Final answer:
Ethanol can be manufactured from starch through enzymatic hydrolysis, fermentation, and distillation. Manufacturing ethanol from cellulose includes an additional pretreatment step due to cellulose's β-1,4 glycosidic linkages that resist common starch-degrading enzymes.
Step-by-step explanation:
Manufacturing Ethanol from Starch and Cellulose
To manufacture ethanol from starch, the process begins with the hydrolysis of starch into sugar units like glucose by using enzymes, such as amylase. The glucose is then fermented by yeast or bacteria to produce ethanol and carbon dioxide. This process is known as fermentation and is followed by the distillation of the fermented mixture to separate ethanol from the mixture, increasing its concentration.
The production of ethanol from cellulose requires an additional step known as pretreatment. Cellulose in biomass needs to be broken down into sugars before it can be fermented. The pretreatment can involve physical, chemical, or enzymatic steps. This is due to the different structures of cellulose and starch; cellulose has β-1,4 glycosidic linkages, which make it more rigid and resistant to enzymes that break down starch with α-1,4 and α-1,6 linkages.
While both starch and cellulose are polymers of glucose, their structural differences result in different enzymes being required for their hydrolysis. Specifically, enzymes that hydrolyze starch cannot typically hydrolyze cellulose because of the different positioning of the β versus α glycosidic linkages. This is why ethanol production from cellulose, also known as cellulosic ethanol, is generally seen as more challenging than ethanol production from starch.