Microreactors Make it Big: Can Micro- or
Milli-Reactors be Used in Multi-Ton Production Plants?
One of the current challenges facing the process industry is a
change in product portfolio away from commodities to customer-specific
specialties. The paradigm shift in process technology production from the batch
principle to the continuous flow process based on micro- and millireactors
offers great advantages in many cases and is now showing initial success on an
industrial scale. — My, how you've grown! Micro- and millireactors bring process
intensification in specialty chemistry and pharmacy
Flow chemistry or microreaction technology (MRT) is a technology platform that has the potential to offer tremendous
benefits in many process engineering applications. MRT is able to
replace discontinuous batch processes with a continuous process in which
reactions take place in structures of greatly reduced size. The main components
are mixers with excellent mixing speed and heat exchangers with high heat
transfer rates. Added to this is the associated support infrastructure, such as
sensors, valves, pumps or analytics.
With the help of microreaction technology, complex or challenging
reactions can be precisely controlled, which can, for example, help to increase
the safety of chemical production. In addition, plants can be built smaller,
realized with lower investment and operated more efficiently. A particular
advantage lies in the high specific surface to volume ratio of the
micromodules, resulting in excellent heat and mass transport properties.
Development of Micro-Reaction
Technology (MRT)
The beginning of the technology platform microreaction technology
goes back to about 1995, when Prof. Wolfgang Ehrfeld, at that time director of
the Institute of Microtechnology in Mainz, Germany, raised the question: If the
topic “micro” in microelectronics has led to such enormous increases in
performance and innovations, why should this not be possible in the area of
process technologies? He invited representatives of chemical, pharmaceutical
and automotive industries to an industrial consortium to explore the potential
of micro-process technology.
Trials showed that it was possible to achieve significantly higher yields for the raw materials when using mixers with
microchannels than with established technology for a selected example
reaction (the Andrussow reaction for hydrocyanic acid production in the gas
phase). From that day, Ehrfeld took over the baton as a pioneer for this
technology platform.
In 1997, the first IMRET, the International Conference on
Microreaction Technology, took place — marking the start of a new tradition.
In fact, 2017 saw the 14th IMRET in Beijing, PR China. With the first
conference, the Chemical Engineering and Technical Chemistry community started
a wave on process intensification with microreaction technology as an important
aspect. Many companies and research institutes recognized the enormous
opportunities and potentials offered by microreaction technology and the
associated process intensification. As a result, first test balloons of MRT
were used in various development laboratories and chemical and pharmaceutical
manufacturing plants.
Process Intensification and other
Benefits of MRT
Flow Chemistry creates a fundamentally new process environment.
Better process control and significant miniaturization of reactive volumes are
the key elements of MRT. The focus is on better mixing and superior temperature
control with barely measurable temperature gradients across the entire reaction
volume — conditions that are almost impossible to achieve in a classic
batch reactor.
Another advantage is that the reaction parameters can be better
adapted, resulting in higher purity, yields, and selectivity. The small reactor
volumes in the Flow Chemistry/MRT also allow the extension of physical process
conditions to higher or lower temperatures or pressures in a simultaneously
safe and fully controlled unit. The most important advantages of continuous
operation in micro- and millireactors are these:
·
ultrafast mixing
·
highly efficient heat transfer
·
short defined residence times
·
easy process control due to low system inertia
·
high operational reliability due to minimal hold-up
·
short development times
Particularly in the case of fast, highly exothermic reactions with
explosive or toxic substances, these properties of the continuous flow reactors
are advantageously noticeable. Because of the high security risk, these
processes either cannot be handled in batch reactors or often are difficult to
handle.
Application fields of
Micro-Reaction Technology
The establishment of the technology platform micro- and
millireactors is currently a not to be underestimated topic in the market
worldwide. Many reputable chemical and pharmaceutical companies are using this
technology in their companies, mostly in R&D, as a test balloon. Once the
first hurdle of the paradigm shift Batch-to-Conti has been taken, the second
hurdle is the full deployment of technology into production.
Unfortunately, current production facilities are missing or may
not be mentioned, which considerably increases the hurdle regarding the
decision of board. Attractive high-potential segments include, for example,
peroxides, sulfonation and ethoxylation, hydrogenation, lithiation, ozonolysis,
multistep syntheses in one process step, or the production of AI/APIs, to name
just a few. The potential is therefore broad and a screening of the internal
product portfolio could be advantageous.
