Biodiesel is an advanced biofuel made by the transesterification of animal fat or vegetable oil. When animal fats or vegetable oils react with ethanol or methanol in a transesterification process, the process converts fats and oils into biodiesel and glycerol (a coproduct).
Unlike a fossil fuel, biofuel is made from organic matter (biomass). Biodiesel fuel is gaining traction as a renewable fuel primarily due to the need to replace fossil fuels and reduce the global carbon footprint.
The search for a clean fuel based on renewable energy led to the development of a diesel fuel replacement derived from plant material (plant oils) or renewable feedstock.
In this post, we will learn more about biodiesel and why biodiesel is a clean fossil fuel substitute.
What is Biodiesel?
Biodiesel is a biodegradable, non-toxic, and renewable fuel manufactured from animal fats, vegetable oils, or recycled restaurant grease. Biodiesel is otherwise known as fatty acid methyl ester (FAME) or rapeseed methyl ester (RME). Unlike ethanol, biodiesel is not made from sugar or starch.
Biodiesel is also distinct from renewable diesel because renewable diesel is derived from biomass using the thermal depolymerization process. However, biodiesel consists of methyl and ethyl esters of fatty acids derived from the transesterification process.
Sources of biodiesel
The most well-known sources of biodiesel include:
- Algae
- Animal tallow
- Canola oil
- Corn oil
- Other feedstock oils (grapeseed oil, palm oil, and sunflower oil)
- Soybean oil
- Yellow grease (recycled cooking oil or used cooking oil (UCO))
Biodiesel regulations and advocacy
Biodiesel regulations govern its manufacturing and distribution with respect to mandatory compliance. For example, the renewable fuel standard (RFS) program that was renewed and expanded in 2007 requires the use of advanced biofuels such as biomass-based diesel in the U.S. transportation sector.
Government policies and laws and tax incentives are supporting the growth of biodiesel as an alternative fuel for federal, state, and public utility fleets.
For example, Clean Fuels Alliance America (formerly known as the National Biodiesel Board (NBB)) advocates for federal tax credits and works with federal agencies to grow biodiesel’s role in the agriculture and transportation sectors.
The National Renewable Energy Laboratory (NREL) has dedicated national centers and collaborative research facilities apart from research programs to conduct research on new-age bioenergy technologies for solving energy challenges.
Biodiesel Production Process
Although biodiesel is made in different ways, such as blending, pyrolysis, and micro-emulsion, the most common biofuel production method is the transesterification of oils or fatty acids.
Transesterification is a chemical process that reduces the viscosity of vegetable oils and makes them usable in diesel engines:
Alcohol + Catalyst + Triglycerides → Biodiesel + Glycerol
First, alcohol combines with a catalyst and then triglyceride molecules chemically break down, with alcohol replacing the glycerides in the oil—forming a fatty ester and creating glycerol as a by-product.
The resulting linear ester molecules formed by esters from fatty acids and alcohol constitute biodiesel. These molecules have a flash point lower than the original triglyceride and also have a lower boiling point, lower molecular weight, and lower viscosity.
The commonly used catalysts for the transesterification process are sodium hydroxide (NaOH), known as “caustic soda,” and potassium hydroxide (KOH), known as “caustic potash” or “lye.”
