Project ForgeTwo elemental gases (A and B) are reacting to form a liquid (C) in a steady state process as per the reaction A+B→C. The single-pass conversion of the reaction is only 20% and hence recycle is used. The product is separated completely in pure form. The fresh feed has 49 mol% of A and B each along with 2 mol% impurities. The maximum allowable impurities in the recycle stream is 20 mol%. The amount of purge stream (in moles) per 100 moles of the fresh feed is _____
Explanation
The purge stream is bled from the recycle loop, so it shares the recycle stream's composition (design target: 20 mol% impurities). At steady state, all impurities entering with the fresh feed must leave via the purge (impurities are otherwise inert and don't react or get separated with C). Impurity balance: 2 mol (in 100 mol fresh feed) = 0.20 × Purge, so Purge = 2/0.20 = 10 mol. (The 20% single-pass conversion determines reactor/recycle sizing, not the purge molar flow, which is fixed purely by the impurity balance.)
Source: GATE CH 2014 (2014)
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