Mass Transfer
Steam distillation is not recommended to be used, if the

Material can not be distilled by indirect heating even under low pressure, because of the high boiling temperature
Material to be distilled is thermally unstable or has the tendency to react with other components associated with it, at the boiling temperature
Azeotropic mixture is to be separated and the final product is miscible with water
Liquids decompose, if distilled directly at atmospheric pressure

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Mass Transfer
Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)

Decreases pressure drop, decreases surface area
Increases pressure drop, increases surface area
Increases pressure drop, decreases surface area
Decreases pressure drop, increases surface area

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