Phenol oxidation in supercritical water

Abstract

The oxidation of phenol has been accomplished in subcritical and supercritical water. Seventy experiments were performed in an isothermal, plug-flow reactor at temperature from 300 to 420°C, pressures from 188 to 278 atm, and residence times from 4 to 111 seconds. The initial phenol concentrations ranged from 2.8 × 10 −4 to 5.3 × 10 −3 M, and the oxygen concentrations were between 6.5 × 10 −5 and 6.4 × 10 −2 M at reaction conditions. The oxidation experiments covered essentially the entire range of phenol conversions. The experimental results were consistent with the global reaction order for phenol being in the range of1/2and 1, and with the global reaction order for oxygen being greater than zero. The conversion increased with increasing pressure, which may either suggest that the reaction order with respect to water was greater than zero, or that the apparent activation volume was less than zero. A variety of reaction products were detected, including mono- and di-car☐ylic acids, dihydroxybenzenes, phenoxyphenols, and dibenzofuran, indicating that the oxidation of phenol in supercritical water may involve a complex set of multiple reactions. The concentrations of metals in the reactor effluent were very low, indicating that corrosion effects were likely not a complicating factor in this study. No metals were detected in the solid material collected in the reaction product filter, also indicating an absence of corrosion effects.