Stirred Tank Reactors (CSTR)

The residence time distribution (RTD) of an ideal CSTR follows an exponential decay profile — meaning a fraction of the entering reagent exits immediately while some material remains for extended periods. For reactions where narrow residence time distribution is important (e.g., polymerisations or reactions sensitive to over-processing), multiple CSTRs in series are used, with the RTD of n CSTRs in series approaching plug-flow behaviour as n increases. In flow chemistry practice, 2–5 CSTRs in series are commonly used to achieve the combination of back-mixing (beneficial for highly exothermic reactions where temperature spikes must be damped) and plug-flow character.

For laboratory and kilo-lab scale, CSTR units are available in glass-jacketed formats (10 mL to 5 L) with precision overhead stirring, PT-100 temperature sensing, and level control. At pilot and production scale, CSTR units in SS 316L or Hastelloy C-276 with external jacket heating/cooling, multiple reagent inlet nozzles, internal baffles, and control valve-based level and feed management are used. Magnetic coupling agitators are available for completely sealed designs required for highly toxic or air-sensitive chemistries. Slurry handling — critical for reactions producing solid products (e.g., salt formation, crystallisation) — is addressed through bottom-discharge valve designs, slurry pumps, and smooth internal geometry to prevent fouling.