Microreactor 1

Microreactor

Microreactor technologies developed at LLNLuse micromachining techniques to miniaturize the

reactor design. Applications include fuelprocessors for generating hydrogen, chemical

synthesis, and bioreaction studies.

A microreactor or microstructured reactor or microchannelreactor is a device in which chemical reactions take place in aconfinement with typical lateral dimensions below 1mm; the mosttypical form of such confinement are microchannels.[1] Microreactorsare studied in the field of micro process engineering, together withother devices (such as micro heat exchangers) in which physicalprocesses occur. The microreactor is usually a continuous flow reactor(contrast with/to a batch reactor). Microreactors offer many advantagesover conventional scale reactors, including vast improvements inenergy efficiency, reaction speed and yield, safety, reliability,scalability, on-site/on-demand production, and a much finer degree ofprocess control.

History

Gas-phase microreactors have a long history but those involving liquids started to appear in the late 1990s.[1] One ofthe first microreactors with embedded high performance heat exchangers were made in the early 1990s by theCentral Experimentation Department (Hauptabteilung Versuchstechnik, HVT) of Forschungszentrum Karlsruhe[] inGermany, using mechanical micromachining techniques that were a spinoff from the manufacture of separationnozzles for uranium enrichment.[] As research on nuclear technology was drastically reduced in Germany,microstructured heat exchangers were investigated for their application in handling highly exothermic and dangerouschemical reactions. This new concept, known by names as microreaction technology or micro process engineering,was further developed by various research institutions. An early example from 1997 involved that of azo couplingsin a pyrex reactor with channel dimensions 90 micrometres deep and 190 micrometres wide.[1]

BenefitsUsing microreactors is somewhat different from using a glass vessel. These reactors may be a valuable tool in thehands of an experienced chemist or reaction engineer: Microreactors typically have heat exchange coefficients of at least 1 megawatt per cubic meter per kelvin, up to

500 MWm3K1 vs. a few kilowatts in conventional glassware (1 l flask ~10kWm3K1)). Thus,microreactors can remove heat much more efficiently than vessels and even critical reactions such as nitrationscan be performed safely at high temperatures.[2] Hot spot temperatures as well as the duration of high temperatureexposition due to exothermicity decreases remarkably. Thus, microreactors may allow better kineticinvestigations, because local temperature gradients affecting reaction rates are much smaller than in any batchvessel. Heating and cooling a microreactor is also much quicker and operating temperatures can be as low as100 C. As a result of the superior heat transfer, reaction temperatures may be much higher than in conventionalbatch-reactors. Many low temperature reactions as organo-metal chemistry can be performed in microreactors attemperatures of 10 C rather than 50 C to 78 C as in laboratory glassware equipment.

Microreactors are normally operated continuously. This allows the subsequent processing of unstableintermediates and avoids typical batch workup delays. Especially low temperature chemistry with reaction timesin the millisecond to second range are no longer stored for hours until dosing of reagents is finished and the nextreaction step may be performed. This rapid work up avoids decay of precious intermediates and often allowsbetter selectivities.[3]

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Continuous operation and mixing causes a very different concentration profile when compared with a batchprocess. In a batch, reagent A is filled in and reagent B is slowly added. Thus, B encounters initially a high excessof A. In a microreactor, A and B are mixed nearly instantly and B won't be exposed to a large excess of A. Thismay be an advantage or disadvantage depending on the reaction mechanism - it is important to be aware of suchdifferent concentration profiles.

Although a bench-top microreactor can synthesize chemicals only in small quantities, scale-up to industrialvolumes is simply a process of multiplying the number of microchannels. In contrast, batch processes too oftenperform well on R&D bench-top level but fail at batch pilot plant level.[4]

Pressurisation of materials within microreactors (and associated components) is generally easier than withtraditional batch reactors. This allows reactions to be increased in rate by raising the temperature beyond theboiling point of the solvent. This, although typical Arrhenius behaviour, is more easily facilitated in microreactorsand should be considered a key advantage. Pressurisation may also allow dissolution of reactant gasses within theflow stream.

