CPB 415 –Chemical Kinetics and Reactor Design
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CPB 415 –Chemical Kinetics and Reactor Design
Semester Project
2021
Objective:
Design a reactor to produce 10000 metric tons/year of maleic anhydride from butane.
Reaction Details:
Maleic anhydride is an industrially important commodity chemical used primarily in the production of polyester resins. The current commercial process to produce maleic anhydride employs a vanadium-phosphorous-oxide catalyst (VPO) to selectively oxidize butane:
C4H10 + 3.5 O2 g C4H2O3 + 4 H2O DelHR= -1236 kJ/mol
However, side reactions to produce CO and CO2 are also important:
C4H10 + 6.5 O2 g 4 CO2 + 5 H2O DelHR= -2656 kJ/mol
C4H10 + 4.5 O2 g 4 CO + 5 H2O DelHR= -1526 kJ/mol
Reaction Kinetics
Reaction kinetics have been obtained from the literature (Sharma, 1991) that are to be used for your design. The above reactions have been rewritten as the following three reactions:
C4H10 + 3.5 O2 g C4H2O3 + 4 H2O
C4H2O3 + p O2 g (6-2p) CO + (2p-2) CO2 + H2O
C4H10 + n O2 g (13-2n) CO + (2n-9) CO2 + 5 H2O
Where n and p are coefficients obtained from the kinetic study, n=5.5, p=1 for your design.
Reaction rates for these three reactions are given by:
r1=k1P1a1/(1+K2P2)
r2=k2P2/(1+K2P2)2
r3=k3P1a3
where P1 = partial pressure of butane and P2 = partial pressure of maleic anhydride.
The following kinetic parameters are suggested (rate constants at 400oC):
k1=0.96 x 10-6 kmol/kg s atm0.54
k2=0.29 x 10-5 kmol/kg s atm
k3=0.15 x 10-6 kmol/kg/s atm0.54
E1=E3=93100 J/mol
E2=155000 J/mol
a1=a3=0.54
K2=310 atm-1
Reactor Configuration
The reactor to be designed is a packed bed reactor with multiple reaction tubes with external cooling. External cooling is to be provided by a mixed salt. It is assumed that the temperature of the salt is constant. The tube diameter is to be 30 mm OD to maximize heat transfer. Heat transfer is a significant issue in this reactor due to the large exothermicity of the oxidation reactions.
Design Basis
A reactor is to be designed with a total production of 10000 metric tons per year, which would be considered a world-class plant. The reactor will be in operation 95% of the time. The feed will consist of 1.7% butane in air. Total inlet pressure is 1.9 atm, and the total molar flow rate is 100 x 10-3 kmol/hr. Pressure drop should be considered using the Ergun equation. The reactor should operate with a conversion of 85%. The following information may be helpful for your design:
Overall heat transfer coefficient (based on outside area) = 106 W/m2 K
Catalyst diameter = 3 mm
Void fraction (e) = 0.45
rB=3.11 x 103 kg/m3
Changing the catalyst diameter by a factor of 10 did not affect reactor performance
External mass transfer limitations are negligible
DelHf (maleic anhydride) = -3.942 x 105 J/mol
Deliverables
You are to consider your design in several parts, and satisfy the following requirements:
1. Model the maleic anhydride reactor assuming an inlet temperature of 300oC and a salt temperature of 380oC, calculating the number of reactor tubes and mass of catalyst required. The exiting composition and graphs depicting partial pressures, total pressure, and temperature as functions of reactor length should be reported.
2. What safety concerns are there for this reaction? How could you design your reactor to account for these concerns? For example, you might consider the effects of varying the salt temperature on the resulting temperature profiles.
Please show the results of your simulations in a brief report. This report should include a list of the assumptions you made, the equations used to simulate the reactor, and the results (plots listed above should be included). You should also address the safety concerns, and the size of the reactor needed for the given production rate. Please note that you are expected to do a detailed design, so many of the assumptions you have made in the past (isobaric, mean heat capacities, etc.) should not be made. Please see Dr. Hohn if you have questions about what a reasonable assumption is.
Requirements for CPB 515
Choose at least two other variables to vary and conduct a systematic study of the effects of those variables. Include your discussion of how these variables change the maleic anhydride reactor behavior in your report. Note that your report should be expanded to include this discussion beyond the ~5 pages described above.
2022-11-25