Study On Isobutene Oligomerization Over Supported Zinc Sulfate Catalyst

As an important way to produce high octane gasoline,isobutene dimerization has the advantages of green,clean,high efficiency and energy saving.How to improve C₈⁼selectivity while maintaining catalytic activity is the challenge of industrialization.Therefore,it is especially important to develop new catalysts.In recent years,supported sulfate catalysts have received extensive attention in the field of olefin polymerization due to their simple preparation process,good thermal stability and easy regeneration process.In this thesis,a series of supported ZnSO₄ catalysts were prepared by using incipient wetness method and they were tested in the isobutene oligomerization.The catalysts consist of Al₂O₃ and SiO₂ as carriers and ZnSO₄ as the active components.The effects of ZnSO₄ loading and activation temperature on the structure,surface acid properties of catalysts were investigated.The structure-activity relationship was discussed.The reaction mechanism of isobutene oligomerization was studied by comparing ZnSO₄/Al₂O₃ with ZnSO₄/SiO₂ catalysts.And it provided theoretical and experimental guidance for industrialization of catalysts.The conclucions are as followings:1.A series of supported sulfate catalysts over Al₂O₃ were prepared by using incipient wetness method.The structure,texture and acid properties of catalysts were characterized by XRD,N₂-adsorption desorption,NH₃-TPD and Py-FTIR,and their catalytic performance in isobutene dimerization were compared.The results showed that the weak acid,medium strong acid and strong acid can catalyze the isobutene oligomerization,and the reactivity is related to total acid of the catalyst.If acid amount of the catalyst is too small,it will not provide sufficient active sites for the reaction.The C₈⁼selectivity was compared under the similar reactivity and the results showed that increasing the relative contents of L acid was favorable for C₈⁼formation.2.The supported ZnSO₄ catalysts?ZnSO₄/SiO₂?were prepared by incipient wetness method with SiO₂ as carrier.The effect of ZnSO₄ loading on the catalytic performance was studied.As the ZnSO₄ loading increases,the catalytic activity first rises and then decreases.When ZnSO₄ loading is 2 wt%,the catalytic activity is the highest.It was found by XPS characterization that the catalytic activity was related to its surface Zn⁺relative content.When ZnSO₄ loading is 2 wt%,both the Zn⁺relative content on the catalyst surface and catalytic activity are the highest.Under the reaction conditions of 50°C,2 MPa and LHSV 3 h^-1,the isobutene conversion and C₈⁼selectivity reached 85%and 76%,respectively.3.Reaction mechanism of isobutene oligomerization over supported ZnSO₄ catalysts?ZnSO₄/Al₂O₃,ZnSO₄/SiO₂?was proposed.The characterization of the structure,surface acid properties of catalysts showed that the isobutene oligomerization over ZnSO₄/Al₂O₃ was catalized by Lewis acid with Zn²⁺as the active sites,While it was carried out on ZnSO₄/SiO₂catalized by Lewis acid with Zn⁺as the active sites.Compared to the dimer selectivity of isobutene oligomerization over the sulfate supported catalysts,Zn⁺showed better selectivity for C₈⁼product in the reaction.