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Ethanol derived from biomass feedstocks is a biofuel that can be mixed with or substituted directly for gasoline to address the concerns of the transportation industry. The ethanol industry’s history goes back to the oil crisis in the 1970s that raised the concern about a lack of reliable energy sources in the U.S. Since then, the technology used in the ethanol production process has improved substantially with newer plants generally having more efficient production processes. Today, ethanol is produced from various crops such as corn, grain sorghum, wheat, sugar, and other agricultural

feedstocks. Currently, about 90 percent of the ethanol production processes in the U.S. use corn as the major feedstock. The rest comes mainly from using grain sorghum, barley, wheat, and other crops as feedstocks (Northeast Regional Biomass Program, 2001). Currently, most of the nation’s ethanol production capacity is concentrated in the Midwest, where the Corn Belt provides abundant and cheap corn feedstock.

3.2.1 Sugar ethanol production technology

Modern ethanol technology is quite well established and efficient with the basic process being similar to that of making alcoholic beverages. Traditional ethanol production facilities include both wet- and dry-milling operations. These two processes differ mainly by the initial treatment of the grain and the feed co-products. In the wet-mill process, corn is soaked to separate the grain into many parts. Then starch is fermented

into ethanol, similar to the dry mill process, or processed into cornstarch or corn syrup (Ethanol Industry Outlook, 2002). Wet-mill facilities are plants that produce various high-valued products such as high-fructose corn syrup (HFCS), dextrose, glucose syrup, vitamins, food and feed additives, corn gluten meal, corn oil, etc. In the dry-mill process, “the clean corn is ground and mixed with water to form a mash. The mash is cooked, and enzymes are added to ferment the sugars, producing a mixture containing ethanol and solids. The beer (alcohol-water mixture) is then distilled and dehydrated to create fuel- grade 99-percent ethanol. The solids remaining after distillation are dried to produce distillers’ dried grains (DDG) with 27-percent protein and are sold as an animal feed supplement” (Shapouri, Gallagher, et al., 2002, p. 2)

Most of the new ethanol plants in the U.S. are in the form of dry mills. The well- established design of dry-mill facilities has reduced the capital cost substantially. Some new plants cost about $1.07 per annual gallon unlike the earlier facilities that cost

between $1.75 to $2.00 per annual gallon (Shapouri, Gallagher, et al., 2002). In addition, “new dry-mill ethanol plants are more energy efficient, requiring about 36,000 Btu’s of thermal energy and 1.1. Kilowatts of electricity to produce one gallon of ethanol” (Shapouri, Gallagher, et al., 2002, p. 2).

3.2.2 Cellulosic ethanol production technology

As it was mentioned earlier, the U.S. ethanol industry is starch-based with corn being a primary feedstock. However, corn and other starches and sugars are only a small fraction of biomass that can be used to make ethanol. The starch-based ethanol industry may not be economically viable without subsidies and/or mandates that required using ethanol

blends to satisfy octane and oxygenate levels (NRC, 1999). The National Research Council has suggested that the ethanol production research and development programs produce technology that will foster production of products that are cost competitive with fossil fuel alternatives. The U.S. Department of Energy is also promoting the

development of ethanol from cellulosic feedstocks as an alternative to conventional petroleum transportation fuels, because conversion of lignocellulosic biomass such as crop residue (corn stover, wheat straw) and perennial grasses is theoretically much more efficient than conversion of corn grain. A lignocellulosic-based system could use

virtually all of the harvested plant material, feedstocks produced on less productive land, and materials that would be considered waste (e.g., waste from wood products

processing and crop residue).

Advanced bioethanol technology allows fuel ethanol to be made from cellulosic (i.e. plant fiber) biomass, such as agricultural and forestry residues, industrial waste, material in municipal solid waste, trees, and grasses. Cellulose and hemicellulose, the two main components of plants, which give plants their structure, are also made of sugars, but those sugars are tied together in long chains. Advanced bioethanol

technology can break those chains down into their component sugars and then ferment them to make ethanol. In general, cellulosic feedstock is converted to ethanol through processes that are very similar to those used in traditional ethanol production. However, unlike traditional ethanol conversion, sugars must be formed from the cellulosic material as a first step. Once formed, these sugars can be fermented and distilled into ethanol. A

simplified generic configuration of the hydrolysis fermentation process is given in Figure 2.

Figure 2. Generalized biomass to ethanol process (Source: Hamelinck et al. 2005)

A number of developers in the ethanol industry have advanced the bioethanol technology. Among these developers are BC International (BCI), Arkenol, Masada Resource Group, Iogen/Petro Canada, to name a few. Currently there are several commercial companies which are in the planning or construction phase of commercial bioethanol plants. For example, Arkenol will use the concentrated acid methods in its ethanol plant at RioLinda (Sacramento County, California), which will use rice straw as the biomass feedstock. The same methods will be used by the Masada Resource Group in its municipal solid waste-to-ethanol facility in Orange County, New York (Mann & Bryan, 2001). BCI and the U.S. Department of Energy Office of Fuel Development have formed a cost-shared partnership to develop a 20-mgpy biomass-to-ethanol plant in Jennings, Louisiana. This plant will use dilute acid hydrolysis method to recover sugar from bagasse (sugar cane waste) and rice hulls. However, the major problem with

production of cellulosic ethanol is that although there are few cellulosic ethanol pilot projects in various locations throughout the United States, there is presently no full-scale operational plant anywhere in the U.S. (Northeast Regional Biomass Program, 2001). This lack of an existing conversion plant creates a higher degree of uncertainty associated with the design for this process.

There are three basic types of ethanol-from-cellulose process designs: 1) acid hydrolysis; 2) enzymatic hydrolysis; and 3) thermochemical. The most common among these processes is acid hydrolysis (Badger, 2002). Badger (2002) argues that “virtually any acid can be used in the process; however, sulfuric acid is most commonly used since it is usually the least expensive. There are two basic types of acid processes: dilute acid and concentrated acid. Most dilute acid processes are limited to a sugar recovery

efficiency of around 50%. The reason for this is that at least two reactions are part of this process. The first reaction converts the cellulosic materials to sugar and the second reaction converts the sugars to other chemicals. The biggest advantage of dilute acid process is its fast rate of reaction, which facilitates continuous processing. The biggest disadvantage is its low sugar yield. For rapid continuous processes, in order to allow adequate acid penetration, feedstocks must be reduced in size so that the maximum particle dimension is in the range of a few millimeters” (p. 18-19).