azeotropic distillation


Also found in: Wikipedia.

azeotropic distillation

[¦āz·ē·a‚trō·pik ‚dis·tə′lā·shən]
(chemical engineering)
A process by which a liquid mixture is separated into pure components with the help of an additional substance or solvent.

Azeotropic distillation

Any of several processes by which liquid mixtures containing azeotropes may be separated into their pure components with the aid of an additional substance (called the entrainer, the solvent, or the mass separating agent) to facilitate the distillation. Distillation is a separation technique that exploits the fact that when a liquid is partially vaporized the compositions of the two phases are different. By separating the phases, and repeating the procedure, it is often possible to separate the original mixture completely. However, many mixtures exhibit special states, known as azeotropes, at which the composition, temperature, and pressure of the liquid phase become equal to those of the vapor phase. Thus, further separation by conventional distillation is no longer possible. By adding a carefully selected entrainer to the mixture, it is often possible to “break” the azeotrope and thereby achieve the desired separation.

Entrainers fall into at least four distinct categories that may be identified by the way in which they make the separation possible. These categories are: (1) liquid entrainers that do not induce liquid-phase separation, used in homogeneous azeotropic distillations, of which classical extractive distillation is a special case; (2) liquid entrainers that do induce a liquid-phase separation, used in heterogeneous azeotropic distillations; (3) entrainers that react with one of the components; and (4) entrainers that dissociate ionically, that is, salts. See Salt-effect distillation

Within each of these categories, not all entrainers will make the separation possible, that is, not all entrainers will break the azeotrope. In order to determine whether a given entrainer is feasible, a schematic representation known as a residue curve map for a mixture undergoing simple distillation is created. The path of liquid compositions starting from some initial point is the residue curve. The collection of all such curves for a given mixture is known as a residue curve map (see illustration). These maps contain exactly the same information as the corresponding phase diagram for the mixture, but they represent it in such a way that it is more useful for understanding and designing distillation systems.

Schematic representation of the residue curve maps for ternary mixtures with one minimum- boiling binary azeotropeenlarge picture
Schematic representation of the residue curve maps for ternary mixtures with one minimum- boiling binary azeotrope

Mixtures that do not contain azeotropes have residue curve maps that all look the same. The presence of even one binary azeotrope destroys the structure. If the mixture contains a single minimum-boiling binary azeotrope, three residue curve maps are possible, depending on whether the azeotrope is between the lowest- and highest-boiling components, between the intermediate- and highest-boiling components, or between the intermediate- and lowest-boiling components.

Nonazeotropic mixtures may be separated into their pure components by using a sequence of distillation columns because there are no distillation boundaries to get in the way. The situation is quite different when azeotropes are present, as can be seen from the illustration. It is possible to separate mixtures that have residue curve maps similar to those shown in illus. a and c by straightforward sequences of distillation columns. This is because these maps do not have any distillation boundaries. These, and other feasible separations for more complex mixtures, are referred to collectively as homogeneous azeotropic distillations. Without exploiting some other effect (such as changing the pressure from column to column), it is impossible to separate mixtures that have residue curve maps like illus. b.

A large number of mixtures have residue curve maps similar to illus. c, and therefore the corresponding distillation is given the special name extractive distillation.

Heterogeneous entrainers cause liquid-liquid phase separations to occur in such a way that the composition of each phase lies on either side of a distillation boundary. In this way, the entrainer allows the separation to “jump” over a boundary that would otherwise be impassable.

References in periodicals archive ?
During the initial stage of the polymerization, the temperature was maintained at 80-110[degrees]C, the reaction mixture was heated under reflux for 20 min, and the water generated during the formation of the phen-ate was essentially removed from the reaction mixture by azeotropic distillation.
Nest, the resulted precipitate was dehydrated by benzene azeotropic distillation," she added, saying, "After calcination, the obtained powder was consisted of approximately uniform nanocrystals.
2002), (b) chemical trapping, (c) inert gas passage, and (d) azeotropic distillation (Olah et al.
Gel Sciences is also developing applications for Engineered Response(TM) and Smart Lyogel(TM) responsive polymers in adhesives, paints and coatings, oil field fluids, azeotropic distillation, and laboratory scale separations in conjunction with major OEM partners.
Then, in a process called azeotropic distillation, he separated cyclodextrin from the cyclododecanone--which could then be reused.
He has published over 220 technical papers in the area of process control and design (8 in the area of azeotropic distillation alone).
reactive distillation , three-phase distillation, heterogeneous azeotropic distillation, etc.
Hands-on guidance for the design, control, and operation of azeotropic distillation systems
Practical in focus, the book fully details the design, control, and operation of azeotropic distillation systems, using rigorous steady-state and dynamic simulation tools.
Our technical expertise includes binary and multicomponent distillation, extractive distillation, azeotropic distillation, reactive distillation, liquid-liquid extraction, absorption, stripping, heat transfer, fluid flow, instrumentation and controls.
The drying of ethanol is one of the hardest and most critical parts of fuel ethanol production and GEA Wiegand has pioneered key technology developments and methods such as molecular sieves, pervaporation membranes, and azeotropic distillation to remove water from raw alcohol.
Vital to the success of the joint venture is its prominent expertise in separations technologies, including fractional distillation, extractive distillation, azeotropic distillation, liquid-liquid extraction, reactive distillation, absorption, stripping and acid gas removal.