Biodiesel Basics
Biodiesel is one of many alternative fuel options that has the potential to help reduce oil dependence and global warming pollution. But done wrong, biodiesel can actually increase global warming pollution and cause other environmental problems, such as deforestation and loss of biodiversity. With good policies in place to promote sustainable low carbon fuels, like a low carbon fuel standard, biodiesel can be an important part of a clean fuel mix. Together with fuel economy improvements and reductions in travel demand, cleaner alternative fuels can help our transportation system meet energy security and environmental goals.
What is biodiesel?
Today’s Use of Biodiesel
Global Warming Impacts and Benefits
Conventional Pollutants: Impacts and Benefits
Biodiesel versus gasoline in cars and light trucks
Biodiesel is a renewable fuel derived from vegetable oil or animal fats that can be added to petroleum diesel as a blend or used on its own. In the United States, most biodiesel is made from soybeans. Biodiesel is also made from canola oils and from waste stream sources including used cooking oils or animal fats.
In the developing world, biodiesel is produced from palm oil, sunflowers, and other sources. In Indonesia, there is significant concern that biodiesel may be causing deforestation, as native forests are removed to make way for palm oil plantations.
Biodiesel makes up a tiny, but growing, fraction of diesel use in the US. Between 2004 and 2006, biodiesel use increased tenfold, from about 25 million gallons to 250 million gallons. Yet, as of 2007, biodiesel comprised less than one percent of total highway diesel fuel use. According to the National Biodiesel Board, production capacity is continuing to grow so that nearly two billion gallons of biodiesel could be produced by mid-2008
Due to high biodiesel costs, engine compatibility issues, and cold weather operating concerns, biodiesel is often blended with conventional diesel fuel. Common biodiesel blends are B20 (20% biodiesel and 80% petroleum diesel) and B2 (2% biodiesel and 98% petroleum diesel). The environmental benefits associated with using biodiesel scale with the percentage of biodiesel contained in the fuel blend.
Certified low-level biodiesel blends can be used in most traditional diesel vehicles without engine modification. The use of higher-level biodiesel blends tends to require engine modification and other usage considerations.
Global Warming Impacts and Benefits
According to a model developed by the Argonne National Laboratory (ANL), neat (100%) biodiesel from soybeans can cut global warming pollution by more than half relative to conventional petroleum based diesel. The emissions benefits are higher for canola oil. In the future, non-conventional sources like algae may have the potential to provide dramatic (90%) reductions in global warming pollution. However, significant technological hurdles remain before algae and other advanced feedstocks can be processed into biodiesel for commercial purposes.
It is important to note that the ANL model of global warming impacts does not take into account changes in land use. When soybeans are used for fuel, they are taken out of the market for food. This increases prices and stimulates demand that farmers around the world respond to by bringing more land into cultivation. With soybean production increasing in the Amazon, it is possible that the lifecycle global warming pollution of soybean biodiesel is even higher than petroleum diesel, once indirect land use changes are considered (see our fact sheet on land use changes for more details).
When biodiesel is made from recycled food oil or other waste products these land use considerations do not apply. Also advanced technologies including biomass gasification may allow the use of other waste streams to be converted to synthetic diesel fuels, expanding the pool of potentially low carbon diesel.
In addition to land use, there is also some controversy over the emissions impact of fertilizer use and other land use practices (such as tillage practices). As a result, the estimated emissions from biodiesel can be expected to change as our understanding of the lifecycle improves.
Large scale production of biodiesel would require more virgin plant oils or other waste stream sources to meet larger demands. However, such large-volume biodiesel use could raise concerns about genetically modified crops, pesticide use, and land-use impacts common to ethanol and all other plant-based fuels. Crops for biodiesel must be grown in a manner that supports wildlife habitat, minimizes soil erosion, avoids competition for food crops, and does not rely on the use of harsh chemicals and fertilizers.
Conventional Pollutants: Impacts and Benefits
Although biodiesel’s lifecycle emissions impact depends on the source and fuel blend, biodiesel can offer distinct environmental advantages over petroleum diesel fuel. As shown in Figure 1, the use of biodiesel blends in an existing diesel vehicle can reduce the emissions of the tailpipe pollutants associated with conventional diesel including particulate matter (PM or soot) and hydrocarbons (HC). However, using biodiesel may result in greater emissions of smog-forming nitrogen oxides than using conventional diesel.
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On a lifecycle basis the estimates of global warming pollution for biodiesel vary greatly depending on how land use is accounted for. Particularly, the effects of displaced crop production can have significant impacts, especially if it is moved to previously virgin forest land.
Biodiesel versus gasoline in cars and light trucks
For conscientious consumers who already own a diesel vehicle, using high-blend biodiesel offers an opportunity to make an impact on petroleum use and global warming emissions today. But keep in mind that the overall magnitude of emission reduction depends on the source of the biodiesel and the amount of the biodiesel in the blend. Additionally, note that the emissions of smog-forming nitrogen oxides may increase.
New car-buyers seeking to minimize their vehicle’s environmental impact should focus on vehicle efficiency, along with tailpipe emissions, not the vehicle’s potential to use an alternative fuel. Gasoline-powered models are better than traditional diesel and biodiesel vehicles on toxic soot and smog-forming emissions. Diesels can produce as much as 10 to 20 times more toxic particulates than their gasoline counterparts, more than can be made up for with the use of biodiesel. Diesels fair even worse when it comes to smog-forming nitrogen oxide emissions, with greater than 20 times the emissions of a comparable gasoline vehicle.
The Environmental Protection Agency’s (EPA) new "Tier 2" standards will hold diesel vehicles to the same emission standards faced by gasoline vehicles. Once these new standards are fully in effect in model year 2009, new diesels will be cleaner than they are today, but diesel still has a long way to go to match the emissions performance of the many fuel-efficient conventional and hybrid electric gasoline-powered vehicles on the road today.
