Biodiesel is a type of renewable fuel made from natural sources such as vegetable oils, animal fats, or used cooking oil. It is made up of long chemical chains called fatty acid esters. Most biodiesel is created from fats.

The history of biodiesel began in 1853 when scientists J. Patrick and E. Duffy first used a chemical process called transesterification on vegetable oil. This happened before Rudolf Diesel developed the diesel engine. Diesel’s engine was originally designed to use mineral oil, but it successfully ran on peanut oil during the 1900 Paris Exposition. This event showed that vegetable oil could be used as a fuel. Interest in using vegetable oil as fuel returned during times when resources were limited, like during World War II. However, problems such as high viscosity and engine deposits made it difficult to use. In the 1930s, a new method was discovered to change vegetable oil into fuel, which led to modern biodiesel production.

The properties of biodiesel depend on its source and how it is made. According to the National Biodiesel Board, biodiesel is a type of mono-alkyl ester. It has been tested in trains and power generators. Biodiesel has a higher boiling and flash point than regular diesel, mixes slightly with water, and has good lubricating qualities. Its energy content is about 9% less than standard diesel, which affects how efficiently it burns. Biodiesel production has improved over time, moving from using vegetable oil directly to using transesterification, a process that lowers viscosity and improves burning. A by-product of biodiesel production is glycerol, which is used in other industries.

Biodiesel is mainly used for transportation. It is being developed as a "drop-in" fuel, meaning it can work in existing diesel engines and fuel systems without changes. However, it is usually mixed with regular diesel, often less than 10%, because most engines need modifications to run on pure biodiesel. The amount of biodiesel in a blend is shown by a "B" number. B100 means pure biodiesel, while B20 means 20% biodiesel and 80% regular diesel. These blends balance the environmental benefits of biodiesel with the performance of regular diesel. Biodiesel blends can also be used for heating.

The environmental effects of biodiesel depend on factors like the type of raw material used, how land is used, and production methods. Biodiesel may reduce greenhouse gas emissions compared to fossil fuels, but concerns include land use changes, deforestation, and the debate over whether using land for fuel production affects food prices and availability. This debate focuses on how biodiesel production might impact food supplies and its overall carbon footprint. Despite these challenges, biodiesel remains an important part of global efforts to reduce fossil fuel use and address climate change.

Blends

Blends of biodiesel and regular diesel fuel are commonly sold at gas stations and other places where diesel fuel is available. Many countries use a system called the "B" factor to describe how much biodiesel is in a fuel mix:

• Fuel that is 100% biodiesel is called B100
• Fuel that is 20% biodiesel and 80% regular diesel is called B20
• Fuel that is 10% biodiesel and 90% regular diesel is called B10
• Fuel that is 7% biodiesel and 93% regular diesel is called B7
• Fuel that is 5% biodiesel and 95% regular diesel is called B5
• Fuel that is 2% biodiesel and 98% regular diesel is called B2

Blends with 20% or less biodiesel can usually be used in diesel engines without major changes, though some manufacturers may not cover damage caused by these blends under warranty. The B6 to B20 blends meet the ASTM D7467 standard. Pure biodiesel (B100) can also be used, but it may require engine changes to prevent problems with performance or maintenance. B100 can be mixed with regular diesel in several ways:

• Mixing in storage tanks before fuel is loaded into trucks
• Adding biodiesel and regular diesel to trucks in specific amounts
• Delivering both fuels to trucks at the same time for mixing
• Using pumps to measure and mix exact amounts of biodiesel and regular diesel

Biodiesel must meet certain quality standards, including the European standard EN 14214, the ASTM International D6751 standard, and the National Standard of Canada CAN/CGSB-3.524. The ASTM D6751 standard outlines rules for testing biodiesel blends mixed with regular diesel fuel. This standard includes tests to check properties like flash point and kinematic viscosity.

