Wet air oxidation of phenol: Factors that may influence global kinetics

Wet air oxidation is presented as a technique for removal of organic pollutants found in waste water streams. The oxidation of phenol has been achieved at moderate temperatures (T=473 K) and pressures (3.0 MPa total pressure) with up to 95% destruction in less than 30 minutes. An increase in either oxygen concentration or temperature has a positive influence on reaction rate, with temperature following an Arrhenius dependence. The influence of pH is shown to be complex. For a 0.01 mol(-1) phenol solution significant destruction was obtained; however, when the initial pH was modified to either less than two or between neutrality and ten, practically no change in phenol concentration was observed. When oxidation is carried out in strong alkali media (pH>12) reaction rate is enhanced significantly. Addition of small quantities of hydrogen peroxide resulted in enhanced rates of oxidation even at low temperatures (373 K). When hydrogen peroxide is added, oxygen plays a negligible role in the initial reaction, only becoming significant once the hydrogen peroxide has been consumed. The nature and geometry of the reactor has been found to play an important role in free radical termination steps, with metal surfaces likely to enhance significantly decomposition of organic radicals.