Solvent Extraction: If you are given a mixture of oil and water. How will you separate the components? In this instance, solvent extraction can be used. In this article, you will learn more about this, including its separation principle, technique, and applications. Depending on the nature of the mixture, several separation procedures such as crystallisation, filtration, evaporation, sublimation, distillation, chromatography, solvent extraction, and so on are applied.

This is also known as liquid-liquid extraction (LLE) and partitioning, which is a technique for separating chemicals based on their respective solubilities in immiscible liquids. Immiscible liquids are those that cannot be mixed together and split into layers when agitated together. These liquids are typically water and an organic solvent. Read this article to learn more about solvent extraction methods and solvent extraction principles.

What is Solvent Extraction?

The process of isolating an organic compound from its aqueous solution by shaking it with solvent is known as solvent extraction. It is also called differential extraction.

Solvent Extraction Principle

When an organic compound, whether solid or liquid, is present as a solution in water, it can be recovered from the solution by shaking the solution with a suitable organic solvent. The organic solvent selected should be such that:

1. The given solid must be much more soluble in the organic solvent than in water.
2. Water and organic solvents should not be miscible to each other.

The most common organic solvent used is ether. However, benzene and acetone can also be used. But alcohol is not the proper solvent because water and alcohol are highly miscible with each other.

Solvent Extraction is Governed by Which Law?

It is based on the distribution law. It is also called the Nernst’s distribution law. It states that if a solute \(\rm{X}\) distributes itself between two immiscible solvents \(\rm{A}\) and \(\rm{B}\), at constant temperature and \(\rm{X}\) is in the same molecular condition in both solvents, then

\(\frac{{{\text{Concentration}}\,{\text{of}}\,{\text{X}}\,{\text{in}}\,{\text{A}}}}{{{\text{Concentration}}\,{\text{of}}\,{\text{X}}\,{\text{in}}\,{\text{B}}}}{\text{ = }}{{\text{K}}_{\text{D}}}\)

The constant \(\rm{K_D}\) or \(\rm{K}\) is called the Distribution coefficient or Partition coefficient, or Distribution ratio.

If \(\rm{C}_1\) denotes the concentration of the solute \((\rm{X})\) in the solvent, \(\rm{A}\) and \(\rm{C}_2\) the concentration of solute \((\rm{X})\) in the solvent \(\rm{B}\), then Nernst’s Distribution law can be represented as \(\frac{{{{\text{C}}_{\text{1}}}}}{{{{\text{C}}_{\text{2}}}}}{\text{ = }}{{\text{K}}_{\text{D}}}.\)

Solvent Extraction Methods

The aqueous solution of the given solute is taken in a separating funnel. It is mixed with the desired organic solvent. The funnel is closed, and its contents are shaken vigorously. It is then allowed to remain undisturbed for some time. Water and organic solvent will form separate layers, and the solid or liquid solute will be transferred from the aqueous layer to the organic layer as it is more soluble in an organic solvent. In the funnel, the solvent forms the upper layer while the water forms the lower layer.

The two layers can be recovered by opening the stop cock and collecting them in separate bakers. On evaporating the organic solvent, the solute can be recovered.

Solvent Extraction Diagram

For example, benzoic acid from water may be extracted from its aqueous solution by using benzene. Then benzoic acid may be finally recovered from its solution by distilling off the organic solvent.
This process can also be used to separate two organic liquids such as aniline and water.

Factors Affecting the Solvent Extraction

In a given quantity of solvent, the amount of organic substance extracted depends upon the number of extractions. The larger the number of extractions, the greater is the amount of substance extracted. Therefore, it is better to extract several times with smaller quantities of solvent than once with the entire solvent provided.
For example, benzoic acid from water may be extracted from its aqueous solution by using benzene. Then benzoic acid may be finally recovered from its solution by distilling off the organic solvent.

Preparation of Microspheres by Solvent Extraction Method

The microsphere preparation by method is as follows:

• 1. The bioactive compound is dissolved in the suitable matrix material.
• 2. Microdroplets are formed.
• 3. The solvent is removed, if necessary suitable extraction agents are used.
• 4. Microspheres are harvested and dried.

These microspheres are widely used in drug delivery systems.

Application of Solvent Extraction

1. It is used in perfumes, vegetable oil, biodiesel processing, etc.
2. By this method, plutonium irradiated from nuclear fuel can be recovered and which is reused as nuclear fuel.
3. It is used to segregate hazardous contaminants from sludge and sediments.
4. It is used in the drug industry like preparation of microspheres.
5. It is used for the separation and purification of organic compounds.

Summary

In this article, you have enlightened with solvent extraction, also called differential extraction. You are also able to explain the principle, procedure, law and application of it. Apart from this, you can explain its method microspheres. You can make use of this knowledge in separating different types of immiscible liquid with the difference in their densities.

FAQs

Q.1. Where is solvent extraction used?
Ans: Solvent extraction is used for isolating an organic compound from its aqueous solution, separated by immiscible solvents. It is also used for the preparation of microspheres.

Q.2. What are the different types of solvent extraction?
Ans: Liquid/liquid, liquid/solid and acid/base are the three most common types of solvent extraction.

Q.3. Why is solvent extraction important?
Ans: Solvent extraction is important for isolating an organic compound from its aqueous solution.

Q.4. What is the principle of solvent extraction?
Ans: When an organic compound, whether solid or liquid, is present as a solution in water, it can be recovered from the solution by shaking the solution with a suitable organic solvent. The organic solvent selected should be such that the given solid must be much more soluble in the organic solvent than in water. Water and organic solvents should not be miscible to each other.

Q.5. What are the advantages of solvent extraction?
Ans: Solvent extraction is an easy method of separation with low energy consumption. It is also an easy continuous process.

Q.6. What is the process of solvent extraction?
Ans: It is the process of isolating an organic compound from its aqueous solution by shaking it with solvent. The organic solvent selected should be such that the given solid must be much more soluble in the organic solvent than in water. Water and organic solvents should not be miscible to each other.