Ethanol is a biodegradable, high-octane motor fuel derived from the sugars, starches, and cellulosic matter found in plants. This kind of biofuel has been used as a fuel or additive since the days of Henry Ford’s Model T. Virtually every gallon of gasoline consumed in the United States today contains fuel ethanol.
Ethanol is part of our nation’s solution to reducing our dependency on fossil fuels, lowering fuel prices, creating domestic jobs, boosting the farm economy, and cleaning our environment.
Ethanol is also known as a renewable fuel made from various plant materials collectively known as “biomass.” With more than 95% of U.S. gasoline contains ethanol, typically E10 (10% ethanol, 90% gasoline), to oxygenate the fuel and reduce air pollution. It’s available as E85, or high-level ethanol blends. Ethanol fuel can be used in flexible fuel vehicles, which can run on high-level ethanol blends, gasoline, or any blend of these.
Ethanol (CH3CH2OH) is a clear, colorless liquid. It is also known as ethyl alcohol, grain alcohol, and EtOH. It has the same chemical formula regardless of whether it is produced from starch- and sugar-based feedstocks, such as corn grain (as it primarily is in the United States), sugar cane (as it primarily is in Brazil), or from cellulosic feedstocks (such as wood chips or crop residues).
Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements prevent engine knocking and ensure drivability. Low-octane gasoline is blended with 10% ethanol to attain the standard 87 octane requirement. It is the main component in high-level ethanol blends.
Ethanol contains less energy per gallon than gasoline, to varying degrees, depending on the volume percentage of ethanol in the high-level blend. Per gallon, ethanol contains about 30% less energy than gasoline. E85 contains about 25% less energy than gasoline.
Ethanol Energy Balance
In the United States, ethanol is primarily produced from the starch in corn grain. Recent studies using updated data about corn production methods demonstrate a positive energy balance for corn ethanol, meaning that fuel production does not require more energy than the amount of energy contained in the fuel.
Cellulosic ethanol, which is produced from cellulosic feedstocks, is expected to improve the energy balance of ethanol, because cellulosic feedstocks are anticipated to require less fossil fuel energy to produce ethanol. Biomass used to power the process of converting non-food-based feedstocks into cellulosic ethanol is also expected to reduce the amount of fossil fuel energy used in production. Another potential benefit of cellulosic ethanol is that it results in lower levels of life cycle greenhouse gas emissions.
There are two primary ethanol production processes: wet milling and dry milling. Roughly 90% of the industry today uses the dry mill process, while the remaining 10% are wet mills.
In dry milling
The entire corn kernel is first ground into “meal.” The meal is slurried with water to form a “mash.” Enzymes are added to the mash to convert the starch to sugar. The mash is cooked, then cooled and transferred to fermenters. Yeast is added and the conversion of sugar to ethanol begins. After fermentation, the resulting “beer” is separated from the remaining “stillage”. The ethanol is then distilled and dehydrated. The ethanol is then blended with about 2% denaturant (such as gasoline) to render it undrinkable and exempt from beverage alcohol tax. It is then ready for shipment. The stillage is sent through a centrifuge that separates the solids from the solubles. These co-products eventually become distillers grains (a nutritious livestock feed), as well as corn distillers oil (a feed ingredient and feedstock for biodiesel production).
In wet milling
The grain is first separated into its component parts through soaking. After steeping, the slurry is processed through grinders to separate the corn germ. The remaining fiber, gluten and starch components are further segregated. The gluten component (protein) is filtered and dried to produce animal feed. The remaining starch can then be fermented into ethanol, using a process very similar to the dry mill process.
What is E10?
- 10% ethanol blend
- Today all vehicles run on E10
- E10 is interchangeable with gasoline
- Nearly all gas today includes 10%
What is E15?
The U.S. Environmental Protection Agency (EPA) defines E15 as gasoline blended with 10.5%-15% ethanol. In 2011, EPA approved E15 for use in conventional vehicles of model year 2001 and newer, through a Clean Air Act waiver request, based on significant testing and research by the Department of Energy’s Vehicle Technologies Office. Stations are not required to sell E15. E10 remains the limit for passenger vehicles older than the 2001 model year, and for other engines and vehicles that use gasoline, such as lawn mowers, motorcycles, and boats.
Vehicles approved for E15 use:
- Flexible fuel vehicles
- Conventional vehicles of model year 2001 and newer
Vehicles prohibited from using E15 (Read more Why Should Use E15?):
- All motorcycles
- All vehicles with heavy-duty engines, such as school buses and delivery trucks
- All off-road vehicles, such as boats and snowmobiles
- All engines in off-road equipment, such as chain saws and gasoline lawn mowers
- All conventional vehicles older than model year 2001
There are several EPA requirements and regulations that fueling stations must adhere to when selling E15. The most significant requirements are implementation of a misfueling mitigation plan (MMP). The misspelling is a concern for conventional vehicles older than 2001, and an MMP reduces the risk of misfueling.
The E15 is not yet widely available. It is sold in a few Midwestern states by stations that already offer E85.
What is E85?
E85 is a term that refers to high-level ethanol-gasoline blends containing 51%-83% ethanol, depending on geography and season. E85 can be used in flexible fuel vehicles (FFVs), which are commonly available from domestic and foreign automakers. Use the Vehicle Cost Calculator to look up FFV fuel economy, fuel costs, and greenhouse gas reductions.
Other than lower gas mileage, motorists driving FFVs will see little difference when using E85 versus gasoline. Depending on the actual ethanol content, it has less energy per gallon than gasoline to varying degrees (mileage penalty lessens as the ethanol content decreases).