Studies On The Catalysts For Oxidative Dehydrogenation Of Butene To Butadiene

As one of the most important organic chemical raw materials, the demand for butadienegrows gradually. Meanwhile, the increasingly stringent environmental regulations alsopromote the need of isobutane and isobutene for the production of alkylate gasoline andMTBE. Accompanied by the production of isobutane and isobutene, large amount of n-buteneis also by-produced. Thus, the process of oxidative dehydrogenation of n-butene for butadienecan achieve the efficient utilization of reaources. This thesis mainly focused on the catalystsfor oxidative dehydrogenation of n-butene to butadiene and aimed to improve the conversionof n-butene and the selectivity of butadiene.Bismuth molybdate catalysts with different phases prepared at different conditions wereinvestigated. Differences in reaction performances were proved and the reaction conditionswere optimized. Catalysts were prepared by coprecipitation method, and catalyst reactionperformances were investigated in fixed bed reactor. The results showed that both-Bi2Mo3O12and γ-Bi2MoO6had high stability, while the structure of β-Bi2Mo2O9wasthermally unstable at400°C and could be decomposed into-Bi2Mo3O12and γ-Bi2MoO6. Theperformance of β-Bi2Mo2O9is between those of-Bi2Mo3O12and γ-Bi2MoO6, and inaccordance with the performace for the mechanical mixed catalyst with-Bi2Mo3O12:γ-Bi2MoO6mole ratio at1:1, which indicated that β-Bi2Mo2O9was decomposed into-Bi2Mo3O12and γ-Bi2MoO6at a mole ratio of1:1. Due to the synergistic effect, when-Bi2Mo3O12: γ-Bi2MoO6weight ratio was1:9, the catalyst showed the best catalytic activity.In the γ-Bi2MoO6catalyst reaction system, the optimal reaction conditions were as follows:the reaction temperature390℃, space velocity400h-1, n(n-butene): n(O2): n (H2O)=1:0.75:9.In order to conform to the requirements for the industrial application, the supportedbismuth molybdate catalysts with different carriers were prepared by impregnation method and their reaction performances were also investigated. Among them SiO2was proven to bethe best carrier. The catalyst exhibited the best reaction performance when the particle size ofSiO2ball was100-200mesh and the loading amount was30%, which may be determined byproper dispersion of the active ingredient. In addition, this catalyst also showed a relativelygood stability.In the multicomponent bismuth molybdate catalyst system, the synergy between thedivalent metals as well as the amount of the molybdate would affect the catalyst performance.Moreover different optimal molybdate weight ratios were obtained when using differentdivalent metals in the multicomponent bismuth molybdate catalysts. Compared withγ-Bi2MoO6catalyst, Ni6Co3Fe3BiMo12O51catalyst prepared by coprecipitation methodperformed better and the conversion of n-butene could be improved by11%while butadieneyield was about5%higher.Oxidation dehydrogenation of n-butene to butadiene on bismuth molybdenum systemcatalyst performs in the way of lattice oxygen selective oxidation, following Mars-vanKrevelen mechanism. The study of the reaction performance and lattice oxygen mobility ofthe catalyst demonstrates that lattice oxygen mobility is an important factor for the reactionperformance.