Chemical Reaction Engineering
Scope
Rate laws and reactor sizing, temperature effects, selectivity, catalysis, and nonideal flow.
Concepts to own
- Rate-law determination from batch data by the integral or differential method; order and rate constant; Arrhenius k = A exp(−E/RT).
- Ideal design equations: batch t = NA0 ∫dX/(−rA V); CSTR V = FA0 X/(−rA); PFR V = FA0 ∫dX/(−rA).
- First-order results: CSTR X = kτ/(1 + kτ); PFR X = 1 − exp(−kτ). For positive order the PFR always wins.
- Multiple reactions: instantaneous and overall selectivity and yield; reactor type and feed strategy control the product distribution.
- Adiabatic energy balance: T = T0 + (−ΔHr)X / Σ(θi Cp,i).
- Catalysis: LHHW rate forms, effectiveness factor, Thiele modulus, internal and external diffusion limits, deactivation.
Traps
- Treating space time τ = V/v0 as residence time when density changes.
- Reporting per-pass conversion when overall conversion with recycle is requested.
- Mismatching rate units (mol/L·s) with flow units (kmol/h).
- Ignoring heat effects in a strongly exothermic adiabatic reactor.
Worked example
With k = 1 h⁻¹ and τ = 1 h: CSTR X = 1/(1+1) = 0.50; PFR X = 1 − e⁻¹ = 0.63; three equal CSTRs in series give X = 1 − 1/(1 + 1/3)³ = 0.58.
Rule of thumb: CSTRs in series approach PFR behavior; four to six are usually enough for design purposes.