Conventional Hydrothermal Synthesis of MFI Zeolite in Methanol Solution.

Abstract

The synthesis of zeolites through more efficient, environmentally friendly, and cost-effective methods was deemed significant in both industrial applications and academic fields. Conventional hydrothermal synthesis strategies have encountered difficulties in producing pure silica MFI zeolite (silicalite-1) under amine-free conditions. This was primarily attributed to the competitive growth of quartz, keatite, or magadiite during the crystallization process. In this work, it was found that the lack of nucleation ability was an important reason for the poor crystallization stability of the methanol solution. Well-crystallized silicalite-1 zeolites with uniform particle sizes were achieved through the cooperative guidance of methanol and seed crystals. Large-scale experiments with silicalite-1 zeolite demonstrated good reproducibility. Combined with the TG-IR and N2 adsorption-desorption results, it was observed that, when an extremely small amount of seed (0.97 wt %) was introduced, methanol could play a role as a crystallization promoter in the hydrothermal synthesis system. Furthermore, a lower alkaline-to-silica ratio and water-to-silica ratio were conducive to the progression of the crystallization process. In summary, this work presented a hydrothermal synthesis strategy for the synthesis of silicalite-1 zeolite in a methanol solution without the need for a large amount of seeds and provided an effective pathway for the low-cost, large-scale production of silicalite-1 zeolite.