1. Yousef Ghotok Joseph Havelin Wednesday, 23rd April 2008
Chemical Reaction Engineering
Dr. Robert P. Hesketh
Dr. Concetta LaMarca
Reactor Design Project synthesis of Maleic Anhydride through Partial Oxidation of n-butane
Yousef Ghotok Joseph Havelin
Wednesday, 23rd April 2008

2. Outline Background, Process Reactions, and Rate Expressions
Initial Calculations
Case I  Reactor Volume Using Simple Reaction Rate Expression
Case II  Pressure Drop and Reactor Configuration
Case III  Multiple Reactions
Case IV  Energy Balance for Multiple Reactions
Case V  Optimization of Reactor Design

3. Background, Process Reactions, and Rate Expressions
Maleic anhydride is a cyclic organic chemical with formula C4H2O3.
Primary Use: Synthesis of Unsaturated Polyester Resins
N-butane is the most common feedstock used in production of maleic anhydride.
Bergman and Frisch discovered synthesizing maleic anhydride from n-butane by catalyzing the oxidation reaction.
By 1985, all commercial producers of maleic anhydride in the US used n-butane as their feed.
Worldwide Production: 1,359,000 tons per year
US Production: 273,800 tons per year

4. Background, Process Reactions, and Rate Expressions
The partial oxidation of n-butane at the surface of the catalyst produces maleic anhydride and water, and side reactions produce carbon monoxide, carbon dioxide and water.
Catalyst used is vanadium-phosphorus oxide ((VO)2P2O7).
Reactor Type  Fixed-Bed Reactor
Advantages: easy use and low maintenance demand
Disadvantages: hot spots and pockets of diluted butane

5. Background, Process Reactions, and Rate Expressions
Balanced Stoichiometric Equation: Cases I and II
C4H O2 → C4H2O3 + 4H2O
Rate Equation: Cases I and II
rM = k1 · CB
Pseudo-First Order Rate Constant: Cases I and II
k1 = · 106 exp(-15649/T) [m3/kgcat-sec]
Reactions From the Oxidation of N-Butane: Cases III, IV, and V

6. Background, Process Reactions, and Rate Expressions
Reaction Pathway Diagram: Cases III, IV and V
Reaction Rate Expressions: Cases III, IV and V
Rate Constants and Parameters

7. Initial Calculations Assumptions: Open system at steady state
Negligible changes in kinetic and potential energy
Negligible work
14 days’ worth of downtime per year
Inlet gas 1.7 mol% n-butane
80% conversion rate; side reactions not considered in this preliminary stage
25,000 tons/year production rate
Reference temperature = 25 ºC = 298 K

8. Initial Calculations Stoichiometric Tables: Molar Stoichiometric Table
Mass Stoichiometric Table

9. Case I
Additional Assumptions: Isothermal Reactor Model to Estimate the Reactor Volume
Isothermal Temperature = 673 K
Bulk Density = 900 kgcat/m3
Void Fraction = 0.44
Particle Diameter = 5 mm
Inlet Pressure = 1.5 bar

10. Case I Polymath: Isothermal Packed Bed Reactor Model Results
Stream Flows
Aspen Plus®: RPLUG Reactor
Stream Flows

11. Case I Polymath: Isothermal Packed Bed Reactor Model
Effect of Catalyst Weight and Temperature on Conversion

12. Case II
Additional Assumptions: Pressure Drop in the Fixed-Bed Reactor Must not Exceed 1/10 the Initial Pressure
Pressure drop along the length of the reactor

13. Case II Polymath: Isothermal Packed Bed Reactor Model Results
Stream Flows
Aspen Plus®: RPLUG Reactor
Stream Flows for Single Tube Reactor
Stream Flows for Multi-Tube Reactor

14. Case II Polymath: Isothermal Packed Bed Reactor Model
Effect of Catalyst Weight and Temperature on Conversion

15. Case II Polymath: Isothermal Packed Bed Reactor Model
Effect of Length on Pressure Drop

16. Case II
Comparison of Three Models

17. Case III Additional Assumptions:
Side reactions and byproducts are taken into consideration
Polymath: Isothermal Packed Bed Reactor Model
Results
Stream Flows
Aspen Plus®: RPLUG Reactor
Stream Flows for Multi-Tube Reactor
Stream Flows for Single Tube Reactor

18. Case III Polymath: Isothermal Packed Bed Reactor Model
Effect of Reaction Temperature on Selectivity of Maleic Anhydride

19. Case III Aspen Plus®: RPLUG Reactor
Effect of Reactor Length on Molar Flows

20. Case III
Comparison of Three Models

21. Case IV Additional Assumptions: Non-isothermal
Energy Balance taken into consideration
Heat exchanger with constant coolant temperature, Ta = 673 K
Overall Heat Transfer Coefficient = 105 J/(m2*K*s)

22. Case IV Polymath: Non-Isothermal Packed Bed Reactor Model Results
Stream Flows
Aspen Plus®: RPLUG Reactor
Stream Flows for Multi-Tube Reactor

23. Case IV
Aspen Plus®: RPLUG Reactor
Effect of Varying Ta On Hot Spot

24. Case IV Comparison of Isothermal and Real Reactor Models: Polymath
Aspen

25. Case V Optimal Reactor Conditions: Criteria Met: Minimal reactor size
Minimized cost
Constant selectivity throughout runs
Gain < 2
Pressure Drop < 10%