| 摘要: | 全氟化物(PFCs, Perfluorinated Compounds)為全球溫暖化潛勢極高之氣體，且存活於大氣中之時間達千年以上，因此造成地球溫暖化問題逐漸受到重視；而為有效控制日益嚴重之全球溫暖化現象，於1997年12月日本京都所召開的溫室效應氣體管制會議中，便將包括PFCs及CO2、CH4、HPFCs、N2O等氣體列為管制項目。PFCs的排放控制方式除了提高製程中之利用率外，尚可採用替代化學物、回收再利用和破壞削減等方法；而相較於替代化學物開發的不易、回收再利用的高成本，破壞削減是現階段控制PFCs之主要方法。本研究嘗試以實驗室規模之介電質放電系統，針對PFCs中之SF6進行低溫電漿處理，並藉由反應氣體組成、供電電壓、供電頻率及氧氣含量等重要參數進行控制，探討線管式與填充床式放電系統對SF6轉化率和產物生成之影響。實驗結果顯示，於添加氧氣之線管式反應器系統中，SF6之轉化率隨供電電壓及供電頻率上升而增加；當氣流中之氧含量增加時，SF6之轉化率隨之上升，然而過量的氧氣將不利於SF6之轉化。當供給電壓為20kV、供電頻率為150Hz、壓力為1atm、操作溫度為293K、氣體組成為[SF6]/[O2]/[Ar]/[N2] = 300 ppmv:12 %:40 %:N2 balance時，所獲得之SF6轉化率為91 %。當反應器結合觸媒填充床時，供給電壓為20kV、供電頻率為150Hz、壓力為1atm、操作溫度為293K、氣體組成為[SF6]/[O2]/[Ar]/[N2] = 300 ppmv:20 %:40 %:N2 balance時，所獲得之SF6轉化率為73 %。就產物之分析而言，於線管式與填充床式反應器皆選擇氣體組成較單純的情況作分析。SF6轉化反應之主要生成的產物以SO2、SO2F2及SOF4為主。系統耗能部份，線管式與填充床式反應器系統所需之操作能量隨供電電壓、供電頻率增加而升高；而填充床式反應器將有效降低系統操作所需之能量。本研究已證實介電質放電系統結合觸媒填充床轉化SF6之技術確實可行，深具發展潛力。 Perfluorinated compounds (PFCs) have great potentials in causing global warming and they may exist in the atmosphere for thousands of years. Therefore, emission of PFCs and its associated global warming attract more and more public attention. To effectively alleviate the increasingly deteriorated phenomenon, the Kyoto Environmental Regulatory Council in 1997 reached a consensus to abate CO2, CH4, PFCs, HPFCs, N2O emissions. In addition to increase the efficiency of utilizing PFCs, the semiconductor industry applied alternative chemicals, recovery/recycle systems and abatement techniques. Owing to difficult development in alternative chemicals and high cost in recovery/recycle systems, the abatement techniques turns to be the primary way to control PFCs emission at present stage. This study investigates the feasibility of applying dielectric barrier discharge (DBD) technology for destroying and removing PFCs from gas streams. The target PFCs selected for this study is SF6, which is commonly used in semiconductor industry as etching carrier or in power industry as insulator. A bench-scale experimental apparatus has been designed and constructed in this study for evaluating the effectiveness of DBD for SF6 removal. Dependencies of removal efficiency achieved with DBDs on operating parameters including applied voltage, composition of the gas stream, applied frequency and oxygen concentration, and power consumption are also investigated. Experimental results indicate that operating the system at higher oxygen gases and applied voltage can enhance the removal efficiency of SF6 achieved with DBD. However, high concentrations of O2 in the gas stream may actually decrease the removal efficiency due to their electronegative properties. More than 91% removal efficiencies have been achieved with this apparatus for SF6 when 20 kV is applied for the gas stream containing [SF6]/[O2]/[Ar]/[N2] = 300 ppmv: 12%: 40%: N2 balance at 293 K, 1atm. In addition, 73% removal efficiencies for SF6 have been achieved with this apparatus combined with catalysts for the gas stream containing [SF6]/[O2]/[Ar]/[N2] = 300 ppmv: 20%: 40%: N2 balance at 293 K, 1atm. The energy yield of SF6 achieved with plasma combined catalysis(CPC) were significantly higher than this apparatus without packed catalysts. With the application of DBD, SF6 molecules can be dissociated and oxidized to other smaller molecules (i.e. SO2, SO2F2 and SOF4). This preliminary study demonstrates the feasibility of applying a novel technology for destroying and removing PFCs from gas streams. Further research should be carried out to identify and quantify the final by-products for better understanding of the removal mechanisms. |
