(222as) SAFT-? Mie Group Contribution Approach for Branched and Cyclic Molecules | AIChE

(222as) SAFT-? Mie Group Contribution Approach for Branched and Cyclic Molecules


Chremos, A. - Presenter, Imperial College London
Papaioannou, V., Imperial College London
Galindo, A., Imperial College London
Jackson, G., Imperial College London
Adjiman, C. S., Imperial College London

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.