title: Molecular Simulations of CO2 and H2 Solubility, CO2 Diffusivity, and Solvent Viscosity at 298 K for 27 Commercially Available Physical Solvents
author: Wei Shi
description: CO2 and H2 solubilities, CO2/H2 solubility selectivities, CO2 diffusivities, and solvent viscosities in 27 commercially available physical solvents at 298 K were calculated from molecular simulations using the CHARMM36 all-atom force field for most solvents, and the simulation results were compared with available experimental data. The van der Waals radius parameters for solvents were slightly tuned to reproduce the experimental solvent density. The simulated CO2 solubilities are comparable with the experimental data, with an average absolute difference of 28%. For the homologous compounds containing the −(OCH2CH2)– repeat unit, both simulated and experimental data show that CO2 solubility decreases when the number of repeat units is increased; CO2 solubilities in these homologous compounds exhibit almost a perfect positive linear correlation with the solvent free-volume fractions. The simulated H2 solubilities and CO2/H2 solubility selectivities are also comparable with the experimental data, with differences of 22% and 17%, respectively. The H2 solubilities in all solvents studied in this work correlate very well with the solvent free-volume fractions, exhibiting a positive linear correlation coefficient of 0.84. Additionally, simulations show that CO2 solubility decreases when the temperature is increased. In contrast, H2 solubility increases at elevated temperature, which is partly due to the increased solvent free-volume fraction at elevated temperature. Finally, although the viscosity difference tends to be large (30%–246%) between simulation and experiment, both simulated and experimental data exhibit a similar solvent viscosity trend. Furthermore, simulations show that CO2 diffusivities in solvents are very strongly correlated with the solvent viscosities and the relationship between them is given by DCO2 = (2.6 ± 0.3) × 10–9/ηsolvent0.59 ± 0.03.