Hydrogen/hydrocarbon phase equilibrium modelling with a cubic equation of state and a Monte Carlo method

Because of the lack of experimental hydrogen/hydrocarbon phase equilibrium data in high temperature and pressure conditions as for example those encountered in hydrotreatment processes, accurate models are required to extrapolate data. In this work, two approaches are tested for the phase equilibrium modelling of mixtures containing hydrogen and different hydrocarbon families, as n-alkanes, iso-alkanes, alkenes, cycloalkanes, aromatics and polyaromatics. The first one is a flash calculation involving the improved Peng–Robinson equation of state coupled with the binary interaction parameter of Moysan [J.M. Moysan, M.J. Huron, H. Paradowski, J. Vidal, Chem. Eng. Sci. 38 (1983) 1085–1092]. This parameter only depends on temperature and not on the hydrocarbon properties, providing thus a convenient way for the simulation of heavy fractions with ill-defined physico-chemical properties. However the extrapolation of this model to high temperatures is questionable. The second one is a Monte Carlo simulation using the AUA4 potential for hydrocarbon and the Darkrim potential for hydrogen, including the quadrupole moment of this molecule [F. Darkrim, J. Vermesse, P. Malbrunot, D. Levesque, J. Chem. Phys. 110 (1999) 4020–4027]. Both approaches lead to accurate reproduction of equilibrium data. The Monte Carlo method is more predictive, as it requires no interaction parameter. This approach is therefore recommended when any experimental data are available to validate the simulation results, despite a longer computer time. Hydrogen/polyaromatics mixtures are not well predicted with this method, but this could be improved by including the quadrupole moment of aromatic molecules in future work.