Simplified model for the hydrodynamics and reaction kinetics in a gas-liquid-solid three-phase fluidized-bed photocatalytic reactor:: Degradation of o-cresol with immobilized TiO2

The hydrodynamics and reaction kinetics in gas-liquid-solid three-phase fluidized-bed photocatalytic reactors were examined. The effects of initial o-cresol concentration, intensity of UV light, catalyst loading and size of TiO2 photocatalyst, and the dispersion of catalytic particles on the degradation rate of o-cresol used as a model pollutant were examined. The photocatalytic decomposition of o-cresol was reasonably described by the Langmuir-Hinshelwood kinetics. The rate constant of photocatalytic degradation was found to be proportional to TiO2 surface area and the square root of UV light intensity. For the design and scale-up of an external light irradiation fluidized-bed photoreactor, a phenomenological model was developed. The simplified model for the average light intensity was linked to a one-dimensional sedimentation-dispersion model describing catalyst particles concentration profiles in the photoreactor and then to the reaction kinetics. The sedimentation-dispersion model could reasonably describe the photocatalyst particles distribution in the reactor under either the completely or incompletely suspended condition. The evaluated local UV light intensity in the fluidized bed photoreactor was used to determine the rate parameters in the Langmuir-Hinshelwood kinetics. The predictions of the proposed model, in which the UV light intensity profile due to the axial distribution of catalysts is taken account of, were compared well with the experimental results for the photocatalytic degradation of o-cresol using three commercial immobilized TiO2 photocatalysts with different particle size. The model presented may be used as a tool for design and scale-up of three-phase fluidized bed photoreactors. The effect of the introduction of a draft tube into the photoreactor was also investigated, and it was found that the draft tube causes more uniform photocatalyst distributions and as a result higher photodegradation rates.