Crystallization from a solution

The solution being treated is first concentrated, usually in a multistage concentration unit. The concentrated solution is then guided to the crystallizer where crystallization occurs. The driving force during crystallization is the concentration difference of the dissolved substance in the supersaturated solution and just saturated solution. 

SSC Supersaturation curve X Dissolved solid ratio in solvent Temperature 

With cooling crystallization, solvent supersaturation is greatest at the lowest possible temperature in the crystallizer, and, therefore, a crust forms on the cooling area. To restrict incrustation, the crystallizer must be operated with a small temperature difference between the solvent and cooling agent, which requires large cooling areas. 

Vacuum crystallization needs no heat transfer area in the solution, and therefore no incrustation problem occurs. To increase economic efficiency with evaporation crystallization, with respect to steam input, the process is designed for multistage operation with steam heat recovery. The first stage operates under conditions close to ambient pressure, and the final stage under a vacuum, such that the steam is condensed without compression at the temperature of the available cooling water. 

Once supersaturation of the solution is achieved, crystallization occurs by reducing the supersaturation until the saturation line is reached again. Small seeds are then formed which then grow to crystals (see Chapter 7.2.3). 

---

Iron (III) chloride hexahydrate [10025-77-17, FeCl36H2 0, is a brown-yeUow to orange material that crystallizes from a solution of iron or iron salt dissolved ia hydrochloric acid that coataias an oxidant such as Cfy or nitric acid. The monoclinic crystals contain the complex salt... 

The tertiary metal phosphates are of the general formula MPO where M is B, Al, Ga, Fe, Mn, etc. The metal—oxygen bonds of these materials have considerable covalent character. The anhydrous salts are continuous three-dimensional networks analogous to the various polymorphic forms of siHca. Of limited commercial interest are the alurninum, boron, and iron phosphates. Boron phosphate [13308-51 -5] BPO, is produced by heating the reaction product of boric acid and phosphoric acid or by a dding H BO to H PO at room temperature, foUowed by crystallization from a solution containing >48% P205- Boron phosphate has limited use as a catalyst support, in ceramics, and in refractories. 

Barium nitrite [13465-94-6] Ba(N02)2, crystallines from aqueous solution as barium nitrite monohydrate [7787-38-4], Ba(N02)2 H2O, which has yellowish hexagonal crystals, sp gr 3.173, solubihty 54.8 g Ba(NO2)2/100 g H2O at 0°C, 319 g at 100°C. The monohydrate loses its water of crystallization at 116°C. Anhydrous barium nitrite, sp gr 3.234, melts at 267°C and decomposes at 270 °C into BaO, NO, and N2. Barium nitrite may be prepared by crystallization from a solution of equivalent quantities of barium chloride and sodium nitrite, by thermal decomposition of barium nitrate in an atmosphere of NO, or by treating barium hydroxide or barium carbonate with the gaseous oxidiation products of ammonia. It has been used in diazotization reactions. 

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. 

The filtrate is evaporated under vacuum and the residue is crystallized from a solution of 60 parts of isopropanol in 75 parts of water. There are obtained 9 parts of N-(3-sulfamyl-4-chlorobenzamido)-2-methyl indoline, MP (K) 184° to 186°C, MP (MK) 160° to 162°C (isopropanol/water). [The melting points being determined on a Kofler heater plate under the microscope (MK) or on a Kofler Bank (K)]. ... 

There are as yet no structural data on the mononuclear hydroxo complexes formed at high pH. Schmidbaur et al. (91) have obtained the structure of a compound that had been crystallized from a solution at pH 13.2. The compound contains the anion [Be4(OH)10]2, which has a structure resembling that of adamantane or P4O10, as shown in Fig. 9. 

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... 

Figure 17. Plot of Li isotopic composition vs. temperature of growth for synthetic calcite crystallized from a solution containing Li from L-SVEC (Marriott et al. 2004). The results are most consistent with temperature not being a significant control on mass fractionation of Li during crystallization from aqueous solution, thus essentially eliminating Li isotopes as a paleotemperature proxy in marine carbonates.

Bierenstiel and Schlaf [22] were able to prepare and isolate for the first time the less stable 8-D-galactonolactone by oxidation of galactose with the Schvo s catalytic system, which is based on the dimeric ruthenium complex [(C4Pli4CO)(CO)2Ru]2. The transformation led to the 5-galactonolactone in 93% yield, against 7% of the isolated y-lactone isomer. This procedure also allowed the preparation of 5-D-man-nonolactone in a much better yield (94%) than that reported in an early procedure [23] based on crystallization from a solution of calcium mannonate in aqueous oxahc acid. 

