What is the difference between hydrous ethanol and anhydrous ethanol?
Hydrous ethanol, in technical terms, is a binary homogeneous mixture of ethanol and water in such a ratio that its composition cannot be changed except through e.g. azeotropic distillation, adsorption (mol sieves) and membrane separation. This is because an azeotropic liquid such as an ethanol/water mixture, when boiled, yields vapor with the same ratio of constituents as the original mixture. Thus, once the ethanol concentration reaches 96% through simple distillation, the vapor from the boiling mixture is also 96%, with water comprising the remainder. Further distillation is therefore ineffective, and an additional costly, energy-consuming dehydration process must be employed to achieve the lower water percentage (less than 1%) of anhydrous (or absolute) ethanol. Both hydrous and anhydrous ethanol have proven applications by themselves as automotive and aviation fuels. However, anhydrous ethanol has traditionally been specified in most countries when ethanol is blended with gasoline,