Historical background

In 1853, Patrick Duffy performed a chemical process called transesterification on vegetable oil. This happened 40 years before Rudolf Diesel created the first working diesel engine. Earlier methods for making lamp oil were patented in 1810 in Prague, but these were not shared in official scientific reports. Rudolf Diesel's first engine model, which used a 10-foot (3.05-meter) iron cylinder and a flywheel, successfully ran on its own power in Augsburg, Germany, on August 10, 1893. It used only peanut oil as fuel. To honor this event, August 10 is now called "International Biodiesel Day."

Some sources say Diesel designed his engine to use peanut oil, but this is not true. In his published papers, Diesel wrote that at the 1900 Paris Exhibition, an engine built by the Otto Company ran on arachide (peanut) oil. The engine was originally made for mineral oil but was tested with vegetable oil without changes. The French government at the time was interested in using arachide oil, which grows in Africa, for energy production. Diesel later supported the idea of using vegetable oils for fuel. In a 1912 speech, he said, "The use of vegetable oils for engine fuels may seem unimportant today, but they could become as important as petroleum and coal products in the future."

Although petroleum-based diesel fuels are widely used, many countries studied vegetable oils as engine fuels during the 1920s, 1930s, and World War II. Belgium, France, Italy, the United Kingdom, Portugal, Germany, Brazil, Argentina, Japan, and China tested and used vegetable oils as diesel fuels during this time. Problems arose because vegetable oils are more viscous than petroleum diesel, which can cause poor fuel atomization, leading to deposits and coking in engines. Solutions included heating the oil, mixing it with petroleum diesel or ethanol, or using chemical processes like pyrolysis and cracking.

On August 31, 1937, Georges Chavanne of the University of Brussels was granted a patent for a method to convert vegetable oils into fuel. The process, called alcoholysis (or transesterification), used ethanol (and methanol) to separate fatty acids from glycerol by replacing glycerol with short alcohol molecules. This method is considered the first recorded process for producing biodiesel. It is similar to older methods used in the 18th century to make lamp oil.

In 1977, Brazilian scientist Expedito Parente invented the first industrial process for making biodiesel. This process meets international standards for biodiesel quality and is recognized by the motor industry. As of 2010, Parente's company, Tecbio, was working with Boeing and NASA to develop and certify bioquerosene (bio-kerosene), another fuel he patented.

In 1979, research in South Africa began on using transesterified sunflower oil to produce diesel fuel. By 1983, the process for making engine-tested biodiesel was completed and shared internationally. An Austrian company, Gaskoks, obtained the technology and built the first biodiesel pilot plant in November 1987 and the first industrial-scale plant in April 1989. This plant could process 30,000 tons of rapeseed annually.

During the 1990s, biodiesel production expanded in many European countries, including the Czech Republic, Germany, and Sweden. France began producing biodiesel (called diester) from rapeseed oil, mixing it into regular diesel at 5% and into public transportation fuel at 30%. Car manufacturers like Renault and Peugeot certified truck engines to use up to 30% biodiesel. Tests with 50% biodiesel were also conducted. By 1998, the Austrian Biofuels Institute reported 21 countries had commercial biodiesel projects. Today, 100% biodiesel is available at many service stations across Europe.

Properties

The color of biodiesel can be clear, golden, or dark brown. This depends on how the fuel is made and the type of material used to create it. These differences also affect the fuel's properties. Biodiesel mixes slightly with water, has a high boiling point, and low vapor pressure. Its flash point, which is the temperature at which it can catch fire, is often above 130 °C (266 °F). This is much higher than petroleum diesel, which may have a flash point as low as 52 °C (126 °F). Biodiesel has a density of about 0.88 grams per cubic centimeter, which is higher than petroleum diesel, which has a density of about 0.85 grams per cubic centimeter.

The energy value of biodiesel is about 37.27 megajoules per kilogram. This is about 9% less than regular Number 2 petroleum diesel. The energy density of biodiesel depends mostly on the material used to make it, not the production method. However, these differences are smaller than those for petroleum diesel. Some sources say biodiesel improves engine lubrication and allows fuel to burn more completely. This can increase the energy output from the engine and help balance the higher energy density of petroleum diesel.

