The catalytic oxidation of benzoic acid to phenol in high temperature water

The oxidation of benzoic acid (BA) to phenol (the Dow Phenol Process) has been studied in high temperature water (HTW) using a continuous flow system over various metal oxide heterogeneous catalysts: NiO, CuO, Carulite®, MnO2 and Al2O3. Excellent selectivities (>99%) and good yields for phenol (up to 70%) were obtained. The reaction conditions were optimised by varying the temperature, the pressure and the effect of O2. Experiments were carried out for sustained periods in order to study the catalyst deactivation. The results are presented in most of the cases in dynamic conditions; results observed versus time-on-stream for each catalyst tested. Carulite® 300 catalyst was the most effective with a good activity/robustness over time-on-stream. Activity and regeneration of the catalyst with oxygen is reported. Overall HTW shows considerable potential as a medium for this process. Possibilities for extending this chemistry are discussed.