Alkali effect and kinetic studies on the crystallization of a small pored titanium silicate molecular sieve, ETS-4 using different sources of silica and titanium under stirring

Abstract

A small pored variety of titanium silicate, ETS-4 was synthesized to investigate the effect of alkali content on the crystallization and phase purity using different sources of silica and titanium under stirring at 200 rpm and to calculate activation energy. The results showed that the alkali content significantly affects the crystallization and phase purity depending on titanium source. In addition, regardless of silica and titanium sources, the morphology of ETS-4 is quite different from that synthesized under static condition showing a thin plate-like shape and seems to be significantly affected by stirring. The composition with the shortest reaction time to reach the 100% crystallinity and the purity for different silica and titanium source was chosen and applied to the kinetic study. All the experiments for kinetic study were conducted at 423, 443 and 463 K, respectively. The activation energies for three different stages, nucleation, transition and crystallization were calculated using the modified Avrami–Erofeev equation. The results of kinetic study suggest that the effect of titanium source is more significant than that of silica source; that is, Ludox AS-40 and fumed silica show the most significant temperature dependency on the crystallization for titanium oxysulfate and titanium trichloride as the titanium sources, respectively. The modified Avrami–Erofeev equation to three different stages, nucleation, transition and crystallization for rapid crystallization seems to be an excellent tool to predict the crystallization of ETS-4.