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.
oT
T
o
o
cc
o
F
F
T
T
P
P
AdW
dP
)1(
oPP 1.0
G
DD
G
ppoo 75.1
)1(150)1(3
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:
SelectivityOHCOHCCO
MA
FFF
F
64422
ENERGY BALANCE
where
o This accounts for non- isothermal behavior in the reactor and allows for the optimization of the reactor temperature.
n
iiio
n
iirxni
CpF
qHr
dW
dT
1
1
*
*
TTaq 1000*0258826.0
4*227.0 [=] 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.
inlet
Hotspot
T
TGain
OPTIMIZATION
Throughout the reactor design project this semester each memo submission involved a new aspect of the reactor:
o Volumeo Pressure Dropo Multiple Reactionso 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
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 11.62.54E+0
4
0.0254 22786.72 11.546 2.361885 18155.67 1.29 11.32.48E+0
4
0.0254 22964.74 11.636 2.343576 17892.67 1.28 11.02.42E+0
4
0.0254 23145.57 11.728 2.325267 17631.57 1.27 10.82.37E+0
4
0.0254 23329.26 11.821 2.306958 17372.39 1.26 10.52.31E+0
4
0.0254 23515.90 11.915 2.288649 17115.12 1.25 10.32.26E+0
4
0.0254 23705.54 12.011 2.270339 16859.76 1.24 10.02.20E+0
4
0.0254 23898.27 12.109 2.25203 16606.31 1.23 9.762.15E+0
4
0.0254 24495.72 12.412 2.197103 15857.42 1.2 9.061.99E+0
4
0.0254 26722.61 13.540 2.014011 13485.29 1.1 6.991.54E+0
4
0.0254 29394.87 14.894 1.830919 11304.2 1 5.281.16E+0
4
Memo 3 Table: Number of Tubes and Pressure Drop for 1” Tubes with Varying Length
MOMENTUM BALANCE- MEMO 3
Pressure Drop vs. Reactor Length for Dp = 0.005m
Pressure Drop vs. Reactor Length for Dp = 0.01m
Effects of doubling particle diameter
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 0.04574330 0.03471290 0.03482
ENERGY BALANCE- MEMO 5
New assumptions• Inlet temperature: 563 K• Target conversion: 90%3
• Inlet Pressure = 220,000Pa15
• Bulk density = 1000 kgcat/ m3rxtr
15
• 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
ENERGY BALANCE- MEMO 5Constant Feed Temperature of 563K with Varying Coolant Temperatures
Coolant Temperature (K) Selectivity, SMA
543 0.04004553 0.04138563 0.05352573 0.03831583 0.03716
ENERGY BALANCE- MEMO 5
Inlet Temperature (K) Selectivity, SMA
543 0.05305553 0.05324563 0.05352573 0.05398583 0.05506
Constant Coolant Temperature of 563K with Varying Inlet Temperatures
ENERGY BALANCE- MEMO 5
Aspen Stream Table
INLET OUTLETSpecies Flow (kmol/s) 1-butene 0.136882 0.0119Oxygen 1.77303 1.315Nitrogen 6.64197 6.642Maleic Anhydride 0 0.01739Water 0 0.3051Carbon Dioxide 0 0.2383Acetaldehyde 0 0.06663Methyl Vinyl Ketone 0 0.01471
Pressure (N/m2) 220000 202732
Reactor Configuration: Tubes = 335,867Catalyst Weight = 792,000 kgcatTube Length = 4.481803m
REACTOR SIMULATIONS Memo 2 Memo 3 Memo 4 Memo 5
Single Tube Multi- tube
Reactor Volume (m3) 0.074473 14.8946 14.8946 5.03 792Catalyst Weight (kgcat) 74.473 14894.6 14894.6 5030 792,000Inlet Flows 1-butene (kmol/s) 0.0149 0.0149 0.0149 0.149 0.136882 Oxygen (kmol/s) 0.193 0.193 0.193 0.193 1.77303 Maleic Anhydride (kmol/s) 0 0 0 0 0 Carbon Dioxide (kmol/s) N/A N/A N/A 0 0 Acetaldehyde (kmol/s) N/A N/A N/A 0 0 Methyl Vinyl Ketone (kmol/s) N/A N/A N/A 0 0Outlet Flows 1-butene (kmol/s) 0.00149 0.001583 0.001669 0.001488 0.013683 Oxygen (kmol/s) 0.15277 0.15305 0.03969 0.1502 1.3284 Maleic Anhydride (kmol/s) 0.01341 0.01332 0.01323 0.001469 0.01731 Carbon Dioxide (kmol/s) N/A N/A N/A 0.021165 0.22945 Acetaldehyde (kmol/s) N/A N/A N/A 0.008581 0.06733 Methyl Vinyl Ketone (kmol/s) N/A N/A N/A 0.0023614 0.01486Pressure (Pa) 220,000 220,000 220,000 220,000 220,000Inlet Temperature (K) 673.15 673.15 673.15 623 563Maximum Temperature (K) 673.15 673.15 673.15 623 566.08Coolant Temperature (K) N/A N/A N/A N/A 558Length (m) N/A 1 1.24 0.400275 4.481803
Diameter (m) N/A 4.35 0.0254 0.0258826 0.0258826Number of Tubes 1 1 23,706 23,884 335,867Pressure Drop (%) N/A 5.3 10 0.18 7.97Hotspot Location (m) N/A N/A N/A N/A 0.3924Gain N/A N/A N/A N/A 1.73Conversion of 1-butene 90% 89.40% 88.80% 90% 90%
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 1.935906558 563 566.657912
557 563 564.86977 1.788142
OPTIMIZED REACTOROptimized Reactor
Reactor Volume (m3) 723.4Catalyst Weight (kgcat) 723400Inlet Flows 1-butene (kmol/s) 0.136882 Oxygen (kmol/s) 1.77303 Maleic Anhydride (kmol/s) 0 Carbon Dioxide (kmol/s) 0 Acetaldehyde (kmol/s) 0 Methyl Vinyl Ketone (kmol/s) 0Outlet Flows 1-butene (kmol/s) 0.011874 Oxygen (kmol/s) 1.328376 Maleic Anhydride (kmol/s) 0.172473 Carbon Dioxide (kmol/s) 0.228121 Acetaldehyde (kmol/s) 0.07038 Methyl Vinyl Ketone (kmol/s) 0.015541Pressure (Pa) 240,000Inlet Temperature (K) 563Maximum Temperature (K) 566.65Coolant Temperature (K) 558Length (m) 4.09Diameter (m) 0.025883Number of Tubes 335,900Pressure Drop (%) 6.05%Hotspot Location (m) 0.3275Gain ≤ 2Conversion of 1-butene 0.9
F1
REACTOR1
REACTOR2
F2
SPLITER
MIXER
O2
O1
INLET
OUTLET
REACTOR3
F3
O3REACTOR4
F4
O4
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