Project ForgeMass Transfer
Mass Transfer Operations
GATE 2018
Hard
A feed (20% A, 80% B) is extracted in 2 cross-current stages using equal amounts of pure solvent C per stage (B,C immiscible). 60% of A is extracted in Stage 1. Equilibrium: Y*=1.5X. The mol% A in the Stage-2 raffinate is (rounded off to second decimal place)
3.85 %(± 0.15 accepted)
Explanation
Basis 100: X0=20/80=0.25. Stage1: A remaining=8, X1=0.1. B(X0−X1)=S·1.5X1 ⟹ 80×0.15=S×0.15 ⟹ S=80. Stage2: 80(0.1−X2)=80×1.5X2 ⟹ X2=0.04. A in raffinate2=80×0.04=3.2. Total=83.2. mol%A=3.2/83.2×100=3.85%.
Source: GATE CH 2018 (2018)
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