Question

Please choose correct option
A. Top and bottom product contain non-key components.
B. Minimum reflux ratio is determined using Underwood equation.
C. Throughout the column relative volatility is constant.
D. Separation is defined by heavy and light components.
Choose the correct answer from the options given below:

• A. A and B Only
• B. A, B and D Only
• C. B and C Only
• D. A, C and D Only

Hint:

Remember the "Fenske-Underwood-Gilliland" (FUG) method: Fenske for minimum stages ($N_{min}$), Underwood for minimum reflux ($R_{min}$), and Gilliland for actual stages ($N$).

Answer 1

The Correct Option is B

Concept: Multicomponent distillation involves the separation of mixtures based on "key" components (Light Key and Heavy Key). Non-key components are those that are either much lighter or much heavier than the keys.

Step 1: Analyze multicomponent distillation principles.

• Statement A: Correct. In multicomponent systems, non-key components will distribute based on their boiling points relative to the keys; very light non-keys go to the top, and very heavy ones go to the bottom.
• Statement B: Correct. The Underwood equations are the standard analytical method used to calculate the minimum reflux ratio ($R_{min}$) for multicomponent mixtures.
• Statement C: Incorrect. Relative volatility ($\alpha$) typically varies with temperature and composition as the mixture moves through the column. Constant $\alpha$ is a simplifying assumption, not a rule.
• Statement D: Correct. The degree of separation is specified by selecting two "key" components—the Light Key (LK) and the Heavy Key (HK).

Step 2: Final Selection.
Statements A, B, and D are technically sound for distillation design.