Biodiesel might not be your first choice of fuel at the gas station, but behind the scenes, it’s driving a quiet revolution. This remarkable fuel takes spent oil and food waste and transforms it into an energy-rich, reliable fuel you can use in any diesel vehicle.
Biodiesel is going from strength to strength, with US domestic production climbing from 1 billion gallons in 2010 to just under 3 billion gallons by 2019, exceeding the requirements of the Federal Renewable Fuel Standard.
To help you understand the impact that biodiesel can have as an alternative fuel, we’ve gathered key facts about biodiesel, pros and cons included, so you can evaluate if biodiesel is the future of sustainable fuel.
What is biodiesel?
Biodiesel is a type of diesel made from plant or animal material. In fact, any fuel that can run a diesel engine is diesel, but biodiesel is distinct because of the biomass that the fuel is derived from rather than the crude oil of conventional diesel.
This man-made fuel is made by reacting plant and animal fats with alcohol, producing energy-rich long-chain fatty acid esters that can power an internal combustion engine or be used as heating oil. Biodiesel differs from the spent vegetable oil that may be used to run a converted diesel engine. Biodiesel is a drop-in fuel that can be used interchangeably with regular diesel.
Key characteristics of biodiesel
- Biodiesel is a mono-alkyl ester
- Depending on the biomass and production method, biodiesel has a golden to deep brown color.
- Biodiesel slightly mixes with water
- Biodiesel has a high boiling point (340 to 375 °C/ 707°C), a high flashpoint of 130 °C (266 °F), which is much higher than diesel derived from petroleum
- Biodiesel is alsodenser than conventional diesel at ~0.85 g/cm3
- This fuel contains 37.27 megajoules per kilogram, lower than petroleum-derived diesel
- Biodiesel has a high energy output and burns more completely than conventional diesel despite its lower energy density
- Biodiesel is sulfur-free and contains almost no aromatics
A brief history of biodiesel
The transesterification process that is used to create biodiesel was discovered in 1853. This was several decades before Rudolf Diesel developed the first diesel engine in 1893.
The first functional diesel engine was exhibited as running on peanut oil rather than the mineral oil it had been designed for, at the request of the French government. Rudolf Diesel later noted that, though using vegetable oils as an engine fuel was perceived as insignificant, the time would come when they may be as important as petroleum.
How is biodiesel made?
Biodiesel is remarkable because of its simplicity and easy production from spent vegetable oils or rendered animal fat.
It is made in one of two ways:
- Physical production: This involves heating waste or virgin oil until all fats present are melted, and any water present evaporates. This fuel is then filtered and blended with petroleum hydrocarbons to improve the speed of its ignition and combustion efficiency.
- Chemical production: Biodiesel is also made using the transesterification process. This involves heating and filtering the oil, then combining it with methanol (an organic solvent) or other alcohols and a potassium hydroxide catalyst. This produces biodiesel and glycerol. Methanol is a nasty substance that is subject to environmental controls.
Biodiesel production is subject to quality standards to ensure that it will perform as expected if sold. A range of standards covers biodiesel production and the blends that are available commercially.
Biodiesel is usually available as a blend with petroleum-based diesel. The biodiesel is mixed in at varying proportions, indicated by the letter “B” and a number that is the percentage of biodiesel.
Here are the main blends:
- B100 is pure biodiesel.
- B20 is 20% biodiesel and 80% petroleum-based diesel (petrodiesel)
- B7 is 7 % biodiesel and 93% petrodiesel
- B5 is 5% biodiesel and 95% petrodiesel
- B2 is 2% biodiesel and 98% petrodiesel
The biodiesel/petrodiesel blends are created by mixing in tanks before delivery, splash mixing in tanker trucks when on the road, or inline mixing at the pump.
These biodiesel and petrodiesel blends are standardized to be used in diesel equipment. A biodiesel blend of less than 20% can be used in diesel engines, usually without affecting vehicle manufacturer warranty coverage.
What are the pros of biodiesel?
As Rudolf Diesel suggested, biodiesel has the potential to become just as important as petroleum fuels. As concern grows over the long-term sustainability of fossil fuels, attention is turning to biodiesel as an alternative fuel with high utility. Here are some of the fascinating benefits of biodiesel:
1. Biodiesel is a renewable energy source
Biodisel comes from energy sources that do not become depleted. The vegetable oil that makes biodiesel is available as long as plants like soybeans, sunflowers or canola (rapeseed) can be grown in abundance. This means you can maintain biodiesel supply without concern for fuel scarcity, especially if used oil is used.
In contrast, the oil industry uses non-renewable crude oil to create petrodiesel. Crude oil reserves are becoming depleted, with experts suggesting that there may be as few as 47 years of oil left if consumption continues at the current rate. A transition to biodiesel reduces demands on the existing petroleum supply and prolongs its availability.
