Chapter 4

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# Chapter 4 - PowerPoint PPT Presentation

Chapter 4. Isothermal Reactor Design. Overview. Chapter 1 and 2 focus on mole balances on reactors to predict the volume Chapter 3 focuses on reactions Cahpter 4 combine previous chapters to obtain optimum reactor design . Design Algorithm. Mole balance (reactor type)

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## PowerPoint Slideshow about 'Chapter 4' - salim

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Presentation Transcript

### Chapter 4

Isothermal Reactor Design

Overview
• Chapter 1 and 2 focus on mole balances on reactors to predict the volume
• Chapter 3 focuses on reactions
• Cahpter 4 combine previous chapters to obtain optimum reactor design
Design Algorithm
• Mole balance (reactor type)
• Reaction rate law (reaction type, orders)
• Stoichiometry (reaction coefficients)
• Combine steps 1, 2 and 3
• Evaluate (integrate) either

Analytically Graphically

Numerically Polymath

Liquid Phase Batch

For the irrev, 2nd order reaction

• Mole balance step
• Rate law step
• Stoichiometry step
• Combine step
• Evaluate step
4.3 CSTR

For 1st order and irrev reaction

• Mole balance step
• Rate law step
• Stoichiometry step
• Combine step
• Evaluate step
• Damkohler number Da
• Da gives the degree of conversion in flow reactor
4.3.2 CSTRs in Series
• For equal size CSTRs τ1=τ2=τ operate at the same T k1=k2=k and constant ν0
• For n equal size CSTRs τ1=τ2=…=τn=τ operate at the same T k1=k2=…=kn=k
4.3.3 CSTRs in Parallel
• For identical individual reactor volume, Vi, conversion, Xi, and reaction rate -rAi
• The conversion by each reactor is the same as if the total feed is charged to one large reactor of volume V
4.3.4 2nd order reaction in a CSTR
• For 2nd order, liquid phase reaction in a CSTR
4.4 Tubular Reactors
• Consider 2nd order reaction in PFR

For liquid phase

For constant T and P gas phase

Three reaction types A→nB

• n<1, ε<0 (δ<0) → ν↓, the molecules will spend longer time and ↑X than if v=v0
• n>1, ε>0 (δ>0) ν ↑, the molecules will spend less time and ↓ X than if v=v0
• n=1, ε=0 (δ=0) v=v0
4.5 Pressure Drop in Reactors
• For liquid phase reactions the pressure drop can be ignored because the effect of pressure on the concs is small.
• For gas phase reactions the conc. of the reacting species is directly proportional to the total pressure
• Accounting for the pressure drop is a key factor in the proper reactor operation
4.5.1 Pressure drop and the rate law
• To account for pressure drop differential form design equation must be used
• For gas phase 2nd order reaction in PBR
4.5.2 Flow through a packed beds
• If y is defined as y=P/P0
• For a gas phase reactions in PBR of catalyst particles
• α is the bed characteristics
4.5.4 Analytical solution
• For 2nd order isothermal reaction with ε=0 in PBR

Integrating with X=0 @ W=0 and

Solving for X and W gives