Salt-effect distillation
Salt-effect distillation is a method of extractive distillation in which a salt is dissolved in the mixture of liquids to be distilled. The salt acts as a separating agent by raising the relative volatility of the mixture and by breaking any azeotropes that may otherwise form.
Setup
[edit]The salt is fed into the distillation column at a steady rate by adding it to the reflux stream at the top of the column. It dissolves in the liquid phase, and since it is non-volatile, flows out with the heavier bottoms stream. The bottoms are partially or completely evaporated to recover the salt for reuse.
Usage
[edit]Extractive distillation is more costly than ordinary fractional distillation due to costs associated with the recovery of the separating agent. One advantage of salt-effect distillation over other types of azeotropic distillation is the potential for reduced costs associated with energy usage. In addition, the salt ions have a greater effect on the volatility of the mixture to be distilled than other liquid-separating agents. [1] Commercial usage of salt-effect distillation includes adding magnesium nitrate to an aqueous solution of nitric acid to concentrate it further. Calcium chloride is added to acetone-methanol and water-isopropanol mixtures in order to facilitate separation. [2]
References
[edit]- ^ Smallwood, Ian McN. (2002), Solvent Recovery Handbook (Second ed.), CRC Press, pp. 166–167, ISBN 0-8493-1602-2, retrieved 2007-11-30
- ^ "Salt-effect distillation", McGraw-Hill Dictionary of Scientific and Technical Terms, McGraw-Hill, 2003, retrieved 2007-11-30
See also
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