Synthesis Of Mesoporous ZSM-5and Its Application In Alkylation Of2-Methylnaphthalene With Methanol

Mesoporous zeolites are considered to be potential catalytic materials for combining the advantages of conventional zeolites (hydrothermal stability, strong acidity, shape selectivity) and mesoporous materials (large mesopore contributing to mass transfer), which are significant for catalytic reaction with large molecules.2,6-Dimethylnaphthalene (2,6-DMN) is an important feedstock of high performance polymeric materials such as polyethylene naphthalate (PEN). Methylation of2-methylnaphthalene (2-MN) with methanol to synthesize2,6-DMN via zeolite catalysis is a simple and practical method. However, conventional zeolites have low conversion of2-MN and short lifetime owing to small pore size, which would be improved by mesoporous zeolites. In this thesis, mesoporous ZSM-5samples were synthesized by template methods, characterized by XRD, FT-IR, SEM, TEM and N2adsorption/desorption, and used as catalysts for methylation of2-MN with methanol to produce2,6-DMN.Silica-carbon composition synthesized via in situ sugar decomposition with silica sol, was used as the template of synthesizing of mesoporous ZSM-5. The mesopore size can be turned by varying molar ratios of sugar to silica sol, which can solve the defect of non-ajustable mesopore size via hard template method. The morphology of the obtained zeolites is spherical structure aggregated of clavate particles, and the mesopores are formed by the adjacent particles. High crystalline mesoporous zeolite was synthesized at150℃of crystallization temperature with1:1of ratio of sugar/SiO2,400℃of carbonization temperature, NaAlO2as aluminum source. The prepared mesoporous zeolite presented higher catalytic activity then conventional zeolite with the initial conversion of35%, but lower selectivity of2,6-DMN. The modified ZSM-5with (NH4)2ZrF6showed that the selectivity and yield of2,6-DMN reach to34%and4.3%, respectively.(y-aminopropyl)-triethoxysilane (APTES), owing to relatively low price, was chosen as the silylating agent to synthesize mesoporous ZSM-5by three steps of the preparation of zeolite nuclei, silanization and hydrothermal synthesis. The morphology of the obtained crystals is aggregation with average particle size of300-500nm composed of nanocrystals. The mesoporous ZSM-5with narrow pore distribution can be obtained and adjusted by varying the amount of APTES. The surface area, total pore and mesopore volumes of the resultant zeolite increase with the ratio of APTES to SiO2. The prepared zeolite was used to synthesis of2,6-DMN by methylation of2-MN with methanol. The conversion of2-MN and the yield of2,6-DMN are about40%and5%, respectively. The mesoporous zeolite treated with citric acid has high pore volume for removing the aluminum oxide species which block the micropore and stability for the decreasing of acidity. The high crystalline ZSM-5was synthesized by treated of microwave irradiation with short synthesis time instead of hydrothermal treatment. The crystalline, morphology and catalytic performance of the zeolites were affected by NaOH addition.