Continuous Measurement of Odorant Composition for Liquefied Petroleum Gas

摘要

In Chile, commercial liquefied petroleum gas (LPG) is customarily odorized with dimethyl sulfide (DMS) andtert-butyl mercaptan (TBM) at a rate of about 10 grams of odorant per 1 cubic meter of LPG. The currentcontrol of the odorization practice involves the human nose to detect the odor in some cases, and thedetermination of total sulfur concentration in others. None of those methods provide the speciation of thesulfur species in LPG.On the other hand, both DMS and TBM are higher boiling than propane or butane. Therefore, the odorantconcentration emanating from the odorized liquid is not uniform in the vapors released. Furthermore, the gaswill also be much leaner than the odorized liquid. For those reasons, the Chilean industry recommendsanalyzing the odorant directly from the liquid phase.To address the problem of odorant quantification at the industry this research aims to develop a reliable andobjective measure for odorized LPG that allow not only verify the odorization itself but also quantify thespecies incorporated with the fuel, and other sulfur compounds present naturally in the LPG. In this regard, anAutomated Gas Chromatograph (Auto-GC) with an electrochemical detector was coupled with an LPG valve,which continuously takes samples of 1 μL of liquid propane. The extracted sample is then vaporized andinjected into the Auto-GC to be analyzed.The methodology is capable of distinguishing and quantifying distinct odorants near real-time (within 8minutes), as well as other sulfur impurities present in the LPG such as tetrahydrothiophene (THT) and methylmercaptan (MeSH). Typical retention times for TBM and DMS corresponded to 282 s and 418 s respectively.More importantly, the proposed method provides meaningful information to verify the optimum odorization, i.e.,the minimum value to alert in case of leak and maximum level that assures efficient combustion.