Wet air oxidation is a process in which organic materials in the aqueous phase are oxidized by air at temperatures between 300°F and 600°F and pressures of 1000‐1800 psia. To improve our understanding of the process, its kinetics were studied using a propionic acid solution to simplify both analysis and rate measurements. The aim of the research was to define the regime where the reaction rate is kinetically controlled, to develop a model for the reaction rate and to interpret the model in terms of mechanism. Oxidation appears to proceed homogeneously in the aqueous phase and is probably kinetically controlled between 450° and 550°F. The oxidation appears to take place via two principal routes. Approximately half the propionic acid is oxidized completely to carbon dioxide while the oxidation of the remainder apparently proceeds via acetaldehyde as an intermediate to acetic acid. Acetic acid oxidizes only at a very low rate. A power law rate expression was developed which adequately described the oxidation of propionic acid solutions.

Wet air oxidation is a process for the oxidation of organic matter dissolved or suspended in water. It operates from 300 to 600 F, usually at pressures of 1000 to 1800 psia. The process is not well understood. This paper reports a kinetic study using propionic and butyric acids. Our research has been directed towards three objectives: identification of the kinetic-control regime; development of a rate equation model, and investigation of the oxidation mechanism. Most of the work was performed using propionic acid. Results with this compound appears to be confirmed by studies using butyric acid. With vigorous agitation, the reaction is kinetically controlled below 550°F and is homogeneous in the aqueous phase. Oxygen attack at the α carbon is suggested by the data. This would account for the high yields of acetic acid. This slowly oxidized acid forms via acetaldehyde. A power law rate expression was developed for the oxidation of propionic acid. Work with butyric acid supports the propionic acid results.