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Partial Oxidation of Benzene to Maleic Anhydride
Derek Becht Mike Raymond Eric Nette Matt Hunnemeder
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Overview Project Description Background Assumptions
Solution Methodology Final Design Overall Comparison
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Project Description Reaction: Partial oxidation of benzene
Reactor: Fixed bed reactor Production: M tons/year maleic anhydride Step by step modeling process Fogler H.S. Elements of Chemical Reaction Engineering; Pearson Education: New Jersey, 2006.
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Maleic Anhydride Feed stocks1 Benzene N-Butene N-Butane Major Uses2
Resins Oil Additives Copolymers Benzene: C6H6 N-Butane: C4H10 N-Butene: C4H8 Resins – 63% Oil Additives – Lubricating 10% Benzene yields Cox -> n-butane does not. Does n-butene?
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Financial Considerations
Market Price3,4 Maleic Anhydride: $1.54/kg - $ 1.70/kg Benzene: $929.99/m3 – $940.55/m3 Financial Earnings $20,922,183/yr neglecting all cost, except feed
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Standard Assumptions Open system + steady state
Negligible potential and kinetic energy No mechanical or shaft work Turbulent flow Uniform temperature, pressure, and concentration within the control volume 2 weeks downtime Throughout the whole design process these assumptions were used
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Benzene Specific Assumptions
1.1 mol % inlet benzene5 Conversion, XB, is Dry air Negligible CO2 in air These assumptions are specific to our reactor A. Bielanski, M. N. (1997). V2O5-MoO3 Catalysts for Benzene Oxidation. Applied catalysts ,
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Reactor and Particle Properties
Bulk Density7 = 930 kgcat/m3 V2O5-MoO3 Particle Diameter8 = 0.006m Void Fraction = 0.4 m3gas/m3rxtr Heat Transfer Coefficient8 = W/m2-K Coolant Temperature8 = 653 K Vanadia-Molybdena
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Solution Methodology Ideal Reactor -> Realistic Reactor
Considerations: Pressure drop Side reactions Temperature rise/drop
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Case 1: Ideal Reactor Assumptions Reaction Kinetics
Isothermal One reaction Isobaric Inlet Conditions Feed Rates 658 K Benzene: kmol/s 1.5 atm Oxygen: kmol/s 1.1 mol% benzene Nitrogen: kmol/s
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Conversion Profile A plot was made to study effects of temperature and catalyst weight on conversion Higher temperature, less catalyst required, more conversion Weight of kgcat yields 76.06% conversion at 385 degree celcius
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Heat Duty Profile Reaction is exothermic
As reaction converts more, more energy must be removed to maintain constant temperature
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Case 2: Pressure Drop Additional Assumptions Momentum Equations
Ideal Gas Constant Density Additional Property Viscosity9 = E-5 PaS
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Conversion Profile This includes pressure drop
A catalyst weight of 144,000 kgcat and 385 C yields 76 % conversion Compare to isobaric
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Particle Diameter Larger particles therefore fewer
This leads to larger void space Therefore smaller pressure drop
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Case 3: Multiple Reactions
Mechanism Rate Expressions Note the first path also yields water A, b, c are constants The mechanism was suggested by Hammer The rate expressions are Langmuir and Hinshelwood Increased flow rates 19.3% as a result of side reactions 2 C6H6 + 6 O2 -> 3 C4H2O3 + 3 H2O C6H6 + 6 O2 -> 3 CO + 3 CO2 + 3 H2O
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Molar Flow Rates Oxygen is not shown here because it is in excess
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Selectivity At 658 K (reactor temperature) the selectivity is 0.32
Selectivity decreases with increasing temperature because ?
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Case 4: Energy Balance Additional Assumptions Constant heat capacity
Constant coolant temperature Multi-tube reactor Heat capacity can be assumed constant due to the low Delta T Coolant temperature of 647 K
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Coolant Temperature Increasing the coolant temperature increases the hot spot temperature. The
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Inlet Temperature The effect of varying inlet temperature is almost negligible. It slightly increases the hot spot temperature.
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Final Design: Optimization
Pressure Temperature Pressure (bar) Conversion Pressure Drop % Selectivity Hot Spot (K) 1.5 0.764 9.33 0.319 671.0 1.75 0.823 7.95 0.313 674.0 2 0.867 6.93 0.308 676.9 Inlet Temperature (K) Conversion Selectivity Flow Maleic Anhydride (kmol/s) 648 0.7598 0.3036 1.686E-02 653 0.7625 0.3037 1.692E-02 658 0.7597 0.3035 1.685E-02 668 0.7417 0.3028 1.644E-02
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Overall Comparison Property Initial Design Final Design
Temperature (K) 658 653 Inlet Benzene (kmol/s) Catalyst Weight (kg) 139,750 76,400 Reactor Length (m) 97.4 2.476 Diameter (m) 7.2 6.5 Volume (m3) 150 82.2 Potential Earnings ($/yr) 20,822,183 8,901,617 Pressure Drop 9.95% Selectivity 0.3036 Coolant Gain 1.008 Inlet Gain 0.051 What Changed.. Kinetics Diameter increased, therefore length much smaller
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References 1) Barone et al., United States Patent Patent Issued ) Maleic anhydride - Chemical Profile. < (accessed 01/24/2008). 3) William Lemos. US Price Report – Maleic Anhydride. < (accessed 01/25/2008). 4) Americas Market Summary – Benzene. (accessed 01/24/2008). 5) Sharma R.K. et al. (1984). Selective Oxidation of Benzene to maleic anhydride at Commercially Relevant Conditions. Institution of Chemical Engineers Symposium Series, ) Americas Market Summary – Benzene. (accessed 01/24/2008). 7) U.S. Patents. (1996). Oxide catalyst and process for producing maleic anhydride by oxide catalyst (No filed on ). 8) U.S. Patents. (1978). Process for the Manufacture of Maleic Anhydride (No filed on 10/21/1976). 9) Chemical Database Property Constants. DIPPR Database [Online]. Available from Rowan Hall 3rd Floor Computer Lab. (Accessed on 1/24/2008).
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