{{Unreferenced, date=June 2019, bot=noref (GreenC bot) Micro process engineering is the science of conducting chemical or physical processes (

unit operation In chemical engineering and related fields, a unit operation is a basic step in a process. Unit operations involve a physical change or chemical transformation such as separation, crystallization, evaporation, filtration, polymerization, isomeriza ...

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 Batch production is a method of manufacturing where the products are made as specified groups or amounts, within a time frame. A batch can go through a series of steps in a large manufacturing process to make the final desired product. Batch prod ...

, 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 " microreactors", 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 Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction or component) to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration ...

. For example, the length scale of

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

processes is comparable to that of microchannels or even shorter, and efficient mixing of

reactant In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

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 In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...

s can be conducted almost

isothermal In thermodynamics, an isothermal process is a type of thermodynamic process in which the temperature ''T'' of a system remains constant: Δ''T'' = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and ...

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 Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). 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 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 Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equ ...

mixture of two volume unit of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

gas and one volume unit of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

gas does not propagate in microchannels with a sufficiently small diameter. This property is referred to as the "

intrinsic safety Intrinsic safety (IS) is a protection technique for safe operation of electrical equipment in hazardous areas by limiting the energy, electrical and thermal, available for ignition. In signal and control circuits that can operate with low curre ...

" 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 Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

isotope separation nozzles were first applied to the manufacturing of compact

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

s at the Karlsruhe (Nuclear) Research Center.

Process intensification

History

See also