Promotion of toluene degradation in negative DC corona discharge by magnetic field

Enhancement of the efficiency, energy yield (EY) and COx selectivity of volatile organic compound (VOC) removal by negative DC corona discharge through application of a magnetic field was demonstrated. Experimental studies were carried out in a wire-to-cylinder type reactor composed of an aluminum cylinder with 20 mm inner diameter and a nickel-chrome wire with 0.5 mm diameter located at its axis. Toluene was chosen as the VOC agent. During the experiments, the outer aluminum tube was connected to a high DC voltage, while the central wire was grounded. The stationary magnetic field was supplied by cylindrical permanent magnets producing a magnetic field along the axis. Experimental results demonstrated that the magnetic field could efficiently increase the discharge current, the efficiency of toluene removal, EY, COx selectivity and the production of O3 and NOx. In addition, the above quantities were obviously improved with the increase of magnetic induction strength and magnetic field cover length. For example, at a discharge voltage of 10.6 kV, the removal efficiency value was 79.3% at 0 mT but increased to 85.5% and 91.5% when the magnetic induction strength was increased to 54 mT and 145 mT respectively. The analysis of the outlet gas through GC-MS indicated that the organic byproducts primarily consisted of formic acid, acetic acid, maleic anhydride and benzaldehyde. A possible pathway for toluene degradation was proposed based on these byproducts.