Project ForgeA binary E-F mixture (80% E feed) must be purified to 99.5% E using two distillation columns at pressures P1 and P2. VLE data show a minimum-boiling azeotrope near x≈0.85 at 100 kPa, but no azeotrope in the plotted range (0.8-1.0) at 20 kPa. Column 1 produces a distillate of 0.9 E from the 0.8 feed. If P1, P2 are in kPa, which is correct?
- AP1=100, P2=20, high-purity E from top of column 2
- BP1=100, P2=20, high-purity E from bottom of column 2
- CP1=20, P2=100, high-purity E from top of column 2
- P1=20, P2=100, high-purity E from bottom of column 2
Explanation
Column 1 must reach 0.9 E from a 0.8 feed — impossible at 100kPa since its azeotrope at ~0.85 blocks further enrichment, so P1=20kPa (no azeotrope in this range). Feeding the 0.9 E stream into column 2 at P2=100kPa places it on the far side of that pressure's ~0.85 azeotrope, where the liquid becomes progressively richer in E going down the column — so high-purity E is recovered from the BOTTOM of column 2, with the overhead approaching the azeotropic composition.
Source: GATE CH 2020 (2020)
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