1. Feedstock Preparation: The plant material (e.g., corn) is harvested and processed to obtain the feedstock for ethanol production.
2. Pretreatment: The feedstock may undergo pretreatment to enhance the release of sugars (fermentable carbohydrates). This can involve mechanical processes (e.g., grinding), heat treatments, or enzymatic treatments to break down the plant's cell walls.
3. Hydrolysis: The pretreated feedstock is mixed with water and enzymes (typically a mix of cellulases, hemicellulases, and other enzymes) to break down the polysaccharides (cellulose and hemicellulose) into fermentable sugars like glucose and xylose. This process may occur at high temperatures (e.g., in a cooker) or at moderate temperatures with specialized enzymes.
4. Cooling and Sterilization: The resulting sugar solution is cooled to an appropriate temperature (around 30°C) and sterilized to prevent contamination by unwanted microorganisms.
5. Fermentation: The cooled and sterilized sugar solution is fermented by adding specific yeast strains, such as Saccharomyces cerevisiae. These yeast metabolize the sugars and convert them into ethanol through the process of fermentation.
6. Distillation and Dehydration: The fermented mixture undergoes distillation to separate ethanol from other components. Multiple rounds of distillation may be necessary to obtain a high concentration of ethanol. To achieve anhydrous ethanol (completely free of water), a dehydration process using molecular sieves or other techniques is employed.
7. Purification: The distilled ethanol may undergo additional purification steps to remove impurities and undesired compounds, ensuring its quality as a fuel-grade biofuel.
The final product is high-proof ethanol, which can be blended with gasoline to create biofuel blends commonly used in vehicles and other applications. The exact steps and conditions may vary depending on the specific feedstock and production facility.