Problems Although there have been reactors made for handling particles, microreactors generally do not tolerate

particulates well, often clogging. Clogging has been identified by a number of researchers as the biggest hurdlefor microreactors being widely accepted as a beneficial alternative to batch reactors. So far, the so-calledmicrojetreactor[5] is free of clogging by precipitating products. Gas evolved may also shorten the residence timeof reagents as volume is not constant during the reaction. This may be prevented by application of pressure.

Mechanical pumping may generate a pulsating flow which can be disadvantageous. Much work has been devotedto development of pumps with low pulsation. A continuous flow solution is electroosmotic flow (EOF).

Typically, reactions performing very well in a microreactor encounter many problems in vessels, especially whenscaling up. Often, the high area to volume ratio and the uniform residence time cannot easily be scaled.

Corrosion imposes a bigger issue in microreactors because area to volume ratio is high. Degradation of few mmay go unnoticed in conventional vessels. As typical inner dimensions of channels are in the same order ofmagnitude, characteristics may be altered significantly.

T reactorsOne of the simplest forms of a microreactor is a 'T' reactor. A 'T' shape is etched into a plate with a depth that may be40 micrometres and a width of 100 micrometres: the etched path is turned into a tube by sealing a flat plate over thetop of the etched groove. The cover plate has three holes that align to the top-left, top-right, and bottom of the 'T' sothat fluids can be added and removed. A solution of reagent 'A' is pumped into the top left of the 'T' and solution 'B'is pumped into the top right of the 'T'. If the pumping rate is the same, the components meet at the top of the verticalpart of the 'T' and begin to mix and react as they go down the trunk of the 'T'. A solution of product is removed at thebase of the 'T'.

Microreactor 3

Applications

Glass Microreactors involve microfabricatedstructures to allow flow chemistry to be

performed at a microscale. Applications includeCompound Library Generation, ProcessDevelopment and Compound Synthesis

Synthesis

Microreactors can be used to synthesise material more effectively thancurrent batch techniques allow. The benefits here are primarily enabledby the mass transfer, thermodynamics, and high surface area to volumeratio environment as well as engineering advantages in handlingunstable intermediates. Microreactors are applied in combination withphotochemistry, electrosynthesis, multicomponent reactions andpolymerization (for example that of butyl acrylate). It can involveliquid-liquid systems but also solid-liquid systems with for example thechannel walls coated with a heterogeneous catalyst. Synthesis is alsocombined with online purification of the product.[1] Following GreenChemistry principles, microreactors can be used to synthesize andpurify extremely reactive Organometallic Compounds for ALD andCVD applications, with improved safety in operations and higherpurity products.[6][7]

In one microreactor study a Knoevenagel condensation[8] wasperformed with the channel coated with a zeolite catalyst layer whichalso serves to remove water generated in the reaction:

A Suzuki reaction was examined in another study[9] with a palladium catalyst confined in a polymer network ofpolyacrylamide and a triarylphosphine formed by interfacial polymerization:

The combustion of propane was demonstrated to occur at temperatures as low as 300C in a microchannel setupfilled up with an aluminum oxide lattice coated with a platinum / molybdenum catalyst:[10]

Microreactor 4

AnalysisMicroreactors can also enable experiments to be performed at a far lower scale and far higher experimental rates thancurrently possible in batch production, while not collecting the physical experimental output. The benefits here areprimarily derived from the low operating scale, and the integration of the required sensor technologies to allow highquality understanding of an experiment. The integration of the required synthesis, purification and analyticalcapabilities is impractical when operating outside of a microfluidic context.

NMR

Researchers at the Radboud University Nijmegen and Twente University, the Netherlands, have developed amicrofluidic high-resolution NMR flow probe. They have shown a model reaction being followed in real-time. Thecombination of the uncompromised (sub-Hz) resolution and a low sample volume can prove to be a valuable tool forflow chemistry.[11]

Infrared Spectroscopy

Mettler Toledo and Bruker Optics offer dedicated equipment for monitoring with attenuated total reflectancespectrometry (ATR spectrometry) in microreaction setups. The former has been demonstrated for reactionmonitoring.[12] The latter has been successfully used for reaction monitoring[13] and determing dispersioncharacteristics[14] of a microreactor.

