We have studied the formation rates of HCO3 -/CO3 2-, amine/protonated amine, carbamate/protonated carbamate, and carbonate/protonated carbonate in the course of CO2 absorption at room temperature, and composition changes and CO2 release upon heating at 93 °C for 30 min for aqueous solutions of 9 kinds of alkanolpiperidines using 13C-NMR spectroscopy. The pKa values of these alkanolpiperidines were measured. The initial CO2 capture rates of alkanolpiperidines do not depend on their pKa values, which is quite different from general trends of aqueous amine absorbents. The CO2 release amount of each alkanolpiperidine increased with decreasing pKa, as a general trend. The CO2 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.
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