Isobutene Oligomerization Over Superacid Catalysts

Diisobutenes and triisobutenes are important intermediates in the chemical industry. In this study, the isobutene oligomerization over three superacid catalysts was investigated.SO42-/SnO2was applied in the isobutene oligomerization for the first time in this study, and the performance of the catalyst in the reaction being influenced by the preparation parameters, modification additives of the catalyst as well as reaction conditions was investigated. It was found that SO42-/SnO2prepared from SnCl4·5H2O is more active than that prepared from SnCl2·2H2O. Higher calcination temperature of Sn(OH)4in the range of300-600℃is unfavorable for preparing active and stable catalyst. Calcination temperatures of the SO42-/SnO2catalysts have also significant impacts on the activity and stability. The initial activity of the catalyst for the reaction decreases with the calcination temperature in the range of400～700℃, while the catalyst obtained by calcination at500℃in air displayed the best catalytic stability in all of the tested SO42-/SnO2catalysts. XRD characterization results indicate that SnO2in the catalyst calcined at500℃exclusively presents in tetragonal phase, whereas it appears both in tetragonal phase and monoclinic phase in the catalyst calcined at600℃. NH3-TPD characterization results indicate that total acid sites in population on the catalyst decreases with the calcination temperature in the range of400～700℃, which may be responsible for the initial activity decrease of the catalyst with the calcination temperature increasing. It was found that the SO42-/SnO2catalyst prepared by obtaining a dry Sn(OH)4from SnCl4·5H2O hydrolysis in ammonia without calcination, and impregnating the dry Sn(OH)4in sulphate acid has the highest activity and catalytic stability for the reaction.Over this catalyst, isobutene oligomerization was investigated. It was found that when the weight hourly space velocity was changed from1.5h-1to9.0h-1at50℃, the conversion of isobutene decreased from95.5%to57.9%, accompanied by the selectivity decrease to trimer from60.6%to43.3%and the selectivity increase to dimer from27.3%to51.8%. On the other hand, when the reaction temperature changed from30℃to60℃while holding the weight hourly space velocity at2.5h-1, the conversion of isobutene increased from50.3%to98.0%, accompanied by the selectivity increase to trimer from27.2%to67.0%and the selectivity decrease to dimer from67.2%to26.2%.Under the same reaction temperature of50℃and weight hourly space velocity of2.5h-1, the isobutene conversion obtained in liquid-solid phase reaction was higher than that in gas-solid phase reaction. The catalyst that was deactivated in the liquid-solid phase reaction can be easily regenerated by calcining it at400℃in air for3h, by which the initial activity of the catalyst for the reaction as well as the selectivity to each products were well restored.The isobutene oligomerization was also investigated over xFe-SO42-/ZrO2catalysts. It was found that by adding1.0wt%of Fe in to SO42-/ZrO2, not only the activity of the catalyst for the reaction, the resistant ability of the catalyst to deactivation was also significantly improved.AlCl3/HY catalyst was prepared by treating dry HY with CCl4/N2and applied for the reaction. At the reaction temperature of50℃and the weight hourly space velocity of2.5h-1, the catalyst gave the isobutene conversion of82.6%with the selectivity to trimer of56.8%and the selectivity to dimer of37.4%. The resistant ability of the catalyst to deactivation seems to be worse than the other catalysts. After time on stream of the reaction for4.5h, the activity of the AlCl3/HY catalyst sharply declined.In comparison with SO42-/SnO2, the catalyst of1%Fe-SO42-/ZrO2is more active for the isobutene oligomerization. Nevertheless, the resistant ability of1%Fe-SO42-/ZrO2catalyst to deactivation seems to be worse than that of SO42-/SnO2. The activity of1%Fe-SO42-/ZrO2sharply declined at the time on stream of12h under the reaction conditions of40℃and4.0h-1, while SO42-/SnO2deactivated after time on stream of16h under the reaction conditions of50℃and2.5h-1.