What is the difference between the stripping section and the rectifying section of a distillation column?

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Distillation is generally used to separate homogeneous liquid mixtures, and the two components must meet the conditions for distillation, that is, they must have different volatilities. Let’s discuss it using the simplest two-component continuous distillation. When you turn on the feed pump to start distillation, as the streams of material enter the feed tray of the distillation column, distillation begins immediately. We already know that the volatilities of these two components are different; in other words, when this material is heated and part of the solution vaporizes, the composition of the vapor above the solution differs from that of the liquid phase. Substances with lower boiling points have a higher concentration in the gas phase, while substances with higher boiling points have a higher concentration in the liquid phase. If all of this steam is then condensed, the content of volatile components in the resulting condensate will be higher than that in the original solution. If part of the mixed steam is condensed, it will increase the amount of volatile components in the steam. This process can be repeated many times; as a result, the higher one goes in the tower, the higher the concentration of volatile components becomes, while the lower one goes, the higher the concentration of non-volatile components becomes. Thus, the originally homogeneous mixture of these two components is separated. A distillation column contains many trays, one of which is used for feeding the material; this tray can be located at any position within the column, depending on the composition of the feed and the thermal conditions. Above this feeding tray, moving toward the top of the column, the concentration of volatile components increases gradually until it reaches the composition specified by the operating conditions. The section from a tray on the feed tray up to the top of the tower constitutes the rectification section of the distillation column. From the feed tray all the way to the bottom of the tower, this is the stripping section of the distillation column. The content of volatile components increases in the distillation section, while it decreases in the stripping section; thus, a product with a very high content of volatile components can be obtained at the top of the tower. In the stripping section, the content of poorly volatile components increases, allowing for the production of products with a high concentration of such components at the bottom of the tower. In other words, with the feed point as the boundary, the distillation section is used to purify the light components; it is located above the feed and contains components that are purer than those in the feed, which is why it is called distillation. The stripping section is used to purify the heavier components; below it, the mixture is even less pure, which is why it is called stripping.