Gas phase mass transfer in falling film microreactors (FFMRs) with the absorption of CO2 into aqueous solutions of NaOH was investigated. The overall gas-phase mass transfer coefficient increases with NaOH concentration

but decreases as the concentration of CO2 increases. There exists an entrance effect

hindering the mass transfer

which is caused by the dead volume for gas-phase flow in the gas chamber in FFMRs. The entrance effect has a larger impact in a shorter FFMR owing to the relatively large dead volume with respect to that of gas chamber. A decrease in the depth of gas chamber facilitates the mass transfer process. Therefore

the gas-phase entrance or geometry of the gas chamber should be designed appropriately to reduce the entrance effect and improve the mass transfer.