Quantitative analysis method for absorption mechanism and energy consumption of CO₂ capture by amino acid ionic liquids

Amino acid ionic liquids (AAILs) are attractive candidates for CO₂ capture due to their high solubility for CO₂. Quantitatively analyzing the interaction of amino groups in AAILs with CO₂ and evaluating the energy consumption of CO₂ capture is critical to the molecular design of ideal AAILs. In this work, a thermodynamic model based on the cubic plus association equation of state was proposed to calculate the contribution from the chemical reactions between various stoichiometric ratios of CO₂ and AAIL (N_m:n, m:n is stoichiometric ratio) on CO₂ solubility. The results show that the larger contribution to the CO₂ solubility in [Glu], [Tyr] and [Gln]-IL with strong polar groups is derived from association scheme N_1:2, while the N_1:1 association interaction is the dominant contribution of [Gly], [Ala], [Val] and [Pro]-IL with hydrogen atom or short alkyl side chains, and [VBIm]-IL with multiple amino groups. The N_2:1 association interaction is primary between CO₂ and [Cho][His] or [Cho][Arg]. Besides, the contributions of these association effects are greater than that of dispersion and repulsion to CO₂ solubility. Then, the solvent cyclic capacity and regeneration energy of AAILs in the pressure swing and temperature swing CO₂ capture system were estimated. More amino groups result in higher regeneration energy consumption and do not necessarily increase solvent cyclic capacity. Among the studied AAILs, [Cho][Gly] which exhibits high cyclic capacity and low energy consumption has great potential in CO₂ capture solvent.