Predicting adsorption of n-perfluorohexane (n-C₆F₁₄) on BCR-704 zeolite using the first principle force field method

Grand Canonical Monte Carlo (GCMC) simulations with ab initio force field were used to predict the adsorption isotherms of n-C₆F₁₄ in BCR-704 faujasite (calcium type) zeolite. The force field parameters were derived using the vapor-liquid equilibrium data for the adsorbate molecules, and ab initio data for the adsorbent (zeolite) with argon as a testing particle. The interactions between the adsorbate molecules and the zeolite were represented by using the Lorentz-Berthelot combining rule. Based on a comparison of ab initio and experimental data obtained for methane absorbed on calcium and sodium type zeolites, it was found that the exposed, non-framework calcium cations (Ca²⁺) must be partially hydroxylated. As the force field parameters were determined using ab initio data, we were able to estimate the percentage of hydroxylation without interference from the force field parameters by using the experimental adsorption data of argon and nitrogen. The hydroxylation ratio of calcium cations was estimated to be 63%. Based on this model and the combined force field parameters, the adsorption isotherm of n-C₆F₁₄ on BCR-704 zeolite was predicted and the results are in reasonable agreement with the experimental data.