Study on Adsorption of Water on Na nZSM-5 Type Zeolite by Molecular Simulation

Abstract

Molecular dynamic (MD) quench method and grand canonical Monte Carlo method (GCMC) are used to study the adsorption of water on Na n ZSM-5 type zeolite. The simulated adsorption isotherm is in good agreement with the experimental data reported in literatures. Based on these facts, adsorption of water on Na n ZSM-5 with various n Si/ n Al ratios is predicted. The simulation results indicated that n Si/ n Al ratios of zeolite framework affect the water adsorption and adsorption isotherm greatly and the adsorption amount decreases with the increase in the n Si/ n Al ratio. The above observation can be explained by assumption of the charge influence of Na + cations on the polar water molecules due to the Coulomb force. The adsorbed water molecules are located around Na + cations and Al atoms on the zeolite framework and the average number around Na + cations and Al atoms is four at lower loading. However, hydrogen bonds between the adsorbed water molecules and the oxygen atoms on the zeolite framework exist at higher loading. At the same loading, the isosteric heat decreases as the n Si/ n Al ratio increases.