Estimation of Infinite Dilution Activity Coefficients in Aqueous Mixtures via Molecular Simulation

 

Joseph T. Slusher
Physical and Chemical Properties Division Chemical Science and Technology Laboratory

Molecular dynamics simulations are employed to calculate infinite dilution activity coefficients of water and methanol in binary water/methanol mixtures using a variant of the Kirkwood coupling parameter method.

Differences in residual Gibbs free energies are obtained as integrals over ensemble averages of the derivatives of total potential energy with respect to simple functions of the intermolecular potential energy parameters. The calculated limiting activity coefficients are compared with the experimental values at the same temperature obtained by direct measurement of the water/methanol binary and via extrapolation from vapor-liquid equilibria data.