Modification Of The ZSM-5 Synthesized Without Template And Application In The Alkylation Of Toluene With Ethanol To P-ethyltoluene (PET)

P-ethyltoluene（PET）is an important raw material for organic synthesis,which can be used to prepare p-methylstyrene.Because the separation of ethyltoluene isomers is very difficult,which leads to high production cost,the high para-selective production technology without separation process is urgently needed.And with the large-scale production of coal-based ethanol,the substitution of ethanol for ethylene alkylation to produce p-ethyltoluene can reflect the advantages of raw material resources.Therefore,it has important academic significance and industrial application value to study the preparation of p-ethyltoluene with high para-selective catalyst by toluene-ethanol alkylation.In this study,the HZSM-5 molecular sieve synthesized by template-free method was used as the catalyst parent,toluene and ethanol were used as raw materials,and the optimized synthesis of p-ethyltoluene was studied by using a fixed-bed reactor.The research contents are as follows:（1）Firstly,the single factor experiment was used for horizontal comparison to investigate the influence of conditions on toluene-ethanol alkylation reaction catalyzed by HZSM-5zeolite,and the reaction performance of commercial HZSM-5 catalyst synthesized with template and HZSM-5 catalyst synthesized without template was compared.The results showed that HZSM-5 catalyst synthesized without template in this study had similar toluene-ethanol alkylation performance compared with commercial HZSM-5 catalyst synthesized with template,and the selectivity was almost the same except that toluene conversion rate was slightly lower.The toluene conversion rate of HZSM-5 synthesized without template is up to14%,and the selectivity for p-ethyltoluene is maintained at about 29%.The optimum reaction conditions are as follows:reaction temperature is 330℃;the molar ratio of toluene/ethanol is 6;atmospheric pressure;nitrogen flow rate is 30ml/min;WHSV is 2h^-1.（2）HZSM-5 molecular sieve synthesized without template was used as catalyst parent,and it was modified by impregnation method or liquid phase deposition method to study the influence of different oxide modification on toluene-ethanol alkylation reaction performance.The results showed that the silicon modification reduced the activity of the catalyst and improved the selectivity of p-ethyltoluene,because Si O₂ covered the acid sites on the outer surface of the catalyst,but had no effect on the acidity in the pore channels.Phosphorus modification improved the conversion of toluene,but had no change in the selectivity of p-ethyltoluene,because phosphorous modification transformed strong acid into weak acid and increased the amount of weak acid in the catalyst.Magnesium modification significantly improved the selectivity of p-ethyltoluene but lost more catalyst activity,because magnesium can reduce acid amount and acid strength,and has a greater effect on strong acid sites.（3）The HZSM-5 catalyst was modified by silicon,phosphorus and magnesium,and the influence of modification sequence on the catalytic performance was investigated.The results showed that the optimal loading sequence was Si-P-Mg,and the modified catalyst with loading loads of 6%Si O₂-4%P₂O₅-3%Mg O was the best.Under the optimal reaction conditions,the conversion of toluene is 9.4%and the selectivity of p-ethyltoluene is 99.8%.The stability and regeneration performance of the catalyst were investigated.It was found that the activity of the catalyst decreased gradually after 12h of continuous reaction,but the catalytic performance of the catalyst could basically recover to the level of fresh catalyst after roasting and regeneration,showing good regeneration performance and promising application prospect.