SOLUBILITY MODELING OF SOLIDS IN SUPERCRITICAL FLUIDS USING THE KIRKWOOD-BUFF FLUCTUATION INTEGRAL WITH THE HARD-SPHERE EXPANSION (HSE) THEORY

The hard-sphere expansion (HSE) theory is incorporated in the Kirkwood-Buff fluctuation integral to predict solubilities of solids in supercritical carbon dioxide and ethylene. While an equation-of-state only for pure supercritical solvent is needed in the HSE model and, thus, there is no need to know the critical properties of solids, three adjustable parameters (two molecular size parameters sigma11, sigma12, and one dimensionless parameter alpha12) in the HSE model are determined to fit experimental solubility data. The results on the solubility prediction by the HSE model with the Peng-Robinson equation-of-state for pure component were better than the Peng-Robinson equation-of-state with the classical mixing rule in both cases: (1) when the molecular parameters in the HSE model and the binary interaction parameter k12 in the mixing rule were assumed to be temperature-dependent; and (2) when alpha12 and k12 were considered as temperature-dependent.