Flow chemistry is a well established technique for use at a large scale when manufacturing large quantities of a given material. However, it is relatively new to use it in the laboratory environment.

Flow Chemistry is running a reaction in a continuously flowing stream rather than in a batch container. In other words, pumps move fluid into a tube, and where tubes join one another, the fluids see one another. If these fluids are reactive, a reaction takes place.

Batch Vs Flow

Comparing parameters in Batch vs Flow: - Reaction stoichiometry In Batch this is defined by the concentration of reagents and their volumetric ratio. In Flow this is defined by the concentration of reagents and the ratio of their flow rate - Reaction time In Batch this is determined by how long a vessel is held at a given temperature In flow this is determined by the volume of the reactor, and the bulk flow rate

Flow Reactor scale

It is possible to have flow reactors operating at large scale as already mentioned, however for use in the laboratory, channel/tube scale is likely to be in the region of 50um to 500um. Within this scale range, there are a number of benefits to do with both thermal and mass transfer that allow chemistry to perform very well.

Benefits of flow

- Reaction temperature

Can be far above the solvent boiling point due to easy ability to contain pressure.

- Mixing

At these smaller scales, mixing can be achieved within seconds.

- Thermal transfer

The thermal mass of the fluid is typically far lower than the thermal mass of the system, so massive exotherms can be controlled.

- Time = Position

Position along the flowing stream and reaction time point are directly related to one another. This means that it is possible to arrange the system such that further reagents can be introduced into the flowing reaction stream at precisely the time point in the reaction that is desired.

- Purification

It is possible to arrange a flowing system such that purification is coupled with the reaction. There are three primary techniques that are used: - Solid phase scavenging - Chromatographic separation - Liquid/Liquid Extraction

Other uses of flow

It is possible to run experiments in flow using more sophisticated techniques, such as solid phase chemistries. Professors Steven Ley's group at Cambridge University in the UK has pioneered work that has demonstrated how valuable the coupling of flow chemistry and solid supported chemistries can be. http://leygroup.ch.cam.ac.uk. Some ground breaking work can be seen in the following articles [1],Article,[2]−

Running flow experiments

The practicalties of running flow experiments in normal chemistry laboratories are not simple. It required the coupling of a range of tools that are not so commonly used by chemists. Additionally it is extremely beneficial have a software control system to help manage all of the systems that are allowing the experiment to be performed. The chemist needs to have access to specialist microfabricated devices, tubing connectors and tubing as well as the pumps to displace the reagents.

As a chemist starts to perform experiments it quickly becomes clear that the challenge of controlling the system is more complex than originally anticipated.

External links

MRSP [3]

• Syrris

See also

Microreactor A microreactor is a device that enables chemical reactions to be done on the micro-litre scale. ...