LIQUID-PHASE OXIDATION OF CYCLOHEXANE USING COAPO-5 AS THE CATALYST

Tn this study, CoAPO-5 was found to be an effective heterogeneous catalyst for the liquid-phase oxidation of cyclohexane with glacial acetic acid as the solvent without any promoters being added to the reaction mixture. The effects of cobalt content, BET surface area and dissolved cobalt ions and the kinetics of the reaction were investigated at 5-15 kg/cm(2) and 115-135 degrees C in a semi-batch autoclave reactor. Under these reaction conditions, no induction period was observed. The products of reaction were cyclohexanone, cyclohexanol, dibasic acids, and caprolactone, etc. The ratio of the concentration of adipic acid to succinic acid had a maximum value at the middle stage of reaction. The initial rate of reaction was found to be proportional to the 2.0 power of the cyclohexane concentration and to the 0.5 power of the catalyst loading. The effects of oxygen pressure on the reaction rate depended on the cobalt content and the reaction conditions. The cobalt ions of CoAPO-5 are mainly in the lattice positions and they can transform reversibly between the oxidizing states of Co-II and Co-III. Reaction mechanism and rate expressions were proposed. Since the conversion and selectivity reported in this study were moderately good, and because CoAPO-5 has the advantage of being a durable heterogeneous catalyst, it could prove useful as a catalyst for the one-step liquid-phase oxidation of cyclohexane.