This Small Business Innovation Research (SBIR) Phase I project will address fat, oil, and grease (?brown grease?) reclaimed out of the wastewater collected from restaurant grease interceptors. These contain free fatty acids (?FFA?), glycerides and a significant amount of sulfur compounds (soaps, detergents, etc.). Thus, crude biodiesel produced from sewer brown grease may have a total sulfur concentration greater than 10,000 ppm?well above the 15 ppm limit specified in the biodiesel ASTM standard. It is proposed to examine novel and economical strategies for reducing sulfur in crude biodiesel to meet its ASTM standard: (1) metal sorbent adsorption: using a metal sorbent for selective removal of sulfur out of biodiesel, (2) oxidation-adsorption: oxidizing sulfides to sulfoxides and sulfones, which could be facilely scavenged by clay or silica; and (3) the combination of these two methods for deep sulfur reduction. The broader/commercial impacts of this research are effective remediation of waste grease streams. It is estimated that each year, over 4 billion pounds of brown grease are buried at the landfill sites or dumped at wastewater treatment plants?which could equate to 500 million gallons of biodiesel. Effective remediation of waste grease streams could produce a value-added supply of biomass for energy conversion with an annual market value over $2 billion. Converting sewer brown grease into biodiesel will not only reduce environmental pollutions, but also create jobs and reduce reliance on foreign oils. The use of low-sulfur biodiesel from sewer brown grease will reduce SOx and greenhouse gas emissions.
Supported by the NSF SBIR Phase I program, Midwest Energy Group Incorporated examined innovative approaches for reducing sulfur impurities in biodiesel produced from brown grease. Brown grease is a waste material that is reclaimed from restaurant grease trap wastewater. Sulfur molecules must be removed from crude biodiesel due to stringent regulations and fuel specifications for environmental protection purposes. The U.S. Environmental Protection Agency ("EPA") has mandated the allowable sulfur content in ultra-low sulfur diesel and biodiesel to be 15 ppm or lower. We investigated three strategies for deep-sulfur reductions in biodiesel; (1) the repeated use of metal sorbents, (2) oxidation-scavenging and (3) the combined use of both strategies for desulfurization. We found that zinc-titanium-zeolite sorbents could be repeatedly used for desulfurization while oxidation-scavenging will also help reduce the sulfur content in the biofuel. Biodiesel that meets ASTM D6751 fuel standards was successfully produced in our laboratory from restaurant grease trap waste. Our research work will enable the use of an environmental waste for producing carbon-neutral biodiesel at large scales. It was estimated that over 500 million gallons of the renewable biofuel could be produced each year from the wastewater collected in restaurant grease traps across the U.S. Conversion of such an environmental waste will reduce our reliance on foreign crude oil and create jobs.