
 [OH ] 
[ MEA]
1
k2, MEA

1
k2, MEAk H 2 O
k1


[ H 2O ] 
k2, MEAk MEA
k1
[ MEA] 
k2, MEAk AMP
k1
[ AMP]

2 ,OH
[ AMP]
1
k2, AMP

1
k2, AMPk H 2 O
k1
[ H 2O ] 
k2, AMPk AMP
k1
[ AMP] 
k2, AMPk MEA
k1
[ MEA]
Apparent reaction rate
*

k app  kOV  kOH
]
 [OH
k 2, AMP  15.095 
k 2, MEA k MEA
 1.4825 
416.32
T (K )
k 2, MEA k AMP
 0.0003 
0.0852
T (K )
k 1
k 2, AMP k MEA
k 2, AMP kW
k 1
k 2, MEA  171.18 
1.758
T (K )
k 2, AMP k AMP
k 1
4340.3
T (K )
 0.0067 
k 1
k 1
k 2, MEA kW
k 1
49450
T (K )
 0.5979 
 1.2459 
 0.0027 
93.29
T (K )
353.78
T (K )
0.7754
T (K )
21
Speciation


[MEA], [AMP], [H2O], [OH-]
CO2 Absorption Reaction
R ' NH 2 

(1)
K1
H 2 O  R ' NH 3 
H 3 O   R ' NH 2
(2)
K2
H 2 O  R ' NHCOO  
HCO3  R ' NH 2
(3)
K3
CO2  2 H 2 O 
H 3 O   HCO3
(4)
K4
2 H 2 O 
H 3 O   OH 
(5)
K5
H 2 O  HCO3 
H 3 O   CO3
(6)
K6
CO2  RHN 2  H 2 O 
RNH 3  HCO3
R' NH 


3
R' NHCOO 


CO2 

2
HCO 
CO 

3


2
3
RNH 2 
RNH 

(7)
Electro-neutrality
(8)
MEA Balance
(9)
AMP Balance
3
H O 
OH 

3

(10) Carbon Balance
x
i
 1 .0

H 2 O 
22
Comparison (Model & Experimental data)
Basic
Calculation
at
298
KKK
Bacis
Calculation
at
308
Basic
Calculation
at
313K
Basic
Calculation
at
318K
Basic
Calculation
at
303
100000
100000
100000
kkk
kapp,predict
app,predict
app,predict
app,predict
10000
10000
10000
Ali
(2005)
AliAli
(2005)
(2005)
(2005)
1 Ali
kmol/m3
1 kmol/m3
1 kmol/m3
11kmol/m3
kmol/m3
1.5kmol/m3
kmol/m3
1.5
1.5
1.5
kmol/m3
1.5kmol/m3
kmol/m3
2 2kmol/m3
kmol/m3
2
kmol/m3
2 kmol/m3
2 kmol/m3
3 kmol/m3
33kmol/m3
kmol/m3
kmol/m3
43 kmol/m3
3 kmol/m3
4kmol/m3
kmol/m3
4 4kmol/m3
4 kmol/m3
1000
1000
1000
Single AMP
Single AMP
Single MEA
Single
Single
Single
AMP
AMP
AMP
Single
MEA
Single
Single
Single
MEA
MEA
MEA
100
100
100
100
100
100
1000
1000
1000
10000
100000
kkkapp,exp
app,exp
app,exp
k
app,exp
23
Conclusions

The overall rate constant increases with the absolute
temperature.

At the same mixing ratio, the overall rate constant
increases when the total concentration increases.

An increase in MEA concentration in the blended
solution causes the overall rate constant to change in
a nonlinear manner.


Rate constant => 1:1 < 4:1 < 1:0 < 1:4 < 0:1 (MEA:AMP)
Existing model developed for low amine
concentration provides reasonable prediction for
single amine, but not for the blend.
24
Further work

Mechanism of CO2 absorption into MEA-AMP
blended solution will be further investigated.

CO2-loaded solution will be tested.

Degraded solution will be tested.

Empirical correlation of absorption kinetics will be
developed.
25
Acknowledgement

Faculty of Graduate Studies and Research
(FGSR), University of Regina

Faculty of Engineering, University of Regina

The Natural Sciences and Engineering
Research Council of Canada (NSERC)
26
Thank You
27