Liquid-Liquid Extraction Lecture 23

1. Liquid-Liquid Extraction Lecture 23 26 Nov 2012

2. Overview • Liquid-Liquid Extraction • (solvent extraction) • Pioneered during 1940’s (uranium purification) • Alternative to distillation, absorption/stripping • Energy savings • Sometimes easier separation • Lower temperatures • Usually two distinct phases formed • Usual purpose, to either purify the • Raffinate, or • Solute

3. Liquid-Liquid Extraction Extract • Separation accomplished by chemical differences • Usually in two phase • - light phase • - heavy phase • Usually coupled with another separation technique Feed [s + a] (+b) [a+b] a = solute b = diluent s = solvent Extractor Separator could be: column w/ stages or packing column with moving internals single stage mixer/settler equilibrium stage(s) Solvent Raffinate [b] (+ a & s) [s] let:

4. Example Industrial Processes Seader & Henley (2006)

5. Typical LL Extraction Process Seader & Henley (2006)

6. Equipment Examples Treybal (1980) Seader & Henley (2006)

10. Spray Columns: Seader & Henley (2006)

11. Packed-bed Column Seader & Henley (2006) Light liquid - dispersed phase Treybal (1980)

12. Sieve-tray Extraction Column: light phase dispersed Treybal (1980)

13. Oldshue-Rushton (MixcoLightninCMContactor) column Scheibel column Seader & Henley (2006)

14. Seader & Henley (2006)

15. Podbielniak Extractor Treybal (1980)

16. Equipment Seader & Henley (2006)

17. Equipment Examples Seader & Henley (2006)

18. Equilateral Triangular Diagrams [a] Overall material balance: Component material balance (on a): [b] [s] Rearrange: Lever principle: [s] [b]

19. Equilateral Triangular Diagrams [a] [a] [b] [b] [s] [s] Type I Type II • Examples: • water (b), ethylene glycol (a), furfural (s) • water (b), acetone (a), chloroform (s) • Example: • n-heptane (b), methylcyclohexane (a), aniline (s)

20. Distribution Curves [a] [a] [b] [b] [s] [s] Type I Type II

21. Distribution Curves [a] [a] [b] [b] [s] [s] Type I Type II

22. Distribution Curves [a] [a] [b] [b] [s] [s] Type I Type II

23. Effect of Temperature (and Pressure) Treybal (1980)

24. Effect of Temperature (and Pressure) Treybal (1980)

25. Choice of Solvent • Selectivity separation factor • Distribution Coefficient better if • Insolubility of Solvent better if less soluble in R phase • Solvent Recoverability should be easy to separate solvent from E and R • Density large density differences between the two phases is desired • Interfacial Tension would like large for easier coalescence of dispersed phase • Others: • solvent stable, inert, nontoxic, nonflammable, low cost • low viscosity • low vapor pressure • low freezing point

26. Mixer – Settler (single stage extraction) Purified Raffinate [a] Raffinate Feed Purified Extract Solvent settler mixer New Solvent Extract Recycled Solvent solvent recovery solvent recovery [b] [s] Raffinate Feed 1 stage Black Box: Solvent Extract Material balance:

27. Mixer – Settler (single stage extraction) given: find: [a] Component material balance (on a in feeds): [b] [s] Component material balance (on a in products):

28. Mixer – Settler (single stage extraction) Minimum Solvent (rate): [a] [b] [s] Maximum Solvent (rate):

29. Cross-Current (multi-stage extraction) Final Extract [a] Stage 1 Stage 2 Stage 3 Feed Final Raffinate Solvent Solvent Solvent [b] [s] Final Extract:

30. Continuous Multistage CountercurrentExtraction [a] Feed Raffinate 1 N 2 N-1 Extract Solvent Total MB: [b] [s] Total MB on a: If known (specified), then flowrates can be found.

31. Continuous Multistage CountercurrentExtraction [a] Feed Raffinate 1 N 2 N-1 Extract Solvent Total MB: Operating Point: MB from feed to N-1 stage: [b] [s]

32. Continuous Multistage CountercurrentExtraction [a] Feed Raffinate 1 N 2 N-1 Extract Solvent Now step off to find number of equilibrium stages: [b] [s]

33. Questions?