Isopropyl Alcohol from Propene and Water

Isopropyl alcohol is made mainly by adding water to propene (propylene). In direct hydration, more common in Europe, propene of over 90 % purity and water react at high pressure over a solid acid catalyst. (The indirect route, common in the USA, goes through sulphate esters made with sulphuric acid, and a third route hydrogenates acetone.) The alcohol is then separated by distillation, but isopropyl alcohol and water form an azeotrope: plain distillation stops at 87.9 % alcohol and 12.1 % water. Dry alcohol is made by azeotropic distillation with an entrainer such as cyclohexane.