Insight into heterogeneous catalytic wet oxidation of phenol over a Ru/TiO 2 catalyst

Abstract

The kinetics of wet oxidation of phenol over a Ru/TiO 2 catalyst was studied in the temperature range of 175–200 °C, oxygen partial pressure range of 0.34–1.38 MPa and a catalyst loading range of 0.5–1 kg m −3 at near neutral conditions (pH∼6.5). Also studied was the effectiveness of this catalyst in a strongly alkaline medium (pH>12). The catalyst used for the purpose was powdered 5% Ru/TiO 2. This heterogeneous catalyst was found to be very effective for oxidation of phenol and the acetic acid formed, at near neutral conditions. However, the amount of acetic acid formed in its presence in a strongly alkaline medium was very high. The effects of the addition of hydroquinone as a free radical initiator and t-butanol as a free radical scavenger on wet oxidation of phenol were studied in presence of this catalyst at near neutral conditions and also in a strongly alkaline medium. The rate of reaction was enhanced in the presence of the Pyrex liner which reduces the destruction of free radicals by the reactor wall. Addition of hydroquinone enhanced wet oxidation of phenol which is expected because hydroquinone is known to be a free radical initiator. On the other hand, the presence of t-butanol, a free radical scavenger, reduced the rate of degradation of phenol.