A Simple Method of Evaluating Alkanolamine Absorbents for Post-Combustion CO2 Capture

Carbon dioxide (CO2) capture by aqueous amine solutions has been developed to facilitate CO2 capture and storage (CCS) technology. In the present study, gas scrubbing tests were performed using twelve alkanolamine absorbents, including a variety of primary, secondary, and tertiary amines, with some hindered amines. The resulting absorption characteristics are discussed in the context of the pK(a) values of the amines as well as the C-13-NMR spectra and reaction kinetics. The absorption rate (alpha(')(CO2)) was revealed to correlate strongly with the reaction rate constant (k(2)) of the CO2- amine second order reaction. A linear equation, log(10)(k(2)) = A center dot alpha(')(CO2)+B, was derived for the aqueous amine solutions evaluated in the current study. For the experimental conditions of 20% CO2 gas and 2 mol/ L amine solution, the constants A and B were 0.0285 and -0.4564 for the primary and secondary amines, and 0.0107 and -0.3726 for the hindered amines, respectively. Furthermore, the correlation between the reaction rate constants and pK(a) values of the hindered amines could be expressed as ln(k(2)) = 0.436pK(a)+12.92-5,379/T.