Ethanol fuel is an alcohol-based fuel made by fermenting simple sugars from plants like corn, sugarcane, and other organic materials. It can also be created from petroleum products. Ethanol is the same type of alcohol found in alcoholic drinks, but it is most often used as a fuel for vehicles, either alone or mixed with gasoline. This helps reduce the use of fossil fuels and lowers greenhouse gas emissions. Brazil and the United States are the largest producers of ethanol globally, together supplying most of the world's ethanol. Many countries require ethanol to be mixed with gasoline for use in cars.

Ethanol has been used as a fuel since the early 1900s. Brazil started using it widely in the 1970s during an energy crisis. Improvements in vehicle technology and government policies have helped ethanol become more common worldwide. Ethanol’s chemical formula is C₂H₅OH, and it burns cleanly, producing carbon dioxide and water. Its high octane rating makes it suitable for engines that operate at high compression. Most ethanol is made by fermenting sugars with microorganisms, followed by distillation and dehydration. A small amount is also made from ethylene, a chemical derived from petroleum.

Ethanol is considered a renewable energy source, but its production has environmental and economic challenges. Sugarcane-based ethanol in Brazil uses less energy and creates fewer carbon emissions compared to gasoline. However, corn-based ethanol in the United States has smaller environmental benefits. Growing crops for ethanol can affect food prices, water use, and land use. Emissions from producing and burning ethanol depend on the materials used and the production methods. Scientists are studying new ways, like cellulosic ethanol, to make ethanol more sustainable and reduce its environmental impact.

Common ethanol fuel mixtures are used globally. Pure ethanol (either with or without water) can only be used in engines designed for it. Anhydrous ethanol, which has no water, can be mixed with gasoline for use in cars, but the engines must be modified because ethanol has less energy than gasoline. Even though ethanol is less efficient than gasoline, it burns more completely, producing fewer harmful gases and less pollution. This makes ethanol a cleaner alternative to traditional gasoline.

History and Use

Global ethanol production for transport fuel increased three times between 2000 and 2007. Over time, ethanol production has generally grown, but it decreased in 2020 because of the COVID-19 pandemic. Ethanol-blended fuel is commonly used in Brazil, the United States, Canada, and Europe. In the United States, most cars today can use fuel blends with up to 15% ethanol. In 2011, ethanol made up 10% of the U.S. gasoline supply from domestic sources. Some cars designed for flexible fuel can use up to 100% ethanol.

The first car made to run entirely on ethanol was the Fiat 147, introduced in Brazil by Fiat in 1978. Since 1976, Brazil’s government has required ethanol to be mixed with gasoline. Since 2007, the legal mix has been about 25% ethanol and 75% gasoline (E25). By December 2011, Brazil had 14.8 million flex-fuel cars and trucks and 1.5 million flex-fuel motorcycles that regularly use pure ethanol (E100).

World ethanol production for transport fuel increased three times between 2000 and 2007, from 17 billion liters to over 52 billion liters. From 2007 to 2008, ethanol’s share of global gasoline fuel use rose from 3.7% to 5.4%. In 2011, global ethanol fuel production reached 84.6 billion liters, with the United States and Brazil being the largest producers. These two countries accounted for 62.2% and 25% of global production, respectively. In May 2017, U.S. ethanol production reached 57.54 billion liters.

Chemistry

During ethanol fermentation, sugars such as glucose found in corn, sugarcane, or other crops are changed into ethanol and carbon dioxide.

Ethanol fermentation does not always produce only ethanol. Other substances, like acetic acid and glycols, may also form. These substances are mostly removed during the purification process. Fermentation happens in a water-based solution. After fermentation, the solution contains about 15% ethanol. Ethanol is then separated and purified using adsorption and distillation.

When ethanol burns, it reacts with oxygen to create carbon dioxide, water, and heat.

Starch and cellulose are long chains of glucose molecules. Ethanol can also be made from cellulosic materials, such as plant fibers. This process requires a pretreatment step that breaks down cellulose into glucose and other sugars. These sugars can then be fermented. The final product is called cellulosic ethanol, which shows its source.