Biodiesel contains almost no sulfur. While petroleum diesel uses sulfur compounds to provide lubrication, biodiesel has good lubricating qualities and high cetane ratings. These features make biodiesel useful as an additive to ultra-low-sulfur diesel (ULSD) fuel to help with engine lubrication. Biodiesel with higher lubricity can help extend the life of engine parts that rely on fuel for lubrication. These parts may include high-pressure injection pumps, pump injectors (also called unit injectors), and fuel injectors, depending on the engine type.

Applications

Biodiesel can be used as pure fuel (B100) or mixed with petroleum diesel in most diesel engines. However, newer engines with very high-pressure systems (29,000 psi) have limits, such as B5 or B20, depending on the manufacturer. Biodiesel dissolves materials differently than petroleum diesel and can damage natural rubber parts in older vehicles (mostly made before 1992). These parts are often replaced with FKM, which does not react with biodiesel. Biodiesel can also remove old deposits from fuel lines where petroleum diesel was used. This may clog fuel filters if pure biodiesel is used suddenly. Therefore, it is advised to replace fuel filters after switching to biodiesel for the first time.

After the Energy Policy Act of 2005, biodiesel use in the United States increased. In the UK, a law requires suppliers to include 5% renewable fuel in all transport fuel sold by 2010, which means 5% biodiesel (B5) for road diesel.

In 2005, Chrysler (then part of DaimlerChrysler) released Jeep Liberty CRD diesel vehicles in Europe with 5% biodiesel blends, showing some acceptance of biodiesel. In 2007, DaimlerChrysler said it would expand warranty coverage to 20% biodiesel blends if biofuel quality in the United States improved.

Volkswagen stated that some of its vehicles can use B5 and B100 biodiesel made from rapeseed oil, as long as it meets the EN 14214 standard. Using this biodiesel will not void warranties. Mercedes-Benz does not allow biodiesel blends above 5% (B5) due to concerns about fuel quality. Damages from using non-approved fuels are not covered under its warranty.

In 2004, Halifax, Nova Scotia, updated its bus system to run entirely on fish-oil based biodiesel. Initial mechanical issues occurred, but the fleet was fully converted after improvements. In 2007, McDonald’s UK began producing biodiesel from restaurant waste oil to power its fleet.

The 2014 Chevy Cruze Clean Turbo Diesel is rated for up to B20 (20% biodiesel/80% diesel) compatibility. Virgin Trains West Coast ran the UK’s first biodiesel train in 2007, using a mix of 80% petroleum diesel and 20% biodiesel. The British Royal Train used 100% biodiesel in 2007, supplied by Green Fuels Ltd. A government proposal to convert UK railways to biodiesel was later replaced with plans for electrification.

A railroad in Eastern Washington tested a 25% biodiesel/75% petroleum diesel blend in 2008, using fuel made from canola grown near the tracks. In 2007, Disneyland began using B98 (98% biodiesel) for park trains but switched to biodiesel made from its own used cooking oil in 2009. The Mt. Washington Cog Railway added a biodiesel locomotive in 2007. The Grand Canyon Railway used used cooking oil to power its train in 2009. In 2014, India announced plans to use 5% biodiesel in its diesel engines.

Biodiesel can also be used as a heating fuel in homes and businesses. It is mixed with heating oil and standardized differently from transportation diesel. Bioheat fuel is a special blend of biodiesel and heating oil, trademarked in the US and Canada. Heating biodiesel is available in blends up to 20%, though research is ongoing about its effects. Older furnaces may have rubber parts affected by biodiesel, but they can burn biodiesel without changes. Care is needed to remove residue from petroleum diesel, which can clog pipes. Starting with biodiesel blends and gradually increasing the mix helps avoid clogs. Biodiesel cleaning can improve furnace efficiency.

Massachusetts requires 2% biofuel in home heating diesel by 2010 and 5% by 2013. New York City has a similar law.

Biodiesel can dissolve crude oil, making it useful for cleaning oil spills. In experiments, biodiesel removed up to 80% of oil from cobble and sand, and 30% from gravel. Oil-biodiesel mixtures are removed with skimmers and break down easily due to biodiesel’s biodegradability.

