Prediction of Henry's constants for supercritical fluids using a van der Waals equation of state

Henry's constants for supercritical solutes are usually estimated from the infinite dilution activity coefficient and a hypothetical standard state for the solute as a pure Liquid. The fugacity at this hypothetical standard state is estimated by extrapolation of the solute's vapor pressure curve beyond the critical point. Here, an alternative approach is used, where Henry's constant of a solute can be calculated from the fugacity (or vapor pressure) of the solvent and the ratio of solute and solvent liquid-phase fugacity coefficients. This approach eliminates the need for a hypothetical standard state and results in expressions that are analogous to Regular Solution Theory and the van Laar equation. A simple, modified van der Waals equation of state (mvdW EOS) is developed and used to demonstrate the utility, and limitations, of this approach. (C) 1998 Elsevier Science B.V.