Selective Synthesis Of 2, 6-Dimethylnaphthalene By Methylation Of 2-Methylnaphthalene With Methanol

Selective synthesis of 2,6-dimethylnaphthalene (2,6-DMN), a preferred intermediate of high performance polymeric materials, has been widely studied. Methylation of 2-methylnaphthalene (2-MN) with methanol is a more promising route to produce 2,6-DMN owing to the simple technologic process, cheap and wide source of raw materials. In this work, the effects of zeolites with different types and particle size and different modification materials on methylation of 2-MN were studied to prepare the catalysts with high activitation and stability, high 2,6-/2,7-DMN ratio and high 2,6-DMN selectivity and yield. The reasons for deactivation of catalysts were explored by TG and regeneration and the methylation of 2-MN was carried out under supercritical condition.The effects of different types of zeolite, reaction temperature, WHSV of 2-MN and the percentage of beohmite as a binder on methylation of 2-MN were studied. It is found that HZSM-5 is the preferred parent catalyst. The appropriate reaction conditions are: 400 ℃, 0.5 h^-1 of WHSV and the weight ratio of zeolite to beohmite being 1/1.The micrometer-scale ZSM-5 with a 38 SiO₂/Al₂O₃ was selected as parent catalyst to be modified with (NH₄)₂SiF₆ (NH₄)₂BF₆, (NH₄)₂TiF₆ and (NH₄)₂ZrF₆, respectively, by isomorphic substitution method. The results show that when ZSM-5 is modified, its catalytic performances such as the selectivity of DMNs, 2,6-DMN, p,P-DMN, ratio of 2,6- to 2,7-DMN and yield of 2,6-DMN are enhanced. Among them, the Zr modification with (NH₄)₂ZrF₆ is the best. About 10% of 2-MN conversion, 56% of 2,6-DMN selectivity, and the highest 3.0 ratio of 2,6- to 2,7-DMN are obtained on modified micrometer-scale ZSM-5 with 0.5 molar ratio of exchangeable Zr in the solution to Al in the framework. By analyses of XRD, XRF, NH₃-TPD, FT-IR and UV, it was thought that the performance improvement of ZSM-5 is mainly ascribed to the weakening acid strength and enlarging pore dimensions of ZSM-5 owing to partial incorporation of Zr into the framework. The comparison research shows that the effect of incorporation of Zr on performance is superior to that of Ti at the same conditions.Nano-scale ZSM-5 with shorter pore channels was selected as parent catalyst and was modified with individual Zr or Si or their co-modification by isomorphic substitution method. The prepared catalysts were used to synthesize 2,6-DMN by methylation of 2-MN at atmospheric pressure. The effect of the percentage of methanol and 1-MN in reactant was investigated and the results showed that Si-modification mainly improves the stability of...