Dive Into Azeotropic Distillation: Essential Techniques


Distillation is a common technique of separation in the field of chemical engineering and organic chemistry. It entails separating constituents from one another by reference to their varying boiling points. The term azeotrope refers to a mixture of liquids that cannot be separated by simple distillation; this results from the fact that vapors formed during boiling contain the same proportions of liquids as the liquid itself, thus having constant boiling point.

In this blog, we will delve into azeotrope distillation looking at its principles, types and practical applications. Get set for some interesting science lessons!

What is an Azeotrope?

Azeotrope is a unique mixture of liquid. It has different behaviour from the ideal mixtures during distillation. In an azeotropic mixture, components form solution at a constant boiling point. Thus, both the vapour and the liquid phases have the same composition at the point of azeotropy, which does not follow Raoult’s Law. According to Raoult’s Law, vapor pressure of mixture is proportional to mole fractions of its components.

The formation of azetopes comes about due to non-ideal interactions between these constituents that can cause either positive or negative deviations from Raoult’s law”. The University of California Berkeley study says that up to 90% of binary mixtures will show these behaviors if they are subjected to specific conditions.

Simple Azeotrope Distillation

Types of Azeotropes (Positive and Negative)

Two types exist based on boiling points compared with their pure components; these are known as positive azeotrope and negative azeotropes. For instance, ethanol-water azeotrope boils at 78.2°C while that for pure ethanol and water boils respectively at 78.4°C and 100°C. In this case, it is seen that the predicted vapor pressure by Raoults law is lower than that observed in reality.

However, negative azeotropes have higher boiling points than their individual components such as toluene whose boiling point stands at 110.6°C against 84.1 °C for its corresponding azetorope). According to Raoults law, vapor pressures should be equal, but in this case it is not so.

TypeDefinitionBoiling PointExampleDeviation
Positive AzeotropeAzeotrope with a boiling point lower than any of its pure componentsLower than pure componentsEthanol-water azeotrope: 78.2°C (Ethanol: 78.4°C, Water: 100°C)Positive deviation (vapor pressure higher than Raoult’s law prediction)
Negative AzeotropeAzeotrope with a boiling point higher than any of its pure componentsHigher than pure componentsBenzene-water azeotrope: 80.1°C (Benzene: 80.1°C, Water: 100°C)Negative deviation (vapor pressure lower than Raoult’s law prediction)
Positive & Negative Azeotropes

Homogeneous vs. Heterogeneous Azeotropes

This classification is done based on how they appear after condensation or distillation; homogeneous ones result into single uniform liquid phase whereas heterogeneous ones separate into two distinct liquids phases once condensed or distilled”. Ethanol-water azeotrope is an example of homogeneous azetorope.

On the other hand, heterogeneous azeotropes separate into two different liquid phases when condensed. A vapor phase for a heterogeneous azetorope differs significantly from individual liquid phases as it can be evidenced in the water-toluene system. Therefore, upon condensation it forms two layers; one rich in water while the other is toluene-rich.

It is crucial to know whether an azetoropoe is either homogeneous or heterogeneous because presence of several liquid contents may make separation of require components difficult. If it was not known how these mixtures behave, developing processes that can efficiently separate them would be a difficult task. For instance, extractive distillation or pressure-swing distillation techniques have to be applied in order to overcome difficulties arising from separating such azetoropes by simple distillations alone.

rotary evaporator distillation

Practical Applications of Azeotropic Distillation

After having known the basics about azeotropes, let’s now see how different industries apply azeotropic distillation to separate such challenging mixtures. Chemical manufacturing and food and beverage production are among many methods that employ this powerful technique.

Chemical Industry Uses

The chemical industry uses the azeotropic distillation process extensively. It is employed when purifying solvents and producing high purity chemicals. For instance, dehydration of ethanol can be carried out through azeotropic distillation process. The ethanol forms an azeotrope with water at 95.6% ethanol concentration, creating a mixture of ethanol and water. Shifting the azeotropic point by adding another component like benzene leads to pure ethanol being separated from the mixture.

Pharmaceutical Applications

Azingropic distillation is very important in pharmaceutical industry. It is used in purification and recovery of valuable solvents for drug synthesis purposes. Many common solute pairs make up azetrophic mixtures including ethyl acetate – ethanol and methanol – acetone. Pharmaceutical companies can efficiently recycle these solvents by employing azetropic distillation knowledge in their separation processes which reduces loss and cost.

Food and Beverage Industry Applications

The use of zeotropic distillation method in the food industry helps in generating alcohol with high purities intended for soft drinks as well as food flavorings. In order to obtain anhydrous ethanol that will be used for alcohol beverages, there is big problem posed by the shape of an azetrope formed between ethonal-water.For example, fermentation of sugars usually results into mixture of water and ethanol thus getting pure ethanol from it becomes difficult due to breaking this azetrope different methods are applied during Azetrapic Distillations such as Extrative Distillations using glycerol as material separation agent or Pressure-Swing Distillations.

In 2019, global beverage grade ethanol production exceeded 23 billion liters, according to the International Center for Alcohol Policies. This means that efficient azeotropic distillation processes have a big role in the industry.

Employing Azeotropic Distillation Techniques with Rotary Evaporation

Rotary evaporation, commonly known as rotovap, is a versatile instrument for demonstrating and studying small-scale azeotropic distillation. It is an appropriate technique to exploit when separating liquid mixtures that form azeotropes. Azeotropes are mixtures having constant boiling points that are unseparated by fractional distillation method. The work of the rotary evaporator is to enable clear observation of the behavior of azeotropes and investigation of its principles.

