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CN2116 Quiz One (March 7 2009)

Please enter this assessment number in your answer sheet: 01

1. The time taken for the unimolecularreaction AR to reduce the concentration

of A from 0.1M to 0.05M is 10 minutes. What is the time taken to reduce the

concentration of A from 0.08M to 0.04M?

(a) 10 min; (b) longer than 10 min; (c) shorter than 10 min; (d) inadequate

information to arrive at a numerical answer

2. It is found that in the gas phase reaction A R in excess of inert, the

concentration of A first falls linearly with reactor length and then exponentially.

This is indication of

(a) a first order reaction, (b) a zero order reaction, (c) a down- shifting order reaction;

(d) an up-shifting order reaction

3. Three unequal sized CSTRs (1 L, 2 L, and 3 L respectively) are connected in

parallel to convert a fresh feed to 90% completion. What will be the impact if the

2 L reactor is taken out of the service?

(a) Loss of 10% in product throughput

(b) Loss of 33.3% in product throughput

(c) Loss of 50% in product throughput(d) Loss of 66.6% in product throughput

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4. Calculate the composite A values for the following competing reactions carried

out with an equimolar mixture of A and B

(desired)

2 (side reaction)

A B R

A S

(a) 0A

; (b) 1A

; (c ) 0.5A

; (d) cannot be computed

5. The following instantaneous yield curve was obtained from an experimentalisothermal PFR and is characteristic of

(a) a series reaction

(b) a parallel reaction(c) a reaction following Michaelis-Menten kinetics

(d) This is not possible as instantaneous yield function must always be positive

6. Currently an isothermal CSTR is used to produce B from A according to the

liquid phase reaction A B . The feed is an aqueous solution of A available at

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cA

-1/rA

0Ac =1 mole/l, and the concentration of B in the product is

Bc = 0.95 mole/l. A

recent market survey calls for an increase in both the production rate and the

product quality (B

c ) in order to stay competitive and profitable. As a process

engineer you are asked to evaluate which of the following options is best for the

company.

(a) Decrease the flow rate through the CSTR

(b) Increase the reaction temperature(c) Increase the concentration of A in the feed

(d) Add a series or parallel-connected CSTR.

7. The following (reciprocal) rate curve was obtained experimentally from anisothermal batch reactor. Which of the following statements holds the most truthassuming that the concentration range covers all values of design interest?

(a)The curve can be used for the design of all types of reactors

(b)The rate curve can only be used for the design of batch and plug flow tubularreactors

(c)The rate curve is useful for the design of all types of reactors provided that theprocess feed has the same composition as the feed used in the determinationof the above rate curve.

(d)None of the above

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8. If A is the reactant, can cAincrease during the course of an isothermal & isobaric

reaction?

a. It is absolutely not possible

b. Possible for an expanding reacting system

c. Possible for a contracting reacting systemd. Possible only if the decrease in the moles of A due to reaction is less than

the extent of volume contraction due to reaction

9. What conclusion(s) can you draw from the following instantaneous yield curves?

(a) The reaction involved is ; 1A rR r

(b) The reaction involved is ; 1A rR r

(c) The reactions involved are 1 2; ; 1A rR A sS r . Both reactions are of

the same order and 1 2E E

(d) The reactions involved are 1 2; ; 1A rR A sS r . Both reactions are of

the same order and 1 2E E

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10. In the following series-parallel reactions in aqueous solution, R is the desiredproduct and S is the side product

1

2

A B R

R A S

Which of the following statements is correct?

(a)The overall reaction is 2A B S

(b) constantA R S

c c c

(c) 2 constantR A Bc c c

(d) constantB R S

c c c

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CN2116 (2110) Quiz One (Set One)

March 13 2010

All reactions are carried out at constant temperature and pressure unless indicated

otherwise.

1. Identify ALLthe correctstatements in the list of statements below. Please note that

each incorrect response will nullify a correct response.

(a)For first order reactions, the time taken to reduce the reactant concentration to 1/eof the initial value is independent of the choice of the initial value.

(b)The (-1/rA) vs cAplot obtained from a laboratory CSTR can always be used forthe design of industrial PFRs so long as the feed concentration for the latter falls

within the range of concentrations studied in the laboratory.(c)PFR is the reactor of choice for harvesting the intermediate product R in the first

order irreversible series reactions A

R

S. Hence CSTR should be used if thedesirable product is S.

(d)Recycle does not matter to CSTRs since the latter are already perfectly mixed.This is true for CSTRs in series too.

