Continuous Stirred Tank Reactor (CSTR) - Vapourtec (2024)

A continuous stirred tank reactor (CSTR) is a type of chemical reactor that is widely used in industrial processes to produce chemicals, pharmaceuticals, and other products. In a CSTR flow reactor, reactants are continuously fed into the reactor vessel, where they are mixed and allowed to react, producing the desired products.

The CSTR consists of a large tank or vessel, typically made of stainless steel, which is equipped with a stirring mechanism, such as a mechanical stirrer or an agitator, that keeps the reactants in motion and ensures that they are well-mixed. The reactants are introduced into the tank through inlet ports, and the products are continuously removed through outlet ports.

The key feature of a CSTR is its constant stirring, which ensures that the reactants are evenly distributed throughout the vessel and that the reaction proceeds at a uniform rate. This allows for precise control over the reaction conditions, such as temperature, pressure, and concentration, which can be adjusted by controlling the flow rates of the reactants and products.
CSTRs are particularly well-suited for reactions that require high conversion rates or produce intermediate products, as the continuous mixing ensures that the reaction proceeds to completion. They are also commonly used in bioreactors for the cultivation of microorganisms, such as bacteria or yeast, which require constant stirring to ensure optimal growth and metabolic activity.

Overall, CSTRs are a versatile and reliable tool for industrial processes that require continuous, high-volume production of chemicals or other products.

In flow chemistry, a continuous stirred tank reactor (CSTR) equipped with features to continuously feed and exhaust reactants is an example of a mechanically mixed flow reactor.

Flow Chemistry and the Continuous Stirred Tank Reactor (CSTR)

For practical use in flow chemistry, a single CSTR flow reactor suffers from back mixing. It also gives poor control of residence time. A wide range of residence times is often referred to as a broad residence time distribution (RTD, see below). Each molecule of reagent does not necessarily flow through the reactor at the same time. The back mixing and broad RTD combine to limit the performance of a single CSTR flow reactor. For most reactions, the back mixing and variable residence time have a negative impact on product yield, selectivity, and space yield for the reactor.

For flow chemistry, continuous stirred tank reactors are often used in cascades of 3 or 4 CSTRs. By adopting this configuration of multiple CSTR’s the residence time control can be much improved and the back mixing significantly reduced.

The image below shows a Vapourtec R-Series flow chemistry system configured with a series cascade of four CSTRs.

Residence Time Distribution in CSTR

The following figures compare the RTD for continuous stirred tank reactors. The RTD of single and multiple cascades of CSTRs are compared with the RTD for a plug flow reactor (PFR).

The figure below compares the RTD for a typical single CSTR with a cascade or four and eight Vapourtec CSTRs.

The figure below shows the RTD for three different sizes of plug flow reactors (PFR). Note the tighter RTD than even for the cascade of eight CSTRs.

Examples of continuous stirred tank reactors

References:

[1] Schmidt, Lanny D. (1998).The Engineering of Chemical Reactions. New York: Oxford University Press.ISBN0-19-510588-5.