Two-Dimensional Modeling of an Externally Irradiated Slurry Photoreactor

Abstract

A batch cylindrical photocatalytic reactor, externally irradiated by 1-6 UV fluorescent lamps and containing a stirred slurry of polycrystalline TiO 2 , was modeled by coupling a modified Langmuir-Hinshelwood kinetics together with a two-dimensional light intensity field. The radiation field has been determined on the main assumptions of diffuse radiation, isotropic scattering and negligible backward reflected photon flow. The model has been applied to the photocatalytic oxidation of organic substrates which do not undergo homogeneous photochemical degradation. The model is characterized by the following four parameters: the kinetic constants of substrate adsorption, desorption and degradation and the exponent of the power law expressing the kinetics dependence on the light intensity. The model constants may be determined by applying a simple least-squares best fitting procedure.

Validation of a two-dimensional modeling of an externally irradiated slurry photoreactor

“…A batch cylindrical photoreactor (internal diameter 32 mm, height 188 mm) containing 150 mL of aqueous suspension, externally irradiated by 1-6 fluorescent lamps, previously described [15], was used. The distance between the axis of each lamp and that of the reactor was 75 mm.…”

“…The radiation intensity values inside an irradiated scattering medium can be evaluated by solving the radiation transfer equation (RTE) which expresses the radiation energy balance at a fixed wavelength k along a given direction as previously reported [16,17]:…”

“…The in-scattering term contains the phase function, which gives the probability of scattering between the direction of radiation propagation and the other directions. The sum of the absorption and scattering coefficients, k and s, respectively, is the Napierian extinction coefficient [18] of the medium, e. The main assumptions of the Schuster-Schwarzschild approach (which applies for isotropic scattering) [19] are likely to be valid in the present case and they allow to solve the RTE equation [14,15]. Under these assumptions, the Kubelka-Munk solution is obtained (the emission term can be neglected due to the low operative temperatures) [20]:…”

“…As far as the lamps placed in axial position is concerned, the light intensity distribution of a multi-lamps photoreactor was deeply explored too [12]. However, to the best of our knowledge, models for externally irradiated cylindrical reactors have been reported only by Yoshihawa et al [13], Tokumura et al [14] and -very recentlyby Palmisano et al [15,16].…”

“…The present paper is a development of a previous study [15] and proposes a two-dimensional model for the radiation field in a batch cylindrical photoreactor, externally irradiated by 1-6 UV fluorescent lamps, coupled with a modified Langmuir-Hinshelwood kinetics. The model has been validated by comparing the results with those of various photocatalytic runs of 4-nitrophenol (NP) degradation in aerated aqueous suspensions of commercial TiO 2 catalyst.…”