Synthesis Of Nano ZSM-5and Application In The Preparation Of2,6-dimethylnaphthalene By Alkylation Of2-methylnaphthalene With Methanol

Nano-zeolite and hierarchical zeolites are expected to be applied widely in the bulk molecular shape-selective catalysis, due to their high activity, thermal stability, ion exchange and well mass transfer performance.2,6-dimethylnaphthalene(2,6-DMN) is the most important intermediate of high performance polymeric materials polythylene naphtalate(PEN). Selective synthesis of2,6-DMN via methylation of2-methylnaphthalene (2-MN) with methanol is a promising route due to simple process and abundance raw materials. The key problem of restricting industrialization is that the current catalyst is incapable of this shape-selective reaction. In this thesis, based on the recently studies on nano-zeolite, new nano catalyst, such like hierarchical crystalline ZSM-5and hollow nanoscale ZSM-5were synthesized without using second template for overcoming the activity and stability disadvantage of traditional zeolite catalyst on alkylation. High2,6-DMN selectivity can also be obtained after modification. The prepared zeolite was characterized by XRD, FI-IR, SEM, N2adsorption-desorption and NH3-TPD to investigate the framework, morphology and acidity.The hierarchical zeolites had been synthesized successfully via dry gel convert (DGC) method from different initial sol reactant. The results indicated that the zeolite with much more mesoporous volume than the nano-zeolite aggregation crystallized by hydrothermal method can be obtained by DGC method, which presented more stable activity. The nano-zeolite with intercrystalline mesopore was synthesized via DGC method from supersaturated gel, selected TEOS as silica source. The hierarchical zeolite exhibited well catalytical performance on alkylation reaction, the conversion of2-MN decreases from30%to25%, the highest2,6-DMN selectivity and yield is35%and6.2%, respectively. The effect of zeolites with different ion-exchanged time on alkylation was also investigated. The result indicated that the existence of Na+in zeolite will increase the2,6-DMN selectivity to45%. The zeolite contained Na+has higher stability and lower activity compared the sample without Na+. The catalytical activity of zeolite after alkali treatment and (NH4)2ZrF6modified is similar to the parent sample, but the DMN,2,6-DMN selectivity and yield on modified catalyst are much higher than parent sample,82%,44%,9%, respectively. The nano-zeolite could be synthesized under different temperature. The BET of the zeolite increases with the crystalline temperature, and the crystal size is related to the saturation of the precursor when without alkali metal ion. The Zr proton was embedded into the framework of the zeolite by isomorphous substitution to obtain the ZSM-5partially substituted by Zr. The zeolite modified by Zr performed well on alkylation, the highest2,6-DMN selectivity and yield are42%and6.6%, respectively, both higher than that of parent zeolite. The micro-mesoporous Al2O3-ZSM-5composite was synthesized via sol-gel method, it performed well on alkylation, especially on2,6-DMN selectivity(43%) and yield(9.7%).Hollow nano ZSM-5was synthesized via one-step hydrothermal crystallization method by adding NaH2PO4as the promoter to the sol-gel. The prepared zeolite was used to synthesis of2,6-DMN by methylation of2-MN with methanol. The characterizations show that the addition of NaH2PO4promoter results in the larger crystal, more regular crystal morphology and more uniformed size, especially, hollow crystalline structure. The hollow zeolites exhibit higher selectivity of2,6-DMN and better stability. The2-MN conversion decreases from28%to over25%after the reaction of12h, and the highest2,6-DMN yield is10.5%.