The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by
A. Increasing the gas film co-efficient
B. Increasing the liquid film co-efficient
C. Increasing the total pressure
D. Decreasing the total pressure
Answer: Option A
This Question Belongs to Chemical Engineering >> Mass Transfer
The correct answer is: B. Increasing the liquid film coefficient
Explanation:
In the absorption of SO₂ in air using dilute NaOH, the process involves a gas-liquid reaction, where:
SO₂ (gas) diffuses through the gas phase to the interface
Then it dissolves in the liquid
Finally, it reacts with NaOH in the liquid phase
Key Point:
Since SO₂ is quite soluble in water and rapidly reacts with NaOH, the liquid-phase resistance becomes dominant.
Hence, the overall mass transfer coefficient is controlled by the liquid film.
Increasing the liquid film coefficient (e.g., by agitation or increasing liquid velocity):
Reduces liquid-side resistance
Substantially increases the overall mass transfer coefficient
Why not the others?
A. Increasing gas film coefficient: Has limited impact, since gas-side resistance is not rate-limiting.
C/D. Changing pressure: Total pressure has minimal effect here because SO₂ is already very soluble and chemically reactive.
✅ Final Answer: B. Increasing the liquid film coefficient
The correct answer is B
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