Photon Transport Phenomena: Radiation Absorption and Scattering Effects on Photoreactors.

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

Photochemical Processes in Continuous-Flow Reactors. From Engineering Principles to Chemical Applications

World Scientific

Lugar: Londres; Año: 2016; p. 97 - 122

Heterogeneous photocatalysis employing solid semiconductors has been applied to solve a wide variety of environmental problems involving the degradation of chemical pollutants and the inactivation of pathogen microorganisms, both in gas and liquid phase. Particularly, heterogeneous photocaltaysis is able to transform refractory organics into readily biodegradable compounds, and eventually mineralized them into carbon dioxide and water. All photocatalytic reactions are initiated by absorption of radiant energy by the catalyst, which promotes an electron from the valence band to a vacant conduction band, leaving a positive hole in the valence band. These charge carriers can then participate in reduction and oxidation reactions with chemical species adsorbed on the surface of the photocatalyst. The rate of the initial radiation-activated step is proportional to the absorbed energy through a property defined as the local volumetric rate of photon absorption (LVRPA) [Cassano et al., 1995]. The LVRPA represents the amount of photons that are absorbed per unit time and unit reaction volume. To evaluate the LVRPA, we must know the radiation intensity at each point inside the photocatalytic reactor. Intensity values can be obtained from the Radiative Transfer Equation (RTE). To solve the RTE in slurry reactors, in which solid catalytic particles are suspended in aqueous solutions, the optical properties of the catalyst suspension are needed.This chapter includes a derivation of the RTE together with the presentation of some methods that can be employed to solve this equation. Also, a detailed description of the experimental method to measure and calculate the optical properties of the catalyst suspension is given. Finally, a practical application showing the kinetic modeling of the photocatalytic degradation of an organic compound (the pharmaceutical clofibric acid) is presented. In this example, the optical properties experimentally measured are used in the LVRPA calculation.