Caterpillar mixers

Kleine Reaktoren mit grower Zukunji, Chemische Rundschau, April 2002 PAMIR study large commercial potential large industrial interest market volume standardization strategic cooperations time horizon potential for pharmaceuticals and fine chemistry Clariant pilot with caterpillar mixer [211],... 

OS 40] [R 21] [P 29] A much larger dependence of yield on reaction temperature was observed for the caterpillar mixer-scale-up set-up than for the inter digital mixer-laboratory set-up [48]. At temperatares above ambient, significant decreases in yield of the order of several tens percent were determined. 

A caterpillar steel mini mixer can be connected to conventional tubing, either stainless steel or polymeric, to prolong the residence time. The caterpillar mixer as all types of split-recombine mixers, profits from high volume flows (e.g. 100 1 h and more at moderate pressure drops) at favorable pressure drop (not exceeding 5 bar) as its internal microstructures can be held large [25-28]. 

For a more detailed description of the hydrodynamics of the caterpillar mixer, respective images and the performance of a second-generation caterpillar device see the corresponding section in Section 4.1. 

Figure 5.29 Special-type multi-purpose micro devices and mixing tee used for investigation of CO2 absorption. Comparison of their reactor performance as a function of the residence time. Micro bubble columns ( ) 1100 pm x 170 pm, (A) 300 pm x 100 pm and (T) 50 pm x 50 pm Interdigital mixer ( ) (40 pm) caterpillar mixer (A) (850 pm ramp) mixing tee (0) (1 mm) [5],...

As a predecessor device, a caterpillar mixer with step-like internal structure was fabricated without horizontal splitting layer and no separation of the streams [66],... 

M 60] [P 54] The impact of having truly separated flows was shown by CFD simulations [7]. An essential part of the flow splitting, besides having split channels which recombine later, is a splitting plane which cuts the flow like a knife. These design aspects are central parts of an optimized SAR caterpillar mixer. 

There are two ways for scale-out with caterpillar mixers. One is to enlarge the mixing unit cell, i.e., the corresponding channel width, depth and length, while keeping the width-depth length ratio constant, i.e., maintaining the type of ramp... 

Fig. 6.3 Caterpillar mixers (600 pm inner channel width and depth, all) with 0, 2, 4, 8, or 12 mixing units, connected in a serial manner.

Fig. 6.4 Caterpillar mixers (eight mixing units, all) with 800, 1200, or 2400 pm channel width and depth [27].

Fig. 6.5 Segregation index, as defined in Ref. [28], for mixing of aqueous solutions in caterpillar mixers with 800,1200, or 2400 pm channel width and depth [27], The smaller the segregation index, the better is the mixing and the shorter is the mixing time.

There is also another scale-out issue similar to that practiced for the caterpillar mixer. By slight enlargement of internal dimensions, throughput may be increased,... 

Fig. 6.16 Cream manufacturing plant (top) and its core element, the microstructured eight-component caterpillar mixer (bottom).

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. 

Figure 4.19 Caterpillar mixer, (a) Schematic of SAR showing structured walls, (b) Snapshot of the 600 im size caterpillar mixer. The size is defined for entrance channel. Courtesy Fraunhofer ICT-IMM, Germany.

The micromixer with structured internal surfaces (e.g., caterpillar mixer, discussed in the later section) show different trends compared to the other microchannels. It shows quadratic dependency of the pressure loss on the flow velocity according to the following equation [16] ... 

To create fine dispersion in microcapillaries, a micromixer (e.g., caterpillar mixer) needs to be attached upstream. At elevated flow velocity the static internals create dispersion, and as a result, part of the continuous phase flows in the form of small droplets in the dispersed phase. 

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].

Bas-relief micromixers induce transversal motion, when miscible liquids are considered, to mix by convection [92,93]. In the gas-liquid case to be considered here, the mechanism for bubble formation is yet unclear, but likely related to shear forces coming from a similar liquid motion in the dispersed flow. Caterpillar mixers induce such transversal motion by ramp-like microstructures, lifted up and down, placed in one channel at the bottom and ceiling [4] (see also Ref. [S6]). Caterpillar mixers were developed as family of devices with grouped capacity using smart enlargement of the internal chaimel and have high volume flows, for example,... 

First, kinetic investigations and reaction optimization were performed on laboratory scale. The setup (Figure 6.4) consisted of a caterpillar mixer (M) by the IMM (Institut fur Mikrotechnik Mainz, Germany) (www.imm-mainz.de) and a stainless steel capillary (ID 2 mm, V= 17.8 ml), which were both thermostated. The substrates (SI and S2) were dissolved in toluene and dosed with rotary piston pumps. The reaction mixture was quenched in an aqueous NaHCOs solution (S3). These first feasibility studies with a 7.6-fold excess of DAST showed that the reaction can be handled at temperatures up to 105 °C, delivering conversions up to 60%. 

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