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CHEM0077 C2 Catalysis and Chemical Process Technology Coursework

Answer all 4 questions. Type out all answers where possible but write out derivations and      make sketches by hand. The numbers in parentheses at the end of each question, indicates the provisional allocation of marks, 50 marks in total.

1) A reacts with B to form C and D according to the following overall reaction:

A + B → C + D (∆! "  = −40 # $ )

A, B, C and D are gases under all practical conditions and there are no likely side-reactions. A mechanism for this reaction can be proposed consisting of the following four steps:

A + * ⇄ A*

B + * ⇄ B*

A* + B* ⇄ C + D* + *

D* ⇄ D + *

a)   Derive a rate expression for the overall reaction based on the mechanism above,         assuming that the surface reaction, step 3, is the rate-determining step. Show all steps in your working.

b)   Derive the initial rate version of the rate expression derived in (a).

c)   How does the initial rate expression derived in (b) further simplify if A binds much more strongly to the surface than B and D? What is the reaction order in PB , the partial pressure of B, under these conditions?

d)  Discuss the optimal temperature and pressure for performing this reaction industrially.

e)   What is the most appropriate chemical reactor choice for this reaction? Explain your answer, clearly stating why your chosen reactor is the optimal choice.

2) An unsaturated fatty acid E is catalytically hydrogenated over a heterogeneous catalyst into a partially saturated fatty acid F according to the following overall reaction:

E + H2 → F (∆! "  = − 120 # $ )

E and F are both liquids under all industrially relevant conditions while H2 is a gas. F can be further hydrogenated to a fully saturated fatty acid G, which is undesired.

What is the most appropriate chemical reactor choice for this reaction? Explain clearly why your chosen reactor is the optimal choice.

3) An alkene I is hydrogenated to an alkane J over a noble metal heterogeneous catalyst according to the following overall reaction:

I + H2 → J (∆! "  = − 30 # $ )

I, J and H2 are all gaseous at all relevant conditions.

a)   What reactor do you suggest to use for measuring the initial rate of this reaction? Explain your answer.

b)   The initial reaction rate for this reaction is shown to depend on the gas velocity in the reactor. Explain this observation.

c)   What is likely to happen to the initial reaction rate at high gas velocities and why?

d)  What is likely to happen to the conversion of I, rather than the reaction rate, in a suitably chosen reactor when increasing the gas velocity and why?

e)   What can you say about the activation energy that will be measured for this reaction under the conditions in (b) and its significance?

4) An alcohol K is catalytically dehydrated to an alkene L according to the following overall reaction:

K → L + H2O             (∆! "  = +40 # $ )

K has a boiling point of 120º C under atmospheric pressure, while L boils at -7º C. Side reactions include the formation of the ether (M, boiling point 140º C) and aldehyde (N, boiling point 70º C) of K.

a)   Discuss the optimal temperature and pressure for performing this reaction industrially.

b)   Sketch an outline of an industrial process for converting K into L, assuming that the   single-pass conversion of K is limited to 40%. Include in your sketch any purification and separation steps and label all streams.