2. Biodiesel is clean burning
Though biodiesel is less energy-dense than petrodiesel, it burns more completely, leaving little contamination when it is consumed. The C19 and C20 hydrocarbon chains of the most common forms of biodiesel burn to produce carbon dioxide and water. Biodiesel releases up to 2.59 kg of carbon dioxide per kilo of fuel burned versus 3.17 kilos when petrodiesel burns.
Because biodiesel comes from growing plants that use carbon dioxide to synthesize sugar, the combustion of biodiesel is “carbon-neutral,” and does not increase the net amount of carbon dioxide in the atmosphere.
3. Biodiesel has a positive energy balance
Biodiesel is also favored because of its positive energy balance, which makes it a better fuel option than biogas, hydrogen, and ethanol. For example, soybean biodiesel releases almost 5 units of energy for every unit of fossil fuel-derived energy.
Biodiesel production from crude glycerol also creates a net energy gain with an energy balance that is greater than 1. Each 1 million kg of biodiesel produced from glycerol yields a net energy gain of over 5000 GJ.
4. Any country can produce biodiesel
The simplicity of ingredients and production means that biodiesel can be made anywhere in the world. It offers the promise of fuel self-sufficiency in countries that are reliant on expensive oil imports. Many tropical developing countries can cultivate peanuts for oil that efficiently converts into biodiesel for industrial processes.
In Africa, biofuel production is currently largely limited to South Africa, but many countries recognize biofuels like biodiesel can help to improve their energy security and reduce petroleum demand. For uptake to become widespread, countries require the policies and infrastructure that can take advantage of the steady growth in biofuel production.
5. You can use biodiesel as a vehicle fuel
It’s remarkable that you can take old cooking oil, convert to biodiesel and use it like regular biodiesel in your vehicle. Diesel vehicles can use biodiesel without being specifically built or converted for this purpose.
In many places, you can fill up a vehicle with a biodiesel blend at the pump, with the most common blend being the B20 blend mentioned above.
Biodiesel is beneficial to fuel for internal combustion engines because it has a high cetane number which reduces ignition delay and makes the engine easier to start. Biodiesel also increases the lubricity of the engine so that its moving parts do not wear as much.
6. You can make biodiesel yourself
Because this diesel is made with cooking oil, with the right reagents, anyone can make biodiesel. You can combine waste and virgin cooking oil with alcohol and potassium hydroxide to create biodiesel and glycerol. This may be an appealing project to individuals who aspire to be self-sufficient:
However, the production of biodiesel is subject to quality protocols and the handling and disposal of hazardous substances and waste. Some jurisdictions may also require people who make biodiesel to declare its production or get a pollution prevention and control permit.
7. Biodiesel reduces fuel consumption from non-renewable sources
One of the main benefits of biodiesel is that it reduces the amount of petrodiesel that is used. This takes the pressure off the fossil fuels, improving energy security and balance. Biodiesel is widely used to power buses and other public transportation like these Kyoto buses that run on soybean diesel:
8. Waste can be transformed into biodiesel
Biodiesel provides massive scope for turning food waste into a credible fuel, known as waste-to-fuel (WtF). We can use waste materials throughout the biodiesel production process. Cooking oil, waste animal fats, and lipids derived from municipal waste are the most common source materials for conversion.
Petrochemicals have also innovated biodiesel production processes, with use of microorganisms including bacteria, yeasts, wastewater-grown microalgae feedstock and oleaginous fungi. Novel biological catalysts like calcium oxide from waste shell materials are also being explored.
9. Biodiesel is biodegradable
An additional benefit of biodiesel is the speed of its biodegradation, which is much faster than conventional petrodiesel. All biodiesels are biodegradable, though the breakdown rate depends on the diesel’s fatty acid chains.
The process is driven by microorganisms that the enzymes that can break down the chemical bonds in the diesel, altering its structure over time. Many biodiesels will be over 90% degraded after 30 days compared to under 25% for conventional diesel.
10. Biodiesel causes less air pollution
Vehicle engines are subject to emissions standards, irrespective of the fuel type, so biodiesel needs to have a favorable emissions profile. Biodiesel is sulfur free and releases fewer particulates into the air. Though biodiesel generates nitrogen oxide, catalytic conversion in diesel vehicles makes nitrogen emissions from biodiesel negligible.
11. Biodiesel is safe to handle and transport
Biodiesel is less volatile than diesel, making it easier to handle, transport and store. It has a high flash point of 130°C (266°F) more than double that of petrodiesel (52°C/ 125°F). If biodiesel spills, its biodegradability means that it causes less environmental impact if spilled.
