Ideal PFR and CFSTR treat a pollutant by first-order kinetics at the same inlet concentration, flow and target outlet concentration. Which comparison is true?
Correct answer: (A) PFR always requires less volume
Explanation
For positive removal and first-order decay,$V_{PFR}=(Q/k)\ln(C_0/C)$ and $V_{CSTR}=(Q/k)(C_0/C-1)$. Since ln r<r−1 for r>1,the PFR needs less volume. Thus **A**. At zero removal both volumes vanish, the trivial excluded limit.
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