(374d) Fuel Production From Waste Oils and Greases

The Northeast U.S. has the highest population density in the nation and, as a result produces very large amounts of organic rich waste which represents a significant biomass resource. If properly converted, portions of the waste can be utilized as a feedstock for liquid fuel production. This research work is focused on the manufacture of liquid fuels that can replace middle distillates from waste oil and grease produced by the general population in this region. This feedstock is generally characterized by its rancidity and variability: very high free fatty acid content, triglyceride content in the 0 to 20% range, and about 40% emulsified water content.

Three separate routes to the production of fuels have been explored. Each of these starts with a thermal conversion process in which water, temperature, and pressure is used to convert all mono-, di-, and triglycerides to fatty acids (and proteins to fatty amids and amines). The excess water is removed from the feedstock for further conversion. This feedstock is mainly fatty acids in the C14 to C 18 range. The first downstream route is the conversion to esters (Biodiesel) through acid esterification. A homogeneous catalyst (sulfuric acid) was selected over heterogeneous catalysts in development work to date to avoid issues related to possible contaminants and catalyst poisoning. A two-stage conversion (esterification), followed by a polishing step, has been shown to produce a fuel product which appear to meet required ASTM standards. The second downstream route is conversion to hydrocarbons via decarboxylation. This is a much higher pressure and temperature route but offers the potential for the production of truly infrastructure-compatible fuels. A range of catalysts and conditions have been explored based on prior published results with oleic acid as a model compound feed. Conversion efficiencies as high as 94% have been measured using nickel and iron- based catalysts. The third route involves direct combustion of the fatty acids as a fuel for stationary applications such as boilers and furnaces. In tests of basic combustion performance, emissions, elastomer seal compatibility, and corrosion of fuel system components, this fuel has been found to be a promising commercial product. An economic comparison of these alternatives, including plant design estimation, capital and operating cost estimates, and product value is underway.