Download - Liquid-Liquid Extraction Lecture 23
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Liquid-Liquid ExtractionLecture 23
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26 Nov 2012
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Overview
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• 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
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Liquid-Liquid Extraction
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• Separation accomplished by chemical differences
• Usually in two phase• - light phase• - heavy phase
• Usually coupled with another separation technique
let:
xassociatedwithmequilibriuinyphaseextractinsolutefractionmassyphaseraffinateinsolutefractionmassx
*
Extract
Solvent
Feed
Raffinate
[a+b]
[b] (+ a & s)
[s + a] (+b)
[s]
a = soluteb = diluents = solvent
Separator could be:column w/ stages or packingcolumn with moving internalssingle stage mixer/settlerequilibrium stage(s)
Extractor
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Example Industrial Processes
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Seader & Henley (2006)
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Typical LL Extraction
Process
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Seader & Henley (2006)
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Equipment Examples
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Seader & Henley (2006)
Treybal (1980)
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Spray Columns:
Seader & Henley (2006)
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Seader & Henley (2006)Packed-bed Column
Treybal (1980)
Light liquid - dispersed phase
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12Treybal (1980)
Sieve-tray Extraction Column: light phase dispersed
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13Seader & Henley (2006)
Oldshue-Rushton (Mixco Lightnin CMContactor)
column Scheibel column
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14Seader & Henley (2006)
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Podbielniak Extractor
15Treybal (1980)
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Equipment
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Equipment Examples
17Seader & Henley (2006)
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Equilateral Triangular Diagrams
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[s] [b]
[a]
Rearrange:
mixturecombinedkgMmixtureextractkgEmixtureraffinatekgR
][][][
Overall material balance:][kgMER
Component material balance (on a):MxEyRx MER
RM
ME
xxxy
ER
[s] [b]
Lever principle:
MREM
me
ER
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Equilateral Triangular Diagrams
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[s] [b]
[a]
[s] [b]
[a]
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)
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Distribution Curves
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[s] [b]
[a]
[s] [b]
[a]
Type I
Type II
Rx
Ey
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Distribution Curves
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[s] [b]
[a]
[s] [b]
[a]
Type I
Type II
Rx
Ey
Rx
Ey
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Distribution Curves
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[s] [b]
[a]
[s] [b]
[a]
Type I
Type II
Rx
Ey
Rx
Ey
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Effect of Temperature (and Pressure)
23Treybal (1980)
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Effect of Temperature (and Pressure)
24Treybal (1980)
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Choice of Solvent
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• 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
raffinateb
a
extractb
a
xx
yy
1;1 better
1K
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Mixer – Settler (single stage extraction)
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ExtractSolvent
Feed Raffinate
mixer settlerNewSolvent
solventrecovery
solventrecovery
PurifiedRaffinate
PurifiedExtract
Recycled Solvent
Black Box: Rx
ExtractSolvent
Feed Raffinate1
stageFx
Sy Ey
F R
S E
Material balance:ERSF M
[s] [b]
[a]
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Mixer – Settler (single stage extraction)
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[s] [b]
[a]
Component material balance (on a in feeds): MxSyFx MSF
SFSyFxx SF
M
Component material balance (on a in products): MxEyRx MER
RE
RM
xyxxME
given: SyFx SF ,,, find: REyxMx ERM ,,,,,
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Mixer – Settler (single stage extraction)
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[s] [b]
[a]
Minimum Solvent (rate):
Maximum Solvent (rate):
SD
DF
yxxx
DSFD
FS
min
SK
KF
yxxx
KSFK
FS
max
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Cross-Current (multi-stage extraction)
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[s] [b]
[a]
Final Extract
Feed FinalRaffinateFx
F1x
Solvent
Stage1
Sy
1y
1R
S
1E
2x
Solvent
Stage2
Sy
2y
2R
S
2E
3x
Solvent
Stage 3
Sy
3y
3R
S
3E
Final Extract: 321 EEE
321
332211
EEEEyEyEyyFE
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Continuous Multistage Countercurrent Extraction
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[s] [b]
[a]
1x
Extract Solvent
Feed Raffinate1Fx
1y 2y
F1R
1E2E
SyS
2 2x
3y
2R
3E2Nx
1Ny
2NR
1NEN-1 1Nx
Ny
1NR
NEN
NRNx
Total MB: MRESF N 1
SFSyFxx SF
M
Total MB on a:
If known (specified), thenflowrates can befound.
Nxy &1
NRE &1
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Continuous Multistage Countercurrent Extraction
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[s] [b]
[a]
1x
Extract Solvent
Feed Raffinate1Fx
1y 2y
F1R
1E2E
SyS
2 2x
3y
2R
3E2Nx
1Ny
2NR
1NEN-1 1Nx
Ny
1NR
NEN
NRNx
Total MB: 1EFSRN MB from feed to N-1 stage: 11 EFER NN
Operating Point: 1EFR
R
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Continuous Multistage Countercurrent Extraction
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[s] [b]
[a]
1x
Extract Solvent
Feed Raffinate1Fx
1y 2y
F1R
1E2E
SyS
2 2x
3y
2R
3E2Nx
1Ny
2NR
1NEN-1 1Nx
Ny
1NR
NEN
NRNx
Now step off to find number of equilibrium stages:
R
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Questions?
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