Studies On Cyclohexane Oxidation Dehydrogenation To Cyclohexene

Cyclohexene is an important intermediate for the production of organic chemical industrial products, is considered as the optimal raw material in producing cyclohexanol, cyclohexanone and adipic acid, has a very important prospects for industrial applications. In the process of cyclohexane oxidation dehydrogenation to cyclohexene, the source of raw material range extensive, can continuous production in a fixed-bed reactor use of non-noble metal catalysts, has important significant and broad prospects, it provides a new route for the preparation of cyclohexene.In this thesis, a series of Na or surfactant modified VMgO catalysts were prepared by combining hydrothermal crystallization method. The influence of reaction conditions were investigated in a fixed-bed reactor, and optimized the reaction technology. The research content and experimental result were listed as follow:1) In the research of Na modified VMgO catalysts in cyclohexane dehydrogenation reaction, compared the catalytic activity of unmodified and different alkali metals (Li, Na, K) modified VMgO catalysts, the results showed that the catalytic activity of unmodified VMgO was the best, benzene was the main product; Na-VMgO catalyst has the highest yield of cyclohexene compared with the other alkali metals modified catalysts. Then, the effects of catalytic performance of different Na and V load capability and reaction conditions were investigated. The experimental results showed that, the highest cyclohexene yield of16.6%and cyclohexene selectivity of39.1%were obtained on15Na-12VMgO under the conditions of reaction temperature=410℃, gas flow rate=33ml/min (O2flow rate=13ml/min, N2flow rate=20ml/min), cyclohexane weight hourly space velocity (WHSV)=3.9h-1. In addition, the effects of sodium were investigated by XRD, N2-physical adsorption, FT-IR, H2-TPR, UV-Vis. The result showed that, doped of Na could inhibit the generation of Mg2V2O7, which led to the deep dehydrogenation of cyclohexane to benzene, the oxidative capacity of Mg3V2Og which was the active ingredient of cycohexane dehydrogenation to cyclohexene was reduced.2) In the research of surfactant and Na modified VMgO catalysts in cyclohexane dehydrogenation reaction, catalysts were prepared used different amount of surfactant, Na and V load content, the change of surface active ingredient were characterization by XRD, N2-physical adsorption, FT-IR, H2-TPR, UV-Vis. The result showed that, after crystallization with surfactant the specific surface area improvement significantly, more active center can be provide, the cyclohexane has a higher conversion. When the content of Na was more than V, on the surface of catalysts will formed NaVO3crystalline phase, otherwise, magnesium vanadate will generate on the surface of catalysts, simultaneously, the doped of Na could inhibit the generation of Mg2V2O7, therefore, in order to effectively inhibit the generation of aggregation vanadate species on the catalyst surface the load content of Na and V must appropriate. Catalytic activity study found that under the conditions of nsDBs:nMgo=0.15:1, reaction temperature=410℃, gas flow rate=40ml/min (O2flow rate=20ml/min, N2flow rate=20ml/min), cyclohexane weight hourly space velocity (WHSV)=3.9h-1, the catalyst of22Na-12VMgO obtained the highest yield17.6%of cyclohexene, corresponding the conversion of cyclohexane was35.2%, the selectivity of cyclohexene was50%.3) In the research of the impact of different additives on the reaction of the oxidative dehydrogenation of cyclohexane, the optimal catalyst22Na-12VMgO(nsDBs:nMgo=0.15:1)was used, under the optimal reaction conditions:reaction temperature=410℃, total gas flow rate=40ml/min(N2flow rate=20ml/min, O2flow rate=20ml/min), cyclohexane weight hourly space velocity (WHSV)=3.9h-1the influence of H2O, Ho Ac, H2O and HoAc solution were investigated. The research found that, add H2O or HoAc into the reaction can improve the selectivity of cyclohexene, however, the conversion of cyclohexan decreased significantly. When m(HoAc):m(C6H12)=1.6, the conversion of cyclohexane reach maximum of11.1%, the selectivity of cyclohexene almost100%.