Computational study on amino acid base ionic liquids (AAILs) for gas separation using COSMO-RS

Abstract. Greenhouse gases, especially carbon dioxide (CO2), are a major contributor to global warming and poses a significant threat to the environment. Amino Acid based Ionic Liquids (AAILs) show strong potential as durable solvents with high CO2 capture capacity, making them well-suited for long-term, large-scale applications to address this issue. This work is focused on the absorption study of various gases, such as methane (CH4), nitrogen (N2), oxygen (O2), and CO2 in AAILs using computational chemistry and molecular simulations. Capturing more gases involves trapping them within molecular structures, stabilizing them for future use or storage, and enabling efficient purification for various applications. Hereby, eighteen types of food grade AAILs, including 1-Butyl-3-methylimidazolium [BMIM], Tetrabutylphosphonium [P(C4)4] cations along with nine amino acids [AAs] (Alanate [ALA], Histidinate [HIS], Glycinate [GLY], Prolinate [PRO], Arginate [ARG], Lysinate [LYS], Leucinate [LEU], Valinate [VAL] and Methionate [MET]) anions are selected. Henry constant (KH), activity coefficient (ϒ), and sigma (σ) profiles and potentials are predicted through the Conductor-like Screening Model for Real Solvents (COSMO-RS) model for potential solvents using simulations studies. The value of KH is inverse to the solubility of gases in AAILs. COSMO-RS results suggest that the ILs with cation [P(C4)4] exhibit improved CO2 capture capacity (with K_H=62 to 72) as compared to [BMIM] cation (K_H=98 to 130) used in AAILs. The top three [P(C4)4] based ILs are selected to predict the solubility of a mixture of gases, comprising of CH4, N2, O2, and CO2. The phosphonium-based ILs possess a significant capacity for CO2 capture and can be effectively utilized in various industrial sectors. The package of COSMO-RS enables a reliable pre-experimental forecast within 1–10% relative deviation (RD), which also satisfies the practical application in research and development.