Current methods of ethanol production

Basic process

The major producers of ethanol are the United States and Brazil, followed by China. According to statistics by the Renewable Fuels Association, the United States produced nearly 5 billion gallons of ethanol in the year 2006 with Brazil following with nearly 4.5 billion. The majority of the ethanol production used fermentation of sugars. The plant source in the United States is predominately corn, while Brazil relies sugar cane. Sugarcane production is more efficient than corn production due to the higher levels of fermentable sugars in sugar cane: less energy is needed to convert starches to sugars (Pimentel).

Dry Milling Method (most common)

  1. Milling
    Corn is ground into a powder called meal.

  2. Conversion of starch to sugar
    Water is added to the meal and enzymes that convert starches into sugar are added. High temperatures (around boiling) cook this mixture to reduce bacteria levels.

  3. Fermentation
    Yeast is added to the mixture and over two days, the yeast convert sugars to alcohol, producing carbon dioxide as a waste product in the process. The resulting 10% concentration ethanol-containing mixture is called beer.

  4. Distillation
    Ethanol and water's boiling points differ and distillation, the boiling of the ethanol and water to purify ethanol takes advantage of this.

    • Stillage
      The solids from fermantation is called stillage and can be used as a feedstock for cattle.

  5. Final purification
    The ethanol psses through a molecular sieve and a poisonous denaturant is added to the alcohol to prevent human consumption.

Sources

"Biofuels in the US Transportation Sector". Energy Information Administration. Feb. 2007. 4 Jan. 2008 http://www.eia.doe.gov/oiaf/analysispaper/biomass.html.

"Ethanol Production". Western Plains Energy. 17 Dec. 2005. 5 Jan. 2008 http://www.westernplainsenergy.biz/ethanol.html.

"How Ethanol is Made". Renewable Fuels Association. 2006. 5 Jan. 2008 http://www.ethanolrfa.org/resource/made/.

"Industry Statistics". Renewable Fuels Association. 2006. 6 Jan. 2008 http://www.ethanolrfa.org/industry/statistics/.

Pimentel, David, and Tad W. Patzek. "Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower". Natural Resources Research 14.1 (2005): 65-76.