The Maximum Boiling Azeotropes or Positive Azeotropes

An azeotrope is considered a mixture of liquids so that the proportion of these does not change. One can say that the term ‘azeotrope’ refers to the process of constant boiling point. It occurs because of the formation of vapour with the boiling process, and the ratios of the present constituents remain the same. The azeotrope is classified into two parts, i.e., minimum boiling azeotropes & maximum boiling azeotropes. 

What does the Word ‘Maximum Boiling Azeotropes’ mean?

Maximum boiling azeotropes boil at a greater temperature than the boiling point of each component in a pure form, e.g., 68 percent nitric acid and 32 percent water by mass. 

Applications of Azeotropes

Here are some of the applications of the azeotropes:

• The azeotropes help in separating the azeotropic mixture.
• The azeotropes can measure the standards in detectors, columns, and chromatographs.
• For example, the azeotrope gets separated in water and acid solution. 

Separation of Azeotropes

• The pressure changes composition to the mixture that enriches the distillate with the required component.
• Another technique is the additional involvement of the entrainer in which the substance alters the volatility of the components.
• The evaporation involves the separation of components with the help of a membrane. 

What are the Categories of Azeotropes?

Many types of azeotropes exist, such as positive, negative, heterogeneous. Let’s discuss all the different kinds of azeotropes in detail.

1. Positive azeotropes:

• Positive azeotropes are the mixtures of azeotropes that show large positive deviations. 
• The boiling points for such azeotropes are less than the constituting boiling points. 
• The types of mixtures are the mixtures that spill the most vapour pressure with the lowest boiling point.
• For example, suppose the azeotropic mixture is 96% and contains 4% water, then it is a positive azeotrope. It shows the sizeable positive deviation as per Raoult’s law. 

2. Homogeneous azeotropes:

• The homogeneous azeotropes contain the mixture in all specific ratios with others.
• For example, any ethanol can be mixed with the water amount to make a form of a homogeneous mixture.

3. Negative azeotropes:

• The negative azeotropes show the significant deviation of negative charges with Raoult’s law.
• The boiling points for such azeotropes are much higher than the constituents boiling points. 
• The azeotropes spill the low vapour pressure with the more high boiling points.
• For example, the mixture of hydrogen chloride and water is considered negative azeotropes. This mixture shows the negative deviation according to Raoult law.

4. Ternary azeotropes:

• The constituents of the ternary azeotropes are not fully miscible.
• Such types of azeotropes are considered hetero azeotropes.
• For example, let’s take the case of the azeotrope mixture of chloroform and water. When one shakes it and leaves it as two separate layers, the mixture boiling point is at 53.30 C. The water point is 1000C & chloroform is 61.20 C.

5. Heterogeneous azeotropes:

• The azeotropic mixture is not fully miscible, so that the azeotropes can be found in the miscibility gap.
• As per Raoult’s law, the phase splitting can occur for a small amount of boiling azeotropes with a considerable amount of azeotropes.
• For example, the mixture of an azeotrope is chloroform and water. So, when one shakes it and leaves it as two separate layers, the mixture’s boiling point is at 53.30 C. The water point is 1000C & chloroform is 61.20 C.

The Main Characteristics of the Maximum Boiling Points

1. Boiling points:

The boiling azeotropes are higher than the constituents boiling points.

2. Interaction:

There is excellent interaction between the solutes-solutes and solvents-solvents. Such molecules are more robust as compared to the solute solvent. And that, as a result, occurs at the low boiling point. 

3. Volume:

The solution volume is much higher than the individual sums’ volumes. This is due to the increased interaction of the solvent & solute molecule.

4. Maximum boiling azeotropes:

The highest boiling azeotropes are 68% of the nitric acid.

5. Constituents:

The mixture enthalpy of the main constituent is positive.

Conclusion

There is a big difference between the maximum boiling azeotropes and the minimum boiling azeotropes. The positive azeotropes are higher than the constituents’ boiling points. These azeotropes show significant deviation of positive charges with Raoult’s law. The mixture type gets the most vapour pressure with the lowest boiling point.