Fluidized bed photoreactors using composites of titania CVD-coated onto quartz sand as photocatalyst: Assessment of photochemical efficiency

Photocatalytic oxidation of oxalic acid in dilute aqueous solution, in a fully illuminated fluidized bed reactor

“…Thus, the unavoidable segregation suffered by the particles of the photocatalyst composite (which have a given size distribution) must be taken into account. First of all, as already shown in a previous work (Pozzo et al, 2006), the local optical properties of the FB become affected by axial changes in the solid hold-up because, as the voidage of the fluidized bed steadily increases toward the upper zone (where the smaller particles predominate), the light energy is then able to penetrate further (low volumetric extinction). Conversely, in the lower region of the FB, featuring a smaller bed voidage and a higher concentration of coarser particles, the light extinction intensifies, so that the penetration depth of the radiation is much smaller.…”

“…: only one particle size can exist at each FB level), the integro-differential radiation transfer equation (RTE), was solved and validated in a previous work (Pozzo et al, 2006). The corresponding e a (x, y), that is, the LVRPA at position x, y in the reactor (see Fig.…”

“…(In what follows it will be also assumed, as a first approximation, that the decreasing occupation of the TiO 2 surface by species B is a linear function of time and the LVRPA. ); (5) the concentration of adsorbed oxygen on the titania surface is taken as proportional to the concentration of oxygen in the solution (Zalazar et al, 2005), which was kept constant in all the experimental runs by bubbling air into the aqueous solution; (6) also, and according to Blanco et al (2001) it can be postulated that oxygen adsorbs in different sites than oxalate ions do; (7) the steady state approximation may be applied for unstable reaction intermediates such as hydroxyl and other radicals, electrons and semiconductor holes, (8) the local generation rate of the hole-electron pairs, r g , can be adequately established by the 2D radiation field modeling in the FB given by Pozzo et al (2006), as briefly outlined above.…”

“…In a previous work (Pozzo et al, 2006), a methodological approach to determine the radiation field profile in a FB of the titania-quartz sand composite was presented. As a result, a functional dependency between the specific volumetric optical parameters (that is, the spectral absorption and scattering coefficients) with bed height was proposed and validated, by assuming a perfect size-classification model for the FB (viz.…”

“…Yet, because of the low initial concentrations of oxalic acid that were employed, 10-40 ppm (i.e. under the saturation range of titania, Pozzo et al, 2006), the concentration profiles in the reactor had to be modeled as dependent on both time and reactor height.…”