Phase equilibria in water containing binary systems from molecular based equations of state

This paper presents a study of phase equilibria for water + carbon dioxide, water + nitrogen and water + n-alkane binary mixtures using the CPA, SAFT and PC-SAFT molecular-based equations of state together with a simple monoparametric mixing rule. These systems have Type III phase behaviour according to the Van Konynenburg classification, with the critical line having a temperature minimum and extending to temperatures above the water critical temperature, with gas–gas immiscibility of the second kind at high pressures. We consider different association models for water and their influence upon phase equilibria correlations. These models predict the general shape of the global phase diagrams of these mixtures qualitatively using a single binary interaction parameter for the whole temperature range. However, the simultaneous prediction in a quantitative way of critical loci, three-phase equilibria and equilibrium compositions is only possible with the PC-SAFT model. We consider transferable binary interaction parameters for n-alkane containing series.