1. Chemical Reaction Engineering: Reactor Design Project
Caitlin Boyd
Katherine Ross
April 23, 2008

2. Overview Elements of Reactor Design
Reaction of 1-butene to maleic anhydride
Preliminary Plug Flow Reactor Design
Inclusion of Energy Balance
Optimization Process
Optimized Reactor
Conclusions

3. Elements of Reactor Design
Momentum Balance & Pressure Drop
Reaction Mechanism
Kinetics
Conversion
Production and Selectivity
Energy Balance
Thermodynamic Stability
Optimization
Assumptions

4. Momentum Balance and Pressure Drop
The momentum balance accounts for the pressure change in the reactor.
where
Pressure drop cannot exceed 10% of initial pressure.

5. 1-butene to maleic anhydride
Reaction Mechanism
1-butene to maleic anhydride
(1) C4H O2  C4H2O H2O
(2) C4H O2  4 CO H2O
(3) C4H O2  2 C2H4O
(4) C4H O2  C4H6O + H2O

6. Kinetics Preliminary Reaction Kinetics (1 Reaction) rm = k1 * pB
where pB is partial pressure of 1-butene and
k1 = x 105 *exp(-11569/T) [=] kmol/ kgcat-bar-s

7. Kinetics
Kinetics for Multiple Reactions from Literature1

8. Conversion of Reactant
The goal conversion of 1-butene found in literature was 90%.1 This was used as a basis for all reactor models throughout the design process.
X stands for conversion, FBT0 is the initial flow of 1-butene and FBT is the outlet flow of 1-butene.

9. Production and Selectivity
Goal Production: 40,000 metric tons/ year
Selectivity of maleic anhydride, the desired product, was found by the following equation:
Selectivity

10. Energy Balance
where
This accounts for non- isothermal behavior in the reactor and allows for the optimization of the reactor temperature.
[=] kJ/ kgcat-s

11. Thermodynamic Stability
The reactor gain was analyzed to determine whether the reactor was thermodynamically stable. The gain analysis involves raising the coolant fluid temperature one degree and finding the how much the hotspot temperature changes.
A gain less than two indicates a thermodynamically stable reactor.

12. Optimization
Throughout the reactor design project this semester each memo submission involved a new aspect of the reactor:
Volume
Pressure Drop
Multiple Reactions
Energy Balance
The final challenge was to optimize a reactor in both Polymath and Aspen that would include these aspects.

13. Initial Reactor Assumptions
90% conversion of 1- butene
Phosphorous and vanadium oxide catalyst2
Inlet pressure of 2.2 bar
Reactor at 400oC
Catalyst bulk density of 1000 kgcat/ m3
Void fraction: 0.45

14. Reactor Volume – Memo 2
Catalyst weight was calculated to be kgcat
Effect of Catalyst Mass on Conversion at Various Temperatures

15. Momentum Balance- Memo 3
Memo 3 Table: Number of Tubes and Pressure Drop for 1” Tubes with Varying Length
Multi-tubular, 1in. Diameter, Length varies from 1 meter to 1.3 meter
d (meter)
# tubes Ac G βo
length (m) P% ΔP
0.0254
11.457
1.3
11.6
2.54E+04
11.546
1.29
11.3
2.48E+04
11.636
1.28
11.0
2.42E+04
11.728
1.27
10.8
2.37E+04
11.821
1.26
10.5
2.31E+04
11.915
1.25
10.3
2.26E+04
12.011
1.24
10.0
2.20E+04
12.109
1.23
9.76
2.15E+04
12.412
1.2
9.06
1.99E+04
13.540
1.1
6.99
1.54E+04
14.894 1
5.28
1.16E+04

16. Momentum Balance- Memo 3
Effects of doubling particle diameter
Dp= 0.005m
Dp= 0.01m
length (m) P% ΔP
1.3
11.6
2.54E+04
5.24
1.15E+04
1.29
11.3
2.48E+04
5.12
1.13E+04
1.28
11.0
2.42E+04
5.00
1.10E+04
1.27
10.8
2.37E+04
4.89
1.08E+04
1.26
10.5
2.31E+04
4.77
1.05E+04
1.25
10.3
2.26E+04
4.66
1.03E+04
1.24
10.0
2.20E+04
4.55
1.00E+04
1.23
9.76
2.15E+04
4.44
1.2
9.06
1.99E+04
4.12
1.1
6.99
1.54E+04
3.18 1
5.28
1.16E+04
2.40
Pressure Drop vs. Reactor Length for Dp = 0.005m
Pressure Drop vs. Reactor Length for Dp = 0.01m

