Catalytic wet air oxidation of phenol by CeO2 catalyst--effect of reaction conditions.

The effect of catalyst loading, oxygen pressure, reaction temperature and phenol concentration on phenol conversion and total organic carbon (TOC) conversion, using CeO(2) as the catalyst, was investigated. There appeared a maximum rate of phenol conversion and TOC conversion as the catalyst loading increased. With phenol concentrations in the range of 400-2500 mg/L and oxygen pressure of 0.5 or 1.0 MPa, the optimal catalyst loading was 1.0 g/L, while it was 2.0 g/L at an oxygen pressure of 1.5 MPa. With a phenol concentration of 5000 mg/L, the optimal loading was 2.0 g/L for all oxygen pressures tested. Catalyst loading influences the reaction via the free-radical chain reaction involved in the catalytic wet air oxidation of phenol. Regarding oxygen pressures, at a phenol concentration of 400mg/L, the influence of the tested pressures (0.5, 1.0 and 1.5 MPa) on the 3h conversion of phenol was negligible, while the effect was significant for higher concentrations of phenol. The effect of oxygen pressure on TOC conversion was more profound, especially at a higher phenol concentration. At a pressure of 0.5 MPa, except for concentration of 400mg/L, the CO(2) selectivity barely exceed 80% at best, and was less than 25% with a phenol concentration of 5000 mg/L. At a pressure of 1.5 MPa, the selectivity was as high as 90% even for a concentration of 5000 mg/L. As was expected, increase of reaction temperature shortened the time taken to reach 50% phenol conversion. In addition, TOC conversion also increased with reaction temperature. Working from these observed results, optimal operating conditions were proposed.