Photo: Filling up at Propel Biodiesel by Spencer T., on Flickr
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Car racing is not a sport that’s likely to earn a gold star for being environmentally friendly. It relies heavily on non-renewable fossil fuels such as gasoline and petroleum derivatives such as nitromethane (used for drag racing). But a few exceptions may be blazing an eco-trail for the future of car racing. In September 2012, a racecar built by a team at Utah State University set a new land speed record of 103 km/h in the small-engine streamliner class (long, low, aerodynamic and custom-built). The official record was set using the required petroleum diesel fuel, but the racecar was just as speedy when the team used renewable biodiesel. Alberta, Canada is home to the world’s first 100% biodiesel jet car (drag racing car with a jet engine), named Prairie Gold. This 7 500 horsepower jet car can top 400 km/h using renewable biodiesel made from canola oil.
Biodiesel is a renewable liquid biofuel that can be used just like petroleum-based diesel in compression-ignition internal combustion engines. Both diesel and biodiesel spontaneously ignite when mixed with compressed air, and the engines harness the energy released during combustion to power the vehicle. Petroleum-based diesel has become the dominant fuel for compression-ignition engines, but the original model built by Rudolph Diesel over 100 years ago was designed to burn vegetable oil, a feedstock for modern biodiesel.
Biodiesel Chemistry is All about Esters
Conventional diesel is a mixture of hydrocarbon chains of different lengths, typically between 10 and 18 carbon atoms per chain. Cetane (or n-hexadecane) is a predominant diesel hydrocarbon with a molecular formula of C16H34 (see Figure 1). Biodiesel is chemically similar to petroleum diesel but instead of hydrocarbon chains, it is composed of fatty acid methyl esters (FAMEs). Esters are compounds of an organic acid, in this case a fatty acid, and an alcohol, in this case methanol. FAMEs (biodiesel) are commonly produced from the triacylglycerols found in animal fats or vegetable oils. Triacylglycerols have three fatty acid molecules attached to one glycerol molecule (an alcohol), so they are another kind of ester. A transesterification reaction converts the triacylglycerol esters into fatty acid methyl esters. All that’s needed for the transesterification reaction is an alcohol and a chemical catalyst. Methanol is the most commonly used alcohol, and the base sodium hydroxide is the most commonly used catalyst. The basic reaction is
Figure 1 shows the production of biodiesel in more chemical detail. Glycerol, also called glycerin, is the only byproduct of the transesterification reaction. For commercial biodiesel plants, it is economically feasible to purify the glycerin for other uses. Glycerin is an ingredient in the manufacturing of many consumer goods, including soap, body lotion, cosmetics, candy, pop, cellophane, urethane foam and nitroglycerin explosives.
Figure 1: Biodiesel Chemistry.
(A) Summary of the typical biodiesel production pathway.
(B) More detailed chemistry of the transesterification reaction that converts triacylglycerols (fatty acid esters
of glycerol) to biodiesel (fatty acid methyl esters, FAME). The ester bonds are highlighted in yellow. The
generation of the 3 FAME per 1 triacylglycerol actually occurs sequentially for each of the three fatty acids.
(C) A typical biodiesel FAME is shown beside a typical petroleum diesel hydrocarbon chain. The FAME is
palmitic acid methyl ester (methyl palmitate) and the diesel hydrocarbon is cetane (hexadecane).
Fatty Feedstocks from Farm to Fryer
Triacylglycerols are the constituents of all types of fats and oils, both of which are lipids. Fats are lipids that are solid at room temperature and oils are lipids that are liquid at room temperature. Many different kinds of fats and oils are used as biodiesel feedstock. In Canada, the most common feedstocks are canola oil, tallow, and yellow grease. Canola is a valuable oilseed crop, grown primarily in Western Canada. In the U.S., soybeans are the most common biodiesel crop feedstock. Tallow is rendered beef fat that comes from slaughterhouses and leather tanneries. Other animal fats such as pork lard and poultry fat are also used. Yellow grease is waste cooking fat/oil that comes from restaurant deep fryers and food processing plants. No matter the source of the feedstock, the transesterification reaction that generates biodiesel is the same. Canadian plants produce around 236 million litres of biodiesel per year.
