by Maria Gerveni, Scott Irwin, Todd Hubbs (University of Illinois and U.S. Department of Agriculture/FarmDocDaily) Biomass-based diesel has long played an important role in compliance with the U.S. Renewable Fuels (RFS) mandates (e.g., farmdoc daily, July 19, 2017). The two main types of biomass-based diesel fuels used to comply with the RFS mandates are “biodiesel” and “renewable diesel.”
Historically, biodiesel production has substantially outpaced renewable diesel production. This began to change in recent years due to a boom in building out renewable diesel production capacity. The boom has been large enough to have a substantial impact on the price of fats and oils feedstocks used to produce biomass-based diesel. This article is the first in a series that will examine the renewable diesel boom and its impact on U.S. agriculture.
We begin the series today with a discussion of the differences between biodiesel and renewable diesel fuels. Currently, biomass-based diesel fuels are produced from organic lipid feedstocks that contain free fatty acids, such as vegetable oils, animal fats, or recycled grease (AFDC, 2022a,b). While biodiesel and renewable diesel are both categorized as biomass-based diesel fuels and can be produced using the same feedstock, they are distinctly different types of fuels that differ in several important characteristics.
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First, FAME biodiesel contains oxygen, which causes FAME to have approximately seven percent less energy by volume. Second, the higher oxygen content of FAME can limit the length of time it can be stored due to oxidation that causes corrosion. Third, FAME’s chemical composition can make it more susceptible to microbial fouling when poor storage tank management is present, which may result in the corrosion of storage tanks and clogging of fuel lines. Fourth, FAME biodiesel has a relatively high temperature where it will begin to freeze and form visible crystals. This is known in technical terms as the cloud point of the fuel.
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For example, biodiesel has desirable lubricity characteristics due to its chemical composition. This feature helps prevent premature engine wear.
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It should also be noted that it is not unusual for a small amount of biodiesel to be blended with renewable diesel for lubricity purposes.
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While the same organic fats and oil feedstocks are used to make both fuels, the production processes are radically different. Biodiesel uses a relatively simple chemical reaction production process. For this reason, biodiesel is normally blended with petroleum diesel to be used in modern diesel engines. In contrast, renewable diesel is fully refined and cracked using petroleum refining technology. This results in a “drop-in” hydrocarbon fuel that meets the same technical specifications as petroleum diesel, and as such, can be used as a complete replacement for petroleum diesel.
The next article in this series will examine the basic economic framework for biodiesel and renewable diesel markets and the policies that provide support for the sector. READ MORE
What’s the Difference between Biodiesel and Renewable (Green) Diesel? 2020 revision (Advanced Biofuels USA)