Liquid liquid extraction

1. Topic:
Liquid – Liquid Extraction
Mass Transfer Operations(2150501)
CHEMICAL ENGINEERING DEPARTMENT

2. Contents
• Introduction to Extraction
• The Equilateral Triangular Diagram
• Purpose of Extraction
• Liquid-Liquid Extraction
• Liquid-Liquid Equilibria(LLE)
• Classification extraction processes
• Choice of solvent
• Advantages of solvent extraction
• Application of Extraction
• Distribution law
• Typical Extraction System In Industry
• Classification Of Extractor
• Types Of Extractor
• Mixer-Settler
• Decanter

3. Introduction to Extraction
• Liquid-liquid extraction (also known as solvent extraction) involves
the separation of the constituents (solutes) of a liquid solution by
contact with another insoluble liquid.
• Solutes are separated based on their different solubilities in different
liquids.
• Separation is achieved when the substances constituting the original
solution is transferred from the original solution to the other liquid
solution

5. • The simplest liquid-liquid extraction involves only a ternary (i.e.3
components) system.
• The solution which is to be extracted is called the feed, and the liquid
with which the feed is contacted is the solvent.
• The feed can be considered as comprising the solute A and the
"carrier" liquid C. Solvent S is a pure liquid.
• During contact, mass transfer of A from the feed to the solvent S
occurs, with little transfer of C to S.
• The solvent (with the solute) is then permitted to separate from the
carrier liquid.

6. •The solvent-rich product of the operation is called the extract, and the
residual liquid from which solutes has been removed is the raffinate
•In some operations, the solutes are the desired product, hence the
extract stream is the desirable stream.
•In other applications, the solutes may be the contaminants that need to
be removed, and in this instance the raffinate is the desirable product
stream.

7. The Equilateral Triangular Diagram
B
A S
P
%A%S
%B

9. Figure 8.1 Typical liquid-liquid extraction process.

10. Purpose of Extraction
• To separate closed-boiling point mixture
• Mixture that cannot withstand high temperature of distillation
• Example:
- recovery of penicillin from fermentation broth solvent: butyl
acetate
- recovery of acetic acid from dilute aqueous solutions solvent:
ethyl-acetate

11. Liquid-Liquid Extraction
• Solvent
• Solution
• Extract(E)
• Raffinate(R)

12. • Extraction – is the process by which a solute is transferred from one
phase to a new phase.
• Liquid-liquid extraction, also known as solvent extraction and
partitioning, is a method to separate compounds based on their relative
solubility's in two different immiscible liquids, usually water and an
organic solvent.
• Process of dissolved substance transferring from one phase to another
phase, which are immiscible or restrictedly miscible, is named liquid-
liquid –partition or partition between two phase of liquids.

13. Liquid-Liquid Equilibria(LLE)
• A liquid-liquid extraction system contains at least three components
A. Carrier liquid in feed
B. The extracting solvent
C. The Solute
• For example, in the process of extraction of penicillin from the
fermentation broth. Where penicillin is the solute (c),water is the
carrier (a) and butyl acetate is the solvent (b).
• The equilibrium data for a liquid-liquid system are of vital importance
in the selection and design of an extraction equipment.

14. Classification extraction processes:
• Periodical extraction - is the process in which separatory funnel
(which contain substance which extragent) is shaked
• Continuous extraction
• Countercurrent extraction

15. Choice of solvent
•Factors to be considered:
•Selectivity
•Distribution coefficient
•Insolubility of solvent
•Recoverability of solute from solvent
•Density difference between liquid phases
•Interfacial tension
•Chemical reactivity
•Cost
•Viscosity, vapour pressure
•Flammability, toxicity

16. Advantages of solvent extraction
• Selectivity of extraction directly from fermentation broths or from
reaction medium in the case of biotransformations wherein whole cells
or enzymes are used for conversion of a substrate into a desired
product.
• Reduction in product loss due to hydrolytic or metabolic/microbial
degradation as the product is transferred to a second phase with
different physical and chemical properties.
• Suitability over a wide range of scales operation.

17. EQUIPMENT FOR EXTRACTION
1. Mixer-settlers
2. Packed extraction towers
3. Perforated-plate
towers
4. Agitated
tower extractors
5. Pulse columns
7. Auxilary equipment
[stills, evaporators, heaters and
condenser]
6. Centrifugal
extractors

18. Application of Extraction
• Extraction processes are well suited to the petroleum industry because
of the need to separate heat-sensitive liquid feeds according to
chemical type (e.g. aliphatic, aromatic, naphthenic) rather than by
molecular weight or vapour pressure.
• Other major applications exist in the biochemical or pharmaceutical
industry, where emphasis is on the separation of antibiotics and protein
recovery.
• In the inorganic chemical industry, they are used to recover high-
boiling components such as phosphoric acid, boric acid, and sodium
hydroxide from aqueous solutions.

19. Distribution law
• At equilibrium, the ratio of the concentrations of the solute in the two
phases is given by CE/CR = K
• The distribution constant K, must be greater than 1 if the desired
product is extract stream.
• The distribution constant K, must be lesser than 1 if the desired
product is raffinate stream.

20. Typical Extraction System In Industry
• An extraction system always includes at least 1 distillation column (or
other separation process) to recover solvent from the extract phase. If
the solvent exhibits some degree of miscibility in the feed, then a
second separation process (normally distillation) is required to recover
solvent from raffinate.

21. Classification Of Extractor

22. Types Of Extractor
• Single Stage • Multi Stage

23. Types of Extractor Equipment
• Single Stage
1. Mixer-Settler
2. Decanter
• Multi Stage
1. Mixer-settler Battery
(MSB)
2. Mechanically
Agitated Extractors
i. Scheibel Extractor
ii. Rotating Disk
Contactor (RDC)
iii.Pulse Extractors

24. Mixer-Settler
• Mixer-settlers are still widely used because of their reliability,
operating flexibility, and high capacity. They can handle difficult-to-
disperse systems, such as those having high interfacial tension and/or
large phase density difference.
• They can also cope with highly viscous liquids and solid-liquid
slurries. The main disadvantages are their size and the inventory of
material held up in the equipment.
• For multiple unit operations, considerable capital costs may be needed
for pumps and pipings.

25. Mixer-Settler
• The mixer and settler can be integral or separate. The operation may
be continuous or batchwise.

26. Decanter
• Settlers (or sometimes known as decanter), can be as simple as
involving simple dispersion, where the entering liquid is dispersed into
droplets.
• The droplets are then allowed to settle by gravity in the main part of
the vessel.
• Most settlers consist of a horizontal vessel, because the separating
efficiency is proportional to the area of the phase interface.
• To increase the size of the droplets and hence their settling rate, the
dispersion may be passed through a coalescer (packing or wire mesh)

27. Decanter