Chemical Reaction Engineering: Reactor Design Project

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. Reaction Mechanism 1-butene to maleic anhydride • (1) C4H8 + 3 O2 C4H2O3 + 3 H2O • (2) C4H8 + 6 O2 4 CO2 + 4 H2O • (3) C4H8 + O2 2 C2H4O • (4) C4H8 + O2 C4H6O + H2O

6. Kinetics • Preliminary Reaction Kinetics (1 Reaction) rm = k1 * pB where pB is partial pressure of 1-butene and k1 = 3.8075x 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 74.473kgcat 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

16. Momentum Balance- Memo 3 Effects of doubling particle diameter 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) C4H8 + 3 O2 C4H2O3 + 3 H2O • (2) C4H8 + 6 O2 4 CO2 + 4 H2O • (3) C4H8 + O2 2 C2H4O • (4) C4H8 + O2 C4H6O + H2O http://www.bartek.ca/images/chemical.jpg

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

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 = 0.227 kJ/ m2-s-K • Coolant temperature: 558 K • E.B. used to locate and control reactor hotspot

22. Energy Balance- Memo 5 Constant Feed Temperature of 563K with Varying Coolant Temperatures

23. Energy Balance- Memo 5 Constant Coolant Temperature of 563K with Varying Inlet Temperatures

24. Energy Balance- Memo 5 Aspen Stream Table Reactor Configuration: Tubes =335,867 Catalyst Weight = 792,000 kgcat Tube Length = 4.481803m

25. Reactor Simulations

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.

27. Optimized Reactor

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. 1983. Vol 22. No. 4, 570-577 2Varma, R. L.; Saraf, D. N.; Journal of Catalysis; [online] 1978, 55, 351-272