Involvement of free radicals in the aqueous-phase catalytic oxidation of phenol over copper oxide

In this study, CoAPO-5 was found to be an effective heterogeneous catalyst for the liquid-phase oxi- dation of cyclohexane with glacial acetic acid as the solvent without any promotors 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/cm2 and 115–135°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 CoII and CoIII. Reaction mechanism and rate expressions were proposed. Since the conversion and selectivity reported in this study were mod- erately 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.

Liquid-phase oxidation of cyclohexane using CoAPO-5 as the catalyst

Catalytic oxidation of aqueous p-chlorophenol and p-nitrophenol solutions

For reactions necesitating a solid catalyst and which invoive both reisuvely volatile and nonvclarile reactants, three-phase reactirs are required. Equipment used to achieve intimate contacting of the three phases has been procominantly in the form of slurry reactors, analogous to the stirred-tank homogenous system, or fixed-bed reactors in which the two fluid phases flow through a stationary bed of catalyst particles. Trickle-bed reactors are a type ofthe second classification in which both gas and liquid flow downward through the catalyst bed. Such systems avoid the disadvantage of separating small catalyst particles from the fluid product streams associated with slurry reactors, and also avoid the limitation of flow rates uncountered with upflow or countercurrent flow through fixed beds.

H.J. Neuburg

Papers

Heterogeneous liquid-base oxidation of cyclohexene with manganese dioxide as catalyst