Catalyst Preparation And Reaction Conditions Research Of Methyl Benzoate Hydrogenation

Benzaldehyde used widely as fine chemical intermediates are mainly produced via the hydrolysis of benzyl chloride at present,which results in a considerable amount of chlorides in the final product and the consequent corrosion of reactors.To produce chloride-free benzyl alcohol,many methods have been exploered includings selective oxidation of toluene,hydrogenation of benzonic acid,and hydrogenation of methyl benzoate.Selective oxidation of toluene to benzaldehyde is much more attractive due to its economical advantages,but the yield of benzaldehyde is too low to satisfy the demand from industrial application.Hydergenation of benzonic acid is also not implementary,since this process required a large molar raito of hydrogen to benzonic acid and the usage of a lot solvent to dissolve the reactant.In comparison,selective hydrogenation of methyl benzoate is much feasible as it can be couducted with a low molar ratio of hydrogent to methyl benzoate.A series of Mn-Cr-Zr O₂ catalysts have been prepared and examined in the selective hydrogenation of methyl benzoate.Effects of catalyst composition,structure,pores and acid-base properties have been characterized and related to the catalytic performance of Mn-Cr-Zr O₂.According to the obtained experimental results,several conclusions have been drawn,as listed below:1.Loadings of Mn and Cr of Mn-Cr-ZrO₂ catalysts affected both of crystalline phase of Zr O₂ and the overall catalystic performance in the hydrogenation of methyl benzoate.It was found that the catalyst surface area increases because of addition of Cr.With increasing the Cr contents,m-Zr O₂ transformed to t-Zr O₂,reducing the catalyst pore size.The Cr with low content made the catalyst acidity and the consequent acid-catalyzed product such as benzyl methyl ether increase,and the Cr with high content made the catalyst alkaline and the consequent basic-product such as benzyl benzoate rise.Introduction of Mn to Cr-Zr O₂ suppressed the transformation of Zr O₂ from monloclinic to tetragonal phase and reduced its surface acidity,but little effect on its surface alkaline and the consequent basic-catalyzed products.Under conditions of 390 ^oC,0.4 MPa,0.5 h^-1and the molar ratio of hydrogen to ester at 10:1,the conversion of 90.1%and the selectivity of 88.6%were achieved on the Mn-Cr-Zr O₂ catalyst with 2 wt%Cr and 8 wt%Mn.2.Catalytic activity and stability of Mn-Cr-ZrO₂ catalysts were examined and discussed in terms of catalyst pores.Introduction of the pore creating agent in the preparation procedure of Mn-Cr-Zr O₂ catalysts improved significantly their surface areas,pore volumes and the mean pore sizes.As a result,the catalyst with large mean pore sizes（>10 nm）stability was prolonged to even 250 h without obvious decline in activity and selectivity.