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

Abstract We have studied the formation rates of HCO 3 – /CO 3 2– , amine/protonated amine, carbamate/protonated carbamate, and carbonate/protonated carbonate in the course of CO 2 absorption at room temperature, and composition changes and CO 2 release upon heating at 93 °C for 30 min for aqueous solutions of 9 kinds of alkanolpiperidines using 13 C-NMR spectroscopy. The p K a values of these alkanolpiperidines were measured. The initial CO 2 capture rates of alkanolpiperidines do not depend on their p K a values, which is quite different from general trends of aqueous amine absorbents. The CO 2 release amount of each alkanolpiperidine increased with decreasing p K a, as a general trend. The CO 2 release amounts of 1-HE-PD, 2-HM-1-M-PD, 3-HM-1-M-PD, and 4-HM-1-M-PD increased with increasing concentrations.