A computational study of the adsorption of n-perfluorohexane in zeolite BCR-704

Monte Carlo simulations in the grand canonical and Gibbs ensembles were carried out to predict the adsorption isotherms of argon, nitrogen, and n-perfluorohexane in BCR-704, a faujasite-type calcium aluminosilicate with a Si/Al ratio of 1.6. Starting from existing force fields for the sorbate molecules and a transferable force field for all-silica zeolites, attempts were made to develop a force field that would reproduce the experimentally determined argon and nitrogen adsorption isotherms in BCR-704. However, good agreement for the nitrogen adsorption isotherm could only be obtained either for a set of force field parameters with a greatly reduced partial charge on the calcium cation or using a larger partial charge and assuming that co-adsorbed water molecules are present at the temperature used for the argon and nitrogen adsorption isotherms. Predictions of the adsorption isotherm for n-perfluorohexane in BCR-704 using the latter force field parameters and the FAU-X structure with a water/calcium ratio of 1 yield good agreement with the experimental benchmark data.