Bioethanol is categorized into first, second, third, and fourth generations based on the feedstock used to produce it:

 Bioethanol is categorized into first, second, third, and fourth generations based on the feedstock used to produce it: 

First generation

Made from edible materials like sugar, starch, or vegetable oil. This generation of bioethanol is controversial because it competes with food production. 

Second generation

Made from non-edible materials like agricultural and forest residues, perennial grasses, cellulose, hemicellulose, lignin, or pectin. While second generation bioethanol has some potential, it's not enough on its own to meet the world's energy demand. 

Third generation

Made from aquatic biomass like algae, or from engineered biofuel crops. 

Fourth generation

Made from engineered plants and microorganisms that capture and sequester carbon dioxide. This generation of bioethanol uses technology to capture carbon dioxide released during fuel production and store it underground. 

Each generation of bioethanol has different technologies and end products, and different feed properties and operating parameters. Third and fourth generation bioethanol are still in early development and require more research and development before they can be commercially viable.