Environmental Engineering Reference
In-Depth Information
5
Extraction
For problems, sweat is a good solvent.
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5.1
Objectives
1 Determine the number of equilibrium stages in a partially miscible system using a:
(a) cross-flow cascade;
(b) countercurrent cascade.
2 Determine the minimum solvent flowrate.
3 Determine the number of equilibrium stages for an extraction process with intermediate
feed stages.
4 Use the McCabe-Thiele graphical method to determine the number of equilibrium
stages for completely immiscible systems.
5.2
Background
Extraction is a process in which one or more solutes are removed from a liquid by trans-
ferring the solute(s) into a second liquid phase (the mass-separating agent, or MSA), for
which the solutes have a higher affinity. Just as in other separations involving an MSA, the
two phases are brought into intimate contact with each other, then separated. Extraction
depends on differences in both solute solubility and density of the two phases. The sol-
ubility difference of the solute between the two liquid phases makes separation possible,
while the difference in density allows the two liquid phases to be separated from each
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