Final Exam Fall 2013

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Final ExamChemical Reaction Engineering

December 19, 2013

Name______________________________________________________

Read the exam through first. Please write legibly. Answer all questions completely, clearlyindicating final answers and showing work. Closed book, notes and electronics.

Problem 1. (12 pts) Draw residence time distribution for the following cases using an inert pulsetracer. Please indicate average residence times for each reactor.

Reactor

SystemRTD Graph

Reactor

SystemRTD Graph

PFTR CSTR+CSTR

CSTRInfinite CSTRs in

series

CSTR + PFTR PFTR + PFTR

E

t

E

t

E

t

E

t

E

t

E

t


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Name_________________________________________________ Final Exam, Fall 2013

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Problem 2. (12 pts) Fill in the table to the type of catalysts

Homogeneous Heterogeneous

a) Typical Catalyst Phase

b) Typical Reactant Phase

c) Give 1 advantage of

use

d) Give 1 disadvantage of

use

e)

Example catalyst

f) Example reaction(does not have to be

for catalyst in e)

Problem 3. (10 pts) What does weak mixing versus strong mixing in mass-transfer dominatedreactions illustrate? Explain in 2-3 sentences. Use drawings if necessary to supplement your

explanation.


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Problem 4. (20 points). Explain what ideal addition polymerization is in 2-3 sentences. Also

provide an example of how the reaction steps proceed, defining the species as necessary.

Provide the mass balance for [AM3] in a PFTR.


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Problem 5. (16 points). You have an aqueous, strongly acidic reaction A 2B that is

significantly exothermic. You want to operate at moderately-low conversions to control the

heating of the reactor. Explain what type of reactor you should use, the reactor material and anysafety and environmental concerns. Justify your decisions.


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Problem 6. (20 pts)A first order reaction A + D B + C (r = kCA) is carried out in an aqueous

solution in an adiabatic CSTR. The feed is equimolar in A and D at a concentration of 2.5 M

each, and the volumetric flowrate is 0.04 L/sec. The reactor volume is 25L and the residencetime is 625 sec. The reactor was observed to operate at a single steady-state temperature of

225C. The rate constant coefficient for this reaction is 5.9x105sec

-1. The activation energy is

75 kJ/mol. The enthalpy of reaction is -12.3 kcal/mol. Determine the conversion of the reactor atsteady state and the feed temperature.


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Problem 7. (15 pts) You have designed a new continuous process for the manufacturing of

yogurt. In this process, you feed a mixture of 2000 spores of active cultures/min in 10 L/min of

milk into a CSTR. Your finished yogurt needs to have 106 active spores/L. If the spores

multiply in the form S 5S, with a rate r = kCs, with a k = 0.25 hr-1

, what is the residence time

for this reactor?


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Problem 8. (20 pts) A pseudohomogeneous rate of the irreversible 1storder reaction AB was

found to be 2x10-2

mol/L sec when the conc of A was 0.25 M. This is equivalent to having a

pseudohomogeneous rate constant of 0.080 sec-1

.a) If the catalyst used had a surface area of 300 m

2/g, a density of 3.3 g/cm

3and a void

fraction of 0.4, what is the surface reaction rate expression (mol/cm2sec)?

b) What reactor volume will you need to process 90 L/sec of 2.0 M A to 85% conversion ina slurry reactor?


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Problem 9. (20 pts). Your copper ore processing plant has a 10,000 gallon waste tailings pond

that you feed an acidic combination of copper and surfactant to. The copper settles with time

and the surfactant decomposes with excess O2 aerated through the pond. Normally, you allowthe waste to process in a batch reactor-type situation for 6 months to get the surfactant

concentration down from 2x10-2

M to the environmentally-benign level of 1x10-7

M before

releasing to the natural waterway.

Unfortunately, the muskrat population has increased significantly in the area lately. They have

burrowed a hole in the tailings pond dam, creating a stream flowing at 100 gal/hr leading to the

nearby river that flows at 150,000 gal/hr at 0.5mph. Your tailings pond had a concentration ofsurfactant at the time of the breach of 3.62x10

-4M. How far down river do you have to go to

reach the environmentally-benign level of surfactant? You may assume first order kinetics in

surfactant and a well-aerated river.


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Problem 10. (15 pts). The plot shows data for an enzyme reaction both with and without

inhibition. Identify which curve is from an inhibited system, and identify the type of inhibition.

The answer must be justified, not just guessed.

-1/rS

1/CS

Curve A

Curve B

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Final Exam Fall 2013