FRACTIONAL DISTILLATION: PROCESS, APPLICATIONS - CHEMISTRY - 2025

The fractional distillation is a physical process that emulates the technique simple distillation based on the boiling point of the species being used to separate mixtures of homogeneous type of various substances present in liquid or mixtures phase heterogeneous liquid-solid type not volatile.

In this sense, the fractional distillation method involves the evaporation of the liquid species, the condensation of the most volatile species in increasing order of their boiling point and the subsequent collection of the substance that was initially desired to be obtained.

It is a method used for centuries in human civilizations in a rudimentary way. The efficiency of distillation allows it to continue to be used today in both industrial and laboratory settings.

The principle of this technique is used in a large number of applications in different fields of science or industry.

Fractional distillation process

Fractional distillation consists of the separation of a solution into its constituents that are in the liquid state, based on the difference between their boiling points and being applied when this difference is less than approximately 25 ° C.

Thus, when a mixture whose boiling points differ considerably is placed under heating, when the boiling temperature of the most volatile component is reached, a vapor phase will form, which will mostly contain this substance at the beginning.

Then, as the temperature continues to rise and as time passes, multiple cycles of evaporation and condensation continually occur (each cycle is known as a "theoretical plate"), until the constituent with the lowest boiling point emerges first.

In each cycle, the constitution of the vapor phase found in the column accumulates a larger quantity of the component with the highest volatility, which is why this substance is essentially in its pure state when it reaches the top of the fractionation column.

Fractional distillation equipment

In laboratories, equipment is used that consists in the first place of a flask or distillation flask made of glass, in which the solution is placed, which is placed directly under heating. A few boiling stones are placed inside this balloon to control this process.

This flask is attached to a fractionating column via a three-neck connector, where the length of the column determines how complete the distillation will be.

That is, the longer the column, the more effective the separation will be. In addition, a thermometer is required to record the temperature over time, so that the distillation process can be controlled.

Likewise, the internal structure of the column is designed to simulate several successive simple distillations, which happens because the steam gradually rises up the column, temporarily condenses at the top and rises repeatedly.

Next, the outlet of this column is connected to a condenser that causes the vapor of the separated and purified substance to cool down.

This is stored in a specific container to collect it, increasing the temperature again until reaching the boiling point of the next component, the second most volatile, repeating the process described, in which each component is stored in a specific container for it.

Applications

Being one of the most important and widely used methods in the separation of liquid mixtures, this physical separation technique has many benefits that are observed in the large number of applications that have been given both in industry and in the laboratory.

- Starting with the industrial-scale uses of fractional distillation, in oil refining facilities it is used to separate crude oil into its component fractions.

In this sense, it is used to obtain and process natural gas that is extracted in these industrial processes. In addition, it is used in chemical plants and petrochemical processes for the processing of substances such as phenol or formaldehyde.

- It is used in cryogenic air separation plants to decompose the air in the atmosphere into its main constituents.

- Fractional distillation is used for desalination of seawater.

- On a laboratory scale, it is used in the purification of reagents and products, such as in obtaining cyclopentadiene through the distillation of commercial dicyclopentadiene.

- It is used to recycle solvents that have already been used, through purification through this technique.

Examples

Fractional distillation of petroleum

In the case of oil, fractional distillation is carried out in equipment of enormous dimensions, called distillation towers, which emulate fractionation columns and are specifically designed for the separation of crude oil in different cuts or streams according to its range. boiling.

This boiling range refers to the range of the boiling points of each separated fraction, since they are mixtures of hydrocarbons with different components and, therefore, have different boiling points.

Before entering the distillation tower, the crude oil is heated to a temperature of approximately 400 ° C, to vaporize this substance and it is separated in the column in increasing order of its boiling range.

In this way, the most volatile cuts such as gases (propane, butane…), gasoline and naphtha are in the upper part of the column, and as it descends, the “heavier” streams are found, such as lubricants or residual components.

Some fractions extracted from the tower (such as gasoline) are added and improved for later commercialization; other cuts such as diesel are used as feed or fuel for other processes within the industry.

Other streams such as residual substances are introduced into other processes that separate them into their constituents and give them other uses, or their commercial value is increased.

References

1. Wikipedia. (sf). Fractional distillation. Recovered from en.wikipedia.org
2. Chang, R. (2007). Chemistry, Ninth edition. Mexico: McGraw-Hill.
3. Britannica, E. (nd). Distillation. Retrieved from britannica.com
4. LibreTexts. (sf). Fractional distillation. Recovered from chem.libretexts.org
5. Kelter, PB, Mosher, MD, and Scott, A. (2008). Chemistry: The Practical Science. Obtained from books.google.co.ve
6. BBC. (sf). Fractional distillation. Recovered from bbc.co.uk