In 2001, UC Riverside installed a 6-megawatt backup power system using B100 biodiesel. This reduced emissions of smog, ozone, and sulfur, improving air quality near schools and hospitals.

Effects

The power output of biodiesel depends on its blend, quality, and the conditions under which it is burned. For example, the thermal efficiency of B100 (pure biodiesel) compared to B20 (a blend of 20% biodiesel and 80% petroleum diesel) changes because the energy content of the blends differs. Thermal efficiency is influenced by fuel characteristics such as viscosity (how thick or thin the fuel is), specific density (how much the fuel weighs for a given volume), and flash point (the temperature at which the fuel can ignite). These characteristics change as the blend or quality of biodiesel changes. The American Society for Testing and Materials sets standards to evaluate the quality of fuel samples.

One study found that the brake thermal efficiency of B40 (a blend of 40% biodiesel and 60% petroleum diesel) was better than traditional petroleum fuel at higher compression ratios (21:1). As compression ratios increased, the efficiency of all fuels and blends improved. However, B40 was the most efficient at a compression ratio of 21:1 compared to other blends. The study suggested that this improvement in efficiency was due to differences in fuel density, viscosity, and heating values.

Some modern diesel engines are not designed to use biodiesel, while many heavy-duty engines can run on biodiesel blends up to B20. Traditional direct injection systems operate at about 3,000 psi (pounds per square inch) at the injector tip, while modern common rail systems operate at over 30,000 psi. Components in fuel systems must function across a wide temperature range, from below freezing to over 1,000°F (560°C). Diesel fuel must burn efficiently and produce as few emissions as possible. As emission standards become stricter, fuel systems are designed to control harmful emissions. Traditional inline injection systems are more tolerant of lower-quality fuels than common rail systems. The higher pressures and tighter tolerances in common rail systems allow better control over fuel atomization (how finely the fuel is broken into droplets) and injection timing, which improves engine efficiency and emission control. Components in fuel systems work together to ensure the fuel and engine operate efficiently. If fuel does not meet system specifications, the fuel system’s performance may be damaged. Parameters like spray pattern and atomization are closely linked to injection timing.

A study found that during atomization, biodiesel and its blends create larger fuel droplets than traditional petroleum diesel. Smaller droplets in petroleum diesel are due to its lower viscosity and surface tension. Droplets at the edges of the spray pattern were larger than those in the center, likely because pressure drops faster at the edges. The size of droplets was related to their distance from the injector tip. B100 (pure biodiesel) had the greatest spray penetration because of its higher density. Larger droplets can reduce combustion efficiency, increase emissions, and lower engine power. Another study found that biodiesel has a short injection delay due to its higher viscosity. This delay, along with biodiesel’s higher cetane rating (which affects how quickly it ignites), may lead to poor atomization and fuel-air mixing during ignition. However, this delay might help reduce nitrogen oxide (NOx) emissions.

Emissions from diesel fuel combustion are regulated by the U.S. Environmental Protection Agency (EPA). To meet EPA standards, fuel systems must control combustion and reduce emissions. Technologies like exhaust gas recirculation (EGR) and diesel particulate filters (DPF) are used to reduce harmful emissions.

The feedstock (raw material) used to make biodiesel can affect exhaust emissions, even when blended with petroleum diesel. A study by Chonbuk National University found that a B30 blend (30% biodiesel) reduced carbon monoxide emissions by about 83% and particulate matter emissions by about 33%. However, NOx emissions increased without an EGR system. With EGR, a B20 blend significantly reduced engine emissions. The California Air Resources Board found that biodiesel had the lowest carbon emissions among tested fuels, including ultra-low-sulfur diesel, gasoline, corn-based ethanol, compressed natural gas, and biodiesel from different feedstocks. Emissions varied based on the feedstock used. Soy-based biodiesel had the highest carbon emissions, while biodiesel from used cooking oil had the lowest.

Studies on biodiesel’s effect on diesel particulate filters found that sodium and potassium carbonates in biodiesel may help convert ash into catalysts, but this can cause particulates to build up in the DPF, clogging it and interfering with the filter’s regeneration process. A study on jathropa biodiesel blends showed that using biodiesel in engines with EGR systems reduced fuel efficiency and torque. CO and CO₂ emissions increased with higher EGR rates, but NOx emissions decreased. Jathropa biodiesel blends had acceptable opacity levels, while traditional diesel exceeded acceptable standards. EGR systems helped reduce NOx emissions within certain operating ranges.