Ethanol is also made industrially from ethylene. This process involves adding water to the double bond in ethylene, which happens in the presence of a catalyst and high heat.

Most ethanol is produced through fermentation.

Production

Bioethanol is a type of renewable energy. It can be made from plants used in farming, such as hemp, sugarcane, potatoes, cassava, and corn. People have debated whether bioethanol is helpful in replacing gasoline. Some concerns include higher food prices because growing crops needs a lot of farmland, and whether making and using ethanol uses too much energy or causes pollution. These issues are especially important when ethanol is made from corn.

Ethanol fuel can be made in several ways, but the most common method is fermentation. To produce ethanol on a large scale, the basic steps are: using yeast to turn sugars into ethanol, distilling to separate ethanol from other substances, removing water (the method used depends on the ethanol’s purpose), and sometimes adding chemicals to make it safe for use.

Before fermentation, some plants need their carbohydrates, like cellulose and starch, to be broken down into sugars. This process is called saccharification. For example, breaking down cellulose is called cellulolysis (see cellulosic ethanol). Enzymes are used to change starch into sugar.

Ethanol is made by yeast turning sugar into ethanol. Right now, yeast can only work directly with sugars. Two parts of plants—starch and cellulose—are made of sugars and could, in theory, be turned into sugar for fermentation. However, only sugar (like in sugarcane) and starch (like in corn) can be converted economically.

Scientists are interested in making ethanol from plant cellulose, which is called cellulosic ethanol. This method could be important in the future, but it is not used widely now because it is not cost-effective.

For ethanol to be used as fuel, most of the water and yeast must be removed. After fermentation, the mixture is heated so ethanol evaporates. This process, called distillation, separates ethanol, but it can only reach about 95–96% purity because of a special mixture of water and ethanol that forms during boiling. This mixture is called hydrous ethanol and can be used as fuel alone. However, it does not mix well with gasoline in all amounts, so more steps are needed to remove water before combining it with gasoline.

There are three main ways to remove water from ethanol. One method, called azeotropic distillation, adds chemicals like benzene or cyclohexane to the mixture. This creates a new mixture that can be separated into pure ethanol and other substances. Another method, extractive distillation, adds a special chemical to increase ethanol’s ability to separate from water. A newer method, used by many modern ethanol plants, uses molecular sieves—tiny materials that trap water molecules. This method saves energy compared to older methods.

Recent research shows that removing all water before mixing ethanol with gasoline may not always be needed. Instead, the water-ethanol mixture can be blended directly with gasoline, and the way the liquids interact can help remove water without extra steps.

Ethanol absorbs water from the air, which can lower its fuel value and cause problems like engine failure. Because of this, ethanol fuel must be stored in tightly sealed containers. Ethanol cannot be easily transported through pipelines like gasoline because it mixes with water.

The amount of water an ethanol-gasoline blend can hold without separating depends on the ethanol percentage. For example, E30 (a blend with 30% ethanol) can hold up to about 2% water. If a blend has more than 71% ethanol, water and gasoline can mix in any amount without separating. However, more water in the fuel can reduce how far a vehicle can travel. Higher ethanol content allows E30 and hydrated ethanol to be stored together safely. At lower temperatures, less water is allowed in the blend.

While biodiesel systems for home and business use have been available for years, ethanol production systems for personal use have been slower to develop. In 2008, two companies introduced home-scale ethanol systems. One system, the AFS125, can make both ethanol and biodiesel. Another system, the E-100 MicroFueler, is designed only for ethanol.

Engines

In the United States, ethanol fuel has a "gasoline gallon equivalency" (GGE) value of about 1.5. This means that 1.5 times the volume of ethanol is needed to replace the energy of 1 gallon of gasoline. Even though ethanol is often cheaper than gasoline, when comparing prices using GGE, ethanol is usually not less expensive because its price is multiplied by 1.5. High ethanol mixtures are used in some racing engines because ethanol has a very high octane rating, which works well with engines that have high compression ratios.

Ethanol contains about 34% less energy per unit volume than gasoline. This means that using pure ethanol in a vehicle could reduce the distance it can travel by 34% compared to using pure gasoline, assuming the same fuel efficiency. However, ethanol’s high octane rating allows engines to be designed more efficiently by increasing their compression ratios.