Purification is accomplished by crystallization from a solution prepared from the crude product and 100 mL of water at a maximum temperature of 50°. (The time at this temperature should be kept minimal.) Filtration of the nearly saturated solution through coarse fiber-glass paper (Whatman GF/A) removes impurities of low solubility. At 0° the solid product crystallizes slowly 12 hours are required for complete deposition. The orange solid is collected on a filter and dried under atmospheric conditions (not vacuum). Yield 17.0 g, 66% of theory. Water of hydration is lost under low humidity conditions or under vacuum. Anal. Calcd. for Na6V10O2g 18H2O V, 35.89 H20, 22.84. Found V, 35.51 H20, 22.65%. 

When diphenyhnagnesium is crystallized from a solution containing l,3-xylyl-18-crown-5, an X-ray crystal-structure determination showed the formation of rotaxane 116 (Figure 56) . Only four of the five oxygen atoms of the crown are involved in coordination to magnesium, two with a relatively short bond distance [2.204(3) and 2.222(4) A] and two with a longer bond distance [2.516(4) and 2.520(4) A]. The C(l)-Mg-C(2)... 

V(urea)6]I3 crystallizes from a solution of the sulfate on adding potassium iodide. The oxygen atoms of the urea molecules form an octahedron twisted T about the three-fold axis with V—O lengths of 1.98 A.286 The magnetic susceptibility of the iodide and perchlorate salts... 

Biiltemann 2 observed that vanadium ammonium alum separates out in blue crystals from a solution containing sulphuric acid, but from solutions containing a weak acid, or from neutral solutions, red crystals are obtained. (The chromium alums can also be prepared in differently coloured modifications.) The analytical data, melting-point, electrical conductivity, rate of efflorescence, and general behaviour of both kinds of crystals are identical, so that it is difficult to ascribe different constitutions to them. Meyer and Markowitz3 have shown that both forms separate out when the molecular proportion of sulphuric acid in the solution is less than that theoretically required, and attribute the red colour to the presence of traces of vanadous oxide, V203, or its hydroxide, V(OH)3. Vanadium rubidium and vanadium ciesium alums behave in the same way. A vanadium guanidine alum has also been prepared.4... 

A plant is to make 10,000 lb/hr of urea crystals from a solution that contains 75% dissolved salt. The material balance and operating conditions are shown on the sketch. Key crystallization data are given by Bennett (1981, p. 452) as... 

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]... 

Actually, the mechanism for the formation of HAP crystalline during the process under consideration is very complex and some suggestions proposed for the mechanism cannot be supported by experimental evidence so details of the chemical aspect will not be discussed here. In any case, precipitation, i.e., crystallization from a solution, must be involved in the process so the fact that liquid-continuous impinging streams cause strong micromixing and pressure fluctuation would favor the synthesis of nano HAP. 

When sodium nitrate and potassium chloride are dissolved, the solution contains four ions, Na+, NOa , K+, CP, and from these ions not only could the two original salts be reconstructed, but also two new salts, potassium nitrate and sodium chloride, through a regrouping of the radicals. Which of the four salts will crystallize from a solution containing the four ions depends solely... 

This influence of the structure of a surface must be felt particularly when a solid crystallizes from a solution. Indeed, the experience of chemists over the centuries may be summarized by the motto of the ancient philosophers, Natura facit non saltus, meaning that nature does not like abrupt changes. As Zerfoss (45) pointed out, if one wants to grow a large perfect crystal from an aqueous solution, one has to select a substance which reveals its affinity for water not only... 

Ammonium carbonates.4—The normal carbonate, (NH4)2C03,H20, is produced by the action of ammonia on the solid commercial carbonate (p. 239) or its aqueous solution, and also by a similar process from ammonium carbamate.5 On account of its insolubility in concentrated ammonia solution, the salt crystallizes out. It can also be prepared by dry distillation of the commercial product, or by crystallization from a solution in dilute alcohol.5 It is also produced by heating barium or strontium carbonate with ammonium chloride or nitrate,6 and is stated to be formed by heating a mixture of nitric oxide and acetylene in presence of spongy platinum.7... 

Cupric pyrophosphate, Cu2P207.—The anhydrous salt is precipitated as a greenish-white powder by addition of sodium pyrophosphate to a solution of a cupric salt.8 The pentahydrate crystallizes from a solution containing cupric sulphate and sodium metaphosphate.9... 

ArI(OAc)2 can be crystallized from a solution of either ArICl2 or ArlO in acetic acid. ArI(0N02)2 can be obtained by reacting silver nitrate with a solution of those iodine compounds in acetonitrile. 

---