“Flow chemistry,” also referred to as “plug flow” or “continuous flow chemistry,” is the process of carrying out chemical reactions in a pipe or conduit.
This concept defines a wide range of chemical processes that take place in a continuous, flowing stream, usually in a reactor zone. The application of this phenomenon is based on the concept of pumping reagents using many types of reactors to perform specific reactions.
Common Types
The most familiar forms of reactors are plug flow reactors and column reactors, while more sophisticated reactor designs may be required for certain chemical processes – e.g., electrochemical reactors, photoreactors, etc.
The reactive species are pumped together at a mixing point and flow down through a temperature-controlled tube or pipe. This process offers significant advantages such as faster reactions, cleaner products, safer reactions, and easy scale-up.
Flow reactors, for example, those produced by Amar Equipment, can be easily pressurized to heat reactions 100-150ºC above their standard boiling point, increasing reaction rates 1000-fold. We call this process “superheating.”
Selection of Preferred Parameters
Amar Equipment’s flow reactors allow excellent selectivity in the course of a reaction. In addition, rapid diffusion mixing avoids the problems associated with batch reactors. The large surface area to volume ratio allows for instantaneous heating or cooling and ultimate temperature control.
Benefits & Uses
We now mention two valuable examples of flow-through chemistry
Oxidation of a primary alcohol
Williamson Ether Synthesis
Flow chemistry allows only a tiny amount of unstable intermediates at any time. The large surface area also facilitates exotherm control. Reaction products leaving a flow reactor can flow into an aqueous workup system or a solid-phase scavenger column.
Additional Remarks
Automated flow chemistry allows rapid variation of conditions on a tiny scale, e.g., 100 µL. Parameters such as reaction time, temperature, the ratio of reagents, concentration, and the reagents themselves can be changed quickly.
One chemical reaction can follow another, separated by a solvent, with each reaction purifying the previous one. Nevertheless, minimize scale-up problems by ensuring excellent mixing and heat transfer. Higher flow rates and associated larger reactors can be used to efficiently produce kilogram quantities.
Flow chemistry facilitates reaction conditions that you cannot achieve in a batch, such as a 5-second reaction at 250 ºC.
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