If ethanol production in Brazil exemplified the extrapolation of a mature technol­ogy for sugar-based fermentation and subsequent distillation, the development of the second major ethanol fuel market — from corn in the United States — adopted a different approach to alcohol production, adapting and developing that employing starchy seeds in the production of malt and grain spirits (bourbon, rye, whiskey, whisky, etc.). The biological difference from sugar-based ethanol fermentations lies in the carbon substrate, that is, starch glucan polymers (figure 1.13). Historically, seeds and grains have been partially germinated by brewers to generate the enzymes capable of depolymerizing “storage” polysaccharides. With whisky, for example, barley (Hordeum vulgare L.) seeds are germinated and specialized cells in the seed produce hydrolytic enzymes for the degradation of polysaccharides, cell walls, and proteins; the “malted” barley can be used as a source of enzyme activities to break down the components of starch in cooked cereals (e. g., maize [Zea mays L.]) sol­ubilized in sequential hot-water extractions (which are combined before the yeast cells are added) but not sterilized so as to maintain the enzyme activities into the fermentation stage.3435 Starch is usually a mixture of linear (amylose) and branched (amylopectin) polyglucans. For starch hydrolysis, the key enzyme is a-amylase, active on a-1,4 but not a-1,6 linkages (in amylopectin); consequently, amylose is bro­ken down to maltose and maltotriose and (on prolonged incubation) to free glucose and maltose, but amylopectin is only reduced to a mixture of maltose, glucose, and

oligosaccharides containing a-1,6-linked glucose residues, thus limiting the amount of fermentable sugars liberated (figure 1.14). Cereal-based ethanol production plants use the same biochemical operations but replace malted grains with a-amylase and other polysaccharide-degrading enzymes added as purified products.

For much of the twentieth century, ethanol production as a feedstock in the formation of a large number of chemical intermediates and products was dominated in the United States by synthetic routes from ethylene as a product of the petrochemical industry, reaching 8.8 x 105 tonnes/year in 1970.36 The oil price shocks of the early 1970s certainly focused attention on ethanol as an “extender” to gasoline, but a mix of legislation and economic initiatives starting in the 1970s was required to engender a large-scale bioprocessing industry; in particular, three federal environmental regulations were important:3738 [6]

Although ethanol was always a good oxygenate candidate for gasoline, the compound first approved by the Environmental Protection Agency was methyl tertiary butyl ether (MTBE), a petrochemical industry product. Use of MTBE increased until 1999, but reports then appeared of environmental pollution incidents caused by MTBE spillage; state bans on MTBE came into force during 2002,39 and its consumption began to decline (figure 1.15). In the Midwest, ethanol was by then established as a corn-derived, value-added product; when the tide turned against MTBE use, ethanol production increased rapidly after showing little sustained growth for most of the 1990s (figure 1.16). California, New York, and Connecticut switched from MTBE to ethanol in 2004; after 2006, with many refiners discon­tinuing MTBE use, U. S. ethanol demand was expected to expand considerably.40 In the seven years after January 1999, the number of ethanol refineries in the United States nearly doubled, and production capacity increased by 2.5-fold (figure 1.17). In 2005, the United States became the largest ethanol producer nation; Brazil and the United States accounted for 70% of global production, and apart from China, India,

FIGURE 1.15 MTBE consumption in the United States. (Data from the U. S. Department of Energy, Energy Information Administration.)

FIGURE 1.16 Ethanol production in the United States. (Data from the Renewable Fuels Association, including a projected figure for 2007.)

France, and Russia, no other nation accounted for more than 1% of the total etha­nol produced. To further underline the perceived contribution of renewable fuels to national energy use, the 2005 Energy Policy Act created a Renewable Fuels Standard that envisioned renewable fuel use increasing from 4 billion gallons/year in 2006 to

7.5 billion gallons/year in 2012. This implies a further expansion of ethanol produc­tion because of the dominant position of E85 (85% ethanol, 15% gasoline) vehicles in the AFV and hybrid-fuel marketplace (figure 1.18).

