Biodiesel is a renewable biofuel, a form of diesel fuel, derived from biological sources like vegetable oils, animal fats, or recycled greases, and consisting of long-chain fatty acid esters. It is typically made from fats.
The roots of biodiesel as a fuel source can be traced back to when J. Patrick and E. Duffy first conducted transesterification of vegetable oil in 1853, predating Rudolf Diesel's development of the diesel engine. Diesel's engine, initially designed for mineral oil, successfully ran on peanut oil at the 1900 Paris Exposition. This landmark event highlighted the potential of vegetable oils as an alternative fuel source. The interest in using vegetable oils as fuels resurfaced periodically, particularly during resource-constrained periods such as World War II. However, challenges such as high viscosity and resultant engine deposits were significant hurdles. The modern form of biodiesel emerged in the 1930s, when a method was found for transforming vegetable oils for fuel use, laying the groundwork for contemporary biodiesel production.
The physical and chemical properties of biodiesel vary depending on its source and production method. The trade association National Biodiesel Board defines "biodiesel" as a mono-alkyl ester. It has been experimented with in railway locomotives and power generators. Generally characterized by a higher boiling point and flash point than petrodiesel, biodiesel is slightly miscible with water and has distinct lubricating properties. Its calorific value is approximately 9% lower than that of standard diesel, impacting fuel efficiency. Biodiesel production has evolved significantly, with early methods including the direct use of vegetable oils, to more advanced processes like transesterification, which reduces viscosity and improves combustion properties. Notably, biodiesel production generates glycerol as a by-product, which has its own commercial applications.
Biodiesel's primary application is in transport. There have been efforts to make it a drop-in biofuel, meaning compatible with existing diesel engines and distribution infrastructure. However, it is usually blended with petrodiesel, typically to less than 10%, since most engines cannot run on pure biodiesel without modification. The blend percentage of biodiesel is indicated by a "B" factor. B100 represents pure biodiesel, while blends like B20 contain 20% of biodiesel, with the remainder being traditional petrodiesel. These blends offer a compromise between the environmental benefits of biodiesel and performance characteristics of standard diesel fuel. Biodiesel blends can be used as heating oil.
The environmental impact of biodiesel is complex and varies based on factors like feedstock type, land use changes, and production methods. While it can potentially reduce greenhouse gas emissions compared to fossil fuels, concerns about biodiesel include land use changes, deforestation, and the food vs. fuel debate. The debate centers on the impact of biodiesel production on food prices and availability, as well as its overall carbon footprint. Despite these challenges, biodiesel remains a key component in the global strategy to reduce reliance on fossil fuels and mitigate the impacts of climate change.
Blends of biodiesel and conventional hydrocarbon-based diesel are 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:
100% biodiesel is referred to as B100
20% biodiesel, 80% petrodiesel is labeled B20
10% biodiesel, 90% petrodiesel is labeled B10
7% biodiesel, 93% petrodiesel is labeled B7
5% biodiesel, 95% petrodiesel is labeled B5
2% biodiesel, 98% petrodiesel is labeled B2
Blends of 20% biodiesel and lower can be used in diesel equipment with no, or only minor modifications, although certain manufacturers do not extend warranty coverage if equipment is damaged by these blends. The B6 to B20 blends are covered by the ASTM D7467 specification. Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. Blending B100 with petroleum diesel may be accomplished by:
Mixing in tanks at manufacturing point prior to delivery to tanker truck
Splash mixing in the tanker truck (adding specific percentages of biodiesel and petroleum diesel)
In-line mixing, two components arrive at tanker truck simultaneously.
Metered pump mixing, petroleum diesel and biodiesel meters are set to X total volume.
Biodiesel has a number of standards for its quality including European standard EN 14214, ASTM International D6751, and National Standard of Canada CAN/CGSB-3.524.