Density-based UNIFAC model for solubility prediction of solid solutes in supercritical fluids

Abstract

A new theoretical expression of group interaction parameter as a function of fluid density was put forward in this work. The group interaction parameters between the supercritical solvents (carbon dioxide, ethane, fluoroform and chlorotrifluoromethane) and the functional groups of solutes at reference fluid density were presented, which exhibit good compatibility with the UNIFAC Vapor-Liquid Equilibrium (VLE) group interaction parameters. For the solid Solute + C2H4 systems, satisfactory solubility data representation results can be obtained using the UNIFAC VLE group interaction parameters of “CC”. This density-based UNIFAC model was examined for the solubility of 20 solid solutes in 5 supercritical solvents (51 systems, 1111 data points); the Average Relative Errors (ARE) in solubility prediction are 19.1%, 18.7%, 21.6%, 20.4% and 12.8% for CO2, C2H6, C2H4, CHF3 and CClF3 correspondingly. In the case of each UNIFAC group being one molecule, the density dependent expression of group interaction parameter derived in this model may be applicable to other activity coefficient models (UNIQUAC, Wilson, NRTL) containing binary interaction parameters for solubility prediction of solids in supercritical fluids.