Sugar crops, fermentation

Alcoholic Fermentation. Certain types of starchy biomass such as com and high sugar crops are readily converted to ethanol under anaerobic fermentation conditions ia the presence of specific yeasts Saccharomyces cerevisia and other organisms (Fig. 6). However, alcohoHc fermentation of other types of biomass, such as wood and municipal wastes that contain high concentrations of cellulose, can be performed ia high yield only after the ceUulosics are converted to sugar concentrates by acid- or enzyme-catalyzed hydrolysis ... 

About 10 million gallons of the fermentation alcohol is derived from wastes such as sulfite liquor or whey, but the balance presently depends on damaged grain or sugar, crop surpluses and molasses. Relative costs of ethylene and carbohydrates will change this in a few years, but no reversal to ethanol-based ethylene is likely in this country for much longer, perhaps through 1990. ... 

Feedstock Options. Ethanol may be produced via fermentation (with yeast) of 6-carbon or 12-carbon sugars from a number of carbohydrate sources including sugar crops, starch crops, or lignocellulosic materials. 

Starches present in grains or root crops are readily converted to sugars for fermentation to ethanol. With the shortages of food in developing nations, grains would probably not be used for fuel. Therefore, we will consider only sugar crops and molasses to be available for ethanol production. In the initial part of the analysis, we will identify the countries where sufficient sugar is exported or molasses produced to allow production of ethanol to replace 1000 barrels of petroleum fuels. 

The fermentation of starchy or sugar crops to bioethanol is performed using a series of different processes which are dependent on the raw material used. A general hioethanol process includes milling, liquefaction, saccharification, fermentation, distillation and dehydration, as shown in Figure 6.1. 

FIGURE 26.11 Industrial fermentation process for ethanol production. (Carbohydrates from sugar crops can be directly used for fermentation, whereas starch and other organic material must be converted into a... 

Conventional biorefineries Starch (corn, wheat, cassava) and sugar crops (sugarcane, sugar beet), wood Pretreatment, chemical and enzymatic hydrolysis, catalysis, fermentation, fractionation, separation Commercial Sugar, starch, oil, dietary fibers, pulp and paper... 

---