Effect Of Particle Size And Si/Al Ratio Of ZSM-35 On The N-Pentene Skeletal Isomerization

Due to the relatively high etherification activity,i-olefins can be the better raw materials of high octane gasoline additives,and also play a very important role in industrial production and daily life.In view of the problems of poor stability and high cost of the catalysts for the isomerization of n-alkenes,in this paper,ZSM-35 molecular sieve was synthesized by different methods,and the synthesis conditions of ZSM-35 molecular sieve were explored.The influence of Si / Al ratio and particle size of ZSM-35 molecular sieve on the isomerization of pentene skeleton was also studied.Firstly,ZSM-35 zeolites was synthesized by static seed crystallization,and its isomerization performance was investigated.The results showed that when using the static seed crystallization method,the synthesis range of ZSM-35 zeolites was narrow,and the solid yield and the actual Si / Al ratio ware not relatively lower.With the increase of Si / Al ratio,the acid strength of weak acid and strong acid decreased.When the Si /Al ratio was low,because of the strong acid strength,the polymerization rate was faster,the carbon deposition rate in the active center of catalyst increased,and the catalytic stability decreased.With the increase of Si / Al ratio,the strength and quantity of acid decreased,the polymerization rate decreased,and the catalytic stability increased.However,with the further increase of Si / Al ratio,the acid strength become weaker and the amount of acid decreased,which lead to the decrease of catalytic stability.When the Si / Al ratio was 100～120 and the actual Si / Al ratio is 40～50,the catalyst showed the best catalytic performance.Then ZSM-35 zeolites was synthesized by dynamic seedless method.The results showed that the dynamic seedless method could be synthesized without seed.the solid yield and the actual Si / Al ratio was relatively higher,and the catalytic stability was relatively better.The effect of Si / Al ratio of zeolite synthesized by dynamic seedless method was similar to that by static seedless method,which showed a trend of increasing first and then decreasing.Because the relative crystallinity,solid yield and the actual Si /Al ratio of ZSM-35 zeolites synthesized by dynamic seedless method were relatively higher,the range of Si / Al ratio of the best reaction was reduced,about 30～40.And further,the synthesis conditions of ZSM-35 zeolites with different particle size and the effect of particle size on the catalytic performance were studied.The results showed that the crystallization time had little effect on the particle size of zeolite.With the increase of crystallization temperature,the particle size of zeolite would increase.With the addition of organic template,although the molecular sieve with nanometer size could be successfully synthesized,it contained heterocrysts,so further research was needed.In the appropriate range of Si / Al ratio,the appropriate particle size would reduce the debris of molecular sieve,increaseed the number of pores of molecular sieve,and had moderate acid strength and acid quantity,which would help to improve the isomerization performance.Finally,the Ni and Mo transition metals were loaded on the ZSM-35 zeolite to carry out a preliminary study on the bifunctional catalysts for isomerization and hydrogenation.The results show that the catalyst had certain hydrogenation performance,but it was difficult to achieve selective hydrogenation,so further research was needed.