Crystal cooling process

A stable crystalline form for chocolate depends primarily on the method used to cool the fat present in the Hquid chocolate. To avoid the grainy texture and poor color and appearance of improperly cooled chocolate, the chocolate must be tempered or cooled down so as to form cocoa butter seed crystals (31). This is usually accompHshed by cooling the warm (44—50°C) Hquid chocolate in a water jacketed tank, which has a slowly rotating scraper or mixer. As the chocolate cools, the fat begins to soHdify and form seed crystals. Cooling is continued to around 26—29°C, during which time the chocolate becomes more viscous. If not further processed quickly, the chocolate will become too thick to process. 

FIG. 18 66 Forced-circulation baffle surface-cooled crystallizer. (Swenson Process Equipment, Inc.)... 

In the multistage process described on Fig. 20-14 feed enters one of several crystallizers installed in series. Crystals formed in each crystallizer are transferred to a hotter stage and the liquid collected in the clarified zone of the crystallizer is transferred to a colder stage and eventually discharged as residue. At the hot end, crystals are transferred to a vertical purifier where countercurrent washing is performed by pure, hot-product reflux. TSK refers to this multistage process as the countercurrent cooling crystallization (CCCC) process. In... 

Fig. 17 B/E-p dependence of the critical temperatures of liquid-liquid demixing (dashed line) and the equilibrium melting temperatures of polymer crystals (solid line) for 512-mers at the critical concentrations, predicted by the mean-field lattice theory of polymer solutions. The triangles denote Tcol and the circles denote T cry both are obtained from the onset of phase transitions in the simulations of the dynamic cooling processes of a single 512-mer. The segments are drawn as a guide for the eye (Hu and Frenkel, unpublished results)...

A sample in the primary crystallization field of phase C will behave differently during crystallization. Here phase C precipitates with composition identical to C (no solid solubility) during cooling keeping the A B ratio in the melt constant until the melt hits the intersection of the two primary crystallization fields. At this temperature a will start to precipitate together with further C and from this point on the cooling process corresponds to that observed for the sample with overall composition P after this sample reaches the same stage of the crystallization path. 

A batch cooling crystallization is one of the most commonly used crystallization method. In this process super saturation of a liquid is achieved by means of a cooling process. The solubility of the solute (in the solvent) decreases with a decrease in temperature this leads to precipitation of the solute. 

Clavilier s currently recommended procedure is as follows. Two cooling processes of the crystal after flame-annealing treatment are carried out between steps (a) and (b) in Fig. 1 i.e., air cooling until the temperature of the crystal becomes 200-300°C and cooling in pure water under an H2 -I- Ar stream. The transfer of the crystal into the cell in step (c) of Fig. 1 with a droplet of H2 + Ar-saturated pure water on the crystal face is important for protecting the crystal surface from impurities in air. Then the crystal surface is exposed to the solution by the dipping method of Fig. 1. 

Sometimes crystallographers consider that measuring a crystal at very low temperature is a kind of panacea, able to solve all defects of the sample, all kinds of experimental errors, and enhance the response indefinitely. Young students might be disappointed to leam that these miracles do not take place. A bad crystal sample remains as such even at 10 K, and sometimes it becomes even worse because the cooling process and the residual stress induced by a temperature gradient may produce further damage to the sample. Many other kinds of experimental problems and sources of error (for example absorption, extinctions, disorder, etc.) are not attenuated by the low temperature. 

Parison cooling significantly impacts the cycle time only when the final parison thickness is large. In thin blown articles the mold is opened when the pinched-off parts have solidified so that they can be easily stripped off thus they are the rate-controlling element in the cooling process. For fast blow molding of even very thin articles, the crystallization rate must be fast. For this reason, HDPF, which crystallizes rapidly, is ideally suited for blow molding, as are amorphous polymers that do not crystallize at all. 

It is also assumed that the composition of the grown crystal does not change in the cooling process. As is well known for the case of finite quantity of melt, the composition of melt (liquid) and solid change along the liquidus and solidus curves, respectively. 

The second approach is thru the modification of the Compn B formulation and the elimination of cast charge defects, especially at the interface with the projectile base. Studies have centered primarily in the utilization of crystal control agents — polymeric materials, HNS, etc, the finish on the interior of the projectile, and on controlled loading cooling processes... 

To illustrate the usage of implicit finite difference schemes, we will solve the cooling process of an amorphous polymer plate. Since an amorphous polymer does not go through a crystallization process we will assume a constant specific heat2. The implicit finite difference for this equation can be written as,... 

Crystallization — The process of forming solid crystals from solution, melted or polycrystalline phase. Used to separate solid and liquid phase or preparing high purity materials. Crystallization from solution is the most common example of solid-liquid separation. In the process, the solid crystals are formed from supersaturated solution (the solution that contains more soluble molecules, ions etc. that it would under equilibrium conditions). Usually the supersaturated solution is obtained either by cooling the solution, evaporating the solvent, pH change, or adding another solvent. The crystallization process can be induced electrochemically (- electro deposition, electro crystallization). The most common ex-... 

Solvent Crystallization. Two processes, one utilizing acetone (Armour) and the other employing methanol (Emery), are well known. Using the latter, fatty acid is dissolved in 90 percent aqueous methanol in a 1 2 acid/ solvent ratio by the application of heat. The resulting solution is then cooled to H 5°C in a multi-tubular crystallization chamber equipped with scrapers for efficient heat transfer. The crystallized fatty acids are removed by filtration. The filter cake is melted and stripped of any residual solvent to yield the refined stearin fraction, and then the liquid stearin is converted to flakes or powder by a variety of processes, for example, chill roller, and the like. The mother liquor from the filtration is stripped to obtain the olein fraction. The separated stearin and olein fractions have a variety of commercial applications in both the chemical and food processing industries. 

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