Partial Oxidation of Propylene to Acrolein

Final Design PresentationApril 23, 2008Kerri M. MayMegerle L. ScherholzChristopher 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 Conversio

n

Inlet Percent of Propylene (mol %)

Inlet Percent of Air (mol

%)

250-450 1-3.4 85 2 98

Process Background Continued• Assumptions

• Given for final design• Deviations for other models discussed

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)

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-sr3co2 = rate of formation of carbon dioxide, kmol/kgcat-sr3co = 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-sk12 = rate constant for propylene reaction to acrolein,

m3/kgcat-sk13co2 = rate constant for propylene reaction to carbon

dioxides, m3/kgcat-sk13co = rate constant for propylene reaction to carbon

monoxide, m3/kgcat-sk14 = rate constant for propylene reaction acetaldehyde,

m3/kgcat-sCo = 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

• Pre-exponential Factors and Activation Energies

Units 350°C 375°C 390°Cka, (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

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

k13co20.00026 (m3/kgcat-s) 0

k13co 43401302 (m3/kgcat-s) 154.2247

k14 24.78652 (m3/kgcat-s) 71.1104734

Design ProcessReactor 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▫Volume- 19.08 m3

▫Diameter- 3.4 m▫Length- 2.01 m▫Number of Tubes- 17920 (1” Dia.)

Final Design ContinuedInlet Flows (kmol/s)

Polymath Outlet (kmol/s)

Aspen Plus ® 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 ContinuedPolymath Aspen Plus ®

Pressure Drop 6.59 % 6.54 %

Conversion 85.05 % 85.17 %

Selectivity of Acrolein 1.71 1.71

Selectivity of Others 0.48 0.48

Hot Spot Temperature

405.257 °C 405.393 °C

Hot Spot. Location 0.18 m 0.21 m

Gain 1.16 1.17

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 Cited1. Maganlal, Rashmikant, et al. Vapor phase oxidation of propylene to

acrolein. 6437193 United States, August 20, 2002.2. Chemical Database Property Constants. DIPPR Database [Online]. Available

from Rowan Hall 3rd Floor Computer Lab. (Accessed on 1/24/2008).3. LaMarca, Concetta, PhD. Chemical Reaction Engineering Design Project.

February 2008. Chemical Engineering Department, Rowan University, Glassboro.

4. 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.

5. Chemical Database Property Constants. DIPPR Database [Online]. Available from Rowan Hall 3rd Floor Computer Lab. (Accessed on 1/24/2008).

6. 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

7. 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

8. 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