For E10 (a fuel blend of 10% ethanol and 90% gasoline), the increase in fuel use in unmodified vehicles is small (up to 2.8%) compared to regular gasoline. The increase is even smaller (1–2%) when compared to oxygenated or reformulated gasoline blends. For E85 (a blend of 85% ethanol and 15% gasoline), the effect is much larger. E85 produces less fuel efficiency than gasoline and requires more frequent refueling. Actual performance depends on the vehicle. According to EPA tests in 2006, E85 vehicles had an average fuel economy that was 25.56% lower than vehicles using unleaded gasoline. Flex-fuel vehicles in the U.S. are designed to use E85, which has an octane rating of about 94–96. This rating is similar to premium gasoline, so E85 should be compared to premium gasoline when considering performance. Ethanol is not suitable for most aircraft, motorbikes, or small engines, though some aircraft, like the Embraer EMB 202 Ipanema, are designed to use ethanol in specific models.

High ethanol blends can cause problems during cold weather because ethanol increases the energy needed for fuel to evaporate. If the fuel’s vapor pressure drops below 45 kPa, it becomes hard to start a cold engine. To avoid this, the U.S. and Europe limit E85 use in flexible fuel vehicles to ensure proper performance in cold conditions. In very cold regions of the U.S., ethanol blends are reduced to E70 during winter, even though it is still labeled as E85. In areas where temperatures drop below –12 °C (10 °F), engine heaters are recommended for both gasoline and E85 vehicles. Sweden also reduces ethanol blends to E75 during winter months.

In Brazil, flex-fuel vehicles can use up to E100 (pure ethanol with up to 4% water). This blend reduces vapor pressure more quickly than E85, so Brazilian flex vehicles are built with a small gasoline reservoir near the engine. During cold starts, pure gasoline is injected to help start the engine. This feature is especially important in Brazil’s southern and central regions, where winter temperatures often drop below 15 °C (59 °F). In 2009, an improved flex engine design was introduced that eliminates the need for a separate gasoline reservoir. Volkswagen do Brasil launched the Polo E-Flex in 2009, the first Brazilian flex-fuel model without an auxiliary tank for cold starts.

In many countries, cars are required to use ethanol blends. All Brazilian light-duty vehicles are built to run on ethanol blends up to 25% (E25). Since 1993, Brazil has required ethanol blends between 22% and 25%, with 25% required by mid-2011. In the U.S., all light-duty vehicles are built to use E10 (10% ethanol). By the end of 2010, over 90% of gasoline sold in the U.S. was blended with ethanol. In 2011, the U.S. Environmental Protection Agency (EPA) allowed E15 (15% ethanol) to be sold for cars and light trucks made in 2001 or newer.

Since 1999, more vehicles worldwide have been built to run on any ethanol blend from 0% to 100% without modifications. Many cars and light trucks in North America and Europe are designed to use E85 (85% ethanol), while in Brazil, vehicles can use E100 (100% ethanol). Older vehicles used alcohol and oxygen sensors to adjust fuel injection for different ethanol blends. Newer vehicles rely on oxygen and airflow sensors to estimate ethanol content. Engine control computers can also adjust ignition timing to improve performance when higher ethanol percentages are detected. These adjustments are supported by knock sensors, which detect engine knocking and help prevent damage.

In June 2021, India raised its goal to blend 20% ethanol into fuel by 2025. At the time, ethanol blending was at 8%, with a target of 10% by 2022. The government plans for oil companies to sell 20% ethanol-blended fuel starting in 2023. States with surplus ethanol, like Maharashtra and Uttar Pradesh, will lead the effort. India also requires new vehicles to be compatible with 20% ethanol blends. Automakers must produce ethanol-compatible vehicles by 2022. Some environmental groups are concerned that higher ethanol use might encourage crops that use a lot of water, such as sugarcane and rice, and suggest focusing on crops like millets instead.

