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Concept
Flow chemistry
Résumé
In flow chemistry, also called reactor engineering, a chemical reaction is run in a continuously flowing stream rather than in batch production. In other words, pumps move fluid into a reactor, and where tubes join one another, the fluids contact one another. If these fluids are reactive, a reaction takes place. Flow chemistry is a well-established technique for use at a large scale when manufacturing large quantities of a given material. However, the term has only been coined recently for its application on a laboratory scale by chemists and describes small pilot plants, and lab-scale continuous plants. Often, microreactors are used.
Reaction stoichiometry: In batch production this is defined by the concentration of chemical reagents and their volumetric ratio. In flow this is defined by the concentration of reagents and the ratio of their flow rate.
Residence time: In batch production this is determined by how long a vessel is held at a given temperature. In flow the volumetric residence time is given by the ratio of the volume of the reactor and the overall flow rate, as most often, plug flow reactors are used.
Choosing to run a chemical reaction using flow chemistry, either in a microreactor or other mixing device offers a variety of pros and cons.
Reaction temperature can be raised above the solvent's boiling point as the volume of the laboratory devices is typically small. Typically, non-compressible fluids are used with no gas volume so that the expansion factor as a function of pressure is small.
Mixing can be achieved within seconds at the smaller scales used in flow chemistry.
Heat transfer is intensified. Mostly, because the area to volume ratio is large. As a result, endothermic and exothermic reactions can be thermostated easily and consistently. The temperature gradient can be steep, allowing efficient control over reaction time.
Safety is increased:
Thermal mass of the system is dominated by the apparatus making thermal runaways unlikely.
Smaller reaction volume is also considered a safety benefit.
Source officielle
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