Distillation columns are given first priority in separation techniques and mostly for multicomponent separations. When a feed mixture having more than two components or compounds in it than it is termed as multicomponent mixture. So for obtaining the individual compounds from the mixture a technique of volatility or difference in vapor pressure and their boiling points can used for developing a separation technique by supplying heat.

If the components in mixture have different boiling points at constant pressure, than by maintaining those temperature at different location in  the distillation column, that particular component can be separated from fixed temperature plate location. The products can be separated as side streams from the distillation column.

Multicomponent distillation becomes difficult for azeotropic and close boiling component mixtures. Purity of the distillate product are disturbed during continuous operations and difficult to control. But a packed and sieve tray design are mixed to develop a mulitcomponent distillation column so that the components can be separated by controlling the temperature of the packed bed and providing enough contact area and time for separation.   
model diagram of distillation column PID
Distillation column