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