A crossover equation of state for associating fluids

In this work we extend the crossover (CR) modification of the statistical-associating-fluid-theory (SAFT) equation of state (EOS), recently developed and applied for non-associating systems [Ind. Eng. Chem. Res. 38 (1999) 4993] to associating fluids. Unlike the previous crossover EOS that was based on the parametric linear model for the universal crossover function Y, the new CR SAFT EOS is based on Fisher’s recent parametric sine model. This model can be extended into the metastable region and gives analytically connected van der Waals loops in the two-phase region. We show that for associating fluids the new CR SAFT EOS not only yields a better description of the PVT and VLE properties of fluids in the critical region, but also improves the representation of the entire thermodynamic surface. A comparison is made with experimental data for pure normal methanol, ethanol, propanol, butanol, pentanol, and hexanol in the one- and two-phase regions. The CR SAFT EOS reproduces the saturated pressure and liquid density data with an average absolute deviation (AAD) of about 1%. In the one-phase region, the CR SAFT equation represents the experimental values of pressure with an AAD less than 1% in the critical and supercritical region and the liquid densities with an AAD of about 2%.