(e)The rate law for the reversible reaction A B C D is 1 2A B C Dr k c c k c c

2. In a contracting reaction system mAR (where m>1) carried out at constant T,P, thedecrease in the concentration of A is partly compensated by the reduction in the

reaction volume. What is the maximum concentration of A possible in a contracting

reaction system?

(a)Greater than 0Ac(b)Equal to 0Ac(c)Smaller than 0Ac(d)None of the above

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3. Consider the following reactions in an aqueous solution, which of the following

concentration relationships is correct?

2

0.5 2

A R S

T U

where , , and are molar extents of reactions

( ) / 2 constant

( ) / 2 constant

( ) / 2 2 / 2 constant

( ) 2 / 2 2 constant

A R S

A R T

A R S T U

A R S T U

a c c c

b c c c

c c c c c c

d c c c c c

4. Two CSTRs of sizes 1L and 2L are connected in series with the 2L reactor leading

the 1L reactor. The reaction of interest is an aqueous-phase reaction with negativeorder kinetics. If it is desired to improve the efficiency of the reactor operation (i.e.

increasing the product concentration, product throughput, or both), which of the

following measures will you endorse?

(a) Convert the two CSTR into batch reactors

(b) Reverse the reactor sequence(c) Connect the reactors in parallel

(d) Decease the operating temperature

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5. What are the conditions needed to express the 2nd

order kinetics 2A

r kc as

2Ap A

dpk p

dt in a batch reactor?

(a) unconditionally; (b) constant T, (c) constant V, (d) constant T and V

6. Determine the reaction order of a liquid phase reaction from the following

concentration-time curve

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(a)Second order, (b) first order; (c) zero order, (d) none of the above

7. Indicate which of the following contacting schemes would maximize the yield of R

per mole of A converted in the following competing reactions:

1 1

2

2 2 1 2

A B

A

A B R r k c c

A S r k c E E

(a) Isothermal operation at lowest possible temperature in a plug flow reactor

(b) Isothermal operation at highest possible temperature in a mixed flow reactor

(c) Rising temperature profile, B in plug flow, A in mixed flow(d) Decreasing temperature profile, B in plug flow, A in mixed flow

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8 Which of the following reactor arrangements should be used to handle the reactionwith the following rate curve? cA0=10, cA= 1

(a) A PFR from cA0 to cA=4 followed by a CSTR from cA=4 to cA= 1

(b) A CSTR from cA0 to cA=4 followed by a PFR from cA=4 to cA= 1(c) A PFR from cA0 to cA=1

(d) A recycle PFR from cA0 to cA=4 with R=1

9. Three unequal sized CSTRs (1L, 2L, and 3L respectively) are connected in parallel to

handle the conversion of a fresh feed to 90% completion. If the 2L reactor is all of asudden broken down, what will be the reduction in the product throughput if the

product quality is to be maintained at the same level as that before the breakdown?

(a) Loss of 10%

(b) Loss of 33.3%

(c) Loss of 50%(d) Loss of 66.6%

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10. At present 91% conversion of A is converted into product by a first order kinetics in a

single mixed flow reactor. We plan to add in series two more reactors of the same

size as the one in use. What will be the new treatment rate if the conversion is keptunchanged?

(a) approximately 5 times; (b) approximately 8 times; (c) approximately 10 times; (d)approximately 15 times

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All reactions are isothermal unless indicated otherwise.

1. R is produced from the liquid phase reaction 2A R R . A feed with the

composition 0 01 mol/l, 0.01 mol/lA Rc c is available. The rate law is A Rr c c

Which of the following statements is correct?

