Microreactors optimal operation

To develop an EOF based system. Watts et al. have conducted an extensive study on peptide synthesis, where they prepared a library of peptide derivatives within a computer-controlled microreactor system operating under EOF [25-28]. The authors demonstrated that dipeptides could be prepared from pre-activated carboxylic acids. They optimized the reaction using the pentafluorophenyl (PFP) ester of Fmoc- 3-alanine 4 with amine 5 to give dipeptide 6 quantitatively in 20 min (Scheme 14.2). This represented a significant increase in yield compared with the traditional batch synthesis, where only a 50% yield was obtained in 24 h. 

Another important point is the integration of sensors into the microreactor. A full integration is often not economical. This section explains new ways for an appropriate technology. For optimal operation of microreactors, we need to measure... 

Adler, P. M., Optimal design and operation of a separating microreactor,... 

The same features were found for pilot-size microreactor operation (see Figure 5.30). Brightness and transparency were the same, and the color strength could even be increased to 149% [65]. The mean particle size was even smaller than the lab-scale microreactor processing (microreactor D5o = 90nm, s=1.5 batch D5o = 600nm, s = 2.0), probably because of process optimization. 

In less than one minute, half of the 2,4-dihydroxybenzoic acid is decomposed already at 160 °C in the microreactor setup [39, 40]. This demonstrates the need to find optimal process parameters for temperature and residence time to achieve efficient high-p,T operation, which is achieved by detailed parameter variation (e.g., as statistical analysis. Design of Experiments, DoE). In this way, the best operation point was foimd (200 °C 40 bar 2000 mL h 16 s). There is also the question of substrate selectivity, e.g., the isomeric product 2,6-dihydroxybenzoic acid exhibits lower decarboxylation rates. 

As approaches to high-throughput experimentation, process intensification and process optimization continue to develop and show value to the researcher, then the engineer or the analytical chemist will be under increased pressure to use microanalysis tools. This will be to evaluate the operations of the microreactors (such as diagnostics of the microchaimels and composition of the reactor). The results of these applications will be seen in distributed manufacturing approaches and number-up versus scale-up of processes. These successes in engineering will also increase the demand for the effective use of microanalytical instrumentation. 

A microreactor that contains a number of different catalysts fixed in different compartments connected via a microfluidic network or reactor modules connected by microtubing may well be the optimal chemical production unit. Each compartment may operate simultaneously, which leads to efficient use of the microreactor. Different combinations of steps in cascade reactions may give a whole range of products (Fletcher et al., 2002 Song et al., 2003). 

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