Liquid Liquid Extraction:

1. Liquid Liquid Extraction: • The separation of the components of a liquid mixture by treatment with a solvent in which one or more of the desired components is preferentially soluble is known as liquid–liquid extraction. • Liquid-liquid extraction, also known as solvent extraction, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid phase engineering-resource.com

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3. Typical liquid-liquid extraction operations utilize the differences in the solubilities of the components of a liquid mixture. The basic steps involved include:1. Contacting the feed with the extraction solvent.2. Separation of the resulting phases3. Removal/recovery of solvent from each phase. Some Basic Steps & Extractor Design engineering-resource.com

4. Liquid-liquid extraction principles Feed phase contains a component, i, which is to be removed. Addition of a second phase (solvent phase) which is immiscible with feed phase but component i is soluble in both phases. Some of component i (solute) is transferred from the feed phase to the solvent phase. After extraction the feed and solvent phases are called the raffinate (R) and extract (E) phases respectively. engineering-resource.com

5. continued • Normally one of the two phases is an organic phase while the other is an aqueous phase. • Under equilibrium conditions the distribution of solute i over the two phases is determined by the distribution law. • After the extraction the two phases can be separated because of their immiscibility. Component i is then separated from the extract phase by a technique such as distillation and the solvent is regenerated. engineering-resource.com

6. Let's see an example. Suppose that you have a mixture of sugar in vegetable oil (it tastes sweet!) and you want to separate the sugar from the oil. 

You observe that the sugar particles are too tiny to filter and you suspect that the sugar is partially dissolved in the vegetable oil. What will you do? engineering-resource.com

7. How about shaking the mixture with water Will it separate the sugar from the oil? Sugar is much more soluble in water than in vegetable oil, and, as you know, water is immiscible (=not soluble) with oil. Did you see the result?The water phase is thebottom layer and the oil phase is the top layer, because water is denser than oil. *You have not shaken the mixture yet, so sugar is still in the oil phase. engineering-resource.com

8. By shaking the layers (phases) well, you increase the contact area between the two phases.The sugar will move to the phase in which it is most soluble: the water layer Now the water phase tastes sweet, because the sugar is moved to the water phase upon shaking.**You extractedsugarfrom the oil with water.**In this example,water was the extraction solvent ;the original oil-sugar mixture was the solution to be extracted; and sugar was the compound extracted from one phase to another. Separating the two layers accomplishes the separation of the sugar from the vegetable oil engineering-resource.com

9. Did you get it? .....the concept of liquid-liquid extraction? Liquid-liquid extraction is based on the transfer of a solute substance from one liquid phase into another liquid phase according to the solubility. Extraction becomes a very useful tool if you choose a suitable extraction solvent. You can use extraction to separate a substance selectively from a mixture, or to remove unwanted impurities from a solution. In the practical use, usually one phase is a water or water-based (aqueous) solution and the other an organic solvent which is immiscible with water. The success of this method depends upon the difference in solubility of a compound in various solvents. For a given compound, solubility differences between solvents is quantified as the "distribution coefficient" engineering-resource.com

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11. Extraction is in many ways complementary to distillation and is preferable in the following cases: (a) Where distillation would require excessive amounts of heat, such as, for example, when the relative volatility is near unity. (b) When the formation of azeotropes limits the degree of separation obtainable in distillation. (c) When heating must be avoided. (d) When the components to be separated are quite different in nature. engineering-resource.com

12. Examples: • Important applications of liquid–liquid extraction include the separation of aromatics from kerosene-based fuel oils to improve their burning qualities. • The separation of aromatics from paraffin and naphthenic compounds to improve the temperature-viscosity characteristics of lubricating oils. engineering-resource.com

13. Extraction Examples; Extraction of penicillin from fermented broth by contact with amyl or butyl acetate Recovery of acetic acid from dilute aqueous solutions by contact with ethyl acetate (fingernail polish solvent) or ethyl ether engineering-resource.com

14. Example • The constituents of liquid mixtures are distributed between the two phases resulting in some degree of separation (which can be improved by a multistage contact) and the phases are separated from one another based on the density differences of the liquid phases. For example, acetone may be preferentially extracted from a solution in water with the help of chloroform. The resulting chloroform phase contains a large part of acetone, but little water. engineering-resource.com

15. Example • Thus, if a solution of acetic acid in water is contacted with a solvent such as ethyl acetate then two phases will results. The extract (ester/organic layer) will contain most of acetic acid in ethyl acetate with a small amount water. The raffinate (aqueous layer) will contain a weak acetic acid solution with a small amount of ethyl acetate. The amount of water in the extract and ethyl acetate in the raffinate depends upon their solubilties in one another. engineering-resource.com

16. Measures of effectiveness: Distribution ratio: • In solvent extraction, a distribution ratio is often quoted as a measure of how well-extracted a species is. • The distribution ratio (D) is equal to the concentration of a solute in the organic phase divided by its concentration in the aqueous phase. • Depending on the system, the distribution ratio can be a function of temperature, the concentration of chemical species in the system, and a large number of other parameters. Sometimes, the distribution ratio is referred to as the partition coefficient engineering-resource.com

17. Separation factors: The separation factor is one distribution ratio divided by another; it is a measure of the ability of the system to separate two solutes. For instance, if the distribution ratio for nickel (DNi) is 10 and the distribution ratio for silver (DAg) is 100, then the silver/nickel separation factor (SFAg/Ni) is equal to DAg/DNi = SFAg/Ni = 10. engineering-resource.com

18. Extraction processes: liquid–liquid extraction operations, may be carried out either as a batch or as a continuous process. engineering-resource.com

19. Batch Extraction: engineering-resource.com

20. Continuous two-stage operation: engineering-resource.com