Molecular Dynamics Simulation Study on CO2 Physical Absorption Mechanisms for Ethylene-Glycol-Based Solvents Using Free Energy Calculations
Molecular mechanisms of CO2 physical absorption are significant for the development of higher-performance CO2 absorbents. In this study, the free energy profiles for CO2 approaching several types of ethylene glycol (EG)-based solvent molecules and their derivatives (diols, ethers, and alkanes, etc.) were evaluated using molecular dynamics simulations. A desolvation barrier appeared in the free energy profiles in the pure component solvent, corroborating the negative contribution of a void effect on CO2 affinities. The profiles in vacuum were also estimated to investigate the functional group effects in a constituent solvent molecule. The profiles for the EG-based solvent molecules showed similar minimum values to their derivative diols, while the values for their derivative ethers and alkanes were markedly higher. CO2 solubility is certainly determined by two major factors: the specific CO2 affinities of the constituent hydroxyl groups and a steric void effect near an absorbed CO2 molecule.