Fuel ethanol production in the United States has been almost exclusively from corn, although sorghum (Sorghum bicolor L.), barley, wheat, cheese whey, and brewery waste have made small contributions. A detailed study of sugar sources for ethanol production concluded that only sugarcane molasses offered competitive feedstock and processing costs to established corn-based technologies (figure 1.19), although annual capital cost investments could be comparable for corn, sugarcane, and sugarbeet molasses and juice as rival feedstocks.41 Corn ethanol production developed from wet milling of corn; data compiled in the mid-1990s indicates that more than 70% of the large ethanol facilities then used wet milling.38 Wet milling, schematized in figure 1.20, produces four important liquid or solid by-products:

• Corn steep liquor (a lactic acid bacterial fermentation product, starting from ca. 5% of the total dry weight of the grain extracted with warm water, with uses in the fermentation industry as a nitrogen source)42

• Corn oil (with industrial and domestic markets)

• Corn gluten feed (a low-value animal feed)

• Corn gluten meal (a higher-value, high-protein animal feed)

Together with the possibility of collecting CO2 from the fermentation step as a saleable commodity, this multiplicity of products gave wet milling flexibility in times of variable input and output prices, although requiring a higher initial capital invest — ment.38 Other sources of flexibility and variation in the wet milling procedure arise at the starch processing stage; while a-amylase is used to liquefy the starch, saccharifi­cation (using glucoamylase) can be differently controlled, at one extreme producing

— Electric

Hydrogen

Liquefied natural gas Liquefied petroleum gas Diesel-electric hybrid

FIGURE 1.18 Alternative — and hybrid-fuel vehicles. (Data from U. S. Department of Energy, Energy Information Administration.)

a high-glucose, low-solids substrate for fermentation and at the other producing a low glucose concentration but which is continually replenished during the fermentation by the ongoing activity of the glucoamylase in the broth.

In contrast to wet milling, dry milling produces only CO2 and distillers dried grains with solubles (DDGS) as by-products but has become the favored approach for corn ethanol production because of lower start-up costs.43 Dry milling should conserve more of the nutrients for yeast growth in the fermentation step — in particular, nitrogenous inputs (free amino acids, peptides, and protein), inorganic

FIGURE 1.20 Outline of corn wet milling and ethanol production.

and organic phosphates, and some other inorganic ions (potassium, sodium, mag­nesium, etc.) — but this has little, if any, impact on overall process economics (table 1.2). A detailed account of a dry milling process was published by Alltech in 2004.44 The scheme in figure 1.21 is a simplified derivative of the information provided then as a representative example of the complete bioprocess for ethanol and DDGS.

Unlike Brazilian sucrose-based ethanol, corn-derived ethanol has been technology-driven, especially in the field of enzymes and improved yeast strains with high ethanol tolerance and may be (or become) capable of yielding up to 23% by volume of ethanol in batch fermentations within 60 hours.44 45 Typical commercially available enzymes used liberate the sugars present in starches. Their properties are summarized in table 1.3. Innovations in biocatalysts and fermenta­tion engineering for corn ethanol facilities are covered at greater length in chapter 3. The availability of enzyme preparations with increasingly high activities for starch degradation to maltooligosaccharides and glucose has been complemented by the use of proteases that can degrade corn kernel proteins to liberate amino acids and peptides to accelerate the early growth of yeast cells in the fermentor; protein digestion also aids the access of amylases to difficult-to-digest starch resi­dues, thus enhancing overall process efficiency and starch to ethanol conversion. table 1.4 contains indicative patents and patent applications awarded or filed since 2003 for corn ethanol technologies.

As the multiplicity of U. S. corn ethanol producers has increased, the relative contributions of large and small facilities have shifted: in 1996, Archer Daniels Midland accounted for more than 70% of the total ethanol production, but by late

