SIMPLE DISTILLATION: PROCESS AND EXAMPLES - CHEMISTRY - 2025

The simple distillation is a process in which the vapors produced from a liquid are brought directly to a condenser, in which low temperature vapor and condensation.

It is used to separate a volatile component from the non-volatile components present in a liquid. It is also used for the separation of two liquids present in a solution with very different boiling points.

Basic setup of a simple distillation. Source: Pixabay

Simple distillation is not an efficient method for the separation of two volatile liquids present in a solution. When the temperature of it increases by supplying heat, the kinetic energy of the molecules also increases, which allows them to overcome the cohesion force between them.

Volatile liquids begin to boil when their vapor pressure equals the external pressure exerted on the surface of the solution. Both liquids contribute to the composition of the vapor formed, the presence of the more volatile liquid being greater; that is, the one with the lowest boiling point.

Therefore, the more volatile liquid makes up most of the distillate formed. The process is repeated until a desired purity or the highest possible concentration is reached.

Simple distillation process

In simple distillation, the temperature of a solution is increased until it boils. At that moment the transition between the liquid to gaseous states occurs. This is observed when a constant bubbling begins in the solution.

Equipment

The equipment for simple distillation usually consists of a burner or a heating blanket (see image); a round refractory glass flask with a ground glass mouth, to allow its coupling; and some glass beads (some use a wooden stick) to reduce the size of the bubbles formed.

The glass beads serve as bubble-forming nuclei, which allow the liquid to boil slowly, avoiding overheating that results in the formation of a kind of giant bubbles; even capable of expelling a mass of liquid out of the distillation flask.

Attached to the mouth of the flask is a refractory glass adapter with three mouths, which are made of ground glass. One neck is attached to the distillation flask, a second neck is attached to the condenser, and the third neck is closed through the use of a rubber stopper.

In the picture, the mount lacks this adapter; and instead, the thermometer and a direct connector to the condenser are placed through the same rubber stopper.

Condenser

The condenser is a device designed to fulfill the function that its name indicates: to condense the steam that moves through it. Through its upper mouth it is coupled to the adapter, and through its lower mouth it is connected to a balloon where the distillation products are collected.

In the case of the image, they use (although it is not always correct) a graduated cylinder, to measure the distilled volume at once.

The water that circulates through the outer jacket of the condenser, enters it through its lower part and exits through the upper part. This ensures that the condenser temperature is low enough to allow condensation of the vapors produced in the distillation flask.

All the parts that make up the distillation apparatus are fixed by clips connected to a metal support.

A volume of the solution to be subjected to distillation is placed in the round flask with a suitable capacity.

Proper connections are made using graphite or grease to ensure efficient sealing, and heating of the solution begins. Simultaneously, the passage of water through the condenser begins.

Heating

As the distillation flask is heated, an increase in temperature is observed on the thermometer, until a point is reached where the temperature remains constant. This remains so even if the heating continues; unless all volatile liquid has completely evaporated.

The explanation for this behavior is that the boiling point of the component with the lowest boiling point of the liquid mixture has been reached, in which its vapor pressure equals the external pressure (760 mm Hg).

At this point, all the heat energy is expended in the change from the liquid state to the gaseous state that involves the expiration of the intermolecular cohesion force of the liquid. Therefore, the supply of heat does not translate into an increase in temperature.

The liquid product of the distillation is collected in properly labeled flasks, the volumes of which will depend on the volume originally placed in the distillation flask.

Examples

Distillation of water and alcohol

You have a 50% alcohol in water solution. Knowing that the boiling point of alcohol is 78.4 ° C and the boiling point of water is approximately 100 ° C, then can a pure alcohol be obtained with a simple distillation step? The answer is no.

By heating the alcohol-water mixture, the boiling point of the most volatile liquid is initially reached; in this case, alcohol. The steam formed will have a higher proportion of the alcohol, but there will also be a high presence of water in the steam, since the boiling points are similar.

The liquid collected from the distillation and condensation will have an alcohol percentage greater than 50%. If this liquid is subjected to successive distillations, a concentrated alcohol solution can be achieved; but not pure, since the vapors will continue to drag water to a certain composition, forming what is known as an azeotrope

The liquid product of the fermentation of sugars has an alcohol percentage of 10%. This concentration can be brought to 50%, as in the case of Whiskey, by simple distillation.

Liquid-solid separation

A solution of a salt in water consists of a liquid that can be volatilized and a non-volatile compound with a high boiling point: salt.

By distilling the solution, pure water can be obtained in the condensation liquid. Meanwhile, at the bottom of the distillation flask the salts will settle.

Alcohol and glycerin

There is a mixture of ethyl alcohol, with a boiling point of 78.4ºC, and glycerin, with a boiling point of 260ºC. When subjected to simple distillation, the vapor formed will have a very high percentage of alcohol, close to 100%.

Therefore, a distilled liquid with a percentage of alcohol, similar to that of steam, will be obtained. This happens because the boiling points of liquids are very different.

References

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2. Whitten, Davis, Peck & Stanley. (2008). Chemistry. (8th ed.). CENGAGE Learning.
3. Dragani, Rachelle. (May 17, 2018). Three Examples of Simple Distillation Mixtures. Sciencing. Recovered from: sciencing.com
4. Helmenstine, Anne Marie, Ph.D. (January 02, 2019). What is Distillation? Chemistry Definition. Recovered from: thoughtco.com
5. Dr Welder. (sf). Simple Distillation. Recovered from: dartmouth.edu
6. University of Barcelona. (sf). Distillation. Recovered from: ub.edu