A crossover equation of state for associating fluids

In this work we extend the crossover (CR) modification of the statistical-a ssociating-fluid-theory (SAFT) equation of state (EOS), recently developed and applied for non-associating systems [Ind. Eng. Chem. Res. 38 (1999) 499 3] 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 mod el can be extended into the metastable region and gives analytically connec ted van der Waals, loops in the two-phase region. We show that for associat ing 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 mad e with experimental data for pure normal methanol, ethanol, propanol, butan ol, pentanol, and hexanol in the one- and two-phase regions. The CR SAFT EO S 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 t han 1% in the critical and supercritical region and the liquid densities wi th an AAD of about 2%. (C) 2001 Elsevier Science B.V. All rights reserved.