Photocatalytic activity and scale-up effect in liquid-solid mini-fluidized bed reactor

Photocatalytic degradation of methylene blue was studied in three mini-fluidized bed reactors, with Fe3+/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. In the reactor of Fe3+/TiO2/quartz tube with glass beads (d = 3 mm, initial bed height H0 = 15 mm), due to addition and fluidization of glass beads, mass transfer coefficient increased 11-13 times and apparent reaction rate constant increased 4.9 times compared to the empty tube. In the reactor of quartz tube with Fe3+/TiO2/glass beads (d = 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 inner diameter (ID) beds. In the reactor of Fe3+/TiO2/quartz tube with Fe3+/TiO2/glass beads which combined the advantages of above two forms of catalyst, 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. Degradation rate per unit reaction volume in Fe3+/TiO2/quartz tube with glass beads (Rav,I) and that in quartz tube with Fe3+/TiO2/glass beads (Rav,II) were introduced to quantitatively describe the processing ability and scale-up effect. The values of Rav,I of 1 mm ID bed were between 4.5 and 1.8 times to 3 mm ID bed when glass beads increased from empty tube to H0 = 15 mm. The values of Rav,II of 1 mm ID bed were about 1.4-1.9 times to 3 mm ID bed 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.