Academic researchMicroreactors, and more generally, micro process engineering, are the subject of worldwide academic research. Aprominent recurring conference is IMRET, the International Conference on Microreaction Technology.Microreactors and micro process engineering have also been featured in dedicated sessions of other conferences,such as the Annual Meeting of the American Institute of Chemical Engineers (AIChE), or the International Symposiaon Chemical Reaction Engineering (ISCRE). Research is now also conducted at various academic institutions aroundthe world, e.g. at the Massachusetts Institute of Technology (MIT) in Cambridge/MA, University of IllinoisUrbana-Champaign, Oregon State University in Corvallis/OR, at University of California, Berkeley in Berkeley/CAin the United States, at the EPFL in Lausanne, Switzerland, at Eindhoven University of Technology in Eindhoven, atRadboud University Nijmegen in Nijmegen, Netherlands and at the LIPHT [15] of Universit de Strasbourg inStrasbourg and [16] of the University of Lyon, CPE Lyon, France.

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Market structure

Glass Microreactor. The channels of the chip inthe picture are 150 m wide and 150 m deep.

Depending on the application focus, there are various hardwaresuppliers and commercial development entities to service the evolvingmarket. One view to technically segment market, offering and marketclearing stems from the scientific and technological objective ofmarket agents:a. Ready to Run (turnkey) systems are being used where the

application environment stands to benefit from new chemicalsynthesis schemes, enhanced investigational throughput of up toapproximately 10 - 100 experiments per day (depends on reactiontime) and reaction subsystem, and actual synthesis conduct at scalesranging from 10 milligrams per experiment to triple digit tons peryear (continuous operation of a reactor battery).

b.b. Modular (open) systems are serving the niche for investigations on continuous process engineering lay-outs,where a measurable process advantage over the use of standardized equipment is anticipated by chemicalengineers. Multiple process lay-outs can be rapidly assembled and chemical process results obtained on a scaleranging from several grams per experiment up to approximately 100kg at a moderate number of experiments perday (3-15). A secondary transfer of engineering findings in the context of a plant engineering exercise (scale-out)then provides target capacity of typically single product dedicated plants. This mimics the success of engineeringcontractors for the petro-chemical process industry.

c.c. Dedicated developments. Manufacturer of microstructured components are mostly commercial developmentpartners to scientists in search of novel synthesis technologies. Such development partners typically excel in theset-up of comprehensive investigation and supply schemes, to model a desired contacting pattern or spatialarrangement of matter. To do so they predominantly offer information from proprietary integrated modelingsystems that combine computational fluid dynamics with thermokinetic modelling. Moreover, as a rule, suchdevelopment partners establish the overall application analytics to the point where the critical initial hypothesiscan be validated and further confined.

Example of a flow reactor system.

References[1] Recent advances in synthetic micro reaction technology Paul Watts and Charlotte

Wiles Chem. Commun., 2007, 443 - 467,[2] D.Roberge, L.Ducry, N.Bieler, P.Cretton, B.Zimmermann, Chem. Eng. Tech. 28

(2005) No. 3, online available (http:/ / www. lonza. com/ group/ en/ company/ news/publications_of_lonza. -ParSys-0002-ParSysdownloadlist-0001-DownloadFile. pdf/1_050510_Microreactor Technology A Revolution for the Fine Chemical andPharmaceutical Industries. pdf)

[3] T.Schwalbe, V.Autze, G.Wille: Chimica 2002, 56, p.636, see also MicroflowSynthesis (http:/ / www. mrsp. net/ MRSP_Chimica_Oggi. pdf)

[4] T.Schwalbe, V.Autze, M. Hohmann, W. Stirner: Org.Proc.Res.Dev 8 (2004) p.440ff, see also Continuous process research and implementation from laboratory tomanufacture (http:/ / www. mrsp. net/ MRSP_lo-res. pdf)

[5][5] and literature cited therein[6] Method of Preparing Organometallic Compounds Using Microchannel Devices, 2009, Francis Joseph Lipiecki, Stephen G. Maroldo,

Deodatta Vinayak Shenai-Khatkhate, and Robert A. Ware, US 20090023940 (http:/ / www. freepatentsonline. com/ y2009/ 0023940. html)[7] Purification Process Using Microchannel Devices, 2009, Francis Joseph Lipiecki, Stephen G. Maroldo, Deodatta Vinayak Shenai-Khatkhate,

and Robert A. Ware, US 20090020010 (http:/ / www. freepatentsonline. com/ y2009/ 0020010. html)[8] Knoevenagel condensation reaction in a membrane microreactor Sau Man Lai, Rosa Martin-Aranda and King Lun Yeung Chem. Commun.,

