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an abnormal backward flow of body fluids
pour or rush back; "The blood regurgitates into the heart ventricle"
repeat after memorization; "For the exam, you must be able to regurgitate the information" (同)reproduce
feed through the beak by regurgitating previously swallowed food; "many birds feed their young by regurgitating what they have swallowed and carried to the nest"

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〈食物〉‘を'吐く / 食物をもどす;逆流させる

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/05/08 00:49:04」(JST)

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This article is about using reflux in chemical engineering and chemistry. For other usage, see Reflux (disambiguation).

The reflux system in a typical industrial distillation column

Reflux is a distillation 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.

Reflux in industrial distillation

The term reflux ^[1]^[2] 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.

Reflux to apply energy to chemical reactions

Laboratory reflux apparatus for adding energy to a chemical reaction

A liquid reaction mixture is placed in a vessel open only at the top. This vessel is connected to a Liebig or Vigreux condenser, such that any vapours given off are cooled back to liquid, and fall back into the reaction vessel. The vessel is then heated vigorously for the course of the reaction. The purpose is to thermally accelerate the reaction by conducting it at an elevated temperature (i.e. the solvent's boiling point).

The advantage of this technique is that it can be left for a long period of time without the need to add more solvent or fear of the reaction vessel boiling dry as any vapour is immediately condensed in the condenser. In addition, as a given solvent will always boil at a certain temperature, one can be sure that the reaction will proceed at a constant temperature. By careful choice of solvent, one can control the temperature within a very narrow range. The constant boiling action also serves to continuously mix the solution, although a magnetic stirring rod mechanism is often used to achieve a uniform solution. This technique is useful for performing chemical reactions under controlled conditions that require substantial time for completion.

The diagram shows a typical reflux apparatus for applying energy to chemical reactions. It includes an optional beaker of water between the reactants and the heat. This is often used as a safety precaution when using flammable reactants and a Bunsen burner in order to keep the flame away from the reactants. In modern laboratories, open flames are avoided due to the many flammable solvents often in use, and electrical heating, (i.e., with a hot plate or mantle) is preferred. Furthermore, a high boiling, thermally stable silicone oil is generally used to immerse the reaction vessel, rather than water which evaporates too readily to be useful for lengthy reactions. Using an oil bath, temperatures of up to several hundred degrees can easily be achieved, which is higher than the boiling point of most commonly used solvents. If even higher temperatures are required, the oil bath can be replaced with a sand bath.

Reflux in laboratory distillation

Laboratory apparatus using reflux to supply energy to chemical reactions. An Erlenmeyer flask is used as a receiving flask. Here the distillation head and fractionating column are combined in one piece.

The apparatus shown in the diagram represents a batch distillation as opposed to a continuous distillation. The liquid feed mixture to be distilled is placed into the round-bottomed flask along with a few anti-bumping granules, and the fractionating column is fitted into the top. As the mixture is heated and boils, vapor rises up the column. The vapor condenses on the glass platforms (known as plates or trays) inside the column and runs back down into the liquid below, thereby refluxing the upflowing distillate vapor. The hottest tray is at the bottom of the column and the coolest tray is at the top. At steady state conditions, the vapor and liquid on each tray is at equilibrium. Only the most volatile of the vapors stays in gaseous form all the way to the top. The vapor at the top of the column then passes into the condenser, where it cools until it condenses into a liquid. The separation can be enhanced with the addition of more trays (to a practical limitation of heat, flow, etc.). The process continues until all the most volatile components in the liquid feed boil out of the mixture. This point can be recognized by the rise in temperature shown on the thermometer. For continuous distillation, the feed mixture enters in the middle of the column.

Reflux in beverage distillation

By controlling the temperature of the condenser, a reflux still may be used to ensure that higher boiling point components are returned to the flask while lighter elements are passed out to a secondary condenser. This is useful in producing high quality alcoholic beverages, while ensuring that less desirable components (such as fusel alcohols) are returned to the primary flask. For high quality neutral spirits (such as vodka), or post distillation flavored spirits, a process of multiple distillations or charcoal filtering may be applied to obtain a product lacking in any suggestion of its original source material for fermentation.

References

^ Kister, Henry Z. (1992). Distillation Design (1st Edition ed.). McGraw-Hill. ISBN 0070349096.
^ Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook (6th Edition ed.). McGraw-Hill. ISBN 0070494797.

External links

Distillation column components

Gallery

Toluene is refluxed with sodium-benzophenone desiccant before it is distilled to give pure oxygen- and water-free toluene.
Industrial fractionating columns all of which use reflux
Organic synthesis apparatus using reflux

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