Study On Vapour Phase Hydrogenation Of Benzoic Acid To The Benzaldehyde

Benzaldehyde is an important intermediate in fine chemical industries, which is mainly used for the manufacture of pharmaceuticals, agrochemicals, perfumes and flavors. Benzaldehyde could be synthesized from many methods, such as the partial oxidation of alkyl aromatics, the halogenation of alkyl aromatics followed by hydrolysis, the halogenation of aromatic acids followed by hydrolysis and the Rosenmund reduction. However, the selectivity and the yield of benzaldehyde were very low, and a large number of harmful wastes were produced for the above methods. The direct hydrogenation of benzoic acid or methyl benzoate to benzaldehyde was a more preferable method for the synthesis of benzaldehyde from the view point of green technology. A large number of metal oxides, including alkali earth oxides, transition metal oxides and rare earth oxides, had been suggested for using as catalysts for the selective hydrogenation of benzoic acid and methyl benzoate. Among these metal oxide catalysts, manganese oxide had shown the higher conversion of benzoic acid or methyl benzoate, and the higher selectivity of benzaldehyde at low temperature.In this dissertation, the zinc oxide catalysts and the MnOx/Al2O3 catalysts prepared by the impregnation method were primarily studied. When using MnOx/Al2O3 prepared by the impregnation method as catalyst, effects of loading amount of MnO, reduction temperature, reaction temperature and the space velocity of hydrogen on the conversion of benzoic acid and the selectivity of benzaldehyde were investigated. When using zinc oxide as catalyst, effects of preparation method and reaction temperature were investigated. The results showed that the zinc oxide catalysts and the MnOx/Al2O3 catalysts prepared by impregnation method all had the higher activity. The conversion of benzoic acid could almost reach 100% at suitable reaction temperature, space velocity of hydrogen and H2/ benzoic acid molar ratio, however, the selectivity of benzaldehyde was lower. Besides, a large number of by-product benzene and toluene was generated in this process, which was...