高效觸媒電漿反應器分解含有機氯化物廢氣

Abstract

二氯甲烷(CH2Cl2)是一種工業上常見的含氯揮發性有機化合物(CVOC)，其排放不僅對人類健康和環境產生有害影響，更是減緩了臭氧層的恢復。目前工業上主要是利用觸媒催化燃燒的方式來去除氣流中的二氯甲烷，但二氯甲烷中的氯原子會毒化觸媒，導致後續的處理效率下降。因此發展一個全新方式來去除工廠廢氣中的二氯甲烷有其必要性。 本研究利用自行設計的介電質屏蔽放電型電漿反應器結合不同觸媒來處理含有 ppm 濃度等級 CH2Cl2 之工廠模擬廢氣，利用電漿產生大量高能活性物質與二氯甲烷非彈性碰撞後達到分解效果，預期將二氯甲烷高效降解成HCl、CO2等產物。本文中分別使用兩種氣體作為載流氣體，分別為0.23%氧氣加上氮氣以及空氣，在未使用觸媒、氣體流速1040 mL/min、滯留時間76.72 ms、二氯甲烷進料濃度1650 ppm、接近電能使用(~10 W)的條件下，使用0.23%氧氣加上氮氣作為載流氣體時可以到達98.7%的二氯甲烷移除率而空氣卻只能達到71.2%。至於降解後的含氯產物，在11 kVpp、20 kHz的輸入電壓下，0.23%氧氣加上氮氣中鹽酸的生成超過了80%，但仍有約13.8%的CCl4、1.7%的CHCl3生成；以空氣作為載流氣體時，鹽酸選擇率則為56%，同時伴隨著HClO(~22%)、CCl4(7.04%)的生成。 考量到純電漿降解過程中經常伴隨氯仿、四氯化碳等有毒副產物，因此嘗試在電漿放電區域中加入200 mg觸媒，希望藉此來改變降解的最終產物。研究發現在電漿與觸媒的共同作用下，二氯甲烷平均移除率、產物選擇率均有顯著的改善，以空氣作為載流氣體為例，表現最佳的觸媒Co3O4/HZSM-5在相同的電能使用下提升了44%的移除率，在抑制四氯化碳的生成同時提升鹽酸的選擇率(~80.4%)。此外，本研究應用XRD、SEM、EDS、XPS等儀器對觸媒的特性進行測定分析，並針對觸媒活性結果進行了說明。

Dichloromethane (CH2Cl2, DCM) is a common chlorine-containing volatile organic compound (CVOC) widely used in various industrial processes. However, its release into the environment can have harmful effects on both human health and the environment, especially in slowing down ozone recovery. As a result, there is a growing need for effective methods to remove DCM from industrial exhaust gas streams. In this study, we used a self-designed Dielectric Barrier Discharge (DBD) reactor combined with different catalysts, to treat exhaust gas streams containing ppm-level concentrations of DCM. The plasma system generated a large number of high-energy reactive species, which degraded DCM in the exhaust gas into HCl and CO2. Two different carrier gases were used in this research: 0.23% O2 balanced with N2 and air. Under the conditions of no catalyst, a gas flow rate of 1040 mL/min, a residence time of 76.72 ms, a DCM feed concentration of 1650 ppm, and an approximate power usage of 10 W, DCM removal efficiency is 98.7% under 0.23% O2 balanced with N2, while DCM removal efficiency is only 71.2% under air atmosphere condition. However, it was considered that although the plasma was highly reactive, there were often chlorine-containing byproducts produced during the decomposition process. For example, at an input voltage of 11 kVpp and frequency of 20 kHz, using 0.23% O2 balanced with N2 as carrier gas, it exhibited over 80% HCl formation, with approximately 13.8% CHCl3 and 1.7% CCl4 formation. In comparison, the HCl selectivity under air atmosphere condition was 56%, accompanied by the formation of HClO (~22%) and CCl4(7.04%). Considering the presence of toxic byproducts such as CHCl3 and CCl4 during the plasma-alone degradation process, an attempt was made to introduce 200 mg of catalyst into the plasma discharge region to alter the final degradation products. It was found that the average removal efficiency of dichloromethane was significantly enhanced in the presence of plasma and catalyst. Taking air as an example, the best-performing Co3O4/HZSM-5 catalyst achieved a 44% improvement in removal efficiency under the same power consumption, suppressing CCl4 formation while enhancing HCl selectivity (~80.4%) at the same time. In addition, the instruments XRD, SEM, EDS, and XPS were also used to evaluate the characteristics of the catalysts and explain the results of the activity.