2003, 218 - 219,

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[9] Instantaneous Carbon-Carbon Bond Formation Using a Microchannel Reactor with a Catalytic Membrane Yasuhiro Uozumi, Yoichi M. A.Yamada, Tomohiko Beppu, Naoshi Fukuyama, Masaharu Ueno, and Takehiko Kitamori J. Am. Chem. Soc.; 2006; 128(50) pp 15994 - 15995;(Communication)

[10] Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in a microchannel reactorGuoqing Guan, Ralf Zapf, Gunther Kolb, Yong Men, Volker Hessel, Holger Loewe, Jianhui Ye and Rudolf Zentel Chem. Commun., 2007,260 - 262,

[11] A Microfluidic High-Resolution NMR Flow Probe Jacob Bart, Ard J. Kolkman, Anna Jo Oosthoek-de Vries, Kaspar Koch, Pieter J.Nieuwland, Hans (J. W. G.) Janssen, Jan (P. J. M.) van Bentum, Kirsten A. M. Ampt, Floris P. J. T. Rutjes, Sybren S. Wijmenga, Han (J. G.E.) Gardeniers and Arno P. M. KentgensJ. Am. Chem. Soc.; 2009; 131(14) pp 5014 - 5015;

[15] http:/ / www-lipht. u-strasbg. fr/ Interface/ index. php[16] http:/ / www. lgpc. fr/ Objets|LGPC

Article Sources and Contributors 7

Article Sources and ContributorsMicroreactor Source: http://en.wikipedia.org/w/index.php?oldid=547482866 Contributors: A Doon, Anna6, Calvero JP, Cubic Hour, Daniele Pugliesi, Dekisugi, Deli nk, Demericdebellefon,Dougher, DrTorstenHenning, Editore99, Flowsynthesis, Gaius Cornelius, Gene Nygaard, Gilligan mark, Goonybananas, Gurch, IX2007, Jim Douglas, Joolshoops, Junkers42, Kasparkoch, Khalidhassani, LGreiner, LilHelpa, M stone, Mark Arsten, Microreacteur, Mikeblas, Mindmatrix, MissMarpel, NHSavage, Patricksears, Penth, Peripitus, RSStockdale, Rifleman 82, Rjwilmsi, SimonP,Siroxo, Sixsnowflakes, Squids and Chips, Strongbow501, Twisp, V8rik, Wsv131, 113 anonymous edits

Image Sources, Licenses and ContributorsImage:LLNL-microreactor.jpg Source: http://en.wikipedia.org/w/index.php?title=File:LLNL-microreactor.jpg License: Public Domain Contributors: Lawrence Livermore NationalLaboratory (LLNL).Image:Syrris Chip.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Syrris_Chip.jpg License: Public Domain Contributors: Gilligan_mark (talk) (Uploads)Image:Knoevenagelmicroreactor.png Source: http://en.wikipedia.org/w/index.php?title=File:Knoevenagelmicroreactor.png License: Creative Commons Attribution-ShareAlike 3.0 UnportedContributors: Original uploader was V8rik at en.wikipediaImage:Suzukimicroreactorreaction.png Source: http://en.wikipedia.org/w/index.php?title=File:Suzukimicroreactorreaction.png License: GNU Free Documentation License Contributors:User:RonhjonesImage:PropaneCombustionInmicrochannelreactor.png Source: http://en.wikipedia.org/w/index.php?title=File:PropaneCombustionInmicrochannelreactor.png License: GNU FreeDocumentation License Contributors: -Image:Glass-microreactor-chip-micronit.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Glass-microreactor-chip-micronit.jpg License: Public Domain Contributors: MicronitFile:FlowStart CloseUp.jpg Source: http://en.wikipedia.org/w/index.php?title=File:FlowStart_CloseUp.jpg License: Creative Commons Attribution-Sharealike 3.0 Contributors: Kasparkoch

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MicroreactorHistoryBenefitsProblemsT reactorsApplicationsSynthesisAnalysisNMRInfrared Spectroscopy

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