2

GROUP 1, GROUP 13

Your company is planning to increase their production based on the current demand.

As a process engineer, you are given task to design a new reactor system that gives

80% conversion. Due to the limitation from the upstream process, you have to

maintain the incoming flow rate of reactant A at 100 mol/s. You are given a set of

reaction rate data based on existing reactor system as shown in Table Q1. However,

based on the new layout, you found that the available new space is much smaller. The

existing reactor system consists of PFR and CSTR arranged in series, with PFR as a

first reactor to achieve 50% conversion then followed by CSTR. Propose an

appropriate reactor system and evaluate the percentage reduction of the total volume,

if any. Use Levenspiel plot to explain your answer.

Table Q1: Reaction rate data

X 0.0 0.2 0.4 0.5 0.6 0.8

-rA

(mol/dm3.min) 10.00 16.67 50.00 50.00 18.18 8.00

[25 Marks]

3

GROUP 2, GROUP 14

A nobel winning professor has found a new formulation to produce chemical M-16. It is a

simple decomposition reaction of gaseous chemical DxN with another reactant which is

called MqF. He found that one mole of DxN reacts with one mole MqF to produce three

mole of M-16, and the reaction follows elementary rate law. The entering molar flow rate

of DxN is 50% of total flow rate. Assuming that the temperature and pressure are at 22°C

and 1 atm, respectively, construct the stoichiometry table and write the concentration of

each species in term of the conversion. Plot the concentration profile for each species.

[25 Marks]

4

GROUP 3, GROUP 15

The liquid phase isomerization of butane

104HCn 104HCi

was carried out adiabatically and the data is given in TABLE Q1 below. The molar flow

rate of n-butane is 50 kmol/hr.

Table Q1: Conversion vs. reaction rate data

Conversion, X Reaction rate, -rA (kmol / m3h)

0.0 39

0.2 53

0.4 59

0.6 38

0.65 25

a. Calculate the volume of reactor required to achieve 40% conversion in:

i. a plug flow reactor.

[5 marks]

ii. a continuous flow reactor.

[5 marks]

b. Suggest the best reactor combination that gives the lowest reactor volume

to achieve 60% conversion and the intermediate conversion between the

reactor.

[9 marks]

c. Calculate the total reactor volume for the reactor scheme you have

proposed in part (b).

[6 marks]

5

GROUP 4, GROUP 16

The liquid phase reaction

A → B + C

is carried out in a batch reactor at 60oC. The data is recorded in Table Q2.

TABLE Q2

t (hr) 0 1 2 3 4

CA (mol/dm3) 1 0.8 0.5 0.1 0.05

a. By using an appropriate method, determine the reaction order and the rate

constant for the reaction.

[20 marks]

b. You are required to design a suitable flow reactor for 90% conversion for the

above reaction. The flow reactor will operate at 100oC. Do you have sufficient

data to proceed with the design? If no, propose suitable experiments for you to

obtain the data and outline the analysis required for you to find the missing data.

[5 marks]

GROUP 5, GROUP 17

The gaseous reaction 𝐴 → 𝐵 has a unimolecular reaction rate constant of 0.0015

min-1 at 80 oC. The reaction is to be carried out in parallel tubes of 5 m long and 20 mm

inside diameter under a pressure of 20 atm at 190 oC. A production rate of 1000 kg/hour

of B is required. Given an activation energy of 20 000 J/mol, with each A and B have

molecular weights of 58,

a. How many tubes are needed if the conversion of A is to be 80%. Assume

perfect gas laws.

[15 marks]

b. If CSTR is to be used, what would be the volume of the reactor to achieve

80% conversion of A?

[5 marks]

c. Comment on your findings from part a and part b

[5 marks]

GROUP 6, GROUP 18

A well-known professor has found a new solution called chemical Z that is useful to treat

pollution in waste water.

2X + Y→ 4Z

The initial reaction rate was measured as a function of temperature when the

concentration of A was 3 mol/dm3 nd B was 2 mol/dm3. These data recorded in TABLE

Q1:

TABLE Q1: Initial reaction rate data

-rx(mol/dm3.s) 0.002 0.046 0.72 8.33

T(K) 300 320 340 360

a. Determine the rate constant of the reaction and write reaction rate in term

of concentration.

[10 marks]

b. If the reaction is carried out in a batch reactor with the initial concentration

of X at 0.2 mol/dm3, at a temperature of 27C, estimate the required volume

of the reactor to achieve 40% conversion of A

[15 marks]

GROUP 7, GROUP 19

The irreversible liquid phase reaction

A B + C

Is carried out in a batch reactor. The following data were collected from the experimental

work:

TABLE Q2: Rate data for liquid phase reaction

t (min) 0.0 2.0 4.0 6.0

CA (mol/dm3) 2.00 1.41 0.99 0.70

a. Analyse the data and prove that the reaction is elementary. Hence, find the

reaction rate constant, k, for the reaction.

[12 marks]

b. If the entering volumetric flow rate is 10 dm3/min, evaluate the volume required

to achieve 95% conversion in:

i. a continuous stirred tank reactor.

[5 marks]

ii. a plug flow reactor.

[5 marks]

c. If you were to repeat the experiment to determine the kinetics, what

parameters would you vary? Explain your answer.

