Question

Give 8 differences of Equilibrium (or flash distillation) and Simple batch (or differential distillation)

Answer 1

DIFFERENTIAL DISTILLATION/ BATCH DISTILLATION

1.It is a batch and a single stage distillation.

2.The vapor formed over a short period is in equilibrium with the liquid, the total vapor formed is not in equilibrium with the residual liquid. Then, at the end of the process, the liquid that remains (and is concentrated in the less volatile component) is removed as bottom product.

3. No reflux is returned to the still, and no stages are provided inside the column.

4. Infinite time is not provided. So, the separation achieved is not the maximum achievable separation.

5. The values of the distillate and residue obtained are based upon the amount of separation required.

6. The pressure reducing valve is not used before the feed enters the unit.

7. Here, separation is achieved but not till equilibrium. Equilibrium means maximum achievable separation.

8. Differential distillation can be used for comparable volatilities. It also uses the Rayleigh equation.

FLASH DISTILLATION

1. Flash distillation is the continuous process.

2. The definite fraction of the liquid feed is vaporized in such manner that the vapor must be "in equilibrium" with the residual liquid. Hence it is also called as "equilibrium distillation".

3. Flash distillation also does not involve the use of reflux but infinite time is provided.

4. As infinite time is provided, so separation takes place till equilibrium is achieved.

5. As the data generated is equilibrium data between the vapor and liquid phases, so this data can be used to plot the T-x-y diagram.

6. Flash distillation involves the use of Pressure reducing valve.

7. Flash distillation acts as an ideal stage as the end result is to achieve equilibrium. Equilibrium means maximum achievable separation and that is achieved here.

8. Flash distillation fails when the separating components are of comparable volatility. It requires the use of distillation with reflux.

Diagrams are as follows: