Study On The Synthesis Of ZSM-5 Zeolite And Its Catalytic Stability For Toluene Alkylation With Methanol To P-xylene

P-xylene（PX）is one of the most important aromatic products.It is mainly used in the production of terephthalic acid（PTA）.PTA is further reacted with ethylene glycol（EG）to produce polyethylene terephthalate（PET）.At present,p-xylene is mainly obtained by catalytic reforming of naphtha.The process of p-xylene production by alkylation of toluene with methanol uses toluene with excess capacity and methanol from coal chemical industry as raw materials to produce p-xylene with high selectivity,which greatly reduces the separation energy consumption.It is conducive to not only promoting the balanced development of China’s petrochemical industry and coal chemical industry,but also realizing the energy saving and emission reduction of aromatics production,which is in line with China’s overall plan of‘carbon neutralization and carbon peaking’.Therefore,it is particularly important to promote the industrialization of this technology as soon as possible.The aim of this paper is to prepare industrial ZSM-5 catalyst for severe reaction conditions.The effects of basicity range on the morphology of ZSM-5 zeolite,as well as the influence of hydrogenation metal to the stability of ZSM-5 catalyst for alkylation of toluene with methanol are fully investigated.The specific research content is as follows:Firstly,a series of ZSM-5 zeolites with different Si O₂/Al₂O₃ ratios were synthesized by using cheap silicon source,aluminum source and structure directing agent as raw materials.The suitable n（Na₂O）/n（Al₂O₃）range for ZSM-5 zeolite synthesis was investigated when the Si O₂/Al₂O₃ was controlled to be 30-120.The basis of adjusting and controlling the morphology,pore structure and acid properties of ZSM-5 zeolites in low-cost system was provided.The scale-up synthesis and modification of kilogram catalyst were realized and successfully applied in industrial practice.Additionally,the catalytic performance of modified ZSM-5 zeolite for the alkylation of toluene with methanol to p-xylene was investigated.The intrinsic relationship between the conversion,selectivity and stability of the catalyst was illustrated.The effective method to control the catalytic performance of ZSM-5 zeolite was built.On the above basis,this thesis focuses on investigating the effects of ZSM-5 zeolite grain size,as well as introducing hydrogenation metals on the stability of the catalyst.1)A series of ZSM-5 molecular sieves with different grain sizes were prepared,and the selectivity of p-xylene were controlled to be higher than 97%by modifying with Si O₂.The effect of grain size on the stability of Pt/ZSM-5 catalyst was investigated.It was found that the catalyst with smaller grain size exhibited better stability.2)The influence of impregnation solvent to the catalytic performance of Pt/ZSM-5 was investigated.The results showed that the[Pt（NH₃）₄]²⁺species which was formed by impregnating Pt with chloroplatinic acid in ammonia solution partly entered into the molecular sieve.Thus,the hydrogenation activity and stability of the catalyst were improved.3)Ni was introduced into ZSM-5 zeolites by impregnation and in-situ encapsulation.The effect of different methods on the coke-resistant capacity was investigated.It was found that in-situ encapsulated Ni species can make the catalyst have higher hydrogenation activity,which is conducive to the improvement of catalyst stability.