Theoretical and experimental studies of membrane wetting in the membrane gas–liquid contacting process for CO 2 absorption

Abstract

A systematic simulation has been carried out in membrane contactors to study CO 2 capture by water and diethanolamine (DEA) aqueous solutions from a CO 2/N 2 mixture under the wetted and the non-wetted operation modes. Two types of microporous hollow fiber membrane modules made of polypropylene (PP) and polyvinylidene fluoride (PVDF) hollow fibers were used to conduct CO 2 absorption experiments. The corresponding experimental data were used to verify simulated results. Experimental study showed that the membrane wetting could not be completely avoided especially in the case of chemical absorption. Both experimental and theoretical study disclosed that the membrane wetting would result in a significant drop of CO 2 flux. The simulation results further revealed that for the physical absorption of CO 2 by water, the proportion of membrane phase resistance in the overall mass transfer resistance increased from less than 5 to about 90% when the operation mode was shifted from non-wetted to wetted. As for the chemical absorption, analysis on the mass transfer resistance revealed that the ratio of the membrane resistance increased sharply from 10 to 70% when only 10% membrane length was wetted. With the introduction of an extra resistance caused by the membrane wetting, the mass transfer in the wetted membrane phase finally became the rate-controlling step. It was not as effective to enhance the CO 2 flux by increasing the inlet gas velocity or the liquid velocity as in the non-wetted mode of operation.