Preparation Of HZSM-5 Zeolite And Research On Catalytic Esterification

Tetrabutyl pyromellitate（TBPM）is an environmentally friendly plasticizer,which is a functional plasticizer with wide application and development prospect.In this paper,HZSM-5 zeolite,as a catalyst,was used in the synthesis reaction of TBPM plasticizer.This paper aims to synthesize HZSM-5 zeolite with small grain size and hierarchical pore,thereby helping to catalyze macromolecular reaction by increasing the specific surface area of zeolite and shortening the diffusion path.The specific surface area,grain size,acid properties and pore structure of molecular sieve were adjusted by adding additives and seeds in this paper.HZSM-5 zeolites were synthesized by three-step hydrothermal method using L-aspartic acid（LAA）,castor oil（CO）,soluble starch（ST）and monosodium glutamate（MG）as additives.The structure and acidity of HZSM-5 zeolite were analyzed by XRD,SEM,BET and NH₃-TPD.The results indicate that LAA and MG could reduce the grain size of zeolite,while CO and ST not reduced the grain size.All the four additives introduced mesopores into the molecular zeolite crystal.M-HZSM-5 zeolite synthesized with sodium glutamate as additive has smaller grain size,larger specific surface area and pore volume,and its specific surface area and pore volume were 320.94 m²/g and0.213 m L/g,respectively.The acid content of M-HZSM-5 zeolite is high,and the total acid content is 283μmol/g.Higher conversion of pyromellitic dianhydride was observed in TBPM reaction.Using M-HZSM-5 as catalyst,the esterification reaction process was optimized,which obtained the optimal process conditions,as follows:reaction time was 5 h,temperature was 200°C,alcohol-anhydride ratio was 5:1,and the amount of catalyst was 4%of the mass of pyromellitic dianhydride.Using monosodium glutamate as the promoter,the effects of synthesis conditions on the structure and catalytic performance of HZSM-5 zeolite were investigated.the optimal preparation conditions of HZSM-5 zeolite were determined as follows:low-temperature crystallization temperature was 50°C,low-temperature crystallization time was 48 h,monosodium glutamate was added after TEOS,and the amount of sodium glutamate was 5%of the total reaction solution mass.The zeolite synthesized under this condition has micro-mesoporous structure,small particle size,maximum specific surface area of 361.14 m²/g,pore volume of 0.204 m L/g,total acid amount of 356μmol/g,and pyromellitic dianhydride conversion rate of 92.1%.Based on the optimal preparation conditions of HZSM-5 zeolite,different kinds of crystal were compounded,and the effects of seed crystal types and seed addition on the structure and properties of HZSM-5 zeolite were investigated.The results showed that the grain size of HZSM-5 zeolite was significantly reduced by adding seed crystal.The molecular sieve with A-1 seed crystal had higher crystallinity,smaller particle size and larger acid amount.when the addition amount of A-1 was 1.4%of the total mass of the reaction solution,the synthesized 1.4A1-M-HZSM-5 zeolite had larger specific surface area and pore volume,that were 385.70 m²/g and 0.205 m L/g,respectively.Its the total acid content was 414μmol/g,and the conversion rate of pyromellitic dianhydride reached 95.6%.after being reused for 6 times,the conversion of pyromellitic dianhydride can still reach 93.5%.