| The pulp and paper industry produces a variety of paper products based on renewable resources,while discharging a large numbers of toxic water bodies pollutants that are difficult to degrade,endangering the environment and human health.TiO2 photocatalytic oxidation technology has been widely used in the degradation of pollutants because of its strong oxidation ability and environment-friendly.However,the photocatalytic efficiency of TiO2 is still limited by the characteristics of photocatalyst and the structure of photocatalytic reactor,which hinders its industrial application.Therefore,from the two aspects of photocatalyst and photocatalytic reactor,the research on the simulation of optical properties which can improve the light absorption efficiency of TiO2 photocatalyst and the numerical simulation of magnifying photocatalytic reactor has important theoretical guidance and practical significance for the industrial application of photocatalytic oxidation technology.In this thesis,TiO2 nanotubes（TiNAs）and TiO2 nanoparticles（TiNPs）were used as different morphologies of photocatalysts,and the shallow pool photocatalytic reactor was taken as the research object;by analyzing the physical fields involved in the photocatalytic process,such as light radiant field,reaction kinetics,mass transport and momentum transfer,the numerical simulation of optical properties of TiNAs and TiNPs and the multi-physical field coupling simulation of photocatalytic reactor were carried out based on related experiments,the main research work is as follow:1.The optical absorption properties of TiNAs and TiNPs were studied by combining experiment and numerical simulation.Two different morphologies of TiNAs and TiNPs photocatalysts were prepared,and their morphologies and UV-vis absorption spectra were characterized respectively;The UV-vis absorption spectra and electric field distribution of TiNAs,the absorption and scattering cross sections and scattering electric field distribution of TiNPs were simulated by wave optics theory.The results showed that the UV-vis absorption spectrum of TiNAs increased with the increase of tube diameter and tube length,and decreased with the increase of tube spacing（TiNAs density）.The local electric field enhancement effect in TiNAs open nanotubes was found,which is beneficial to enhance their light absorption.TiNPs has obvious ultraviolet light scattering characteristics,and its scattering characteristics at long wavelength（for example,365nm）were higher than those at short wavelength（for example,254nm）,which indicated that the scattering effect of TiNPs in photocatalytic system could not be ignored,that is,affecting the distribution of light radiation field in the system.2.Combining with experiment and numerical simulation,the method to determine the radiation characteristics of light source and the absorption or scattering characteristics of water treatment medium in wastewater photocatalytic oxidation system was studied.The tubular light source and shallow pool photocatalytic reactor were taken as the research objects,and Rhodamine B,papermaking wastewater and TiO2 suspension system were used as different water treatment media.Based on the experimental measurement results of optical irradiance,two simulation methods of geometrical optics and radiation in participating medium were used to study the radiation characteristics of light source and absorption or scattering characteristics of different water treatment media in wastewater photocatalytic oxidation treatment system by the simulated values of light irradiance being in agreement with the experimental values through parametric scanning simulation.The results showed that geometrical optics can simulate the two-dimensional distribution of light irradiance in water treatment medium,which is suitable for the simulation of light radiation field distribution on the surface of photocatalyst（such as TiNAs）in the supported system,and the radiation in the participating medium can simulate the two-dimensional and three-dimensional distribution of light irradiance in water treatment medium,which is suitable for the simulation of light radiation field distribution in supported photocatalyst surface（such as TiNAs）and suspension system（TiNPs）.3.A method for determining the intrinsic reaction kinetic constants independent of the spatial variation of light irradiance in different photocatalytic systems was proposed.A kind of intermittent shallow pool photocatalytic reactor with uniform mixing and convenient adjustment to obtain different photon absorption local rate（LRPA）of photocatalysts was designed.The photocatalytic degradation experiments of Rhodamine B and papermaking wastewater were carried out with TiNAs and TiNPs as supported and suspended photocatalysts,and the intrinsic reaction kinetics of supported and suspended photocatalytic systems were studied respectively.Combining the optical absorption properties and light radiation field distribution,the different LRPA of photocatalyst could be obtained by adjusting the distance between light source and photocatalyst.The results showed that the intrinsic first-order kinetic model of photocatalytic degradation of pollutants could be fitted by using LRPA and incident light irradiance of TiNAs and TiNPs,and the intrinsic kinetic constants independent of the spatial variation of light irradiation were obtained.4.The multi-physical field coupling simulation method of intermittent shallow pool photocatalytic reactor and the preliminary simulation of reactor scale-up were studied.Taking the intermittent shallow pool photocatalytic reactor as the simulation object and the intrinsic kinetic constants of TiNAs as the experimental basis,the multi-physical field coupling of reaction kinetics with light radiation field,flow field and mass transfer field was realized by step-by-step coupling through the analysis of the internal relationship between reaction kinetics and various physical fields.Furthermore,the established multi-physical field coupling simulation method was verified based on the intrinsic kinetic constants of TiNPs.The scale-up simulation of the reactor was carried out based on the simulation of photocatalytic degradation of Rhodamine B by TiNAs.The results showed that:（1）the photocatalytic degradation mainly occurred near the surface of the photocatalyst exposed to light without stirring,and the concentration distribution in the whole reactor became uniform with stirring.The concentration distribution of pollutants was not affected by different revolutions（uniform distribution）,and the simulated concentration-time curves at different revolutions were consistent with the experiments,which verified that the photocatalytic reaction was not affected by velocity mass transfer.（2）The simulated degradation curves of Rhodamine B were in good agreement with the experiments under the different simulated irradiance of TiNAs surface（or TiNPs liquid surface）.（3）When the surface area of TiNAs and the volume of the reactor were simultaneously expanded by four times,the light irradiance distribution on the surface of TiNAs became uniform,and the degradation rate of Rhodamine B（120 min）by TiNAs photocatalysis increased from 81.4%to 98.8%,with an increase of 21.3%The research work in this thesis is helpful to understand the optical properties of different morphologies of photocatalysts,provide a multi-physical field coupling simulation method for the numerical simulation of photocatalytic reactors,and also provide method guidance for the design and scale-up study of wastewater photocatalytic oxidation reactor. |
