THE SYNTHESIS OF ZSM-5 AND THETA-1 IN THE PRESENCE OF DIETHANOLAMINE - THEORETICAL MODELING OF ZSM-5

The synthesis of zeolites from gels comprising silica, alumina, potass ium and/or sodium hydroxide or chloride, diethanolamine, and water has been studied previously, and several zeolites including Theta-1 and Z SM-5 were synthesized. Diethanolamine was considered to have both a po re-filling role and charge-compensatory role (if the amine group was p rotonated), and hence its overall effectiveness as a stabilizer depend s upon the type of zeolite structure and the aluminum content. From th ese considerations, a model has been proposed which has been used to p rovide information on the stabilizing effect of diethanolamine within Theta-1 and ZSM-5. For a range of framework aluminum contents and dist ributions, the model was used to calculate the fraction of diethanolam ine which was protonated and the ratio of metal cations to aluminum. A good agreement was observed between calculated and experimentally obt ained data. The importance of the SiO2/Al2O3 ratio on the formation of ZSM-5 and Theta-1 may be explained in terms of the relative stability afforded by the pore-filling effect of diethanolamine and its charge- compensating role. From these considerations, the model may be used to predict the gel SiO2/Al2O3 ratio required to produce the two zeolites . The SiO2/Al2O3 ratios calculated using the model are in good agreeme nt with the values obtained from experiments.