title: Oxidation of p-hydroxybenzoic acid by UV radiation and by TiO2/UV radiation: comparison and modelling of reaction kinetic.
abstract: The phenolic compound p-hydroxybenzoic acid is very common in a great variety of agroindustrial wastewaters (olive oil and table olive industries, distilleries). The objective of this work was to study the photocatalytic activity of TiO2 towards the decomposition of p-hydroxybenzoic acid. In order to demonstrate the greater oxidizing power of the photocatalytic system and to quantify the additional levels of degradation attained, we performed experiments on the oxidation of p-hydroxybenzoic acid by UV radiation alone and by the TiO2/UV radiation combination. A kinetic model is applied for the photooxidation by UV radiation and by the TiO(2)/UV system. Experimental results indicated that the kinetics for both oxidation processes can be fitted well by a pseudo-first-order kinetic model. The second oxidation process can be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K(pHB), and the second order kinetic rate constant, k(c), were 0.37 ppm(-1) and 6.99 ppm min(-1), respectively. Finally, a comparison between the kinetic rate constants for two oxidation systems reveals that the constants for the TiO2/UV system are clearly greater (between 220-435%) than those obtained in the direct UV photooxidation.
authors.affiliation: Departamento de Ingenieria Quimica y Energetica, Universidad de Extremadura, 06071, Badajoz, Spain. jbelther@unex.es
authors.forename: J B
authors.initials: JB
authors.lastname: De Heredia
authors.forename: J
authors.initials: J
authors.lastname: Torregrosa
authors.forename: J R
authors.initials: JR
authors.lastname: Dominguez
authors.forename: J A
authors.initials: JA
authors.lastname: Peres
mesh_terms: D002384:Catalysis; D004396:Coloring Agents / Q000737:chemistry; D062385:Hydroxybenzoates / Q000737:chemistry*; D007700:Kinetics; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid
chemical_list: D004396:Coloring Agents; D062385:Hydroxybenzoates; C009495:titanium dioxide; D014025:Titanium