Study The Reaction Process Of Hydrogenation Of Benzene To Cyclohexene

Cyclohexene is an important raw material with an active double bond, which iswidely used in industrial preparation of nylon-6, nylon-66et al. Selective hydrogenationof benzene to cyclohexene is a suitable method for obtaining large scale of cyclohexene.The key of the method is to choose the optimal catalyst and reaction system. Thus, thisthesis focuses on the preparation and characterization of the catalyst used in selectivehydrogenation of benzene to cyclohexene. And then the reaction conditions and theadditive of reaction system are studied.The catalyst precursor is preparated by coprecipitation method with RuCl3·xH2O asthe active component precursor, ZnSO4·7H2O as the promoter precursor and NaOH as theprecipitation agent. The conditions of the catalyst preparation are as follows: temperatureis50℃, the pH of solution is9.5, and the dispersant is ethanol. The catalyst precursor isreduced by hydrogen under the pressure of4MPa. The appropriate conditions of reductionare that the stirring rate is500r/min, the temperature is140℃, and the time of reducing is4h. Then the catalyst after reducing is leached under the conditions of50℃, NaOHconcentration of15%for5h. The Ru-Zn catalyst after leaching is obtained by washingwith deionized water finally.The Ru-Zn catalyst is used in the hydrogenation of benzene to cyclohexene reaction.The result shows that the conversion of benzene is80%, the selectivity of cyclohexene is60%, and the yield of cyclohexene achieves48%. The characterization results of thecatalyst indicate that the specific surface area is48.41m2/g, the particle size is5nm, andthe element quality content of Ru and Zn are94.17%and5.83%.The conditions of hydrogenation of benzene to cyclohexene reaction are optimized.The optimum conditions are as follows: reaction temperature140℃, reaction pressure5MPa, pH5.5, ratio of water to benzene2:1. Under above conditions, the yield ofcyclohexene achieves the maximum value49.36%at the benzene conversion of80.21%.The Ru-Zn catalyst is pretreated under the conditions of temperature140℃, hydrogenpressure5MPa, stirring rate600r/min for10h. After the pretreatment, benzene (VBZ:VH2O=1:2) is added to the autoclave and the stirring rate is adjusted to900r/min. Then thereaction is began. The effects of different additive on the benzene selective hydrogenationare investigated. Firstly, the effect of the sulfate and chloride is tested. The suitableinorganic additives are ZnSO4·7H2O, CoSO4·7H2O, ZnCl2and MgCl2. Next, the effect of adding organic additives is studied. The conversion of benzene is improved by addingethylenediamine, PEG-400and PEG-6000. The selectivity of cyclohexene is increased byadding diethanolamine and diethylamine. Finally the effect of the ionic liquid on reactionis investigated. The conversion of benzene can be obviously improved using themethylimidazolium tetrafluoroborate ionic liquid as additives. On the contrary, theselectivity of cyclohexene can be increased using brominated methylimidazolium ionicliquid as additives. But for additives researching, the preferable effect is inorganic asappropriate additives.