Chemical Reaction Engineering Questions and Answers – Parallel Reactions Design – Selectivity and Reactor Yield

«
»

This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Parallel Reactions Design – Selectivity and Reactor Yield”.

1. Selectivity in parallel reactions is defined as the ratio of___
a) Moles of desired product formed to the moles of undesired material formed
b) Moles of undesired product formed to the moles of desired material formed
c) Moles of product formed to the moles of reactant consumed
d) Moles of reactant consumed to the moles of product formed

Explanation: Selectivity is defined for a parallel reaction. For a reactant A forming product B and an undesired product C, selectivity is the ratio of B to C.

2. The reaction yield is defined as the ratio of ____
a) Moles of reactant reacted to the moles of product formed
b) Moles of product formed to the moles of reactant reacted
c) Moles of desired product formed to the moles of undesired material formed
d) Moles of product formed to the moles of reactant fed

Explanation: For a reaction, A → R, yield is $$\frac{C_R}{C_{A0}-C_A},$$
Where, CA0 is the initial concentration of reactant
CA is the final concentration of reactant
CR is the final concentration of product

3. For the parallel reaction, A→B and A→C, if B is the desired product and the reaction A→B is of positive order n1 and C is the undesired product and the reaction A→C is of negative order n2, then increasing the concentration of A _____
a) Decreases desired product selectivity
b) Increases desired product selectivity
c) Initially increases and then decreases desired product selectivity
d) Does not affect desired product selectivity

Explanation: Selectivity = $$\frac{Rate \, of \, B \, formed}{Rate \, of \, C \, formed}$$
Selectivity α$$\frac{C_A^{n1}}{C_A^{n2}}$$ α C$$_A^{n1-n2}.$$ As n2 is negative, increasing CA increases the selectivity of B.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

4. For the parallel reaction, A→B of order n1 and A→C of order n2, if B is the desired product, then which of the following reactor/ combination of reactors is used if n1 > n2?
a) CSTR
b) CSTR followed by Bubbling bed reactor
c) PFR
d) CSTR followed by PFR

Explanation: To maximise C$$_A^{n1-n2}$$, PFR is used. If n1-n2 > 0, the average concentration inside the reactor is maximum.

5. For the parallel reaction, A→B, represented as (-rA) = k1CA5 and A→C represented as (-rA) = k2CA3, theideal reactor preferred is ____
a) CSTR
b) CSTRs in parallel
c) CSTRs in series
d) PFR

Explanation: Selectivity = $$\frac{k_1 C_A^5}{k_2 C_A^3}$$ α CA2
To increase the yield of product, CA should be large. Hence, PFR is used.

6. If the reactions A→B and A→C are represented as (-rA) = k1CA3 and (-rA) = k2CA6 of activation energies 130 and 150 J/ mol, then which of the following is the right selection of process parameters to increase selectivity of B?
a) CSTR, High temperature
b) PFR, High temperature
c) CSTR, Low temperature
d) PFR, Low temperature

Explanation: Selectivity = $$\frac{k_1 C_A^3}{k_2 C_A^6} = \frac{k_1}{k_2}$$ CA-3
By Arrhenius equation, k = Ae$$^\frac{-E_a}{RT}$$
Since E1 < E2, temperature has to be decreased to increase the yield of B.

7. If A→B, (rB) = k1CA2 and A→C, (rC) = k2CA1, then the yield of C is ____
a) $$\frac{k_2}{k_2+k_1 C_A}$$
b) $$\frac{k_2}{k_2+k_1}$$
c) $$\frac{1}{k_2+k_1 C_A}$$
d) $$\frac{k_2}{k_1 C_A}$$

Explanation: Yield of C = $$\frac{k_2 C_A}{k_2+k_1 C_A^2}$$
Yield of C = $$\frac{k_2}{k_2+k_1 C_A}$$

8. If CA0 = 20 mol/L and the initial concentration of the products B and C are 0, CA = 4 mol/L, then the final concentration of B in CSTR (in mol/L) is ____
A→B, (rB) = 0.2CA3
A→C, (rC) = 0.1CA1
a) 20.4
b) 15.51
c) 32.56
d) 40.54

Explanation: Yield = $$\frac{0.2C_A^3}{0.2C_A^3+0.1C_A^1} = \frac{C_B-C_{B0}}{C_{A0}-C_A}$$
CB = 15.51 mol/ L.

9. The final concentration of product is related to the yield as ____
a) Final concentration = Yield × Reactant fed
b) Final concentration = Yield / Reactant fed
c) Final concentration = Yield × Reactant converted
d) Final concentration = Yield / Reactant fed

Explanation: Yield = $$\frac{Product \, formed}{Reactant \, converted}$$
Product formed = Yield × Reactant converted.

10. If for the parallel reactions A→B and A→C, if the final concentration of B is 26 mol/ L and A converted is 36 mol/L, then the final concentration of C is ____
a) 15
b) 5
c) 6
d) 10

Explanation: CA0 – CA = 36
CB = 26
CC = A converted – B formed
CC = 10 mol/L.

Sanfoundry Global Education & Learning Series – Chemical Reaction Engineering.

To practice all areas of Chemical Reaction Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!