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 ([N₁₁₁₁]­[GLY]), tetrabutylammonium glycinate ([N₄₄₄₄]­[GLY]), and 1,1,1-trimethylhydrazinium glycinate ([aN₁₁₁]­[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 [aN₁₁₁]⁺. The activation energy barriers for CO₂ absorption on [GLY]⁻ and [aN₁₁₁]⁺ 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