Microreactors processing

Recently, microstructured reactors have stepped into chemical production [4] and thus microreactor process and plant design, including economic incentives, is the issue at this time. For this purpose, large-capacity microstructured apparatus is needed ( micro inside, fist- to shoebox size outside ) and plant concepts have to be proposed which include all process steps. 

Temperature profile of the phenyl boronic acid synthesis along the major steps of the process flow scheme. The difference in the temperatures of the conventional batch and the microreactor processes stand for the reduction in energy consumption and respective heat-transfer equipment when using the latter [10]... 

Investigation, analysis and optimization of exothermic nitrations in microreactor processes, in Matlosz, M., Ehrfeld, W., Baselt, j. P. (Eds.), Microreaction Technology - IMRET 5 Proc. of the 5th International Conference on Microreaction Technology, pp. 446 54, Springer-Verlag, Berlin (2001). 

Fig. 5. Earnings and total costs for a commercial microreactor process, for the real-life micro-flow case, three processes intensified or numbered-up microflow cases, and a batch benchmark case (Courtesy of Swiss Chemical Society)...

Using the high-p,T microreactor processing, the Kolbe-Schmitt synthesis was completed within less than 1 min at comparable yields, i.e., a reaction time reduced by a factor of approximately 2,000 was achieved (see Fig. 6). This corresponds to an increase in space-time yield by a factor of 440. 

The increased interfacial area in the microreactor led to an increased pressure drop. The energy dissipation factor, the power unit per reactor volume, of the microreactor process was thus higher (sv = 2-5 kW/m3) than that of the laboratory trickle-bed reactors (sv = 0.01-0.2 kW/m3) [277]. This is, however, outperformed by the still larger gain in mass transfer so that the net performance of the microreactor is better. 

P-Amino adds were chosen for demonstrating feasibility of microreactor processing, as there are no chiral centers that may complicate the analysis of the products [6], Peptides are typically synthesized by solid-phase chemistry on polymer beads, a route discovered by and named after Merrifield [7,8]. These polymer supports are expensive. Additional steps for linkage to and deavage from the polymer are required. Hence, the motivation is to test solution chemistries as an alternative to the Merrifield approach. 

Electroosmotic-driven microreactor processing gave quantitative yield of the dipeptide in only 20 min, whereas batch synthesis under the same conditions gave only 57% yield needing 24h [6,9]. 

In comparison to the conventional automated synthesis, the radiochemical yield and purity of the compound obtained by microreactor processing was higher and also had shorter synthesis time [21]. Multiple doses of2-deoxy-2-[18F]fluoro-D-glucose for positron emission tomography imaging studies in mice were prepared. Today, 2-deoxy-2-[18F]fluoro-D-glucose is routinely produced in about 50 min with the use of... 

With the use of microreactor processing, 70% conversion was achieved that gave only product and no side product [4]. Actually, the micro reactor conversion is lower than the conversion for batch, but the former is now the preferred route as the separation of the product from the reactant can be accomplished, whereas product, as mentioned, can be hardly purified from the side product. A throughput of 300 g/h was achieved. 

Table5.2 Impurityand optical purityofthe batch and microreactor processes in the (S)-2-acetyl tetrahydrofuran synthesis [29].

As a result of microreactor processing, the reaction temperature could be increased up to —20 °C at a residence time of only 15 s [50]. The reduction was done at 10-25 °C within several minutes. The quality of the product and the throughput were comparable to that derived from the minibatch processing. A throughput of about 100-200 g/day was achieved. 

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