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Tools

We use different experimental and mathematical methods to support the design of continuous microreaction processes and their corresponding microfluidic components.

Process Analysis

To diagnose and track microreaction processes, rapid spectroscopic and calorimetric analysis techniques as well as process sensors are being developed and adapted to the reaction process. With a high degree of temporal and spatial resolution we can analyse products and by-products and can obtain kinetic, mechanistic and safety-related data. More information can be found here. 

Design and Qualification of Microstructured Reactors

One important element in the development of microreactor processes is the design of tailored microfluidic components. Both mathematical methods and numerical simulation tools (e. g. Computational Fluid Dynamics, CFD) as well as standardised experimental measurement methods are applied. These generate quantitative and qualitative data concerning important performance characteristics, for example the mixing efficiency and residence time behaviour of microstructured reactors.

To characterise the residence time behaviour of microfluidic components, we have developed special spectroscopic measurement techniques based on tracer tracking and the corresponding mathematical modelling tools, which demonstrate the relationship between the fluid channel design and the residence time characteristics.

For further information, see:
D. Bošković, S. Löbbecke, Modelling of the residence time distribution in micromixers, Chem. Eng. J. 2008, S135, 138-146.

Experimental setup for measuring the residence time characterstics of micromixers and microreactors.

 

Exemplary measurement of the residence time distribution at different positions within a passive mixing microreactor.

To describe the mixing performance of micromixers and microreactors qualitatively and quantitatively we use experimental methods that we have developed for liquid and liquid/liquid fluid systems. The methods are based on the spectroscopic analysis of mixing sensitive reactions (modified Villermaux/Dushman reaction) and the spectroscopic analysis of the extraction of solvatochromic dyes in a two phase system.

For further information,see:
S. Panić, S. Löbbecke, T. Türcke, J. Antes, D. Bošković, Experimental Approaches to a Better Understanding of Mixing Performance of Microfluidic Devices, Chem. Eng. J. 2004, 101, 409

 

Experimental methods to characterise the mixing performance of microreactors for liquid and liquid/liquid fluid systems.

With CFD, we can make statements about the process either in advance or during the development of the process using approximative calculations of the flow conditions as well as of the heat and mass transfer and hence other aspects linked to these factors such as mixing efficiency, residence time and pressure drop. Simulations provide information on process conditions not just for selective points but with virtually unlimited scope in terms of time and space. Moreover, modern CFD tools provide extensive options for visualisation of the calculated process conditions.

In order to take account of the special effects that occur in the micro-range, such as boundary layer phenomena and the high surface-to-volume ratio, we must select CFD tools with appropriate calculation models and include the corresponding microeffects in our considerations, if necessary by modifying or supplementing the programs (e. g. with user-defined subroutines).

 

Visualisation of the fluid dynamics in threedimensional microchannel structures using CFD (sample simulation)

 

Surface Modification and Catalysis

The high surface-to-volume ratio of micro-structured reactors is usually discussed in the context of more intensified heat transfer and used to exploit corresponding advantages. However, the relatively large surface area in microreactors can also be used to exploit other interactions with the reaction media.

At the Fraunhofer ICT, we are pursuing two central applications in this area. Firstly, we use targeted chemical modifications to influence the surface properties of the microchannels. For example, we can modify the inner surfaces of our glass reactors in a targeted manner with hydrophilic, hydrophobic or superhydrophobic properties and therefore alter the wetting and flow behaviour in the microreactor depending on the type of substances involved.

Secondly, we use the large interior surface area of our microreactors to covalently attach organic catalysts. In this way, we link the advantages of catalyst immobilisation with those of continuous microreaction technology, especially in regard to more intensified mass and heat transfer. Significant improvements in catalyst performance and space-time yield have already been achieved for catalytic liquid phase processes - compared to the macroscopic reference processes.

Recent publication:
L. Soldi, W. Ferstl, S. Löbbecke, R. Maggi, C. Malmassari, G. Sartori, S. Yada, Use of immobilized organic base catalysts for continuous-flow fine chemical synthesis, Journal of Catalysis 2008, 258, 289-295

 

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Chemical modification of glass surfaces: from hydrophilic to superhydrophobic  

Covalent attachment of organic catalysts to glass substrates

 

         
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