Transcript Partial Oxidation of Propylene to Acrolein Final Design Presentation April 23, 2008

Partial Oxidation of Propylene to
Acrolein
Final Design Presentation
April 23, 2008
Kerri M. May
Megerle L. Scherholz
Christopher M. Watts
Overview
• Introduction
• Process Background
• Design Process
▫
▫
▫
▫
Determination of Volume
Pressure Drop
Multiple Reactions
Heat Effects
• Optimization
• Final Design
• Conclusion
Introduction
• Design of fixed-bed reactor
• Production of acrolein by partial oxidation
▫ CH2 = CH - CH3 + O2 → CH2 = CH – CHO + H2O
• 13,500 Mtons/year with a 2 week downtime
▫ Corresponds to 0.007941 kmol/s
• Original design: ideal/isobaric/isothermal
• Final design: pressure drop, multiple reactions
and heat effects
• Optimized using selectivity and gain
Process Background
• Literature Operating Conditions (1,2)
Temperature
(°C)
Pressure
(atm)
Percent
Conversion
Inlet
Percent of
Propylene
(mol %)
Inlet
Percent of
Air (mol %)
250-450
1-3.4
85
2
98
Process Background Continued
• Assumptions
Parameter
Value
Particle Size
5 mm (3)
Bulk Density
1415 kg-cat/m3-rxtr (4)
Packed Bed Void Fraction
0.38 (4)
Tube Diameter
1 in. (0.0254 m)
Viscosity of Air at 390°C
3.15 x 10-5 kg/m-s (5)
Coolant Temperature
673K (390°C)
Overall Heat Transfer Coefficient
227 J/W-m2-K (3)
• Given for final design
• Deviations for other models discussed
Process Background Continued
• Stoichiometric Flow Rates
Inlet Compositions Outlet Compositions
Mole (kmol/s)
Mole (kmol/s)
Propylene
0.0093420221
0.0014013
Oxygen
0.0888951791
0.0809545
Inert Nitrogen
0.0382188797
0.3821888
Acrolein
0
0.0079407
Water
0
0.0079407
Total
0.4804259982
0.480426
Process Background Continued
• Catalyst chosen based on kinetics
▫ Bismuth molybdate (6)
• Co-current Heat Exchanger Fluid
▫ Exothermic reaction
▫ Molten Salt used as coolant fluid
▫ Sodium tetrasulfide (7)
 Melting temperature (294°C)
Process Background Continued
▫ Selectivity of Acrolein
▫ Selectivity of Other Profitable Products
▫ Gain
Process Background Continued
• Reaction Kinetics of Byproducts (6,8)
▫ Reaction Pathway
▫ Assumptions:
 Steady State
 Single-site oxygen adsorption
 Rate of oxidation of acrolein to carbon oxides is
negligible compared to other rates
Process Background Continued
• Reaction rates for the formation of
acrolein and byproducts (6,8)
Where:
r2 = rate of formation of acrolein, kmol/kgcat-s
r3co2 = rate of formation of carbon dioxide, kmol/kgcat-s
r3co = rate of formation of carbon monoxide, kmol/kgcat-s
r4 = rate of formation of acetaldehyde, kmol/kgcat-s s
ka = rate constant for oxygen adsorption, (kmol-m3)1/2/kgcat-s
k12 = rate constant for propylene reaction to acrolein, m3/kgcat-s
k13co2 = rate constant for propylene reaction to carbon dioxides,
m3/kgcat-s
k13co = rate constant for propylene reaction to carbon monoxide,
m3/kgcat-s
k14 = rate constant for propylene reaction acetaldehyde, m3/kgcat-s
Co = concentration of oxygen, kmol/m3
Cp = concentration of propylene, kmol/m3
n12 = number of moles of oxygen which react with one mole of
propylene to produce acrolein, kmol/kmol
n13co2 = number of moles oxygen which react with one mole of
propylene to product carbon dioxide, kmol/kmol
n13co = number of moles of oxygen which react with one mole of
propylene to produce carbon monoxide, kmol/kmol
n14 = number of moles of oxygen which react with one mole of
propylene to produce acetaldehyde, kmol/kmol
Process Background Continued
• Rate Constants at 325, 350, and 390°C
Units
350°C
375°C
390°C
ka, (kmol- m3)1/2/kgcat-s
0.5281 ±0.41
0.99928±1.33
1.46097±0.15
k12, m3/kgcat-s
2.19±0.14
3.86±0.37
5.38±0.35
k13, m3/kgcat-s
2.7±0.18
2.94±0.31
2.70±0.27
k14, m3/kgcat-s
0.273±0.21
0.452±0.55
0.628±0.71
• Pre-exponential Factors and Activation Energies
Rate Constants
Pre-exponential Factor, A
Activation Energy, E (kJ/mol)
ka
1073.975 (kmol-m3)1/2/kgcat-s
87.197232
k12
631.754 (m3/kgcat-s)
77.074937
k13co2
0.00026 (m3/kgcat-s)
0
k13co
43401302 (m3/kgcat-s)
154.2247
k14
24.78652 (m3/kgcat-s)
71.1104734
Design Process
Reactor 1
Reactor 2
Reactor 3
Reactor 4
Volume
Pressure Drop
Mult. Reactions
Heat Effects
Volume (m3)
21696.1
4174.6
22.51
19.19
Num. Tubes (1” Dia.)
