1

Kinetics of CO2 Absorption into

MEA-AMP Blended Solution

Roongrat Sakwattanapong Adisorn Aroonwilas

Amornvadee Veawab

Faculty of EngineeringUniversity of ReginaSaskatchewan, Canada

Presented at the Annual Research Review Meeting, University of Texas at Austin, Jan 10-11, 2008

2

Outline

Introduction & Research Motivation

Research Objective

CO2 Absorption Experiments

Experimental Results and Discussion

Kinetic Model for MEA-AMP System

Conclusions

Acknowledgement

3

Introduction CO2 capture technology Reduction in GHG emissions

Low pressure flue gas Chemical absorption into amines

Performance of CO2 absorption

Higher performance [Smaller unit] Lower cost

Feed Gas

Treated Gas CO2

Liquid Solvent (Lean)

Liquid Solvent (Rich)

REGENERATIONCOLUMN

ABSORPTIONCOLUMN

Absorption solventsAbsorption solvents

Process DesignProcess Design

4

Introduction (Solvent Characteristics)

Blended-alkanolamines Blended alkanolamines have been receiving a great deal of interest.

Low energy requirement with acceptable absorption rate

MEA DEA MDEA

Absorption efficiency or rate

rCO2 = k2 [CO2][Amine]

k2 ~ 6000 to 7500

m3/kmol-s

k2 ~ 550 to 1600

m3/kmol-s

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

CO2 solubility

(mol CO2/mol Amine)

0.5 0.5 1.0

5

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.)

6

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

Research Objective

7

CO2 Absorption Experiment

Water Bath

Feed Tank

Receiver

Bubble Flow Meter

Gas Flow Meter

Saturation Cell

Heat Exchanger

Wetted Wall Cell

Equalizer

Condenser

Gas in

Gas out

Wetted Wall Column Diameter = 12 mm, OD (stainless steel)

Column height = up to 100 mm.

Temperature measurement at different locations

8

CO2 Absorption Experiment (cont’d)

9

0

1

2

3

4

3.0 3.1 3.2 3.3 3.4 3.5

1000 K/T

109

DC

O2 (

m2/s

ec)

This study

Versteeg and van Swaaij, 1988

Nijsing et al., 1959

Yoon et al., 2003

Rowley et al., 1997Perez and Sandall, 1973

Takahashi et al., 1982

Perry and Green, 1984

System Verification Measurement of diffusion coefficient for CO2-water

system

T = 298 – 325 K

2

2

2

22

2 2 CO

cCOCOCO

p

tHND

THCO

2044exp108249.2 6

2

3/13/23

3

2

gV

dht

Lc

10

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

MEAkDH

pN MEAMEACO

MEACO

COMEACO ,2,

,, 2

2

2

2

MEADp

HNk

MEACOCO

MEACOMEACOMEA

,

2,,

,222

22 1

11

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

12

Test Parameters Condition

Molar mixing ratio 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)

Temperature 298, 303, 308, 313, and 318 K

Total amine concentration

1.0 , 1.5, 2.0, 3.0, and 4.0 kmol/m3

Test Condition for MEA-AMP Blend

13

Experimental Results Overall rate constant (kOV)

Parametric effects on kOV (Temperature, Amine conc., MEA-AMP

mixing ratio)

ovBlendCOBlendCO

COBlendCO kD

H

pN ,

,, 2

2

2

2

BlendCOCO

BlendCOBlendCOov Dp

HNk

,

2,,

22

22 1

DN2O-mixed (109 m2/s)

0.5

0.75

1

1.25

1.5

1.75

2

0.5 0.75 1 1.25 1.5 1.75 2Correlation from this study

Rep

ort

ed

data

Mandal et al., 2005

Li and Lai, 1995

HN2O-mixed (kPa.m3/kmol)

3500

4000

4500

5000

5500

6000

6500

7000

3500 4000 4500 5000 5500 6000 6500 7000Correlation from this study

Rep

ort

ed

data

Mandal et al., 2005

Li and Lai, 1995

Regression of diffusion coefficient and Henry’s constant for MEA-AMP blend.

