Micromixer, multilamination-type

When a T-shaped mixer is used, the product selectivity is essentially the same as for the macrobatch reactor (Scheme 6.4). The use of the YM-1 mixer, a splitting-and-recombination-type micromixer (see Chapter 7), increases the selectivity, however, a significant amount of dialkylation product is still produced. The use of the IMM multilamination-type micromixer results in excellent selectivity of the monoalkylation product. The amount of dialkylation product is very small. Therefore, the product selectivity strongly depends on the manner of mixing. 

Therefore, the observed selectivity is the disguised chemical selectivity caused by an extremely fast reaction. The reaction using a microflow system, however, gives rise to a dramatic increase in the product selectivity. The monoalkylation product was obtained in excellent selectivity and the amount of dialkylation product was very small. In this case, a solution of the N-acyliminium ion and that of trimethoxy-benzene are introduced to a multilamination-type micromixer at —78°C and the product solution leaving the device was immediately quenched with triethylamine in order to avoid the consecutive reactions. Extremely fast 1 1 mixing using the micromixer and efficient heat transfer in the microflow system seem to be responsible for the dramatic increase in the product selectivity. 

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. 

In the case of Y- or T-shaped micromixers, a decrease in the channel width to shorten mixing time leads to a decrease of production volume per unit time. To solve this problem interdigital multilamination micromixers have been developed. In this type of micromixer, two fluids are separated into many small narrow streams, which are arranged to contact each other alternately. The mixing takes place at interfaces of such sub-streams by molecular diffusion. The IMM (Institute of Microtechnik Mainz) single... 

Figure 4.18 Different types of multilamination micromixers, (a) liquid flows lO-IOOOmI h", (b) 138 microchannels flow 3501 h" at 3.5 bar, (c) 20 ml h", and (d)...

Sprogies et al. compared micromixers for use in extractions based on emulsions [32]. They revealed that a multilamination mixer is more efficient than a simple T-junction, whereas a nozzle-type mixer and a split-and-recombine mixer show the best results for emulsification and thus for extraction. 

Figure 22.13 Micromixers employed in the experimental setups for surfactant dispersion. The V-type mixer of FZK (a) is a parallel multilamination micromixer whereas the caterpillar mixer of IMM (b) is a split-and-recombine micromixer (serial multilamination) [3].

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