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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.

Contents 1 Setup 2 Usage 3 References 4 See also

[edit] Setup

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.

[edit] Usage

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]

[edit] References

1. ^ Smallwood, Ian McN. (2002), Solvent Recovery Handbook (Second ed.), CRC Press, pp. 166–167, ISBN 0849316022, http://books.google.com/books?id=GcjME0wiMVsC&pg=PA166&lpg=PA166&dq=%22salt+effect+distillation%22&source=web&ots=2LZD-V50yV&sig=9hJuSASlhr2YnbdijAForfqWCqQ#PPA166,M1, retrieved 2007-11-30 
2. ^ "Salt-effect distillation", McGraw-Hill Dictionary of Scientific and Technical Terms, McGraw-Hill, 2003, http://www.answers.com/topic/salt-effect-distillation, retrieved 2007-11-30 

[edit] See also

• Distillation
• Extractive Distillation
• Azeotrope

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