Study On The Alkylation Performance Of Ethylbenzene And Ethylene Over Modified ZSM-5 Zeolite Catalyst

Para-diethylbenzene（PDEB）is an important organic chemical raw material,which is mainly used as a desorbent in the process of catalytic reforming of naphtha to produce para-xylene.On the other hand,p-divinylbenzene generated by high-temperature dehydrogenation of p-diethylbenzene is a multi-purpose cross-linking agent in the industrial production process,and has strong application value.The process of producing p-diethylbenzene by alkylation of ethylbenzene and ethylene is independently developed in China,and has the advantages of simple process principle and abundant raw material sources.But the biggest problem of this process is that the catalyst is easy to coke,has weak anti-coking ability and short life.The fundamental reason is that the alkylation of ethyl styrene is accompanied by many side reactions such as ethylbenzene disproportionation and p-diethylbenzene isomerization.The occurrence of these side reactions will lead to the formation of aromatic macromolecules in the catalyst pores that are difficult to diffuse out of the pores,and eventually lead to coking and deactivation of the catalyst.In response to the above challenges,this paper firstly used cheap water glass as silicon source and aluminum sulfate as aluminum source to synthesize ZSM-5 with different silicon-alumina ratios,and investigated the effect of silicon-aluminum ratio on the catalytic performance of ethylbenzene and ethylene alkylation;The catalyst with an aluminum ratio of45 achieved kilogram scale-up synthesis.On this basis,the effects of hydrothermal treatment under different conditions on the acidity,pore structure and anti-coking ability of ZSM-5 catalyst were systematically studied.The results show that the temperature and time of hydrothermal treatment have a significant effect on the stability of the catalyst,and the optimal hydrothermal treatment conditions are:T=550°C,t=3 h,WHSV_H2O=1 h^-1.Among them,the HT-550-3-1 catalyst showed the best stability,and the conversion rate decreased by only 2.6 percentage points after running for 32h.Thermogravimetric analysis found that its carbon deposition was much lower than that of the HZSM-5 precursor（1.38 wt.%vs 5.08 wt.%）.The main reason is that hydrothermal treatment under suitable conditions can control the acid amount and acid strength of the catalyst and generate abundant mesopores.The reduction of acid content can reduce the occurrence of side reactions,improve the selectivity of p-diethylbenzene,and inhibit the formation of coke deposits in the catalyst;the increase of mesopore volume can reduce the influence of internal diffusion and improve the coke capacity of the catalyst.The combined effect of hydrothermal treatment on the acid properties and pore structure of ZSM-5 zeolite resulted in a significant improvement in the stability of the catalyst.Using Z5-HT catalyst as the matrix,the effects of single element modification and composite modification of silicon,phosphorus,magnesium and lanthanum on the properties of the catalyst and the alkylation performance of ethylbenzene and ethylene were investigated.By correlating the effects of different types of modifier dosages on the pore structure and acid properties of the catalyst and the performance of ethylbenzene and ethylene alkylation,it was found that appropriate amount of Si and La modification could effectively improve the activity of ZSM-5 without significantly affecting the activity of ZSM-5.The selectivity of p-diethylbenzene is more than 95%,and the stability of the catalyst can be improved.Therefore,the Z5-HT catalyst was further modified to prepare the Z5-HT-9Si-4La catalyst.The reaction process was 456 h.Among them,the conversion rate of ethylbenzene is higher than 12.1%,and the selectivity of p-diethylbenzene is higher than 97.0%,which has a good industrial application prospect.