Since 1989, Sweden has used ethanol-based diesel engines in city buses, trucks, and waste collection vehicles. These engines, made by Scania, use a fuel called ED95, which is 93.6% ethanol, 3.6% ignition improver, and 2.8% denaturants. The ignition improver allows the fuel to ignite in diesel engines. These engines were also used in the UK but are now being phased out.

A 2004 study by MIT and an earlier paper by the Society of Automotive Engineers found a way to use ethanol more efficiently than traditional fuel blends.

Production by country

In 2011, the United States produced 13.9 billion U.S. gallons (5.3 billion liters; 1.16 billion imperial gallons) of ethanol fuel, and Brazil produced 5.6 billion U.S. gallons (2.1 billion liters; 4.7 billion imperial gallons). Together, these two countries made up 87.1% of the world's total ethanol production, which was 22.36 billion U.S. gallons (8.46 billion liters; 1.862 billion imperial gallons). Financial support and other industry efforts are helping new ethanol industries grow in countries like Germany, Spain, France, Sweden, China, Thailand, Canada, Colombia, India, Australia, and some Central American nations.

Since the 1970s, Brazil has operated an ethanol fuel program. This program has made Brazil the second-largest ethanol producer globally (after the United States) and the largest exporter of ethanol. Brazil’s program uses modern equipment and inexpensive sugarcane as a raw material. The leftover sugarcane waste, called bagasse, is used to create heat and electricity. In Brazil, no light vehicles now run on pure gasoline.

Environment

Biomass must go through several steps to make ethanol fuel: growing, collecting, drying, fermenting, distilling, and burning. These steps need resources and systems to support them. The energy balance, or how much energy is used compared to how much energy is produced from ethanol, is important. A 2007 report by National Geographic found that making corn ethanol in the U.S. uses about 1 unit of fossil-fuel energy to create 1.3 units of ethanol energy. In Brazil, making sugarcane ethanol uses 1 unit of fossil-fuel energy to create 8 units of ethanol energy. Energy balance estimates vary because different reports use different methods and assumptions. For example, one study found that sugarcane ethanol returns 8 to 9 units of energy for each unit used, while corn ethanol returns about 1.34 units. Ethanol production from corn uses less petroleum than gasoline production.

Carbon dioxide, a greenhouse gas, is released during fermentation and burning ethanol. Plants absorb carbon dioxide as they grow, which helps balance emissions. When made using certain methods, ethanol releases fewer greenhouse gases than gasoline.

Compared to regular gasoline, ethanol burns without creating tiny particles. It burns with oxygen to form carbon dioxide, carbon monoxide, water, and acetaldehyde. The Clean Air Act requires adding oxygen to gasoline to reduce carbon monoxide emissions. MTBE, a former additive, is being replaced because it pollutes groundwater, making ethanol a better alternative. Ethanol production may cause air pollution from fertilizers like ammonia.

E85 fuel, a type of ethanol, may increase air pollution deaths by 9% in Los Angeles, a large city with many cars. It raises ozone levels, increasing smog and worsening health issues like asthma.

In Brazil, where ethanol is widely used, studies found higher levels of formaldehyde and acetaldehyde in the air compared to Japan, where ethanol is not used. Calculating the exact amount of carbon dioxide from ethanol production is complex and depends on how ethanol is made. A calculation should include:

• The cost of growing the plant material.
• The cost of transporting the plant material to the factory.
• The cost of turning the plant material into ethanol.

Other factors that may or may not be considered include:

• Changes in land use where plants are grown.
• Transporting ethanol to where it is used.
• How efficiently ethanol works compared to gasoline.
• Carbon dioxide emissions from car tailpipes.
• Benefits from byproducts like animal feed or electricity.

A graph from the UK government shows data about renewable fuel requirements. Corn ethanol reduces greenhouse gas emissions by about 7.4%. A 2007 National Geographic article said corn ethanol reduces emissions by 22% compared to gasoline, and sugarcane ethanol reduces emissions by 56%. Ford reports a 70% reduction in emissions using bioethanol in one of their vehicles.

Producing ethanol requires tilling new soil, which releases greenhouse gases. It may take many years of reduced emissions to balance this initial release. For example, converting grasslands to corn fields for ethanol could take about 100 years of annual savings to offset the initial emissions.

