GATE 2026 CH – Question 20
A binary mixture of butane and butadiene is to be separated in an extractive distillation using furfural. Furfural lowers the activity of butadiene more than it does for butane. Consider the distillation sequence shown in the figure.
[Figure: two columns in series. The feed and a recycle stream of X, Y, Z enter the first column. A nearly pure stream X leaves the top of the first column, and its bottom goes to the second column. A nearly pure stream Y leaves the top of the second column and a nearly pure stream Z leaves its bottom and is recycled to the first column.]
Match the component labels in Group I with chemical species in Group II.
| Group I | Group II |
|---|---|
| P. Component X | 1. Butane |
| Q. Component Y | 2. Butadiene |
| R. Component Z | 3. Furfural |
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Show answer and explanation
Correct answer: (A) P-1, Q-2, R-3
Explanation
Furfural lowers the activity of butadiene more, so butadiene becomes less volatile than butane in its presence. In the first column butane (X) goes out at the top, while butadiene and furfural leave at the bottom. The second column separates them: butadiene (Y) is the top product and furfural (Z), the heaviest, is the bottom product that goes back to the first column as the solvent. So P-1, Q-2, R-3.