Crystallization from concentrated solution

Anhydrous p-dextrose can be crystallized from concentrated solutions or melts at 90% solids at a temperature above 100°C. By carefully controlling conditions, a product containing a high percentage of anhydrous p-dextrose can be obtained. 

Two hydrates have been described. The monohydrate, AgF,H20, forms yellowish cubes,4 or large, deliquescent, tetragonal crystals,5 decomposed by heat with formation of a basic salt, AgaF(OH), and evolution of hydrogen fluoride. The dihydrate, AgF,2HaO, crystallizes from concentrated solution in hard, transparent prisms.6... 

Hydroquinone and A-methyl-p-aminophenol (Metol) form superadditive mixtures and a complex, Metoquinone , consisting of one hydroquinone and two Metol molecules, was proposed by Lumiere, Lumiere and Seyewtz [44] to be the species with higher activity than the separate agents. A similar complex between hydroquinone and l-phenyl-3-pyrazolidinone (Phenidone) consisting of one molecule of hydroquinone and one molecule of Phenidone has been observed in the solid state by Kurosaki [45] and Mutter and Schneider [46]. Although these complexes can be crystallized from concentrated solutions of hydroquinone and Metol, and hydroquinone and Phenidone, there is no evidence of their existence in solution. 

Polymers crystallized from concentrated solutions exhibit more complex crystalline morphology (7). In dilute solutions, polymer coils are isolated from each other, but if the concentration increases, association and entanglement among the chains are favored. Therefore, there is a greater probability that a chain forms part of various crystallites, thus producing aggregated lamellae in multilayer morphologies. 

Further, Zn(OH)2 readily dissolves in an excess of alkali bases to give zincate ions, probably of the type [Zn(0H)3(H20)] or [Zn(OH)4]2". At high hydroxide concentrations the only species observed in solution is the latter 9 solid zincates such as NaZn(OH)3 and Na2[Zn(OH)J can be crystallized from concentrated solutions. 

Readily soluble in water the dihydrate crystallizes from concentrated solution at greater dilutions, hydrolyzes with formation of Sn(OH)Cl quite soluble in acetone, amyl alcohol, ethyl acetate, and absolute methanol and ethanol. 

I. Depending on the thickness, golden yellow to dark brown flakes elongated brown crystals from concentrated solutions. Soluble in hot water (partial decomposition). The powder pattern distinquishes it from the black form (appearance of lattice defects). Brown HgCls 4HgO has a remarkably wide phase range, from 3.82 to 4.00 HgO. 

These are required to operate the process plants at low temperatures, production of organic chemicals, crystallisation and separation of crystals from concentrated solutions, condensation of volatile solvents, etc. 

We have learned several things from the current SANS study of polyethylene crystallization from concentrated solutions. (1) The detection sensitivity of the volume fraction degree of crystallinity is estimated to be 10 . That allows for measuring the kinetics during the induction stage of polymer crystallization. 

Beryllium Nitrate. BeryUium nitrate tetrahydrate [13516-48-0], Be(N02)2 4H2O, is prepared by crystallization from a solution of beryUium hydroxide or beryllium oxide carbonate in a slight excess of dilute nitric acid. After dissolution is complete, the solution is poured into plastic bags and cooled to room temperature. The crystallization is started by seeding. Crystallization from more concentrated acids yields crystals with less water of hydration. On heating above 100°C, beryllium nitrate decomposes with simultaneous loss of water and oxides of nitrogen. Decomposition is complete above 250°C. 

Little was done after Biot s discovery of optical activity until 1848, when Louis Pasteur began work on a study of crystalline tartaric acid salts derived from wine. On crystallizing a concentrated solution of sodium ammonium tartrate below... 

The structures of the solids isolated from strongly alkaline solutions cast a shadow of doubt over the simple model in which the only species formed are Be(OH)3 and BelOH) . Of course what crystallizes from a solution may well be a species with low equilibrium concentration as the process of crystallization is driven by the insolubility of the product. Nevertheless it is clear that relatively little effort has... 

