Flow Chemistry - Benefits of Flow

Benefits of Flow

• Reaction temperature can 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 intensfied. Mostly, because the area to volume ratio is large. Thereby, endothermal and exothermal reaction can be thermostated. 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.
  • The reactor operates under steady-state conditions.
• Flow reactions can be automated with far less effort than batch reactions. This allows for unattended operation and experimental planning. By coupling the output of the reactor to a detector system, it is possible to go further and create an automated system which can sequentially investigate a range of possible reaction parameters (varying stoichiometry, residence time and temperature) and therefore explore reaction parameters with little or no intervention.
• Multi step reactions can be arranged in a continuous sequence. This can be especially beneficial if intermediate compounds are unstable, toxic, or sensitive to air, since they will exist only momentarily and in very small quantities.
• 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.
• 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
• Reactions which involve reagents containing dissolved gases are easily handled, whereas in batch a pressurised "bomb" reactor would be necessary.
• Multi phase liquid reactions (e.g. phase transfer catalysis) can be performed in a straightforward way, with high reproducibility over a range of scales and conditions.
• Scale up of a proven reaction can be achieved rapidly with little or no process development work, by either changing the reactor volume or by running several reactors in parallel, provided that flows are recalculated to achieve the same residence times.