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CEIC2005: Chemical Reaction Engineering

TERM 2, 2021

FINAL EXAM — SAMPLE PAPER

[SAMPLE PAPER] QUESTION 1.

Consider the following reaction:

A + 5 B + 6 C −−−→ 3 D + 3 E

Determine a) the rate law and b) the rate coefficient from the following data:

Experiment [A] (M) [B] (M) [C] (M) Initial Rate (M/s)

8.0 × 10−4

3.2 × 10−3

6.4 × 10−3

3.2 × 10−3

Ensure that you justify your work with appropriate calculations or plots.

[SAMPLE PAPER] QUESTION 2.

Catalytic hydrolysis reactions of organophosphates (OP) are becoming increasing studied, as

most OP are highly toxic and persist in the environment after use. Common uses include pes-

ticides that linger in the environment and as chemical warfare agents. The generalised reaction

for OP hydrolysis is:

where the P containing functionality is cleaved from the organic, producing generally less toxic

intermediates. Catalysts are often needed to facilitate these reactions, particularly for the hy- drolysis of chemical warfare agents that are chemically stable by design. To screen for candidate

OP hydrolysis catalysts, para-nitrophenyl phosphate (pNPP) hydrolysis is often used as a test- bed reaction as it is one of the less toxic of the OP and the reaction can be monitored via UV-Vis spectroscopy. The aqueous phase reaction is:

This reaction does not proceed forward at neutral pH and higher, while at pH ~ 2.0 the Ea of

the uncatalysed reaction is 108.8 kJ/mol.

Cerium-based oxides are often a candidate material for catalytic OP hydrolysis reactions. Pro-

vided with this exam are [pNPP] vs time data at 25, 30, 40, and 50 ∘ C for a Ce2O3 nanoparticle

catalyst under aqueous reaction conditions at neutral pH.

(a) Assuming first-order reaction kinetics, calculate the rate coefficient at each temperature. Note that Ce3+-based catalysts tend to deactivate at longer reaction times and higher tem-

peratures.

(b) Calculate the activation energy of the catalysed reaction.

Organophosphate hydrolase (OPH) is an enzyme discovered in bacteria that can perform organo-

phosphate hydrolysis reactions, as the name suggests. For this reaction at room temperature,

KM = 556 µM and max = 1.48 µM/s at neutral pH using an OPH concentration of 2.56 nM. The Ea is 32.64 kJ/mol.

(d) Calculate the turnover frequency of OPH under these conditions.

(e) Calculate the catalytic efficiency of OPH under these conditions.

(f) Considering both enzymatic and heterogenous catalysed reactions, identify which method

would be best for OP hydrolysis reactions.

[SAMPLE PAPER] QUESTION 3.

A thick, rich vegetable soup on a cold winter day can be prepared according to traditional recipes

such as the one below. This is “slow food”, with time needed to extract and combine flavours.

Most home-made and gourmet foods are prepared via batch or semi-batch processes and that makes large scale production in commercial kitchens problematic.

Traditional Semi-batch Vegetable Soup Recipe

flour

vegetable oil

finely chopped onions

cubed root vegetables (pumpkin, potato, carrot)

grated root vegetables

finely chopped celery

chopped herbs (parsley, basil)

vegetable stock powder

chilli powder

water

1) Cook onions in 1/4 of the oil until translucent (10 min)

2) Add water and vegetable stock powder, bring to boil

3) Add all root vegetables, return to boil and keep gently boiling for 2 hours

4) Add celery, herbs and chilli

5) Allow to cool for 2-4 hours

6) Reheat the soup mix

7) Meanwhile, mix flour into remaining hot oil and cook for 3-4 min until thickened

8) Add flour/oil mix to the rest of soup and heat through

Our start-up company is going to develop and sell a machine able to make gourmet vegetable

soup as a continuous process. It needs to produce 15L/h of soup. We will focus mostly on the

reaction engineering aspects of the design, while being aware of the process context.

(a) Neatly sketch a diagram of a process for continuous soup production. Standard symbols for unit operations are not required; a labelled diagram is sufficient.

(b) Estimate the space-time of each reactor within the cascade to estimate the total size of the soup producing machine.

(c) Which operations within your design might you seek to speed up? What experiments would you need to conduct to do so? Clearly describe the Aim, Method and Data Analysis Procedure that would be used for each experiment. (Guidance: 400 to 800 words)

(d) What size machine will you claim is achievable in order to secure the funding that is needed to develop it? (Guidance: 200 words)

Appropriate assumptions and simplifications will need to be made with careful justification

given for each part of the question. Always prioritise quality over quantity in your answers.

[SAMPLE PAPER] QUESTION 4.

A simple A −−−→ B reaction is to be undertaken in a CSTR but the purity requirements of the

concentration of A is 0.75 mol L− 1, the input volumetric flow rate is 0.110 L s− 1 and the rate