All About Ethanol: A Renewable Fuel Source

Ethanol is a clear, colorless liquid that has become an increasingly important renewable fuel source. Also known as ethyl alcohol drinking alcohol or grain alcohol, ethanol is made from the fermentation of sugars derived from plants such as corn, sugar cane, and switchgrass. When blended with gasoline, ethanol decreases harmful vehicle emissions and reduces dependence on fossil fuels. In this comprehensive guide, we’ll explore how ethanol is made, how it’s used, and the pros and cons of this alternative fuel.

How Ethanol is Made

There are a few different methods used to produce ethanol but the most common process involves fermenting sugar derived from plant materials. Here is a step-by-step overview

• Feedstock selection: Corn is the primary feedstock used to make ethanol in the United States due to its high starch content. Other crops include sugar cane, sugar beets, wheat, sorghum, barley, and potatoes. Cellulosic sources like switchgrass and agricultural residues can also be used.

• Pretreatment: The feedstock undergoes milling, chopping, or grinding to make the sugars more accessible. Heat, chemicals, or enzymes may be applied to break down the biomass further.

• Saccharification: The pretreated feedstock is mixed with water and enzymes to convert starches and cellulose into fermentable sugars like glucose. Acids can also be added to catalyze the reaction.

• Fermentation Yeast is added to metabolize the sugars converting them into ethanol and carbon dioxide. The mash is kept warm and agitated to optimize conditions for fermentation. Common yeasts include Saccharomyces cerevisiae and Zymomonas mobilis.

• Distillation: The fermented mash is distilled to separate the ethanol from the solids and remaining water. This concentrates the ethanol to around 95% purity.

• Dehydration: To obtain 100% pure ethanol, the water must be completely removed. This is achieved by adding agents like triethylene glycol or molecular sieves which absorb any remaining water molecules.

• Denaturing: To make the ethanol undrinkable, it is denatured by adding a small amount of a foul-tasting chemical like gasoline. This is done for fuel applications.

How Ethanol is Used as a Fuel

The largest use of ethanol is as a renewable transportation fuel additive to reduce greenhouse gas emissions and cut dependence on fossil fuels. Here are some key uses:

• E10: A low level blend of 10% ethanol mixed with 90% gasoline that can be used in any gasoline vehicle. This accounts for 98% of gasoline sold in the U.S.

• E15: A blend with 15% ethanol and 85% gasoline approved for use in most vehicles model year 2001 and newer.

• E85: A high level blend with 85% ethanol and 15% gasoline specifically intended for “flex-fuel” vehicles. Requires engine modifications to handle higher ethanol concentrations.

• ED95: A blend with a minimum 95% ethanol used in specially designed heavy-duty vehicles and buses. Requires significant engine conversion.

• E100: 100% ethanol can power vehicles specifically engineered to run on this renewable fuel. Brazil has the largest E100 fleet.

Adding ethanol boosts the octane rating of gasoline and improves engine performance. However, the high water affinity of ethanol can lead to corrosion issues in some older gas tanks, fuel lines, and engines.

Benefits of Ethanol as a Fuel

Using ethanol blended fuels offers many benefits:

• Reduces dependence on finite fossil fuel resources like coal, oil, and natural gas

• Made from renewable, plant-based feedstocks that recycle atmospheric CO2

• Burning ethanol emits less greenhouse gas compared to pure gasoline

• Produced domestically, boosting local economies and energy independence

• High octane rating improves engine efficiency and performance

• Oxygenating effect reduces harmful tailpipe emissions

• Biodegrades quickly and is less toxic than gasoline spills

• Feed production supports agricultural prices and provides animal feed byproducts

• Suitable for existing distribution networks and gasoline vehicle engines

Drawbacks and Challenges

However, ethanol use also presents some drawbacks and challenges:

• Ethanol has 33% less energy per gallon compared to gasoline, reducing fuel economy.

• High water affinity can corrode fuel systems not designed for ethanol.

• More land and fertilizer is needed to grow crops for ethanol production. This raised food prices in the past.

• Net greenhouse gas reductions are modest once factors like land use changes are considered.

• Limited ethanol production capacity constrains further growth in use.

• Distribution, storage, and blending infrastructure needs expansion to handle increasing volumes.

Developing Advanced Biofuels

To overcome technical barriers, extensive research aims to develop “drop-in” biofuels that can directly substitute gasoline without modifications. Advanced biofuels on the horizon include:

• Cellulosic ethanol: Made from non-food plant parts like grasses, stalks, and wood chips through processes that unlock sugars in cellulose and hemicellulose. Could utilize waste biomass.

• Biobutanol: Has an energy content closer to gasoline and mixes more easily at higher percentages. Can be made from corn and cellulosic biomass.

• Biodiesel: Produced by converting oils like soybean oil into fatty acid methyl esters (FAME) through transesterification. Used in diesel engines.

• Renewable diesel: Chemically similar to petroleum diesel but made by hydrotreating fats and oils in a refinery. A “drop-in” replacement.

• Biogas: Methane produced from the anaerobic digestion of organic matter. Can be compressed as renewable natural gas (RNG).

The Future of Ethanol

Ethanol will continue playing an important role in reducing transportation emissions as use of renewable fuels grows. Wider adoption depends on improved efficiency, lower costs, and integration with advanced biofuels. With ongoing innovations in production technology and feedstocks, ethanol offers a valuable tool for transitioning towards a clean, sustainable energy future.