The rectification is a thermal separation process in which the more volatile components of a mixture are recovered and concentrated. The supply of thermal energy vaporizes the more volatile components and the ascending vapor phase comes in contact with descending liquid (reflux of volatile components). The contact usually occurs in trays or packages installed in a column. Increasing the number of rectification steps increases the concentration of the most volatile component. This means that the concentration of the low-volatility component is increased by the forwarding of the top product of the first rectification column into a second column. Rectification is often used to purify alcohols, but usually ground streams are used to preheat the cold stream and optimize overall energy requirements. It can be combined with other technologies.