EQUATION OF STATE FOR SMALL, LARGE, POLYDISPERSE, AND ASSOCIATING MOLECULES - EXTENSION TO FLUID MIXTURES

Statistical associating fluid theory (SAFT) has been extended to mixtures using rigorous statistical mechanical expressions for the hard-sphere, chain, and association terms. In contrast to previous equations of state, only the dispersion term requires mixing rules (averaging equations for SAFT parameters). We use two approaches to deriving the mixing rules, a van der Waals one-fluid approximation (vdW1) rooted in conformal solution theory and a volume-fraction (vf) approximation similar to group-contribution equations of state. We test these approaches on 60 phase equilibrium data sets for asymmetric (small + large) and associating binaries. While both sets of mixing rules, vdW1 and vf, are found to be adequate away from the critical region, the vf predictions are found to be more accurate near the critical region.