Reaction Kinetics (Methanol Synthesis)

Reaction Kinetics

(Methanol Synthesis)

Your task is to convert syngas (CO, H 2 ) for further processing into methanol (CH 3 OH). To
this end, a new copper/zinc catalyst has been developed which has promising potential.
Reactions for methanol synthesis (new zinc-based catalyst):

���� 2��2 ⇆ ����3���� ∆H Rxn@298K: -91 kJ/mol
����2 + 3��2 ⇆ ����3���� + ��2�� ∆H Rxn@298K : -41 kJ/mol
(Note: In this report, we will consider only the forward reactions).

Your assignment is to produce a report ultimately detailing (1) the determination of reaction
kinetics and (2) how you optimized your methanol synthesis reactor (3) the impact of
reaction kinetics uncertainties on the optimized result.

(1) The following data has been obtained for the methanol synthesis reactions using a
constant volume batch reactor. All reactions can be treated as irreversible.

��3
���� +2 → ����3������4
����2 + 3��2 → ����3����2��
Reaction conducted with excess hydrogen (H 2 ):

t(s) C CO (M) t(s) C CO2
(M)
0 0.500 0 1.400
1 0.330 1 0.570
2.5 0.221 3 0.270
5 0.142 5 0.170
10 0.083 7 0.130
20 0.045 10 0.090
40 0.024 15 0.060
60 0.016 30 0.030

Reaction conducted with excess carbon dioxide (CO 2 ) but no carbon monoxide (CO):

t(s) C H2 (M)
0 0.900
0.5 0.502

��3
���� + 2��2 → ����3����
T( o C) ��3
300 0.86
400 1.81
500 3.07
600 4.88
700 6.62

��4

����2 + 3��2 → ����3����2��
T( o C) ��4
500 17
600 21.1
700 25.4
800 29
900 33.1
1 0.352
1.5 0.258
3 0.122
6 0.043
12 0.012

Reactions conducted with excess carbon monoxide (CO) but no carbon dioxide (CO 2 ):

t(s) C H2 (M)
0 0.750
0.2 0.600
0.5 0.444
1.0 0.269
2.0 0.098
3.0 0.036
4.0 0.013
5.0 0.005

Further examination of the reaction determines a temperature dependence of the reaction
rate constants. The following data has been obtained for the reactions (Units for the
reaction rate constant are M (mol/L) and s (seconds)):
In the appendix of the report,
calculations
and the figures should be
clearly presented
showing how the reaction rate
expressions
associated

With the methanol synthesis were obtained.

(2) Use the reaction kinetics obtained to report the conversion for (a) 1m long PFR
reactor (b) 10m long PFR reactor. Identify the optimal reactor volume numerically
(using Excel Spreadsheet) for each case and discuss how you came to this decision
based on your modeling and other supporting information. Explain how you
determined the appropriate number of tubes and the diameter of the tubes inside the
reactor – provide a sketch of the final reactor design showing major dimensions (this
does not need to show every tube inside reactor! – only present an example of one
and the geometric arrangement/spacing of the nearest

Neighbors). You should present a plot of conversion (X) as a function of reactor
volume when discussing and justifying the determination of the optimal size (allowing
V to become extremely large at a diminishing return on X is not a good answer!). For
each reactor calculate the pressure drop using Ergun equation – plot pressure drop
(∆P) as a function of reactor length, and also plot ∆P as a function of the catalyst means size
(0.1mm to 10mm in increments of 0.1mm)
– discuss the pros and cons of changing the catalyst size. Critically analyze adding CO 2
(up to 500kgmole/h) to the feed of the methanol synthesis reactor. For the optimal
reactor, sizes plot the concentration profiles of reactants and products as a function of
the length of reactors. Also, plot density vs. reactor length; Report the production of
methanol (tonne/yr).
(3) Perform a sensitivity analysis (± 10% for methanol synthesis reaction kinetic orders
obtained in part (1) – you only need to identify maximum and minimum cases) w.r.t.
Conversion (X), reactor volume (V), and methanol production for the methanol
synthesis reactors. The impact of this error on the reactor conversion for the 1m and
10m PFR must be presented and discussed, and all values presented in the final
report should contain the resultant errors (e.g., Methanol production = 300,000 (±
20,000) tonne/yr).

A final report must be produced, which addresses all the tasks above and
discusses the choice of catalyst, reactors, and production rates w.r.t. Industrial
process. You should read supplemental literature provided on LMS and use all
pertinent information when discussing your final reactor design. Discuss in detail
how well you think the PFR reactor models a real industrial reactor for methanol
synthesis production – clearly identify to what extent PFR is appropriate and to
what extent it is not.

Additional information:
Assume ideal gas law applies when determining thermodynamic
properties. Reactor feed rate is 5,000kgmol/h of syngas (feed ratio H 2
–to-CO is 2:1)).
Limits for methanol synthesis reaction conditions:
Temp = 300 o C.
Pressure = 20Bar.
Reaction is gas
phase.
The additional feed of CO 2: up to 500kgmol/h.
The catalyst used for methanol production reactions is a novel spherical Zinc based catalyst with the following information:
Mean Size: 3
mm Void
fraction: 0.5
Particle sphericity: 0.5