Predicting Henry's Law constants of volatile organic compounds present in bourbon using molecular simulations.

Abstract

Henry’s Law describes the partitioning of molecules into liquid and gas phases at low concentrations. Henry’s Law, which is based upon a species-dependent constant and the gas phase partial pressure, is useful for predicting phase behavior of dilute solutes. However, Henry’s Law constants are difficult to measure experimentally or to predict using structure-property or thermodynamic models. Herein, molecular simulations were used to calculate Henry’s Law constants for 18 volatile organic compounds (VOCs) present in bourbon. The novel simulations analyzed solvation thermodynamics of small organic molecules in 120 proof ethanol. A fast-growth non-equilibrium free energy method was used in which the VOC of interest was removed or added, thus affecting the overall thermodynamic properties of the system. Work distributions for forward and reverse transitions were analyzed. The Gibbs free energy of solvation for each VOC was thus estimated, which is directly related to the chemical potential of the VOC, thus providing access to Henry’s law constants. Results of models were compared to values of aqueous solvation from literature. The results of the simulations were precise over multiple iterations, but a lack of experimental data with respect to solvation in ethanol-water solutions presents difficulties in assessing the accuracy of presented models.