Liquid-Liquid Extraction Lecture Nov 2012

Overview 2 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

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

Example Industrial Processes 4 Seader & Henley (2006)

Typical LL Extraction Process 5 Seader & Henley (2006)

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

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10 Spray Columns: Seader & Henley (2006)

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

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

13 Seader & Henley (2006) Oldshue-Rushton (Mixco Lightnin CMContactor) column Scheibel column

14 Seader & Henley (2006)

Podbielniak Extractor 15 Treybal (1980)

Equipment 16 Seader & Henley (2006)

Equipment Examples 17 Seader & Henley (2006)

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

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

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

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

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

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

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

Choice of Solvent 25 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

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

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

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

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

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

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

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

Questions? 33