[3 marks]

GROUP 8, GROUP 20

The production of ethylene, C2H4, from pure ethane, C2H6, is an elementary, irreversible

reaction that proceeds as follows:

C2H6 (g) C2H4 (g) +H2 (g)

The reaction takes place in a plug flow reactor operating isothermally at 1100 K and a

pressure of 6 atm. The reaction rate constant, k, is 0.072 s-1 at 1000 K, and the activation

energy is 82,000 cal/ g mol. Assume no pressure drop in the reactor. The required

conversion of ethane is 80%.

a. If the required production rate of ethylene is 150 mol/s, calculate the required

entering molar flow rate of ethane.

[2 marks]

b. Calculate the required volume of the plug flow reactor for 80% conversion of

ethane.

[15 marks]

c. Due to space constraint, the person in charge of the fabrication work has

decided to bend the reactor into U-tube shape instead of one long tubular pipe.

When the reactor was put in operation, the actual conversion is less than 80%.

In your opinion, what is the cause of this discrepancy? Suggest how to improve

the reactor performance to achieve the desired production of ethylene.

[8 marks]

GROUP 9, GROUP 21

The homogeneous gas decomposition of phosphine, (PH3) is carried out in a plug flow

reactor (PFR) at 649oC and 11.4 atm. The reaction is first order with the value of rate

constant, k, of 10hr1. The feed consist of 67 mole% phosphine and 33 mole% inert. The

feed contains 50 mol/hr of phosphine and the desired conversion is 90%. The

stoichiometric equation is as follows:

4PH3 (g) P4 (g) + 6H2 (g)

a. Calculate the volume of PFR to achieve 90% conversion [16 marks]

b. Give and explain TWO (2) reasons adding inert to the reaction [4 marks]

GROUP 10, GROUP 22

A reaction proceeds as follows:

1

2

1

2

22

k

A A B

k

A B

A B D r k C C

B U r k C

Propose a suitable reactor and its arrangement to maximize the production of D.

[5 marks]

b. A reactant A reacts to produce a main product P and two by-products Q and R

according to the following reaction:

1

2

3

1

2

2

0.5

3

k

A A

k

A A

k

A A

A P r k C

A Q r k C

A Y r k C

The reaction rate constant for the above reactions are:

4 1

1

7 3 1 1

2

3 0.5 1.5 1

3

4.0 10

1.0 10

5.4 10

k s

k m mol s

k mol m s

i. A stream containing 1500 mol/m3 of A at a volumetric flow rate of 2.0 x 10-4

m3/s is processed in a continuous stirred tank reactor (CSTR). Calculate the

volume of the CSTR that gives a maximum selectivity for the production of P.

[10 marks]

ii. It has been proposed to increase the production of P by adding another reactor

to the reactor in part (b). What type of reactor should it be and how should it be

connected to the reactor in part (b)? Explain the basis of your choice.

[5 marks]

GROUP 11, GROUP 23

The elementary irreversible liquid phase reaction, A + B C, is carried out adiabatically

in a flow reactor. An equal molar feed of A and B is fed to the reactor at 40°C with a

volumetric flow rate of 2 dm3/s. The entering concentration of A is 0.2 mol/dm3. The

information on the heat capacity, heat of formation at 273 K and reaction rate constant is

given below.

𝐻𝐴0 = −20

𝑘𝑐𝑎𝑙

𝑚𝑜𝑙

𝐻𝐵0 = −15

𝑘𝑐𝑎𝑙

𝑚𝑜𝑙

𝐻𝐶0 = −41

𝑘𝑐𝑎𝑙

𝑚𝑜𝑙

𝐶𝑝,𝐴 = 𝐶𝑝,𝐵 = 30𝑐𝑎𝑙

𝑚𝑜𝑙 • 𝐾

𝐶𝑝,𝐶 = 40𝑐𝑎𝑙

𝑚𝑜𝑙 • 𝐾

𝑘 = 0.008𝑒𝑥𝑝 [𝐸

𝑅(1

300−1

𝑇)]

𝑑𝑚3

𝑚𝑜𝑙 • 𝑠 𝑤𝑖𝑡ℎ 𝐸 = 8,000

𝑐𝑎𝑙

𝑚𝑜𝑙

a) Evaluate the best reactor between a PFR and CSTR to achieve 40% conversion.

Justify your answer.

[20 marks]

b) The required conversion is increased to 80%. Will the reactor that you have

proposed in part (a) is still the best reactor for the process? Justify you answer.

[3 marks]

c) Give ONE (1) reason for the difference that you have observed between part (a)

and part (b) in relation to the effect of temperature on the reaction.

[2 marks]

GROUP 12, GROUP 24

The reaction of A producing only one product B is to be carried out adiabatically in a flow

reactor at 300 K with the presence of 10 mol% of inert. The reaction obeys elementary

reversible reaction with a specific reaction rate of 25 hr-1 at 340 K. Assume that the costs

of 1 m3 of CSTR and PFR are the same; evaluate the most economical reactor to be used

for the reaction in order to produce 30% conversion of A.

Additional informations:

𝛥𝐻𝑅𝑥𝑜 = −5000

𝐽

𝑚𝑜𝑙𝐴

𝐸 = 56 𝑘𝐽

𝑚𝑜𝑙

𝑘𝐶 = 2.05 𝑎𝑡 300 𝐾

𝐶𝐴0 = 7.5 𝑘𝑚𝑜𝑙

𝑑𝑚3

𝐶𝑝,𝐴 = 100 𝐽

𝑚𝑜𝑙 • 𝐾

𝐶𝑝,𝐵 = 100 𝐽

𝑚𝑜𝑙 • 𝐾

𝐶𝑝,𝐼𝑛𝑒𝑟𝑡 = 120 𝐽

𝑚𝑜𝑙 • 𝐾

[25 marks]