CSTRs

Continuous stirred‑tank reactors (CSTRs) are a type of reactor commonly used in chemical, biochemical, and process engineering. In a CSTR the reactants are introduced continuously, and the contents are well mixed by mechanical stirrers or internal baffles, resulting in uniformly mixed contents throughout the reactor volume. The outlet flow rate equals the inlet flow rate, maintaining constant volume.

The mass balance for a single‑reactant, first‑order reaction in a steady‑state CSTR is given by: F_A0 – F_A + V·kC_A = 0, where F_A0 is the inlet molar flow of A, F_A is the outlet molar flow, V is the reactor volume, k is the reaction rate constant, and C_A the concentration of A at the reactor exit. Solving yields C_A = F_A0 / (F + V·k), showing how increasing flow rate reduces residence time and product conversion. Heat balances similarly account for heat of reaction, heat transfer to/ from the coolant, and the adiabatic temperature change.

CSTRs are favored for reactions that produce heat, for continuous production of fine chemicals, or for biological processes such as fermentation. Their major advantage is continuous operation and easy control of residence time. However, they typically require larger volumes than plug‑flow reactors to achieve the same conversion and can face issues with backmixing if the stirrer is ineffective.

Typical applications include manufacturing of polymers, pharmaceutical intermediates, and wastewater treatment. CSTRs are also used in teaching laboratories to illustrate reactor kinetics, heat transfer, and mass‑transfer phenomena.