Extraction and washing

extraction and washing

1. EXTRACTION AND WASHING

2. EXTRACTION It is defined as the removal of solid constituents from the solid or liquid or semi solid by means of suitable solvents Extract- compound contain all the constituents which are soluble in solvent Menstrum- Solvent used for extraction process Marc- residue obtained after the extraction process

3. PRINCIPLE The solvent used for extraction which diffuse into the compound to dissolve the desired compounds The solution in compound pass in the opposite direction and mix with the surrounding liquid . An equilibrium is established between the solute inside the compound and the solvent surrounding

4. Rate of solution = driving force/resistance. d w /d t  =  K l A ( y s  -  y )     d w /d t  is the rate of solution K l  is the mass-transfer coefficient A  is the interfacial area y s   and  y are the concentrations of the soluble component in the bulk of the liquid and at the interface. It is usually assumed that a saturated solution is formed at the interface   y s  is the concentration of a saturated solution at the temperature of the system. Rate of extraction

5. Rate of extraction A mass balance on the solute gives the equation dw = Vdy V is the quantity of liquid in the liquid stream. Vdy/dt = Kl A(ys - y) which can then be integrated over time t during which time the concentration goes from an initial value of y0 to a concentration y, giving loge [(ys - y0)/ (ys - y)] = tKlA/V.

6. Factors influence the extraction process Nature of compound Type of Solvent used Temperature pH Size of particle

7. THEORIES Schoenemann’s Diffusion theory The rate of extraction depends on the rate of diffusion Soaking theory Not only the rate of diffusion but also the rate of dissolution of the substances in the solvent critically affect the rate of extraction Karnowsky’s Capillary velocity Theory It represents the rate of extraction as a function of the rate of flow in the capillaries.

8. Methods of extraction Liquid–liquid extraction Solid-phase extraction Acid-base extraction Supercritical fluid extraction Ultrasound-assisted extraction Heat reflux extraction Microwave-assisted extraction

9. Extraction system

10. Equipments Commercial extractor Phase contact by gravity Phase contact by centrifugal force

11. Mixer-Settler

12. Mixer-Settler

13. Mixer-Settler

14. Advantage reliability, operating flexibility, high capacity, It can handle difficult-to-disperse systems such as those having high interfacial tension and large phase density difference Disadvantage their size and the inventory of material held up in the equipmen Mixer-Settler

15. Pulse Extractors

16. Low axial mixing High extraction efficiency which are due to uniform distribution of energy over a cross-section of the column Uniform distribution of droplets in the column. Pulse Extractors

17. Unagitated Column Extractors

18. Unagitated Column Extractors

19. Mechanically Agitated Extractors Classified according to mechanical motion patterns Rotary-agitated columns Reciprocating or vibrating-plate columns.

20. Rotary-agitated columns Scheibel columns Rotating disk contactor Oldshue-Rushton Columns Kuhni columns Reciprocating column Karr columns. Mechanically Agitated Extractors

21. Scheibel columns

22. Rotating disk contactor

23. Oldshue-Rushton Extractor

24. Kuhni Extractor

25. Karr Reciprocating-Plate Extractor

26. Equilibrium diagram

27. Equilibrium diagram

28. Equilibrium diagram

29. Equilibrium diagram

30. Washing Washing is identical to extraction Water is used as solvent Water is cheap and readily available The washing is designed to remove unwanted residue material

31. The concentration remaining with the solid after washing x 1  =  x [ x w  / x w (1 +  y )] =  x [1/(1 +  y )]     after two washings: x 2  =  x 1 [1/(1 +  y )] =  x [1/(1 +  y )] 2  and so after n washings: x n  =  x [1/(1 +  y )] n     Washing