Biodiesel Quality Affected by Sulfur Content Originated from Different Feedstocks and a Database for the Same
According to the EPA’s regulations, June 1, 2006 is the deadline nationwide to start to comply with stringent limitations on the sulfur content of highway diesel fuel. The sulfur content in most diesel fuel will transit from low-sulfur diesel (LSD) to ultra-low sulfur diesel (ULSD). In other words, the sulfur content in the diesel fuel has to meet the 15 ppm sulfur standards. To ensure that the diesel sold at the pump still meets the standard, diesel refiners have to enforce a more stringent criterion to lower sulfur content far below 15 ppm, even as low as 3~4 ppm, due to the concerns of possible contamination between the refinery’s gates and retail pumps (National Petrochemical & Refiners Association, 2006) .
Biodiesel, used as transportation fuel, will have to meet the same standard. Generally, biodiesel contains lower sulfur than fossil diesel. However, currently the biodiesel industry does not have the capability, as petroleum refineries, of refining the fuel to remove sulfur to the level as specified by EPA. According to our preliminary study on six feedstocks for biodiesel production, the sulfur content in the raw materials was typically between 20 to 30 ppm, with the highest of 44 ppm. After processing, the sulfur content in the crude glycerol by-product was in the similar level as in raw oils, indicating that the sulfur content in the biodiesel product may be higher than 15 ppm (Thompson and He, 2006) . It was also noticed that elemental composition of the same vegetable oil may vary according to the soil conditions where the seed oil crops grow. If high free fatty acid feedstocks are used, such as animal fats, the sulfur content in such feedstocks is expected to be higher due to the presence of proteins.
There are many questions raised regarding how the sulfur content in the feedstocks affects the biodiesel quality. How does the sulfur content vary among the feedstocks? How does the sulfur distribute between the biodiesel product and the crude glycerol by-product? Is the sulfur content of a feedstock affected by its soil conditions where it is grown? Is there a correlation between the fatty acid profiles and the sulfur content? These are the very important questions. To comply with EPA regulations, biodiesel needs to meet the same ULSD standard as fossil diesel. However, to the best of the PI’s knowledge, there is no published information that systematically addresses these issues. As a leader in biodiesel research and utilization, University of Idaho has the responsibility to help the biodiesel producers, distributors, and consumers gain the knowledge on biodiesel quality as affected by the sulfur content of different feedstocks.
Therefore, the goal of this project is to conduct a thorough research on the sulfur issues related to biodiesel feedstocks, sulfur distribution/accumulation, and its effect on fuel quality through the tasks specified above. Upon the accomplishment of the project, a database will be established to document the findings for use by the biodiesel industry, government agencies, consumers, and general public as a guideline in compliance with federal policy of ultra-low sulfur transportation fuels.