A new intermolecular potential model for the n-alkane homologous series

A new model for the n-alkane homologous series has been developed, parametrized to the vapor-liquid coexistence properties for a range of chain lengths. The model utilizes the Buckingham exponential-6 potential to describe the nonbonded interaction energy. Histogram reweighting grand canonical Monte Carlo methods were used to determine the model parameters. The new model reproduces the experimental saturated liquid and vapor densities and vapor pressures for ethane through octane to within average absolute deviations of 0.5%, 2.1%, and 2.2% respectively. Critical temperatures and densities were also found to be in good agreement with experiment. Critical pressures are slightly overestimated for longer chain lengths. Comparisons were made to the TraPPE [J. Phys. Chem. B 1998, 102, 2569.] and NERD [J. Chem. Phys. 1998, 108, 9905.] models. The two previous models reproduce the liquid properties with comparable accuracy to the proposed model; however, the new model was found to describe the vapor pressures more accurately. Liquid densities were determined for the new model for chain lengths as long as C₇₈. Agreement to experiment is within 1% at atmospheric pressure. Phase diagrams were calculated for mixtures of ethane-heptane, ethane-decane, ethane-eicosane, and octane-dodecane. The new model achieves near-experimental predictive accuracy for these mixtures.