Advanced oxidation processes for the degradation of rho-hydroxybenzoic acid 2: Photo-assisted Fenton oxidation

Oxidation of P-hydroxybenzoic acid in aqueous solution by the photo-assiste d Fenton reaction (Fe (2+) + H2O2 + UV) has been studied. The effects of fe rrous ion concentration (0.05, 0.14 and 0.29 mmol dm(-3)), temperature (10, 20, 30 and 40 degreesC), and initial hydrogen peroxide concentration (0.7, 1.4, 2.2 and 2.9 mmol dm(-3)) on the p-hydroxybenzoic acid conversion were established. Experimental results indicate that the kinetics of this oxida tion process fits pseudo-first-order kinetics well. The overall kinetic rat e constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH.) generated in the s ystem. The importance of these two reaction paths for each specific value o f ferrous ion concentration, temperature and initial hydrogen peroxide conc entration was evaluated. A semi-empirical expression is proposed for the ov erall reaction rate which takes into account both oxidation pathways and is a function of operating variables. (C) 2001 Society of Chemical Industry.