A Generalized Antoine Equation to Estimate Vapor Pressure Predicted By the SRK Equation

The Soave-Redlich-Kwong (SRK) equation of state may be used to predict vapor pressure for any substance, but the calculations require a complex algorithm. A generalization of the simple Antoine equation replicates vapor pressure predictions of the SRK equation. This is done by introducing two similarity variables, adjusted temperature denoted by η and adjusted pressure denoted by Ψ. The goal of this project was to further develop this generalized Antoine equation. The first improvement used a computer code written in the Maple® programming language to search for generalized Antoine constants (A, B, and C) which more closely fit the SRK vapor pressure predictions. Four distinct sets of constants fit the vapor pressures within 0.05 percent for adjusted temperatures from 1.0, the critical point, down to 0.15. The second improvement was finding a single equation for each of the Antoine constants as a function of the upper limit of a user-specified adjusted temperature range. Using ranges of width 0.20, each of the constants was given by a single polynomial equation for adjusted temperatures as low as 0.40.