Making ethanol requires large-scale farming. If all U.S. corn were used for ethanol, it could replace 12% of U.S. gasoline use. Some say ethanol production causes deforestation, but others note forests are often not suitable for farming. Farming may harm soil, reduce water quality, increase pesticide use, and affect communities. New technology helps farmers use fewer resources to produce the same output.

Cellulosic ethanol is a new method that may reduce land use issues. It uses all parts of plants, not just starch, and could double ethanol yields. This reduces the need for more land and resources. Using all plant materials, like gluten, lowers the carbon footprint because the same amount of fertilizers and chemicals can produce more ethanol. This technology is now being developed for commercial use.

Using biomass to make electricity for electric vehicles may be better for the climate than using biomass for ethanol, according to a 2009 study. Scientists continue to improve cellulosic ethanol and battery technology.

For each billion gallons of ethanol-equivalent fuel used in the U.S., the combined climate and health costs are $469 million for gasoline, $472–952 million for corn ethanol (depending on production methods), and $123–208 million for cellulosic ethanol (depending on the plant material used).

Efficiency of common crops

If ethanol production becomes more efficient or new materials are used, it might become more cost-effective in the United States. Scientists are studying ways to increase ethanol production from corn using scientific methods. When oil prices stay high, using other materials like cellulose to make ethanol becomes a practical option. Leftover materials like straw and wood chips can be turned into ethanol. Fast-growing plants like switchgrass can grow on land that isn't good for other crops and produce a lot of ethanol in a small area.

Reduced petroleum imports and costs

A reason for producing large amounts of ethanol in the U.S. is that it helps improve energy security by reducing the need for oil imported from other countries and replacing it with energy made in the U.S. Producing ethanol uses a lot of energy, but most of that energy comes from coal, natural gas, and other sources, not from oil. In 2006, the U.S. imported 66% of the oil it used, while it had more coal available than needed and imported only 16% of the natural gas it used. By using ethanol instead of oil-based fuels, the U.S. shifts energy use from foreign sources to domestic ones.

In 2008, U.S. ethanol production helped lower retail gasoline prices by between US$0.29 and US$0.40 per gallon compared to prices without ethanol production.

Applications and Projects

Ethanol fuel has become more important in motorsport events.

• In 1927, Leon Duray placed third in the Indianapolis 500 auto race using a car powered by ethanol fuel. In 2006, the IndyCar Series used a fuel mix with 10% ethanol. In 2007, the mix changed to include 98% ethanol.
• The American Le Mans Series used E10, a fuel with 10% ethanol, in 2007 instead of pure gasoline. In 2008, E85, a fuel with 85% ethanol, was allowed in the GT class, and teams started using it.
• In 2011, three national NASCAR stock car series required a switch from gasoline to E15, a mix of Sunoco GTX unleaded racing fuel and 15% ethanol.

Australia’s V8 Supercar championship uses Shell E85 as its racing fuel. The Stock Car Brasil Championship uses E100, which is pure ethanol. Ethanol fuel is also used in some rocket-powered aircraft. As of 2010, small amounts of ethanol were used in lightweight rocket-racing planes.

Project Gaia is a U.S. non-governmental, non-profit organization that helps create a market for alcohol-based fuels in Ethiopia and other developing countries. The project believes alcohol fuels can help solve fuel shortages, environmental damage, and health problems caused by traditional cooking methods. Gaia works in Ethiopia, Nigeria, Brazil, Haiti, and Madagascar. It is also planning projects in other countries.

BioEthanol for Sustainable Transport was a four-year project funded by the European Union. Nine regions in Europe, Brazil, and China participated in the project.

Research

Ethanol research looks into different materials, new catalysts, and better ways to make ethanol. The company Ineos made ethanol using plant material and waste from wood. Scientists changed the bacteria E. coli by adding genes and enzymes from cow stomachs, allowing it to create ethanol from corn stover, which is the leftover parts of corn plants after harvesting. Other materials that could be used include city waste, reused items, rice hulls, sugarcane bagasse, wood chips, switchgrass, and carbon dioxide.