Free energy of solvation and Henry's law solubility constants for mono-, di- and tri-ethylene glycol in water and methane

Free energy of solvation (i.e. residual chemical potential) and Henry's law solubility constants were estimated for mono ethylene glycol (MEG), diethylene glycol (DEG) and triethylene glycol (TEG) with water and methane as solvents at both 298 K and 1 atm and at 283 K and 80 atm using molecular dynamics simulations. Three methods of calculating free energies of solvation were compared: free energy perturbation (FEP), thermodynamic integration (TI) and Bennett acceptance ratio (BAR) method. The solubility constants were estimated based on the obtained free energies and were compared to the previously reported values. We found that free energy differences obtained using the three applied methods agreed very well. For both MEG and DEG the estimated solubility constants were within the same order of magnitude as previously reported solubility constants and therefore in good agreement. The estimated solubility constants of TEG were found to be about an order of magnitude smaller than the lowest reported value, and would still yield a reasonable estimate of residual chemical potential due to the logarithmic dependence.

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