| 摘要: | 本研究為開發一套自動化定溫(isothermal)的氣相層析儀系統(Gas Chromatography, GC)，搭配逆吹(back flush)的設計，可達管柱自我調理的功能，而不需高溫烘烤，可大幅降低分析時間與電力耗損，並且兼具長期量測與穩定之特性。藉由分離管柱的組合搭配，可應用於三種不同的量測目標上：一、溫室效應氣體的監控；二、煙道中甲烷與非甲烷總碳氫的量測；三、生質氣體的組成成份分析。實驗系統的主要架構為兩組二位十孔閥，藉由搭配適宜的管柱組合與偵測器，可達對不同的分析物種分離偵測的目的。管柱為自製的填充管柱，當填充不同的靜相材料，即可應用於不同分析目的之量測工作。溫室氣體系統量測目標物種有二氧化碳(CO2)、甲烷(CH4)、氧化亞氮(N2O)，利用火焰離子偵測器(flame ionization detector, FID)偵測CH4與CO2、電子捕獲偵測器(electron capture detector, ECD)用於偵測N2O。由於CO2無法直接被FID所偵測，因此，CO2進入偵檢器之前，會先經過鎳觸媒(methanizer)轉化裝置使其還原成CH4再進入FID偵測，此系統可於10分鐘內完成一次大氣分析。甲烷與非甲烷總碳氫的部份，則使用單一十孔閥連接FID即可達成分析之目的，每筆實驗分析時間為5分鐘。生質氣體部份，使用GC-FID分析CH4與C2 ~ C4的主要成份；GC-TCD分析H2、O2、N2、CO、CO2等氣體，每筆實驗數據分析時間為5分鐘。溫室氣體系統實際應用於採樣分析，於2012年02月14日在大台北都會區進行採樣，目的為觀察人為活動對溫室氣體排放之影響與干擾，並將分析結果與地圖繪整成濃度地形圖(contour mapping)，其結果顯示部份地區含有高度排放CH4與CO2，明顯為排放熱點(hotspot)；N2O的濃度則無明顯排放源，濃度分佈較為一致。而生質氣體系統實際應用於生質物炭化製程產氣組成成份分析，可對複雜成份的主要物種分離且偵測，並且因分析時間快速，可以即時反映製程狀況，藉由產物組成資訊以評估製程中之溫度、原料、效率等參數的影響，作為製程最佳化之依據，使生質能產品發揮最大經濟價值。In this study, an automated and isothermal gas chromatographic (GC) system was designed and constructed to analyze low-boiling non-methane hydrocarbons (NMHCs) and greenhouse gases (GHGs). The GC system used two different column sets and detectors. The back-flush design was adopted for the system to permit column self-cleaning and conditioning under an isothermal condition. By doing so, continuous analysis of target gases without losing separation efficiency became possible. Each cycle of analysis took five to ten minutes with a sample aliquot of 2 mL.To analyze greenhouse gases of CO2, CH4 and N2O, two types of detectors were used, one is the flame ionization detector (FID) for CH4 and CO2 detection, the other is the electron capture detector (ECD) for N2O detection. Because CO2 cannot be detected by FID directly, it must be reduced into CH4 by a Ni catalyst under a hydrogen flow. The system used two packed columns, i.e., Hayesep Q as the precolumn and Porapack Q as the analytical column kept at 70℃ inside the GC oven. The reproducibility (RSD) was better than 1% (N=7). The linearity was greater than 0.9999 for the range of 750 ~ 8200 ppbv for CH4, 150 ~ 1600 ppmv for CO2, and 160 ~ 1700 ppbv for N2O. The limits of detection (LOD) are 138.34 ppbv, 3.42 ppmv and 2.30 ppbv for CH4, CO2 and N2O, respectively. In later study, the system was applied to canister analysis. Contour plots were made to reveal “hotspot” of emission over the great Taipei metropolitan area. In the future, the system can be further expended to include more greenhouse gases, such as SF6.In the application of determining methane and total non-methane hydrocarbons contents, the system used only one flame ionization detector (FID). Separation was made by a Unibeads 1S pre-column, and a Porapack Q analytical column kept at 70℃. Each cycle of analysis can be completed within 5 minutes.In the biogas application, we use two different column sets and detectors to target H2, O2, N2, CO, CO2, CH4, and selected low-boiling NMHCs. For the category of permanent gases such as H2, O2, N2, CO, CO2, thermal conductivity detector (TCD) was employed for detection. Separation was made by a Hayesep D pre-column, and two analytical columns packed with Molecular sieve 5A and Hayesep Q, respectively, operated at 70℃. The CH4 and NMHC channel are detected by FID. For this purpose, two different lengths of Unibeads 2S columns were used as the pre-column and analytical column. NMHCs from C1 (CH4) to C4 (1-butene) can be analyzed within 5 minutes. Coupling of this GC system to a biogas reactor will be conducted to monitor on-line the composition of biogas in a continuous manner under various process conditions. |
