|dc.description.abstract||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.