Study On The Catalytic Performance Of 2-methylnaphthalene Acylation And Alkylation Zeolite Molecular Sieves

2-methyl-6-propylenaphthalene（2,6-MPN）and 2-methyl-6-isopropylnaphthalene（2,6-MIPN）are important upstream products for the synthesis of polyethylene naphthalate（PEN）.The main routes for the synthesis of2-methyl-6-propylenaphthalene and 2-methyl-6-isopropylnaphthalene are Friedel-Crafts acylation and alkylation.The traditional Friedel-Crafts reaction usually uses strong solid acid Al Cl₃ as the catalyst.Despite the high reaction efficiency and product yield,the environmental pollution caused by the difficulty in separating the catalyst from the reaction system cannot be ignored.Therefore,it is currently an urgent issue to develop suitable green catalysts to catalyze acylation and alkylation,and to meet the requirements of high efficiency,low energy consumption and low pollution.In this paper,the Hβmolecular sieve was modified by the alkali cation exchange method.The pore size,specific surface area,pore volume,acid strength and type of the modified catalyst changed greatly compared with those before the modification.The preparation conditions of the modified catalyst were investigated and the reaction conditions were optimized.The better modification conditions were obtained as follows:the alkali type was Ba（OH）₂,the concentration of Ba（OH）₂ solution was0.05mol/L,the alkali treatment temperature was 80℃,the alkali treatment time was1h,and the calcination temperature was 580℃.The optimized acylation reaction conditions are listed as follows:molar ratio of reaction raw materials is 1:1.2,solvent dosage is n_（2-MN）:n_（S）=1:1.5,catalyst dosage is 2 g,reaction temperature is 160℃,reaction time is 7 h.The conversion of 2-methylnaphthalene was 70.74%,and the selectivity of 2,6-product was 47.41%.Zeolite molecular sieves were modified using the impregnation method,which is to adjust the ratio of silicon to aluminum and the strength and quantity of acid centers.The effect of the modified Hβzeolite on the catalytic performance of2-methylnaphthalene and propionic anhydride acylation reaction,and the reaction conditions and modification conditions were optimized.The experimental results show that under the optimal conditions,compared with the modified Hβmolecular sieve,the catalytic reaction performance of modified molecular sieve increased by about 22.7%（the pre modified Hβmolecular sieve conversion rate of2-methylnaphthalene was 62.8%,and selectivity of 2-methyl-6-propylenaphthalene was 50.2%）,and the modified catalyst can be reused for 3 times;The structure of reactants and products was optimized by Gussian software,and the molecular dynamics diameter（d_x）of compounds in the reaction system was calculated to be:d2-methylnaphthalene=0.88 nm,dpropionic anhydride=0.85 nm,d2-methyl-6-propionylnaphthalene=0.97nm,d_{propionic acid}=0.47 nm,respectively.The modified catalyst was characterized by XRD、SEM、BET、XRF、Py-IR and NH₃-TPD.From the reaction results and characterization results,it can be seen that the strong acid center of Hβmolecular sieve has a great influence on the acylation reaction performance.The reaction mechanism was investigated by in-situ infrared spectroscopy.It was found that propionic anhydride decomposed rapidly into C₂H₅CO-and C₂H₅COO-after being heated,and combined with 2-methylnaphthalene to form2-methyl-6-propionylnaphthalene and propionic acid under the action of acidic catalyst.The alkylation of 2-methylnaphthalene was catalyzed by H-type zeolite mo lecular sieve.The reaction conditions were optimized with HUSY molecular sie ve as the most suitable H-type zeolite.When the reaction time was 4h,the m olar ratio of reaction raw material n_{（2-methylnaphthalene）}:n_{（Pr OH）}=1:1,and the amount of catalyst was 3 g,the reaction effect was good,the conversion of 2-methyl naphthalene reached 71.89%,and the selectivity of 2,6-MIPN reached 62.70%.