Oligomerization Of Isobutene Over Solid Acid Catalyst Containing Fluorine

In recent years, as an environment-friendly catalyst, solid acids became the research focus for oligomerization of olefins. In this thesis, the F-/SO42-/TiO2-SiO2solid acid was applied in the isobutene oligomerization for the first time, and the activity and stability of catalyst as well as the selectivity to products influenced by catalyst preparation parameters and reaction conditions were studied.The characterization of the catalysts with N2adsorption-desorption and pyridine adsorption FTIR indicates that the2F4S/TS catalyst, which was prepared by loading4wt.%H2SO4(leading to4S/TS) followed by2wt.%NH4F on TiO2-SiO2mixed oxide (TS), has much larger BET surface area, pore volume, larger diameter of maximum pores (dM), more medium and strong acid sites in amount, and larger L/B ratio (the ratio of Lewis acid sites to Bronsted acid sites in population) compared with6S/TS that was prepared by loading6wt.%H2SO4on TS. Under the reaction conditions of T=50℃,p=1.8MPa, WHSV=3h-1, both of isobutene conversion and selectivity to the trimers increased in the order:4S/TS<6S/TS<2F4S/TS.It was found that the temperature for the preparing the TS mixed oxide significantly influences structure and property of the2F4S/TS catalyst. When the temperature increased to120℃from100℃, BET surface area, pore volume and dM greatly increased to the ultimate2F4S/TS catalyst, while the acid sites in amount and L/B ratio have not much difference. However, when the temperature increased to150℃, both BET surface area and pore volume were slightly decreased, while the acid sites in amount and L/B ratio increased so much. From the TS prepared at150℃, the most active2F4S/TS catalyst was obtained, over which the largest isobutene conversion and selectivity to trimers were obtained under the aforementioned reaction conditions.The characterization of the catalysts with X-ray diffraction and TG and Py-FTIR indicates that the crystallite size of anatase increased with the calcination temperature increasing in the range of300-500℃. Meanwhile, medium and strong acid sites in amount decreased and L/B ratio increased, which make the optimal temperature for the catalyst calcination appeared at400℃.Under the conditions of p=1.8MPa and WHSV=3h-1, both isobutene conversion and the selectivity to trimers increased with the reaction temperature increasing in the range of30-60℃. Further increasing the temperature led to a decrease of the selectivity. Under the reaction conditions of p=1.8MPa and T=50℃, both isobutene conversion and the selectivity to trimers decreased with the space velocity increasing in the range of1.8-9h-1.The reaction was conducted under the reaction conditions ofp=1.8MPa, T=50℃and WHSV=3h-1with time on stream. Deactivation of the2F4S/TS catalyst under the reaction conditions appeared at the time on stream of8h. For the catalyst that lost about its50%activity (at the time on stream of15h), a re-calcination at400℃in air for4hours led to an essential activity regeneration.