Ethanol Fuel Production

Brian Luk
October 24, 2010

Submitted as coursework for Physics 240, Stanford University, Fall 2010


Ethanol fuel has been lauded as a viable alternative to petroleum-based fuels, offering not only less pollution to the environment, but also a sustainable source of energy. Interestingly enough, ethanol fuel is made from exactly the same liquid courage that college students use to wash away their sorrows every weekend. Ethanol fuel is an alternative to gasoline, and is manufactured from the conversion of carbon-based feed stocks such as sugarcane, sugar beets, switchgrass, corn, and barley. Ethanol is currently used in gasoline for vehicles. Most vehicles run on mixtures of gas and ethanol; this mixture is common at most gas stations across the country.

Advocates posit that ethanol fuel has the potential to bring us to a point where the United States becomes independent of imported oil from other countries. On the other hand, opponents say that ethanol fuel cannot possibly be fully viable as a replacement to petroleum-based fuels, though it will be able to slightly ameliorate our dependence on other countries for oil. To make an adequate hypothesis concerning the feasibility of ethanol fuel as a replacement for oil as an energy source, it is necessary to investigate the process of ethanol fuel production, and compare the process for different countries. This report, specifically, will compare ethanol fuel production in the United States and Brazil.

Some Background

The process of ethanol fuel production involves fermentation, distillation, and dehydration. The general process is shown below. The process begins with photosynthesis, during which plants make sugar which is broken down into ethanol.

Adding these three reactions and balancing, the net reaction simply becomes light → heat. In the first step, ethanol is produced by microbial fermentation of sugars (i.e. starch and cellulose). Currently, only the sugar and starch portions can be economically converted into ethanol. In the next step, distillation, the water is removed from the ethanol. The purity is limited to approximately 95% at this step due to the formation of a low-boiling water-ethanol azeotrope. This azeotrope can be used as fuel on its own, but it is immiscible in gasoline; further distillation is therefore necessary in order for the mixture to burn with gasoline in gasoline engines. This further distillation occurs during the dehydration process, when extra water is removed from the solution.

Ethanol Fuel in the United States

The US is currently the world's leader in ethanol production and consumption. Mixtures of ethanol and gasoline are used by most vehicles on the road in the United States today, which can be seen by anyone interested enough to read the signs at gas stations across the country. In 2009, an estimated 8.4 million cars capable of running on 85% ethanol-gas mixtures were on the road, and three states (Missouri, Hawaii, and Minnesota) require ethanol to be blended with gasoline for motor fuels. [1] Despite the growing widespread use of ethanol fuels, the topic is surrounded by controversy within the United States. Firstly, producing ethanol from corn (which is the method used in the US) is approximately 5 to 6 times less efficient than producing it from sugarcane. As a result, ethanol production from corn, or maize, depends on subsidies. [3] These subsidies to pay fuel blenders and ethanol refineries, along with the consumption of a food crop to produce the fuel as well as the use of vast expanses of land for maize production, have been cited as reasons for the rising cost of corn. [2] Sugarcane is not used in the US because it does not grow as efficiently in the less tropical conditions of the US. Sugar beets have been suggested as an alternative, as they produce approximately the same amount of ethanol as corn without requiring as high overheads. Corn produces only about 330-424 gallons/acre of ethanol and has a greenhouse gas savings of only 10-20% over petroleum-based gasoline. [3] In a 2004 report by the International Energy Agency, researchers estimated that only approximately 1.34 units of fuel energy were returned for each unit of energy expended. [4] This low "energy balance" is due to the energy expenses in the distillation process used in the United States, as well as the low ethanol production from corn.

