The Research On Synthesis Of ZSM-35 Zeolite With Small Crystal Size And Performance Of Skeletal Isomerization Of N-butene

The.crystal size of zeolite is a very important property parameter.Compared with the conventional one,zeolite with small crystal size means larger external sueface,more active sites and shorter and structured channels,which make the small crystal size zeolite show better performance in the catalysis reaction,such as higher activity and selectivity,longer catalytic life,improved capacity of resistance to coke deposits,sulfur and heavy metal.Thus,it was worthwhile that the study on zeolites small crystal size in industrial field.In this thesis,highly-crystallized ZSM-35 zeolite with small crystal size had been synthesized successfully through hydro-thermal system.The samples were characterized by the means of XRD,SEM,TEM,NH3-TPD?BET and XRF analyses.The scale-up synthesis experiments also were completed in the 2L autoclave,which obtained the good results as the original.The resultant ZSM-35 zeolite were applied in the skeletal isomerization of n-butene,and the effects of reaction conditions(reaction time,tempreture and weight hourly space velocity),grain size and SiO2/Al2O3 on the catalytic performance were investigated systematically.In the paper,ZSM-35 zeolite was prepared via hydro-thermal method with a aluminosilicate reaction slurry having the following mole ratio content:SiO2/Al2O3=10?30,H2O/Al2O3=10?400,R/SiO2=0.5?20,OH-/SiO2=0.03?0.3.The factors of the systhesis of ZSM-35 zeolite were investigated,shch as template,alkalinity,water amount,seed,stirring speed,aging step,and crystallization time so on.The influence of three templates on the crystallinity of ZSM-35 zeolite was ranked:pyrrolidine>ethylenediamine>cyclohexane.The sample synthesized with ethylenediamine as the template could achieve smaller grain size than pyrrolidine.In our experiments,the suit alkalinity,namely OH-/SiO2,ranged from 0.03 to 0.18,the best OH-SiO2 for 0.06?0.12.Increasing the alkalinity of the system could favor reducing the partical size of ZSM-35 zeolite.However,the alkalinity was too high,which would cause the crystal size of ZSM-35 zeolite become larger.The diminution of water of the synthetic system would cause the crystal size of products smaller.However,adverse tendency was presented once the amount of H2O was below the limit value.With reducing the ratio of H2O/SiO2,the relative crystallinity of ZSM-35 zeolite rose first and then fell.The amount of seed to system of ZSM-35 zeolite could not affect the crystal size obviously,while the grain size of seed had a significant impact on that.Results indicated that higher rotating speeds(0?300r/m)of the autoclave could contribute to decreasing the grain size and increasing the crystallinity of ZSM-35 zeolite.The addition of seed could reduce the crystal size of ZSM-35 zeolite obviously.The aging of reaction gel under low-tempreture condition could accelerate the nucleation process,so that more crystal nucleus was producted.Results showed that the product ZSM-35 zeolite had smaller crystal size,higher relative crystallinity when the gel was aging for 10h at 40?.Skeletal isomerization of n-butene was investigated over ZSM-35 zeolite catalysts,and the influence of reaction condition on the catalytic performance was syatematically studied.The evaluation results showed that the excellent skeletal isomerrization performance was exhibited with isobutene selectivity of 95%and isobutene yield for 45%under the optimizied reaction condition(T=400?,WHSV=7.0h-1).Under an optimized reaction conditions,ZSM-35 zeolite with smaller crystal sizes exhibited not only high isobutene yield but also good stability during the skeletal isomerization of n-butene.