This paper describes important features of an equation of state compositional simulator that are required for the simulation of the VAPEX process: (1) asphaltenes precipitation, and (2) fluid mixing by molecular diffusion and convective dispersion. The asphaltenes precipitate is modelled as a pure solid that may flow as a suspension in the oil phase, or deposit onto the rock surface. It is shown that this model is capable of modelling the important mechanisms of asphaltenes precipitation in the VAPEX process. The growth of the solvent chamber is governed by molecular diffusion and convective dispersion, with the latter being the dominant mechanism. Sensitivity runs are performed with different dispersivity coefficients, showing their effect on fluid mixing and chamber growth.