| dc.description.abstract | In light of the incident of propylene explosion occurred on August 1, 2014 in southern Taiwan resulting in heavy casualties, an analytical means capable of detecting trace amounts of fuel or industrial gases in the vicinity of storage facilities, pipelines, factories, etc. is in dire need of development. As a result, an automated gas chromatographic (GC) system capable of measuring ambient levels of methane, ethane, ethylene (ethane), propane and propylene (propene) was developed. The system used chemical sorbents with Peltier electric cooling technique to trap ethane, ethylene, propane and propylene at -30℃. Subsequently, thermal desorption (TD) at 300℃ was made to inject analytes to GC with flame ionization detection (FID). Because of the extremely high gaseous nature of methane, a section of tubing of about 0.5 mL in the sorbent trap unit was used as the sample loop for analyzing methane.
To increase the monitoring time coverage, two identical sorbent traps were installed on a two-way 10-port switching valve to alternate sample injections. While one trap was in the process of TD injection and GC separation, the other was performing sampling. The GC method adopted the isothermal-backflush strategy for rapid cycling and self-cleaning of the columns to permit continuous long-term monitoring. Two columns, i.e, a packed column of Unibeads 2S and a capillary Na2SO4 PLOT column, were used as the pre-column and the analytical column, respectively. The system allowed high-boiling residues in the sample to be backflushed from the precolumn, while the low-boiling analytes separated by the PLOT column were detected by FID. Each cycle of analysis was completed in six minutes. Precision as the relative standard deviation (RSD) was assessed to be better than 2.1%, and linearity (R2) was better than 0.9902% for the five target gases.
Simulation of leakage of natural gas and liquefied petroleum gas (LPG) was conducted by detecting excess methane and propane as episodes, while the system was monitoring the five gases in the laboratory air for a period of five days. | en_US |