From Lab to Production:
Process Intensification
Channel dimensions on a micrometer scale are not suitable for use
in production as they are too susceptible to blockages, do not meet the
robustness requirements of a production plant and only allow relatively small
throughputs. Scale-up to production therefore requires scale-up to the
millimeter scale, which preserves the advantages of microtechnology in terms of
heat transfer performance and mixing speed.
Ehrfeld Mikrotechnik has introduced an integrated scale-up concept
for this purpose. Here, the transition of channel geometries from the
micrometer to the millimeter scale takes place already in the laboratory, i.e.
on channel geometries that match those in the later production plant. The
turnover, yield, process parameters and product qualities determined in this
way can be directly transferred to the conditions in production reactor with
the same channel geometries.
Scale-up on a pilot scale is eliminated, although of course the
tests with real raw material qualities from the production to investigate
fouling, cleaning processes and service life can’t be resigned. The integrated
scale-up concept very quickly leads to the transfer of scale to production. The
next step is then carried out on the basis of tube bundle reactors/heat
exchangers by so-called numbering-up: The throughput is increased by connecting
channels in parallel to a channel bundle within the reactor.
How to Setup a Micro Reactor
In the Miprowa technology, the reactor is constructed analogously
to a tube bundle heat exchanger, wherein the round tubes are replaced by
rectangular channels. The surface to volume ratio, compared to standard 1 "
(25.4 mm diameter) tubes, is increased by a factor of more than six
through these rectangular channels, providing improved heat transfer. Static
mixing inserts in these channels ensure efficient mixing and intensified heat
transfer. Heat transfer coefficients in aqueous material systems of about 2,200 W/m²K can
be generated.
Successful feasibility studies with this technology resulted in
significantly higher yields and significantly better product qualities. The
same yields and qualities were obtained in a validation phase with a reactor on
a pilot scale as in the laboratory, with a slightly enlarged channel cross
section, which corresponded to the later production scale. In addition,
technical raw materials were used and long-term runs were carried out to
investigate the pollution and clogging behavior. Corrosion testing revealed
that in this case, a corrosion resistant Hastelloy material as the reactor
material achieved the required corrosion resistance.
Multi-Ton Millireactor
Shaoxing Eastlake High-Tech is an agrochemical producer founded in
1990 near Shanghai, PR China. The company not only serves the Chinese market,
but also exports its products to more than 20 countries, including the US and
EU. In 2002, the company was awarded for Zhejiang High-Tech Enterprise.
Shaoxing Eastlake High-Tech has been seeking new, promising technologies over
the past decade to replace more than 20 traditional batch reactors. Driven by
guidelines, environmental regulations and safety considerations, they evaluated
the flow chemistry/MRT market to implement a highly exothermic alkoxylation
reaction.
Among other things, Shaoxing Eastlake High-Tech threw an eye on
the Miprowa technology. The final decision for Ehrfeld then fell due to the
integrated scale-up concept in so-called interface modules. This concept
enables the scale-up from laboratory to production scale using the same channel
geometries in the laboratory as later in the production reactor. Another point
not to be neglected was the use of robust metallic materials such as stainless
steel and Hastelloy.
Micro Reactors:
Expectations Exceeded
The German-made 7.50 meter long and more than five tons of weight
production reactor was commissioned in China in just two weeks, with product
already meeting the specifications.
After six months of continuous operation, the reactor was opened
for control purposes. During the inspection of the reactor from the inside and
outside, no contamination or clogging could be detected. This shows that the
reactor runs under full conversion and ideal selectivity under absolutely low
by-product formation.
After inspection, the reactor was restarted and runs smoothly
until today. Shaoxing Eastlake is currently screening its product portfolio
for further promising reactions that can be converted into milli-reactors for
continuous process management, and in 2017 purchased two identical reactors to
further increase production capacity.
The MRT Success Story: Big
Future for Process Intensification
Because of this success story, the last hurdle on the way of
introducing flow chemistry/MRT in the market is eliminated with a reference
project on a production scale runs continuously and successfully with a
production capacity of several thousand tons of product per year.
This paves the way for the establishment of MRT as a valuable
process technology. Now it is up to the decision-makers of the chemical and
pharmaceutical industries to take on the baton and thereby break new ground in
process technologies.
05/23/2018 |
Author / Editor: Anne Kaaden, Dr.-Ing. Joachim Heck* / Dominik Stephan
PROCESS WORLDWIDE
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