Alkylation Of Toluene With Methanol Into Para-Xylene Over ZSM-5

Highly selective preparation of p-Xylene by alkylation of toluene with methanol is an effective way to increase the yield of p-xylene in the future.Alkylation of toluene with methanol on ZSM-5 zeolite was studied in this paper.This paper includes two parts: In the first part,aiming at large grain ZSM-5,we explored how to improve the catalytic performance by controlling the thickness and pore structure.In the second part,the core-shell structure ZSM-5 with rich silicon on the outer surface was prepared by dry gel conversion,and the effects of crystallization time,loading of silica and calcination process on the catalytic performance were investigated.Large grain ZSM-5 with 20 ?m length was synthesized.The selectivity of large grain zeolite to p-xylene could reach 70% without modification.At the same time,the thickness of zeolite can be regulated by introducing heteroatom boron into the synthesis process,and the crystal structure and pore structure of the catalyst are not changed.The reaction data show that the selectivity of the catalyst can be increased by 10 percentage points by adding 3% heteroatom boron.Large grain ZSM-5 has high selectivity but low life and fast deactivation rate.Alkali treatment can improve the diffusivity of catalysts,but also can destroy the pore structure of zeolites and make them lose shape selectivity.In this paper,the effects of alkali treatment conditions on the shape selectivity of ZSM-5 catalysts were investigated.It was found that the treatment of ZSM-5 with 0.2 mol/L TPAOH could maximize the selectivity to xylene,increase the life of the catalysts,and reduce the carbon deposition and carbon deposition rate.The core-shell structure ZSM-5 was prepared.A layer of inert S-1 was loaded on the outer surface to reduce the isomerization of p-xylene and improve its selectivity.In this paper,the dry gel conversion of small grain ZSM-5 was first explored.,the traditional monolithic catalyst preparation method was used to prepare ZSM-5 with silicon source and n-butylamine as template.After treatment at 200 C for 120 h,the silicon-rich ZSM-5 on the outer surface was prepared.At the same time,its selectivity to para-xylene was improved.In the process of trying to increase the load of silica,it was found that it would be difficult to crystallize if the load of silica was increased in the traditional n-butylamine system.By improving the crystallization conditions,the strategy of impregnated TPAOH recrystallization was explored to solve the above problems.In TPAOH system,the dry gel conversion experiments of industrial catalysts were carried out.Firstly,the effect of crystallization time on the catalyst was investigated.It was found that when the loading was constant,the weak acidity of the catalyst increased and the activity and selectivity of the catalyst increased with the prolongation of crystallization time.Increasing the amount of silica coating will seriously affect the catalytic activity.The calcination process is not conducive to the shape selectivity of the catalyst after the conversion of dry rubber.Finally,the optimum treatment conditions were determined to be SiO 2 with 80% loading mass fraction,no roasting and crystallization at 180 C for 72h.