Equation of state for square-well chain molecules with variable range, extension to associating fluids

Abstract

The equation of state developed in our previous work for square-well chain molecules with variable range (SWCF-VR EOS) was further extended to associating fluids. The association contribution is directly calculated by Liu et al.’s association equation which was proposed based on the sticky-shield method. For the real pure associating fluids, the SWCF-VR EOS has six temperature-independent model parameters obtained by fitting the saturated pressures and/or liquid molar volumes. The results are satisfactory with the overall average absolute deviations (AADs) of 0.76% and 0.75% for saturated vapor pressures and liquid molar volumes of 78 pure fluids in wide temperature ranges. The heat of vaporization for 17 associating fluids were well predicted using these molecular parameters. The good relations between the molecular parameters and the molecular weights were observed. By using a simple mixing rule with only one adjustable binary interaction parameter k ij for the cross well depth ɛ ij , the SWCF-VR EOS can satisfactorily reproduce the vapor–liquid equilibria (VLE) of binary mixtures at reduced and elevated pressures containing self- and cross-associating interaction. Furthermore, the VLE for ternary mixtures can be successfully predicted by using the obtained binary interaction parameters.