Experimental evaluation of highly efficient primary and secondary amines with lower energy by a novel method for post-combustion CO2 capture

In this work, a novel method in terms of reaction energy was proposed to evaluate the potential amine absorbents for post-combustion CO2 capture, including two key parameters, i.e. the molar Gibbs energy change (ΔrGm) of proton combination with amine and the molar reaction enthalpy (ΔrHm) of protonated amine dissociation into amine and proton, which are calculated by the Van’t Hoff equation. Firstly, the equilibrium acid dissociation constant (Ka) of seven primary and secondary amines were experimentally determined at 293–323 K. The calculated ΔrGm and ΔrHm values obtained by the novel method indicated that the 2-(ethylamino)ethanol (EAE) and 2-(methylamino)ethanol (MAE) were the alternative promising absorbents among the seven tested amines, with a relatively low ΔrGm of about −57.0 kJ/mol and ΔrHm of 49.7 kJ/mol. In addition, seven amine solutions with molar concentration of 2.5 M and 5.0 M were investigated by the rate-based fast screening method to validate the reliability and applicability of the novel method. The comprehensive comparison of the absorption rate, desorption rate, CO2 equilibrium solubility and cyclic capacity, also demonstrated the same conclusion that EAE and MAE solutions presented good CO2 capture performances. The 2.5 M and 5.0 M EAE solutions obtain the highest energy efficiency for CO2 capture with the highest cyclic capacity, which is about 52.9% and 32.3% higher than those of Monoethanolamine (MEA) solution, respectively. Additionally, the structure-activity analysis of seven amines suggested that the addition of hydroxyl group can obviously decrease the absorption rate and energy consumption of amine solution for CO2 removal, the alkyl group addition on or close to amino group with steric hindrance is favorable for the CO2 capture performance, while the addition of methyl group on amine molecular without steric hindrance can reduce the CO2 cyclic capacity. What’s more, four tertiary amines were also investigated by using these two approaches, and the compared results further validated the accuracy and applicability of the proposed novel method.