International Journal of Thermophysics, Vol. 9, No. 5, 1988 Phase Equilibria of Associating Fluids of Spherical and Chain Molecules 1 G. Jackson, 2 W. G. Chapman, 2 and K. E. Gubbins 2 The development of equations of state for strongly associating fluids and fluid mixtures has proved over the years to be a difficult problem. The first-order perturbation theory solution of a resummed cluster expansion has been used to investigate the effect of molecular associations on the critical and phase coexistence properties of fluids with one and two off-center attractive sites. The individual molecules are represented by hard-sphere repulsive cores with square-well attractive sites. Model systems comprising chains of hard spheres have also been examined. Isothermal-isobaric Monte Carlo simulations of hard-sphere fluids with one and two attractive sites are shown to be in good agreement with the results of the theory. A simple van der Waals mean-field term is also added to account for the dispersion forces. The critical points and phase equilibria of the associating fluids are determined for various values of the strength and range of the attractive site, as well as for different chain lengths. The theory can treat fluids with strong hydrogen-bonding associations such as the carboxylic acids the aliphatic alcohols, hydrogen fluoride, water, etc. KEY WORDS: associating fluids; computer simulations; equation of state; mixtures; perturbation theory; phase equilibrium. 1. INTRODUCTION Binary and ternary mixtures of industrial interest often include components which associate strongly with themselves and/or each other. Examples of these systems are the aliphatic alcohol-alkane, alkane-water, alcohol-water, alcohol-aromatic, and water-aromatic mixtures; typical ternary systems are the alkane-alcohol-water and aromatic-alcohol-water 1 Paper presented at the Tenth Symposium on Thermophysical Properties, June 20-23, 1988, Gaithersburg, Maryland, U.S.A. 2 School of Chemical Engineering, Cornell University, Ithaca, New York 14853, U.S.A. 769 0195-928X/88/0900-0769506.00/0 9 1988 Plenum Publishing Corporation