Ethanol from corn

Compared with other alternative motor fuel options (reformulated gasoline, compressed or liquefied natural gas, ethanol from corn or coal, methanol and electricity), propane has the lowest greenhouse gas emissions except for natural gas. According to a 1998 study by the Institute of Transportation Studies, greenhouse emissions from propane vehicles arc 21.8 percent less than from gasoline or diesel. 

Effect of Germ and Fiber Removal on Production of Ethanol from Corn... 

Currently, most biorefineries are based mainly on a single product line with potentially one or two byproducts. Thus, an ethanol plant produces ethanol from corn starch, with distiller s grain as a byproduct. Greater product flexibility and, consequently, greater opportunities for profitability would derive from a plant producing a variety of alcohols, especially higher alcohols whose market prices range from 0.77 to 1.87/kg. 

The maj ority of these new plants are corn dry-grind ethanol plants. Approximately 2.5-2.7 gal of ethanol, 17.5 lb of dried distiller s grain (DDG), and 17 lb of carbon dioxide are produced from each bushel of corn processed through a corn dry mill (2). Since 1980, process improvements in enzymes, thermal-tolerant yeasts, molecular sieves, and cogeneration have achieved a 50% reduction in the energy required to produce ethanol from corn (2). Further improvements in efficiencies and reductions in production costs can be expected in the future. 

Getting ethanol from corn consists of five steps grain grinding, mash cooking, starch liquefaction, saccharification and fermentation, followed by ethanol separation and dehydration. Before fermentation, the starch has to be converted to soluble dextrin by liquefaction in the presence of specific enzymes, such as a-amylase. This process takes place at temperatures above 100 °C at suitable pH and residence time. Then, another enzyme glucoamylase is added that transforms the... 

Fig. 33.1. Starch a biopolymer of glucose molecules used today in the United States as the basis for production of fuel ethanol from corn grain.

Ethanol has a high octane value and is used as a gasoline blending component. It can be manufactured as a renewable fuel by fermentation of sugars using S. cerevisae. Compare the costs of producing ethanol from corn in Decatur, IL, and from sugar cane in Mobile, AL. 

Most current commercial ethanol production is from the fermentation of sugar and starch crops. Yeast can rapidly convert sucrose to ethanol with a theoretical carbon conversion of 67%. The production of ethanol from corn grew to about 1.9 billion gallons in 2001. This accounted for 90% of the total ethanol production and an estimated 615 million bushels of corn (6.2% of total corn produced) were consumed. The remaining 10% of ethanol production was by fermentation of grain sorghum, barley, wheat, cheese whey, and potatoes. 

In addition to ethanol from cellulose, cellulase enzymes play a minor role in the production of ethanol from corn. In this process, most of the glucose is from starch. Cellulase enzymes offer the opportunity to increase the glucose yield by hydrolyzing a portion of the cellulose to glucose, as well as decreasing the viscosity of the ground corn [25]. 

Fig. 7. Fermentation of hemicellulose-cellulose hydrolysate to ethanol from corn cob using Saccharomyces 1400 (pLNH33) [61]...

McAloon A, Taylor P, Yee W. Determining the cost of producing ethanol from corn starch and lignoceUulosic feedstocks. Technical report, NIAEL/TP-580—28893. Golden, CO National Renewable Energy Laboratory October 2000. 

Taylor F, Mcaloon A J, Craig J C, Yang P, Wahjndi J, Eckhoff S R (2001), Fermentation and costs of fuel ethanol from corn with quick-germ process , Appl. Biochem. Biotechnol., 94,41-49. 

For additional information on the production of ethanol, see the essay Biofuels that precedes Experiment 27. In this essay, the production of ethanol from corn for use in automobiles is discussed, along with the production of ethanol from other sources such as plant cellulose. 

At present, the annual production capacity of fuel ethanol from corn is 1.02 million ton and test production of fuel energy from sorghum is 5,000 tons in China, respectively. The annual production capacity of bio-diesel is about 20,000 tons by using waste oil, barbadosnut, Chinese pistache and coleseed etc. as raw materials. 

Figure 9.4 Ethanol from corn, a renewable fuel source...

When used as a replacement for gasoline, ethanol has a lower energy content, by about 34% per unit volume. This, and other factors, such as costs in energy required to produce the agricultural feedstock, esp>edally corn, have created doubts about the wisdom of an ethanol-based program as a renewable energy source. Production of ethanol from corn is 5 to 6 times less efficient than producing it from sug-... 

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