Comparison And Analysis Of Hydrogenation Activity Of Aromatic Acid For Synthesizing Chlorine-free Aromatic Aldehydes

As a very important intermediate in Pharmaceuticals, pesticides, dyes, Aromatic aldehydes products development in land is rapid in recent years. With continuous exploitation of many new uses and good export demand, the market demand is growing fast. Aromatic aldehydes products have become the hot domestic fine organic chemical raw materials. There are a lot of methods to synthesize Aromatic aldehydes such as alkyl aromatic hydrocarbon oxidation, Hydrolysis of halogenated alkyl aromatic hydrocarbon, hydrogenation of halogenated aromatic acid, aromatic alcohol oxidation or dehydrogenation, but these synthesis technology exists different shortcomings and aldehydes yield is not satisfied. Therefore, a series industrial catalyst for hydrogenation of aromatic acid to aromatic aldehydes, which is economically and friendly to environment were conceived and prepared by co-precipitation method in our laboratory. The effect of catalyst layer temperature, hydrogen space velocity, surfacial acidity-alkalescence of catalyst and substituted group on hydrogenation of benzoic acid,p-toluic acid,terephthalic acid have been investigated. At Xiamen YongQuan Spice Company, the hydrogenation of benzoic acid to chlorine-free benzaldehyde was studied in small and pilot plant scale. The experimental results show that the hydrogenation reaction temperature over this catalyst is considerably lowered comparing that on traditional catalysts, meanwhile, the high activity and selectivity of the catalyst are also maintained. In the same experimental conditions, the results showed that the hydrogenation reactivity of the substituted benzoic acid with electron-donating group was higher than benzoic acid. In the reaction of pilot plant scale, the selectivity to benzaldehyde of 83 % and the conversion of benzoic acid of 99.0 % are achieved under the condition that reaction temperature, pre-reduction time of catalyst, pressure of hydrogen, pressure ratio of hydrogen and benzoic acid , gas hourly space velocity of hydrogen were controlled at 370±5℃,50 h, 1.4×10⁵ Pa -1.6×10⁵Pa,40: 1-50: 1, 650 dm³Â·kg^-1·h^-1- 750 dm³Â·kg^-1·h^-1 respectively.