Synthesis And Assembly Of Hierarchical MFI Zeolites

Hierarchical zeolites combined the advantages of both nanozeolite and mesoporous material. On the basis of its’ highly acidity, hydrothermal stability, porous structure, shape selectivity and good mass transfer capacity, zeolites may play an important role in heavy oil conversion and macromolecule catalysis. Nowadays, in order to reduce diffusion path lengths and improve mass transport, many people are trying to synthesize high active zeolites by controlling the zeolite morphology, reducing the size of zeolite crystals, and introducing mesopores in zeolites through various strategies. So zeolite microsphere with the aggregates of small primary crystals and mesopores is preferred because of their easy handling and high catalytic activity. In order to solve the problems for the separation and recovery of nanozelites, we chose MFI zeolites as study object and synthesized hierarchical zeolite aggregates through different strategies including the following parts:Part one:we chose n-amines as single template and synthesized hierarchical zeolite aggregates through one step. We investigated the effect of the synthesis conditions on the zeolite morphology including templates, sodium content, H2O/SiO2ratio, silica source and aluminium content. The template role of n-amine in synthesizing zeolites was also discussed.Part two:we synthesized hierarchical zeolite aggregates by post-treating TS-1zeolites with bridged organosilane, as silanization agent can make zeolites nanoseeds aggregate into large entities. The obtained TS-1aggregates of50μm were assembled by the nanocrystalline zeolites of around150nm in size. The assembled zeolite aggregates with interparticle mesopores not only solve the filtration problem, but also reduce the diffusion resistance and retain high reactivity.Part three:as some inorganic salts can promote zeolites crystallization, we added diammonium phosphate into zeolite synthesis system and investigated zeolite crystallization process. We studied the effect of diammonium phosphate content and adding time. After the addition of phosphate, both relative crystallinity and reactivity of zeolite had a minor improvement. It is regrettable that we can’t obtain TS-1 aggregates by this method.