Written and maintained by CASRAI Editorial Board
Last updated
A chemical microreactor is a continuous-flow reactor whose channels are typically under 1 mm across. The small channels give a high surface-to-volume ratio, which is why heat, mass transfer and light delivery are easier to control than in a flask. The main trade-offs are clogging and uneven flow when channels are multiplied to raise output. This page covers the chemical meaning of the term; nuclear microreactors are a separate topic (see below).
Short answer
In chemistry and chemical engineering, a microreactor is a reactor with small lateral dimensions, usually below 1 mm, operated mostly in continuous flow rather than as a batch in a flask or vessel (Wikipedia, “Microreactor”, read 2026-11-08). Reagents are pumped through channels, mix and react along the channel, and leave as product. The field that studies these devices is called micro process engineering.
Definition and scope
Microreactors sit inside the wider practice of flow chemistry and process intensification: doing a reaction in a smaller, better-controlled volume instead of a large stirred vessel. They are used for fast, strongly exothermic, hazardous or light-driven reactions, where control of temperature and mixing matters more than raw volume. A microreactor is not a bioreactor; for the cell-culture vessel see what is a bioreactor.
How a microreactor works in practice
The defining feature is geometry. Small channels mean a high surface-to-volume ratio. A 2025 review of nitration chemistry in Beilstein Journal of Organic Chemistry (doi:10.3762/bjoc.21.132) states that chip-based reactors give “exceptional heat and mass transfer capabilities due to their high surface-to-volume ratios, ensuring precise temperature control and enhanced safety, particularly for highly exothermic nitration” (read 2026-11-08). The same review describes the device types used in nitration work as tubular, chip-based and small-scale continuous stirred-tank reactors (CSTRs).
A 2026 review of flow amination in Molecules (31(7):1151, doi:10.3390/molecules31071151) notes that plug flow is typically achieved in coil or packed-bed reactors (read 2026-11-08).
Where it matters: three documented cases
Strongly exothermic reactions
For nitration, the Beilstein review ties the high surface-to-volume ratio of chip reactors to tighter temperature control and improved safety. This is the clearest example of why a small channel is not just a small flask.
Photochemistry
The Molecules review states that the high surface-to-volume ratio of microreactors ensures uniform irradiation and effectively mitigates the light attenuation problem described by the Beer-Lambert law. In a wide vessel, light is absorbed near the wall and the interior stays dim; a narrow channel keeps the whole liquid path close to the light source.
Palladium-catalysed amination
The same review reports that limited solubility of reagents or salts can cause clogging and eventual reactor failure in flow Pd-catalysed amination. Flow is therefore not automatically the better choice when solids form.
Advantages and limits, traced to sources
| Topic | What the source says | Source |
|---|---|---|
| Heat and mass transfer | High surface-to-volume ratio gives precise temperature control and enhanced safety for highly exothermic nitration | Beilstein J. Org. Chem. 2025 (doi:10.3762/bjoc.21.132) |
| Photochemistry | Uniform irradiation; mitigates light attenuation described by the Beer-Lambert law | Molecules 2026, 31(7):1151 |
| Clogging | Limited solubility of reagents or salts can cause clogging and eventual reactor failure in flow Pd-catalysed amination | Molecules 2026, 31(7):1151 |
| Scale-up by numbering up | Struggles with uniform flow distribution across parallel microchannels because of manufacturing tolerances, fouling-induced pressure imbalances and gas bubble entrapment | Beilstein J. Org. Chem. 2025 |
Scale-up
The nitration review names three approaches to scale-up: external numbering up (more complete reactors in parallel), internal numbering up (more channels inside one device) and sizing up (larger channels). Numbering up is attractive because each channel keeps the geometry that made the small device work, but the review cautions that it “inherently struggles” to deliver uniform flow across parallel microchannels. Wikipedia likewise describes scale-up by adding channels and lists clogging by particulates as the barrier most often cited, with pump pulsation as another practical issue (read 2026-11-08).
For how a route is developed and moved toward manufacture, see organic process research and development. For reference works on industrial processes, see Ullmann’s Encyclopedia of Industrial Chemistry. Reactions that are air- or moisture-sensitive are often prepared in a glove box before being pumped into a flow system.
Common misunderstandings
- “Microreactor” always means a nuclear power unit. No. Nuclear microreactors are small power reactors, a separate subject that Wikipedia treats on its own page (“Nuclear microreactor”). This page is about chemical reactors.
- Smaller is always safer or better. Small volume and good heat transfer help with exothermic chemistry, but the reviews above document clogging and flow maldistribution as real failure modes.
- Scale-up is just running more channels. Numbering up works only if flow is distributed evenly, which is the weak point the Beilstein review identifies.
FAQ
Is a microreactor the same as a nuclear microreactor?
No. A chemical microreactor is a small-channel continuous-flow reactor for chemical synthesis. A nuclear microreactor is a small nuclear power reactor. The names overlap but the technologies and fields do not.
How is a microreactor scaled up?
By numbering up (external or internal) or by sizing up. Numbering up keeps channel dimensions but must keep flow uniform across parallel channels, which manufacturing tolerances, fouling and gas bubbles can disrupt.
Sources
- “Continuous-flow-enabled intensification in nitration processes”, Beilstein J. Org. Chem. 2025, doi:10.3762/bjoc.21.132 (PMC12415922), read 2026-11-08.
- “Flow Chemistry as an Enabling Technology for Process-Intensified Amination Reactions: A Decadal Review”, Molecules 2026, 31(7):1151, doi:10.3390/molecules31071151 (PMC13074803), read 2026-11-08.
- Wikipedia, “Microreactor”, https://en.wikipedia.org/wiki/Microreactor, read 2026-11-08 (definition framing only).
