開發甲烷/非甲烷總烴分析儀應用於污染源觸發採樣

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题名:	開發甲烷/非甲烷總烴分析儀應用於污染源觸發採樣
作者:	林天立;Lin, Tien-Li
贡献者:	化學學系
关键词:	觸發自動採樣系統;總碳氫與非甲烷總碳氫;Trigger automatic sampling system;THC and tNMHCs
日期:	2019-07-29
上传时间:	2019-09-03 14:28:39 (UTC+8)
出版者:	國立中央大學
摘要:	本研究目的為開發可應用於周界中非甲烷總碳氫化合物 ( total non-methane hydrocarbon, tNMHC ) 的分析方法，以現今普遍使用之抽氣式觸媒法為基礎，成功設計出獨特以流動注射的觸媒法 ( flow injection )，希冀降低偵測下限，並應用於工業廠區周界空氣的連續監測。實驗主要分為三個部分，第一部分為工業區周界中 tNMHC 的分析方法開發，並將此方法應用於自製的總碳氫分析儀。而常見分析總碳氫方法的系統可分為兩類 : 1. 使用分析管柱的層析法 2.使用觸媒轉化的觸媒法，管柱層析法為使用層析管柱在定溫的條件下將甲烷與 VOCs 分離，利用分流的方式分別得到總碳氫 ( total hydrocarbon, THCs ) 與甲烷的訊號，將兩者相扣即得到 tNMHC的數值；觸媒法則使用觸媒催化的效果消除甲烷以外的 VOCs，並使用電磁閥控制樣品是否流經觸媒反應槽的方式，分別得到 THC 與甲烷的訊號，最後兩者相扣得到 tNMHC的數值。本次實驗以觸媒法為基礎，開發了不同於以往連續抽氣方式的流動注射法 ( flow injection )，使用樣品迴圈 ( sample loop ) 來儲存定量的樣品，以瞬間注射的方式將樣品注入到偵測器，而得到類似層析峰的效果，以此種模擬層析出峰的方式，比起連續式持續的通過轉化觸媒，可大幅增加觸媒的使用壽命。第二部分為開發取代十孔氣動閥 ( valco 10 port valve ) 的鋁塊式注射器，此部分沿用先前實驗室開發出鋁塊預埋式氣體歧管 ( pre-drilled aluminum block manifold ) 的設計理念，將 Valco 10 port valve內部的流道加工於鋁塊當中，搭配電磁閥 ( solenoid valve ) 控制樣品的流向，達到與氣動閥相同的效果。兩者相比較下，鋁塊注射器有較小的體積，且製作的成本相對較低，在標準品連續的測式上，相對標準偏差 (relative standard deviation, RSD) 也小於 5 % ，在未來的系統應用上有很大的潛力。第三部分為將自製的總碳氫分析儀搭配自動採樣裝置，以觸發的方式驅動自動採樣器捕捉高濃度的污染事件，並應用於工業廠區周界的 VOCs連續監測。近年來發生多起工業區的氣爆的事件，而大多數的意外皆源於易燃氣體的大量外洩所致，由於廣大的廠區內存在著眾多的閥件、氣體傳輸管線與儲槽，多數的閥件在經過長時間的運作下，將產生磨耗或風化的情況，最終導致易燃氣體的大量洩漏而引發氣爆的危機。因此本實驗室使用自製的總碳氫分析儀，以快速分析的方式連續監測廠區周界 VOCs 的濃度，最後以 GC/MS/FID 分析捕捉到的污染事件樣品。 ;A new method to analyze ambient total non-methane hydrocarbons (tNMHC) were developed. Modified from the continuous flow catalyst method commonly used today, a unique method of flow injection was successfully designed aiming at achieving a lower detection limit than the continuous flow type when monitoring ambient air. The experiment is divided into three parts. The first part is to develop methods for tNMHC measurement at the perimeter of industrial zones, which can be divided into two types of chromatography based versus catalytic based. The first type mainly uses chromatographic columns to separated methane from NMHC in isothermal condition, and the total hydrocarbon (THC) and methane signals are individually obtained by splitting the sample flow into two, with one going to an empty column and the other going to a chromatographic column. The value of tNMHC is obtained by the THC value subtracting the methane value. The second type uses catalyst to oxidize NMHC without oxidizing methane. The sample flow alternatively going through the catalyst vs. not going through the catalyst yields the signals of methane vs. THC. Subsequently, the tNMHC value is obtained by subtracting the methane value from that of THC. While the second type is more of a conventional design where the sample flow is continuous, a modified method was derived based on the concept of flow injection. A sample loop and a switching value were used to inject sample in a fill-and-flush manner. This so-called flow injection mode would produce signals that mimic chromatographic peaks, which in theory not only can decrease the detection limit, but also greatly prolong the life spend of the catalyst. The second part is the development of an aluminum block injector to replace the commercial 10-port switching valve. Precision machining technology was adopted to make multiple flow paths inside the aluminum block, and 8 solenoid valves were used to control the flow directions of the sample to achieve the same effect as the switching valve. In comparison, the aluminum block injector has a small volume and the production cost is relatively low. Relative standard deviation (RSD) is better than 5%. This self-developed manifold is expected to be applicable in many areas of trace gas analysis. The third part of this thesis is to use the self-built THC analyzer to trigger canister samples to capture pollution plumes for detailed chemical composition. For testing, the analyzer was deployed at the perimeter of a refinery plant. The continuous monitoring last one month with minute resolution with preset trigger levels to capture pollution event samples. This field test resulted in capturing 13 event samples, which were analyzed by in-lab GC/MS/FID for 108 compounds.
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