Crystallization precipitation prior

It should be noted that mini-contact test results tend to overestimate a wine s stability and therefore the effectiveness of prior treatment. This statement is based on work by Boulton (1982). After 2 hours contact, only 60-70% of the endogeneous tartrate has crystallized and therefore the increase in weight of the crystal precipitate is minimized. These results are interpreted to mean that the treatment was more effective, or the wine more stable, than was actually the case. In order to make the mini-contact test faster, more reliable and compatible with the dynamic contact process, the Martin Vialatte Company proposed the following variant in 1984 seeding a wine sample with 10 g/1 of cream of tartar and measuring the drop in conductivity at 0°C. 

The solubility product constants K,p = exp(—AG /KT) are 2.5x10 and 5.0 X 10 , respectively. Prior values from approaches to solubility equilibria on poorly crystallized precipitates were significantly larger (Baes and Mesmer 1976). One would expect the K°p measured from finely divided precipitates to be larger, rather than smaller, than that determined from well-crystallized solids used for calorimetry. However, Kragten and Decnop-Weever (1987) found K% [La(OH)j] = 1.6 x 10 in the most recent study of a series of lanthanide-hydroxide equilibrium studies by the precipitation borderline method. 

Nucleation and growth mechanisms are described in detail in texts on precipitation (Sohnel and Garside, 1992), and crystallization (Mullin, 2001 Mersmann, 2001 and Myerson, 2001). Granulation is considered in Sherrington and Oliver (1981), Stanley-Wood (1990) and Pietsch (1991) whilst comminution is dealt with in Prior etal. (1990). 

OS 40[ [R 21[ [P 29]To corroborate HPLC results, obtained prior to yield analysis, preparative isolation of the product was achieved by precipitation and filtration of the crystals [48]. A crystal mass up to about 44 g was so isolated at a yield of up to 81%. The product was of high purity (> 98% of the total crystal mass). 

In dim red light, the weighed hydrazide contained in one of the 500 ml flasks (ca. 67 g 95% of theory) is washed into a 1000 ml beaker with 263 ml IN hydrochloric acid. 239 ml distilled water, 239 ml ethanol (95%), and 37 ml 2,4-pentanedione are added, and the well-mixed solution left to stand in the dark at room temperature until the reaction is complete, i.e., about 30 minutes. The reaction mixture is neutralized with the addition of 263 ml 1 N sodium hydroxide, and the beaker covered with parafilm and refrigerated to ensure complete precipitation. The pyrazole is filtered at the pump, the mother liquor being returned to the beaker and used to wash out the last few crystals, washed with cold water, and sucked dry under a stream of dry nitrogen. The product is dried in vacuo over barium oxide or phosphorus pentoxide for at least twelve hours before proceeding to the next step, wherein anhydrous conditions will increase yield. Hofmann calls for drying the pyrazole in vacuo at 60°, which indicated the product to be fairly stable. So all the hydrazide is converted prior to aminization. 

Using coprecipitation methods with a suitable mixture of solutions described above, the resulting LDH materials are often poorly crystallized and exhibit compositional fluctuations due mainly to the difference in the values of the pH at which the precipitation of M(II)(OH)2 and M(III)(OH)3 hydroxides occurs. Consequently, the chemical formula of the final material may not reflect the composition of the solution prior to the precipitation as noted in Chapter 1. Controlling the amount of anion incorporated under such conditions is very difficult. A "chimie douce method has been proposed by Delmas et al. in an effort to overcome this problem [181,182]. The process is illustrated schematically in Fig. 8. Since the synthesis starts from a highly crystalline layered y-oxyhydroxide precursor, it was suggested that this favored the formation of very crystalline LDHs with controllable M(1I)/M(III)... 

Prior to crystallization in the relining of sugar, bleaching of the syrup is required. This is sometimes effected through treatment of the solution with calcium hypochlorite, usually in the presence of calcium phosphate which serves as a buffer and aids in the final precipitation or calcium from the bleached solution. 

Hono et al. [64, 65] confirmed that Cu in both amorphous Fev sSiia.sBgNbsCui and Fe89Zr7B3Cui alloys forms clusters prior to primary crystallization and the Cu clusters act as heterogeneous nucleation sites for bcc-Fe(Si) precipitates. They also confirmed orientation relationships between the Cu clusters and bcc-Fe crystals and concluded that the heterogeneous nucleation of the bcc-Fe phase is due to the lower interfacial free energy for nucleation [66]. 

Quinoxalinones have been suggested for the chromatography of keto acids [184,185]. They are produced by reaction with aromatic o-diamines, as shown in Scheme 4.21 (p. 77). A solution of 60 mmol of sublimed o-phenylenediamine in 100 ml of 10% acetic acid was mixed with a solution of 30 mmol of the keto acid in 30 ml of water. The precipitated quinoxalinone was filtered after 15 min, washed with water, dried and crystallized from methanol. Prior to the GC analysis proper, it had to be converted into a silyl derivative 5—50 /ul of about a 1% solution of quinoxalinone in dry pyridine was mixed with 20 jul of a pyridine solution of the internal standard (6-methyl-2-naphthol, p-nitrophenyl phenyl ether). A 200-/lz1 volume of BSA and 50 of pyridine were added. As the silylation proceeded very quickly, the reaction mixture could be injected immediately. 

Classical methods of separation [7] are (1) fractional crystallization, (2) precipitation and (3) thermal reactions. Fractional crystallization is an effective method for lanthanides at the lower end of the series, which differ in cation radius to a large extent. The separation of lanthanum as a double nitrate, La(N03)3-2NH4N03-4H20, from praseodymium and other trivalent lanthanide with prior removal of cerium as Ce4+ is quite a rapid process and is of commercial significance. Other examples are separation of yttrium earths as bromates, RE(Br03>9H20 and use of simple nitrates, sulfates and double sulfate and alkali metal rare earth ethylenediamine tetraacetate complex salts in fractional crystallization separation. 

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