# COUNTERCURRENT LIQUID- LIQUID EXTRACTION

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```					COUNTERCURRENT LIQUID-
LIQUID EXTRACTION
SOLVENT REQUIREMENTS
• PFD FOR MULTISTAGE COUNTERCURRENT
EXTRACTION

• STAGE TO STAGE MASS BALANCE
• Xr = Xf * (mS/F – 1)/ ( [mS/F] n+1 -1)

http://www.cheresources.com/extraction.shtml
DEFINITION OF EXTRACTION FACTOR
EXTRACTION FACTOR
• FOR A SPECIFIC NUMBER OF STAGES ,n, A
HIGHER E FACTOR RESULTS IN MORE
EFFECTIVE EXTRACTION
• LOWER PRACTICAL LIMIT FOR E IS ABOUT 1.3
FOR MOST OPERATIONS

http://www.cheresources.com/extraction.shtml
COMPARISON FOR CROSS AND
COUNTERCURRENT TRAINS

http://www.cheresources.com/extraction.shtml
http://terpconnect.umd.edu/~nsw/ench250/extract3.htm
Process Specification (Change the number in yellow cells. Other cells in this
worksheet contain formula.)
Flow rate of the raffinate
R = 300phase
Flow rate of the extract
E = 200phase
Inlet composition of the raffinate
xin = 0.03phase
Outlet composition of the raffinate
xout = 0.001phase
Inlet composition of the extract
yin =     0phase
K=       3Partition coefficient
Calculated Variable:
S     2=K*E/R
Find the number of equilibrium stages required by forcing the following
f(N)=0.
= (xin-xout)/(xin-yin/K) - (S^(xN+1)-S)/(S^(xN+1)-
f(xN) =    -01)
¬ via |Goal Seek| by setting f(xN) to a value of 0 by changing
xN = 3.954xN.
Since a fractional stage does not make physical sense, set the number to be an
integer.
N=      4
http://terpconnect.umd.edu/~nsw/ench250/extract3.htm
Find the raffinate composition. (We prepared a matrix A and a vector b to handle up to 14 stages.)
Define the yellow cells to be A and b. As N changes, we need to manually redefine A and b to match
their size.
The following matrix A and vector b describe the material balance equation around each
stage.
xi-1 - (1+S)*xi + S*xi+1 = 0 for i=1,2,...,N
-3 2 0     0    0    0    0    0    0    0    0    0    0 0       -0.03
1 -3 2    0    0    0    0    0    0    0    0    0    0 0           0
0 1 -3    2    0    0    0    0    0    0    0    0    0 0           0
0 0 1    -3    2    0    0    0    0    0    0    0    0 0           0
0 0 0     1   -3    2    0    0    0    0    0    0    0 0           0
0 0 0     0    1   -3    2    0    0    0    0    0    0 0           0
A= 0 0 0        0    0    1   -3    2    0    0    0    0    0 0    b=     0
Summary                                      0 0 0     0    0    0    1   -3    2    0    0    0    0 0           0
Stage Raffinate x Extract y                 0 0 0     0    0    0    0    1   -3    2    0    0    0 0           0
0 0.03000 0.09000                      0 0 0     0    0    0    0    0    1   -3    2    0    0 0           0
1 0.01452 0.04355                      0 0 0     0    0    0    0    0    0    1   -3    2    0 0           0
2 0.00677 0.02032                      0 0 0     0    0    0    0    0    0    0    1   -3    2 0           0
3 0.00290 0.00871                      0 0 0     0    0    0    0    0    0    0    0    1   -3 2           0
4 0.00097 0.00290                      0 0 0     0    0    0    0    0    0    0    0    0    1 -3          0

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