Crystallization was carried out by the rapid cooling method in ethanol (EtOH) solutions. Various amounts of Me-est and Pr-est crystals were dissolved in ethanol at 323 K. After the crystals completely dissolved, the solution was rapidly cooled to 298 K to perform the crystallization. The slurry was sampled at constant intervals and filtered to separate the crystals from the solution. The concentration of the solution was measured by a UV spectroscopic method. After drying the separated crystal, the crystal stmcture was examined by powder X-ray diffraction (XRD) using the RINT2200 (Rigaku). The crystal stractures were analyzed with a single crystal, by a Rigaku R-AXIS with Cu-Ka radiation. 

Fig. 11.10 Change in concentration of Pr-est in the crystallization from MeCN solutions...

Odorless, yellow, orthorhombic or monoclinic crystals from ethanol. Solution in concentrated sulfuric acid is orange-red and fluoresces green under exposure to UV light (quoted, Keith and Walters, 1992). 

Quite a few complexes with the bidentate pentasulfido ligand are also known. The first reported was the homoleptic and optically active complex [Pt(85)3] (15) (53, 64, 65, 68, 69, 176). Brick-red (NH4)2[Pt(85)3] 2H20 is formed from the reaction of K2[PtCl6] with aqueous (NH4)28 solution. Addition of concentrated HCl results in the separation of maroon (NH4)2[Pt8i7] 2H20 (54). The [Pt(85)3] ion crystallizes from the solution as a racemate, which can be resolved by forming diastereoisomers. Upon crystallization, [Pt8,7] undergoes a second-order asymmetric transformation, so that the solid contains an excess of the (—) enantiomer (54). 

Recently, Edye et al, (4) described a fermentation process which used a mutant strain of Zymomonas mobilis to produce high concentrations of fructose and ethanol when grown on a concentrated sucrose medium. Johns and Greenfield (5) proposed ethanolIc crystallization as a means of recovering the fructose from the broth. The kinetic behaviour of fructose crystallization from ethanolIc solution has not been previously reported, and this work Investigates these crystallization kinetics. 

If crystallization is carried out from concentrated solutions, multilamellar aggregates are formed. In particular, melt crystallization of polyethylene gives bunched-up lamellae with an overall spherical symmetry. The space between the lamellae contains uncrystallized amorphous polymer. These objects are called spherulites, and their radii grow linearly with time, in spite of their intricate morphological features [9]. Another remarkable feature of spheruhtes formed by linear polyethylene is that they are gigantically chiral, although the molecules are achiral. 

Spontaneous explosions of lead azide also take place during crystallization from saturated solution in ammonium acetate. A detailed study of this phenomenon has been made by Taylor and A. T. Thomas [105]. When the concentration of the solutions and the temperature and conditions of cooling were carefully controlled, they were able to predict the time at which spontaneous explosions occur. E.g. ... 

This salt is much more difficult to obtain in dry, pure form than is the corresponding sulfate. It is very soluble in water, but from concentrated solution it is deposited in crystals which in color are almost identical with those of the sulfate. Upon exposure to air, even during filtration with the pump, the crystals turn yellow through oxidation. Probably this is not due to greater ease of oxidation on the part of the solid salt but to the physical conditions that prevail. The saturated, cold solution is very viscous and sticky, and absorbent paper absorbs this liquid very slowly. Owing to the great solubility of the salt, the solution has a low vapor pressure and does not tend to evaporate in the air. Consequently, the crystals remain coated with a film of concentrated mother liquor which oxidizes very fast in the air. 

Orthophosphoric acid of a high degree of purity may be prepared by crystallizing the acid from concentrated solutions. These solutions are obtained by removing water from ordinary syrupy phosphoric acid at low temperature and pressure. This concentration must be performed with care, since the incomplete removal of water results in the... 

Essentially, the key process in the preparation of ultrafine powders by reaction-precipitation is crystallization from a solution. As mentioned in the previous chapter, crystallization from a solution includes two steps nucleation and crystal-growth. Both can occur only in a supersaturated solution and spontaneous nucleation can occur only when the concentration of the solute in the solution is over the super solubility of the substance involved. The rate equation for nucleation derived from the principles of thermodynamics is represented by [ 182]... 

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