Department of Chemical Sciences, Universita di Padova, 35131 Padova, Italy.
Environ Sci Technol. 2009 Dec 15;43(24):9386-92. doi: 10.1021/es9021816.
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.
不同类型的电晕放电，由直流（正负直流）和正脉冲（+脉冲）高电压产生，被应用于在室温常压下通过氧化去除甲苯。通过比较三种不同的电晕区在处理效率、产物、对湿度的响应方面的差异，以及对于直流电晕区的电流/电压特性和离子分析，获得了对该过程的深入了解。处理效率按+直流< -直流< +脉冲的顺序增加，与最近报道的相关系统的数据相比，脉冲处理的效率非常显著。在-直流条件下，实现了高甲苯转化率和产物选择性，CO(2)和 CO 占所有反应碳的约 90%。通过 APCI-MS（大气压化学电离-质谱）进行的离子分析，为解释直流电晕的电流/电压特性提供了有力的依据。所有实验结果都与以下假设一致，即在+直流电晕的情况下，甲苯氧化是通过与离子（O(2)(+*)、H(3)O(+)及其水合物、NO(+)）的反应在干燥和潮湿空气中都引发的。相比之下，在-直流的情况下，没有发现甲苯与负离子有任何显著反应的证据。还得出结论，在潮湿空气中，OH 自由基参与了由-直流和+脉冲电晕诱导的甲苯氧化的初始阶段。