14MEA : AMP = 1 : 1

General representation

Effect of Temperature

15

Effect of Temperature (cont’d)

Individual Mixing Ratio

MEA : AMP ratio

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)

MEA : AMP ratio

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)

16T = 318 K

General representation

Effect of Amine Concentration

17

Individual temperatures

Effect of Amine Concentration (cont’d)

18

Without Synergy Effect

Effect of Mixing Ratio General Representation

MEA : AMP ratio

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)

MEA : AMP ratio

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)

AMP MEA

19

Single AMP

Single MEA

Individual Temperatures

Effect of Mixing Ratio (cont’d)

20

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)

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.

Kinetic Model for MEA-AMP System

COONHRRNHRRCO k

k'

1'

2

2 NCOORRBHBCOONHRR Bk ''

CO2-MEA System

Bk

k

AMPCOkr

B

AMPAMPCO

1

2,2,

12

Bkk

MEACOkr

B

MEAMEACO

1

2,2,

12

CO2-AMP System

21

Overall reaction of CO2-MEA-AMP System

Apparent reaction rate

OHCOAMPCOMEACOovov rrrCOkr ,,,2222

Kinetic Model (cont’d)

][* OHkkk

OHOVapp

][][][

11][

][][][

11][

][

1

,2

1

,22

1

,2,2

1

,2

1

,22

1

,2,2

*

22 MEAk

kkAMP

k

kkOH

k

kkk

AMP

AMPk

kkMEA

k

kkOH

k

kkk

MEAOHkk

MEAAMPAMPAMPOHAMPAMPAMPMEAMEAMEAOHMEAMEA

OHOV

)(

3.4340095.15,2 KT

k AMP

)(

758.10067.0

1

,2

KTk

kk AMPAMP

)(

32.4164825.1

1

,2

KTk

kk MEAAMP

)(

0852.00003.0

1

,2

KTk

kk WAMP

)(

4945018.171,2 KT

k MEA

)(

29.935979.0

1

,2

KTk

kk MEAMEA

)(

78.3532459.1

1

,2

KTk

kk AMPMEA

)(

7754.00027.0

1

,2

KTk

kk WMEA

22

Speciation [MEA], [AMP], [H2O], [OH-]

CO2 Absorption Reaction

( 1 ) 2332 '' 1 NHROHNHROH K 2' NHR

( 2 ) 232 '' 2 NHRHCONHCOOROH K 3' NHR

( 3 ) 332232 HCOOHOHCO K NHCOOR '

( 4 ) OHOHOH K32

42 2CO

( 5 ) 23332

5 COOHHCOOH K 3HCO

( 6 ) 332226 HCORNHOHRHNCO K 2

3CO

2RNH

( 7 ) E l e c t r o - n e u t r a l i t y 3RNH

( 8 ) M E A B a l a n c e OH 3

( 9 ) A M P B a l a n c e OH

( 1 0 ) C a r b o n B a la n c e

0.1ix OH 2

( 1 ) 2332 '' 1 NHROHNHROH K 2' NHR

( 2 ) 232 '' 2 NHRHCONHCOOROH K 3' NHR

( 3 ) 332232 HCOOHOHCO K NHCOOR '

( 4 ) OHOHOH K32

42 2CO

( 5 ) 23332

5 COOHHCOOH K 3HCO

( 6 ) 332226 HCORNHOHRHNCO K 2

3CO

2RNH

( 7 ) E l e c t r o - n e u t r a l i t y 3RNH

( 8 ) M E A B a l a n c e OH 3

( 9 ) A M P B a l a n c e OH

( 1 0 ) C a r b o n B a la n c e

0.1ix OH 2

23

Comparison (Model & Experimental data)

Single AMPSingle MEASingle AMPSingle MEASingle AMP

Single MEASingle AMPSingle MEA

Single AMPSingle MEA

24

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.

Conclusions

25

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.

Further work

26

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)

Acknowledgement

27

Thank You