Isothermal Reactor Design 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