Ethanol Production

The Sugarcane Ethanol Production Process

Technologically, the process of producing sugarcane ethanol from sugar is simpler than converting corn into sugarcane ethanol. Converting corn into sugarcane ethanol requires additional cooking and the application of enzymes, whereas the conversion of sugar primarily requires only a yeast fermentation process and the removal of water. The energy requirement for converting sugar into sugarcane ethanol is about half that for corn.

The sugarcane ethanol production process begins with cultivating and harvesting sugarcane at a cane field. The cane is then processed at a sugar mill, where the cane stalks are shredded and crushed to extract the cane juice. The byproducts of the juice extraction process are cane molasses and bagasse. Sugarcane molasses is used in the production of alcohol beverages, fuel alcohol and for direct human consumption. Bagasse can be used to produce steam and generate electricity within the plant. Excess electricity produced can be sold to utility grids.

After sugarcane juice is extracted at the mill, it is then transformed into alcohol at a distillery through a fermentation process using yeasts as the catalyst. The fermentation process takes four to twelve hours and generates a significant amount of CO2 and heat. Fermentation can be conducted in batches or continuously, using open or closed fermentation tanks. Cooling is applied to maintain the resulting fermented wine mixture. Much of the CO2 that is generated during the fermentation process can be captured and converted into marketable products, such as dry ice, liquid CO2 for soft drinks, fire-fighting foams, filtration products and various industrial uses.

After fermentation, the sugarcane ethanol is distilled from other byproducts, resulting in a level of purity of approximately 95%. This mixture is often referred to as “hydrous sugarcane ethanol” because it contains 5% water. Hydrous sugarcane ethanol can be commercially used, but cannot be blended with gasoline. An additional reactant, such as cyclohexane, is needed in order to dehydrate the sugarcane ethanol, by forming a tertiary azeotropic mixture with water and alcohol. Anhydrous sugarcane ethanol is nearly 100% pure and can be blended with gasoline.

Sugarcane is bulky and relatively expensive to transport and must be processed as soon as possible to minimize sucrose deterioration. In order to save costs, sugarcane ethanol is often produced near a sugarcane field at a sugarcane mill with an adjoining distillery plant.