Wednesday, June 6, 2018

TECH SPECIAL..... Microreactors Make it Big: Can Micro- or Milli-Reactors be Used in Multi-Ton Production Plants?


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 placemarking 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 volumeconditions 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" (25.4mm 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 2,200W/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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