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Separation of CO2 by single and mixed aqueous amine solvents in membrane contactors: fluid flow and mass transfer modeling


Removal of carbon dioxide from gas mixtures is of vital importance for the control of greenhouse gas emission. This study presents a numerical simulation using computational fluid dynamics of mass and momentum transfer in hollow-fiber membrane contactors. The simulation was conducted for physical and chemical absorption of CO2. A mass transfer model was developed to study CO2 transport through hollow-fiber membrane contactors. The model considers axial and radial diffusions in the contactor. It also considers convection in the tube and shell side with chemical reaction. The model equations were solved by numerical method based on finite element method. Moreover, the simulation results were validated with the experimental data obtained from literature for absorption of CO2 in amine aqueous solutions as solvent. The simulation results were in good agreement with the experimental data for different values of gas and liquid velocities. The simulation results indicated that the removal of CO2 increased with increasing liquid velocity in the tube side. Simulation results also showed that hollow-fiber membrane contactors have a great potential in the area of gas separation specially CO2 separation from gas mixtures.

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A :

Cross-section of shell (m2)

C 0 :

Inlet CO2 concentration (mol/m3)

C :

Concentration (mol/m3)

\( C_{{\text{CO}}_{2}{\text{-}}{\text{membrane}}}\) :

CO2 concentration in the membrane (mol/m3)

\( C_{{\text{CO}}_{2}{\text{-}}{\text{shell}}}\) :

CO2 concentration in the shell (mol/m3)

\( C_{{\text{CO}}_{2}{\text{-}}{\text{tube}}}\) :

CO2 concentration in the tube (mol/m3)

C i :

Concentration of any species (mol/m3)

C i-shell :

Concentration of any species in the shell (m2/s)

C in :

Absorbent concentration at the inlet (mol/m3)

C inlet :

Inlet concentration of CO2 in the shell (mol/m3)

C outlet :

Outlet concentration of CO2 in the shell (mol/m3)

D :

Diffusion coefficient (m2/s)

\( D_{{\text{CO}}_{2}{\text{-}}{\text{membrane}}}\) :

Diffusion coefficient of CO2 in the membrane (m2/s)

\( D_{{\text{CO}}_{2}{\text{-}}{\text{tube}}}\) :

Diffusion coefficient of CO2 in the tube (m2/s)

D i-shell :

Diffusion coefficient of any species in the shell (m2/s)

J i :

Diffusive flux of any species (mol/m2 s)

\( J_{{{\text{CO}}_{2} }} \) :

Mass transfer rate of CO2 (mol/(m2 s))

k :

Reaction rate coefficient of CO2 with absorbent (m3/mol s)

L :

Length of the fiber (m)

m :

Physical solubility (–)

n :

Number of fibers

P :

Pressure (Pa)

Qshell :

Gas flow rate (ml/min)

Qtube :

Liquid flow rate (ml/min)

r 1 :

Tube inner radius (m)

r 2 :

Tube outer radius (m)

r 3 :

Shell inner radius (m)

r :

Radial coordinate (m)

R :

Module inner radius (m)

R i :

Overall reaction rate of any species (mol/m3 s)

Re :

Reynolds number (–)

t :

Time (s)

T :

Temperature (K)

T l :

Liquid temperature (K)

T g :

Gas temperature (K)

u :

Average velocity (m/s)

U g :

Gas velocity (m/s)

U l :

Liquid velocity (m/s)

V :

Velocity in the module (m/s)

V z-shell :

Z velocity in the shell (m/s)

V z-tube :

Z velocity in the tube (m/s)

x p :

Constant used in (29) (–)

x w :

Constant used in (30) (–)

z :

Axial coordinate (m)




Volumetric flow rate (m3/s)




Module volume fraction


Loading of CO2 in amine (kmol of CO2/kmol of amine)

\( \upeta \) :

CO2 removal efficiency


Gas viscosity (Pa.s)


Density (kg/m3)


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Correspondence to Azam Marjani.

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Shirazian, S., Marjani, A. & Rezakazemi, M. Separation of CO2 by single and mixed aqueous amine solvents in membrane contactors: fluid flow and mass transfer modeling. Engineering with Computers 28, 189–198 (2012).

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  • Gas separation
  • Membrane contactor
  • CFD
  • Numerical simulation
  • Mass transfer