Dehydration Methods
There are a number of dehydration methods that can be used for dehydration of approximately 90% hydrous ethanol leaving the conventional distillation unit to 99.5% fuel grade ethanol. These methods are basically divided into three groups:
1. Adsorption methods
2. Distillation methods — mainly azeotropic and extractive distillations
3. Membrane-based methods
In azeotropic and extractive distillations a third component is added to the ethanol-water mixture that helps to break the ethanol — water azeotrope, and these methods are mostly used in older ethanol plants. Adsorption-based methods are a more energy efficient alternative to distillation-drying methods. This method is more popular in current corn — and sugarcane-based first generation ethanol plants. Membrane-based pervaporation is another technique mostly under development as an ethanol dehydration method.