In chemistry, a condenser is laboratory apparatus used to condense vaporsthat is, turn them into liquidsby cooling them down.
Condensers are routinely used in laboratory operations such as distillation, reflux, and extraction. In distillation, a mixture is heated until the more volatile components boil off, the vapors are condensed, and collected in a separate container. In reflux, a reaction involving volatile liquids is carried out at their boiling point, to speed it up; and the vapors that inevitably come off are condensed and returned to the reaction vessel. In Soxhlet extraction, a hot solvent is infused onto some powdered material, such as ground seeds, to leach out some poorly soluble component; the solvent is then automatically distilled out of the resulting solution, condensed, and infused again.
Many different types of condensers have been developed for different applications and processing volumes. The simplest and oldest condenser is just a long tube through which the vapors are directed, with the outside air providing the cooling. More commonly, a condenser has a separate tube or outer chamber through which water (or some other fluid) is circulated, to provide a more effective cooling.
Laboratory condensers are usually made of glass for chemical resistance, for ease of cleaning, and to allow visual monitoring of the operation; specifically, borosilicate glass to resist thermal shock and uneven heating by the condensing vapor. Some condensers for dedicated operations (like water distillation) may be made of metal. In professional laboratories, condensers usually have ground glass joints for airtight connection to the vapor source and the liquid receptacle; however, flexible tubing of an appropriate material is often used instead. The condenser may also be fused to a boiling flask as a single glassware item, as in the old retort and in devices for microscale distillation.
History The water-cooled condenser, which was popularized by Justus von Liebig, was invented by Weigel, Poisonnier, and Gadolin, and perfected by Göttling, all in the late 18th century. Several designs that are still in common use were developed and became popular in the 19th century, when chemistry became a widely practiced scientific discipline.
General principles Designing and maintaining systems and processes using condensers requires that the heat of the entering vapor never overwhelm the ability of the chosen condenser and cooling mechanism; as well, the thermal gradients and material flows established are critical aspects, and as processes scale from laboratory to pilot plant and beyond, the design of condenser systems becomes a precise engineering science.
Temperature In order for a substance to condense from a pure vapor, the pressure of the latter must be higher than the vapor pressure of the adjacent liquid; that is, the liquid must be below its boiling point at that pressure. In most designs, the liquid is only a thin film on the inner surface of the condenser, so its temperature is essentially the same as of that surface. Therefore, the primary consideration in the design or choice of a condenser is to ensure that its inner surface is below the liquid's boiling point.
Heat flow As the vapor condenses, it releases the corresponding heat of vaporization, that tends to raise the temperature of the condenser's inner surface. Therefore, a condenser must be able to remove that heat energy quickly enough to keep the temperature low enough, at the maximum rate of condensation that is expected to occur. This concern can be addressed by increasing the area of the condensation surface, by making the wall thinner, and/or by providing a sufficiently effective heat sink (such as circulating water) on the other side of it.
Material flow The condenser must also be dimensioned so that the condensed liquid can flow out at the maximum rate (mass over time) that the vapor is expected to enter it. Care must also be taken to prevent the boiling liquid to enter the condenser as splattering from explosive boiling, or droplets created as bubbles pop.
Carrier gases Additional considerations apply if the gas inside the condenser is not pure vapor of the desired liquid, but a mixture with gases that have a much lower boiling point (as may occur in dry distillation, for example). Then the partial pressure of its vapor must be considered when obtaining its condensation temperature. For example, if the gas entering the condenser is a mixture of 25% ethanol vapor and 75% carbon dioxide (by moles) at 100 kPa (typical atmospheric pressure), the condensation surface must be kept below 48 °C, the boiling point of ethanol at 25 kPa.
Moreover, if the gas is not pure vapor, condensation will create a layer of gas with even lower vapor contents right next to the condensing surface, further lowering the boiling point. Therefore, the condenser's design must be such that the gas is well-mixed and/or that all of it is forced to pass very close to the condensation surface.
Liquid mixtures Finally, if the input to the condenser is a mixture of two or more miscible liquids (as is the case in fractional distillation), one must consider the vapor pressure and the percentage of the gas for each component, which depends on the composition of the liquid as well as its temperature; and all these parameters typically vary along the condenser.
Coolant flow direction Most condensers can be divided in two broad classes.
The concurrent condensers receive the vapor through one port and deliver the liquid through another port, as required in simple distillation. They are usually mounted vertically or tilted, with the vapor input at the top and the liquid output at the bottom.
The countercurrent condensers are intended to return the liquid toward the source of the vapor, as required in reflux and fractional distillation. They are usually mounted vertically, above the source of the vapor, that enters them from the bottom. In both cases, the condensed liquid is allowed to flow back to the source by its own weight.
The classification is not exclusive, since several types can be used in both modes.
Historical condensers Straight tube
The simplest type of condenser is a straight tube, cooled only by the surrounding air. The tube is held in a vertical or oblique position, and the vapor is fed through the upper end. The heat of condensation is carried away by convection.
