Micromixer interdigital

A microreactor was also applied to this reaction. The slit interdigital micromixer was purchased from IMM (Mainz, Germany). The width of the interdigital channels is 25 pm. HPLC pumps were used to feed the two reaction solutions. One is a mixture of Boc-AMP and 1.2 molar equivalents of r-BocaO. The other is a 50% aqueous KOH solution. The microreactor was immersed in a temperature controlled cooling bath at 15 °C. The product was quenched with an acid, and samples were taken for HPLC analysis. 

Hessel, V., Hardt, S Lowe, H., ScHONEELD, F., Laminar mixing in different interdigital micromixers - Part I Experimental characterization, AIChE... 

Drese, K., Optimization of interdigital micromixers via analytical modeling -exemplified with the SuperFocus mixer, Chem. Eng.J. 2004, 101, 403 107. 

Lob, P., Drese, K. S., Hessel, V., Hardt, S., Hofmann, C., Lowe, H., Schenk, R., Schonfeld, F., Werner, B., Steering of liquid mixing speed in interdigital micromixers - from very fast to deliberately slow mixing, Chem. Eng. Technol. 2003,... 

Figure 4.42 High-pressure interdigital micromixer made of steel (by courtesy of IMM).

All other devices showed only the increasing part of such dependency that is, the highest performance was obtained at the longest residence time [318]. The best conversions of interdigital micromixers and caterpillar minimixers of 78 and 70%, respectively, still exceed notably the performance of a conventional mixing tee (1 mm inner diameter). 

A slit-type interdigital micromixer was used for fast mixing [30] and compared to a tubular reactor and five Kenics mixers connected in series. Details on further components of the micromixer rig were not given, but most likely a capillary reactor was added for efficient heat exchange. 

In a microscale tubular reactor, Swern oxidations were performed between —20 and 20 °C. Mixing was performed stagewise with a series of rapid mixing functions (see Figure 5.22) [57,58]. First, dimethyl sulfoxide and trifluoroacetic anhydride were contacted in an interdigital micromixer followed by a stainless steel tube reactor Rl. After addition of the alcohol and reaction in reactor R2, the mixture was then contacted with a triethylamine solution and passed through two more reactors (R3 and R4) to complete the reaction. 

As industrial relevant Friedel-Crafts reaction, the synthesis of Bisphenol-F, a material for epoxy resin, from phenol and formaldehyde was chosen [57]. This reaction involves formation of higher order condensates such as tris-phenols. To minimize the latter, the molar ratio of phenol to formaldehyde is set to a very high value (30-40), which is more than 15 times larger than the amount theoretically necessary. Three types of micromixers were used. These are a T-shaped mixer with 500 pm inner diameter, a multilaminating interdigital micromixer with 40 pm channels and a so-called self-made K-M micromixer with center collision mixing. 

Table 7.4 Comparison of mixing performance of three interdigital micromixers (8 L/h)...

Numerical simulations of styrene free-radical polymerization in micro-flow systems have been reported. The simulations were carried out for three model devices, namely, an interdigital multilamination micromixer, a Superfocus interdigital micromixer, and a simple T-junction. The simulation method used allows the simultaneous solving of partial differential equations resulting from the hydrodynamics, and thermal and mass transfer (convection, diffusion and chemical reaction). 

Yoshida et al. [36] have studied the effect of fast mixing of miscible systems by measuring the selectivity towards mono-alkylation in the Friedel-Crafts alkylation of aromatics. They observed a 20-fold increase in the relative selectivity of the mono-alkylate over the di-alkylated system when using a micromixer instead of a conventional batch reactor. In the cycloaddition of the N-acyHminium ion to styrene [36], 50-80% of the cycloadduct is typically lost towards polymeric byproducts. Using an interdigital micromixer, the yield to the cycloadduct increased from 20-50% to almost 80%. 

Fig. 6.18 Flow sheet of the laboratory-scale microreactor configuration of the phenyl boronic acid microreactor process, equipped with an interdigital micromixer. (Courtesy of the American Chemical Society [30].)...

Micromixer-tube reactor plants have been employed both at laboratory and pilot-scale [30]. For initial process development, a triangular ( focusing ) interdigital micromixer was used (Fig. 6.18), while for the pilot scale-out a caterpillar mixer was connected to four tubes of different hydraulic diameter by a five-port valve. 

Process development was carried out at laboratory scale using a slit-type interdigital micromixer-reactor [31]. The whole flow guidance was provided by the micromixer and the outcoming solution was collected in a vessel. 

A slit-type interdigital micromixer has been used [34]. Details on the type of plant as well as on the processing were not given. 

The reactants were contacted in a high-pressure interdigital micromixer followed by a capillary reactor, all immersed in an oil bath [45,46]. Pure bromine and pure aromatic were fed, mixed and reacted. By a high-temperature, high-pressure (high-p,T) route, the side-chain bromination of meta-nitrotoluene was achieved. This allows one to extend the operational range much beyond the boiling point, which is the technical limit of many reactions carried out batchwise. 

A numerical study of the free-radical polymerization of styrene (Scheme 6.15) compared the behavior of an interdigital micromixer with a T-junction and a straight tube [37, 48], The diffusion coefficient of the reactive species was varied to simulate the viscosity increase during a polymerization. The performance of the polymerization turned out to be largely dependent on the radial Peclet number. This dimensionless number is defined as the ratio of the characteristic time of diffusion in the direction perpendicular to the main flow to the characteristic time of convection in the flow direction (i.e., the mean residence time) and, therefore, is directly proportional to the characteristic length of the reactor. 

Table 6.4 Performance data for the free-radical polymerization of styrene at two monomer concentrations. The behavior of three reactors is compared - flask, T-junction (Tj), and high-pressure interdigital micromixer (HPIMM) by experiment and by modeling [49].

Hardt S, Schonfeld F (2003) Laminar mixing in different interdigital micromixers II. Numerical simulations. AIChE J 49(3) 578-584... 

Hardt, S., Schdnfeld, F. Laminar mixing in interdigital micromixers with different mixing chambers - Part 2 Numerical simulations, AIChE Journal 49, (2003) 578-584. 

V. (2004) g/l-Dispersion in interdigital micromixers with different mixing chamber geometries. Chem. Eng. /, 101 (1-3), 75-85. 

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