Distillation

Question 1

Distillation relies on what…

Answer 1

…the differences in the volatilities of the different components

Question 2

The vapour, under ideal conditions, is always richer in…

Answer 2

…the more volatile component than the liquid

Question 3

What are three main methods of distillation

Answer 3

• Differential distillation
• Flash/equilibrium distillation
• Rectification

Question 4

What are the main criteria for consideration

Answer 4

• purity of the product
• operating cost
• capital cost

Question 5

The composition of the product in batch distillation depends on…

Answer 5

• the still composition
• number of plates in the column
• reflux ratio used

Question 6

What is an azeotrope

Answer 6

When the composition of the vapour is the same as that of the liquid and no further enrichment can be obtained by straightforward distillation

Question 7

Give an example of a mixture that would form an azeotrope

Answer 7

Ethanol-water

Question 8

What component is added to an azeotropic mixture

Answer 8

An entrainer

Question 9

What is the purpose of the entrainer

Answer 9

To increase the relative volatility of the two key components - it will cause the volatility of one component to increase more than the other

Question 10

For extractive distillation to be effect what must be kept in mind…

Answer 10

• the solvent must be chosen to affect the liquid phase behavior of the key components differently
• the solvent must have a higher boiling point than the key components and must be relatively non volatile
• the solvent should not form additional azeotropes with the components in the mixture
• the distillation column should have two feed, one for the primary feed and the other for the solvent which should be above the primary feed

Question 11

What is extractive distillation

Answer 11

A rectification process where a solvent is added to a feed stream to alter the volatilities of the key components without the formation of any additional azeotropes

Question 12

What is distillation used for

Answer 12

To split liquid mixtures into their individual components

Question 13

What is batch distillation?

Answer 13

The more volatile component is evaporated from the still which therefore becomes progressively richer in the less volatile constituent. Distillation is continued, either until the residue of the still contains a material with an acceptable low content of the volatile material, or until the distillate is no longer sufficiently pure in respect of the volatile component.

Question 14

What is azeotropic distillation

Answer 14

This is a distillation process that is done whereby an additional component is added to generate a new lower boiling point azeotrope that is hetereogenous