Sulfur Content in Selected Oils and Fats and their Corresponding Methyl Esters

According to Environmental Protection Agency (EPA) regulations, the use of ultra-low sulfur diesel (ULSD) has been mandated for all on-highway transportation diesels since 2006. To comply with the EPA regulations, biodiesel must meet the same ULSD standard for total sulfur which is set at a maximum of 15 ppm. Generally, biodiesel contains lower sulfur than fossil diesel. However, due to the diversity of biodiesel feedstocks, questions have been raised about their sulfur content and the sulfur content of the biodiesel made from them. The objective of this research was to gain basic knowledge about how the sulfur content in biodiesel is affected by the sulfur content of different feedstocks. Sulfur in oilseeds, seed meals, oils and fats, and biodiesel were investigated according to ASTM D5453. Samples of different feedstocks for biodiesel production were investigated. Results showed that sulfur content varies greatly from one source to another. The highest sulfur in seeds and meals was found in rapeseed and mustard, at the level of 9,000 and 15,000 ppm, respectively. Oils from mechanical expeller presses contained very low levels of sulfur, although some were still higher than 15 ppm. Animal fats and waste vegetable oils contained relatively higher sulfur levels and were frequently above 15 ppm. It was observed that sulfur was significantly reduced when the oils and fats were processed into biodiesel. Results showed that most of the biodiesel samples investigated in this study contained less than 15-ppm sulfur. Feedstocks which contain a high percentage of free fatty acids (FFA) must be treated with sulfuric acid to reduce the FFA level before transesterification. In these cases, care is needed during phase separation to exclude sulfur from the fuel layer.