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Theory
To analyze the
liquid-liquid extraction column, there is only a need for a few equations, which
include the overall and component mass balances. To create a balance that relates inlet and outlet streams, the
overall mass balance is used. (Elementary Principles of Chemical Processes
2nd Edition, pg 85)
|
F + S =
E + R |
(1) |
F, S, E, and R in the above equation
represent feed, solvent, extract, and raffinate mass flow rates,
respectively. The extract is the new
mixture exiting the bottom of the column, while the raffinate is the more pure
component exiting the top of the column.
A further analysis
may be needed to relate the compositions of the streams to the flow rates. By doing this, it is possible to find
unknown compositions or flow rates of any stream. The component mass balances for a three-component system are
given as follows: (Elementary Principles of Chemical Processes 2nd
Edition, pg 89)
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F •
XAF + S • XAS = E • XAE + R• XAR (Component A) |
(2) |
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F • XBF +
S • XBS = E • XBE + R • XBR (Component B) |
(3) |
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F •
XCF + S • XCS = E • XCE + R • XCR
(Component C) |
(4) |
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Variables of Interest |
Description |
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F |
Feed flow rate |
|
S |
Solvent
flow rate |
|
E |
Extract flow rate |
|
R |
Raffinate flow rate |
|
XAF |
Component A composition in feed stream |
|
XAS |
Component A composition in solvent stream |
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XAE |
Component A composition in extract stream |
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XAR |
Component A composition in raffinate stream |
|
XBF |
Component B composition in feed stream |
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XBS |
Component B composition in solvent stream |
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XBE |
Component B composition in extract stream |
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XBR |
Component B composition in raffinate stream |
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XCF |
Component C composition in feed stream |
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XCE |
Component C composition in extract stream |
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XCS |
Component C composition in solvent stream |
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XCR |
Component C composition in raffinate stream |
NOTES:
1) A more advanced analysis of
liquid-liquid extraction can be found in Perry's Chemical Engineers'
Handbook 7th Edition in Section 15, and Transport Processes
and Unit Operation 3rd Edition in Chapter 12.
2) The following web site is useful in creating a computer
generated ternary plot:
http://www.sfu.ca/~marshall/ternplot.htm
Last modified:
November 26, 2001 Created by Team
#2
