Oxidation of p-hydroxybenzoic acid by Fenton's reagent

Fenton's reagent has been shown to be a feasible technique to treat phenoli c-type compounds present in a variety of food processing industry wastewate rs. A model compound, p-hydroxybenzoic acid was oxidised by continuously pu mping two solutions of ferrous iron and hydrogen peroxide. Typical operatin g variables like reagent feeding concentrations and flowrate, temperature a nd pH were studied. A mechanism of reactions based on the classical Fenton's chemistry was assu med, and computed concentration profiles of the parent compound, ferrous io n and dihydroxybenzene were compared to experimental results. The model qua litatively predicted the influence of several operating variables, however, calculated results suggested the presence of parallel routes of substrate elimination and/or a initiating rate constant with a higher value. The low efficiency of a well-known hydroxyl radical scavenger (tert-butyl alcohol) also supports the contribution of oxidising species different from the hydr oxyl radical to substrate removal. Further evidence of the presence of reactions different from the hydroxyl r adical oxidation was observed from comparison of the simultaneous Fenton's or UV/H2O2 oxidations of p-hydroxybenzoic acid, tyrosol and p-coumaric acid . (C) 2000 Elsevier Science Ltd. All rights reserved.