Continuous Stirred Tank Reactors
What is a Continuous Stirred Tank Reactor?
A Continuous Stirred Tank Reactor (CSTR) is an agitated vessel used in flow chemistry, that has a continuous feed of reactants and a continuous discharge of the reaction mixture (product). The feed and discharge rates are controlled to maintain constant reaction conditions (concentration, temperature and reaction rate) ensuring a consistent product stream is produced.
How do Continuous Stirred Tank Reactors work in a series?
The behaviour of a CSTR is often approximated or modelled by that of an ‘ideal CSTR’, which assumes perfect mixing. In a perfectly mixed reactor, the reagent is instantaneously and uniformly mixed throughout the reactor upon entry. Consequently, the output composition is identical to the composition of the material inside the reactor, which is a function of residence time and reaction rate.
The CSTR is the ideal limit of complete mixing in reactor design, which is the complete opposite of a plug flow reactor (PFR). In practice, no reactors behave ideally but instead fall somewhere between the mixing limits of an ideal CSTR and a plug flow reactor.
Characteristics of a CSTR
There are well-defined key advantages to using flow technologies as compared to standard batch chemistry methods:
Run at a steady state with a continuous flow of reactants and products
Feed assumes a uniform composition throughout the reactor
The exit stream has the same composition as in the tank
Relationship between reactants and product within a CSTR
Continuous Stirred Tanks in Series Model
highlighting the relationship between reactants and products within CSTRs in series
When CSTRs are in series, the previous reactor operates at a higher concentration than the following reactor, therefore the rate and the conversion are greater than the subsequent reactor in series, which then builds on the conversion in the previous reactor.
The continuous stirred tanks in series model is used to determine the number of theoretical stages, or 'plugs', within a flow reactor. The greater the number of theoretical stages, the nearer the flow reactor is to true plug flow reactors.
It should be noted that true plug flow is a theoretical ideal that is never practically achieved, and is defined as an infinite number of theoretical stages or 'plugs'. AM Technology defines a practical flow reactor benchmark as a flow reactor with ten theoretical stages or more.
The Coflore Reactor range is built to act like continuous stirred tank reactors. The Coflore ACR, for example, works in a way such that each individual reactor cell behaves like an independent CSTR chemical reactor. Each reactor cell mimics the behaviour of a single CSTR so that when they're connected to one another, the material is pumped through each reactor cell in a series, with continuous chemical reactions occurring one after another.
Check out how the Coflore ACR's mechanically agitated reactor cell block works in more detail below.