In this work, CO2 capture from a CO2/N-2 mixture was investigated in a membrane gas absorption (MGA) process experimentally and theoretically. 2-Amino-2-methyl-1-propanol (AMP) and piperazine (PZ) as activators were added into met hyldiethanolamine (MDEA) solution, respectively, to form two aqueous solutions of activated MDEA. The experiments of CO2 absorption into the activated MDEA aqueous solutions were carried out in a hollow fiber module. The activated mechanisms which combined chemical reaction mechanisms and a shuttle mechanism were presented to explain the activation phenomena in the course of gas-liquid mass transfer. A mathematical model was developed to simulate the mass-transfer behavior of the MGA. Both experimental and simulation results show that, the activated MDEA solutions can maintain lower CO2 concentration of gas outlet of the module with an increase of liquid CO2-loading of liquid inlet as compared with the non-activated MDEA solution. The mass transfer can be effectively enhanced in MGA for CO2 capture when a little amount activators are added into the MDEA solution. Activator PZ has an advantage over activator AMP in mass-transfer enhancement of MGA. The mass-transfer fluxes of the activated MDEA solutions are significantly higher than that of MDEA solution. Effects of operation conditions such as gas and liquid flow rates on mass-transfer enhancement are limited. The model simulation is validated with experimental data. (c) 2006 Elsevier B.V. All rights reserved.