Reflux condenser

Condenser (laboratory)

In a laboratory, a condenser is a piece of laboratory glassware used to cool hot vapors or liquids. A condenser usually consists of a large glass tube containing a smaller glass tube running its entire length, within which the hot fluids pass.

The ends of the inner glass tube are usually fitted with ground glass joints which are easily fitted with other glassware. The upper end is usually left open to the atmosphere, or vented through a bubbler, or a drying tube to prevent the ingress of water or oxygen.

The outer glass tube usually has two hose connections, and a coolant (usually tap water or chilled water/anti-freeze mixture) is passed through it. For maximum efficiency, the cold water always enters through the bottom fitting, and exits through the top fitting. Multiple condensers may be connected in series. Normally a high flow rate is not necessary to maintain a cooling surface.

Applications

Condensers are often used in reflux, where the hot solvent vapors of a liquid being heated are cooled and allowed to drip back. This reduces the loss of solvent allowing the mixture to be heated for extended periods.

Condensers are used in distillation to cool the hot vapors, condensing them into liquid for separate collection. For fractional distillation, an air or Vigreux condenser is usually used to slow the rate at which the hot vapors rise, giving a better separation between the different components in the distillate.

For microscale distillation, there are commercially available apparatus which include the "pot", the Claisen head, and the condenser fused into one-piece. This reduces the hold-up volume, and obviates the need for ground glass joints preventing contamination by grease and air leaks.

Air-cooled

Air condenser

An air condenser is the simplest sort of condenser. There is only one tube, and the heat of the fluid is conducted to the glass, which is cooled by air. It is related to the retort used by alchemists. The air condenser is usually used for fractional distillation, and it can be packed with some material such as glass beads, metal pieces, or Raschig rings to increase the number of effective plates.

Vigreux condenser

A Vigreux condenser is a modification of the air condenser. It is usually used as a fractionating column for fractional distillations. Unlike straight-walled columns, a Vigreux column has a series of downward-pointing indentations on the inside wall which serve to dramatically increase the surface area without increasing the length of the condenser. Because of their added complexity, Vigreux columns also tend to be considerably more expensive than traditional straight-walled designs.

Water-cooled

Liebig condenser

The Liebig condenser is the most basic water-cooled design. The inner-tube is straight, making it cheaper to manufacture. Though named after the German chemist Justus Baron von Liebig, he cannot be given credit for having invented it because it was already in use for some time before him. However, it is believed that he popularized the device.

The true inventors, all of them inventing it independently, were the German chemist Christian Ehrenfried Weigel in 1771, the French scientist, P. J. Poisonnier, in 1779 and the Finnish chemist Johan Gadolin in 1791.

Liebig himself incorrectly attributed the design to the German pharmacist Johann Göttling who had made improvements to the Weigel design in 1794.

The Liebig condenser is much more efficient than a simple retort due to its use of liquid cooling. Water can absorb much more heat than the same volume of air, and its constant circulation through the water jacket keeps the condenser's temperature constant. Therefore a Liebig condenser can condense a much greater flow of incoming vapour than an air condenser or retort.

Graham condenser

A Graham condenser has a spiral coil running the length of the condenser. There are two possible configurations for a Graham condenser. In the first, the spiral contains the coolant, and the condensation takes place on the outside of the spiral. This configuration maximizes flow capacity since vapors can flow over and around the spiral.

In the second configuration, the jacket tube contains the coolant, and the condensation takes place inside the spiral. This configuration maximizes collected condensate, since all the vapors must flow through the entire length of the spiral, thus having prolonged contact with the coolant.

Dimroth condenser

Dimroth condenser is somewhat similar to the Graham condenser. It has an internal double spiral for the cooling medium so that both the coolant inlet and outlet is at the top. The vapors travel through the jacket from bottom to top. Dimroth condensers are more effective than conventional coil condensers. They are often found in rotary evaporators. It is named after Otto Dimroth.

Allihn condenser

The Allihn condenser or bulb condenser or simply reflux condenser is named after Felix Richard Allihn.

The Allihn condenser consists of a long glass tube with a water jacket. There is a series of large and small constrictions on the inside tube, each increasing the surface area upon which the vapor constituents may condense. Ideally suited for laboratory-scale refluxing.

Friedrichs condenser

A Friedrichs condenser (sometimes Friedrich condenser), also known as a spiraled finger condenser, consists of a large, spiraled internal cold finger-type capillary tube disposed within a wide cylindrical housing. Coolant flows through the internal cold finger; accordingly, vapors rising up through the housing may condense on the cold finger as it is cooled. Compared to a Graham condenser of similar dimension, which also includes a spiral internal tube, the Friedrich condenser often provides more efficient condensing because the Friedrich condenser provides greater effective surface area for cooling. That is, vapors may be cooled not only by the coolant flowing through the internal cold finger, but also by the interior wall of the cylindrical housing.

The spiral cold finger-type apparatus now known as the Friedrichs condenser was invented by Fritz Walter Paul Friedrichs, who published a design for this type of condenser in 1912.

Other coolants

The above water cooled condensers called be used with other chilled liquids such as refrigerated ethanol which can be thermostatically cooled in a recycling pump unit. These condensers can cool below 0 oC, and so might be used if for example one wishes to heat a reaction to reflux in say dimethyl ether which boils at about -20 oC.

Solid dry ice or acetone/dry ice mixture can also be used as a coolant in a cold finger as a coolant.

Gallery

References

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