Study On Catalysts And Kinetics Of Liquid-Phase Oxidation Of Toluene By Air

Benzaldehyde and benzoic acid, which are important intermediates and polymer monomers, can be widely and extensively used in organic synthetic industry, such as composites, surfactants, dyes and other fine chemical products. The liquid-phase oxidation of toluene by air is main producing process of benzaldehyde and benzoic acid, which is environmentally friendly for its mild reaction conditions, high yield and good safety. Therefore, this work is to investigate the catalysis and kinetics of the liquid-phase oxidation of pure toluene by using cobalt acetylacetonate (II) [Co(acac)2] or cobalt/manganese/zirconium ethylhexanoate as catalysts separately and benzoic acid as initiator in a stirred tank reactor without the effect of the mass transfer.The catalysis of Co(acac)2, the effects of temperature and catalyst concentration on the oxidation reaction of toluene were firstly studied in this paper. It was found that the ability of deep oxidation decreased in spite of the increase of the reaction time, it displayed better catalytic activity in producing benzaldehyde and benzoic acid during the early reaction, but benzyl alcohol instead during the later reation period. The optimum reaction temperature was 165℃. High concentration of catalyst was beneficial to the production of benzoic acid, and in addition, did not accelerate the oxidation reaction rate, but increased the active time of the reaction. In order to clarity the reaction kinetics of liquid-phase oxidation of toluene, the experiments were carried out at different temperatures. A kinetic model was proposed based on previous studies of our lab and the kinetic parameters were determined from the experimental results.Then, using cobalt/manganese/zirconium ethylhexanoate as catalysts, the effects of the reaction time, temperature, concentrations of catalysts especially the contents of zirconium on the reaction process were discussed, and found that the optimum reaction conditions were 165℃.120μg/g (Co:Mn:Zr=11:3:1). Besides, the catalyst systme not only had a strong synergistic effect, but also proceeded effectively on the reaction if the contents of cobalt. manganese and zirconium were in a proper range. Last but not the least, this paper investigated the catalytic performances of three kinds of catalysts:cobalt/manganese/nicked, cobalt/manganese/zirconium, and cobalt acetylacetonate (Ⅱ). Compared with cobalt acetylacetonate (Ⅱ), the first two kinds of catalysts showed more stable catalytic activity. Besides, zirconium, as an addictive, could significantly inhibit the deposition phenomenon, and could speed up the production of benzaldehyde and benzyl alcohol. Cobalt acetylacetonate (Ⅱ), the optimized catalyst with cobalt (catalyst) and ketone (promoter) combined in one molecular, displayed better catalytic activity in producing benzaldehyde and benzoic acid during the early reaction, however benzyl alcohol instead during the later reation period, which suggested that if more comprehensive and systematic researches were taken, this catalyst will have much broader prospects for development.