There are several important parts in a rotary evaporator namely: rotating flask, heating bath, condenser and collection flask. The rotating flask containing the liquid mixture is partially submerged in the heating bath. When it rotates, it forms a thin film of this mixture on the inner side of this flask thereby increasing the surface area for evaporation.The resulting vapor passes through condenser where it is cooled and condensed back into liquid form, after which it is collected at collection flask.

rotovap distillation

Showcasing Azeotropes with Rotary Evaporator

Precise control over distillation conditions is possible due to uses of rotary evaporator in azeotropic distillation. You can optimize both evaporation rate and separation efficiency of azetropic mixture by regulating temperature of heating bath and rotation speed of the flasks.Meanwhile reduced pressure applied by the vacuum pump used with rotatory evaporator decreases boiling point for effective heat sensitive operation.

Rotary evaporators are excellent tools to introduce students to lab-scale examples of idealized behavior. For example, you can simply prepare an ethanol-water combination inside the rotary evaporator’s flask thus creating a simple example of an azeotrope.The composition hereof remains unchanged during distillation at 95.6% ethanol irrespective of how long you run your process.

Also demonstrated was what happens if benzene is added to the ethanol-water mixture as a third component. This causes a shift in distillate composition such that pure ethanol may be collected.

When you want to buy rotary evaporators of high quality for your ideal solutions studies or when performing dehydration experiments, check out the GWSI products. A well-known supplier of lab equipment, GWSI offers various rotary evaporators, cold traps, temperature control units and vacuum pumps. Their rotary evaporators are ISO9001 and CE certified so that accurate reaction data would come out from them and assist you in developing business further. Rotary evaporators manufactured by GWSI have a size range of 1 L to 50 L.Therefore they have high thermal stability making them last longer and provide maximum output for your azotropic distillation research.


Taking everything into account, azeotropic distillation is an excellent method for separating mixtures of liquids that form azeotropes. We can effectively remove impurities from chemicals, solvents and other important materials when we comprehend these things: how azeotropes are formed and the various classes under which they fall.

From chemical industry through pharmaceuticals to food production, recovery by means of azeotropic distillation is crucial for obtaining ultra-pure components. On top of easy demonstration and study of such phenomena using lab equipment like rotary evaporators.

With all the knowledge and techniques discussed in this article you have what it takes to tackle any challenges presented in your way to accomplishing successful azetropic distillations.


Why is Azeotropic Distillation Preferred for Certain Mixtures?

Azeotropic distillation separates mixtures that enter azeotrope, i.e., two compounds forming a mixture that satisfies certain conditions. In such cases simple distillation methods do not work. The constant boiling point mixture and vapor-liquid equilibrium of azeotropes make it impossible to separate the components on the basis of their individual volatilities. Thus, a third component may be introduced in azeotropic distillation, or pressure changes may be used to change the azeotropic composition; this helps separate the desired substances. This range of techniques are particularly advantageous when dealing with mixtures deviating significantly from Raoult’s law.

Azeotrope Distillation

Can Azeotropes Be Separated by Simple Distillation?

No! Simple distillation cannot break down azeotropes as they exist in constant-boiling solutions where vapor-liquid equilibrium is fixed at one specific composition. The vapor and liquid phases have identical compositions precisely at azetrophic points in an azetrope mixture. This is why they cannot be separated under ordinary distillation methods even if fractionating columns are used. Breaking the azeotrope and enabling further separation requires special processes like extractive distillations or azeotropic distillations.

How do vapor and liquid phases differ in azeotropic mixtures?

The vapour and liquid phases of any given solution are identical at its azetropic point due to non ideal behaviour between the components resulting in deviations from Raoult’s law. Vapor pressure exceeds predictions for some positive deviation from Raoult’s law system that shows lower temperature boiling point while negative deviation leads vapor pressures lower than predicted producing unusually higher boiling points; thus differentiating them from other systems with similar characteristics but not exactly identical ones . It is this condition where there is no difference between vapor and liquid phases, which is why azeotropic mixtures cannot be separated by simple distillation.

What is extractive distillation and how is it different from azeotropic distillation?

Azeotropic distillation and extractive distillation are sophisticated methods for separating azeotropes but they differ in their mode of operation and the kind of entraining agent employed.

In extractive distillations, a high boiling solvent is mixed with an azetropic mixture. In this case, the solvent changes the relative volatility of the components. The vapor liquid equilibrium behavior changes because the solvent interacts differently with each component. As such, without forming new azeotropes, this makes it possible to separate the original substances from each other. An extractive agent typically refers to a polar solvent which is selective toward one component among others in an azetrope system. Nitric acid is used as extractive agent for separation of ethanol-water systems.

On the other hand, in azeotropic distillations an entrainer that forms another azeotrope containing one or more of the original components is added to themixture. The choice of entrainer depends on its miscibility with one component and immiscibility with another component. Ternary exists whereby binary itself does not exist when there is presence of immiscible third element. Normal processes can be used to separate this new composition; thus allowing complete removal by stripping once again leaving behind purified components free from impurities brought about by entrainers.The most important criteria in designing efficient azeotropic distillations are: proportions of unboiled mixture’s constituents and maximum boiling point vapor composition

To summarize, extractive distillation is a process that involves the use of a high boiling solvent to alter the relative volatilities of the constituents in any mixture. Simultaneously, azeotropic distillation applies an entrainer to produce a new azeotrope that can be separated by conventional methods. Both techniques are powerful separation tools for azeotropic mixtures. The preferred system and aims determine either of them selected.

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