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{{Unreferenced|date=June 2019|bot=noref (GreenC bot)}}
'''Micro process engineering''' is the science of conducting chemical or physical processes ([[unit operation]]s) inside small volumina,
typically inside channels with diameters of less than 1 mm
(microchannels) or other structures with sub-millimeter dimensions.
These processes are usually carried out in continuous flow mode, as opposed to [[batch production]], allowing a throughput high enough to make micro process engineering a tool for chemical production. Micro process engineering is therefore not to be confused with [[microchemistry]], which deals with very small overall quantities of matter.

The subfield of micro process engineering that deals with chemical
reactions, carried out in microstructured reactors or
"[[microreactor]]s", is also known as '''microreaction technology'''.

The unique advantages of microstructured reactors or ''microreactors'' are [[enhanced heat transfer]] due to the large surface [[area-to-volume ratio]], and enhanced [[mass transfer]]. For example, the length scale of [[diffusion]] processes is comparable to that of microchannels or even shorter, and efficient mixing of [[reactant]]s can be achieved during very short times (typically milliseconds). The good heat transfer properties allow a precise temperature control of reactions. For example, highly
[[exothermic reaction]]s can be conducted almost [[isothermal]]ly when the microstructured reactor contains a second set of microchannels ("cooling passage"), fluidically separated from the reaction channels ("reaction
passage"), through which a flow of cold fluid with sufficiently high
[[heat capacity]] is maintained. It is also possible to change the temperature of microstructured reactors very rapidly to intentionally achieve a non-isothermal behaviour.

==Process intensification==

While the dimensions of the individual channels are small, a micro process engineering device ("microstructured reactor") can contain many thousands of such channels, and the overall size of a microstructured reactor can be on the scale of meters. The objective of micro process engineering is not primarily to miniaturize production plants, but to increase [[Yield (chemistry)|yields]] and selectivities of chemical reactions, thus reducing the cost of chemical production. This goal can be achieved by either using chemical reactions that cannot be conducted in larger volumina, or by running chemical reactions at parameters (temperatures, pressures, concentrations) that are inaccessible in larger volumina due
to safety constraints. For example, the detonation of the [[stoichiometric]] mixture of two volume unit of [[hydrogen]] gas and
one volume unit of [[oxygen]] gas does not propagate in microchannels
with a sufficiently small diameter. This property is referred to as the
"[[intrinsic safety]]" of microstructured reactors. The improvement of yields and selectivities by using novel reactions or running reactions at more extreme parameters is known as "process intensification".

==History==

Historically, micro process engineering originated around the 1980s, when mechanical micromachining methods developed for the fabrication of [[uranium]] [[isotope separation]] nozzles were first applied to the manufacturing of compact [[heat exchanger]]s at the [[Forschungszentrum Karlsruhe|Karlsruhe (Nuclear) Research Center]].

==See also==
* [[Flow chemistry]]
* [[Microreactor]]

[[Category:Chemical process engineering]]
[[Category:Microtechnology]]

Micro process engineering - Revision history

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