KINETIC MODELING OF THE PHOTOCATALYTIC DEGRADATION OF CLOFIBRIC ACID

SATUF, M. L.; MANASSERO, A.; ALFANO, O. M.

Jacksonville

Conferencia; 17th International Conference on Semiconductor Photocatalysis and Solar Energy Conversion; 2012

Redox Technologies Inc.

The occurrence of pharmaceuticals in the aquatic environment has become a subject of major concern due to their potential harmful effects. Particularly, blood lipid regulators are largely consumed and they are frequently detected in groundwater and drinking water. Clofibric acid (CA), the active metabolite of the lipid regulator clofibrate, is hardly biodegradable and cannot be completely eliminated in wastewater treatment plants. Photocatalytic degradation of CA has already been demonstrated. Furthermore, reaction intermediates have been identified and reaction pathways have been proposed. However, intrinsic kinetic data has not yet been published. The aim of the present work is to obtain a kinetic model to simulate the photocatalytic degradation of CA in slurry reactors. Experimental runs have been performed in a cylindrical reactor with a circular flat window. UV radiation was provided by a halogenated mercury lamp (150W Powerstar HQI from OSRAM). The incident radiation flux, experimentally measured by ferrioxalate actinometry, is 3.14 x 10-8 Einstein/(s cm2). The reactor operates in a closed recirculating circuit driven by a peristaltic pump. The system is completed with a storage tank equipped with a water-circulating jacket to ensure isothermal conditions during the reaction time (20 °C). The tank contains a device for withdrawal of samples, a thermometer, and a gas inlet for oxygen supply. The reaction system was continuously fed with oxygen. The reactor volume is 54 mL, and the total volume is 1000 mL. Experiments have been carried out with different catalyst concentrations (0.1; 0.25; 0.5; 1.0 g/L TiO2 Degussa P25) and levels of irradiation (30, 65 and 100 %). Based on mechanistic reaction steps, kinetic equations for CA and two main intermediates, 4-chlorophenol (4-CP) and benzoquinone (BQ), have been developed. Accurate estimation of the radiation field inside the photoreactor must be accomplished to obtain kinetic information useful for design and scale-up purposes. The Monte Carlo method was applied to know the spatial distribution of radiation absorption in the reaction space. This information was introduced in the reaction rate expressions and kinetic parameters were evaluated from experimental data. Figure 1 represents the experimental and predicted concentrations of CA, 4-CP and BQ for a run performed with 0.5 g/L TiO2 and 100 % irradiation level. The model accurately simulates the degradation of CA in a photocatalytic slurry reactor, and the obtained kinetic parameters are independent of the irradiation conditions and reactor geometry.