Biodiesel – A Renewable Fuel at Gas Stations across Canada
Canada’s Renewable Fuel Standard mandates an average of 2% renewable content in diesel fuel (since 2011), and biodiesel fills this renewable niche. Canola crops, animal fats and yellow grease are all renewable feedstocks. Most commercially available biodiesel is sold as a blend with petroleum diesel, usually between 2 and 20%. Analogous to ethanol-blended gasoline, diesel fuel with 2% biodiesel content is called B2, fuel with 20% biodiesel content is called B20, and pure biodiesel is called B100. In contrast to ethanol-blended gas, all modern diesel engines can run on any level of biodiesel blend with few or no modifications. The use of high-level blends (greater than B20) requires different hoses and gaskets since biodiesel is a much better solvent than conventional diesel. High-level blends also have the potential to gel at low temperatures.
Impressive Greenhouse Gas Reductions with Biodiesel
Transportation is a major contributor to greenhouse gas (GHG) emissions, accounting for 28% of Canada’s emissions in 2010 (Environment Canada). Most transportation-associated GHG is carbon dioxide (CO2). Fossil fuels, such as conventional diesel, store carbon in a non-renewable form. When they are combusted, the CO2 byproduct is released and becomes an atmospheric GHG. On a timescale less than hundreds of millions of years, there is no way to return the carbon in the CO2 to its original fossil fuel storage form.
In contrast, biodiesel feedstocks are renewable carbon sources. Canola crops are grown every year, and livestock are continually born and raised. The advantage of renewable feedstocks is that the CO2 that is released by combusting biodiesel is used by the next season’s canola or animal feed crop for photosynthesis. The carbon is essentially recycled.
Of course, just like fuel ethanol, the manufacturing of biodiesel uses fossil fuels at many stages. A complete lifecycle analysis must be used to fully understand the impact of biodiesel on GHG reductions. Even taking all upstream GHG emissions into account, biodiesel is impressive. For all three common Canadian feedstocks (canola oil, tallow and yellow grease), the B100 GHG emissions are reduced at least 90% compared to petroleum diesel. GHG reductions for B5 are in the 4-5% range. (Natural Resources Canada GHGenius Model, 2010 analysis) Biodiesel outperforms corn ethanol for GHG reductions largely due to the low energy requirement of the transesterification process.
The Energy Balance of Biodiesel is all about the Feedstock
Fuel energy balance is the ratio of the amount of energy delivered by a fuel to the amount of energy consumed in its production. A positive energy balance means that a fuel contains more energy that it took to make. Conventional diesel has an energy balance of 3.9 - 4.3, meaning it contains about four times the energy it took to produce. Canola biodiesel has a very similar energy balance of 3.9 – 4.2. Tallow biodiesel is not quite as good, with an energy balance around 1.6. Yellow grease is the clear winner of the energy balance competition, with a ratio of 11.1 – 16.1.
The Food versus Fuel Debate – Part Two
One of the biggest criticisms of corn ethanol as a biofuel is the diversion of a food crop toward fuel production . In principle, the same ‘food versus fuel’ debate can be applied to biodiesel that uses oil-rich food crops as a feedstock, such as canola or soybeans. However, the Canadian canola biodiesel industry argues that there is usually a canola surplus in Canada, and only a small fraction of the canola harvest is used for biodiesel production. Corn ethanol certainly receives most of the negative attention, probably because corn is a staple grain in many parts of the world, and the fuel ethanol industry is much bigger than the biodiesel industry.
Just as cellulosic ethanol is championed as a more responsible alternative to corn ethanol, there are several non-food crop feedstocks that can be used to make biodiesel. Waste cooking oil, or yellow grease, is already being used commercially. A non-edible oilseed crop called jatropha is a promising biodiesel feedstock. Certain kinds of algae are also being grown for biodiesel feedstock because they readily accumulate oils (see Algae Biodiesel backgrounder for details).
To Learn More:
- For a general overview of biodiesel:
- For more details about the chemistry of biodiesel production:
- For a video about biodiesel production, featuring a Canadian manufacturer:
- Canadian Renewable Fuels Association Biodiesel Factsheet:
- Information about biodiesel race cars:
- For a detailed discussion of the chemistry of biodiesel production, click here.
- For a list of Canadian biodiesel plants and their feedstock:
- Technical report on GHG and energy balance of biodiesel, produced using the GHGenius model from Natural Resources Canada: http://www.ghgenius.ca/reports.php (source of GHG emissions and energy balance data, “2010 Biofuel Analysis” link, free registration required)