The most commonly used separation process in chemistry and related industries is distillation. The area of application extends from the alcohol rectification made in ancient times to the processes of separation of the crude oil into the fractions applied today. Distillation of a liquid mixture is based on the difference between the volatility of the components of the mixture. The greater the relative volatility, the easier it is to separate. In the distillation column, the vapor stream flows downwards towards the column and the liquid flows downwards in the opposite direction. Liquid and vapor come in contact with each other on shelves or fillers.
A portion of the condensate taken from the condenser is returned to the upper part of the column to provide a liquid stream above the feed point, and a portion of the liquid taken from the bottom of the column is again vaporized and supplied to the column again to provide a vapor stream. In the area below the region where the feed stream enters the column, the more volatile component is removed by peeling from the liquid. This section is called stripping zone. In the upper part of the feed point, the concentration of the more volatile component increases. This section is called the enrichment zone.
Columns are usually used by supplying more than one supply current and by taking side currents along the column. This does not alter the basic operation, but makes the analysis of the process more complex. In the case of separation of a relatively volatile component from a desired non-volatile solution in the process, the enrichment zone is omitted in the design work. These columns are called stripping columns.
In some operating modes in which the upper product is desired as steam, only enough liquid is supplied to provide backflow in the column. These types of condensers are called partial condensers. When all of the liquid is condensed, the liquid sent to the column is in the same composition as the top product. In a partial condenser, the vapor flow from the condenser to the backflow is in equilibrium. In fact, by using a simple column, pure bottom and top products can be obtained from a two-component feed. But if the feed contains more than two components, only one pure product can be taken from the top or bottom of the column. For this reason, more columns are usually required to be able to break down a component with many components.