Catalysis-assisted Non-thermal Plasma Technique For Removal Of Toluene

The quality of indoor air has been paid much more attention. Non-thermal plasma (NTP) process is a new technology in air purification. However, such NTP technologies still have a problem of high treatment cost. The aim of this study is to develop a hybrid process of plasma and catalysis to reduce VOCs removal cost.The experiments were carried out using a dielectric barrier discharge (DBD) reactor driven by alternative current (AC) voltage power to remove toluene in air. The influence of output voltage of the AC power supply, resident time of the air flow, discharge space volume, exhaust gas humidification on toluene removal rate and energy efficiency was investigated. In-plasma catalytic system with self-made catalysts (MnO₂, TiO₂, zeolite and Fe³⁺+TiO₂) and post-plasma catalytic system with MnO₂ were used to improve toluene removal rate and energy efficiency.The main conclusions are as follows:Toluene removal rate improves with increasing output voltage of AC power supply, discharge space volume and resident time of the air flow. The increases of water vapor will improve the decomposing efficiency, the quantity of toluene decomposed from exhaust air that contained 6%～8% of water vapor is the highest. Subsequently the toluene removal rate declines. The maximum energy efficiency is 0.81 molC7H8/kWh.The two catalytic-plasma system can both improve toluene removal rate. The activity order of catalysts used in in-plasma catalytic system is zeolite〉TiO₂+Fe³⁺〉MnO₂〉TiO₂, and the selectivity ratio of CO₂ when used catalysts is zeolite〉MnO₂〉TiO₂+Fe³⁺〉TiO₂, the maximum energy efficiency is 6.1 molC7H8/kWh. In post-plasma catalytic system the pH of the solution has an important influence on toluene removal rate, the toluene quantity in the gas and liquid phase can both decrease with pH increasing. The maximum energy efficiency is 5.6 molC₇H₈/kWh.Toluene removal in post-plasma system contains two parts. Firstly toluene decomposes in plasma, and then the resident toluene reacts with ozone in present of MnO₂. When pH<6, ozone and toluene are adsorbed on the surface of catalysts and react. When pH>6, ozone absorbed on MnO₂ is oxidized into active substance and decompose toluene.