Theoretical modeling of the mass transfer performance of CO2 absorption into DEAB solution in hollow fiber membrane contactor

Abstract

4-diethylamino-2-butanol (DEAB), as a novel tertiary amine, shows a promising potential for CO2 capture. In this study, the mass transfer performance of CO2 absorption into aqueous DEAB solution in a non-wetted and partially-wetted mode of hollow fiber membrane contactor (HFMC) was theoretically investigated in comparison with that of monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP). A 2D mathematical model based on finite element method (FEM) was established to solve the steady-state continuity equations for the shell, tube and membrane sides simultaneously. The influences of the operating parameters on the CO2 absorption flux in HFMC including liquid and gas velocity and CO2 partial pressure were comprehensively investigated. The numerical results show that the CO2 absorption flux can increase with the increasing liquid velocity and CO2 partial pressure, and slightly increases with the increasing gas velocity. Moreover, the CO2 absorption performance of aqueous DEAB solution was further compared with different amine solutions, which reveals that the CO2 absorption flux of DEAB is higher than those of DEA, MDEA and AMP, and is also comparable to MEA. The analysis on the mass transfer resistance indicates that the proportion of the membrane mass transfer resistance increased rapidly from 13.7% to 75.3% as membrane wetting ratio increased from 0% to 20%. Instead of the liquid phase, the mass transfer in wetted membrane phase becomes the rate-controlling step ultimately. The increase in the membrane wetting leads to the significant decrease in CO2 absorption performance with 49.4% and 80.5% decrease in CO2 absorption flux and the overall mass transfer coefficient at membrane wetting ratio of 5% and 50%, respectively. Based on the analysis on enhancement factor, it demonstrates that the chemical reaction between CO2 and DEAB for the non-wetted mode generally occurs in the intermediate fast-instantaneous regime and gradually transfers to the instantaneous regime with membrane wetting.