Investigation On Formaldehyde And Toluene Removal By A“storage-oxidation” Cycling Processs

With the rapid development of technology and industry,the widespread use of new products and chemicals has caused a large number of volatile organic compounds（VOCs）emission,which harms the atmospheric environment and human health seriously.Formaldehyde（HCHO）and Toluene（C₇H₈）are two representative VOCs,which are widely used as organic solvents and chemical raw material in the electronics,chemistry,and printing industries.Due to their high toxicity,carcinogenicity and contribution to the formation of secondary pollutants and photochemical smog,the emission of these VOCs is a major environmental concern.Significant efforts have been made to remove low concentration HCHO and C₇H₈.In our previous work,a novel“storage-oxidation”cycling process was proposed for VOCs removal over bi-functional catalysts.VOCs are first enriched on the materials during the storage period at room temperature;and the stored VOCs can be totally converted into harmless CO₂ and H₂O in the regeneration process.The key issue for application of this approach is the design of catalytic materials which should possess balanced properties between storage and regeneration.The materials used for the storage of VOCs such as formaldehyde and toluene should not only possess high and selective VOCs storage capacity,but also be easily regenerated without any release of the VOCs or generation of secondary pollutants.On this basis,a series of research has been carried out and the results were summarized as follows:（1）In removal of HCHO,Boron nitride（BN）nanomaterials with good thermal stability and high specific surface area was selected as a candidate.Due to the low crystallinity,relatively disordered structure,and abundant hydroxyl and amino groups on the surface,BN-800 calcinated in the NH₃ atmosphere exhibited the highest HCHO storage capacity(1.77mmol/g_cat).With assistance of non-thermal plasma（NTP）in regeneration phase,the stored HCHO could be completely oxidized into CO₂ and H₂O.（2）Based on the excellent hydrophobicity and benzene removal performance of TS-1zeolite,we further exploited the"storage-plasma oxidation"cycling process to eliminate toluene over various TS-1 and optimized the discharge parameter.Compared to other catalysts,Ag_1.0Cu_1.0/TS-1-E-NH₃ prepared by ammonia complex adsorption showed the preferable toluene storage performance.Meanwhile,the catalyst could be regenerated for ten cycles in the condition of 21%O₂/RH=50%/N₂,with the discharge power and discharge gap being 15 W and 1.5 mm respectively.The above results showed that TS-1 was also a promising storage material for toluene removal.（3）In order to enlarge the storage capacity of C₇H₈ and meet the needs of industrialization,the beta zeolite was applied the“storage-thermal oxidation”cycling process of C₇H₈ removal.The Si O₂/Al₂O₃ ratio of beta zeolite not only influenced the polarity and hydrophobicity of the molecular sieves,but also had great effects on toluene storage capacity and the thermal stability of the stored toluene,which was directly related to the release of toluene at elevated temperature.Pt_2.0Ag_0.5/β-25 catalyst could totally remove stored C₇H₈ by oxidation in the absent of water;in addition,by controlling the storage time,toluene could be preferentially stored on the silver sites over the Pt_1.0Ag_5.0/β-50 catalyst,which could be suitable for the“storage-thermal oxidation”in dry or humid gas.