N/A
683600
17920
16880
Reactor Dia. (m)
13.6946
21
3.4
3.3
Reactor Len. (m)
147.298
12.05
2.4792
2.24
Cat. Weight (kg-cat)
3.07 x 107
5.91 x 106
31850
27150
Particle Size (mm)
N/A
3
5
5
Nitrogen Feed (kmol/s)
0.382188797
0.3821888
0.4491963
0.439638
Oxygen Feed (kmol/s)
0.088895179
0.08889518
0.0979275
0.095847
Propylene Feed (kmol/s)
0.009342022
0.000934202
0.0117625
0.011512
Inlet Temp. (°C)
350
350
390
390
Inlet Pressure (atm)
1
3
3
3
Pressure Drop (%)
N/A
0.37
7.97
7.82
Acrolein Prod. (kmol/s)
0.007953
0.0079428
0.0079426
0.0079369
Propylene Conversion (%)
85.13
85.02
84.99
85.01
Optimization
• Acrolein Selectivity
 Greater at increased temperatures
 Improved when coolant and inlet temperatures
are equal
 Higher pressure, higher selectivity
 Other Usable Product Selectivity
 Decreased at increased temperatures
 Favored at lower pressures
 Greater when coolant temperature less than the
inlet temperature
Optimization Continued
• Gain
▫ Greater at increased inlet temperature
▫ Independent of coolant and inlet temperature
relationship
• Optimization Conclusion:
▫ Focus on selectivity opposed to gain
Final Design
• Operating Conditions
▫ Temperature- 390°C
▫ Pressure- 3 atm
• Reactor Configurations
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▫
▫
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Volume- 19.08 m3
Diameter- 3.4 m
Length- 2.01 m
Number of Tubes- 17920 (1” Dia.)
Final Design Continued
Inlet Flows Polymath
Aspen Plus ®
(kmol/s)
Outlet (kmol/s) Outlet (kmol/s)
Nitrogen
0.439638
0.439638
0.439638
Oxygen
0.095847
0.0832387
0.0821155
Propylene
0.011512
0.0017208
0.00170713
Acrolein
0
0.0079412
0.00795529
Acetyldehyde
0
0.0009053
0.000906563
Carbon Monoxide
0
0.0005578
0.000561055
Carbon Dioxide
0
0.0031814
0.00317457
Water
0
0.0116804
0.0116909
Total
0.546997
0.5488637
0.547749008
Pressure (Pa)
303975
284200
284080
Temperature (K)
663
665.5059
665.644
Final Design Continued
Polymath
Pressure Drop
Aspen Plus ®
6.59 %
6.54 %
85.05 %
85.17 %
Selectivity of Acrolein
1.71
1.71
Selectivity of Others
0.48
0.48
405.257 °C
405.393 °C
0.18 m
0.21 m
1.16
1.17
Conversion
Hot Spot Temperature
Hot Spot. Location
Gain
Final Design Continued
• Temperature Profile
Conclusions
• Reactor volume decreased with complexity
increase
• Selectivity crucial to optimization
• Final model discussed would operate viably
• Changed reactor dimensions to optimize final
design
Questions?
Works Cited
1.
2.
3.
4.
5.
6.
7.
8.
Maganlal, Rashmikant, et al. Vapor phase oxidation of propylene to acrolein. 6437193
United States, August 20, 2002.
Chemical Database Property Constants. DIPPR Database [Online]. Available from
Rowan Hall 3rd Floor Computer Lab. (Accessed on 1/24/2008).
LaMarca, Concetta, PhD. Chemical Reaction Engineering Design Project. February
2008. Chemical Engineering Department, Rowan University, Glassboro.
Transient Kinetics from the TAP Reactor System: Application to the Oxidation of
Propylene to Acrolein. Creten, Glenn, Lafyatis, David S., and Froment, Gilbert F.
Belgium: Journal of Catalysis, 1994, Vol. 154.
Chemical Database Property Constants. DIPPR Database [Online]. Available from
Rowan Hall 3rd Floor Computer Lab. (Accessed on 1/24/2008).
The reaction network for the oxidation of propylene over a bismuth molybdate catalyst.
Tan, H. S., Downie, J. and Bacon, D. W. Kingston : The Canadian Journal of Chemical
Engineering, 1989, Vol. 67
Physical Properties Data Compilations Relevant to Energy Storage. II. Molten
Salts: Data on Single and Multi-Component Salt Systems. G.J. Janz, C.B. Allen, N.P.
Bansal, R.M. Murphy, and R.P.T. Tomkins Molten Salts Data Center, Rensselaer
Polytechnic Institute, NSRDS-NBS61-II, April 1979
The kinetics of the oxidation of propylene over a bismuth molybdate catalyst. Tan, H. S.,
Downie, J. and Bacon, D. W. Kingston : The Canadian Journal of Chemical Engineering,
1988, Vol. 66