the term azeotrope coined by John Wade and Richard William Merriman in 1911 was derived first by combining the prefix “a,” which means “no,”. it is a Greek term that is derived from boiling and turning. An azeotrope or azeotropic mixture is a mixture of liquids containing two or more components with a unique composition of chemical compounds. it is often called an azeotropic mixture too.
the azeotropic mixture boils at constant temperature and behaves like a single component and boiling the phase of vapor indicates the same liquid phase composition. this phenomenon help to obtain the advantages that a mixture or pure substance with a single component can be handled and stored with lots of ease
usually, an azeotrope mixture have a constant and fixed boiling point and also behaves like a liquid when passing through a vaporous state due to having single component in it. we can control the boiling point at a higher, lower, or intermediate state of the mixture by adding azeotrope.
the cool thing is that the amount of initial composition of constituents of mixtures remains the same at the end. the only thing that providing high steam, constituent possibly will not separate easily by using simple distillation.
Types of azeotropes
Azeotropes can be divided into three types based on their constituents, miscibility, or boiling points:
- No. of constituents or components: if two liquids are mixed to form an azeotrope, it is called binary azeotrope. however, some are made with three or more than three constituents. three constituents made ternary azeotropes, etc.
- Heterogeneous or Homogeneous Azeotropes: if the liquids participate in Azeotropes are miscible, they form solution while, if the liquids are present in two phases, they are called incompletely miscible. hence, the Azeotropes made through incompletely miscible are known as Heterogeneous azeotropes.
- Positive or negative Azeotropes: if the boiling point of the mixture is lower than the boiling point of the constituent element, it forms a positive azeotrope having a minimum boiling point while the vice versa is known as a negative azeotrope. note that Each azeotrope has a characteristic boiling point.
Examples of Azeotrope
- Nitric acid (68.4%)/water, boils at 122 ° C.
- Hydrogen chloride (20%)/water
- Hydrofluoric acid (35.6%)/water, boils at 111.35 ° C (negative azeotrope).
- Perchloric acid (28.4%)/water, boils at 203 ° C (negative azeotrope).
- Sulfuric acid (98.3%)/water, boils at 336 ° C.
- Ethanol (95%)/water, boils at 78.2 ° C.
- Acetone/methanol/chloroform forms an intermediate azeotrope.
the ethanol-water mixture is considered the famous example of azeotrope having 96% of ethanol present. in this mixture, the ethanol boils at 78.2 degrees Celsius. this azeotrope is used to separate alcohol from the mixture by the simple distillation process. hence, 96% of alcohol concentration distilled. by increasing the amount of azeotrope concentration more than 96%, separation made impossible. so, the purity of ethanol is needed and an azeotropic distillation technique must be used.
using Chloroform and water results in a heteroazeotrope. in this way the mixture of two liquids will separate and an upper layer with water dissolved in chloroform at low concentration. on the other hand, the lower layer consists of chloroform having a very small amount of water. when both layers are boiled together at a lower temperature 97% chloroform and 3 % water is produced irrespective of the ratio of the liquids.
a fixed composition is produced with these layers by the condensation process. the top layer produces 4.4% volume of liquid and the bottom layer 95.6%.
What is Azeotropic separation?
where distillation fraction does not work to separate the azeotropic components, we use some other methods which are as follows:
- to get the distillate desired components, the pressure swing method is used for pressure changes. it changes the pressure of a mixture.
- the addition of an entrainment agent is another technique that changes the volatility of azeotropic-like components. sometimes the non-volatile compounds are formed due to the reaction of entrainer components. this method is known as azeotropic distillation.
- using membrane, re-vaporation is used for the separation of different components. this membrane is more permeable than the constituent. the use of a membrane more permeable to the vapor phase of one component than another.
Common Advantages of azeotropes
azeotropes are very helpful for allowing the mixture of flammable components with non-flammable components to get a stable non-flammable mixture. they are very easier to transport and store from one place to another. by using this technique, we can control the dangers of many flammable components. they are not separated in any natural way, hence considered very safe during any spill that occurs. they are easy to separate and retrieve. the azeotropes are recycled by distillation after boiling at desired temperature and pressure, while the non-azeotropic components are collected at the bottom layer at the distillation tower. this is considered the most famous and common azeotropic solvents recovering method.
the azeotropes also allow a mixture to modify it and obtain some unique physical properties that can be useful in a variety of applications.
You May Also Like: