Simulation of the (vapor + liquid) equilibria of binary mixtures of benzene, cyclohexane, and hydrogen

Abstract

Molecular simulations of the (vapor+liquid) equilibria (VLE) for benzene, cyclohexane, and (benzene+hydrogen) and (cyclohexane+hydrogen) were carried out using the Gibbs-ensemble Monte Carlo method with configurational bias. The Buckingham exponential six (exp-6) potential was used for the site–site interactions with no binary interaction parameters; benzene and cyclohexane were described with six interaction sites, and hydrogen with a single site. Simulation results, density, pressure, and vaporization enthalpy for benzene and cyclohexane were in reasonable agreement with experimental data, but critical pressures obtained from extrapolation of the VLE results did not match the experimental values. For (benzene+hydrogen) and (cyclohexane+hydrogen) mixtures mole fractions from simulation were compared with experimental data, the results for liquid phase were in closer agreement with experiment than the results for vapor phase. For the mixtures, results from the PSRK equation of state (PSRK-EOS) predicted the mole fractions for both phases, also vapor densities from molecular simulation were in close agreement with PSRK-EOS. Additionally, the Henry’s law constant (KH) for hydrogen was calculated in separate simulations using test particle insertions, and qualitative agreement with values from experimental VLE data was obtained. For the (benzene+hydrogen) system KH results from PSRK-EOS were closer to experiment than the results from simulation, but, for the (cyclohexane+hydrogen) system results from both methods had similar deviations from experiment. The results for pure substance and mixtures indicate that the combination of the three molecular models used for benzene, cyclohexane, and hydrogen is valid for the simulation of the VLE of their mixtures.