DIRECT HYDROTHERMAL CRYSTALLIZATION OF HIGH-SILICA LARGE-PORT MORDENITE

Hydrothermal crystallization of mordenite has been carried out in the temperature range 393-453 K following the oxide mole composition of th e starting gel as a Na2O : A12O3 : b SiO2: d (TEA)2O : c H2O, where a = 3.9-12.5, b = 30-40, c = 150-1500, and d = 0 or 1.5. Silica sol, wat er glass, and microcrystalline silicon dioxide were used as sources of silica, whereas pseudoboehmite, sodium aluminate, and aluminum sulfat e.16 H2O were used as sources for alumina. A product silica-to-alumina ratio (SAR) ranging between 12 and 35 was found influenced by the sta rting gel composition, nature of the sources of silica and alumina, di lution of the gel, pH, temperature of crystallization, and the use of template (tetraethylammonium bromide). Synthesis efficiency (% yield o f crystalline solid product based on silica and alumina in the startin g gel) was also found to depend upon various parameters during synthes is. Coexistence of other crystalline phases depended on the Na2O conte nt in the starting gel and also on the temperature of the crystallizat ion. Crystallization kinetics fitted in the first-order kinetics equat ion and apparent activation energies for the processes of nucleation ( E(n)) and crystallization (E(c)) were calculated by applying the Arrhe nius equation. Large-port mordenite was obtained in the presence or ab sence of the template with enhanced synthesis efficiency (up to 75%), with the product SAR as high as 35.