Chemical Reaction Engineering
Core concepts
Reaction engineering connects kinetics to reactor design. Understand rate laws, order, rate constants and Arrhenius temperature dependence, and how to determine kinetics from batch data (integral, differential, half-life, initial-rate methods). Master ideal reactor models: batch, CSTR, PFR and PBR, their design equations, and the meaning of space time and space velocity. For multiple reactions, define instantaneous and overall selectivity and yield, and know how reactor choice and concentration profiles affect them. Cover reversible reactions and equilibrium conversion, adiabatic and non-isothermal operation with energy balances, hot spots and stability, and residence time distribution (RTD) with the tank-in-series and dispersion models. Catalysis: active sites, Langmuir–Hinshelwood kinetics, external and internal (Thiele modulus, effectiveness factor) transport limitations.
Traps
Do not confuse conversion with yield or selectivity. CSTR operates at outlet conditions; PFR integrates along the length. For autocatalytic or exothermic systems, multiplicity can occur. In RTD, mean residence time equals V/Q for constant density. Remember Thiele modulus large means strong diffusion limitation (η ≈ 1/φ).
Worked rule of thumb
For first-order reaction in a CSTR, X = kτ/(1 + kτ); in a PFR, X = 1 − e^(−kτ). To reach 90% conversion first order, CSTR needs τ = 9/k while PFR needs τ = 2.3/k - a PFR is far more efficient for positive-order kinetics.
Exam strategy
Write the design equation, substitute the rate law, and integrate or solve algebraically; state the reactor type explicitly.