Sources for Fermentable Sugars Starches

Подпись: C6H10O5 + H2O


The grains generally provide cheaper ethanol feedstock in most regions of the world and industrial conversion may be kept relatively inexpensive because they can be stored more easily than most sugar crops, which often must be reduced to a form of syrup prior to storage. Furthermore, the grain milling ethanol process produces a by-product that can be used for protein meal in animal feed [29]. Fermentation of starch from grains is inherently more complex, involving more steps than sugars because the starch must first be converted to sugar and then to ethanol. A simplified equation for the conversion of starch to ethanol can be written as

As shown in Figure 4.3, in making grain alcohol, the distiller produces a sugar solution from feedstock, ferments the sugar to ethanol, and then sepa­rates the ethanol from water through distillation.

Among the disadvantages in the use of grain are its fluctuations in price. Critics of corn ethanol have made remarks in relation to "fuel versus food" and stated that the recent food price increase has something to do with corn ethanol manufacture, whereas others strongly oppose this view with statis­tical data and logical reasons [31]. Ethanol in the gasoline boosts the fuel’s octane rating and also helps cleaner burning. In the United States, etha­nol is currently the most popular oxygenated fuel additive as discussed in Chapter 3.