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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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chapter 4

Chapter 4

Isothermal Reactor Design

overview
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
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
Liquid Phase Batch

For the irrev, 2nd order reaction

  • Mole balance step
  • Rate law step
  • Stoichiometry step
  • Combine step
  • Evaluate step
4 3 cstr
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
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
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 2 nd order reaction in a cstr
4.3.4 2nd order reaction in a CSTR
  • For 2nd order, liquid phase reaction in a CSTR
4 4 tubular reactors
4.4 Tubular Reactors
  • Consider 2nd order reaction in PFR

For liquid phase

For constant T and P gas phase

slide11

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
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
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
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
4.5.4 Analytical solution
  • For 2nd order isothermal reaction with ε=0 in PBR
slide16

Integrating with X=0 @ W=0 and

Solving for X and W gives