In order to gain a better understanding of CO 2 absorption in a hollow fiber membrane contactor, theoretical simulations have been performed to describe CO 2 capture by distilled water and aqueous diethanolamine (DEA) solutions. The studies were focused on gas phase behaviors by taking the distributions of gas concentration and gas velocity along the flowing direction into account. The corresponding experiments were also carried out in a Celgard MiniModule to verify the simulated results.
In the case of physical absorption, both simulation and experimental results indicate that CO 2 flux increases with the liquid velocity, while the inlet gas velocity has no significant effect on CO 2 flux. The mass transfer resistance mainly exists on the liquid side. In the case of chemical absorption, the CO 2 flux is significantly influenced by the inlet gas velocity while the liquid velocity has a limited effect. The analyses of CO 2 concentration profiles in the gas and liquid phases as well as DEA concentration profile in the liquid phase reveal that CO 2 concentration in the gas phase serves as the rate-determining factor for the reaction between CO 2 and DEA. The significant CO 2 loss in the gas phase results in an interesting DEA concentration profile near the liquid-gas interface. There exists an effective module length L eff , which suggests that increasing the module length is not a useful approach to enhance CO 2 absorption when the module length is longer than L eff .