TABLE 1.2 Estimated Ethanol Production Costs ($/Gallon) from Corn Milling Technologies Wet milling 2005a Dry milling 2005a Dry milling model datab 40 mgyc Dry milling model datab 80 mgyc Feedstock costs 0.712 0.707 0.877 0.840 By-product credits 0.411 0.223 0.309 0.286 Net feedstock costs 0.301 0.484 0.568 0.554 Electricity 0.061 Operating costs 0.058 0.040 0.039 Fuels 0.145 0.211 0.160 0.112 Waste management 0.031 0.007 Water 0.015 0.003 0.004 0.004 Enzymes 0.067 0.042 0.040 0.040 Yeast 0.031 0.005 0.010 0.006 Chemicals 0.055 0.036 0.010 0.013 Denaturant 0.059 0.054 0.072 0.062 Maintenance 0.088 0.062 0.020 0.052 Labor 0.093 0.058 0.010 0.020 Adminstrative 0.055 0.042 Other 0.000 0.004 Total variable cost 1.002 1.065 0.934 0.902 a Shapouri et al., 2006 41 b Dale and Tyner, 2006 43 c mgy = million gallons per year output

2006, this had fallen to just 21%.3846 Although the largest 4 producers still account for 42%, 8 smaller companies each claim 1 to 2% of the total capacity (figure 1.22). The mix of producers includes local initiatives and farmer-owned facilities, and production is heavily concentrated in the Midwest (to minimize transportation costs for raw materials) but with existing and planned expansion in states from Georgia to Oregon. In September 2006, ethanol production capacity in the United States amounted to 5 billion gallons/year, with a further 3 billion gallons/year under construction.46

Presently, ethanol blends commercially available are the 10% (E10) and 85% (E85) versions. The 2004 Volumetric Ethanol Excise Tax Credit made E85 eligible for a 51 cent/gallon tax break; various states (including Pennsylvania, Maine, Min­nesota, and Kansas) levy lower taxes on E85 to compensate for the lower mileage with this fuel. In Hawaii, the tax rate positively discriminates in favor of E85.47 The 2005 Energy Policy Act established tax credits for the installation of a clean-fuel infrastructure, and state income tax credits for installing E85 fueling equipment have been introduced. FFVs capable of using standard gasoline or E85 began to appear in 1995-1998 (Ford), and since then, Daimler Chrysler, General Motors, Isuzu, Lincoln, Mazda, Mercedes Benz, Mercury, and Nissan have introduced

FIGURE 1.21 Outline of corn dry milling and ethanol production.

models as FFVs.47 Usage of ethanol blends is highest in California — 46% of total U. S. consumption.46

Outside North America, construction of the first bioethanol facility in Europe to utilize corn as the feedstock commenced in May 2006 in France; AB Bioenergy France aims to begin production in 2007. The parent company Abengoa Bioenergy (www. abengoa. com) operates three facilities in Spain, producing 5,550 million liters of ethanol a year from wheat and barley grain. A plant in Norrkoping, Sweden, began producing 50 million liters of ethanol annually from wheat in 2001; the product is blended with conventional imported gasoline at up to 5% by volume. These and other representative bioethanol facilities in Europe and Asia are listed in table 1.5. Similar industrial plants, to use a variety of agricultural feedstocks, are presently planned or under construction in Turkey, Bulgaria, Romania, El Salvador, Colombia, and elsewhere.

TABLE 1.3 Typical Enzymes for Fuel Ethanol Production from Cereals Manufacturer and enzyme Type of enzyme Use Properties Novozymes BAN® (Thermozyme®) a-amylase Starch liquefaction Termamyl® a-amylase Starch liquefaction Heat stable Liquozyme® a-amylase Starch liquefaction Heat stable, broad pH tolerance, low calcium requirement Viscozyme® a-amylase Starch liquefaction Optimized for wheat, barley, and rye mashes Spirizyme® Glucoamylase Saccharification Heat stable Alcalase® Protease Fermentation Genencor International Spezyme® a-amylase Starch liquefaction Heat stable Distillase® Glucoamylase Saccharification G-Zyme® Glucoamylase Saccharification Also added pre-saccharification STARGEN™ a-amylase + Saccharification and Enzyme blend glucoamylase fermentation FERMGEN™ Protease Fermentation Fermenzyme® Glucoamylase + Saccharification and Enzyme blend protease fermentation Alltecha Allcoholase I™ a-amylase Starch liquefaction High T™ a-amylase Starch liquefaction Heat stable Allcoholase II™ Glucoamylase Saccharification a Now marketed by Enzyme Technology