Removal of cyclohexane as a toxic pollutant from air using a non-thermal plasma: Influence of different parameters

Abstract

Non-thermal plasmas (NTPs) are a promising technique for abatement of volatile organic compound (VOC) emissions. In this study, the removal of cyclohexane as a toxic pollutant from ambient air was investigated in a dielectric barrier discharge (DBD) reactor at ambient temperature and atmospheric pressure. The effect of specific input energy (SIE) (1.2–3 kJ/L), carrier gases, residence time (1.2–2.3 s) and concentration (220–520 ppm) was evaluated. This work demonstrated that the removal efficiency of cyclohexane increased with increasing specific input energy and residence time. The removal of cyclohexane decreased with increasing concentration at constant SIE and residence time. The main decomposition products were CO2, H2, and lower hydrocarbons (C1–C4). The maximum removal efficiency (98.2%) was achieved at a specific input energy of 3 kJ/L and a residence time of 2.3 s in humidified air. Moreover, maximum O3 concentrations (<10ppm) were observed at 3.0 kJ/L SIE in dry air. NOX was not detected, in any carrier gas. The effect of the presence of water vapour was investigated to determine whether it would reduce the formation of solid residue in the DBD reactor. One of the key findings was that humidification of the air at 25% entirely prevented the formation of solid deposits in the reactor. Humidification not only improved the removal efficiency of cyclohexane, but also increased the yield of H2 and CO2 selectivity. This was due to the formation of potent OH. radicals. In general, this study demonstrates that cyclohexane vapour in air can be almost 100% decomposed to smaller molecules by a non-thermal plasma DBD reactor by optimizing specific input energy (SIE), residence time, humidity, reactor configuration and plasma properties.