Mass Transfer
When the solvent dissolves very little of solute, then

Very small quantity of solvent is required
Solvent of low freezing point should be used
Large quantity of solvent is required to extract the solute
Solvent of low latent heat of vaporisation should be used

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Mass Transfer
Plate efficiency

Increases due to liquid entrainment
Increases due to weeping and dumping of liquid
Is a function of the mass transfer between liquid and vapour
Increases due to foaming

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