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) Temperatur e (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 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 390C 3.15 x 10-5 kg/m-s (5) Coolant Temperature 673K (390C)
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 (294C) 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 390C Units 350C 375C 390C ka, (kmolm3)1/2/kgcat-s 0.5281 0.41
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- 390C 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 Continued Inlet
0.00317457 Water 0 0.0116804 0.0116909 Total 0.546997 0.5488637 0.547749008 Pressure (Pa) 303975 284200 284080 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
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