Comparison of Toluene Removal in Air at Atmospheric Conditions by Different Corona Discharges

Abstract

Different types of corona discharges, produced by DC of either polarity (+/-DC) and positive pulsed (+pulsed) high voltages, were applied to the removal of toluene via oxidation in air at room temperature and atmospheric pressure. Mechanistic insight was obtained through comparison of the three different corona regimes with regard to process efficiency, products, response to the presence of humidity and, for DC coronas, current/voltage characteristics coupled with ion analysis. Process efficiency increases in the order +DC < -DC < +pulsed, with pulsed processing being remarkably efficient compared to recently reported data for related systems. With -DC, high toluene conversion and product selectivity were achieved, CO(2) and CO accounting for about 90% of all reacted carbon. Ion analysis, performed by APCI-MS (Atmospheric Pressure Chemical Ionization-Mass Spectrometry), provides a powerful rationale for interpreting current/voltage characteristics of DC coronas. All experimental findings are consistent with the proposal that in the case of +DC corona toluene oxidation is initiated by reactions with ions (O(2)(+*), H(3)O(+) and their hydrates, NO(+)) both in dry as well as in humid air. In contrast, with -DC no evidence is found for any significant reaction of toluene with negative ions. It is also concluded that in humid air OH radicals are involved in the initial stage of toluene oxidation induced both by -DC and +pulsed corona.

Comparison of styrene removal in air by positive and negative DC corona discharges

“…The decrease of corona current at the conditions of VOCs containing air was also reported by Schiorlin et al (2009), who studied the toluene removal using a positive DC corona discharge. Moreover, they observed that the toluene removal efficiency is insensitive to the varying of RH values.…”

“…This argument is also in agreement with the experimental result that a pronounce decrease in corona current is found in the styrene-containing air. But, it should be noted that the positive corona discharge in reference (Schiorlin et al 2009) was operated in the glow mode. In this study, however, the positive corona discharge is operated in the streamer mode.…”

“…With regard to the negative corona processing, the main reaction pathways for VOCs removal are also related to the radicals/atoms initiated reactions (Schiorlin et al 2009 -and OH -) may involve in the styrene removal reaction in some extent by considering two reasons: (1) reactor space is dominated by ion drift region, (2) in contrast to the positive processing, the effect of humidity on the styrene removal efficiency, ozone production and V-I characteristic are moderate.…”

“…They reported that positive polarity discharge is much more effective than the negative one. While some studies showed that positive corona discharge is superior to the negative one, other studies found opposite results (Yehia et al 2000;Marotta et al 2008;Schiorlin et al 2009). It is still necessary to study the effect of discharge polarities on VOC removal efficiency.…”

Studies on the Electrical Behaviour and Removal of Toluene with a Dielectric Barrier Discharge

“…The abatement of toluene with NTP is already widely studied as well as with or without the combination of various catalysts [12,13]. In this paper, the authors report the first experimental results obtained for toluene destruction in a novel dielectric barrier discharge reactor.…”