In order to gain abetter understanding Of CO2 absorption in a hollow fiber membrane contactor. theoretical simulations have been performed to describe CO2 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, flux increases with the liquid velocity, while the inlet gas velocity has no significant effect on CO2 flux. The mass transfer resistance mainly exists on the liquid side. In the case ofchemical absorption, the CO2 flux is significantly influenced by the inlet gas velocity while the liquid velocity has a limited effect. The analyses of CO2 concentration profiles in the gas and liquid phases as well as DEA concentration profile in the liquid phase reveal that CO2 concentration in the gas phase serves as the rate-determining factor for the reaction between CO2 and DEA. The significant CO2 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, absorption when the module length is longer than L-eff. (c) 2005 Elsevier B.V. All rights reserved.