This set of Chemical Reaction Engineering Interview Questions and Answers for Experienced people focuses on “Microbial Fermentation – 2”.

1. State true or false.

For product limiting microbial fermentation in CSTR with C_{C0}=0, C_{R0}=0 and high C_{A0}, washout occurs at kτ =1.

a) True

b) False

View Answer

Explanation: Maximum production of cells occurs at kτ =2. The concentration at which maximum production rate occurs is C

_{R}= \(\frac{C_R^*}{2}.\)

2. The plot representing the variation of C_{C} with the residence time in a PFR for substrate limiting microbial fermentation reaction is ____

a)

b)

c)

d)

View Answer

Explanation: Initially, the curve is very close to exponential decay. Deviation occurs when C

_{A}and C

_{C}change during the run. With a further increase in time, the microbial cells run out of food.

3. The slope of the curve of \(\frac{C_C}{r_C}\) and \(\frac{1}{C_A}\) for the substrate limiting microbial reaction in a batch reactor is ____

a) \(\frac{C_M}{k} \)

b) \(\frac{1}{k} \)

c) –\(\frac{C_M}{k} \)

d) –\(\frac{1}{k} \)

View Answer

Explanation: The equation representing the kinetics is, \(\frac{C_C}{r_C} = \frac{1}{k} + \frac{C_M}{k}\frac{1}{C_A}.\) The slope is \(\frac{C_M}{k} \) and the line intercept is \(\frac{1}{k}. \)

4. The plot of \(\frac{1}{C_A}\) and τ for mixed flow substrate limiting fermentation reaction in fermenters, assuming no cells in feed stream is ___

a) Quadratic

b) Linear

c) Logarithmic

d) Exponential

View Answer

Explanation: The relationship between C

_{A}and τ for mixed flow fermenter with C

_{C0}=0 is \(\frac{1}{C_A} = \frac{k}{C_M}\) τ – \(\frac{1}{C_M}.\) The plot is linear with a slope \(\frac{k}{C_M}. \)

5. Optimum operations for CSTR carrying out substrate limiting fermentation reaction occurs at ___

a) τ = \(\frac{N}{N-1} \)

b) kτ = \(\frac{N-1}{N} \)

c) kτ = \(\frac{N}{N-1} \)

d) kτ = \(\frac{N^2}{N-1} \)

View Answer

Explanation: The maximum operation for a single mixed flow fermenter occurs at \(\frac{C_A}{C_{A0}} = \frac{1}{N+1}.\) kτ = \(\frac{N}{N-1}. \)

6. The plot representing the variation of rate, r_{C} with C_{A} for Monod type microbial fermentation occurring in a PFR is ____

a)

b)

c)

d)

View Answer

Explanation: The rate is lower at the beginning. There is a leap in rate as reaction proceeds and then the rate decreases. The area under the curve gives the residence time.

7. Given the value of τ_{opt} for product limiting microbial fermentation is 2 hrs, then the value of τ_{washout} (in hour) is ____

a) 1

b) 2

c) 3

d) 4

View Answer

Explanation: τ

_{opt}= 2τ

_{washout}.

τ

_{washout}= 1 hour.

8. If C_{A0} = 8 and C_{M} = 1, the value of N is ____

a) 4

b) 1

c) 2

d) 3

View Answer

Explanation: N = (1+\(\frac{C_{A0}}{C_M}\))

^{0.5}= (1+\(\frac{8}{1}\))

^{0.5}= 3.

9. The value of C_{R,opt} for product limiting microbial fermentation (in kg/m^{3}), given the value of C_{R}*=60 kg/m^{3} is ____

a) 30

b) 20

c) 15

d) 10

View Answer

Explanation: C

_{R,opt}= \(\frac{C_R*}{2} = \frac{60}{2}\) = 30 kg/m

^{3}.

10. The value of τ_{m,washout} given N = 4 and k=1 is____

a) 1.06

b) 1.34

c) 2.45

d) 3.86

View Answer

Explanation: τ

_{m,washout}= \(\frac{N^2}{(N^2-1)k} = \frac{16}{15}\) = 1.06

**Sanfoundry Global Education & Learning Series – Chemical Reaction Engineering.**

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