(663a) Development of Intermolecular Potentials for Thiophenes

The requirement for thermodynamic data of sulfur-containing molecules in the petroleum industry has motivated the need to develop accurate intermolecular potential for these compounds. In particular, the family of thiophenes is the subject of increasing interest due to the presence of these compounds in the desulfurization process of gasolines. Molecular simulation provides an alternative route to experiment to fill existing gaps in thermodynamic data. To this end, we have optimized a new intermolecular Lennard-Jones (LJ) 12-6 potential for the thiophene based sulfur atom where Anisotropic United Atom parameters for the aromatic groups from previous works have been used to model the aromatic rings [1] . No charges have been considered since the dipole present in the sulphur atom is found to be small. The LJ parameters have been optimized using experimental data for the coexistence liquid densities, vaporization enthalpies and vapour pressures of thiophene and benzothiophene. As a starting point we have used the sulphur LJ parameters for thiols and sulfides from a previous work [2]. Monte Carlo simulations in the Gibbs and isobaric-isothermal ensemble have been used to obtain the properties at the conditions selected to carry out the optimization. In addition, grand canonical simulations combined with histogram reweighting have been performed to investigate the phase equilibrium and the critical region of both thiophene and benzothiophene as well as 2-methylthiophene and dibenzothiophene. A recently implemented combination of the Binder parameter with finite size scaling methodologies have been used in order to allow for an accurate and straightforward location of the critical point. The model critical point of thiophene is found to be within 1% of the experimental value. Very good agreement has also been found for the vaporization enthalpy and saturation pressure of thiophene and 2-methylthiophene. The predictions for benzothiophene and dibenzothiophene, where additional aromatic rings are involved, also present good agreement with experimental data although slightly larger deviations are found when compared with the compounds with a single ring.

[1] Ahunbay MG, Perez-Pellitero J, Contreras-Camacho RO, Teuler JM, Ungerer P, Mackie AD, Lachet V Journal of Physical Chemistry B 109 (7): 2970-2976 Feb 24 2005

[2] Delhommelle J, Tschirwitz C, Ungerer P, Granucci G, Millie P, Pattou D, Fuchs AH Journal of Physical Chemistry B 104 (19): 4745-4753 May 18 2000