GC-MS characterization of sulfur species in low temperature distillates of biodiesel from waste grease
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Biodiesel, a renewable fuel alternative, has rapidly increased in production and usage over the past decade serving as an environmentally friendly fuel source. However, dependent upon the source of its feedstock, biodiesel could contain sulfur (S) at levels that could pose significant environmental impacts. Biodiesel from waste grease (i.e., used vegetable oil), for example, usually possesses S higher than the specified quality standards for automotive fuels. In order to produce quality biodiesel from a variety of feedstocks and to continue to take steps towards the production of clean fuel, the present study aimed to identify the sulfur species in “low temperature” distillate fractions of biodiesel produced from waste grease so that strategic means to remove the S-containing impurities can be developed. Solid phase extraction (SPE) was employed to separate and concentrate S-species in industrial samples of low temperature distillates of waste grease-based biodiesels. Organic solvents with different polarities were used to effectively separate polar S-species from non-polar fatty acids and other constituents, creating concentrated sulfur samples. The samples were then analyzed for total S contents. The most S-concentrating samples were then analyzed using gas chromatography-mass spectrometry (GC-MS) to identify individual S-containing compounds. Two sulfur species were eventually identified in the biodiesel distillates: 5-butyl-dihydro-thiophenone, and 6-propyl-tetrahydro-thiopyranone. The molecules are believed to have originally existed as the precursor molecule 4-Mercapto-octanoic acid methyl ester. The results obtained from the present study provide a base for developing effective purification methods to remove S-containing impurities from waste grease-derived biodiesel.