Chemical Enhancement for CO2 Absorption into Dilute Aqueous Amine Solutions

Abstract

Chemical enhancement factors for CO2 absorption into dilute aqueous MEN/DEA solutions in a batch stirred-cell absorber were experimentally determined over a wide range of CO2 loadings. The experimental data are used to examine the validity of two promotion mechanisms: the zwitterion mechanism, by which the carbamate formation is the sole main reaction occurring in the liquid, and the bulk-equilibrium mechanism, by which both the carbamate formation and the carbamate hydrolysis are two fast main reactions to enable the chemical equilibrium to prevail in the bulk-liquid. The results reveal that the zwitterion mechanism satisfactorily predicts the experimental data for CO2 loadings below 0.3, while the bulk-equilibrium mechanism is more competent in describing those for CO2 loadings larger than 0.5. A detailed rigorous thermcx1ynamic simulation shows that the equilibrium extent of the carbamate hydrolysis, which generates free amine in the bulk and hence promotes absorption, increases with the decrease of the initial amine concentration and with the proceeding of CO2 loadings. The experimental re-suits of absorption, therefore, indicate that the extent of the carbamate hydrolysis is insignificant in systems with low CO2 loadings however becoming significant in higher C2 loading systems. The difference between the promotion mechanisms for the absorption of CO2 by dilute aqueous NH3 solutions as previously reported by us and that by MENDEA solutions in this work is also discussed .