(a)The reaction is autocatalytic and elementary(b)A PFR can be used to run this reaction

(c)A recycle PFR with any recycle ratio will always best the PFR(d)The best two-reactor combo to use is a PFR followed by a CSTR

2. The gas phase reaction 2A R is carried out in a train of series-connected

unequal-size CSTRs. The following flow rates are measured at the inlet and outlet

of one of the reactors:

0.5, 1.0

0.25, 1.5

Ai Ri

Af Rf

F F

F F

What are the values of 0 , ,i AfA xF to use in the design equation

0 ( )A Af Aii

Af

F x xV

r

(a)0.5, 0.5, 0.75(b)1.0, 0.5, 0.75

(c)0.5, 0, 0.25

(d)1.0, 0, 0.5

3. The following gas phase reactions are run in a constant pressure batch reactor tothe molar extents of reactions indicated next to them. The feed is a mixture of A,

B and inert with the composition 0 0 0 1 moleA B IN N N

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1

2

3

, 0.5

2 , 0.25

, 0.5

A B C

A D

B E

What is the value of 0/V V ?

(a)1.08(b)1

(c)0.92(d)0.625

4. The following network of PFRs is being used for processing the liquid phase

reaction 2A R to a specified product concentration. If reactor V2 is shut down

for maintenance the flow rates to the remaining reactors are adjusted in order to

maintain the same product quality. Which of the following adjustments will yourecommend?

(a)Decrease the volumetric flow rates to V1, V3, V4 and V5 by 20% each

(b)Increase the volumetric flow rates to V1, V3, V4 and V5 by 20% each(c) Increase the volumetric flow rate to V1 by 60% and decrease the volumetric

flow rates to V3, V4 and V5 by 20%

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(d)Increase the volumetric flow rate to V1 by 100% and decrease the volumetricflow rates to V3, V4 and V5 by 40%

5. A undergoes multiple reactions to form R, S and T. Only R among the products

has market values. The following instantaneous yield curve was obtained frombatch reactor measurements.

R

What of the following conclusions holds the most truth?

V1 =2 L

V2 = 2 L

V3 = 4 L

V4 = 1L

V5 = 1L

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(a)This indicates a parallel reaction system , ,A R A S A T , where all

steps are of different reaction orders (assuming power law kinetics)(b)For maximum yield of R, one should use a CSTR followed by a PFTR which

operates till point B

(c)The reaction system is likely ,A R T A S with A S having a lower

reaction order (assuming power law kinetics)(d)There is something wrong with this instantaneous curve the instantaneous

yield should not be having negative values.

6. For the constant pressure gas phase reaction 2 3A R S starting with pure A

only, which of the following concentration relations is correct?

(a) constant2 3

(b) constant

(c) 2 3 constant

2(d) 2 constant

3

SRA

A R S

A R S

A R S

ccc

c c c

c c c

c c c

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7. Make inference about the following reaction system by examining its long-term

bahavior1

1

2

3

k

k

k

k

A B

B C D

E A

(a)This is a reversible reaction system

(b)This is an irreversible reaction system(c)The reversibility of the above system is controlled by the amount of C added

(d)The reversibility of the above system is controlled by the amount of E added

8. Which of the following rate laws is thermodynamically consistent for the

reversible reaction 2 3A B ?

(a) 3/21 2A Bk c k c

(b)2

1 2

3 41

A B

B

k c k c

k c k c

(c)2 3

1 2

3 41 1

A B

B

k c k ck c k c

(d) None of the above

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9 The following data were obtained from a liquid phase reaction in a CSTRoperating at room temperature:

0 1( / ), 1A CSTRc mole liter V liter

0v (liter/min) 3.58 1.16 0.71 0.11

(mol/liter)Ac 0.8 0.6 0.5 0.2

Which of the following conclusions from the analysis of these data is correct?

(a) The data satisfy power law kinetics with a reaction order n1

(d) The data cannot be fitted to power law kinetics

10. The liquid phase reaction A R with the rate law r kc is currently run in a

PFR with a space time of 1 minusing a feed of pure A. The conversion of A wasfound to be 63.2%. Another reactor is to be added in series to the PFR in order to

boost the conversion of A. Which of the following suggestions will you adopt?

a. Add another PFR of the same size

b. Add a CSTR of the same sizec. Place a CSTR three times the size of the current PFR before the PFRd. Place a CSTR three times the size of the current PFR after the PFR

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All reactions are isothermal and isobaric unless indicated otherwise

1) The high temperature water-gas shift reaction2 2 2CO H O CO H is an

industrially important reaction for hydrogen production. It has the following rate lawunder the prevailing operating conditions:

2 2 2

2 22

2 2 2

[ ][ ]([ ][ ] )

1 [ ] [ ] [ ] [ ]CO H O CO H

CO Hk CO H O

KR

K CO K H O K CO K H

What of the following conclusions are correct? (There may be more than one correct

answer, however, an incorrect response will completely nullify a correct response)

(a)The rate law is thermodynamically consistent(b)Both the forward and reverse reactions are bimolecular(c)When water is present in large excess of CO, the reaction is initially first order in

[CO]

(d)The reaction should be carried out in a recycle plug flow reactor(e)The plot of ln(reaction rates) (measured at fixed concentrations) against reciprocal

temperature (in Kelvin) exhibits Arrhenius behavior.

