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Concept
Reflux
Summary
Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions over a long period of time.
The term reflux is very widely used in industries that utilize large-scale distillation columns and fractionators such as petroleum refineries, petrochemical and chemical plants, and natural gas processing plants.
In that context, reflux refers to the portion of the overhead liquid product from a distillation column or fractionator that is returned to the upper part of the column as shown in the schematic diagram of a typical industrial distillation column. Inside the column, the downflowing reflux liquid provides cooling and condensation of the upflowing vapors thereby increasing the efficiency of the distillation column.
The more reflux provided for a given number of theoretical plates, the better is the column's separation of lower boiling materials from higher boiling materials. Conversely, for a given desired separation, the more reflux is provided, the fewer theoretical plates are required.
A mixture of reactants and solvent is placed in a suitable vessel, such as a round bottom flask. This vessel is connected to a water-cooled condenser, which is typically open to the atmosphere at the top. The reaction vessel is heated in order to boil the reaction mixture; vapours produced from the mixture are condensed by the condenser, and return to the vessel through gravity. The purpose is to thermally accelerate the reaction by conducting it at an elevated, controlled temperature (i.e. the solvent's boiling point) and ambient pressure without losing large quantities of the mixture.
The diagram shows a typical reflux apparatus. It includes a water bath to indirectly heat the mixture. As many solvents used are flammable, direct heating with a Bunsen burner is not generally suitable, and alternatives such as a water bath, oil bath, sand bath, electric hot plate or heating mantle are employed.
Official source
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