As of 2017, blended biodiesel fuels (especially B5, B8, and B20) are commonly used in heavy-duty vehicles, such as transit buses in U.S. cities. Exhaust emissions from these fuels showed significant reductions compared to regular diesel.

Material Compatibility with Biodiesel:
– Plastics: HDPE works well with biodiesel, but PVC degrades slowly, and polystyrene dissolves when exposed.
– Metals: Biodiesel affects copper-based materials (like brass), zinc, tin, lead, and cast iron. Stainless steels (316 and 304) and aluminum are not affected.
– Rubber: Biodiesel can degrade natural rubber in older engine parts. Fluorinated elastomers (FKM) cured with peroxide or base-metal oxides may degrade if biodiesel becomes unstable due to oxidation. Modern synthetic rubbers like FKM-GBL-S and FKM-GF-S used in vehicles are compatible with biodiesel in all conditions.

Production

Biodiesel is usually made through a chemical process called transesterification, which changes vegetable oil, animal fat, or other non-edible materials like used cooking oil into biodiesel. This process can be done in several ways, including using a batch method, heterogeneous catalysts, supercritical processes, ultrasonic methods, or microwave methods.

Chemically, biodiesel is a mixture of long-chain fatty acid mono-alkyl esters. The most common method uses methanol, which is converted into sodium methoxide to create methyl esters, known as Fatty Acid Methyl Esters (FAME). Methanol is often used because it is the cheapest alcohol available. Ethanol can also be used to make ethyl esters, called Fatty Acid Ethyl Esters (FAEE). Higher alcohols, like isopropanol and butanol, can also be used. These alcohols improve the cold flow properties of biodiesel but make the chemical reaction less efficient. A process called lipid transesterification is used to change the base oil into the desired esters. Free fatty acids (FFAs) in the base oil are either turned into soap and removed or converted into biodiesel using an acidic catalyst. After this process, biodiesel burns similarly to petroleum diesel and can replace it in most uses.

The methanol used in biodiesel production is often made from fossil fuels. However, renewable methanol can be made using carbon dioxide or biomass, which avoids using fossil fuels.

A by-product of biodiesel production is glycerol. For every 1 tonne of biodiesel made, 100 kg of glycerol is produced. Glycerol was once valuable and helped make biodiesel production economically viable. However, as biodiesel production increased, the price of glycerol dropped. Scientists are now studying ways to use glycerol as a chemical building block. In the UK, a project called The Glycerol Challenge is exploring these uses.

Crude glycerol, which contains water and catalyst residues, must usually be purified through a process called vacuum distillation. This process uses a lot of energy. Once purified, glycerol (with 98%+ purity) can be used directly or turned into other products. In 2007, companies like Ashland Inc. and Cargill planned to make propylene glycol from glycerol in Europe. Dow Chemical also planned to make epichlorhydrin from glycerol in North America and China. Epichlorhydrin is used to make epoxy resins.

In 2005, global biodiesel production reached 3.8 million tonnes, with 85% coming from the European Union. In 2006, total world production was about 5–6 million tonnes, with 4.9 million tonnes made in Europe (2.7 million tonnes from Germany) and most of the rest from the United States. By 2007, biodiesel production capacity was growing rapidly, with an average annual growth rate of over 40% from 2002 to 2006.

In 2008, European biodiesel production reached 7.8 million tonnes, with a total capacity of 16 million tonnes. This compares to a total diesel demand of about 490 million tonnes in the United States and Europe. In July 2009, the European Union added a tax on American biodiesel imports to help European producers compete.

In 2005–06, global production of vegetable oil for all uses was about 110 million tonnes, including 34 million tonnes each of palm oil and soybean oil. In 2011, U.S. biodiesel production reached over 1 billion gallons, exceeding the 800 million gallon target set by the EPA.

