Tube bundle crystallization

Figure 7.9 A tube bundle crystallization plant of the Hoechst Company. (Reproduced with permission from Rittner and Steiner 1985.)...

Both the Hoechst Tropfapparat and the Proabd are tube bundle crystallization equipment run in the same way, as mentioned above. In principle, every plate or tube bundle heat exchanger can be used as static solid layer crystallizer however, a few special geometrical considerations have to be obeyed. 

Just inside the shell of the tube bundle is a cylindrical baffle F that extends nearly to the top of the heating element. The steam rises between this baffle and the wall of the healing element and then flows downward around the tubes. This displaces non-condensed gases to the bottom, where they are removed at G. Condensate is removed from the bottom of the heating element at H. This evaporator is especially suited for foamy liquids, for viscous liquids, and for those liquids which tend to deposit scale or crystals on the heating surfaces. Vessel J is a salt separator. 

Microfilaments and Microtubules. There are two important classes of fibers found in the cytoplasm of many plant and animal ceUs that are characterized by nematic-like organization. These are the microfilaments and microtubules which play a central role in the determination of ceU shape, either as the dynamic element in the contractile mechanism or as the basic cytoskeleton. Microfilaments are proteinaceous bundles having diameters of 6—10 nm that are chemically similar to actin and myosin muscle ceUs. Microtubules also are formed from globular elements, but consist of hoUow tubes that are about 30 nm in diameter, uniform, and highly rigid. Both of these assemblages are found beneath the ceU membrane in a linear organization that is similar to the nematic Hquid crystal stmcture. 

Work on the production and oxidation of SWNT samples at SRI and other laboratories has led to the observation of very long bundles of these tubes, as can be seen in Fig. 2. In the cleanup and removal of the amorphous carbon in the original sample, the SWNTs self-assemble into aligned cable structures due to van der Waals forces. These structures are akin to the SW nanotube crystals discussed by Tersoff and Ruoff they show that van der Waals forces can flatten tubes of diameter larger than 2.5 nm into a hexagonal cross-sectional lattice or honeycomb structure[17]. 

Errera examined the distribution of alkaloids in plant tissues by histochemistry and found that alkaloids were present in active tissues near the vegetative points, ovule, epidermis and the layer just inside of it, hair, peripheral layers of fruits and seeds, vascular bundle, cork cambium, cork tissues, and latex tube (9). Molisch microscopically investigated 15 kinds of alkaloids as distinguishable crystal forms after treatment with acids or alkaloid reagents, and then histochem-ically examined them in plant tissue and cell sections following treatment with acids or alkaloid reagents (9). Tunmann and Rosenthaler observed histochemi-cally the distribution of alkaloids in tissues and cells of 36 families of plants 10). 

In a bundle, ID lines of molecules confined within one tube can interact with neighboring lines within parallel tubes. As a result, the system can undergo 3D transitions even though the molecular motion is essentially ID. Two kinds of transition have been explored for this highly anisotropic problem. One is condensation of the vapor phase into a liquid [30, 47—50] and the other is crystallization of that liquid [51, 52]. Because these parallel lines of atoms experience weak interchannel interactions (compared with the intrachannel interactions), the transitions occur at very low temperature. Figure 9.11 exemplifies this phenomenon for the case of molecules, for which the intermolecular potential has a well depth of order 3000 K. When confined inside a bundle, the transition is manifested as van der Waals loops appearing below 500 K. 

According to Hoffmann it is possible to substitute iron (III) boride for the elemental boron. The iron boride (finely divided powder) is placed in the tube, where it reacts with the HgS. The reaction starts at 200°C the optimum temperature lies between 300 and 400°C. The resulting B2S3 sublimes into the end of the tube where it forms bundles of fine, hairlike crystals. Vitreous and amorphous residues can be converted to the crystalline form by... 

Fig. 7-33. Ibbe bundle apparatus, usually tubes with fins. During crystal layer formation cooling agent flows through tubes, whereas during exudating of impurities from the crystal layer heating agent flows through the pipes. Impurities may be discharged sectionwise or while melting the crystals.

In this process, the crystallization takes place on the inside of a tube that is cooled from the outside. These tubes are assembled as bundles of up to 1600 tubes. The diameter is up to 70 mm and the length is up to 12-18 m. This process features, as indicated by its name, a falling film on the inside of the tubes for the melt and outside for cooling fluid. The melt coming from a feed tank is continuously circulated (pumped) through the tubes until the crystal coat at the surface reaches the desired thickness, that is, until the required percentage of product from the feed... 

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