Kinetics of CO2 Absorption into MEA-AMP Blended Solution

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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
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Outline

• Introduction Research Motivation
• Research Objective
• CO2 Absorption Experiments
• Experimental Results and Discussion
• Kinetic Model for MEA-AMP System
• Conclusions
• Acknowledgement

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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

Process Design
Absorption solvents
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Introduction (Solvent Characteristics)
MEA DEA MDEA
Absorption efficiency or rate rCO2 k2 CO2Amine 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

• Blended-alkanolamines
• Blended alkanolamines have been receiving a great
  deal of interest.
• Low energy requirement with acceptable absorption
  rate

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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.)
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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

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CO2 Absorption Experiment

• Wetted Wall Column
• Diameter 12 mm, OD (stainless steel)
• Column height up to 100 mm.
• Temperature measurement at different locations

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CO2 Absorption Experiment (contd)
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System Verification

• Measurement of diffusion coefficient for
  CO2-water system

• T 298 325 K

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System Verification (contd)

• Measurement of reaction rate constant for CO2-MEA
  system
• Temperature 298 318 K (at Various liquid flow
  rates)
• MEA concentration 1 4 kmol/m3

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System Verification (contd)

• Measurement of reaction rate constant for CO2-AMP
  system
• Temperature 298 318 K (at Various liquid flow
  rates)
• AMP concentration 1 4 kmol/m3

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Test Condition for MEA-AMP Blend
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

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Experimental Results

• Overall rate constant (kOV)
• Parametric effects on kOV (Temperature, Amine
  conc., MEA-AMP mixing ratio)

Regression of diffusion coefficient and Henrys
constant for MEA-AMP blend.
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Effect of Temperature

• General representation

MEA AMP 1 1
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Effect of Temperature (contd)

• 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)
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Effect of Amine Concentration

• General representation

T 318 K
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Effect of Amine Concentration (contd)

• Individual temperatures

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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)
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Effect of Mixing Ratio (contd)

• Individual Temperatures

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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)

• CO2-MEA System

• CO2-AMP System

• 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.

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Kinetic Model (contd)

• Overall reaction of CO2-MEA-AMP System
• Apparent reaction rate

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Speciation

• MEA, AMP, H2O, OH-
• CO2 Absorption Reaction

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Comparison (Model Experimental data)
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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 gt 11 lt 41 lt 10 lt 14 lt 01
  (MEAAMP)
• Existing model developed for low amine
  concentration provides reasonable prediction for
  single amine, but not for the blend.

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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.

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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)

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Thank You