Abstract:

With the environmental improvement in China, the management of Volatile Organic Compounds (VOCs) are of more significance. Among various VOCs elimination technologies, plasma technology has the advantages including simple process, wide range of pollutants treatment, and strong applicability, suitable for the treatment of VOCs with large air volume and low concentration. Non-thermal arc plasma has the advantages of both cold and thermal plasma, which broadens the application of plasma waste gas treatment technology. However, due to the self-magnetic compression and thermal pinch effect of non-thermal arc, the size of plasma is small, and thus restricts its application in practice. In this paper, a self-developed multi-arc plasma reactor was developed to treat VOCs. Toluene was selected as the representative pollutant in the work. The characteristics of plasma in the reactor and the influence of various parameters on the treatment effect of toluene waste gas were investigated. The results showed that the arc voltage decreased with the increase of discharge current and increased with the increase of working gas flow rate. The size of the multi-arc plasma discharge zone increased obviously, about 1.4 times that of a single arc under the same condition of input power. Furthermore, the stability of the multi-arc plasma had significant improvement due to the interaction among arcs. The removal rate of toluene decreased with the increases of initial concentration and gas flow rate. Under the conditions of gas flow rate of 8 m³∙h^-1, discharge power of 410 W and initial concentration of 2000 mg∙m^-3, the energy efficiency was up to 25.8 g∙kW^-1∙h^-1. Catalyst enhanced the complete decomposition of toluene and significantly improved the conversion of toluene to CO₂ in the plasma reaction, which was cordierite supported nano-Pt placed 30mm below the discharge zone. The selectivity was over 20% higher than that without catalyst. Under the conditions of gas flow rate of 8 m³∙h^-1, discharge power of 490 W and toluene initial concentration of 2000 mg∙m^-3, the CO₂ selectivity reached a maximum of 62%. In addition, the main gas phase intermediates of toluene degradation were benzene and benzaldehyde.

Key words: plasma, multi-arc discharge, toluene, composite catalysis, supported catalyst, cordierite

摘要：

随着中国对环境治理的深入进行,中国对挥发性有机化合物（Volatile Organic Compound,VOCs）治理的要求越来越高。在各种VOCs治理技术中,等离子体技术具有工艺流程简单,可处理污染物种类范围广,适用性强等优点,尤其适合处理大风量、低浓度的VOCs。非热电弧等离子体由于具有兼具冷、热等离子体的优势,拓宽了等离子体废气处理技术的应用范围,因而备受关注。然而,由于非热电弧固有的自磁压缩和热箍缩效应等属性,导致等离子体尺寸较小,制约了其在实际中的应用。该文通过自主研制的多弧等离子体处理VOCs废气反应器,选择代表性污染物甲苯作为被处理对象,考察了反应器中等离子体的特性,各种参数对甲苯废气处理效果的影响。结果表明,电弧电压随放电电流的增大而减小,随着工作气体流量的增大而增大。多弧等离子体放电区尺寸明显增大,约为相同输入功率单个电弧的1.4倍,并且由于多个电弧的相互作用,稳定性明显提高。甲苯去除率随着初始浓度和气体流量的增大而减小,在气体流量8 m³∙h^-1,平均放电功率410 W,初始质量浓度2000 mg∙m^-3的条件下时,能量效率达到最大值25.8 g∙kW^-1∙h^-1。通过在放电区域下方30 mm处使用堇青石负载纳米Pt催化剂,发现等离子体复合催化剂的使用可有助于促进甲苯的完全分解,显著提高甲苯向CO₂的转化,CO₂选择率均比不使用催化剂时高20%以上,在气体流量8 m³∙h^-1,平均放电功率490 W,初始质量浓度2000 mg∙m^-3的条件下,CO₂选择性达到最大值62%。甲苯降解的气相中间产物主要是苯和苯甲醛。

关键词: 等离子体, 多弧放电, 甲苯, 复合催化, 负载型催化剂, 堇青石