Preparation Of Hierarchical β Zeolites For Alkylation Reaction

Friedel-Crafts alkylation reaction is one of the important reactions in the field of fine chemical industry.At present,this kind of reaction mainly adopts the alkylation process with liquid acid and Lewis acid as catalyst,which has a series of problems such as environmental protection and production safety.Therefore,the development of alkylation process with solid acid as catalyst is of great significance to solve the above problems.Among them,theβzeolite in alkylation reaction show some potential applications,but because of its single microporous structure,it has low utilization rate of acid center,conversion frequency（TON）of reactants/products on microporous acid center and diffusion efficiency in catalytic alkylation reaction,especially for the reaction involving large molecules.Thus,its catalytic activity is low and the catalyst is easy to deactivate.Therefore,it is one of the effective methods to solve the above problems by introducing mesopores into the framework of microporousβzeolites and constructing hierarchicalβzeolites.The main research contents of this paper are as follows:（1）Using tetraethylammonium hydroxide（TEAOH）as the template ofβzeolite with microporous structure,[（CH₃O）₃Si C₃H₆N（CH₃）₂C₁₈H₃₇]Cl（TPOAC）as the guide of mesoporous structure,the hierarchicalβzeolite was prepared by one-step hydrothermal synthesis method.The effects of basicity,Si/Al ratio and template dose on the structure and catalytic alkylation performance ofβzeolites were systematically studied.The results show that heterocrystalline hierarchicalβzeolite can be synthesized within the range of gel ratio.When the molar ratio of TPOAC/Si O₂ is 0.02 and the crystallization time is 8 days,Hβ-0.02-8D shows excellent catalytic performance in the alkylation of benzene and mesitylene with benzyl alcohol.Compared with the traditional zeolite Hβ-0-8d,Hβ-0.02-8d shows excellent catalytic performance in the alkylation of benzene and mesitylene with benzyl alcohol.The zeolite has a higher conversion rate of benzyl alcohol（95%vs 65%）and a higher selectivity of diphenylmethane（80%vs 70%）after the reaction,mainly due to its unique mesoporous structure which significantly improves the accessibility of the acid center and TON value of the reactant molecule at the active center.（2）The effectiveness of seed assisted organosilane synthesis of hierarchicalβzeolites was investigated.The effects of seed addition on shortening crystallization time and zeolite structure were studied by adding seed into the synthesis system.The effects of different seed types,crystallization time and seed addition amount on the structure ofβzeolite were investigated.The results show that the addition of seed can effectively shorten the crystallization time of hierarchicalβzeolite.The BET surface area and mesoporous volume ofβzeolite increased significantly with the addition of 1%commercial seed.The BET surface area increased from 741 m²·g^-1 to 808 m²·g^-1,and the mesoporous volume increased from 0.51 cm³·g^-1 to 0.63 cm³·g^-1,and the pore size distribution ofβzeolite was more uniform.The hierarchicalβzeol synthesized with seed support showed comparable catalytic performance in the alkylation of benzene with benzyl alcohol compared with without seed addition.