Corn and Sugarcane Ethanol
Corn and sugarcane are the major feedstocks for bioethanol currently used in the world. Ethanol produced from sugar or starch feedstock like sugarcane and corn is known as first generation ethanol. There are two main methods for the production of ethanol from corn: dry milling and wet milling processes. In the dry milling process the entire corn kernel is ground into flour and referred to as "meal." The meal is then slurried by adding water. Then enzymes are added to the mash that converts starch to fermentable sugar dextrose. Then, pH of the solution is adjusted, and yeast is added for the fermentation. Fermentation usually takes between 40 to 50 hours. After the fermentation is complete, the mixture is distilled to give ~90% ethanol. The ethanol-water mixture is dehydrated to about 200 proof using molecular sieves to produce fuel-grade ethanol. In the wet milling process corn grain is mixed with dilute aqueous sulfuric acid and allowed to soak for 24 to 48 hours. Then the slurry goes through a series of grinders to separate out the corn germ. The hydrolyzed starch solution is then fermented after pH adjustment and the ethanol produced is distilled off, as in the dry milling process.
In sugarcane ethanol production, sugarcane is crushed to collect juice leaving the fiber residue or bagasse. The cane juice which contains 10-15% sucrose is then filtered and sterilized before
Figure 2.1 Annual ethanol production shares of the six largest fuel ethanol producing countries or regions in 2011 .
adding yeast for fermentation. Ethanol produced is separated by distillation.