Study On Experiment And Numerical Simulation On Photocatalytic Synthesis And Degradation Using TiO₂

Recently,photocatalysis has been widely used in pollution control,organic synthesis and other fields.Owing to lack of relevant design parameters,reasonable research methods and effective kinetic data,the photocatalytic reactor is not progressing smoothly,so the technology has not yet be industrialised.This paper investgates the effect of reaction volume,hydrodynamics,and radiation on the TiO₂photocatalysis and the performance of photocatalytic reactors by experimental and numerical methods through reaction kinetics and computational fluid dynamics（CFD）,which is of significance for the design and optimization of photocatalytic reactor.In this work,the experiments on ultraviolet light-induced atom transfer radical polymerization（ATRP）using TiO₂was first conducted.The polymerization is controllable according to the experimental data,and the monomer conversion and polymer dispersion index（PDI）increased with increasing reaction volume.Based on the experiment data,the photo ATRP kinetics was modeled by the global optimization moment method.The simulation results fit the experiment data.It can be concluded that when the reaction volume increases,the termination rate coefficient,K_tand the deactivation rate coefficient,K_dadecrease.Because the specific surface area of reaction solution decreases,the local volume rate of energy absorption（LVREA）decreases.Besides,the increasing reaction volume leads to worse mixing,so the viscosity increases,and K_tand K_dadecrease.Therefore,the radical concentration increases,resulting that the polymerization rate and PDI increase.To sum up,the increase of reaction volum results in bad mixing in the reactor so as to intensifying diffusion during polymerization,which more influences on the polymerization than temperature.Then,in order to investigate the influence of radiation and flow field on TiO₂photocatalysis and the performance of photoreactor,the spatial radiation distribution（SRD）model which can accurately predict the radiation intensity distributed exponentially was proposed based on the Lambert-Beer law.The multiphase hydrodynamics and reaction kinetics in a photocatalytic mini fluidized-bed reactor with three phrases were modelled by the dense discrete phase model（DDPM）.The simulation results from the proposed CFD-DDPM model fit the experiment data,which can be used for forecastng experimental phenomenon.Furthermore,the influence of other radiation factors（radiation incidence angle and number of light sources）on the performance of photocatalytic fluidized bed reactor was investigated.Through analyzing the hydrodynamics of gas-liquid-solid three phases and radiation characteristics,the limitations of the assumption that the radiation field has uniform distribution in photoreactors were proposed,and the effect of the reactant concentration,hydrodynamics and radiation field on the reactant degradation was further discussed.Finally,the relationship among radiation field,flow field and reaction kinetics was discussed.