13C-NMR Study of Acid Dissociation Constant (pKa) Effects on the CO2 Absorption and Regeneration of Aqueous Tertiary Alkanolamines

AbstractWe have studied the formation rates of chemical species such as CO3/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°C for 30min for aqueous solutions of 12 kinds of tertiary alkanolamines using 13C-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