|HUGHES, MICHAEL - Delaware State University|
|CAIRNCROSS, RICHARD - Drexel University|
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2018
Publication Date: 6/1/2018
Citation: Hughes, M., Jones, K.C., Hums, M.E., Cairncross, R.A., Wyatt, V.T. 2018. Identification of sulfur-containing impurities in biodiesel produced from brown grease. Journal of the American Oil Chemists' Society. 95:407-420.
Interpretive Summary: To mitigate the environmental and health concerns caused by sulfur-bearing species in transportation fuels, fuel producers are mandated to produce fuels that contain very little sulfur. Sulfur becomes a part of the fuel because it is a component of the substances, called feedstocks, used to make the fuel. When these feedstocks are converted to fatty acid methyl esters, commonly known as biodiesel, the product can often have sulfur levels that exceed the mandated maximum level of 15 ppm. Feedstocks with the highest amounts of sulfur include greases obtained from restaurants and greases obtained from underground grease traps and waste water treatment plants. To aid in the development of effective techniques used to remove sulfur by distillation or absorption, this project aims to determine the identity of the sulfur-bearing compounds. Identification will provide information relative to how the species are formed and it could lead to the development of more efficient sulfur removal strategies. This research will benefit the biodiesel industry by reducing the cost of sulfur removal and, restaurants, and waste management and water treatment industries by increasing the value of their waste products.
Technical Abstract: Crude biodiesel (Fatty Acid Methyl Esters (FAME)) has been produced from brown grease lipids (BGLs) and subjected to purification by wiped film evaporation (WFE). FAME from waste grease usually contains higher concentrations of sulfur (S) than allowed to meet specified quality standards for biodiesel (15 ppm in the US). BGL-derived FAME was fractionated by two passes through the WFE to produce three fractions: (1) a light distillate, (2) a middle distillate, and (3) a heavy residue. Sulfur concentrations in each distillate fraction was determined to contain up to 50 ppm S. Solid phase extraction (SPE) was used to concentrate the sulfur species so that they could be analyzed by GC analysis using a pulsed flame photometric detector to detect carbon and sulfur and a mass spectrometer to determine the molecular structure of detected compounds. The ethyl acetate fraction obtained by SPE had the highest concentration of sulfur and was, therefore, the best candidate for GC-PFPD analysis. GC-PFPD methods were developed to separate the sulfur species adequately enough for those peaks to be analyzed by GC-MS which matched the peaks identified as epithiols, epi-dithiols, and thiophenes that were in the MS chemical library. MS fragmentation patterns were used to identify other, larger, sulfur bearing species as sulfides and disulfides crosslinked between two FAME molecules. The results obtained from this study provide a foundation for developing effective purification methods to remove S-containing impurities from waste grease-derived biodiesel.