Studies On Photocatalytic Mini-reactors Of Liquid-solid Fluidized Bed And Gas-liquid Bubble Column

Photocatalytic oxidation technology is a kind of green and environmental oxidation technology,and its applications in wastewater treatment and organic synthesis are the important branches in the photocatalysis field.But,the lag of research and development about high efficiency photocatalytic reactor is one of the main factors that prevent the functionization of photocatalytic oxidation technology.In this paper,two kinds of multiphase photocatalytic mini-reactor are fabricated and their photocatalytic properties are studied with the degradation of model reactant methylene blue（MB）.Liquid-solid mini-fluidized bed reactor with inner diameter（ID）of 1-3 mm were fabricated and studied.Photocatalytic activity was investigated in three mini-fluidized bed reactors,with Fe³⁺ doped TiO₂ photocatalyst coated on the inner wall of fluidized bed(Fe³⁺/TiO₂/quartz tube),on the surface of fluidized particles(Fe³⁺/TiO₂/glass beads)or on both.Compared to the Fe³⁺/TiO₂/quartz tube without glass beads,in the reactor of Fe³⁺/TiO₂/quartz tube with glass beads（d1=3 mm,initial bed height H0=15 mm）,the mass transfer coefficient increased 11-13 times and apparent reaction rate constant increased 4.9 times.In the reactor of quartz tube with Fe³⁺/TiO₂/glass beads（d1=3 mm,H0=15 mm）,experimental results were fitted well with a simplified kinetic model.Degradation rate per unit reaction volume reached highest value at voidage of 0.75 for all ID beds.In the reactor of Fe³⁺/TiO₂/quartz tube with Fe³⁺/TiO₂/glass beads,the degradation ratios were 5-35% higher than that in the other two reactors.With the increase of tube ID,scale-up effect was found.When the H0 was 0 mm,the ratio of average reaction rate Rav,I of 1 mm and 3 mm ID bed was 4.5,which indicated that with the increase of tube ID,the scale-up effect was obvious.When the glass beads increased to H0=15 mm,the ratio of Rav,I of 1 mm and 3 mm ID bed reduced to 1.8,indicating that the increase of glass beads leaded to the decrease of scale-up effect.The ratio of average reaction rate Rav,II of 1 mm and 3 mm ID bed was 1.4-1.9 at all H0.Scale-up effect was caused by the variation of radiation flux density,specific surface area,mass transfer distance and light penetration distance.Gas-liquid mini-bubble column reactor with 3 mm ID was studied,the designed novel gas-liquid distributor can disperse a single bubble with diameter of 1481 μm to multiple micro-bubbles with average diameter of 432 μm,and the specific interfacial area based on reactor volume increased from 57.1 m2 m-3 to 133.5 m2 m-3.The rules of quantum yield that 250 nm < λ < 380 nm and 380 nm < λ < 480 nm were summarized and segmental measurement method was proposed to measure the radiation flux by potassium ferrioxalate actinometer.Differential idea was introduced to build the radiation model,and the distribution of radiation flux density of absorbed light at different central angles was obtained.The surface concentration of ?OH was expressed through pseudo-steady state hypothesis,then the surface reaction kinetics model was built,and the values of the parameters kr,kvis and K1 were obtained by fitting.Compared with the laminar flow of only liquid solution（Re G=0,Re L=6.36）,the k L,MB（Re G=0.27,Re L=6.36）increased to about 10 times.With the increase of Re L and Re G,the average ratio of surface and bulk concentration of MB [Cs,MB/CMB]av will rise.With the increase of εG,the reaction rate constant kr increased in a large scale,the kr of εG=0.011 was about 3 times of that of εG=0.Compared with the gas distributor without sieve,the k L,MB increased to about 2 times,the [Cs,MB/CMB]av increased 2.25% and the kr increased to about 2 times of the gas distributor with sieve.Though,under the visible light,the catalyst had a certain degree of photocatalytic activity,the values of quantum yield ?_ap and ?_ac of visible light were much less than that of UV-light.