Microstructured devices

The application of zeolite membranes in microreactors is still in an early stage of development, and suffers sometimes from unexpected problems arising from template removal [70]. However, several application examples of zeolite membranes in microstructured devices have been demonstrated yielding similar advantages as were to be expected from experiences on the macroscale. Because of the high surface to volume ratio of microreactors, the application of zeolite membranes in these systems has great potential. 

Schubert, K., Brandner, J., Fichtnee, M., Linder, G., Schygulla, U., Wenka, A., Microstructure devices for applications in thermal and chemical process engineering, Microscale Therm. Eng. 5... 

ScHUBEET, K., Beandnee, j.. New designs for microstructured devices for thermal and chemical process engineering, in Proceedings of the Micro Chemical Plant - International Workshop, pp. L7 (42-53) (4 Eebruary 2003), Kyoto, )apan. 

J., ScHWESiNGEE, N., A microstructured device for the production of emulsions on demand, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, pp. 159-167 (11-14 March 2002),... 

Several examples of oxidation reactions, both in the liquid and in the gas phase, have been investigated in microreactors. Often the use of the microstructured device allows a better selectivity to the product of partial oxidation, because of a better temperature control on the catalyst surface (see, for instance, several examples in reviews [61a,b]). Indeed, several gas-phase oxidations can be completed in milliseconds, at significantly high temperatures. 

SECM can also be used as a read-out tool for protein and DNA chips. While any scanning technique is perhaps too slow for a routine application, SECM is ideally suited for testing concepts in prototype applications which are later transferred to microstructured devices without moving parts. 

Schubert K et al. Microstructure devices for application in thermal and chemical process engineering. Microscale Thermophys Eng 2001 5 17-39. 

Figure 1.4 Micro mixers (laboratory scale) and micro structured mixers (pilot scale) close the gap with static mixers, yielding apparatus for a multi-scale concept. Today s microstructured devices achieve mixing at up to about 1 m3 fT1 liquid throughput [2, 64] (by courtesy of RSC and Chemical Engineering).

First, the mixing principle is explained in a generic fashion. Then, a device section follows, describing all the different versions of microstructured devices actually realized. Details on the way in which the generic principle is applied are given as well as details on microfabrication and design specifications. 

In a vertically multi-laminating variant of the interdigital principle, the two arrays of the multiple sub-streams, belonging to two fluids, are overlaid in such a way that the above-mentioned alternate arrangement results (see Figure 1.75) [34, 67]. This usually requires the reservoirs to be placed in two different layers of the microstructured device. The sub-stream channels typically start in the two different layers and merge in a common layer. 

Takeda, T., Kunitomi, K., Horie, T., Iwata, K., Feasibility study on the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high temperature gas-cooled reactor, Nucl. Eng. Des. 1997, 168,11-21. Bier W., Keller W., Linder G., Seidel, D., Schubert, K., Martin, H., Gas-to-gas heat transfer in micro heat exchangers, Chem. Eng. Process. 1993, 32, 33-43. Schubert, K., Brandner J., Fichtner M., Linder G., Schygulla, U., Wenka, A., Microstructure devices for applications in thermal and chemical process engineering, Microscale Therm. Eng. 2001, 5,17-39. www.fzk.de, Forschungszentrum Karlsruhe, 17 July 2004. 

The economic benefit is one of the dominant problems if a micro structured reactor plant is used for chemical production. Without any doubt, an overall flow rate through a micro structured device can be achieved that is comparable to that with a conventional batch process. However, the residence time is very short because of the dimensions of a microstructured device. If the reaction kinetics are slow, an additional device is necessary to increase a dwell time. Hence, much effort should be devoted to increasing the reaction rate instead of transferring the standard protocol to a micro structured reactor [13]. 

Modularity is only needed where micro reaction technology is really demanded i.e. for micro fluidic modules. The motto of the developers is thus in analogy with the credo of the authors of this book, not to make microstructured devices as small as possible as many tools as necessary, not as many as possible . 

Keywords Fluid handling, microfiltration, complexity reduction, microstructured device,... 

The isolation of polynucleotides in microstructured devices provides a promising new approach that may be compatible with total integration of subsequent analytical steps and its current status is examined in the following sections. 

Cheng J, Kricka LJ, Sheldon EL, Wilding P (1998) Sample Preparation in Microstructured Devices. 194 215 - 231... 

Cheng, J., Kricka, L.J., Sheldon, E.L., Wilding, P., Sample preparation in microstructure device. In Microsystem Technology in Chemistry and Life Science. Springer-Verlag, Heidelberg, 1998, 215-232. 

The reaction of organolithium compounds with carbon-based electrophiles represents one of the most useful synthetic methodologies for the formation of C-C bonds as such, several groups have investigated these reactions in microstructured devices. 

Figure 1.5 Rhodium honeycomb catalyst microstructure device. The microchannels have been manufactured by wire erosion.

Almost all technologies described so far are suitable for prototyping or for small series production only. It simply takes a lot of time and is therefore costly to manufacture a large number of microstructures by laser ablation or wire erosion and by milling or SLM. This is not so in the case of the etching techniques. Here, a large number of microstructure devices can be very easily generated. 

Ceramic foams can be inserted into microstructure devices made from metals and polymers to enhance the surface area, act as catalyst supports or even work as heaters. Details of these processes can be found in Refs [29-42]. 

---