Specifications and Regulations
Specification D6751 is based on a compilation of efforts from researchers, engine manufacturers, petroleum companies and distributors, and many other fuel-related entities and is intended to ensure the quality of biodiesel used as a blendstock at 20% (B20) and lower blend levels. Any biodiesel used in the United States for blending should meet ASTM D6751 standards. The ASTM standards provide a minimum level of quality for biodiesel regardless of the source of the fuel. Purchasers and sellers can require that biodiesel meet more strin-gent requirements in purchasing specifications. Both parties must agree to these more stringent requirements, and this is becoming an increasingly common practice.
The ASTM D6751 definition of biodiesel states that bio-diesel is composed of “mono-alkyl esters of long-chain fatty acids derived from plant oils or animal fats.” The term mono-alkyl esters indicates that biodiesel contains only one ester linkage in each molecule. Raw or refined plant oils, animal fats, and greases contain three ester linkages and are therefore not legally biodiesel. Bio-diesel can be made from methyl, ethyl, isopropyl, and other alcohols. Virtually all commercial biodiesel pro-duction in the United States today is based on methyl esters. Some research has been conducted on ethyl esters (biodiesel produced with ethanol as the alcohol rather than methanol); however, higher ethanol prices relative to methanol, lower ethyl ester conversions, and the difficulty of recycling excess ethanol from the finished biodiesel have hampered ethyl ester production in the marketplace. Therefore, in this course we will consider only methyl esters.
The definition of biodiesel recognized by both the EPA for fuel registration purposes and the Internal Revenue Service for the blender’s tax credit is essentially the same as the definition in ASTM D6751:
“A fuel comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats, designated B100, and meeting the requirements of ASTM D6751.”
EPAct requires that certain federal, state, and alternative fuel provider fleets acquire a fixed percentage (75% or 90%) of AFVs each year based on the total number of light-duty vehicles they acquire. A light-duty vehicle that is approved by the original equipment manufacturer (OEM) to operate on B100 or a biodiesel blend of B20 or higher qualifies as an AFV under EPAct. As of 2015, there are no light-duty vehicles on the market approved to operate on B100, but there are many that are approved to operate on B20. Neat biodiesel may be more expensive than other alternative fuel options, and OEMs have shown little interest in obtaining approval for on-road vehicles to operate on B100.
Congress amended EPAct through the Energy Conservation Reauthorization Act of 1998. Among other things, the Energy Conservation Reauthorization Act added Section 312 to EPAct, thereby enabling covered federal, state, and alternative fuel provider fleets to earn AFV credits for their use of B20 or higher blends in medium- or heavy-duty vehicles (those vehicles with a gross vehicle weight rating of more than 8,500 pounds), with some limitations. This provision has created significant demand for B20 among government and alternative fuel provider fleets.