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Process Analysis in Microreactors

Many chemical processes offer significant scope for improvement through detailed analysis of the physical-chemical processes on which they are based. The data gained through this analysis can be used to target and optimise specific reaction steps, achieve consistent product quality and finally reduce process costs. However, technical, safety or economic factors often make it difficult or even impossible to install and operate process analysis directly on-site for industrial applications. This is where microreaction technology can help out by investigating technical processes on a microscale and following their progress using adapted process analysis with a high degree of temporal and spatial resolution.

For this reason, we use process analysis in the form of Infrared, Raman and UV/Vis/NIR spectroscopy already in the very early stages of the design and optimisation of chemical processes. Depending on the specific problem, this is adapted to the process as inline, online or at-line measurement technology. Moreover, the very latest imaging techniques allow us to monitor chemical processes in a microchannel in real-time with high spatial resolution using spectroscopy. With the help of fibre optics, we can also apply spectroscopy in a microreactor at
up to 16 discrete positions simultaneously. For visual monitoring of processes in microchannels high-speed microscopy is applied.

We make our processes transparent using the process analysis techniques we have developed. These give us a direct insight into the processes as they are taking place so that we can collect both information about the product composition and kinetic and mechanistic data, which is extremely valuable when designing process components and selecting suitable process conditions. In combination with screening procedures, statistically planned experiments and chemometric analysis it is possible to identify suitable process windows and optimum process
conditions with a high degree of efficiency.

Ankopplung von IR-, Raman- und UV/Vis/NIR-Spektroskopie an Mikroreaktorprozesse.

 

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Process analysis with a high degree of temporal and spatial resolution in microreactors using fibre optics (here: Pushbroom Imaging technique).

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Reaction Calorimetry in Microreactors

Another method of process analysis we have developed is the “concal” calorimetric measuring system. This is one of the smallest and most efficient reaction calorimeters ever developed for continuous operation. It permits calorimetric observation of chemical processes in microreactors – and this almost in real-time.

At the heart of the “concal” system are sensor arrays based on miniaturised Seebeck elements for the localised, quantitative characterisation of heat flows. The sensor arrays consist of up to 40 individual sensors, which can collect data concerning the reaction heat generated in a microreactor with a correspondingly high degree of temporal and spatial resolution. This measurement data can be used to obtain thermokinetic information about the observed chemical reaction.

In addition, “concal” can be used to determine reaction enthalpies and other key safety data for chemical reactions depending on the selected process conditions. As the reactor volume is very small, even targeted investigations of critical process conditions (worst case scenarios) can be safely carried out, which would be difficult or even impossible using conventional calorimetry.

As well as being used for analysis of strongly exothermic reactions, the highly sensitive sensors also permit calorimetric observation of continuous processes with low reaction heat as well as endothermic processes. In addition, the modular design of “concal” makes it possible to adapt the miniaturised Seebeck sensor arrays to different reactor types (liquid, liquid/liquid or gas/liquid reactors) and reactor sizes. With fast calibration and user-friendly measurement software, “concal” is particularly suitable for the calorimetric screening of reaction and process conditions.

A detailed description of our calorimetric measuring system “concal” is avialable here.

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Measuring system “concal”: calorimetric process monitoring in microreactors on basis of of Seebeck sensor arrays.

Selected publications in the area of process analysis and reaction calorimetry:

S. Löbbecke, J. Antes, D. Boskovic, H. Krause, N. Lutz, T. Türcke, W. Schweikert, Analysis and Improvement of Strong Exothermic Nitrations in Microreactors, Trans IChemE 81 (2003), Part A, 760

J. Antes, D. Schifferdecker, S. Loebbecke, H. Krause, A Microstructured Reaction-Calorimeter for the Measurement of Strong Exothermic Reactions, 9th Int. Conference on Microreaction Technology IMRET 9, 06. – 09.09.2006, Potsdam, Germany

W. Ferstl, T. Klahn, W. Schweikert, G. Billeb, M. Schwarzer, S. Löbbecke, Inline Analysis in Microreaction Technology: A Suitable Tool for Process Screening and Optimization, Chem. Eng. Technol. 2007, 30, 370

S. Löbbecke, Integration of Sensors and Process-analytical Techniques, in: N. Kockmann (Ed.), Micro Process Engineering: Fundamentals, Devices, Fabrication and Applications, Wiley-VCH Weinheim 2006, 249

J. Antes, M. Gegenheimer, S. Löbbecke, H. Krause, Reaction Calorimetry in Microreactors: Fast Reaction Screening and Process Design, 12th Int. Conference on Miniaturized Systems for Chemistry and Life Sciences µTAS 2008, 12.-16. Oktober 2008, San Diego, USA

 

Process Sensors for Microreaction Processes

In addition to spectroscopic and calorimetric monitoring of chemical processes in microreactors Fraunhofer ICT integrates also inline process sensors into their microfluidic components to track temperature and pressure at different positions simultaneously with high spatial resolution.

For pressure monitoring, a new generation of miniaturised and robust pressure sensors is used, that have been developed in cooperation with the Wroc³aw University of Technology (Poland) at the Faculty of Microsystem Electronics and Photonics (head of group: Prof. Jan Dziuban).
The microfabricated pressure sensors are based on glass/silicon substrates and can thus be employed even under harsh and strong corrosive conditions in direct contact with the reactants (pressure range up to 7.5 bars).

Up to five pressure sensors can be connected to a single microreactor via screw fittings and can be read out simultaneously by fast electronic measuring equipment.
By tracking the pressure along the microreactor channels the user obtains a variety of crucial process data:

  • data on varying process pressure caused by chemical reactions (e.g. changes in viscosity during polymerisation, gas evolution etc.)
  • fluiddynamic data (e.g flow distribution, pulsation etc.)
  • safety-related data (e.g. blockages and fouling, leackages etc.).

 

Selected publications:

P. Knapkiewicz, R. Walczak, J. Dziuban, The method of integration of silicon micromachined sensors and actuators to microreactor made of Foturan glass, Optica Applicata 2007, 37, 65-72

P. Knapkiewicz, J. Dziuban, D. Boškoviæ, S. Löbbecke, System for multipoint pressure and temperature measuring in a microreactor used for nitration process, Proceed. XXII Eurosensors, 7.-10. September 2008, Dresden, Germany


Photo (left) and schematic setup (right) of miniaturised pressure sensors (developed at: Wroc³aw University of Technology).

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Left: Pressure sensors connected to microreactor and electronic measuring equipment.
Right: Screenshot of pressure monitoring software (here: visualisation of pump pulsation).

 

         
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