Among these are policies to support the production and use of biodiesel, a fuel currently produced from lipid feedstocks such as vegetable oil, animal fat, and waste cooking oil. Although this fuel is already available in small quantities throughout most of the country, several issues have to be resolved for biodiesel markets to expand. This article summarizes the current and potential levels of biodiesel production, issues with transporting biodiesel to market, as well as quality and specifications. Air pollutant emission impacts are also described, along with what is known about how biodiesel affects engine and catalyst durability.
Biodiesel consists of mono-alkyl esters of fatty acids, which are typically methyl esters and are sometimes referred to as fatty acid methyl esters, or FAME (see Figure 1). Monoalkyl esters are typically produced from the lipid feedstocks using a chemical reaction called transesterification. Life-cycle analysis shows that biodiesel contains 2.5–3.5 units of energy for every unit of fossil energy input in its production; and because very little petroleum is used in production of biodiesel, its use displaces petroleum at nearly a 1-to-1 ratio on a life-cycle basis.2-5 Life-cycle analysis also shows reductions in total greenhouse gas emissions (CO2+CH4+N2O), ranging from 60% to over 90%.3,4 This renewable fuel is primarily used as a 2%- to 20%-byvolume blend with petroleum diesel. Biodiesel blends are referred to as “Bxx”; for example, B5 indicates a 5%-byvolume biodiesel blend. Policies supporting the use of biodiesel include the biodiesel blender’s tax credit of US$1.00 per gallon for agricultural feedstocks and US$0.50 per gallon for waste or second-use feedstocks.
More recently, the U.S. Energy Independence and Security Act of 2007 (Pub. L. No. 110-140) mandates the use of 1 billion gallons per year of biomass-based diesel by 2012 and 21 billion gallons of advanced biofuel by 2022.