The neck of the retort is a classical example of a straight tube condenser. However, this kind of condenser may also be a separate piece of equipment. Straight tube condensers are no longer widely used in research laboratories, but may be used in special applications and simple school demonstrations.
Still head
The still head is another ancient type of air-cooled condenser. It consists of a roughly globular vessel with an opening at the bottom, through which the vapor is introduced. The vapor condenses on the inner wall of the vessel, and drips along it, collecting at the bottom of the head and then draining through a tube to a collecting vessel below. A raised lip around the input opening prevents the liquid from spilling through it. As in the tube condenser, the heat of condensation is carried away by natural convection. Any vapor that does not condense in the head may still condense in the neck.
Still head type condensers are now rarely used in laboratories, and are usually topped by some other type of reflux condenser where most of the condensation takes place.
Modern condensers
Liebig
The Liebig condenser is the simplest design with circulating coolant, easy to build and inexpensive. It is named after Justus von Liebig,Kahlbaum, Georg W. A. (1896) "Der sogenannte Liebig'sche Kühlapparat" (The so-called Liebig condenser), Berichte der Deutschen Chemischen Gesellschaft, 29 : 69–71.Speter, Max (1908) "Geschichte der Erfindung des "Liebig'schen Kühlapparat" (The history of the invention of the "Liebig" condenser), Chemiker Zeitung, 32 (1) : 3–5.Schelenz, Hermann, Zur Geschichte der Pharmazeutisch-Chemischen Destilliergerate [On the history of pharmaceutical [and] chemical distillation apparatuses], (Berlin, Germany: Julius Springer, 1911), pp. 84-88. who perfected an earlier design by WeigelChristian Ehrenfried Weigel (1771), Observationes chemicae et mineralogicale (Göttingen; in Latin). The condenser's construction is explained on pp. 8–9 and in a footnote on page 11; the illustration is Fig. 2 on the last page of the book. and GöttlingJohann Friedrich Göttling (1794), "Beschreibung einer sehr bequemen Kühlanstalt bey Destillationenen aus der Blase" (Description of a very convenient cooling apparatus [for use] during distillations from retorts), Taschenbuch für Scheidekünstler und Apotheker (Pocket book for [chemical] analysts and apothecaries), 15th ed. (Hoffmannische Buchhandlung, Weimar), pp. 129–135. and popularized it. It consists of two concentric straight glass tubes, the inner one being longer and protruding at both extremities. The ends of the outer tube are sealed (usually by a blown glass ring seal), forming a water jacket, and is fitted with side ports near the ends for cooling fluid inflow and outflow. The ends of the inner tube, that carries the vapor and condensed liquid, are open.
Compared to the simple air-cooled tube, the Liebig condenser is more efficient at removing the heat of condensation and at maintaining the inner surface at a stable low temperature.
West The West condenser is variant of the Liebig type, with a more slender design, with cone and socket. The fused-on narrower coolant jacket may render more efficient cooling with respect to coolant consumption.
Allihn The Allihn condenser or bulb condenser is named after Felix Richard Allihn (1854–1915).Allihn, F. (1886) "Rückflusskühler für analytische Extractions-Apparate" (Reflux condenser for analytical extraction apparatuses), Chemiker Zeitung (Chemist's Newspaper), 10 (4) : 52.Allihn, F. (1886) "Rückflusskühler für analytische Extractionsapparate" (Reflux condenser for analytical extraction apparatuses), Zeitschrift für analytische Chemie, 25 : 36. The Allihn condenser consists of a long glass tube with a water jacket. A series of bulbs on the tube increases the surface area upon which the vapor constituents may condense. Ideally suited for laboratory-scale refluxing; indeed, the term reflux condenser often means this type specifically.
Davies A Davies condenser, also known as a double surface condenser, is similar to the Liebig condenser, but with three concentric glass tubes instead of two. The coolant circulates in both the outer jacket and the central tube. This increases the cooling surface, so that the condenser can be shorter than an equivalent Liebig condenser. According to Alan Gall, archivist of the Institute of Science and Technology, Sheffield, England, the 1981 catalog of Adolf Gallenkamp & Co. of London (makers of scientific apparatus) states that the Davies condenser was invented by James Davies, a director of the Gallenkamp company.John Andraos, Comments received from named scientists, 2005 e-mail from Gall, p. 28; posted at: CareerChem. In 1904, Gallenkamp was offering "Davies' Condensers" for sale:."Messrs. A. Gallenkamp and Co., Limited," Pharmaceutical Journal, 72 : 691 (21 May 1904). In 1920, Gallenkamp listed "J. Davies" as a director of the company.(Advertisement by Gallenkamp), Nature, 104 : ccciv (5 February 1920).
Graham A Graham or Grahams condenser has a coolant-jacketed spiral coil running the length of the condenser serving as the vapor–condensate path. This is not to be confused with the coil condenser. The coiled condenser tubes inside will provide more surface area for cooling and for this reason it is most favorable to use but the drawback of this condenser is that as the vapors get condensed, it tends to move them up in the tube to evaporate which will also lead to the flooding of solution mixture.