It was the main aim of this work to identify the microscopic origin of the perturbations brought about by a porous environment on the thermal diffusion (Soret effect) of a liquid mixture. For this purpose, non-equilibrium molecular dynamics simulations were carried out on model systems representing hydrocarbons in a porous medium. In keeping with previous simulations, a simplified model, i.e., Lennard-Jones spheres, was used for representing a methane-decane mixture, while the porosity was modelled by the inclusion of quasi-harmonic solids of various sizes and shapes. The model parameters were chosen to yield the proper order of magnitude for a silicate and its interactions with the alkanes. The model was first validated by investigating the equilibrium properties of the system. Then the thermal influence of the porous medium was evaluated and the adsorbing behaviour of the alkanes on the pores was characterized. It was found that the Soret coefficient of the equimolar mixture studied here was lowered by about 30% at 75% porosity. It was also found that this reduction was strongly dependent upon the structure of the porous medium.

A Molecular Dynamics Study of Thermal Diffusion in a Porous Medium. Colombani, J., Galliéro, G., Duguay, B., Caltagirone, J.P., Montel, F., Bopp, P.A.: Physical Chemistry Chemical Physics, 2002, 4[2], 313-21