Basic Principle and Methodology of Flash and Fractional Distillation : Pharmaguideline -->

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Basic Principle and Methodology of Flash and Fractional Distillation

Flash distillation uses vaporization to separate the compounds. Hot liquid mixtures get vaporized when pass from high-pressure to low pressure zone.

Flash Distillation


Flash distillation uses vaporization to separate the compounds. Hot liquid mixtures get vaporized in flash vaporization when they pass from high-pressure zones to low-pressure zones. Liquid vaporizes as pressure is reduced, which reduces the boiling point. The process of vaporization leads to a decrease in temperature as the liquid vaporizes. Vapour molecules with low boiling points become condensed while vapour molecules with high boiling points remain in the vapour phase. These two phases are in contact until saturation occurs. Vapours are allowed to condense further at the bottom, while liquids fall to the bottom and are collected.


Pumping liquid mixtures through heaters raises their temperature and enthalpy. After flowing through a valve, the liquid is partially vaporized as the pressure is reduced. The liquids and vapours separate when they reach a large enough volume, the "flash drum". Due to the close proximity of the vapours and the liquid, the "flash" occurs, and the phases of the product approach equilibrium. Both continuous and multi-level operation are possible. During operation, all inputs are synchronized to outputs, such that the proportions of vapour and liquid in the flash drum remain constant at all times.


  • This chemical is used in the refining of crude oil.
  • By multi-stage flash distillation, it is used to desalinate ocean water.
  • Separating heptane from octane is also possible with this apparatus.

Fractional Distillation


Dissolved liquids are separated through fractional distillation, which entails the separation of miscible liquids. Recurrent distillation and condensation are usually used to separate the mixture into its constituent parts. During heating, fractions of the mixture begin to vaporize, causing separation. Different liquids boil and evaporate at different temperatures, which is the basic principle behind this type of distillation. Due to its low boiling point, the substance with the lowest boiling point is the first to evaporate when the mixture is heated.


The fractional distillation process does not require many apparatuses. Distilling flasks, condensers, receivers, fractionating columns, thermometers and means of heating are included.

The apparatus is set up in such a way that a mixture of two highly volatile miscible liquids A and B is prepared. The solution is added to the distilling flask while the fractionating column is mounted at the tip of the flask. A slow heat is applied to the solution to increase its temperature. In the flask, vapours rise as the mixture begins to boil. Volatile components A are present in this sample. After passing through the fractionating column, the vapors are cooled to form a liquid in the condenser. In the process, the two mixtures are continuously vaporized and condensed until they are completely separated.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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