Hunter Nash LiquidLiquid Extraction

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Hunter Nash Liquid-Liquid Extraction

• Last lecture We used McCabe-Thiele to analyze
  multistage binary distillation in the
• cases of
• Side streams
• Multiple feed streams
•  A partial condenser
• Open steam
• We discussed the algebraic procedure for the
  distillation analysis
• We discussed using a spreadsheet to efficiently
  analyze the distillation process

Todays Lecture Covers Multistage
Liquid-Liquid extraction Specifications for
liquid-liquid extraction cascades Product
points Operating lines and operating points The
Hunter-Nash Procedure Hunter-Nash graphical
construction Stepping off stages Minimum solvent
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Liquid-Liquid Extraction
Liquid-liquid Extraction of ternary systems
involves contacting two equilibrium liquids where
the solvent liquid is immiscible or nearly
immiscible with one of the components of the feed
liquid and miscible with one or more of the
other components.

• Liquid-liquid extraction is also referred to as
• Extraction
• Solvent extraction
• Liquid extraction

In Section 4.5 we used the Ternary Phase Diagram
to analyze Liquid-liquid Extraction for a single
equilibrium stage.
Ternary Phase DiagramSolvent TCE Solute
Acetone Carrier Water
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Ternary Single-Stage Flash Separation
Solute
Plait Point P
Extract
F
Feed
E
Mixing point
R
Raffinate
Tie-lines
S
Solvent C
Carrier
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Liquid-Liquid Extraction Cascades
What if we have a countercurrent cascade of
Liquid-Liquid contacting stages?
Can we use a similar analysis to the one we used
for countercurrent leaching where we had two
condensed phases and complete immiscibility of
the carrier in the solvent? Yes, but different
since in the liquid-liquid case we assume that we
can disengage the phases and we dont have
complete solubility. Can we use a similar
analysis to the one we used for countercurrent
absorption or stripping? Yes, but different
since equilibrium here is given by a
liquid-liquid ternary diagram rather than a
vapor-liquid equilibrium.
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Liquid-Liquid Extraction Specifications
Specifications F, (xi)F, (yi)S, T and one
of 1) S and (xi)RN 2) S and (yi)E1 3) (xi)RN
and (yi)E1 4) N and (xi)RN 5) N and (yi)E1 6) S
and N
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Hunter-Nash Solution for Liquid-Liquid Extraction
Solute
Product Points Step 1) Find the mixing point
MFS Step 2) Determine mixing point compositions
from component material balances or inverse
lever rule Step 3) Since we know RN lies on the
equilibriumcurve and we know (xA)RN we can
determine (xB)RN and (xC)RN Step 4) Since we know
RN, M and E1 lie on a mixing line we can locate
E1 by extending a line from RN through M to the
equilibrium curve where it intersects E1.
Plait Point P
Extract
Feed
E1
Raffinate
M
R1
Tie-lines
RN
Solvent C
Carrier
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Liquid-Liquid Extraction Operating Lines
Operating Points and Lines Mass Balance around
entire cascade We define the operating point P
as thedifference between passing streams
Mass Balance around the first n stages We
rearrange this equation to find thatall passing
streams are related by the sameoperating point P.
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The Operating Point
Operating Points and Lines Mass Balance around an
internal stage We can rearrange the above
expression tofind that Rn is just a mixing point
betweenP and En1.
Replace Rn-1 and Enby P
En
En1
The following figure illustrates this
concept The stream Rn is the mixing point
betweenP and En1 because P is the net flow
intostage n from passing streams Rn-1, and En.
En1
P
n
n
Rn
Rn-1
Rn
The N mass balances around the N
individualstages result in
Extract
S
En
En1
EN-1
E3
E2
EN
Solvent C
E1
1
2
n
N1
N
Raffinate
F
RN-1
Rn
R1
Rn-1
RN-2
R2
RN
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Operating Lines
Operating Lines The raffinate points are mixing
points between P and corresponding extract
points. This is shown graphically in the
following diagram. Notice that to get the point P
we need just F, S, E1 and RN.
Solute
E1
E2
F
E3
Operating Point P
R1
E4
E5
RN
E6
Carrier
S
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Liquid-Liquid Extraction
Solute
Operating Points and Lines Step 1) Locate the
Operating Point by finding the intersection of
operating lines for the leftmost and rightmost
stages a) Draw a line through E1 and F b) Draw
a line through S and RN c) Locate the
intersection P. This point is the operating
point P.
Plait Point
E1
Feed
Operating Point P
M
RN
S
Carrier
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Liquid-Liquid Extraction
Solute
Operating Lines and Tie Lines Stepping Off
Stages Step 1) Locate point R1 from the tie line
intersecting E1 Step 2) Draw a line from the
operating point P through R1 to the extract side
of the equilibrium curve. The intersection
locates E2. Step 3) Locate point R2 from a tie
line. Step 4) Repeat Steps 2 and 3 until RN is
obtained.
Plait Point
E1
E2
Feed
E3
Operating Point P
R1
E4
M
E5
RN
E6
Carrier
Solvent C
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Liquid-Liquid Extraction
Product Points Step 1) MFS Step 2) Determine
mixing point compositions from component material
balances or inverse lever rule Step 3) Since we
know RN lies on a tie line and we know (xA)RN we
can determine (xB)RN and (xC)RN Step 4) Since we
know RN, M and E1 lie on a mixing line we can
locate E1 by extending a line from RN through M
to the equilibrium curve where it intersects E1.
Operating Points and Lines Step 1) Locate the
Operating Point by finding the intersection of
operating lines for the leftmost and rightmost
stage 1a) Draw a line through E1 and F 1b)
Draw a line through S and RN 1c) Locate the
intersection P. This point is the operating point
P.
Operating Lines and Tie Lines Stepping Off
Stages Step 1) Locate point R1 from the tie line
intersecting E1 Step 2) Draw a line from the
operating point P through R1 to the extract side
of the equilibrium curve. The intersection
locates E2. Step 3) Locate point R2 from a tie
line. Step 4) Repeat Steps 2 and 3 until RN is
obtained.
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Liquid-Liquid Extraction Minimum Solvent
Operating Points and Lines Step 1) Locate the
raffinate Operating Line by extending a line
from S through RN Step 2) Extend the tie lines to
intersect the operating line Step 3) The tie
line that intersects furthest from RN gives the
minimum operating point Pmin. Step 4) Extend a
line from Pmin through F to the extract sideof
the equilibrium curve to find E1. Step 5) Extend
a line from E1 to RN. The intersection with
theline SF gives the minimum mixing point.
Solute
Note If the tie lines slope down towards the
solvent side of the diagram, thenthe minimum
operating point will lie on the operating line at
an intersection with a tie line nearest S.
Plait Point
E1
F
Mmin
Pmin
S
RN
Mmax
Carrier
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Liquid-Liquid Extraction Minimum Solvent
Solute
Stepping off Stages for the minimum solvent
case After locating the points Pmin, E1, and
Mminthe stages can be stepped off. If the
minimum solvent is used then the separation will
be pinched off and will require an infinite
number of stages.
Plait Point
E1
F
Mmin
S
Pmin
RN
Carrier
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Hunter Nash Liquid-Liquid Extraction
Todays Lecture Covered Multistage
Liquid-Liquid extraction Specifications for
liquid-liquid extraction cascades Product points
for a cascade Operating lines and operating
points Hunter-Nash graphical construction The
Hunter-Nash Procedure Stepping off stages The
minimum solvent solvent condition