Seeding crystallization

The concentrated mother Hquor contains a large amount of sulfuric acid in a free form, as titanium oxy-sulfate, and as some metal impurity sulfates. To yield the purest form of hydrated TiOg, the hydrolysis is carried out by a dding crystallizing seeds to the filtrate and heating the mixture close to its boiling temperature, - 109° C. The crystal stmcture of the seeds (anatase or mtile) and their physical properties affect the pigmentary characteristics of the final product. 

The less soluble diastereomer (S,S)-57 was obtained in >96% diastereomeric purity by six step-by-step crystallizations of this mixture from hexane or by three crystallizations, when a sample of (S,S)-57 was used as a crystallization seed (Scheme 20) <2003MC121, B-2003MI97>. 

The quality of the mean-field approximation can be tested in simulations of the same lattice model [13]. Ideally, direct free-energy calculations of the liquid and solid phases would allow us to locate the point where the two phases coexist. However, in the present studies we followed a less accurate, but simpler approach we observed the onset of freezing in a simulation where the system was slowly cooled. To diminish the effect of supercooling at the freezing point, we introduced a terraced substrate into the system to act as a crystallization seed [14]. We verified that this seed had little effect on the phase coexistence temperature. For details, see Sect. A.3. At freezing, we have... 

US patent 6,833,379, Crystal modification of torasemide [119], This invention relates to the characterization of a new crystal modification III of torasemide, to a process for its preparation by the use of controlled acidifying of alkaline solutions of torasemide with inorganic or organic acids with or without addition of a crystal seed, to its use as a raw material for the preparation of the crystal modification I of torasemide and of pharmaceutically acceptable salts of torasemide, as well as to pharmaceutical forms containing this new torasemide crystal modification. 

Figure 1. Change in average crystal size with time for ice crystal seeds grown in 6% lactose under batch crystallization conditions.

Figure 3. Changes in size distribution with time during growth of ice crystal seeds in 6% lactose under batch or semi-batch growth conditions, concentration processes based on suspension growth. In addition, the relation of this observed widening to the heat balance conditions needs to be further explored.

Figure 5. Acicular mordenite crystals grown at 200°C and 16 hours using the single-crystal seeds shown in Figure 2. (scanning electron micrographs courtesy of AMR Corp. Burlington, Mass.)...

The metastable (supersaturated) zone between lines AB and CD where spontaneous crystallization is improbable. However, if a crystal seed were placed in such a metastable solution, growth would occur on the seed. 

The method used for the measurement of the metastable region is also the traditional one, i.e., using the light scattered by the newly formed fine crystals to detect the nucleation status. The experimental equipment is shown in Fig. 12.1. The water bath tank is surrounded with a light-proof black screen, with two windows vertical to each other with dimension of 2x3 cm for light beam casting and visual observation, respectively. To parallel the industrial condition of induced nucleation, all the measurements are carried out under conditions with the existence crystal seeds. 

A similar table summarizing the experimental data measured in the FBC. with the same mean diameters of crystal seeds, r/ l0, and under the same operating temperatures, T, was also obtained but it is not given here. 

The mean observed active energies obtained by regression of the experimental data for various crystal seeds with different mean diameters and in different crystallizers are listed in Table 12.4, where, similarly, the subscripts IS and FB denote the parameters in the impinging stream crystallizer and the fluidized bed crystallizer, respectively. ... 

Crystal seeding of the melt and conditioning with formaldehyde (at 0.011 tonnes per tonne urea) may be used. 

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