Partial Oxidation of Benzene to Maleic Anhydride Derek Becht Mike Raymond Eric Nette Matt Hunnemeder

Overview Project Description Background Assumptions Solution Methodology Final Design Overall Comparison

Project Description Reaction: Partial oxidation of benzene Reactor: Fixed bed reactor Production: 50000 M tons/year maleic anhydride Step by step modeling process Fogler H.S. Elements of Chemical Reaction Engineering; Pearson Education: New Jersey, 2006.

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?

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

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

Benzene Specific Assumptions 1.1 mol % inlet benzene5 Conversion, XB, is 0.76 6 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 , 223-261.

Reactor and Particle Properties Bulk Density7 = 930 kgcat/m3 V2O5-MoO3 Particle Diameter8 = 0.006m Void Fraction = 0.4 m3gas/m3rxtr Heat Transfer Coefficient8 = 202.4 W/m2-K Coolant Temperature8 = 653 K Vanadia-Molybdena

Solution Methodology Ideal Reactor -> Realistic Reactor Considerations: Pressure drop Side reactions Temperature rise/drop

Case 1: Ideal Reactor Assumptions Reaction Kinetics Isothermal One reaction Isobaric Inlet Conditions Feed Rates 658 K Benzene: 0.02122 kmol/s 1.5 atm Oxygen: 0.4177 kmol/s 1.1 mol% benzene Nitrogen: 1.577 kmol/s

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 139750 kgcat yields 76.06% conversion at 385 degree celcius

Heat Duty Profile Reaction is exothermic As reaction converts more, more energy must be removed to maintain constant temperature

Case 2: Pressure Drop Additional Assumptions Momentum Equations Ideal Gas Constant Density Additional Property Viscosity9 = 3.2197E-5 PaS

Conversion Profile This includes pressure drop A catalyst weight of 144,000 kgcat and 385 C yields 76 % conversion Compare to isobaric

Particle Diameter Larger particles therefore fewer This leads to larger void space Therefore smaller pressure drop

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

Molar Flow Rates Oxygen is not shown here because it is in excess

Selectivity At 658 K (reactor temperature) the selectivity is 0.32 Selectivity decreases with increasing temperature because ?

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

Coolant Temperature Increasing the coolant temperature increases the hot spot temperature. The

Inlet Temperature The effect of varying inlet temperature is almost negligible. It slightly increases the hot spot temperature.

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

Overall Comparison Property Initial Design Final Design Temperature (K) 658 653 Inlet Benzene (kmol/s) 0.02122 0.02684 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

References 1) Barone et al., United States Patent 4018709. Patent Issued 1977. 2) Maleic anhydride - Chemical Profile. <http://www.the-innovation-group.com/ChemProfiles/Maleic%20Anhydride.htm>. (accessed 01/24/2008). 3) William Lemos. US Price Report – Maleic Anhydride. <http://www.icis.com/v2/chemicals/9076024/maleic-anhydride/pricing>. (accessed 01/25/2008). 4) Americas Market Summary – Benzene. http://www.icis.com/articles/2008/01/29/9096633/NOON-SNAPSHOT. (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, 353-360. 6) Americas Market Summary – Benzene. http://www.icis.com/articles/2008/01/29/9096633/NOON-SNAPSHOT. (accessed 01/24/2008). 7) U.S. Patents. (1996). Oxide catalyst and process for producing maleic anhydride by oxide catalyst (No. 266510 filed on 1994-06-27). 8) U.S. Patents. (1978). Process for the Manufacture of Maleic Anhydride (No. 4070379 filed on 10/21/1976). http://www.freepatentsonline.com/4070379.html 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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