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

Abstract

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 ¹³C-NMR spectra and reaction kinetics. The absorption rate (α′_CO2) was revealed to correlate strongly with the reaction rate constant (k₂) of the CO₂-amine second order reaction. A linear equation, log₁₀(k₂)=A·α′_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(k₂)=0.436pK_a+12.92−5,379/T.