As of 2018, Indonesia was the world’s top supplier of palm oil-based biodiesel, producing 3.5 million tonnes annually and planning to export about 1 million tonnes. Production is expected to reach nearly 12 billion gallons by 2020.

Many types of oils can be used to make biodiesel:
– Virgin oil feedstock: Rapeseed and soybean oils are most common. Soybean oil accounts for about half of U.S. production. Other oils include Pongamia, field pennycress, jatropha, mustard, jojoba, flax, sunflower, palm oil, coconut, and hemp.
– Waste vegetable oil (WVO).
– Animal fats: Tallow, lard, yellow grease, chicken fat, and by-products from fish oil.
– Algae: Grown using waste materials like sewage without competing for land used for food.
– Halophytes: Plants like Salicornia bigelovii can grow in saltwater and produce oil yields similar to soybeans.
– Sewage sludge: Companies like Waste Management and startups like InfoSpi are exploring ways to make biodiesel from sewage.
– Insect oil: Extracted from pupae or larvae, often using solvents. Black soldier fly oil is one example. Hanyang University has patented genetically modified flies with higher fat content for biodiesel.

Some people say waste vegetable oil is the best source for biodiesel, but the supply is too small to meet global energy needs. Animal fats are a by-product of meat production and cooking. Using these fats adds value to the livestock industry. Some biodiesel plants now use chicken fat from Tyson poultry plants to make biodiesel. Small-scale plants also use waste fish oil. An EU-funded project in Vietnam produces 13 tons of biodiesel daily from 81 tons of fish waste, using the fuel to power a fish processing plant.

Current worldwide production of vegetable oil and animal fat is not enough to replace fossil fuels. Some people also worry about the large amount of farming required for biodiesel production.

Energy security

One of the main reasons countries use biodiesel is to improve energy security. Energy security means a nation uses less oil and replaces it with resources found nearby, such as coal, gas, or renewable sources. This allows a country to use biofuels without lowering greenhouse gas emissions. While some people disagree about the overall energy balance, it is clear that reliance on oil decreases. For example, the energy needed to make fertilizers can come from sources other than oil. The US National Renewable Energy Laboratory (NREL) says energy security is the top reason for the US biofuels program. A White House paper titled "Energy Security for the 21st Century" explains that energy security is a major reason for promoting biodiesel. Former EU Commission president Jose Manuel Barroso, speaking at a recent EU biofuels conference, said properly managed biofuels can help the EU have a more secure energy supply by using different energy sources.

Global biofuel policies

Many countries are working to increase the use and production of biofuels, such as biodiesel, as an alternative to fossil fuels and oil. To help grow the biofuel industry, governments have created laws and rules to reduce reliance on oil and encourage the use of renewable energy. Each country has its own policies about how biodiesel is taxed or given money back for its use, import, and production.

In Canada, the Environmental Protection Act Bill C-33 required gasoline to contain 5% renewable fuel by 2010 and diesel and heating oil to contain 2% renewable fuel by 2013. The EcoENERGY for Biofuels Program gave money to help produce biodiesel from 2008 to 2010 at a rate of CAN$0.20 per liter. Each year after that, the rate decreased by $0.04 until it reached $0.06 in 2016. Some provinces also have their own laws about biofuel use and production.

The Volumetric Ethanol Excise Tax Credit (VEETC) was a major source of financial support for biofuels but was set to end in 2010. This program gave a tax credit of US$1 per gallon for biodiesel made from virgin oils and $0.50 per gallon for biodiesel made from recycled oils. Today, soybean oil is used to make soybean biodiesel for many commercial purposes, such as mixing fuel for transportation.

The European Union is the largest producer of biodiesel, with France and Germany as the main producers. To increase biodiesel use, some countries require blending biodiesel into fuels and may give punishments if these goals are not met. In France, a target of 10% biodiesel blending was set but stopped in 2010. To encourage biofuel production, the EU offers tax reductions for meeting certain production goals. In Germany, transport diesel must include at least 7% biodiesel, known as "B7."

