Mass transport phenomena in the membrane absorber for carbon dioxide separation were studied. The membrane absorbers used for the experiment are the hollow fiber membrane modules for microfiltration(MF) and ultrafiltration(UF). And the material of the fibers in the module is polysulfone. The membrane absorber has the advantage of large contact area between the waste gas and the absorbent. However, the membrane absorber inevitably include the disadvantage of additional mass transfer resistance. The membrane absorber has resistances, such as gas-phase resistance, and resistances from the liquid-phase and the membrane-phase. Generally, the first resistance is negligible as compared with the others. And the resistance from the liquid-phase is of the same order as that in the conventional packed column. Thus, the key to the mass transfer problem in a membrane absorber is the resistance from the membrane-phase. The liquid-phase mass transfer resistance was calculated from Graetz-Leveque equation, while the over-all mass transfer resistance was measured from the experiment. Then, the membrane-phase mass transfer resistance can be estimated from these two resistances. The order of magnitude of the membrane-phase mass transfer coefficient in this research is $10^{-7}$cm/sec while that of liquid-phase is $10^{-4}$cm/sec. It means that the dominant resistance in the membrane absorber is in the membrane itself. It is because the polysulfone hollow fiber membrane is partly wetted and the pores of the membrane are logged by water. The water penetration into the pores takes place by capillary force, so even marginal wetting of the fiber can result in the unexpected rapid increase in over-all mass transfer resistance. And the effective diffusivity was calculated from the membrane-phase resistance in order to show how fatal the resistance of the liquid-filled pore is. The order of magnitude of the effective diffusivity in the liquid-filled pore is $10^{-9}$㎠/sec. It is the conclusive evidence of mass transfer hindrance effect by the membrane wetting.