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2) The cyclic reactions , ,A B B C C A are carried out in a batch reactor. What

will you expect to find when the molar extents of reactions for ,A B B C are

equal; and the molar extent of the C A reaction is half as much? It is known that

only A is present in the reactor at the start of the reactions.

(a) There is not net reaction(b) 0

BN

(c)C A

N

d) ( ) / 2C A B

N N N

3) You are provided with a feed stream of fixed specifications to two un-equal size

CSTRs running the second order gas phase reaction 2A B R . How should you

connect the reactors?

(a)Connect the CSTRs in parallel and use equal flow rate in both(b)Connect the CSTRs in parallel and adjust the flow rate to have equal space time in

both.

(c)Connect the reactors in series with the small reactor before the large reactor(d)Connect the reactors in series with the large reactor before the small reactor

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4) For a first order reaction, the time to reach 95% conversion is 3 minutes. If the kineticshas been improved (e.g. through catalysts or elevated temperatures) to reach 95%

conversion in 2 minutes, what will be the reduction in the reaction time for anyconversion?

(a) 33.3%(b) 50%(c) 67%

(d) 100%

5) The gas phase isomerization of A to B (isomerization: a molecular rearrangementreaction in which there is no net change in the number of moles) was studied in a batch

reactor and the following concentration-time curve was obtained. Which of the followingstatements is incorrect?

(a) This is a reversible reaction with an equilibrium constant of 4

(b) A CSTR reactor with a space t ime ~ 20 min can deliver 80% conversion(c) The half-life of the reaction is approximately 3 min

(d) The rate law derived from the batch reactor is applicable to other types of reactors

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Time (min)

0 5 10 15 20 25

cA

(mole/l)

0.0

0.2

0.4

0.6

0.8

1.0

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6) The first order gas phase reaction 2 , (mole/min- )A A

A R r l c is carried out in a

plug flow reactor. The feed is pure A at 0 00.1mole / 1, v / minAc l l . The stream

leaving the reactor has a volumetric flow rate of 1.8 / minl . What is the size of the

reactor?

(a) between 1 and 2 l(b) between 2 and 3 l(c) between 3 and 4 l

(d) between 4 and 5 l

7) A chemical engineer reported the doubling of conversion when the residence time of a

batch reactor was doubled. He then proceeded to propose the conversion of the batchreactor into a CSTR to support continuous operations to reduce the reactor operating cost.

Your comments on his proposal would be:

(a) Yes. I wholeheartedly support this proposal(b) No. He does not know his stuff well a CSTR is always inferior to a batch reactor

(c) I cannot comment as there is insufficient kinetics information for me to analyze thesituation.

(d) Excuse me is this a constant density system?

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8) For the series reaction 1 2k k

A R S where 2 10.1, 1k k , determine the size of

the reactor which can provide the maximum yield of R on A.

(a) 1 1k

(b)1

1 2k

(c)1

2 3k

(d) 13 4k

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9) Among the following reactions, only R is a marketable product. S and T are non-recyclable byproducts that have to be treated as process wastes. A is however recyclable.

1 2

1 1

2

2 2

3

3 3

,

,

,

A B

R B

A B

A B R R k c c

R B S R k c c

A B T R k c c

The suggested reactor operation is:(a) Use a CSTR with high cA and low cB

(b) Use a batch reactor, A is added to B(c) Use a PFR with high cA and cB(d) Use a recycle PFR with high cB and low cA

10) What will happen if one places a recycle (without separation) to an optimallydesigned PFR (for R)running the first order series reactionA R S ?

