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

Highlights • A novel method of high-efficiency amine selection was proposed for CO 2 capture. • Reaction energy of Δ r G m and Δ r H m was applied to evaluate amine absorbents. • The EAE and MAE were selected as the promising absorbents for CO 2 removal. • Eleven amine solutions were investigated by the rate-based screening method. • The acid dissociation constants of eleven amines were determined at 293–333 K. Abstract In this work, a novel method in terms of reaction energy was proposed to evaluate the potential amine absorbents for post-combustion CO 2 capture, including two key parameters, i.e. the molar Gibbs energy change (Δ r G m) of proton combination with amine and the molar reaction enthalpy (Δ r H m) of protonated amine dissociation into amine and proton, which are calculated by the Van't Hoff equation. Firstly, the equilibrium acid dissociation constant (K a) of seven primary and secondary amines were experimentally determined at 293–323 K. The calculated Δ r G m and Δ r H m 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 Δ r G m of about −57.0 kJ/mol and Δ r H m 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, CO 2 equilibrium solubility and cyclic capacity, also demonstrated the same conclusion that EAE and MAE solutions presented good CO 2 capture performances. The 2.5 M and 5.0 M EAE solutions obtain the highest energy efficiency for CO 2 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 CO 2 removal, the alkyl group addition on or close to amino group with steric hindrance is favorable for the CO 2 capture performance, while the addition of methyl group on amine molecular without steric hindrance can reduce the CO 2 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. [ABSTRACT FROM AUTHOR]