Methods of Purification of Organic Compounds

[IIT-MAIN-2016):  The distillation technique most suited for separating glycerol from spent-lye in the soap industry is:

  1. Simple distillation
  2. Fractional distillation
  3. Steam distillation
  4. Distillation under reduced pressure
Distillation under reduced pressure/Vacuum distillation : This technique is mostly applicable for those liquids which undergo decomposition near its boiling point. For example glycerol boils at 290°C with decomposition. But, if the pressure is reduced to 12 mm instead of 1 atm it will boil only at 180°C without decomposition.
That’s why this technique is applicable for separating glycerol from spent-lye in the soap industry. Hence, the correct answer is :D.
More to be known—
  • This technique separates compounds based on differences in boiling points.
  • The reduction in boiling point can be calculated using a temperature-pressure nomograph using the Clausius–Clapeyron relation.
  • Vacuum distillation in petroleum refining
  • Vacuum distillation is often used in large industrial plants as an efficient way to remove salt from ocean water, in order to produce fresh water. This is known as desalination. The ocean water is placed under a vacuum to lower its boiling point and has a heat source applied, allowing the fresh water to boil off and be condensed.

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