In the United Kingdom, the Renewable Transport Fuel Obligation (RTFO) requires fuel companies to mix a certain amount of renewable fuel into their supply, aiming for 12.4% by 2032. The UK also requires B7 diesel (7% biodiesel) and E10 petrol (10% bioethanol). Tax incentives and grants, such as the Bus Service Operators' Grant (BSOG), help support biodiesel use.

Malaysia plans to fully adopt its nationwide B20 palm oil biofuel program by the end of 2022. This program requires biofuel to contain 20% palm oil, known as B20, for use in the transport sector. The program started in January 2020 but faced delays due to rules to stop the spread of the coronavirus.

Issues and concerns

Up to 40% of corn grown in the United States is used to make ethanol, and globally, 10% of all grain is turned into biofuel. If the United States and Europe used 50% less grain for biofuels, it could replace all of Ukraine's grain exports. In some poor countries, rising prices for vegetable oil are causing problems. Some suggest using non-edible oils, like camelina, jatropha, or seashore mallow, which grow on land that is not suitable for food crops or trees. Others argue that farmers might switch from growing food crops to biofuel crops to earn more money, even if the new crops are not edible. This could lead to higher food prices because fewer farmers would be growing food. While changes in farming take time, increased demand for first-generation biofuels is likely to raise food prices. Some people note that poor farmers and countries may benefit from higher vegetable oil prices. Biodiesel made from sea algae would not require land currently used for food, and new jobs in algae farming could be created. In comparison, biogas production uses agricultural waste to make biofuel and also creates compost, which helps improve farming and food production. Recent research has studied how adding special materials, like graphene, to biodiesel can improve engine performance and reduce emissions. However, biodiesel use has environmental effects, including possible reductions in greenhouse gas emissions, deforestation, pollution, and changes in how quickly biodiesel breaks down. According to a 2010 report by the U.S. Environmental Protection Agency (EPA), biodiesel made from soy oil reduces greenhouse gas emissions by 57% compared to petroleum diesel, and biodiesel from waste grease reduces emissions by 86%. Environmental groups like Rainforest Rescue and Greenpeace criticize the growth of plants like oil palms, soybeans, and sugarcane for biodiesel, as this can destroy rainforests and harm ecosystems. The EPA also stated in 2012 that biodiesel made from palm oil does not count toward the U.S. renewable fuel goals because it is not climate-friendly. Indonesia produces most of its biodiesel from palm oil, but clearing land for oil palm plantations threatens rainforests. The environmental impact of biodiesel depends on many factors. While biodiesel can reduce greenhouse gas emissions compared to fossil fuels, growing crops for biodiesel may lead to more emissions if land use changes, such as deforestation, are involved. Algae-based biofuels could solve this problem by using land that is not suitable for farming. Carbon dioxide is a major greenhouse gas. Although burning biodiesel releases carbon dioxide like fossil fuels, plants used to make biodiesel absorb carbon dioxide during growth through photosynthesis. When plants are turned into biodiesel and burned, the stored carbon is released again. Calculating total greenhouse gas emissions from biodiesel involves many steps, including emissions from growing feedstock, transporting it, processing it, and the carbon absorbed by plants. Other factors include land use changes, transportation of biodiesel, engine efficiency, and emissions from tailpipes. If land use changes are not considered, biodiesel from rapeseed and sunflower oil can reduce emissions by 45% to 65% compared to petroleum diesel. Biodiesel from used cooking oil may reduce emissions by up to 85%. However, if growing feedstock causes deforestation, the emissions from clearing forests could outweigh the benefits of using biodiesel. In the United States, biodiesel is the only alternative fuel that has passed all health testing requirements under the Clean Air Act. Biodiesel can reduce particulate emissions by up to 20% compared to low-sulfur diesel and by about 50% compared to fossil fuel diesel. A study by the University of Idaho compared how quickly biodiesel, vegetable oils, and petroleum diesel break down in the environment.

Research

Research has focused on finding better crops and increasing oil production. Other sources, such as human waste, are being explored. In Ghana, the first "fecal sludge-fed biodiesel plant" was built.

Special mustard plants, bred for high oil content, are useful in crop rotation with cereals. After oil is pressed from the seeds, the leftover material can act as a biodegradable pesticide.

