WHAT IS BIODIESEL?
Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl (methyl, ethyl, or propyl) esters. Biodiesel is typically made by chemically reacting lipids (e.g., vegetable oil, soybean oil, animal fat (tallow)) with an alcohol producing fatty acid esters.
Biodiesel is meant to be used in standard diesel engines and is thus distinct from the vegetable and waste oils used to fuel converted diesel engines. Biodiesel can be used alone, or blended with petrodiesel in any proportions.
The Biodiesel Cycle
Blends
Blends of biodiesel and conventional hydrocarbon-based diesel are products most commonly distributed for use in the retail diesel fuel marketplace.
Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix:
Blends of 20% biodiesel and lower can be used in diesel equipment with no, or only minor modifications.
The B6 to B20 blends are covered by the ASTM D7467 specification.
Biodiesel feedstocks
US Biodiesel
Feedstock Utilization
Source: US Energy Information Administration
A variety of oils can be used to produce biodiesel.
These include:
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Virgin oil feedstock – rapeseed and soybean oils are most commonly used, soybean oil accounting for about half of U.S. production. It also can be obtained from Pongamia, field pennycress and jatropha and other crops such as mustard, jojoba, flax, sunflower, palm oil, coconut and hemp;
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Waste vegetable oil (WVO);
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Animal fats including tallow, lard, yellow grease, chicken fat, and the by-products of the production of Omega-3 fatty acids from fish oil.
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Algae, which can be grown using waste materials such as sewage and without displacing land currently used for food production.
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Oil from halophytes such as Salicornia bigelovii, which can be grown using saltwater in coastal areas where conventional crops cannot be grown, with yields equal to the yields of soybeans and other oilseeds grown using freshwater irrigation
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Sewage Sludge – The sewage-to-biofuel field is attracting interest from major companies like Waste Management and startups like InfoSpi, which are betting that renewable sewage biodiesel can become competitive with petroleum diesel on price.