Question

The fractional conversion from an immobilized enzyme continuous stirred tank reactor under steady state operation increases with an increase in agitation speed. This behavior can be attributed to:

• A. reduced internal pore diffusion.
• B. Reduced external film diffusion.
• C. decrease in energy of activation for the enzyme.
• D. enhanced enzyme activity due to mechanical shear.

Hint:

Higher Agitation = Thinner boundary layer = Faster transport to enzyme.

Answer 1

The Correct Option is B

Step 1: Concept
In immobilized enzyme systems, the reaction rate is often limited by the transport of substrate to the catalyst surface.

Step 2: Meaning
External film diffusion is the resistance offered by the stagnant liquid layer surrounding the enzyme particle.

Step 3: Analysis
Agitation reduces the thickness of this stagnant liquid film. As agitation speed increases, the mass transfer of substrate to the enzyme becomes faster, overcoming the external diffusion limitation. Internal pore diffusion is affected by particle size, not agitation.

Step 4: Conclusion
The increase in conversion with stirring speed confirms that the system was limited by external mass transfer. Final Answer: (B)