The NFESC, along with Biodiesel Industries in Santa Barbara, is developing biodiesel technologies for the U.S. Navy and military, which use large amounts of diesel fuel.

A group in Spain, working for Ecofasa, created a biofuel from trash. The fuel is made by treating general urban waste with bacteria to produce fatty acids, which can be used to make biodiesel.

Another method avoids chemicals by using genetically modified microbes.

From 1978 to 1996, the U.S. NREL studied algae as a biodiesel source in the "Aquatic Species Program." Michael Briggs, from the UNH Biodiesel Group, suggested that algae with more than 50% natural oil content could replace all vehicle fuel. These algae could be grown in wastewater treatment ponds, and their oil could be extracted and processed into biodiesel. The remaining dried algae could also be used to make ethanol.

Producing algae for biodiesel on a commercial scale has not yet begun, but studies have been done to estimate oil yields. Unlike crop-based biofuels, algae farming does not require farmland or fresh water and does not reduce food production. Companies are testing algae bio-reactors to scale up biodiesel production. Biodiesel lipids can be extracted from wet algae using a simple reaction in ionic liquids.

Millettia pinnata, also called the Pongam Oiltree, is a leguminous tree that produces non-edible oil. Pongamia plantations for biodiesel have two environmental benefits: they store carbon and produce fuel oil. These trees grow on marginal land unsuitable for food crops and do not need nitrate fertilizers. Pongamia seeds contain about 40% oil by weight and can grow in poor, salty soils. It is a focus of many biodiesel research groups because it produces high-quality oil without competing with food crops. However, growing on marginal land may lead to lower oil yields, which could affect competition with food crops for better soil.

Research on Jatropha curcas, a poisonous shrub-like tree, is ongoing. Scientists are working to improve its oil yield per acre through genetic, soil, and horticultural advancements.

SG Biofuels, a company in San Diego, has used molecular breeding to create hybrid Jatropha seeds with higher yields. These seeds also flower more consistently, resist pests and disease better, and tolerate cold weather.

Plant Research International, part of Wageningen University in the Netherlands, runs the Jatropha Evaluation Project (JEP) to study large-scale Jatropha farming through field and lab experiments.

The Center for Sustainable Energy Farming (CfSEF), a non-profit in Los Angeles, focuses on Jatropha research in plant science, agronomy, and horticulture. Improvements in these areas are expected to increase Jatropha farm yields by 200–300% in the next decade.

Fats, oils, and grease (FOG) from sewage can also be used to make biodiesel.

A group in Russia’s Academy of Sciences published a 2008 study showing they could extract lipids from single-celled fungi and convert them into biodiesel efficiently.

A variant of the fungus Gliocladium roseum, discovered in Patagonia, can convert cellulose into medium-length hydrocarbons similar to diesel fuel. This discovery is linked to the potential production of "myco-diesel."

Researchers at the University of Nevada, Reno, produced biodiesel from oil in used coffee grounds. Their analysis found 10–15% oil content by weight in the grounds. After extracting the oil, it was processed into biodiesel. Producing biodiesel from coffee grounds costs about one U.S. dollar per gallon. However, even if all global coffee grounds were used, the amount of biodiesel produced would be less than 1% of annual U.S. diesel use.

A microreactor has been developed to convert biodiesel into hydrogen steam for fuel cells.

Steam reforming, also called fossil fuel reforming, produces hydrogen gas from hydrocarbon fuels, including biodiesel. A microreactor, or reformer, uses water vapor and liquid fuel under high temperature and pressure. A nickel-based catalyst enables the reaction:

Hydrocarbon + H₂O ⇌ CO + 3H₂ (Highly endothermic)

Further oxidation of carbon monoxide produces more hydrogen and carbon dioxide:

CO + H₂O → CO₂ + H₂ (Mildly exothermic)

As of 2020, researchers at Australia’s CSIRO studied safflower oil from a specially bred variety as an engine lubricant. Researchers at Montana State University’s Advanced Fuel Centre tested the oil in a large diesel engine, calling the results a "game-changer."