A New Approach to Vapor-Liquid Equilibrium Property Prediction from Cubic Equations of State

Vapor pressure prediction is important in a broad range of industrial applications, but general methods applying equations of state require iterative algorithms. In this work, a novel method for vapor pressure calculations was applied to the Soave-Redlich-Kwong (SRK) cubic equation of state. This allowed for an exact solution for the vapor pressure of any substance with a dimensionless expression combining reduced temperature and a function of the acentric factor. Several useful variables in vapor-liquid equilibrium – including reduced phase densities, compressibility, and the ratio of reduced pressure to reduced temperature – could be expressed as functions of this single dimensionless variable. Exact results could be derived for an inverse problem beginning with reduced phase densities as independent variables. When the standard independent variables of temperature and acentric factor were combined with empirical relationships for reduced phase densities, vapor pressure was approximated within 0.05 percent deviation from the exact results for acentric factors from 0.05 to 0.97 and reduced temperatures from 0.16 to 0.98.