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

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

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

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.

1-butene to maleic anhydride 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

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

Kinetics Kinetics for Multiple Reactions from Literature1

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.

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

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

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.

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.

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

Reactor Volume – Memo 2 Catalyst weight was calculated to be 74.473kgcat Effect of Catalyst Mass on Conversion at Various Temperatures

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 22611.44 11.457 2.380195 18420.58 1.3 11.6 2.54E+04 22786.72 11.546 2.361885 18155.67 1.29 11.3 2.48E+04 22964.74 11.636 2.343576 17892.67 1.28 11.0 2.42E+04 23145.57 11.728 2.325267 17631.57 1.27 10.8 2.37E+04 23329.26 11.821 2.306958 17372.39 1.26 10.5 2.31E+04 23515.90 11.915 2.288649 17115.12 1.25 10.3 2.26E+04 23705.54 12.011 2.270339 16859.76 1.24 10.0 2.20E+04 23898.27 12.109 2.25203 16606.31 1.23 9.76 2.15E+04 24495.72 12.412 2.197103 15857.42 1.2 9.06 1.99E+04 26722.61 13.540 2.014011 13485.29 1.1 6.99 1.54E+04 29394.87 14.894 1.830919 11304.2 1 5.28 1.16E+04

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 9767.093 1.2 9.06 1.99E+04 4.12 9070.774 1.1 6.99 1.54E+04 3.18 6998.261 1 5.28 1.16E+04 2.40 5277.399 Pressure Drop vs. Reactor Length for Dp = 0.005m Pressure Drop vs. Reactor Length for Dp = 0.01m

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

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

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

Multiple Reactions- Memo 4 Selectivity Temperature oC Selectivity, SMA 350 0.04574 330 0.03471 290 0.03482

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

Coolant Temperature (K) Energy Balance- Memo 5 Constant Feed Temperature of 563K with Varying Coolant Temperatures Coolant Temperature (K) Selectivity, SMA 543 0.04004 553 0.04138 563 0.05352 573 0.03831 583 0.03716

Energy Balance- Memo 5 Constant Coolant Temperature of 563K with Varying Inlet Temperatures Inlet Temperature (K) Selectivity, SMA 543 0.05305 553 0.05324 563 0.05352 573 0.05398 583 0.05506

Energy Balance- Memo 5 Reactor Configuration: Tubes = 335,867 Aspen Stream Table Reactor Configuration: Tubes = 335,867 Catalyst Weight = 792,000 kgcat Tube Length = 4.481803m INLET OUTLET Species Flow (kmol/s)   1-butene 0.136882 0.0119 Oxygen 1.77303 1.315 Nitrogen 6.64197 6.642 Maleic Anhydride 0.01739 Water 0.3051 Carbon Dioxide 0.2383 Acetaldehyde 0.06663 Methyl Vinyl Ketone 0.01471 Pressure (N/m2) 220000 202732

Reactor Simulations Memo 2 Memo 3 Memo 4 Memo 5 Single Tube   Single Tube Multi- tube Reactor Volume (m3) 0.074473 14.8946 5.03 792 Catalyst Weight (kgcat) 74.473 14894.6 5030 792,000 Inlet Flows 1-butene (kmol/s) 0.0149 0.149 0.136882 Oxygen (kmol/s) 0.193 1.77303 Maleic Anhydride (kmol/s) Carbon Dioxide (kmol/s) N/A Acetaldehyde (kmol/s) Methyl Vinyl Ketone (kmol/s) Outlet Flows 0.00149 0.001583 0.001669 0.001488 0.013683 0.15277 0.15305 0.03969 0.1502 1.3284 0.01341 0.01332 0.01323 0.001469 0.01731 0.021165 0.22945 0.008581 0.06733 0.0023614 0.01486 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 0.400275 4.481803 Diameter (m) 4.35 0.0254 0.0258826 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%

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 559 563 568.593818 1.935906 558 566.657912   557 564.86977 1.788142

Optimized Reactor Optimized Reactor Reactor Volume (m3) 723.4 Catalyst Weight (kgcat) 723400 Inlet Flows 1-butene (kmol/s) 0.136882 Oxygen (kmol/s) 1.77303 Maleic Anhydride (kmol/s) Carbon Dioxide (kmol/s) Acetaldehyde (kmol/s) Methyl Vinyl Ketone (kmol/s) Outlet Flows 0.011874 1.328376 0.172473 0.228121 0.07038 0.015541 Pressure (Pa) 240,000 Inlet Temperature (K) 563 Maximum Temperature (K) 566.65 Coolant Temperature (K) 558 Length (m) 4.09 Diameter (m) 0.025883 Number of Tubes 335,900 Pressure Drop (%) 6.05% Hotspot Location (m) 0.3275 Gain ≤ 2 Conversion of 1-butene 0.9

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

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