Ethanol Fuel in Brazil

Brazil has one of the most, if not the most, successful biofuel programs in the world, utilizing ethanol produced from sugarcane. Combined, Brazil and the US account for 89% of global production of ethanol fuel; in 2007 Brazil produced 4.2 billion gallons of ethanol fuel. [5] Though the ethanol industry is not subsidized by the Brazilian government, the production and use of ethanol as fuel remains strong and is stimulated by low-interest loans for the construction of ethanol distillation facilities, guaranteed purchase of ethanol by the state-owned oil company at a reasonable price, price regulation to ensure competitive pricing of pure ethanol against ethanol-gas blends, and tax incentives. Though guaranteed purchase and price regulation are no longer in effect, the ethanol fuel industry continues to be a success with high efficiency in converting sugars to fuel. Sugarcane in Brazil has an annual yield of 727-870 gallons/acre and has 87-96% greenhouse gas savings over petroleum based fuels. [3] In comparison to the ethanol derived from corn in the United States, sugarcane has a much better energy balance, producing 8-9 units of energy for every unit of energy spent to process it. [4]

Comparing the US and Brazil

With sugarcane as one of the most efficient photosynthesizers in the plant kingdom, Brazil's sugarcane-based ethanol production is far more efficient than the US's corn-based production. Brazilian distillers are able to produce ethanol for 22 cents/liter, compared to the United States' 30 cents/liter. [6] The process to obtain ethanol from corn costs more because corn starch must first be converted into sugar before being distilled into alcohol; sugarcane already contains the sugar in the form necessary to produce ethanol. The table below summarizes differences in the main characteristics of ethanol fuel production between the United States and Brazil.

Characteristic US Brazil
feedstock corn sugarcane
total ethanol fuel production (2009) (million gallons) [5] 10,750 4,200
total area used for ethanol crop (million acres) [7] 24.71 8.90
productivity (gallons per acre) [3] 330-424 727-870
energy balance (energy obtained / energy expended) [4] 1.3-1.6 8.3-10.2
greenhouse gas emission reduction [4] 10-30% 86-90%
cost of production (USD/gallon) [5] 1.14 .83 (no import tax)
Table 1: Comparison of American and Brazilian Ethanol Industries

Closing Remarks

Though the illusion exists that ethanol is the fuel of the future and will be able to meet - and even exceed - the increasing energy demands, the truth is that the American ethanol fuel industry is far from doing so. Made from corn, ethanol in the United States is simply too expensive to produce - even more so than gasoline, which is why there is a need for tax write-offs to encourage ethanol fuel production. With the energy from fossil fuels needed to run farm machinery, fertilize, harvest, and transport corn to ethanol plants and distill the corn into alcohol, it takes almost as much energy to produce ethanol as it provides. The energy gained is only 1.3 times more than the energy put in to produce the ethanol. Put simply, ethanol fuel will not have a future in the United States unless another, more efficient, feedstock is used; more efficient distillation processes can also cut down on production costs, thus making ethanol fuel a much more viable alternative fuel source. At the moment, the United States does not have any shortage of oil; according to the US Minerals Management Service, the coastal waters off the lower 48 states has an estimated 59 billion barrels of oil still to be tapped, thus rendering ethanol production unnecessary at present times. While it is an admirable goal to replace petroleum-based fuels with ethanol fuel, it is not likely that such a goal will be realized in the near future. It would be better to focus on developing techniques to produce ethanol efficiently from cellulose plants or agricultural waste.

© 2010 Brian Luk. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[2] "E85 FFVs in Use in the U.S., Alternative Fuels and Advanced Vehicles Data Center, National Renewable Energy Laboratory, US Department of Energy, 24 May 10.

[2] J. K. Bourne, "Green Dreams," National Geographic, October 2007.

[3] K. Sanderson, "US Biofuels: A Field in Ferment," Nature 444, 673 (2006).

[4] "Biofuels for Transport: an International Perspective," International Energy Agency, April 2004.

[5] J Goldemberg, "Ethanol for a Sustainable Energy Future," Science 315, 808 (2007).

[6] "Fuel for Friendship," The Economist, 1 Mar 07.

[7] J. Goettemoeller and A. Goettemoeller, Sustainable Ethanol: Biofuels, Biorefineries, Cellulosic Biomass, Flex-Fuel Vehicles, and Sustainable Farming for Energy Independence, (Prairie Oak Publishing, 2007), p. 42.