Flow chemistry is also known as continuous flow or plug flow chemistry. In Flow Chemistry, two or more reagents are continuously pumped into a flow-reactor rather than in batch-reactor, where they mix and subsequently react under thermal control. The flow-reactor can be a simple pipe, tube or complex micro-structured devices. The mixing devices and reactors are maintained at sure temperature and pressure range to promote the desired reaction fast and successfully. The reactants may also be exposed to an electrical flux or a photon flux to promote an electrochemical or photochemical reaction.

Flow Chemistry has some major advantages. Mixing can be achieved within seconds and reaction temperature can rise above the solvent's boiling point, resulting in faster reactions. The rapid diffusion mixing avoids the issues found in batch reactors. The high surface area to volume ratio (1000x greater than a batch reactor) enables almost instantaneous heating or cooling and therefore ultimate temperature control, resulting in cleaner products. Flow chemistry allows only a small amount of hazardous intermediate to be formed at any instant. The high surface area also allows excellent control of exothermic reactions using flow-reactor, resulting in safer reactions. Flow Chemistry enables excellent reaction selectivity.

Flow Chemistry with automation enables the quick variation of reaction conditions on a µl-scale. Parameters such as reaction time, temperature, flow, pumped volumes and pressure can all be rapidly varied. One reaction can follow another, separated by solvent, each cleaning out the previous reaction enabling quick reaction optimization. Scale-up issues are minimized due to maintaining excellent mixing and heat transfer. Higher flow rates and correspondingly larger reactors can be used to easily produce kilogram or tonne-scale quantities in that case. Flow chemistry process offers potential for the efficient manufacture of chemical products.

Choosing to run a chemical reaction using flow chemistry, either in a micro-reactor or other mixing device offers a variety of features:

1) Flow of reagents - in flow-reactor, reagent is pumped under pressure and flow continuously through the reactor, this contrasts with batch-reactor where all reagents are loaded into a vessel at the beginning

2) Control of reaction time - reaction time is determined by the time the reagents take to flow through the reactor; this period is called the residence time

3) Control of stoichiometry - reaction stoichiometry is controlled by the relative flow rates of the reactants, the concentration of one reagent relative to another can be increased or reduced simply by pumping that reagent at a higher or lower rate of flow

4) Heat transfer - flow reactors have excellent heat transfer capability when compared with batch reactors, this feature is due to the much greater surface area to volume ratio of flow reactors over batch reactors

5) Mass transfer - reactors designed for flow chemistry have high rates of mass transfer, this is due to the small sizes and good mixing that is possible.

6) Flow chemistry reaction is easily scaled - flow chemistry reactions can simply be run for longer, this produces more material

7) Precise control - flow chemistry reactor offers the chemist precise control of the five critical reaction parameters, which are stoichiometry, mixing, temperature, pressure and reaction time

8) Low inventory of hazardous materials - when reactions are run in continuous flow only small quantities of potentially hazardous materials are “in-process” or “in pipe-line”

9) Telescoped reactions - reactive intermediates don’t need to be isolated, flow reactions can be easily run in sequence or “telescoped”

10) No head-space - flow reactors do not require a head space, the pressure within the reactor is controlled by a device called a back pressure regulator (BPR), with high pressure batch reactors the gas within the head space must be pressurized

11) Very low back-mixing - flow reactors can be arranged to have very little or even no back-mixing