Ethanol production

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Bioenergy > Technologies > Biochemical technologies > Ethanol production


Ethanol production is a Biochemical conversion technology used to produce energy from biomass.

Contents

Types of Ethanol Production

  • Ethanol from sugar
    • Ethanol production begins by grinding up the feedstock so it is more quickly and easily processed. Once ground up, the sugar is either dissolved out of the material, or the starch is converted into sugar. The sugar is then fed to yeast in a closed, anaerobic chamber. The yeast secretes enzymes that digest the sugar (C6H12O6), yielding several products, including lactic acid, hydrogen, carbon dioxide (CO2), and ethanol (C2H5OH).1
  • Ethanol from starch
    • Producing ethanol from starch feedstocks (such as corn, wheat, and cassava) requires an additional step. Starches must first be catalyzed into simple sugars. This process, called saccharification, requires more energy and increases the cost of production.1
  • Ethanol from Cellulose

There are two main types of ethanol production:

Dry-mill fermentation

  • "The “dry-milling” process involves simply grinding the unprocessed, heterogeneous seed into granules."1

Feedstocks for dry-mill fermentation

  • Sugars, Starches and other biomass

Examples: Grains (corn, sorghum, barley), sugars (sugarcane and beets), beer, and other sugars and starches.

    • Pretreatment: dry-mill fermentation
    • Qualifications: Grain processing

Products of dry-mill fermentation

Products of dry-mill fermentation include:

Advantages of Dry-mill fermentation

  • The dry-mill fermentation process is not as expensive as wet mill.

Wet-mill fermentation

  • "The “wet-milling” process soaks grains in water, usually with a sulfurous acid, to separate the starch-rich endosperm from the high-protein germ and high-fiber husks. These wet mills tend to be larger and produce a number of co-products in addition to ethanol."1

Feedstocks for Wet-mill fermentation

  • Mostly: Corn
    • Pretreatment: Wet-mill fermentation
    • Qualifications: Grain processing

Products of Wet-mill fermentation

Products of wet-mill fermentation include:

Advantages of Wet-mill fermentation

  • The wet-mill fermentation process is more versatile than dry mill fermentation, because of the products it yields.

Commercialization Status

  • The current fuel ethanol industry was launched in the US in 1979 with small on-farm plants and in educational institutions. They were very small and inefficient. On average, the efficiency of the plants has increased about 2% per year and the average size today is about 50 million gal/yr. The fossil energy in, to renewable energy out is now about 1 to 1.6 and steadily improving. With innovations being commercialized, that ratio will soon be well over 2:1. Within 2 years it should be 3:1 and within four years it should be possible to incorporate cellulosic feedstocks into standard corn to ethanol plants. In the US, it is now anticipated that a capacity of 15 billion gal/yr from corn, milo, sugar cane and other starch and sugar crops is possible without interfering with the food/feed supply. As long as the price of oil remains over $50/bbl and corn under $3/bushel, with today's incentives, the ethanol industry will continue to grow and prosper.

Sustainability and Environmental Concerns

  • There are critical factors in the advance of the ethanol industry using starch and sugar crops as feedstocks. The industry must ensure the environmental community and the public in general that, as the industry further matures, it will ensure the protection and enhancement of:
  • organic matter in the soils, soil organisms,
  • Water quality and quantity
  • Wildlife and their habitat,
  • Wetlands,
  • Watersheds,
  • Rural communities, through ownership in biorefineries and appropriately keeping the value-added benefits in the farm community.

Societal Impacts

References

1Biofuels for Transportation (draft) (2006, Worldwatch Institute), p.10-12. Used with permission.

Note

This page has been modified from information that was developed by the United States Environmental Protection Agency, Office of Research and Development, in cooperation with the Biomass Coordinating Council of the American Council on Renewable Energy (ACORE). Template:Ethanol production

Bioenergy conversion technologies edit
Technologies categorized by bioenergy processes:

Biochemical: Aerobic, Anaerobic, Landfill gas collection (LFG), Biodiesel production, Ethanol production
Physiochemical:
Thermochemical: Combustion, Gasification, Pyrolysis, Depolymerization
Biorefineries


Technologies categorized by feedstock:
Algae | Cellulosic technology


Technologies by commercialization status:


Analysis of technologies: Life-cycle analysis


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