develop renewable or sustainable energy sources, the desire to develop secure domestic fuel supplies, and an interest in rural development. Interestingly, Hoekman said, neither air quality concerns nor health concerns have been major factors in the push to increase the use of biofuels. “They are somewhat important, but they have not been the main drivers.”

Terminology

Next, Hoekman went over some basic terminology related to biofuels in order to clarify exactly what is meant by various terms. According to ASTM International, biodiesel fuel refers to “mono-alkyl esters of long-chain fatty acids derived from vegetable oils and animal fats.” The term can also refer to trans-esterified triglycerides or to fatty acid methyl esters (FAMEs), which are both closely related to ASTM’s definition. Biodiesel fuel is sometimes referred to as B100.

Renewable diesel is produced from the same feedstocks as biodiesel, Hoekman said, but it is produced through hydroprocessing technologies so that the product is a hydrocarbon (HC), not an ester. It is also referred to as “green diesel.”

Co-processed renewable diesel is a form of renewable diesel that is produced by adding vegetable oils or animal fats to feedstocks that are being hydrotreated to produce diesel fuel, creating a single product that is a mixture of bio and fossil HCs.

Cellulosic biodiesel fuel, or synthetic biodiesel, is produced by pyrolysis or gasification of lignocellulosic feedstocks, such as grasses and woods. The resulting liquid generally requires rather considerable additional processing or upgrading before it can be blended into petroleum fuel stock.

Biodistillate Production Technologies

A variety of different production methods are used to produce the different types of biodistillates. Hoekman illustrated them with a single figure that showed the feedstocks, processing methods, and resulting fuels (see Figure 4-1).

Hoekman pointed out that, as the figure indicates, there are many different types of fats and oils that can be used to produce biodistillates. “And this is an abbreviated list shown here,” he said. The line at the top of the figure represents the traditional biodiesel production pathway that uses methanol in a trans-esterification pathway to produce biodiesel and



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