Liquid-Liquid Extraction is one of the most important mass transfer operations carried out in chemical industries. As the name suggests it is liquid-liquid contact mass transfer operations.
Liquid-Liquid Extraction is the one and only liquid-liquid contact mass transfer operation. Liquid-Liquid Contact is very important because it is used where other operations such as distillation and crystallization are either costly or inefficient.
So in this article, We are going to learn about Liquid-Liquid Extraction. We will start with defining it, then we will see the working of it. After that, we will see applications and factors affecting the operation.
What is Liquid-Liquid Extraction
Liquid-liquid extraction is the process of separation of two liquids that are soluble in each other by adding a third liquid which preferentially dissolves one of the liquid components. Liquid-liquid extraction is a type of extraction process. Another type of extraction is solid-liquid extraction also called Leaching. As the name suggests liquid-liquid extraction is carried out to separate valuable liquid components from a liquid mixture.
Important Nomenclature in Liquid-Liquid Extraction
- The third liquid added to carry out extraction is called the solvent.
- The liquid which is valuable to us and we want to extract it out from the liquid mixture is called the solute liquid.
- The liquid which does not dissolve in the solvent is called the feed solvent.
- After two-phase of liquids get generated, The liquid phase consisting of more amount of solute liquid is called the extract phase. The extract phase generally consists of a solvent with a higher concentration of solute liquid in it. Sometimes feed solvent is also dissolve in small quantities in the solvent.
- The liquid phase contains the remaining solute liquid and the feed solvent is called the raffinate phase.
Liquid-Liquid Extraction Procedure
The liquid-liquid extraction process involves four steps:
- Contact of solvent with feed
- Separation of two liquid phases generated
- Separation of solute liquid from solvent
- Separation of solvent from both liquid phases
Liquid-Liquid Extraction Process
Liquid-liquid extraction can be carried out in batches or in a continuous fashion.
For batch operation, first of all, feed consisting of two soluble liquids is taken into a vessel consisting of a stirrer. Then the solvent is added in measured quantity and stirred well.
The slurry formed is taken out in another vessel in which two insoluble liquid phases are formed. One phase contains more amount of solute liquid with solvent and the other layer consists of the remaining liquid solute with feed solvent.
Both liquid phases are insoluble in each other required rapid mixing to mix them. Delegation of these two liquid phases becomes easier and can be carried out by decantation or centrifuge.
After separating the extract phase solute liquid is separated from solvent and solvent is regenerated and sent back to the mixing tank. The solvent is also recovered from the raffinate phase by using some processes such as distillation.
Applications of Liquid-Liquid Extraction
Liquid-liquid extraction is carried out for liquid mixtures listed below
- The mixture of liquids having a very close boiling point For Example to separate aromatics from a paraffinic feed.
- Mixtures of liquids that are heat sensitive. Ex. Separation of penicillin from fermentation broth by using butyl acetate as solvent.
- Recovery of non-volatile solute liquid
- Recovery of solute liquid from dilute mixtures. Ex. separation of proteins.
- Removal of organic liquids having solubility with aqueous liquids. Examples are the removal of phenol from wastewater.
Liquid-Liquid Extraction Examples
Uses of liquid-liquid extraction are found in every Industry relates to liquid mixtures. Let's get look at some of the important uses/applications of liquid-liquid extraction
Liquid-Liquid Extraction Examples in Metallurgical Industry
- Recovery of copper from acidic dilute copper solution by using Hydroxylamine.
- Removal of H2S from Liquified natural gas by using Monoethanolamine
- In caprolactam manufacturing to produce nylon-6 extraction is an important operation.
Application of Liquid-Liquid Extraction in Petroleum Industry
- Separation of Aromatics from Its mixture with paraffin by suitable solvent.
- Separation of BTX (Benzene, Toluene, and Xylene) from petroleum fraction by using a suitable solvent.
- Separation of phenol from an aqueous mixture by using butyl acetate as solvent.
Application of Liquid-Liquid Extraction in Natural Product Industry
- Long-chain fatty acids can be easily separated from vegetable oil by using Liquid propane as solvent.
Application of Liquid-Liquid Extraction in Pharmaceutical Industry
- Recovery of Penicillin from formation broth by using a suitable solvent such as butyl acetate.
- Recovery of antibiotic.
- Natural vitamin A and D is extracted from fish liver oil by using liquid propane as a solvent.
Factors Affecting Liquid-Liquid Extraction Operation
1. Temperature
Temperature is a major parameter that affects liquid-liquid extraction. An increase in temperature leads to a change in solubility of liquids which may affect the solubility of the solute in a solvent and also solubility of feed solvent in solvent gets affected. So depending on the type of solvent, solute, and feed solvent suitable temperature condition is fixed.
2. pressure
Because in liquid-liquid Extraction, we deal with mostly liquids so pressure doesn't play important role in liquid-liquid extraction.
3. Choice of Solvent
The choice of solvent for liquid-liquid extraction is one of the most important parameters. There are certain criteria for selecting the desired solvent for liquid-liquid operation such as distribution coefficient, selectivity, surface tension, the solubility of solute and feed solvent insolvent, recoverability, and many other factors.
Liquid-Liquid Extraction vs Distillation
- Separating agent: In distillation, separation is carried out using thermal energy. In liquid-liquid extraction, separation is carried out by adding a third liquid called the solvent.
- Utilization: Distillation utilizes differences in volatility also represented as vapour pressure or boiling point. Liquid-liquid extraction utilizes different solubility.
- Degree of separation: Relative volatility is used as a degree of separation for distillation. Selectivity is used as a degree of separation for liquid-liquid extraction.
- Phase Creation: A new phase is created in distillation. A new insoluble Liquid Pahar is created in liquid extraction.
- Mixing and Separation: Separation and mixing are easier in distillation but But extraction separation is hard and mixing is harder.
- Quality of the product: Distillation gives pure product but Extraction doesn't.
- Flexibility in operating conditions: In distillation, there is no flexibility in choosing operation conditions. But in extraction, We get more flexibility than Distillation.
- Requirement: In distillation, we require thermal energy but in extraction, we require mechanical energy for mixing and separation.
- Choice-based on Separation: Distillation is the most preferred technique for liquid-liquid separation, Extraction is secondary.
Conclusion
So in this post, we have talked about what is liquid-liquid extraction, its application, operation, steps, uses, important factors, and also we compared it with distillation, etc. If you found this article helpful you can share it with your friends. You can also comment topic on which you want the article, We will cover that topic in future blogs.
References
Mass Transfer Operations by Robert TREYBAL
Mass transfer and Separation Techniques by Binay K Dutta