333456 SAFT-γ Mie Group Contribution Approach for Branched and Cyclic Molecules

Monday, November 4, 2013
Grand Ballroom B (Hilton)
Alexandros Chremos1, Vasileios Papaioannou2, Amparo Galindo2, George Jackson2 and Claire S. Adjiman3, (1)Department of Chemical Engineering, Centre for Process Systems Engineering, Imperial College, London, United Kingdom, (2)Centre for Process Systems Engineering, Department of Chemical Engineering, Imperial College London, London, United Kingdom, (3)Department of Chemical Engineering, Imperial College London,Center for Process Systems Engineering, London, United Kingdom

Branched hydrocarbons provide an excellent example of how molecular architecture affects macroscopic physical properties, since they are better lubricants and fuels as well as having lower critical temperatures and boiling points than the corresponding linear isomers. Within the framework of the Statistical Associating Fluid Theory (SAFT)[1] the modelling of chain molecules is undertaken by application of Wertheim's first-order thermodynamic perturbation theory (TPT1)[2] where isomers of the same chain length cannot be distinguished. Reformulations of the underlying theory for the explicit accounting of branching have been recently presented.[3] In this work, the modelling of branched alkanes is tackled within a group-contribution approach based on the SAFT-γ Mie framework.[4] Though this essentially involves a TPT1 treatment, the introduction of a functional group within the heteronuclear molecular backbone of the chain molecule will be shown to allow for an effective treatment of the different molecular architecture of branched alkanes, and how this impacts their thermodynamic properties. Parameters for the CH (tertiary) and C (quaternary) functional groups are presented, developed by examining the vapour-liquid equilibria (VLE) of pure branched alkanes as well as mixture data. The C chemical group parameters are particularly challenging to obtain due to their small and yet significant contribution to the thermodynamic properties. We have investigated and developed three approaches to describe the thermodynamic behavior of branched alkanes containing the C group. The differences between the three approaches lay the foundations on how the group contribution may be used within SAFT using the TPT1 approximation to tackle complex molecular architectures.

[1] W.G. Chapman, K.E. Gubbins, G. Jackson and M. Radosz, Fluid Phase Equilib. 52 (1989), pp. 31-38.

[2] M. S. Wertheim, J. Stat. Phys., 35 (1984), pp. 19-34; J. Stat. Phys., 35 (1984), pp. 35-47; J. Stat. Phys., 42 (1986), pp. 459-476; J. Chem. Phys., 87 (1987), p 7323.

[3] B. D. Marshall and W. G. Chapman, J. Chem. Phys., 138 (2013), p. 174109.

[4] C. Avendano, T. Lafitte, C. S. Adjiman, A. Galindo, E. A. Muller and G. Jackson, J. Phys. Chem. B, 117 (2013), p. 2717.


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