Research On Products Distribution And Mechanism For Toluene Removal By Dielectric Barrier Diszcharge Combined With Catalysis

The emission of volatile organic compounds (VOCs) with extensive sources is one of most important air pollution and harmful to human health. Compared with traditional technologies, non-thermal plasma-catalysis (NTP-catalysis) is considered as one of the most promising technologies for environmental pollution control in recent years, with many advantages such as low cost, high removal efficiency, less energy consumption, simple operation, less by-products etc. However, they still have many drawbacks. However, NTP-catalysis still has some problems to solve such as the simultaneous removal of toluene and ozone, analysis of by-products and investigation of synergetic mechanism.Technology of dielectric barrier discharge (DBD) combined with catalyst which performed efficiently in the simultaneous removal of toluene and ozone was applied for toluene descomposition. Effects of various reaction conditions were investigated. The products such as carbon monoxide, carbon dioxide and ozone were quantitatively analyzed. The products of toluene decomposition in gasous and solid phase were confirmed. In addition, the catalysts were characterized and analyzed. Based on the experimental results, the formation mechanism of products was analyzed. The roles of ozone and hydroxy radical in DBD-catalysis system were analyzed and the degradation mechanism was proposed.The main research contents and results were as follows:(1) DBD did not produce ozone and high energetic particles produced could degrade toluene effectively in N2. With higher input voltage (>9.0kV), the promotional effect of water vapor was greater than inhibitional one on toluene removal with N2 as background gas. High concentration ozone was produced when toluene was removed by DBD with air as background gas. Important effects of input voltage, humidity, as well as the initial toluene concentration on toluene removal and ozone outlet concentration were investigated in air.(2) The performance of dielectric barrier discharge was improved with catalyst in plasma. The stimulation of catalyst on the catalytic removal of toluene by nitrogen active species was not obvious. Removal efficiencies of toluene and ozone were higher with catalyst loaded at the back end of nickel foam than at the front end. Water vapor has a negative effect on toluene removal, but it could reduce the outlet concentration of ozone.(3) High removal efficiencies of toluene and ozone could be realized simultaneously with catalysis in plasma. With input voltage of 9.0kV, the toluene removal efficiency was up to 92.8% and that of ozone was above 99% within 80 min. Other species except ozone produced by air discharge had little contribution to toluene removal in post-plasma. Humidity had little effect on the removal efficiencies of toluene and ozone under higher ozone concentration.(4) The heterogenous products produced in toluene removal by DBD-catalysis were the main cause of low carbon balance. Water vapor was beneficial to the conversion of CO to CO2, which could also reduce the by-products and improve carbon balance with catalyst in post-plasma. By-products of toluene decomposition included ring-retaining substances (benzoic acid, benzaldehyde, benzyl alcohol etc.) and ring-cleavage substances (propane, 2-methylbutane, acetaldehyde, formic acid, nitromethane etc.). Base on the analysis of products, the degradation mechanism of toluene was deduced.