(a) There will be more A converted

(b) There will be more R formed leading to an increase in the production rate of R(c) The yield of Rper mole of A convertedwill increase

(d) The yield of Sper mole of A convertedwill increase

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All reactions are assumed to occur at constant temperature and constant pressure unless stated

otherwise

1. Which of the following is an elementary reaction?

a. The water gas shift reaction2 2 2CO(g)+H O(g) CO (g)+H (g) with the rate law of

2 2

2

2

0.36 1(1 )CO H

CO CO

CO H O

P PR kP P

K P P

b. The second order reaction 2A P

c. The unimolecular isomerization reaction3 2 2 2

CF CH Cl CF ClCH F

d. Fermentation of sugar to ethanol by yeast with Michaels-Menton kinetics

2. Calculate the concentration of B in the gas phase reaction 2A B when 50% of A is

reacted. The Feed is a 50:50 mixture of A and an inert gas

a.0

/ 0.4B A

c c

b.0

0.4 / 0.66B A

c c

c.0

0.66 / 0.8B A

c c

d.00.8 / 1B Ac c

3. The following graph is the concentration profile along the length of a plug flow tubular

reactor (PFTR) used for the study of the liquid phase reaction A 2B. The rate law that may

be deduced from such a plot is:

a. A first order reaction

b. A reaction with reaction order between 1 and 2

c. A second order reactiond. A non-power law kinetics

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Length from entrance

0 1 2 3 4 5

cA

0.0

0.2

0.4

0.6

0.8

1.0

4. The first order gas phase reaction A R is carried out in a perfectly mixed continuous

stirred-tank reactor (CSTR). The concentration of R leaving the reactor is 0.9 mol/l using a

feed of pure A at 1 mol/l. What is the concentration of R leaving the reactor when the

volumetric flow rate to the reactor is doubled?

a. cR> 0.9 mol/lb. 0.8< cR 0.9 mol/l

c. 0.5< cR 0.8 mol/l

d. cR 0.5 mol/l

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5. The autocatalytic reaction A + R R + R with the rate law ofR A R

r c c is to be carried out in

a reactor up to 40% conversion of A. Which of the following reactors is most suitable for

such an operation?

a. A CSTR

b. A PFTR

c. A CSTR followed by a PFTR

d. A PFTR with an optimized recycle ratio

6. What of the following combinations of reactors is functionally superior to a single 100llarge

CSTR for a negative order reaction?

a. A 100l PFTR

b. Two 50l CSTRs in series

c. Two 50l CSTRs in parallel with the same exit composition from both reactors

d. A 50l CSTR in parallel with a 60l CSTR for same reactor exit compositions

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7. A 10l PFR and two 10l CSTRs are available to process a reaction with 2nd

order kinetics.

Which of the following arrangements for the reactors would you recommend?

a. Connect the reactors in series in the sequence of 10l PFR, 10l CSTR, 10l CSTR

b. Connect the reactors in series in the sequence of 10l CSTR, 10l CSTR, 10l PFR

c. Connect the reactors in series in the sequence of 10l CSTR, 10l PFR, 10l CSTR

d. Connect the two 10l CSTRs in parallel and place them behind the 10l PFR

8. Consider the following system of first order reactions where R is the desired product.

1 2

0.5A R S

T

Which of the following conclusions is true?

a.max

0

0.25R

A

c

c

b.max

0

0.25R

A

c

c

c.

max

00.25 0.5

R

A

c

c

d.max

0

0.5R

A

c

c

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9. For the following series-parallel reactions where R is the desired product

1 1

2

2 2

,

,

A B

R B

A B R R k c c

B R S R k c c

Which of the following mixing schemes will maximize the yield of R based on per mole of A

supplied?

a. Fast addition of A to B

b. Slow addition of A to B

c. Fast addition of B to A

d. Slow addition of B to A

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10. A undergoes multiple reactions to form R, S and T. Only R among the products has market

values. The following instantaneous yield curve was obtained from batch reactor

measurements.

0cA

B

What of the following conclusions is true?

(a) This indicates a parallel reaction system , ,A R A S A T , where all steps are of

different reaction orders (assuming power law kinetics)

(b) The reaction system is likely ,A R T A S with A S having a higher reaction

order (assuming applicability of power law kinetics)(c) The reaction system is likely ,A R T A S with A S having a lower reaction

order (assuming applicability of power law kinetics)

(d) For maximum yield of R, one should use a PFTR which operates till point B