Biofuel for a Changing World
First published in 2001, the ASTM standard for pure biodiesel (D6751, Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels) has been crucial to industry. The standard ensures that biodiesel works correctly when blended with conventional distillate fuel oils like diesel fuel and heating oil.
D6751 continues to be the foundational quality standard for a biodiesel industry whose U.S. sales have risen from less than 20 million gallons in 2001 to over 1.6 billion gallons in 2013. Recent revisions extend D6751's relevance by giving biodiesel users flexibility in the test method that can be used to meet the standard.
D6751 originally provided biodiesel producers, blenders and users with the information they needed to build a new industry for biodiesel production and use. But as the industry grew, additional needs became apparent:
- Companies needed a set of properties for the finished fuel - not just the blend stocks that made up the fuel - so they could design and optimize equipment that burns the fuel.
- Regulators needed a convenient way to test a finished fuel to ensure its acceptability when the quality of the parent fuels is unknown or when different batches have been intermingled.
- Purchasers wanted one specification to put in their bid specs for finished fuels rather than specifying two products (the diesel or heating oil and the biodiesel used to make the blend).
In addition, the U.S. Environmental Protection Agency's 2006 reduction of maximum allowable sulfur in U.S. diesel fuel, from 500 parts per million to 15 ppm, was also a contributing factor in ongoing revisions to D6751, reinforcing the need to continually evaluate the impact of biodiesel.
The resulting revisions to D6751 have built confidence with fuel users and sellers as well as equipment companies. Key changes made over the years include:
- Modification of B100 to include specifications for stability, sodium/potassium, calcium/magnesium and to reduce the acid number (2006),
- Addition of controls for minor biodiesel components to ensure the fuel would perform as expected with new ultra low sulfur diesel fuel in cold weather (2008),
- Addition of a second grade of biodiesel that had tighter specifications for minor components (2012), and
- Test Method D7668 was added as an alternative to standard D613 for determining cetane number (2015).
The improvements to D6751 and growth of the industry have also resulted in major revisions to ASTM standards for home heating oils and jet fuels. For example, a new B6-B20 grade has been added to the home heating specification (D396), which is based on the use of D6751 biodiesel.
In addition, the maximum amount of biodiesel allowed in the D1655 jet fuel standard was raised from 5 to 50 ppm, with a planned increase to 100 in roughly two years. The increase gives pipeline companies the flexibility to consider transporting biodiesel blends in pipelines that also carry jet fuel while maintaining its quality.
Committee D02 continues to improve its biodiesel specifications as baseline diesel fuel, and the equipment it is burned in, changes over time. This commitment is a key factor in the safe use of biodiesel blends in the marketplace and the dramatic increase in the volume of this industry.
Steve Howell is a founding partner in Marc-IV Consulting and an ASTM fellow. Howell has been the chairman of the ASTM biodiesel task force since 1994 and is a member of the executive subcommittee of the Committee D02 on Petroleum Products, Liquid Fuels and Lubricants.
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