Feedstock starch

Ethanol. Accurate projections of ethanol costs are much more difficult to make than are those for methanol. Large scale ethanol production would impact upon food costs and have important environmental consequences that are rarely cost-analyzed because of the complexity. Furthermore, for corn, the most likely large-scale feedstock, ethanol costs are strongly influenced by the credit assigned to the protein by-product remaining after the starch has been removed and converted to ethanol. 

Starches. In the United States, all potable alcohol, most fermentation industrial alcohol, and most fuel alcohol is currendy made principally from grains com is the principal feedstock for fuel alcohol. Fermentation of starch from grain is somewhat more complex than fermentation of sugars because starch must first be converted to sugar and then to ethanol. This process was known to the ancient Egyptians and Mesopotamians who brewed beer almost 5000 years ago (202). The simplified equations for the conversion of starch to ethanol are... 

Starch A polymeric substance of glucose molecules and a component of many terrestrial and aquatic plants used by some organisms as a means of energy storage starch is broken down by enzymes (amylases) to yield glucose, which can be used as a feedstock for chemical or energy production. 

Use of renewable feedstocks is most likely where they can compete economically with petrochemically derived materials. This already happens in many areas, and it is sometimes forgotten that even in a world that seems to be dominated by chemicals and materials from fossil carbon and other non-renewable sources, industry already uses annually 19.8 MT of vegetable oils, 22.5 MT starch, 28.4 MT of plant fibres and 42.5 MT of wood pulp. These all compete on price and performance with synthetic alternatives. 

Fermenting grains with yeast produces a grain alcohol. The process also works with other biomass feedstocks. In fermentation, the yeast decomposes carbohydrates which are starches in grains, or sugar from sugar cane juice into ethyl alcohol (ethanol) and carbon dioxide. The process breaks down complex substances into simpler ones. 

By 2006, the U.S. had 77 ethanol plants producing more than 3 billion gallons of ethanol per year. Canada produced an additional 60 million gallons. Corn was the feedstock in 62 of the 77 U.S. plants. Other feedstocks included seed corn, corn and barley, corn and beverage waste, brewery waste, cheese whey, corn and milo, corn and wheat starch, potato waste and various sugars. The U.S. had 11 additional plants under construction and 55 proposed. West Central Soy processes soybeans to a food grade oil. Alcohol and a catalyst are then used to produce biodiesel fuel and glycerin. 

Starch-containing plants Another potential ethanol feedstock is starch. Starch molecules are made up of long chains of glucose molecules. Hence, starch-containing materials can also be fermented after the starch molecules have been broken down into simple glucose molecules. Examples of starchy materials commonly used around the world for ethanol production include cereal grains, potatoes, sweet potatoes and cassava. Typical cereal grains commonly used for ethanol production in the EET are rye and wheat. 

AGs and APGs are produced completely with renewable feedstocks such as glucose and fatty alcohols derived from starch and palm kernel oil [34]. AGs, which are mainly the two homologues C12- and C14-1V-methyl glucamide, are manufactured by reductive amination of glucose followed by acylation with fatty acid derivatives [35],... 

Alkyl polyglucosides (APG) and alkyl glucamides (AG) are non-ionic surfactants produced on the basis of renewable feedstocks such as glucose and fatty alcohols, which are derived from starch and palm oil, respectively. 

Microorganisms have also been developed to produce alternative products, such as lactic acid [65], propane-1,3-diol [67], 3-hydroxypropionic acid [68], butane-2,3-diol [69] and numerous other intermediates. For instance, bacteria such as the Clostridium acetobutylicum ferment free sugars to C4 oxygenates such as butyric acid or butanol. They form the C4 oxygenates by Aldol condensation of the acetaldehyde intermediates. The Weizmann process exploits this property to ferment starch feedstock anaerobically at 37 °C to produce a mixture of w-butanol, acetone and ethanol in a volume ratio of 70 25 5 [3],... 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

The compactness and complexity of (ligno)cellulose makes it much more difficult to attack by enzymes with respect to starch. Therefore, the cost of bioethanol production is higher [23], To be cost competitive with grain-derived ethanol, the enzymes used for biomass hydrolysis must become more efficient and far less expensive. In addition, the presence of non-glucose sugars in the feedstock complicates the fermentation process, because conversion of pentose sugars into ethanol is less efficient than conversion of the hexose sugars. 

Before 1900, a large share of the chemical industry was based on biomass it served as a feedstock for chemicals made from wood, sugars, starches, and fats. 

As a matter of fact, most of the processes currently developed to generate biochemicals out of biomass involve fermentation of starch originating from corn, wheat, or rice, for example. The various chemicals obtainable from theses processes and their end applications are listed in Table 10.3. A lot of these fermented biochemicals, however, are not yet economically competitive compared with their petrochemical equivalent, essentially due to the large capital investment in equipment and land needed to implement the fermentation process on an industrial scale. An additional disadvantage of this route is that it competes with feedstock needed by the food industry. More research to reduce the costs of fermentation technology is needed. 

Glnco-amylase enzyme converts the starch into D-glucose. The enzymatic hydrolysis is then followed by fermentation, distillation and dehydration to yield anhydrous bioethanol. Com (60-70% starch) is the dominant feedstock in the starch-to-bioeth-anol industry worldwide. 

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