Protonation constants and thermodynamic properties of amines for post combustion capture of CO2

Abstract The leading process for the post combustion capture (PCC) of CO 2 from coal-fired power stations and hence reduction in greenhouse gases involves capture by aqueous amine solutions. Of the reactions that occur in solution, which include CO 2 hydration, de-protonation of carbonic acid, amine protonation and carbamate formation, the protonation of the amine in the absorber and its subsequent de-protonation in the stripper involve the greatest enthalpy changes. In this study, protonation constants (reported as log 10 K prot ) of selected series of primary, secondary and tertiary alkanolamines/amines over the temperature range 288–318 K are reported. Selected series studied involve primary, secondary and tertiary mono-, di- and tri-alkanolamines, secondary amines including heterocyclic species, and both –CH 2 OH and –CH 2 CH 2 OH substituted piperidines. van’t Hoff analyses have resulted in the standard molar enthalpies, Δ H m o , and molar entropies, Δ S m o , of protonation. Trends in Δ H m o are correlated with systematic changes in composition and structure of the selected series of amines/alkanolamines, while Δ H m o –Δ S m o plots generated linear correlations for the mono-, di-, and tri-alkanolamines, the –CH 2 OH and –CH 2 CH 2 OH substituted piperidines, and the alkylamines. These relationships provide a guide to the selection of an amine(s) solvent for CO 2 capture, based on a greater difference in log 10 K prot between the absorber and stripper temperatures.