Abstract
ABSTRACTDegradation of toluene gas by ozone catalytic oxidation (OZCO) by using a MnO2-based ozone decomposition catalyst (ODC) was investigated to clarify the reactive site of ODC material with O3. An optimum structure for the ODC to remove O3 and toluene were proposed. For honeycomb ODC, toluene degradation by OZCO occurred only around the entrance of the honeycomb ODC, and we expected that a thinner ODC would increase the toluene degradation efficiency. A nonwoven fabric on which ODC was immobilized was developed to decompose O3 and volatile organic compounds simultaneously. The toluene degradation ratio and the mineralization of toluene to CO2 were determined to evaluate the performance of the fabric. Furthermore, the effects of relative humidity and O3 concentration on the decomposition and mineralization ratios were also investigated with or without 254 nm UV irradiation (UV254). The fabric decomposed and mineralized toluene to CO2, even at low O3 concentrations. Although high humidity reduced the degradation ratio of toluene, UV254 irradiation improved the recovery of the degradation ratio and increased the mineralization ratio.
Highlights
Ozone (O3) is a very strong oxidant and has attracted great interest for degrading organic pollutants, such as dyes (Wu et al, 2008a; Cuiping et al, 2009; Srinivasan et al, 2009) and other organic compounds (Perkowski et al, 1996; Yan et al, 2016), in wastewater, and it has been used in pilot-scale wastewater pre-treatment (Lucasa et al, 2010; Somensi et al, 2010)
The removal ratio of toluene decreased gradually with time. This result indicates that intermediate degradation products accumulated on the honeycomb ozone decomposition catalyst (ODC) surface (Qi et al, 2016), and active species generated from O3 reacted with the degradation products and toluene competitively
For UV254+185 irradiation, direct photolysis of toluene gas was expected near the UV lamp, the 185 nm irradiation had little effect on the toluene removal rate for short residence times in the reactor
Summary
Ozone (O3) is a very strong oxidant and has attracted great interest for degrading organic pollutants, such as dyes (Wu et al, 2008a; Cuiping et al, 2009; Srinivasan et al, 2009) and other organic compounds (Perkowski et al, 1996; Yan et al, 2016), in wastewater, and it has been used in pilot-scale wastewater pre-treatment (Lucasa et al, 2010; Somensi et al, 2010). * indicates the species at the catalytic active sites These radicals can react with volatile organic compounds (VOCs) on the ODC surface and the VOCs are decomposed and mineralized to CO and CO2. These reactions are generally called ozone catalytic oxidation (OZCO) and are used to degrade various VOC pollutants in gaseous and aqueous phases (Villasenor et al, 2002; Zhao et al, 2008; Nawrocki, 2013; Jia et al, 2016). A high concentration of O3 is used, and surplus O3 is released from the reactor outlet to the ambient air as exhaust O3. To ensure the effective use of the ODC, the part of the ODC surface to which O3 and VOCs are adsorbed and where the decomposition process occurs should be determined to clarify the optimum structure and amount of ODC materials to install in reactors
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