Mass-Transfer Characteristics of CO2 Absorption into Aqueous Solutions of N-Methyldiethanolamine + Diethanolamine in a T-Junction Microchannel

The mass-transfer process of CO2 absorption into aqueous solution of N-methyldiethanolamine (MDEA) + diethanolamine (DEA) in a T-shaped microchannel was studied using a high-speed camera. The effects of two-phase flow rates and diethanolamine concentration on CO2 absorption efficiency, liquid mass-transfer coefficient kL, specific surface area a, and volumetric mass-transfer coefficient kLa were investigated under slug flow. Results showed that the CO2 absorption efficiency increased with the increase of DEA concentration and liquid flow rate, and decreased with increasing gas flow rate. The kL increased with the increase of liquid flow rate and DEA concentration, while it was insensitive to gas flow rate. For a given liquid flow rate, both kLa and a increased rapidly with gas flow rate and then the trend was slowing down. The increase of liquid flow rate and DEA concentration led to the decrease of the a, whereas the kLa was improved. The enhancement of the liquid flow rate on kL and kLa was more obvious under low DEA concentration. An empirical correlation for predicting the volumetric mass-transfer coefficients kLa was proposed by taking the Hatta number Ha into account for characterizing the effect of chemical reaction.