Zsm-12 Zeolite Catalyzed Synthesis Of 2,6 - Dimethylnaphthalene

ZSM-12 molecular sieve, which was applied to synthesize 2,6-DMN byshape-selective alkylation of naphthalene, was prepared by hydrothermal method. Thestructure and acid property were characterized by XRD, FT-IR, SEM, N₂absorption-desorption, NH₃-TPD, et al. The influence of the composite of gel and thecrystallization manner on the structure, acid property of ZSM-12 was studiedsystematically through preparation process. The result shows that the effect ofcrystallization of ZSM-12 is obviously affected by the alkalinity, the ratio of Si/Al in geland the type and amount of template agent. Increasing the ratio of Si/Al in gel isfavorable to obtain ZSM-12 with high crystallinity. The morphology, distribution of thepore and the acid property of the ZSM-12 are different when TEABr and MTEABr areused as template agent respectively. The ZSM-12 prepared in the dynamiccrystallization manner has more and stronger acid than that prepared in the regularhydrothermal manner. The optimum ZSM-12 preparation conditions: the silica gel andsodium metaaluminate as the sources of silicon and aluminum, TEABr as the templateagent, the composite of gel is OH^-/Si=0.065, TEA⁺/Si=0.125, H₂O/Si=13 and Si/Al≥50,crystallization is at 160℃for 5 days.The influence of solvent, reaction temperature, reaction pressure, space velocityand mole ratio of naphthalene and methanol on catalytic performance of ZSM-12 foralkylation of naphthalene and methanol was investigated to optimize the technologicalconditions. The catalytic performance of ZSM-12 prepared by different ratio of Si/Al,the type of template agent in different crystallization manner for the synthesis of2,6-DMN was investigated under the above reaction condition. The result shows thatZSM-12 performs high catalytic activity and selectivity in the alkylation of naphthaleneand methanol compared with HUSY, Hβand HZSM-5 zeolite, and ZSM-12 is a kind ofproper catalyst for the synthesis of 2,6-DMN. ZSM-12 (Si/Al=50) prepared in thedynamic manner, TEABr as template agent, could further increase the catalytic activityand selectivity for 2,6-DMN. The conversion of naphthalene and the selectivity for2,6-DMN are 64% and 10%, respectively, and the ratio of 2,6-DMN and 2,7-DMN is 1.7.ZSM-12 modified by isomorphous substitution of gallium was prepared. The acidstrength decrease, but new Lewis acid center appears, and the catalytic activity andselectivity for 2,6-DMN both increase. The carbon burning analysis of deactivatedcatalyst was carried out, it can be seen that the building-up of carbon is the major factorfor the deactivation of ZSM-12 catalyst.