12. Biodiesel can have a positive economic impact
The increased adoption of biodiesel has a range of economic benefits that are available to any economy. Aside from the reduction in net greenhouse gas emissions, biodiesels, waste biomass can reduce the amount of waste heading to landfill. Biodiesel production already provides over 70,000 US jobs while reducing petroleum demand.
The use of biodiesel blends also reduces prices at the gas station as its use does not expose countries to the volatility of the international oil markets. Blended fuel is cheaper for motorists and the fall in petroleum demand may also lead to a reduction in gas prices too.
What are the cons of biodiesel?
Biodiesel also has disadvantages that have to be weighed against its benefits. Some downsides of biodiesel are potential barriers to its wider use. Here are the main cons of using biodiesel:
1. Biodiesel varies in quality
One limitation of biodiesel is its wide composition and quality variation, especially if individuals make it. Multiple factors influence the quality of biodiesel including:
- The source of the base oil (virgin oil, used cooking oil, rendered animal fat).
- The fatty acids the base oil contains.
- The production method used to make biodiesel.
- How the diesel is handled and stored after production.
- Climatic conditions in the regions where biodiesel is produced and used.
There have been international efforts to standardize the production and quality of biodiesel. Governments, regulators, and standardization bodies have defined the physical and chemical properties of biodiesel that are suitable for vehicles and industry.
2. Biodiesel struggles to perform in low temperatures
Biodiesel performs differently from petrodiesel in cold temperatures. The cloud point and cold filter plugging point (CFPP) of biodiesel are much higher than conventional diesel which reduces the low-temperature operability and means that the fuel can solidify, forming crystals and gelling in an engine.
For example, the cloud point of soybean biodiesel is 30°C (86°F) versus -35°C (-31°F) for conventional diesel. An additional detail is that the type of vegetable oil that makes the biodiesel impacts clouding and the CFPP by up to 5°C.
Gelled diesel can plug the fuel filter and cause engine breakdown. A solution is to use a biodiesel blend that reduces the fuel’s CFPP and cloud point. B2 and B5 diesel blends perform well in freezing temperatures. Other strategies to prevent cold weather problems include adding anti-gelling agents to the fuel and insulating the fuel lines.
3. Biodiesel is more expensive than petrol and conventional diesel
High production costs hamper biodiesel uptake despite being made from relatively cheap vegetable oil, waste oil, and rendered fats. Many governments subsidize biodiesel, but this fuel can cost more than double wholesale petrol and diesel.
One of the big contributors to the cost of biodiesel is the use of virgin vegetable oils which are also used for food. Demand for cereals, seeds, and vegetable oil drives up the price of biodiesel, especially if yields are low. In the European Union, the mandatory blending of crop biofuels with conventional diesel contributes to high demand and costs.
4. Biodiesel production can harm agriculture
Massive increases in biodiesel production are being achieved by using crops that would otherwise have been for human or animal consumption. Diverting these crops to fuel production means that either more land has to be used for agriculture or food costs increase.
If agricultural land use has to expand, more fertilizer and water resources are used. The fertilizer runoff and sedimentation from farming biofuel crops increase water pollution. Land clearance for agriculture also means that deforestation may speed up, deteriorating the carbon profile of biodiesel.
5. Biodiesel demand drives up food prices
Economic modeling suggests that increased production of biodiesel will drive up food prices as the fuel competes for crop resources with food production. Studies have shown that Biodiesel can precipitate crop price rises of up to 53%. For every billion barrels of annual oil production, crop prices are thought to increase by 2 to 3 percent. When crop prices become too high, the incidence of malnourishment in the developing world increases.
6. Subsidized biodiesel production is creating monoculture
The large fields of corn, canola, and soybean that are cultivated for biodiesel are responsible for creating vast areas of monoculture. This intensive cultivation deteriorates soil fertility wipes out biodiversity and removes habitats for local wildlife. This short film shows the devastating impact of the cultivation of crops for biodiesel:
7. Biodiesel combustion releases nitrogen compounds
Nitric oxide and other nitrogen compounds are one of the most significant disadvantages of biodiesel use. These compounds are toxic and cause acid rain. Unfortunately, there is a fine balance between the generation of nitrogen compounds and the production of soot from burning biodiesel.
8. Biodiesel creates high carbonyl emissions
Air quality regulations for fuels do not routinely address the carbonyl emissions of fuels, but biodiesel is a significant source of these harmful air pollutants. Burning biodiesel releases non-regulated but toxic carbonyl compounds that include:
Biodiesel releases these substances in greater concentrations than conventional diesel.
As you can see biodiesel has a lot going for it, but for true sustainability, resource management will be essential to balance the production of biodiesel with food production.
Waste-to-fuel biodiesel initiatives show promise but they are resource intensive and require dedicated infrastructure that is expensive for many countries to establish. The ascendancy of biodiesel is certainly not slowing down, so watch this space for innovations that make this remarkable fuel even easier to adopt.