Korean Journal of Chemical Engineering, Vol.14, No.3, 184-191, 1997
Application of the Kirkwood-Buff solution formalism and the hard sphere expansion method with the modified mean density approximation to predict solubility of solutes in supercritical fluids
The Kirkwood-Buff solution theory to give the relations between macroscopic thermodynamic properties and the fluctuation integrals (Gij) was utilized to predict solubility of solutes in supercritical fluids. The solvent-solute fluctuation integral (G21) in the derivation for solubility of solute is expressed in terms of the solvent-solvent fluctuation integral (G11) using the hard sphere expansion (HSE) conformal solution method with the modified mean density approximation (MMDA) where the scaling factor (R12) represents the ratio of the first peak heights of the radial distribution functions for the mixture and the reference fluid having the mean density determined from the mean density approximation (MDA). The values of R12 were evaluated by considering it as an adjustable parameter and solving the Ornstein-Zernike equation with the hypernetted chain (HNC) closure, and were compared. It is shown that solubility can be evaluated with an equation of state for pure supercritical fluid, three molecular parameters, and the scaling factor (R12) without knowledge of critical properties of solutes, which can not be measured precisely for some organic solids. This model based on the molecular theory leads to better results in solubility calculations than both the Peng-Robinson equation of state with the classical mixing rule and the previous method with the original MDA instead of the MMDA. It might be due to the superiority of the MMDA over the original MDA.
Cochran HD, Lee LL, Pfund DM, "Structure and Properties of Supercritical Fluid Mixtures from Kirkwood-Buff Fluctuation Theory and Integral Equation Methods," Fluctuation Theory of Mixtures, Matteoli, E.E. and Manssori, G.A. eds., Taylor and Francis, New York, 1991
Ely JF, ACS Symp. Ser., 300, 331, 1986
Hansen JP, McDonald IR, "Theory of Simple Liquids," Academic Press, London, 1986
McHugh M, Paulaitis ME, J. Chem. Eng. Data, 25, 326, 1980
Moshen-Nia M, Modaress H, Mansoori GA, "A Simple Equation of State for Hydrocarbons and Other Compounds," Proceedings of the 1993 Annual Meeting of the Society of Petroleum Engineers, SPE Paper No. 26667. SPE, Richardson, TX, 1993
Tan RKZ, "A Study of the Pair Distribution Functions of Mixtures of Idealized Molecules Using Molecular Simulation," Ph.D. Dissertation, Rice University, 1987