Regulation of Fuels and Fuel Additives: Renewable Fuel Standard ...

Plant Feedstock
Corn a
Table VI.A.1-1
2006 U.S. Ethanol Production by Feedstock
Capacity
MMGal/yr
% of
Capacity
No. of
Plants
% of
Plants
4,516 92.7% 85 83.3%
Corn/Milo 162 3.3% 5 4.9%
Corn/Wheat 90 1.8% 2 2.0%
Corn/Barley 40 0.8% 1 1.0%
Milo/Wheat 40 0.8% 1 1.0%
Waste Beverage b
16 0.3% 5 4.9%
Cheese Whey 8 0.2% 2 2.0%
Sugars & Starches 2 0.0% 1 1.0%
Total 4,872 100.0% 102 100.0%
a Includes seed corn
b Includes brewery waste
There are a total of 94 plants processing corn and/or other similarly processed
grains. Of these facilities, 84 utilize dry milling technologies and the remaining 10 plants
rely on wet-milling processes. Dry mill ethanol plants grind the entire kernel and
produce only one primary co-product: distillers’ grains with solubles (DGS). The coproduct
is sold wet (WDGS) or dried (DDGS) to the agricultural market as animal feed.
Carbon dioxide is also produced in the process and may be recovered as a saleable
product. In contrast to dry mill plants, wet mill facilities separate the kernel prior to
processing and in turn produce other co-products (usually gluten feed, gluten meal, and
oil) in addition to DGS. Wet mill plants are generally more costly to build but are larger
in size on average. As such, approximately 23 percent of the current ethanol production
comes from the 10 previously-mentioned wet mill facilities.
The remaining 8 plants which process waste beverages, cheese whey, or
sugars/starches, operate differently than their grain-based counterparts. These facilities
do not require milling and instead operate a more simplistic enzymatic fermentation
process.
In addition to grain and starch-to-ethanol production, another method exists for
producing ethanol from a more diverse feedstock base. This process involves converting
cellulosic feedstocks such as bagasse, wood, straw, switchgrass, and other biomass into
ethanol. Cellulose consists of tightly-linked polymers of starch, and production of
ethanol from it requires additional steps to convert these polymers into fermentable
sugars. Scientists are actively pursuing acid and enzyme hydrolysis to achieve this goal,
but the technologies are still not fully developed for large-scale commercial production.
As of June 2006, there were no U.S ethanol plants processing cellulosic feedstocks.
Currently, the only known cellulose-to-ethanol plant in North America is Iogen in
Canada, which produces approximately one million gallons of ethanol per year from
wood chips. For more a more detailed discussion on cellulosic ethanol
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