Microreactors process monitoring

Loebbecke, C. S., Schweikert, W., Tuercke, T., Antes, J., Marioth, E., Krause, H., Applications of FTIR microscopy for process monitoring in silicon microreactors, in Proceedings of the VDE World Microtechnologies Congress, MICRO.tec 2000 (25-27 Sept. 2000),... 

Raman spectroscopy has been used to monitor a variety of industrial processes to improve product quality and process understanding [18,19]. The same features that make Raman spectroscopy a useftd technique for traditional process monitoring, such as the short analysis time and ease of optical sampling, mean that it can also be a useful tool for analyzing and understanding chemical reactions performed in continuous microreactors. 

Of course, there are many possibilities for integrating spectroscopic cells into a microreaction system. Because of the small cross-sections within the microfluidic devices, typically no bypass is necessary for such adaptation. Spectroscopic process monitoring can be either realized subsequent to the microreactor setup or direcfly within the microreactor. As an example. Figure 6.1 shows a pragmatic and flexible setup that allows spectroscopic in-line analysis of microreaction processes. This setup was designed for monitoring parameter screenings and allows adaptation of one or more of the above-mentioned spectroscopic methods. Miniaturized optical... 

Online monitoring of processes in microreactor systems has the potential to accelerate process development and continuous operation significantly. One of the main advantages of collecting information about the process, such as conversion, selectivity, side product formation, and so on, online is the option for subsequent automated operation. Since labor costs usually contribute a significant share to the overall total operational costs, automation provides a great opportunity for cost-efficient implementation of continuous-flow technologies. 

Krishnadasan et al. [108] reported the use of a microfluidic reactor to carry out the synthesis of CdSe nanocrystals along with an inline spectrometer to monitor the emission spectra. CdO and Se were pumped into the two inlets of a heated Y-shaped microfluidic reactor. The emission data are fed into a control algorithm that reduces each spectrum to a scalar dissatisfaction coeflEcient. The reaction conditions including CdO and Se reactant flow rates and temperature are adjusted in an effort to minimize this coefficient for an optimum processing condition. Toyota et al. [109] reported a combinatorial synthesis system for CdSe nanocrystals using parallel operation of microreactors combined with an online detector. A multifaceted assessment of reaction parameters was made to achieve optimum control over size, size distribution, yield, and photoluminescence of CdSe nanocrystals (Figure 7.21). 

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