The Study On Systhesis Of Zeolites ZSM-35 And Theirs Catalytic Influences For Butene Skeletal Isomerization

Isobutene is an important organic chemical material,which is used to produce environment-friendly gasoline additive MTBE.With the rapid growth of worldwide demands for MTBE in recent years,the needs of industrial isobutene rapidly increased.Meanwhile,the process of butene skeletal isomerization has become the most potential method to improve the production of isobutene.Zeolite is a kind of important solid acid catalyst.In the research of zeolites,especially as catalysts,the "structure-activity" relationship between zeolites and the corresponding reaction performances,is still one of the most crucial research directions in the field of catalysis.The representative of zeolite ferrierite(FER),ZSM-35,has become one of the most ideal catalysts for the catalytic butene skeletal isomerization,due to fairly good catalytic activity and selectivity on isomerization reaction,because of its unique acid sites and especially the intercrossing pore structure distribution of 8 membered ring and 10 membered ring.In this work,a series of zeolites ZSM-35 were prepared via dynamic hydrothermal synthesis method.The effects of template agent,adding procedure of template agent,content of template agent,amount of water used,ratio of silicon and aluminum,dropping rate of silicon sol,with and without crystal seeds and the crystallization time on crystal structure of ZSM-35.On the top of these,the catalytic performance of butene isomerization were investigated accordingly.The results indicate that,the zeolite ZSM-35 synthesized using pyrrolidine(Py)as the template contains a large number of medium strong acid sites,which can be used to achieve the optimal isobutene selectivity and yield in the isomerization reaction of butene.There is an optimum value of pyrrolidine addition in the synthesis system,Py/SiO2=1.55.With the increase of the water usage in the synthesis procedure,the catalytic activity(isobutene yield)of zeolite ZSM-35 on the isomerization reaction increased first and then maintained at a stable level.The optimum conditions for the synthesis isH2O/SiO2=31.1-37.3.On the study of the effect of Si/Al ratio in synthesis,the experimental results have shown that the ZSM-35 with high crystallinity can not be obtained if the Si/Al ratio is too low(Si/Al<10),while it is easy to induce the formation of the hybrid phase if the Si/Al ratio is too high.Based on our investigation,the optimum range of the Si/Al ratio in the crystallization system of ZSM-35 is Si/Al=12?24.The effect of crystallization time on the structure of zeolite ZSM-35 and the catalytic performance of butene isomerization has been investigated.When the synthesis with crystal seeds,the crystal phase structure of zeolite ZSM-35 can be successfully in 8h crystallization time.If the crystallization time of catalyst extends to 36h in this case,the yield of isobutene reached maximum 35.8%(T.O.S=8h).For the synthesis system without crystal seeds,the crystal phase structure of zeolite ZSM-35 can be gained at the point when the crystallization time reaches 24h.When the 48h crystallization time applied to systhesis procedure in this condition,the yield of isobutene reached maximum 31%(T.O.S=8h)for the catalysts obtained.In conclusing,the addition of crystal seeds accelerated the synthesis of zeolite ZSM-35 crystal.Whatever with or without crystal seeds,the internal framework of zeolite ZSM-35 is basically the structure of Si(1Al)when the required crystallization time is fulfilled and the catalyst can reach a fairly good catalytic activity of the isomerization reaction.The A1 atoms are embedded in the skeleton rather than the edge of the skeleton.The distribution of skeleton A1 is more uniform and stable,and the ratio of Bronsted/Lewis(B/L)acid is the highest,thus medium intensity acid peak is the strongest accordingly.