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Learn the reactor design strategies for optimizing desired product output and managing heat effects in various reactions. Understand temperature profiles, equilibrium considerations, and kinetic limits in exothermic and endothermic reactions. Explore practical solutions like inerts addition, inter-stage coolers, and optimization techniques for desired product yield.
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HW Help How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-) Is this T going to give you S,L or G Can P influence S,L or G? How do you want to run the separation? Safety Issues? Ease of Processing
HW Help How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-), rxn is exo or endo? Is this T going to give you S,L or G? Can P influence S,L or G? How do you want to run the separation? Safety Issues? Ease of Processing
Reactor Design for Selective Product Distribution Sieder, et.al. Chapter 15 Terry A. Ring Chemical Engineering University of Utah
Overview • Parallel Reactions • A+BR (desired) • AS • Series Reactions • ABC(desired)D • Independent Reactions • AB (desired) • CD+E • Series-Parallel Reactions • A+BC+D (desired) • A+CE • Mixing, Temperature and Pressure Effects
Examples • Ethylene Oxide Synthesis • CH2=CH2 + O22CO2 + 2H2O • CH2=CH2 + O2CH2-CH2(desired) O
Examples • Diethanolamine Synthesis
Examples • Butadiene Synthesis, C4H6,from Ethanol
Examples • Maleic Anhydride Synthesis • C6H6 + 9/2 O2 C4H2O3 + 2 CO2 + 2 H2O • C4H2O3 + 3 O2 4 CO2 + H2O • C6H6 + 15/2 O2 6 CO2 + 3 H2O
Rate Selectivity • Parallel Reactions • A+BR (desired) • A+BS • Rate Selectivity • (αD- αU) >1 make CA as large as possible • (βD –βU)>1 make CB as large as possible • (kD/kU)= (koD/koU)exp[-(EA-D-EA-U)/(RT)] • EA-D > EA-U T • EA-D < EA-U T
Maximize Desired Product • Series Reactions • AB(desired)CD • Plug Flow Reactor • Optimum Time in Reactor
Fractional Yield (k2/k1)=f(T)
Real Reaction Systems • More complicated than either • Series Reactions • Parallel Reactions • Effects of equilibrium must be considered • Confounding heat effects • All have Reactor Design Implications • Use Optimizer in Aspen+to evaluate Reactor Design
Reactor Heat Effects Sieder Chapter 15 Terry A. Ring Chemical Engineering University of Utah
Problems • Managing Heat effects • Optimization • Make the most product from the least reactant
Reaction Heat Heuristics • 21-High exothermic heat of reaction: Consider using excess reactant, inert diluents or cold shots of reactant. Consider them early on in the design • 22-Lower exothermic heat of reaction: Use heat exchanger on/in reactor. Or use intercoolers between adiabatic reaction stages. • 23-High endothermic heat of reaction: Consider use of excess reactant, inert diluents or hot shots. Consider them early on in the design. • 24-Lower endothermic heat of reaction: Use heat exchanger on/in reactor. Or use interheaters between adiabatic reaction stages.
Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling
Equilibrium Reactor-Temperature Effects • Single Equilibrium • aA +bB rR + sS • ai activity of component I • Gas Phase, ai = φiyiP, • φi== fugacity coefficient of i • Liquid Phase, ai= γi xi exp[Vi (P-Pis)/RT] • γi = activity coefficient of i • Vi =Partial Molar Volume of i Van’t Hoff eq.
Kinetic Reactors - CSTR & PFR – Temperature Effects • Used to Size the Reactor • Used to determine the reactor dynamics • Reaction Kinetics
Equilibrium and Kinetic Limits • Increasing Temperature Increases the Rate • Equilibrium Limits Conversion
PFR – no backmixing • Used to Size the Reactor • Space Time = Vol./Q • Outlet Conversion is used for flow sheet mass and heat balances
CSTR – complete backmixing • Used to Size the Reactor • Outlet Conversion is used for flow sheet mass and heat balances
Temperature Profiles in a Reactor Exothermic Reaction
Reactor with Heating or Cooling Q = UA ΔT Reactor is a Shell and Tube (filled with catalyst) HX
Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling
Reactor with Heating or Cooling Q = UA ΔT
Managing Heat Effects • Reaction Run Away • Exothermic • Reaction Dies • Endothermic • Preventing Explosions • Preventing Stalling
Inter-stage Cooler Lowers Temp. Exothermic Equilibria
Inter-stage Cold Feed Lowers Temp Lowers Conversion Exothermic Equilibria
Optimization of Desired Product • Reaction Networks • Heuristic 7 • Maximize yield, • moles of product formed per mole of reactant consumed • Maximize Selectivity • Number of moles of desired product formed per mole of undesirable product formed • Maximum Attainable Region – see discussion in Chap’t. 6 SS&L. • Reactors and bypass • Reactor sequences
Engineering Tricks • Reactor types • Multiple Reactors • Mixtures of Reactors • Bypass • Recycle after Separation • Split Feed Points/ Multiple Feed Points • Diluents • Temperature Management
Feed Temperature, ΔHrxn Adiabatic Adiabatic Cooling Heat Balance over Reactor Q = UA ΔTlm
Aspen Units - Rate=kTn e[-E/RT]πCiαi i Rate Units When Rate Basis is Cat (wt), substitute sec–kg catalyst for sec·m3 in each expression above. For either rate basis, the reactor volume or catalyst weight used is determined by the reactor where the reaction occurs.