Question

During batch distillation composition change occurs.
A. Heavy component increases in still
B. Distillate formed from condensation of vapor
C. Vapor formation occurs in still
D. As time passes composition of distillate decreases
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. B, D, A, C
• C. C, A, B, D
• D. C, B, D, A

Hint:

Batch distillation is defined by the Rayleigh Equation. Unlike continuous distillation where compositions are constant at any point, in batch distillation, the "still" is always getting "heavier" (less volatile) as time ticks forward.

Answer 1

The Correct Option is D

Concept: Batch distillation is a non-steady state process where the composition of the liquid in the still and the vapor leaving it change continuously over time.

Step 1: Identify the operational sequence.

• C (Vapor formation occurs in still): Heat is applied to the liquid mixture in the still, causing it to boil and generate vapor enriched in the more volatile component.
• B (Distillate formed from condensation of vapor): This vapor is moved to a condenser where it is cooled back into a liquid state (the distillate).
• D (As time passes composition of distillate decreases): Because the more volatile component is being removed, the remaining liquid in the still becomes leaner, and consequently, the vapor (and distillate) generated becomes progressively weaker in that component.
• A (Heavy component increases in still): As a final result of the process, the concentration of the less volatile (heavy) component in the still steadily increases.

Step 2: Final Sequence.
The logical physical and temporal order is C $\rightarrow$ B $\rightarrow$ D $\rightarrow$ A.