Modelling Real Fluids and Their Mixtures with An Improved SAFT-VR Equation of State for Segments Interacting through Mie Potentials (SAFT-VR Mie)

The concept of using the more realistic Mie potential (Lennard-Jonesium interactions of the general form u(r)=e C(l₁,l₂){(s/r)^l₁-(s/r)^l₂}) as the elementary building block of homonuclear chains of Mie segments within a SAFT-like EOS has proven to be very fruitful in order to model simultaneously the fluid phase behaviour and second-derivative properties of real fluids[1]. Recently, an improved version of the SAFT-VR Mie EOS has been presented. This new theory which is based on a more accurate expression of both the Helmholtz free energy and contact radial distribution function of a fluid of chain molecules interacting through the Mie potential has been shown to reproduce the Monte Carlo simulation data for a broad interval of repulsive and attractive ranges. In this work, we have applied this new SAFT-VR Mie equation of state to real substances (alkanes, alkanols, amines, carboxylic acids, water) and selected binary mixtures. The heat capacity in the compressed liquid region, generally presented as a severe consistency test for EOS, was estimated with percent average absolute deviations (AAD%) close to 2% in each cases. The speed of sound is also accurately captured with deviations below 4%. In addition, we will show that the new EOS also provides a more accurate description of the VLE of the pure substances studied. In order to emphasize the relevance of using a variable repulsive range through the Mie potentials, a comparison with other SAFT-like EOS will be presented (SAFT-VR SW, soft-SAFT[2], PC-SAFT[3]).

[1] T. Lafitte, D. Bessieres, M. M. Piņeiro and J.-L. Daridon, J. Chem. Phys., 124, 024509 (2006).

[2] F. J. Blas and L. F. Vega, Mol. Phys., 92, 135 (1997).

[3] J. Gross and G. Sadowski,Ind. Eng. Chem. Res., 40, 1244 (2001).