17. Multiple Reactions- Memo 4
Assumptions
Isothermal reactor at 623K
Target conversion: 90%
Particle diameter: 0.005m
Bulk density: 1,000 kgcat/m3
Inlet pressure: 2.2 bar
Void Fraction 0.4
Reactions
(1) C4H O2  C4H2O H2O
(2) C4H O2  4 CO H2O
(3) C4H O2  2 C2H4O
(4) C4H O2  C4H6O + H2O

18. Multiple Reactions- Memo 4
Reaction constants were found through a linearization of the ln(K) vs 1/T
Sample Plot of Temperature Dependent K

19. Multiple Reactions- Memo 4
Species Molar Flows vs. Catalyst Weight

20. Multiple Reactions- Memo 4
Selectivity
Temperature oC
Selectivity, SMA
350
330
290

21. Energy Balance- Memo 5 New assumptions
Inlet temperature: 563 K
Target conversion: 90%3
Inlet Pressure = 220,000Pa15
Bulk density = 1000 kgcat/ m3rxtr15
Dp = 5x10-3 m
Φ = 0.45
U = kJ/ m2-s-K
Coolant temperature: 558 K
E.B. used to locate and control reactor hotspot

22. Coolant Temperature (K)
Energy Balance- Memo 5
Constant Feed Temperature of 563K with Varying Coolant Temperatures
Coolant Temperature (K)
Selectivity, SMA
543
553
563
573
583

23. Energy Balance- Memo 5
Constant Coolant Temperature of 563K with Varying Inlet Temperatures
Inlet Temperature (K)
Selectivity, SMA
543
553
563
573
583

24. Energy Balance- Memo 5 Reactor Configuration: Tubes = 335,867
Aspen Stream Table
Reactor Configuration:
Tubes = 335,867
Catalyst Weight = 792,000 kgcat
Tube Length = m
INLET
OUTLET
Species Flow (kmol/s)
1-butene
0.0119
Oxygen
1.315
Nitrogen
6.642
Maleic Anhydride
Water
0.3051
Carbon Dioxide
0.2383
Acetaldehyde
Methyl Vinyl Ketone
Pressure (N/m2)
220000
202732

25. Reactor Simulations Memo 2 Memo 3 Memo 4 Memo 5 Single Tube
Single Tube
Multi- tube
Reactor Volume (m3)
5.03
792
Catalyst Weight (kgcat)
74.473
5030
792,000
Inlet Flows
1-butene (kmol/s)
0.0149
0.149
Oxygen (kmol/s)
0.193
Maleic Anhydride (kmol/s)
Carbon Dioxide (kmol/s)
N/A
Acetaldehyde (kmol/s)
Methyl Vinyl Ketone (kmol/s)
Outlet Flows
0.1502
1.3284
Pressure (Pa)
220,000
Inlet Temperature (K)
673.15
623
563
Maximum Temperature (K)
566.08
Coolant Temperature (K)
558
Length (m) 1
1.24
Diameter (m)
4.35
0.0254
Number of Tubes
23,706
23,884
335,867
Pressure Drop (%)
5.3 10
0.18
7.97
Hotspot Location (m)
0.3924
Gain
1.73
Conversion of 1-butene
90%
89.40%
88.80%

26. Optimized Reactor
An inlet temperature of 563K, a coolant temperature of 558K and an inlet pressure 2.4 bar produce a gain under two.
Other conditions gave a thermodynamically unstable reactor. With these conditions the reactor volume and catalyst weight were changed to give a 90% conversion and optimal selectivity of maleic anhydride.
Coolant temperature (K)
Inlet Temperature (K)
Hotspot Temperature (K)
Gain
559
563
558
557

27. Optimized Reactor Optimized Reactor Reactor Volume (m3) 723.4
Catalyst Weight (kgcat)
723400
Inlet Flows
1-butene (kmol/s)
Oxygen (kmol/s)
Maleic Anhydride (kmol/s)
Carbon Dioxide (kmol/s)
Acetaldehyde (kmol/s)
Methyl Vinyl Ketone (kmol/s)
Outlet Flows
Pressure (Pa)
240,000
Inlet Temperature (K)
563
Maximum Temperature (K)
566.65
Coolant Temperature (K)
558
Length (m)
4.09
Diameter (m)
Number of Tubes
335,900
Pressure Drop (%)
6.05%
Hotspot Location (m)
0.3275
Gain
≤ 2
Conversion of 1-butene
0.9

28. Conclusions
Overall the selectivity from the reaction scheme is not optimal for producing maleic anhydride
When the reaction temperature is above 563K the reaction becomes a runaway
The reactor is too large to be cost effective
After 1983 nothing was published because it was found that butane was a better feedstock

29. References
1Cavani, F., Trifiro, F.; Oxidation of 1-Butene and Butadiene to Maleic Anhydride. Industrial Engineering Chemical Product Research and Development Vol 22. No. 4,
2Varma, R. L.; Saraf, D. N.; Journal of Catalysis; [online] 1978, 55,