We explain what distillation is, examples of this separation method and the types of distillation that can be used.
Distillation uses vaporization and condensation to separate mixtures.
What is distillation?
Distillation is a method of separation of phases, also called mixture separation methods, which consists of the consecutive and controlled use of two other physical processes: vaporization (or evaporation) and condensation, using them selectively to separate the ingredients of a mixture generally of a homogeneous type, i.e., in which their elements cannot be distinguished at first glance.
Mixtures susceptible to distillation may contain two liquids, a solid in a liquid or even liquefied gases, since this method takes advantage of the boiling point of substances, one of the inherent characteristics of matter.
The boiling point is then the precise temperature at which a liquid becomes gas (i.e. evaporates).
Thus, in order for the distillation to be carried out correctly, the mixture must be boiled until it reaches the boiling point of one of the constituent substances, which will then become steam and can be taken to a cooled container, in which to condense and recover its liquidity.
The other integral substance, on the other hand, will remain in the container without alterations; but in both cases we will have pure substances, free of the initial mixture.
You can use: Filtration.
Examples of distillation
Coal uses dry distillation to obtain liquid organic fuels.
Oil refining. The separation of the various hydrocarbons present in the oil is carried out by fractional distillation, storing each compound derived from the cooking of crude oil in separate layers or compartments. These gases rise and condense in upper layers, while denser substances such as asphalt and paraffin remain.
Catalytic cracking. This is the name given to certain vacuum distillations common in oil processing, using vacuum towers to separate the cooking gases from the crude oil. This accelerates the boiling of the hydrocarbons and speeds up the process.
Ethanol purification. To separate alcohols such as ethanol from water during laboratory production, an azeotropic distillation is used, adding benzene or other components to the mixture that promote or accelerate separation, and which can then be easily removed without altering the chemistry of the product.
Coal processing. To obtain liquid organic fuels, charcoal or wood is used by dry distillation processes: in this way the gases emitted during combustion can be condensed.
Thermolysis of mineral salts. By means of dry distillation diverse mineral substances of high industrial utility are obtained, from the emanation and condensation of gases obtained when burning mineral salts.
The still. This is the name given to a device invented in Arab antiquity, whose purpose is to produce perfumes, medicines and alcohol from fermented fruits. The principles of distillation are used in its operation: substances are heated in a small boiler and the gases produced are cooled in a coil that leads to another container.
Production of perfumes. The steam distillation is used to obtain perfumes, boiling water together with preserved flowers, to produce a gas full of the desired odor, and then condensed can be used as a base liquid in the perfumes.
Types of distillation
Distillation can occur in a variety of ways:
Simple distillation. The most elementary is to boil the mixture until the elements are separated. However, it does not guarantee the total purity of the distilled substance.
Fractional distillation. It is carried out by means of a fractionation column: different plates on which evaporation and condensation take place successively, guaranteeing a greater purity in the result.
Vacuum distillation. Using the vacuum pressure generated, the process is catalyzed to reduce the boiling point of the ingredients by half.
Azeotropic distillation. That necessary to break an azeotrope, that is, a mixture whose substances behave as one, even sharing the boiling point. It includes the presence of separating agents, all according to Raoult’s Law.
Steam distillation. The volatile and non-volatile components of a mixture are separated by direct injection of water vapour.
Dry distillation. It consists of heating solid materials without the presence of liquid solvents, obtaining gases and then condensing them in another container.
Improved distillation. Also called alternative or reactive distillation, they are adapted to the specific cases of mixtures difficult to separate or of a same boiling point.