Kinetics of the Oxidation of p-Hydroxybenzoic Acid by the H2O2/UV System

• Published in: Industrial & engineering chemistry research 2001-07, Vol.40 (14), p.3104-3108
• Main Authors: Beltran-Heredia, Jesus, Torregrosa, Joaquin, Dominguez, Joaquin R, Peres, Jose A
• Format: Article
• Language: English
• Subjects: Applied sciences; Biological and medical sciences; Chemistry; Exact sciences and technology; Food industries; Fundamental and applied biological sciences. Psychology; General and physical chemistry; General aspects; Industrial wastewaters; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Pollution; Pollution and sludges; Wastewaters; Water treatment and pollution
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie001069i

The decomposition of p-hydroxybenzoic acid in aqueous solution by UV radiation and by H2O2 /UV radiation has been studied. The experimental results indicated that the kinetics of both oxidation processes fit well by pseudo-first-order kinetics. In the second oxidation process, the overall kinetic rate constant was split into two components:  direct oxidation by UV irradiation (photolysis) and oxidation by free radicals (mainly OH•) generated in the decomposition of H2O2. The effect of pH (2, 5, 7, and 9), temperature (10, 20, 30, and 40 °C), and initial hydrogen peroxide concentration (1, 2.5, and 5 mM) on the conversion of p-hydroxybenzoic acid was established. The importance of these two reaction paths for each specific value of pH, temperature, and initial hydrogen peroxide concentration was quantified. Last, a general expression is proposed for the reaction rate which takes into account both pathways and is a function of known operating variables.