Chemical Reactor Design
Chemical reactor design is the discipline of selecting and sizing reactor vessels that achieve a desired chemical conversion at specified conditions of temperature, pressure, and flow rate. It integrates reaction kinetics, thermodynamics, and transport phenomena to predict concentration and temperature profiles within the reactor. Industrial applications range from petroleum refining and polymer synthesis to pharmaceutical manufacturing and environmental remediation.
Worked Example
Problem
A first-order liquid-phase reaction A → B has a rate constant k = 0.05 min⁻¹ at 80 °C. Feed concentration C_A0 = 2.0 mol/L and volumetric flow rate v₀ = 100 L/min. What CSTR volume is needed for 90% conversion?
Solution
Step 1: Desired conversion X = 0.90, so C_A = C_A0(1 − X) = 2.0 × 0.10 = 0.20 mol/L. Step 2: CSTR design equation: V = v₀ · X / (k · C_A) for first-order reaction in CSTR. Step 3: Exit rate −r_A = k · C_A = 0.05 × 0.20 = 0.010 mol/(L·min). Step 4: V = F_A0 · X / (−r_A) = (v₀ · C_A0 · X) / (−r_A) = (100 × 2.0 × 0.90) / 0.010 = 180 / 0.010 = 18,000 L.
Answer
Required CSTR volume = 18,000 L (18 m³)
Common Reactor Types and Their Characteristics
| Reactor Type | Flow Pattern | Typical Use | Key Equation | Mixing |
|---|---|---|---|---|
| CSTR | Continuous stirred | Liquid-phase reactions | V = F_A0·X / (−r_A) | Perfect mixing |
| PFR | Plug flow | Gas-phase reactions | V = F_A0·∫dX/(−r_A) | No axial mixing |
| Batch | No flow | Specialty chemicals | t = N_A0·∫dX/(−r_A·V) | Well mixed |
| Packed Bed | Plug flow | Catalytic reactions | W = F_A0·∫dX/(−r'_A) | Radial mixing |
| Semi-batch | Partial flow | Controlled addition | Mixed design eqn | Variable |
Interactive Tools
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Related Terms
CSTR
A Continuously Stirred Tank Reactor (CSTR) is an idealised reactor in which perfect mixing is assumed, meaning concentration and temperature are uniform throughout the vessel and equal to the exit stream values. It operates at steady state with continuous feed and product streams, and is described by an algebraic design equation rather than a differential one. CSTRs are widely used in liquid-phase reactions, biological fermenters, and wastewater treatment due to their ease of temperature control and scale-up.
Plug Flow Reactor
A Plug Flow Reactor (PFR) is an idealised tubular reactor in which fluid flows with a flat velocity profile (no axial mixing) so that all fluid elements have the same residence time. Concentration and temperature vary continuously along the reactor length, requiring a differential design equation for analysis. PFRs are preferred for gas-phase reactions, high-temperature processes, and situations where high conversion is required with minimum reactor volume compared to CSTRs.
Reaction Kinetics (engineering)
Reaction kinetics in engineering quantifies the rate at which reactants are converted to products under specified conditions of concentration, temperature, pressure, and catalyst presence. The rate expression (rate law) relates reaction rate to reactant concentrations via a rate constant, and the Arrhenius equation describes the temperature dependence of that constant. Engineering application of kinetics enables the sizing of reactors, optimisation of operating conditions, and prediction of yield and selectivity in industrial chemical processes.
From Latin "reactor" (one that reacts), derived from "re-" (back) + "agere" (to act). The systematic design of chemical reactors emerged as a discipline in the early 20th century, formalised by Damköhler (1930s) and Levenspiel (1950s–60s) in his landmark text "Chemical Reaction Engineering".