Studies Of Preparation And Catalytic Performance Of Propane Dehydrogenation Catalysts

Propylene can be used for the preparation of polypropylene, butanol, phenol, acetone, acrylonitrile and lipid products, among them polypropylene products share the largest proportion. China owns rich resources of liquefied petroleum gas, and propane accounts for 60%, generally as a fuel or directly vent out, which caused a great waste of resources. Thus propane dehydrogenation technology has been getting increasing attention. And the development of efficient dehydrogenation catalyst is particularly important. In this thesis, the catalysts prepared mainly by novel liquid-phase reduction and Pt nanoparticles supported on γ-Al₂O₃. The prepared Pt nanoparticles present a controlled morphology, the smaller the particle size, a uniform distribution and superior performance for propane dehydrogenation through changing the preparation and reaction.In order to improve the investigated accuracy of the propane dehydrogenation reaction conditions, the better dehydrogenation performance of Pt-Sn/γ-Al₂O₃ catalyst was prepared after some attempts. The influence of reaction atmosphere, space velocity, reaction temperature and the molar ratio of hydrogen and air were investigated. The results showed that adding a certain amount of air mixed in the feed, the space velocity of 5200 h-1, the reaction temperature of 590 ℃ and air/hydrogen ratio of 5:4 can achieve best performance. The subsequent study was based on the reaction conditions.Again, the effect of catalyst preparation conditions on the properties for propane dehydrogenation was investigated. Compared with conventional catalysts which prepared by impregnation, catalyst prepared by liquid-phase reduction appeared lower opportunity to reunion with a smaller particle size and uniform distribution by TEM analysis. H2PtCl6 concentration, ratio of PVP and Pt, different types of stabilizer and catalyst calcination temperature also were studied for propane dehydrogenation. The results showed that, H2PtCl6 concentration of 1.0297×10-3⁸.2379×10-4 mol/L, propane conversion and selectivity were relatively high. PVP amount exerted little effect on the propane dehydrogenation performance, so chose the smallest proportion. Compared with PVP, the catalyst prepared by CTAB owned relatively large difference in the propane conversion. Catalyst was calcined at 500 ℃, propane conversion was the superior. If the calcined temperature was too high, Pt nanoparticles would sinter.Additives for Pt-based catalysts exert supurior modification in terms of light alkane dehydrogenation, and then the impact of Sn for Pt/γ-Al₂O₃ catalyst results was examined. The result showed that the addition of Sn can significantly improve the selectivity to propylene and catalyst stability. The option of SnCl2 direct added and the way of Sn first added then Pt made the additive achieved excellent improvement. And then the second additives of K, Ce and Zn also were investigated, including these additive precursor species, adding mode, and the amount of additive. The results showed that this KOH was selected as K source, impregnation reduction method and K content of 1.0 w% were adopted, propane conversion maintained at around 44 % and the proplene yield reached 42 %. The Ce and Zn additives also adopted the same adding way that obtain better dehydrogenation performance, in which the content of Ce was 3 w%, it can achieve the superior yield of propylene. In terms of Zn additive, the selectivity to propylene gradually decreased with the amount of additive increased, while propane conversion trend showed firstly increasing and then decreasing with increasing the amount of the additive.