13C-NMR study of acid dissociation constant (pKa) effects on the CO2 absorption and regeneration of aqueous tertiary alkanolamines

We have studied the formation rates of chemical species such as CO32-/HCO3-, amine/protonated amine, and carbonate/protonated carbonate in the course of CO2 absorption at room temperature and concentration changes after CO2 release upon heating at 93 degrees C for 30 min for aqueous solutions of 12 kinds of tertiary alkanolamines using C-13-NMR spectroscopy. A positive linear correlation was found between the CO2 capture rates of alkanolamines having a normal hydroxyalkyl group and their pKa values. The CO2 capture rates of alkanolamines having a branched hydroxyalkyl group were lower than those in this relationship. The CO2 release amount of each tertiary amine increased with decreasing pKa, as a general trend. N-ethyldiethanolamine (EDEA) showed the largest CO2 release amount and a moderately high rate of CO2 absorption. (C) 2013 The Authors. Published by Elsevier Ltd.