2. ABSTRACT
In recent times chemical compounds need greater speed in the
discovery process, which requires advanced automation. But
majority of the current reactions are still performed by applying
conventional techniques and apparatus.
This has led to severe impact on the scale-up process. With recent
advances in chemical reaction technology, sub-millimetre /sub-
millilitre sized micro structured reactors, mixers and other micro
process components have been developed.
One of these technologies leading to miniaturization of reaction
systems is the ‘Micro reaction technology (MRT)’ and these reactors
are named as ‘Micro reactors.’
Micro reactors gained more importance in the field of chemistry,
molecular biology and pharmaceutical chemistry etc by producing
products in larger volumes. In this context, the present article will
explain various concepts involved in the design
3. HISTORY
Gas-phase microreactors have a long history but those involving liquids
started to appear in the late 1990s. One of the first microreactors with
embedded high performance heat exchangerswere made in the early
1990s by the Central Experimentation Department (Hauptabteilung
Versuchstechnik, HVT) of Forschungszentrum Karlsruhein Germany,
using mechanical micromachining techniques that were a spinoff from
the manufacture of separation nozzles 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 dangerous chemical
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 couplings in a pyrex reactor with channel dimensions 90
micrometres deep and 190 micrometres wide.
4. INTRODUCTION
MRT is a concept, which can increase performance of reactions in a
continuous manner, within well-defined reaction channels, where
typical dimensions are of the order <1000 μm and volumes. MRT which
is growing in its usage is not a new concept, but has been suggested in
the early eighties.
Main features of MRT are that the reaction conditions can be
transferred from laboratory-scale reactors to production sites without
the need for reoptimization of various conditions. MRT has certain
advantages.
Optimal mixing
Effective heat exchange
Small reaction volume
Faster product development
Reduced exposure to hazardous chemicals
5. WHAT ARE MICROREACTORS?
When most people think of reactors, they think of the large
vessels used in chemical and refinery plants. These industrial
reactors are well known for their large size. However, chemical
engineers are finding that a new, smaller type of reactor can be
useful in areas the traditional reactors cannot. These reactors are
called microreactors.
Microreactors are constructed from a network of miniaturized
reaction channels. Unlike the large traditional reactors,
microreactors house chemical reactions to the scale of 5 – 100
ml, and are only a few centimeters in size.
6. WHY ARE MICROREACTORS USEFUL?
Even though microreactors are small, units can tolerate
temperatures and pressures as high as 650° C and 25 bars. This
allows microreactors to carry out, on a small scale, reactions that
are too exothermic or explosive to run at large scale.
Likewise, certain hazardous material can be safely handled in
only very small quantities and cannot be used in large-scale
processes. A microreactor would be an ideal reaction vessel for
this case.
In addition, microreactors require minimal amounts of reagents
and sample to perform tests, since the overall volume in the
reactor is low. The small volumes can also result in getting test
results faster. These advantages, among others, explain why
many different research groups are using microreactors to
miniaturize medical diagnostic assays.
7. Efficient Heat Transfer
Micro reactors with their small surface to volume
ratios are able to absorb heat created from a reaction
much more efficiently than any batch reactor.
In a micro reactor, the heat created by mixing the two
reagents is also detectable. The small inner volume of a
micro reactor (typically less than a millilitre)
combined with its strong heat exchange efficiency
guarantees the safe and stable performance of highly
exothermic reactions over hours.
Even explosive reactants and intermediates can be
handled safely in a micro reactor.
8. Efficient Mixing
Mixing quality is crucial for many reactions where the
molar ratio between reactants needs to be controlled
precisely in order to suppress side reactions.
A sophisticated regime will mix reactants efficiently with a
small path length of a few centimeters.
MRT is currently one of the most innovative techniques in
the field of chemical synthesis and similar fields.
It opens up new ways to develop novel relation process and
to construct advanced economic chemical plants. It is an
innovative alternative to large-scale production in the
chemical industry.
9. Advantages of MRT
Process safety
Novel reaction conditions
Reduced waste conditions
• An improved surface to volume ratio ensures better
temperature control.
• Very efficient mixing inside the reaction cell prevents
concentration gradient.
• The small reaction volume in combination with
efficient heat absorption provides excellent plant
safety.
11. Micro reactors
• Micro reactors offer a much improved control of reaction parameters,
such as temperature and relative concentrations and allow higher
yields, smaller amounts of by-products.
Micro reactors can be fabricated with materials like
Quartz
Diamond
Polymethylmethacrylate
Polydimethylsiloxane
Polyimide
Silicon
Stailness steel
Nickel
Glass is an excellent material for components in micro reaction
technology because of its unique properties and advantages.
12. Industrial Applications
Advantages
Technical advantages
Ecological advantages
Economic advantages
Technical advantages
Good control of chemical reactions
Efficient heat exchange
They can withstand to high pressure and hazardous chemicals
13. Industrial Applications
Ecological advantages
Safe production of chemicals
Safe production of pharmaceutical products
Preservation of resources during production
Reduction of waste disposal
Economic advantages
Numbering up of reactors instead of scale up
Integration of various production steps
Integration of various production steps
14. Disadvantages
• Cost issues
Challenges in numbering up
Clogged tubes
Mechanical pumping may generate a pulsating flow which can
be disadvantageous. Much work has been devoted to
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 when scaling 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 µm may go unnoticed
in conventional vessels. As typical inner dimensions of channels
are in the same order of magnitude, characteristics may be
altered significantly.
16. Production capability and cost
Comparison
The suitability of micro reactors for production was a
priori questioned on three dimensions. It was believed
that particle formation during micro reactors. The
scalability of throughput to meaningful quantities was
doubted. So was ,finally in the absence of concepts on
a basic engineering level, their comparative
economics.
18. Conclusion
Chemical synthesis in micro reactors has
demonstrated broad applicability to the wide universe
of chemical reactions. In many cases better yields and
higher selectivity's are predictability accomplished. As
the technology was proven fit for production and
technologies for the learning of chemistries have been
aggregated, we now expect to see its rapid application
in the synthesis of new chemical entities in high value
added market segments.
19. References
Dr axel kleemann, CPC – cellular process chemistry gmbh,
microreaction technology, available from-
http://www.Iptonline.Com/articles/public/iptnine72noprint
http://www.Sigmaaldrich.Com/etc/medialib/docs/aldrich/bulle
tin/1/al_chemfiles_v9n4.Par.0001.File.Tmp/al_chemfiles_v9n4
S R buddoo, N siyakatshana, and B pongoma, microreactors – A
marvel of modern manufacturing technology: biodiesel case
study, available from
http://researchspace.Csir.Co.Za/dspace/bitstream/10204/2680/1/
buddoo_p_2008
T. Schwalbe, V. Autze, and G. Wille, "Chemical Synthesis in
Microreactors," Chimia 56 (11), 636–649 (2002).