Liquid liquid extraction

The presentation is based on Mass Transfer the major subject of Chemical Engineering. It includes
Separation
Technologies
Typical Applications
Industries
Distillation vs. Extraction
LLE Extraction
LLE extraction Principle
Solvent
Operation Condition
Mode of Operation
Extractor Type
Design Criteria
Equipment for extraction

1. Liquid-Liquid Extraction Mass Transfer

2. Physical Separations Decantation, Coalescing, Filtration, Demisting Evaporation Single Effect, Multiple Effect Distillation Simple, Azeotropic, Extractive, Reactive Extraction Simple, Fractional, Reactive Adsorption Pressure Swing, Temperature Swing Crystallization Melt, Solvent Membranes MF, UF, NF, RO Easy Difficult Difficulty Of Separation Separation Technologies

3. Typical Applications Remove products and pollutants from dilute aqueous streams Wash polar compounds or acids/bases from organic streams Heat sensitive products Non-volatile materials Azeotropic and close boiling mixtures Alternative to high cost distillations

4. Chemical Washing of acids/bases, polar compounds from organics Pharmaceuticals Recovery of active materials from fermentation broths Purification of vitamin products Effluent Treatment Recovery of phenol, DMF, DMAC Recovery of acetic acid from dilute solutions Polymer Processing Recovery of caprolactam for nylon manufacture Separation of catalyst from reaction products Petroleum Lube oil quality improvement Separation of aromatics/ aliphatics (BTX) Petrochemicals Separation of olefins/parafins Separation of structural isomers Food Industry Decaffeination of coffee and tea Separation of essential oils (flavors and fragrances) Metals Industry Copper production Recovery of rare earth elements Inorganic Chemicals Purification of phosphoric acid Nuclear Industry Purification of uranium Industries

5. Distillation vs. Extraction Organic Compound BP [°C] Water Solu. [%] Azeotrope B.P. [°C] Azeotrope Water [%] Typical Reduction Level Methylene Chloride 40 2.0 38.1 1.5 < 50 ppb Acetone 56.2 Infinite Non Azeotropic < 50 ppb Methanol 64.5 Infinite Non Azeotropic < 50 ppb Benzene 80.1 0.18 69.4 8.9 < 50 ppb Toluene 110.8 0.05 85.0 20.2 < 50 ppb Formaldehyde -21 Infinite Non Azeotropic < 1,000 ppm Formic Acid 100.8 Infinite 107.1 22.5 < 500 ppm Acetic Acid 118.0 Infinite Non Azeotropic < 500 ppm Pyridine 115.5 57 92.6 43 < 10 ppm Aniline 181.4 3.60 99.0 80.8 < 10 ppm Phenol 181.4 8.20 99.5 90.8 < 10 ppm Nitrobenzene 210.9 0.04 98.6 88.0 < 10 ppm Dinitrotoluene (2,4) 300.0 0.03 99 – 100 > 90 < 10 ppm Dimethyl Formamide 153.0 Infinite Non Azeotropic < 10 ppm Dimethyl Acetamide 166.1 Infinite Non Azeotropic < 10 ppm n-Methylpyrrolidone 202.0 Infinite Non Azeotropic < 10 ppm Extraction Distillation

6. LLE extraction Principle 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. (a) Bringing the feed mixture and the solvent into intimate contact, (b) Separation of the resulting two phases, and (c) Removal and recovery of the solvent from each phase . The Solute present in the aqueous phase gets partitioned or distributed in both the phases If the solute has solubility in the organic solvent, more of the solute would be present in the organic phase at equilibrium and extraction is said to be more efficient LLE Extraction

7. A – 99 B – 0 C – 1 100 Feed (F) A – 0 B – 50 C – 0 50 Solvent (S) A – 0 B – 50 C – 0.8 50.8 Extract (E) A – 99.0 B – 0 C – 0.2 99.2 Raffinate (R) Fraction Unextracted Distribution Coefficient Extraction Factor

8. Stage 1 Stage 2 1 2 1 2 Modes of Operations Co-current contact Cross flow Counter-current flow

9. Multiple-contact system with fresh solvent

10. Parameters of LLE Process Solvent Operation Condition Mode of Operation Extractor Type Design Criteria

11. Points need to be considered Higher the partition coefficient greater will be the extraction efficiency Large density differences between the extractant and raffinate = better separation if the separation is by gravity alone High viscosity of solvent affect the phase separation. Should have negligible miscibility/ solubility in the aqueous feed to minimize solvent loss Easily recovered and purified for recycling after extraction. Should be easily available and cost effective Low interfacial tension between the phases facilitates the dispersion of phases and improves mass transfer Physio -chemical properties such as boiling point, density, interfacial tension, viscosity, corrosiveness, flammability, stability compatibility with product, availability should be satisfactory

12. Equipment for extraction A high degree of turbulence facilitates intimate contact between the two liquid phases and allows a high rate of mass transfer. Two main types of equipment are used in solvent extraction Vessels in which mechanical agitation facilitates mixing. Vessels in which mixing is done by the counter-current flow of the two liquids themselves.

13. Batch extractor Continuous Column Extractor (a)Design for heavy solvent (b)Design for light solvent (a) (b)

14. (a) Static Bubble column (b) Sieve plate column (c) Agitated column (d) Spray column (e) Packed column (f) Rotating Disc

15. (a) Kuhni column (a) Scheibel column (a) Karr column

16. Types of equipment Stages Flow Rate Resident Time Physical properties of fluid Floor Area Occupied Mixer Settler L H H L-H H Centrifugal L L L L-M M Static Column M M M L-M L Agitated column H M M L-H L *L= LOW H= HIGH M= MEDIUM

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