Modelling of dealumination of aluminium silicate molecular sieves

Abstract

A simplified treatment of the dealumination of aluminium silicate (zeolite like) molecular sieves has been developed that considers both the diffusion of aluminium atoms and the formation and migration of vacancy sites. The instantaneous concentration of aluminium atoms as a function of time and location has been derived according to Fick's second law. Critical parameters affecting the dealumination process are discussed. The calculated results agree with the ratios of silicon to aluminium reported in the literature from infrared and ²⁷Al NMR spectroscopy studies on the commercial aluminium silicate molecular sieves materials Mordenite and ZSM-5, following exposure to air and water vapour.