Crystallizers cooling disc

With mainly continuous operation, the entire melt is converted to a crystal suspension in the crystallizer by cooling, and is followed by a mechanical separation of the solid and remaining melt (mixed vessel crystallizer, cooling disc crystallizer, forced circulation cooler with scraper, crystallizer columns)... 

Figure 8.38. The Gouda MF cooling disc crystallizer a) open type, b) closed type...

Fig. 7-38. Jacket-cooled crystallizer with cooling disc mounted on a rotor to cool stepwise and to considerably avoid backmixing of melt or crystal suspension.

The Bj textures show characteristic helical filamentary growth in cooling from isotropic melt. i- 2 However they denote at least two distinct phases. X-ray measurements clarified that the original By materials, which form freestanding strands, - just like columnar liquid crystals of disc-shape molecules (see Chapter 2), indeed have a columnar phase (hereafter we will label them as Bj j). Other By-type materials (we call them Byu) were foimd to have modulated layer structures. We note that the By and B2 type banana-smectics also form strands of fibers. ... 

A disc of reduced semiconducting rutile crystal 2 cm in diameter and 2 mm thick is heated in air for 10 s at 300 °C. After cooling, circular electrodes, lcm in diameter, are applied symmetrically to the two major surfaces. The chemical diffusion coefficient D for the oxidation reaction in reduced single-crystal TiC is given by... 

Next, the ammoniated brine is carbonated to a point just short of crystallization. Then, the brine is given a final carbonation and cooled to produce the crude NaHC03 crystals. The equipment used in the carbonation step consists of groups of five identical towers having alternate rings and discs in the upper section to assure mixing of the falling... 

The crude acetamide may be recrystallized from a mixture of three parts of benzene to one part of ethyl acetate, or from an alcohol-ether mixture. Dissolve 0.5 g of acetamide in 1 ml of methanol by warming cool, and add 6-7 ml of ether. Cork tube, and cool. If crystals do not separate within a few minutes, even on stirring, add a minute crystal of pure acetamide and allow to stand. Filter the crystals with suction and wash with ether. Place on a paper disc or watch glass and dry in a dessicator. Determine the melting point. 

A) Preparation of Benzidine (Sm.). Prepare about 2 g of hydrazobenzene according to Experiment 30. Dissolve in a small flask 2 g of hydrazobenzene in 15 ml of ether. Place 8 ml of concentrated hydrochloric acid and 8 ml of water in an eight-inch test tube and provide with solid rubber stopper. Cool in an ice-salt mixture. Add the ethereal solution slowly by means of a dropper to the cold diluted acid, and shake vigorously after each addition. When all the hydrazobenzene solution has been added, allow to stand 10 minutes, and add 10 ml of concentrated hydrochloric acid. Allow the tube to remain in the cold bath 15 minutes longer. Filter the benzidine hydrochloride with suction. Wash the crystals with 5 ml of dilute (1 1) hydrochloric acid and finally with two 5 ml portions of ether, and dry on a paper disc. The yield is about 2 g. 

B) Preparation of Dinitrosoresorcinol (Fast Green). Place 80 ml of water and 2 g of resorcinol in a 250-ml beaker. Cool In an ice-salt bath, and add 4 ml of concentrated hydrochloric acid. Add 10 g of ice, then slowly, with stirring, add a solution of 2.6 g of sodium nitrite in 10 ml of water. If the temperature rises above 5° add more ice. When all the solution has been added, allow to stand in the bath for 30 minutes. Filter the yellow brown crystals with suction, and wash with 5 ml of ice water. Dry on a paper disc or porous plate. The yield is about 3 g. 

The hand-warmer contains a supersaturated solution of sodium acetate. (Supersaturation is very similar to supercooling, except that it is the solute, rather than the solvent, that crystallizes when nucleation occurs.) When the heat is required, you click a disc on the hand warmer, which causes nucleation, initiating crystallization of sodium acetate. This releases the latent heat and warms your hands. The hand warmer is reusable because you can re-dissolve all the crystals by heating it, e.g. by placing it in boiling water. As it cools down to room temperature, the solution becomes supersaturated again and, provided no crystals remain, it can be kept in this state until it is needed again. 

The aqueous solution is then concentrated to dryness at an outside temperature of 40 to 45°C and at low pressure. The residue, obtained by drying in a vacuum at 40° to 45°C is triturated in a mortar with ethyl ether and, after filtration, is extracted with 3,400 ml boiling absolute ethanol. The ethanol extract is separated from the undissolved part by filtration, cooled and the product which crystallizes by cooling is filtered and dried at 40°C in a vacuum. In that manner the disc ium (4,4 -disulfoxy-diphenyl)-(2-pyridyD-methane bi-hydrate is obtained, which takes the form of a white solid, according to U.S. Patent 3,528,986. 

Fig. 8.12 The electron TOF transients of a 225 )(xm thick perylene crystal disc in the b direction below, at T = 300 K and F = 22 kV/cm above, at T = 40 K and F = 35.6 kV/cm. Note the strong decrease in the transit time on cooling. After [22].

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