CO 2 absorption by piperazine promoted aqueous ammonia solution: absorption kinetics and ammonia loss

Aqueous ammonia (NH 3 ) solution has been proposed as a promising absorbent for post‐combustion capture of carbon dioxide (CO 2 ). However, when aqueous NH 3 is used alone, the capture process suffers from a low CO 2 absorption rate and high NH 3 loss. In this study, we measured CO 2 mass transfer coefficients and NH 3 loss rate in a wetted wall column study of CO 2 absorption in piperazine (PZ) promoted aqueous NH 3 solution, at NH 3 concentrations of 0.59–4.12 mol/L (M), CO 2 loadings (molar ratio of CO 2 /NH 3 ) of 0 to 0.5, temperatures of 283.15–298.15 K. The second‐order rate constants for the reactions of CO 2 with PZ and NH 3 , which are determined based on the kinetic results from the wetted wall column, agree reasonably well with published values. Addition of PZ to aqueous NH 3 can significantly increase mass transfer coefficients of CO 2 in aqueous NH 3 , but at the expenses of an increase in NH 3 loss. The enhancement by addition of PZ is due to the fast reaction of CO 2 with PZ and PZ carbamate. However, addition of PZ to aqueous NH 3 increases the concentration of free NH 3 in the solvent, thereby increasing NH 3 loss.