DEVELOPMENT OF A MODEL FOR THE WET AIR OXIDATION OF PHENOL BASED ON AFREE-RADICAL MECHANISM

A model for the wet air oxidation of phenol is proposed, based on elem entary radical reactions that are known to occur in the oxidation proc ess. By applying this model to associated experimental data, unknown r ate constants have been calculated using numerical techniques to solve the system of differential equations that describes the proposed mech anism. The activation energy and pre-exponential factor for the elemen tary reaction between phenol and the phenoxyperoxyl radical (PhOO .) w ere estimated to be 47 +/- 3 kJ mol(-1) and 1.7 +/- 0.1 x 10(10) l mol (-1) s(-1) respectively, while values of 126 +/- 4 kJ mol(-1) and 4.7 +/- 0.2 x 10(10) s(-1) were found for the decomposition of phenoxy hyd roperoxide (PhOOH). The operating parameters of temperature, oxygen co ncentration, pH and addition of free radical promoters (H2O2) have bee n studied, and in general, a good agreement has been obtained between experimental data and calculated concentration profiles. According to the proposed mechanism, it is shown that hydroxyl radicals (OH .) and phenoxyperoxyl radicals (PhOO .) are primarily responsible for the des truction of phenol, with perhydroxyl radicals (HO2.) having a less sig nificant role to play in the process. The principles described in this paper may be applied to understand the wet air oxidation mechanism of other organic compounds. (C) 1998 Elsevier Science Ltd. All rights re served.