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Distillation Columns - Fractioning Columns

This page will provide a comprehensive guide to distillation columns and fractionating columns and the role SRS Engineering plays in that.  Find out how columns work and in what type of industries distillation columns can be found.

Distillation is the process of separating two or more miscible liquids by taking advantage of the boiling point differences between the liquids. For methanol and water, heat is added to the mixture of methanol and water and eventually the most volatile component (methanol) begins to vaporize. As the methanol vaporizes it takes with it molecules of water.

The methanol-water vapor mixture is then condensed and evaporated again, giving a higher mole fraction of methanol in the vapor phase and a higher mole fraction of water in the liquid phase. This process of condensation and evaporation continues in stages up the column until the methanol rich vapor component is condensed and collected as tops product (99.5% recovery / 99.5% pure) and the IPA/Water rich liquid is collected as bottoms product.

What is Fractionating columns

SRS Engineering Corporation is premier manufacturer of distillation columns for various applications. Fractional distillation is a method used to separate liquids with similar boiling points. This method relies upon a gradient of temperatures existing in the condenser stage of the equipment.

A vertical condenser is often used in the fractional distillation technique. Extracting products in the liquid stage at the different heights of the column makes it possible for the extraction of liquids that have different boiling points. The greater the distance over which the temperature gradient in the condenser is applied, the easier and the greater separation is.

Heating under Reflex

Heating under reflex allows the mixture including volatile materials to be heated for a long time without loosing any solvent. If a mixture of liquids forms an azeotrope, then that mixture cannot be completely separated by fractional distillation.

What is Raoult's law?

If you have studied Raoult's Law you are probably familiar with the graph of vapor pressure vs. composition at constant temperature. You will probably also be familiar with the boiling point/composition diagram (at constant pressure) that is used to explain fractional distillation. What is often absent from the books is the link between the two diagrams. However, here is the explanation that links the two.

As temperature increases, so does the vapor pressure of a liquid. The vapor pressure/composition diagram is plotted at constant temperature; a series of these plots at different temperatures (fig 1 below) is needed in order to obtain a boiling point/composition diagram. The graph shown is for a mixture of hexane and heptane, which forms an ideal liquid mixture. Since vapor pressure does not increase linearly with an increase in temperature, the vapor pressure lines at the different temperatures are not parallel.

Boiling-point composition diagrams are usually plotted at atmospheric pressure, though for an ideal liquid mixture they'd look more or less the same whatever the chosen pressure. The horizontal line is at 1 atmosphere (760 mmHg), and gives the composition of the liquid that gives rise to a vapor pressure of 1 atmosphere at each temperature.

Francois Marie Raoult
(1830 - 1901)

 

The points thus generated are then transferred to axes having the same composition scale but whose vertical axis is the temperature. The full-size diagram can be seen below.

The boiling point/composition diagram is now completed by putting in the line that represents the vapor composition (shown in red). The vapor in equilibrium with liquid at a given temperature is always richer in the more volatile component. Thus the vapor composition is shown by a point at the same temperature, but whose composition is nearer to the more volatile (lower boiling temperature) constituent.

The link between the vapor pressure/composition and boiling temperature/composition diagrams for non-ideal (azeotropic) mixtures is the same, but such systems give a more complex diagram because of the vapor pressure maximum or minimum.

 

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SRS Engineering Corporation is the leading manufacturer of Distillation Columns and Fractioning Columns.


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  • 25843 Jefferson Ave
  • Murrieta, CA 92562