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Yousef Ghotok Joseph Havelin Wednesday, 23rd April 2008
Chemical Reaction Engineering Dr. Robert P. Hesketh Dr. Concetta LaMarca Reactor Design Project synthesis of Maleic Anhydride through Partial Oxidation of n-butane Yousef Ghotok Joseph Havelin Wednesday, 23rd April 2008
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Outline Background, Process Reactions, and Rate Expressions
Initial Calculations Case I Reactor Volume Using Simple Reaction Rate Expression Case II Pressure Drop and Reactor Configuration Case III Multiple Reactions Case IV Energy Balance for Multiple Reactions Case V Optimization of Reactor Design
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Background, Process Reactions, and Rate Expressions
Maleic anhydride is a cyclic organic chemical with formula C4H2O3. Primary Use: Synthesis of Unsaturated Polyester Resins N-butane is the most common feedstock used in production of maleic anhydride. Bergman and Frisch discovered synthesizing maleic anhydride from n-butane by catalyzing the oxidation reaction. By 1985, all commercial producers of maleic anhydride in the US used n-butane as their feed. Worldwide Production: 1,359,000 tons per year US Production: 273,800 tons per year
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Background, Process Reactions, and Rate Expressions
The partial oxidation of n-butane at the surface of the catalyst produces maleic anhydride and water, and side reactions produce carbon monoxide, carbon dioxide and water. Catalyst used is vanadium-phosphorus oxide ((VO)2P2O7). Reactor Type Fixed-Bed Reactor Advantages: easy use and low maintenance demand Disadvantages: hot spots and pockets of diluted butane
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Background, Process Reactions, and Rate Expressions
Balanced Stoichiometric Equation: Cases I and II C4H O2 → C4H2O3 + 4H2O Rate Equation: Cases I and II rM = k1 · CB Pseudo-First Order Rate Constant: Cases I and II k1 = · 106 exp(-15649/T) [m3/kgcat-sec] Reactions From the Oxidation of N-Butane: Cases III, IV, and V
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Background, Process Reactions, and Rate Expressions
Reaction Pathway Diagram: Cases III, IV and V Reaction Rate Expressions: Cases III, IV and V Rate Constants and Parameters
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Initial Calculations Assumptions: Open system at steady state
Negligible changes in kinetic and potential energy Negligible work 14 days’ worth of downtime per year Inlet gas 1.7 mol% n-butane 80% conversion rate; side reactions not considered in this preliminary stage 25,000 tons/year production rate Reference temperature = 25 ºC = 298 K
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Initial Calculations Stoichiometric Tables: Molar Stoichiometric Table
Mass Stoichiometric Table
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Case I Additional Assumptions: Isothermal Reactor Model to Estimate the Reactor Volume Isothermal Temperature = 673 K Bulk Density = 900 kgcat/m3 Void Fraction = 0.44 Particle Diameter = 5 mm Inlet Pressure = 1.5 bar
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Case I Polymath: Isothermal Packed Bed Reactor Model Results
Stream Flows Aspen Plus®: RPLUG Reactor Stream Flows
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Case I Polymath: Isothermal Packed Bed Reactor Model
Effect of Catalyst Weight and Temperature on Conversion
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Case II Additional Assumptions: Pressure Drop in the Fixed-Bed Reactor Must not Exceed 1/10 the Initial Pressure Pressure drop along the length of the reactor
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Case II Polymath: Isothermal Packed Bed Reactor Model Results
Stream Flows Aspen Plus®: RPLUG Reactor Stream Flows for Single Tube Reactor Stream Flows for Multi-Tube Reactor
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Case II Polymath: Isothermal Packed Bed Reactor Model
Effect of Catalyst Weight and Temperature on Conversion
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Case II Polymath: Isothermal Packed Bed Reactor Model
Effect of Length on Pressure Drop
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Case II Comparison of Three Models
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Case III Additional Assumptions:
Side reactions and byproducts are taken into consideration Polymath: Isothermal Packed Bed Reactor Model Results Stream Flows Aspen Plus®: RPLUG Reactor Stream Flows for Multi-Tube Reactor Stream Flows for Single Tube Reactor
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Case III Polymath: Isothermal Packed Bed Reactor Model
Effect of Reaction Temperature on Selectivity of Maleic Anhydride
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Case III Aspen Plus®: RPLUG Reactor
Effect of Reactor Length on Molar Flows
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Case III Comparison of Three Models
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Case IV Additional Assumptions: Non-isothermal
Energy Balance taken into consideration Heat exchanger with constant coolant temperature, Ta = 673 K Overall Heat Transfer Coefficient = 105 J/(m2*K*s)
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Case IV Polymath: Non-Isothermal Packed Bed Reactor Model Results
Stream Flows Aspen Plus®: RPLUG Reactor Stream Flows for Multi-Tube Reactor
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Case IV Aspen Plus®: RPLUG Reactor Effect of Varying Ta On Hot Spot
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Case IV Comparison of Isothermal and Real Reactor Models: Polymath
Aspen
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Case V Optimal Reactor Conditions: Criteria Met: Minimal reactor size
Minimized cost Constant selectivity throughout runs Gain < 2 Pressure Drop < 10%
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