| 摘要: | 本研究主要針對周界環境中的非甲烷總碳氫化合物 (Non-methane Hydrocarbons, NMHC) 進行分析儀的開發，以及測試在線式熱脫附GC/MS連續監測方法 (簡稱TD-GC/MS) 於監測工業區所排放之有害空氣污染物 (Hazardous Air Pollutants, HAPs)。
依照我國EPA公告之標準方法NIEA A740.10C，現今監測周界NMHC以觸媒法為主要方式，其原理為觸媒於高溫下可轉化除甲烷外之VOCs，因此僅有甲烷會通過觸媒管並流至FID得到甲烷訊號。此外，藉由改變樣品流道，即可使樣品通過空管並獲得總碳氫化合物訊號，隨後由總碳氫化合物濃度扣除甲烷濃度後便可計算出非甲烷總碳氫化合物數值。
本研究第一部分為連續進樣觸媒法之NMHC分析儀之開發。首先嘗試以貴金屬觸媒Pd/Al2O3作為高溫氧化VOCs的材料，經實驗測試鈀金屬觸媒具有良好的物種選擇性與催化能力，僅需少量即可轉化周界中的NMHC，因此該觸媒被應用於自組裝NMHC分析儀內。然而，鈀金屬觸媒易受含氯物種的毒化而使催化能力下降，故本研究於分析儀中改以具有較高耐受性的Hopcalite觸媒進行測試，而結果顯示儀器於連續監測時具有更佳的分析穩定性。
此外本研究也將開發出之觸媒法分析儀，與本實驗室先前開發出之流動注射法 (Flow Injection)，以及適用於煙道NMHC監測標準方法–層析管柱逆吹法 (NIEA A723.74B) 等三種不同方式之分析儀於實驗室內進行十日平行比對，並抽引鄰近實驗室之空氣作為分析樣品。實驗結果顯示，三者皆具有相似的濃度變化趨勢，相較於流動注射法與層析管逆吹法透過程式對峰面積積分而使變異度大，以訊號差做為定量方式的連續進樣法於總碳氫化合物與甲烷的連續監測濃度圖譜上，具有較為良好的精密度。
本研究第二部分為在鄰近六輕石化廠區之地點架設實驗室自行開發TD-GC/MS在線式連續監測系統，並對廠區周圍的HAPs進行定性與定量，於監測期間每小時可獲得一筆HAPs濃度資訊。本研究目的為針對現地質譜連續監測技術，於固定污染源周圍進行穩定性與適用性之實測，第一段監測期主要使用中極性DB-624管柱進行實地分析，第二階段監測期則使用PLOT管柱分析低碳數化合物，如氯乙烯與1,3-丁二烯，由實場監測結果顯示，空氣污染物之濃度變化與鄰近光化測站所提供之數據具有相同趨勢，因此可有效驗證TD-GC/MS方法。
;In this study, a non-methane hydrocarbons (NMHC) analyzer has been designed and validated. An online thermal desorption GC/MS method (denoted as TD-GC/MS) was tested in the field to measure hazardous air pollutants (HAPs) from an industrial complex.
According to the Taiwan EPA NIEA A740.10C method, the analytical method based on catalytic reaction is mainly used to measure ambient NMHC. By exploiting the selectivity of a catalyst, ambient NMHC can be measured with minute resolution. In principle, all NMHC except methane can be oxidized by a selected catalyst at high temperatures. The catalyst is chosen in a way that only NMHC can be oxidized and methane is allowed to pass through the catalyst without oxidation and be detected by a flame ionization detector (FID). Subsequently, the total hydrocarbons including methane is measured by FID. Thus, the NMHC signal can be obtained by subtracting methane from the total hydrocarbons reading.
The first part of the research is to develop the catalytic-type NMHC analyzer. At the early stage, Pd catalysts were tested to oxidize NMHC, and the results indicated that Pd catalysts have sufficient selectivity and efficiency in that only 40 mg Pd catalysts were needed to completely oxidize NMHC; thus Pd catalysts was used in our self-assembled NMHC analyzer. However, Pd catalysts were susceptible to being poisoned by halogen-containing species and the catalytic efficiency decreased over time. Alternatively, Hopcalite as the catalyst was used to replace the Pd catalyst in the NMHC analyzer for further testing. The requirement of long-term stability was achieved in the subsequent numerous tests.
In addition, this study also compared three different types of NMHC analyzers of different working principles, including the catalyst-continuous flow type, the catalyst-flow injection type, and the back-flush GC method (NIEA 723.74B) which is designed to withstand high concentrations of NMHC in the flue gas. To test the stability and performance of the three analyzers, they were placed in the laboratory for 10 days measuring air from neighboring laboratories laden with organic compounds. The results showed that the three analyzers displayed similar variation trends. However, the catalyst-continuous flow NMHC analyzer showed higher precision than the other two since the other two methods calculate NMHC concentrations based on peak integration resulting in a poorer S/N ratio.
The second part is to test an online TD-GC/MS method developed by our laboratory near the sixth Naphtha Cracking Complex. The purpose of this study is to test the long-term stability and applicability of the online TD-GC/MS method. In the first monitoring period, a medium polar DB-624 column was used for the analysis. A PLOT column was used to focus on lighter compounds such as vinyl chloride and 1,3-butadiene in the second monitoring period. Similar results were obtained by the neighboring Photochemical Assessment Monitoring Stations (PAMS) to effectively validate the robustness of the self-developed TD-GC/MS method. |
