Platinum-tin catalysts for dehydrogenation of mixed low hydrocarbons into isobutene

Nowadays,most of the isobutene was obtained as a by-product from both thermal and catalytic cracking processes.Due to growing of demand,butane dehydrogenation to produce isobutene is a valuable process in petrochemical industry.Traditionally,high purity isobutane is used as feedstock for producing isobutene,in which purification process is complex and cost high.In this paper the dehydrogenation process using mixed low hydrocarbons as raw material to produce isobutene was studied over Pt-Sn/Al2O3 catalyst,and the effect of Pt content,Pt/Sn atomic ratio and chlorine content on isobutane conversion and isobutene selectivity were investigated.The results show that the conversion increases with Pt content from 0.20% to 0.40%(mass)and decreases when it is larger than 0.40%(mass).The maximum conversion,35%(vol)even after 8 hours,and the maximum yield of isobutene are obtained at 0.40%(mass)because of smaller particle size and better dispersion of platinum,as shown by TEM results.For the effect of Sn addition,the conversion and the selectivity increase first and then decrease with the Pt/Sn atomic ratio.There is the maximum conversion for the catalyst with Pt/Sn atomic ratio 1∶1,the maximum yield 26% for that with Pt/Sn atomic ratio 2∶3 even after the reaction time of 8 hours.The chlorine content in catalyst was measured by potentiometric titration.The data show that the conversion increases with increase of the chlorine content,while the selectivity declines.There is the best catalyst performance for the catalyst with 0.87%(mass)chlorine.