Monoethanolamine (MEA) aqueous solution has remarkable absorption capability for acid gas such as CO2 and has a potential application prospect in the field of gas separation and purification. Absorption temperature

gas flow rate and MEA concentration were taken into account as influence factors on reaction rate by monitoring the variation of pH in MEA aqueous solution. A conception called specific activity describing the absorption performance of the solution was introduced. The descending rate of pH decreased

saturation time was extended and the pH of final saturation state increased with the increase of solution concentration. With increasing temperature

the descending rate of pH increased and saturation time was shortened

but both of them would maintain a relatively stable value when temperature was high enough. When gas flow rate of CO2 increased

the pH of solution was gradually reducing at a faster rate

and finally

remained stable. The pH of saturated solution reached the lowest level at the flow rate of 70 ml·min-1. The monitoring method was easy to operate and the result was highly accurate so that it could provide a reference for development of CO2 absorption solutions.