Study On Butene Isomerization Catalysts

To resolve isobutene resource shortage problem through isomerization,butene excess resources into isobutene,it is the most simple and direct way.In the paper,the ether MTBE unit carbon after four as a reactant,the raw materials in the preparation of isomerization of isobutene,translated as MTBE unit of raw material,that promoted the utilization of ether carbon four and after changing the ether carbon waste status of four takeaways as scrap.Studies on the isomerization reaction of n-butenes focuse on the catalyst and the reaction process,there is little research on the thermodynamic aspects of the isomerization reaction.So,thermodynamic data on the inter-isomerization among the four butene isomers,i.e.the standard molar enthalpy change,satandard change of molar Gibbs function and standard equilibrium constant,were calculated in the study.Under the typical industrial reaction conditions,the quantity of releasing heat ranges from-16.2 k J/mol to-5.7 k J/mol,which shows that the reaction of n-butenes isomerization into isobutene belongs to the medium-exothermic reaction.The reaction equilibrium constant ranges from 2.807 to 8.115,which shows that this reaction is limited by the thermodynamic equilibrium.By the equilibrium constant method,the equilibrium composition of the four butene isomers in actual industrial reaction temperature was calculated.The results indicate that using any one of n-butenes as an initial feed,if equilibrium is reached,the isobutene equilibrium content is only a function of temperature.From the thermodynamic point of view,the influencing rules of the reaction conditions on the equilibrium conversion of 1-butene in the main and secondary reactions were discussed,which can be used for improving the industrial catalysts and isomerization process.The catalytic performance of the two types of zeolites,i.e.SAPO-11 and ZSM-22,were investigated.The transformation of n-butenes catalyzed by SAPO-11 follows the single molecule isomerization pathway,and the transformation pathway of n-butenes on the ZSM-22 catalysts is polymerization pathway followed by cracking.By the study of catalyst loading scheme,it is found that two schemes can be used for improving isobutene one-pass yield by the polymerization pathway followed by cracking.The one is the grading loading,making the n-butenes feed through the first SAPO-11 bed,then through the second ZSM-22 bed.The other scheme is using the mixture of SAPO-11 and ZSM-22 as the catalyst.The extruded SZ-50 catalyst was prepared by mixing SAPO-11 and ZSM-22.Using the C4 effluent of MTBE unit as the feed,the SZ-50 catalyst exhibits superior catalytic performances and application prospects,with the n-butenes conversion of above 70%,the isobutene yield of above 25%,the propylene yield of 18% and C₅⁺ gasoline yield of 10%.