Research On Structure Activity Relationship And Optimizing Strategies Of Immobilized Photocatalytic Reactors

With the development of the modern industrial development,the energy crisis,greenhouse effects and pollutant emission problems not only limit economic and social development,but also threaten the balance and stability of climate and ecological environment,and even health and safety of human beings.The photocatalytic CO2 reduction and the photocatalytic pollutant degradation technologies have the potential to utilize sunlight as energy to solve the above problems with significant economic and environmental profits,which are consistent with the current requirement of renewable and sustainable development in China.However,despite of the material properties,the insufficient mass transport performance,the radiation transport performance,and the catalyst capacity of photoreactors are the obstacles that prevent this technology from the practical applications.In this paper,the physicochemical mechanism in the single-phase multicomponent reaction systems with photocatalysis is analyzed by establishing the multiphysical quantity transport and energy conversion model of immobilized photoreactors via numerical simulations.The synergistic mass and radiation transport,and efficient of photon-chemical energy conversion mechanisms are proposed considering the photocatalytic kinetic characteristics,the transport characteristics of porous substrates,and the radiation transport characteristics of photoconductive medium,which breaks through the traditional substrate design principles in which the reaction specific surface area is regarded as the single evaluation standard,so that the contradiction between the reaction capacity and transport performance of the substrate is alleviated.Firstly,the rigid body dynamics(RBD)model is introduced to simulate the photocatalytic phenol degradation reaction system in granular packing-bed substrates,in which the effects of particle structure characteristics and light source types on photocatalytic performance are analyzed for system optimizing methods.The results show that the best performance could be obtained with spherical particles of characteristic length being 6 mm in the end illumination reactors(EIR).With the same substrate and total radiation input,the average photocatalytic performance of EIR is 2.8 times and 1.88 times higher than that in the internal illuminating reacotr(IIR)and side illuminating reacotr(SIR).The closed cell phenomenon in the annular particle substrate reduces the efficiency of catalyst on the inner surfaces of particles.The deformation of stretching or flattening has a negative impact on the photocatalytic activity of the substrates packed with eccentric cylindrical and ellipsoidal particles,among which the latter is more harmful.The influence law is opposite for ellipsoidal particles.The photocatalytic performance of porocylindrical particles with 3 holes is 15.9%higher than that with 1 hole.Secondly,RBD and Voronoi tessellation algorithm are introduced to establish the model of photocatalytic degradation of n-butanone(MEK)with β-SiC open-cell foam substrate.The effects of boundary conditions,material properties and foam structure characteristics on the photocatalytic performance are evaluated.The results show that the shadow generated by the open-cell foam will reduce the transmittance of the incident light,thereby reducing the utilization efficiency of the catalyst.The multiLED illuminating system is more suitable for the design of compact photoreactors.For opaque substrate materials,although increasing the diameter of struts or cell densities will increase the catalytic active sites,the decline of mass and radiation transport performance will reduce the photocatalytic efficiency of the system.The transparency difference of the substrate material is proved to be the main reason for the unexpected performance of the open-cell foam substrates.The MEK degradation rate with the glass foam substrate is 30.5%and 25.98%higher than that with the opaque foam and glass annular substrates,respectively.The hyalinization of substrates breaks through the limitation of the cell density on the photocatalytic activity,which enable the micron porous media.Therefore,in order to meet the requirements of Stereolithography(SLA)3D printing porous photocatalytic substrate technology for high-performance substrate morphologies,the different minimal surface structures are evaluated,in which the gyroid and Schwarz D structures show significant advantages as transparent photocatalytic substrates.In addition,the parabolic trough concentrating(PTC)system is introduced to combine with the optical fiber and monolith(OFMR)substrates as a concentrating photocatalytic CO2 reduction reaction system to eliminate insufficient daylighting area of OFMR.The effects of structural characteristic parameters and boundary controlling parameters of OFMR on the photocatalytic efficiency are evaluated.Sacrificing the efficiency of catalyst,the outlet concentration of the product could reach 1.85×10-4 mol·m-3,which is 19.25 times that of pure OFMR.In order to improve the utilization efficiency of catalyst,the diameter of gas channels should be controlled within the range of 1.5 to 2 mm,and the number of gas channels should be odd.When the number of reaction units in series is larger than 3,the reaction density will gradually decrease.When the number of reaction units in series exceeds 5,the organic optical fibers have the risk of overheating and melting.Finally,a model of the porous substrate photocatalytic CO2 reduction reaction system based on 2D lattice Boltzmann method(LBM)is proposed to quickly and accurately simulate the multi-physical quantity transport and energy conversion processes.The 2D CNN-LBM method is introduced to deeply learn the characteristics of the substrate structure to correlate the photocatalytic substrate structures with the surface catalytic performance evaluation parameters.The CNN structure is improved to increase the training efficiency and prediction accuracy.The trained neural network was used to predict the photocatalytic performance of minimal surface substrates of high cell densities.It is found that when the cell density is 60 ppi,the median photocatalytic production of CH4 with Schwarz D substrate is approximately 16.67%higher than that with gyroid substrate.