Quantum Mechanical and Molecular Dynamics Simulations of Dual-Amino-Acid Ionic Liquids for CO2 Capture

Global warming is occurring because of emission of greenhouse gases due to human activities. Capture of CO2 from fossil-fuel industries and absorption of CO2 for natural gas sweetening are crucial industrial tasks to address the threat from greenhouse gases. Amino acid ionic liquids (AAILs) are used for reversible CO2 capture. In this study, the effect of CO2 chemisorption on tetramethylammonium glycinate ([N-1111][GLY]), tetrabutylammonium glycinate ([N-4444] [GLY]), and 1,1,1-trimethylhydrazinium glycinate ([aN(111)][GLY]) were analyzed using density functional theory (DFT) and molecular dynamics (MD) studies. Density functional theory studies predicted different reaction pathways for CO2 absorption on [GLY] and [aN(111)](+). The activation energy barriers for CO2 absorption on [GLY](-) and [aN(111)](+) are 52.43 and 64.40 kJ/mol, respectively. The MD results were useful for mimicking the reaction mechanism for CO2 absorption on AAILs and its effect on physical properties such as the fractional free volume, diffusion coefficient, and hydrogen bonding. Dry and wet conditions were compared to identify factors contributing to CO2 solubility and selectivity at room temperature and elevated temperature. Hydrogen bonding between ion pairs was used to understand the increase in viscosity after CO2 absorption. The MD studies revealed that glycinate and related products after CO2 absorption contribute the most to the increase in viscosity.