GATE 2025 CH – Question 34
Oil is extracted from mustard seeds having 20 wt% oil and 80 wt% solids, using hexane as a solvent. After extraction, the hexane-free residual cake contains 1 wt% oil. Assuming negligible dissolution of cake in hexane, the percentage oil recovery in hexane is ____% (rounded off to the nearest integer).
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Correct answer: 96
Explanation
Take 100 kg of seed: 20 kg oil and 80 kg solids. The hexane-free cake has 1 wt% oil, so the oil in the cake is $x$ with $\frac{x}{80 + x} = 0.01$, which gives $x = \frac{0.8}{0.99} = 0.808$ kg. The oil recovered in the hexane is $20 - 0.808 = 19.19$ kg, which is $\frac{19.19}{20} = 95.96 \approx 96$ %.