corn cob with gas pump illustration

Ethanol and other Bioalchohols

There are four basic bioalcohols (butanol, ethanol, methanol and propanol) that are transformed biologically, meaning the alcohol was generated by plants and living things versus a non-biological source such as petroleum. All these alcohols have energy density described in terms of octane. Regardless of which one is used, alcohol combined with gasoline results in a fuel called gasohol. There are advantages and disadvantages for using each as an alternative fuel source.

Methanol and Ethanol

Both of these alcohols can be derived from fossil fuels and biomass. Ethanol is produced via fermentation and methanol from synthesis gas. They both have a higher octane rating compared to gasoline and are already being used in many countries. Unfortunately, due to their chemical properties they cannot be transported in existing gas pipelines. Both are very corrosive because Halide ions chemically cause corrosivion to fuel systems, rubber hoses and gaskets, aluminum, and combustion chambers. Therefore, it is illegal to use fuels containing alcohol in aircraft (although at least one model of ethanol-powered aircraft has been developed, the Embraer EMB 202 Ipanema). Ethanol also corrodes figerglass fuel tanks such as used in marine engines. For higher ethanol percentage blends, and 100% ethanol vehicles, engine modifications are required.

Another disadvantage is that gallon-for-gallon Ethanol generates less BTU energy than gasoline meaning it takes more fuel (volume and mass) to produce the same amount of work. An advantage of ethanol is that is has a higher octane rating than ethanol-free gasoline available at roadside gas stations and ethanol's higher octane rating allows an increase of an engine's compression ratio for increased thermal efficiency.

Ethanol fuel is the most common biofuel worldwide, particularly in Brazil. Alcohol fuels are produced by fermentation of sugars derived from wheat, corn, sugar beets, sugar cane, molasses and any sugar or starch that alcoholic beverages can be made from (like potato and fruit waste, etc.). The ethanol production methods used are enzyme digestion (to release sugars from stored starches, fermentation of the sugars, distillation and drying. The distillation process requires significant energy input for heat.

Ethanol can be used in petrol engines as a replacement for gasoline; it can be mixed with gasoline to any percentage. Most existing automobile petrol engines can run on blends of up to 15% bioethanol with petroleum/gasoline. Gasoline with ethanol added has higher octane, which means that your engine can typically burn hotter and more efficiently. In high altitude (thin air) locations, some states mandate a mix of gasoline and ethanol as a winter oxidizer to reduce atmospheric pollution emissions.

Blends of gasoline and alcohol are often identified by abbreviations that combine the letter E with a number indicating the percentage of ethanol in the blend. For example, E10 contains 10 percent ethanol, E5 contains 5 percent ethanol, and E7 contains 7 percent ethanol.

Propanol and Butanol

Propanol and butanol are considerably less toxic and less volatile than methanol. Butanol has a high flashpoint of 35 °C, which is a great fire safety benefit but could be problematic when starting an engine on a cold morning.

Butanol is formed by ABE fermentation (acetone, butanol, ethanol) and experimental modifications of the process show potentially high net energy gains with butanol as the only liquid product. Butanol will produce more energy and allegedly can be burned "straight" in existing gasoline engines (without modification to the engine or car), and is less corrosive and less water soluble than ethanol, and could be distributed via existing infrastructures.

Propanol and butanol are made from cellulose in a tricky fermentation process. This process results in an extremely unpleasant smell and will be factor in where a fermentation plant would be located. The big advantage of propanol and butanol as an alternative fuel source is that hey can be transferred via existing gas lines, and they have a better gallon-for-gallon energy efficiency when compared to gasoline.

How Ethanol is Made

Ethanol can be made from many kinds of organic materials, including corn, wheat, grass, sugarcane, seaweed of cellulose left over from making paper, and nearly any other source of carbon. It can also be made from leftover petroleum feedstocks.

To make ethanol, a producer grinds up the feedstock, such as corn, exposing the starch in the plant material. The ground-up feedstock is mixed with water and enzymes and heated to convert the starch to sugar. Adding yeast to the mix helps the sugars ferment into ethanol. The alcohol is then removed through distillation, boiling the mixture so that the alcohol evaporates then catching the alcohol in a container as cools it back into a liquid state.

Sugarcane is an escellent source of ethanol because it naturally contains the sugars that ferment into alcohol. Research is underway to produce ethanol from cheaper biomass materials, such as wood or straw. It is harder to make ethanol from these substances because they do not release their sugars as easily as corn or sugarcane.

Current uses of ethanol and other bioalcohol fuels

Ethanol and other alcohols can be used to power motor vehicles instead of gasoline. In almost all cases the ethanol is mixed with gasoline. Gasoline-powered vehicles have no difficulty using gasoline that contains small amounts of ethanol. Generally this mix must contain at least 10 percent ethanol to qualify as gasohol. Gasohol is widely available in Denmark, Brazil, and the American Midwest. The state of Minnesota requires all gasoline sold there to contain at least 10 percent ethanol.

Many car manufacturers are now producing flexible-fuel vehicles (FFV's), which can safely run on any combination of bioethanol and gasoline, up to 100% bioethanol. They dynamically sense exhaust oxygen content, and adjust the engine's computer systems, spark, and fuel injection accordingly. FFV internal combustion engines are becoming increasingly complex, as are multiple-propulsion-system FFV hybrid vehicles, which impacts cost, maintenance, reliability, and useful lifetime longevity.

Increasing numbers of light trucks are sold as flexible fuel vehicles, capable of burning a variety of fuels, including mixes of gasoline and ethanol and other alternative fuels such as P-Series fuels. Vehicles that can run on pure ethanol are rare and require special engineering to function, which is why fuels for FFVs usually contain at least some gasoline. One common ethanol blend is called E85, which contains 15 percent gasoline and 85 percent ethanol. Producers add this small amount of gasoline to the ethanol to make the vehicle start better in cold weather. E85 is generally priced at about the same level as gasoline.

Ethanol and methanol can both be used as fuels in fuel cells, though ethanol is a less efficient source than methanol. Fuel cells would use the energy stored and released by hydrogen.
Ethanol also has many other uses. It has a low melting point, so it can be added to liquids as an antifreeze. In addition, it can be added to gasoline as an anti-knocking agent. It can also be a safe replacement for MBTE, a fuel additive that has been found to present environmental problems.