Radiation absorption and degradation of an azo dye in a hybrid photocatalytic reactor

Results are presented for the photocatalytic degradation of an azo dye, reactive blue 69, in a novel hybrid photocatalytic reactor, illuminated by solar radiation and artificial light, under different experimental conditions. A radiative transfer model, based on the P1 approximation, is proposed to evaluate the distribution of local volumetric rate of photons absorption (LVRPA) in the reaction space of the hybrid photocatalytic reactor. This radiation transfer model, together with a first order kinetic model, is used to fit the experimental results. The model correlates well with the experiments, and values for an apparent first order kinetic constant for the degradation of RB69 are obtained. The proposed radiative transfer model (P1 approximation) is simple enough to allow for an analytical solution, yet complex enough to take into account scattering of radiation in all directions and to all orders. Simulations show a distribution of LVRPA that varies smoothly at small catalyst concentration, and is very quickly attenuated for high concentrations. Around of 70% of photons supplied by both illumination sources to the hybrid photocatalytic reactor are absorbed by the catalyst. The experimental results show the decolorization degree increases as catalyst concentration increase. In relation to mineralization process, the removal of total organic carbon is nearly complete after 5 hours irradiation. This indicates that not only the azo bond breakage is carried out, but also that the intermediate species are mineralized. The apparent kinetic constant has a dependence on catalyst concentration which is described by an adsorption model. Addition of oxygen by means of an air diffuser proves to be beneficial to the process.