Gas-phase Photocatalytic Oxidation Of Volatile Organic Compounds With Fluidized-bed Optical Fibers Reactor

In recent years, the photocatalytic property of TiO₂ to remove volatile organic prollutants in the air has makes it a promising candidate for use in photocatalysis. The design of photocatalytic reactor is a key to improve the photocatalytic efficiency. There are mass transport limitation and low efficiency of light utility in conventional fixed-bed reactor systems, and existing fluidized-bed photocatalytic reactor has the disadvantage of uneven light transmission. Combined with the advantage of high mass transfer efficiency of fluidized-bed, a gas-solid fluidized-bed photocatalytic reactor that employed quartz optical fiber to transmit light and evenly arrange light sources was designed and used for photocatalytic degrading of volatile organic compounds (VOCs). The research can be summarized as following:(1) The fluided-bed optical fiber photocatalytic reactor was optimized. Optimized the flow pattern by adjusting the size distribution of the catalyst and the total flow rate of the gas and determined the optimal parameters of the fluided-bed. The photocatalyst particle was 60¹20 mesh, and range of quality was 1.00g¹.01g, mass ratio of 60⁸0mesh, 80¹00 mesh, 100¹20 mesh catalyst was 1:2:2, static bed height of fluidized-bed was about 27mm; when the total flow of reaction gas was 106mL/min, the height of fluidized-bed could be measured as 36mm or so. The photocatalyst were characterized using SEM, BET. Combining the characterization results, selected the TiO₂/SiO₂ with 10% loading in the degradation experiment.(2) Selected the optical fiber marked 138 as the object, and used potassium ferric oxalate method and UV-B radiation for the determination of intensity of the optical fiber by regulating the output light intensity of UV light source. The result of the light intensity test was following: the intensity of the optical fiber linearly increased with the intensity of the light source. The light intensity measured by potassium ferric oxalate method at 10mm from the head of the optical fiber showed a linear relationship with the light intensity measured by UV radiation meter at the same distance.(3) Choosed acetone as the target pollutants, and used fluidized-bed optical fiber photocatalytic reaction system for degradation experiments under the best conditions of the fluidized-bed. The light intensity, initial concentration of acetone, catalyst loading amount and different composition of the gas were studied. The results showed that when the intensity of light source was 100%, the volume fraction of oxygen was 10%, the loading amount of catalyst was 10% and the initial concentration was 150ppm, the photocatalytic degradation rate of acetone was 56.5%, the quantum efficiency was 1.05%, the conversion activity per unit mass of catalyst was 4.01μmol/(g catalyst·min). Increasing the intensity of light source would increase the degradation rate of acetone. Otherwise, increasing the initial concentration would reduce the degradation rate of acetone. The degradation rate of acetone increased with the increase of O₂ content in the reaction gas, the degradation rate of acetone and light utilization efficiency were the highest when the O₂ content was 10%. The degradation rate of acetone first increased and then decreased with the increase of the content of H₂O in the reaction gas. When the content of H₂O was 1%, the degradation rate of acetone reached 66.6%. The degradation rate of acetone increased with the increase of catalyst loading, however, the conversion activity per unit mass of catalyst decreased with the increase of catalyst loading.(4) Choosed trichloroethylene (TCE) as the target pollutants, and used fluidized-bed optical fiber photocatalytic reaction system for photocatalytic degradation experiments. The light intensity, initial concentration of TCE, catalyst loading amount and different content of O₂ or H₂O in the gas were studied. The results showed that when the intensity of light source was 100%, the volume fraction of oxygen was 10%, the loading amount of catalyst was 10% and the initial concentration was 150ppm, the maximum rate of photocatalytic degradation of TCE was 68.2%, the quantum efficiency was 1.27%, the conversion activity per unit mass of catalyst was 4.84μmol/(g catalyst?min). Increasing the intensity of light source would increase the degradation rate of TCE. Otherwise, increasing the initial concentration would reduce the degradation rate of TCE. TCE degradation rate increased with the increase of O₂ content, the degradation effect were almost the same when the O₂ content was 10%, 5% or 2.5%. The degradation rate of TCE first increased and then decreased with the increase of the content of H₂O in the reaction gas. When the content of H₂O was 1%, the degradation rate of TCE reached as high as 70.9%.(5) Comparing with the fluidized-bed optical fiber photocatalytic reactor, used fixed-bed optical fiber photocatalytic reactor for photocatalytic degradation of acetone and TCE. The results showed fluidized-bed optical fiber photocatalytic reactor not only had a higher ability to remove acetone and TCE, but also had higher quantum efficiency and reaction rate than fixed-bed optical fiber photocatalytic reactor under the same conditions.