Effect Of Ion Modifications On The Catalytic Performance Of Nano-HZSM-5 Zeolite In Butene Cracking

The effects of modifying nano-HZSM-5 zeolite with different alkali metal ions and high valence metal cations(HVMC) on the zeolitic acidity and its catalytic performance in butene cracking were studied in a small fixed-bed reactor.By using catalyst characterization means such as,XRF,NH₃-TPD and TG,the following results are obtained:(1) Compared with HZSM-5,ethylene-propylene selectivity was improved to different degree by modifing the H-type zeolite with alkali metal ions.Although the alkali metal ion loadings at which catalysts exhibited the best ethylene-propylene selectivity were different among Li,Na and K,the best ethylene-propylene selectivity obtained with Li,Na and K modified catalysts all fall in 50-60%.Besides,these catalysts exhibited similar reaction stability.Ethylene-propylene selectivity was also improved in catalysts modified with HVMC. And the best ethylene-propylene selectivity of naon-ZSM-5 modified with HVMC A was as high as 63%.The conversion of butene isomers was decreased to different degree over the zeolitic catalysts modified with alkali metal ions and high valence metal cations,The transformation of butene isomers was seen becoming more and more difficult at the sequence of butene-1,trans-butene-2,cis-butene-2,iso-butene.(2) The effects of reaction conditions on the cracking of butenes were studied with DLOP-1 catalyst,HVMC modified HZSM-5.Results show that,low pressure,suitable space velocity,and high temperature were beneficial for improving ethylene-propylene selectivity. The suitable conditions were featured by 1 atm,T=450～540℃,and WHSV=1.5～3.5 h^-1.(3) Under optimum reaction conditions,DLOP-1 catalyst displayed stable activity during a 1000 h time-on-stream.During the long-term operation,the ethylene-propylene selectivity and the yield of propylene were seen at about 50%,and in between 26%-28%,respectively.