(180aa) Prediction of Vapour-Liquid Equilibria and Second-Derivative Properties with the SAFT-Gamma Group Contribution Approach

The SAFT-&gamma EOS[1] has recently been developed as group contribution methods derived entirely within an equation of state to describe fluids of heteronuclear molecules which are formed from fused square-well segments of different types. The different groups are then defined in terms of one or multiple[2] spherical segments characterized by size and attractive energy (well-depth and range) parameters, and shape factor parameter which describes the contribution that each segment makes to the overall molecular properties. For associating groups a number of bonding sites are also included on the segment introducing two additional energy and range parameters. The formulation of SAFT-&gamma as a continuum fluid theory offers the key advantage that the binary interaction parameters between groups can be obtained directly from an examination of pure component properties alone. This is particularly useful in predicting the properties of fluid mixture (vapour-liquid and liquid-liquid equilibria, VLE and LLE) when no experimental data on the mixture are available. In this work we will present the extension of the theory to deal with heteronuclear molecules formed from Mie (Lennard-Jonesium interactions of varying repulsive and attractive range) segments of different type. Using this more realistic inter-segment potential as an elementary building block of a homonuclear SAFT-like EOS[3] has proven previously to be highly accurate in predicting second-order derivative properties (e.g., isobaric heat capacity, isobaric thermal expansivity, speed of sound) of complex fluids. First, in order to assess the accuracy of the SAFT-&gamma Mie EOS obtained, the thermodynamics properties are compared with computer simulation results for chains of fused heteronuclear Mie segments. Regarding the good agreement obtained in each cases, we then show that the use of generalized Lennard-Jones potential of this type in the context of the SAFT-&gamma group contribution approach allows for the simultaneous description of both VLE and second-derivative properties of pure fluids (alkanes, alkanols, n-alkylbenzenes, mono-and diunsaturated hydrocarbons) and their mixtures.

[1] A. Lymperiadis, C. S. Adjiman, A. Galindo and G. Jackson, J. Chem. Phys. 127, 234903 (2007)

[2] A. Lymperiadis, C. S. Adjiman, G. Jackson and A. Galindo , Fluid Phase Equilib.. 274, 85(2008)

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