Biodiesel (also spelled bio-diesel) is a diesel fuel produced from plant oils or animal fats. It is commonly sold blended with diesel derived from petroleum. Common blends include “B2” (2% biodiesel), “B5” (5% biodiesel), “B10” (10% biodiesel) and “B100” (100% biodiesel).
Biodiesel is a biofuel like ethanol, with which it is often confused. However, ethanol is made from sugar or starch, and is used in vehicles that run on gasoline. Biodiesel is made from oils and fats and is used in vehicles that run on diesel fuel.
Biodiesel is also not the same as straight vegetable oil (also known as “SVO”). A normal diesel engine will eventually be damaged through the use of straight vegetable oil or straight animal fat fuel.
Biodiesel production
Biodiesel is made by chemically combining a vegetable oil or animal fat with an alcohol (such as methanol or ethanol) and a catalyst (usually sodium hydroxide or potassium hydroxide) via a process known as transesterification. This produces an alkyl ester of fatty acid, containing an alcohol group attached to a single hydrocarbon chain comparable in length to that of diesel (C10H22 to C15H32)1.
Co-products
- Glycerin (C3H8O3) (also called glycerol) is the primary co-product of biodiesel production.1
- Glycerin can be used as soap, as well as in the cosmetic industry and its sale can offset the cost of biodiesel production.1
- “The ‘meal’ left in the seed after oil has been removed is currently sold as an animal feed.”1
Characteristics
- Due to the wide variety of oils and fats that can be used to produce biodiesel, there is a greater range in the characteristics of biodiesel fuels than for ethanol fuel.”1
- Some oils are shorter or more saturated – characteristics that affect the viscosity and combustibility of the biodiesel.1
- Biodiesel contains 88-95% as much energy as diesel fuel.1
- However, biodiesel can also improve diesel lubricity and raise the cetane value, meaning that in many cases diesel has a similar fuel efficiency.1
- “The alcohol component of biodiesel contains oxygen, which helps to complete the combustion of the fuel, reducing air pollutants such as particulates, carbon monoxide, and hydrocarbons.”1
- Biodiesel contains practically no sulfur, so it can help reduce emissions of sulfur oxides.”1
Feedstocks
Biodiesel can be produced from any vegetable oil or animal fat, including waste vegetable oil produced by restaurants. There are also several experimental feedstocks including algae, which can be grown off of various types of waste.
- In Europe, rapeseed oil is the major feedstock used to make biodiesel, with some sunflower oil also used.1
- “In the United States, biodiesel has generally been made from soybean oil as more of this is produced domestically than all other sources of fats and oils combined.”1
- In tropical and sub-tropical countries, there are a wider variety of feedstocks being considered including both edible and non-edible oils.
- Edible oil feedstocks include palm oil and coconut oil.
- Non-edible oils include jatropha, castor beans and pangamic pinnata.
Making biodiesel
This YouTube video, “The Process of Making Biodiesel,” provides one introduction to the topic:
Safe Chemical Handling in Biodiesel Production
Safety is extremely important, because while biodiesel itself is non-flammable and biodegradable, the chemicals used to make it can be extremely dangerous.
Methanol is colorless and tasteless and can cause blindness or death if it enters the body through the nose, mouth, or skin. It is a cumulative poison: repeated, brief exposures can cause a toxic reaction. Methanol is also very flammable, and burns with an almost invisible flame, making the fire difficult to see. Methanol vapors are heavy and can travel along the ground to a source of ignition.
Sodium hydroxide and potassium hydroxide are strong bases which can burn unprotected skin and kill nerve cells before pain can be felt. When sodium hydroxide or potassium hydroxide is mixed with alcohol and stirred, a fine mist can be produced which can cause irritation to the respiratory tract.
Drawbacks
- “Biodiesel blends are sensitive to cold weather and may require special anti-freezing precautions, similar to those taken with standard number-2 diesel.”1
- “Long-term storage of biodiesel can be a concern because it may oxidize, although additives can ensure stability.”1
- “Biodiesel acts like a detergent additive, loosening and dissolving sediments in storage tanks and also causing rubber and other components to fail; these concerns are typically minimal at low-level blends of biodiesel, and at higher blend levels problems can be avoided with some attention to the materials used in engine fuel injectors and the overall fuel handling system.”1