Crystallization practice

After the seed crystals had arrived it was found that crystallization practically always occurred when amounts of 100 g of any laboratory sample were slowly warmed over a period of a day, after cooling to liquid-air temperatures. This occurred even when great precautions were taken to exclude the presence of seeds. However, it was found readily possible, by temperature manipulation alone, to produce crystalline or supercooled glycerol at will. 

About 70-80 per cent of the biacetyl monoxime is recovered on crystallization. Practically all of the monoxime left in the mother liquor can be recovered by steam distillation. The recrystallized and dried compound melts at 76.5°. Purification by distillation is not recommended. 

The performance of many process equipment encountered in crystallization practice is often profoundly affected by the flow properties of the liquid media. Heat transfer, for example, may be severely impeded in thick sluggish liquors or magmas crystallization may occur only with difficulty, and filtration and washing of crystalline product may be impaired (Mullin, 1961). Since viscosity is a function of temperature the viscosity at the average temperature of crystallization is considered. The viscosity of the solvent can be estimated using the following group contribution model (ICAS, 2003)... 

Electroneutrality may also be implemented by imposing the requirement that F(000) equal the number of electrons in the unit cell. The equation F(000) = ne can be treated as an observation, with a weight sufficient to keep the crystal practically neutral, but sufficiently small such as not to dominate the least-squares treatment. This slack constraint (Pawley 1972) has been applied in electron density analysis by Hirshfeld (1977). 

This chapter will discuss the main concepts associated with crystallization practice, and will describe the main types of equipment used nowadays, together with some indications of their performance and applicability. 

Cuprous Iodide, Cu.O. cubic while crystals, practically insoluble in H 0 or alcohol, soluble in NHjOH. potassium iodide, or potassium cyanide. Used in Sandmeyer s reaction lo synthesize aryl chlorides. Cupric Oxide. CuO, black cubic crystals, insoluble in IFO. soluble in HCI. NHjOH. or ammonium chloride. Used as a green and blue colorant in ceramics. 

The relatively low productivity is quite common in colloid systems or in nanoparticle formation. It is always a question of consideration to decide about what productivity is still acceptable and on what expense, although there is a strong rule in the crystallization practice the particle size and productivity can t be changed independently of each other. 

Phenolphthalein White or yellow-white crystals. Practically insoluble in water soluble in alcohol and in solutions of alkali hydroxides. Transition interval from pH 8.0 (colorless) to 10.0 (red). 

In Sections III and IV, the principles of nucleation and growth were discussed separately. Now the crystallization process as a whole will be considered. In any practical application of crystallization, a stable solid phase must first be formed from the metastable liquid phase, and then additional molecules are deposited on the nucleus to form the macroscopic crystalline solid. Since nucleation and growth are taking place simultaneously, the theoretical principles discussed earlier are difficult to apply quantitatively to crystallization practice. Consequently, empirical expressions are still generally used in the design of equipment and prediction of its operation. 

Crystallization. The filtered thick juice is now sent to the vacuum-pan for boiling. It is essential to use low temperatures (65 to 80°C) in this process to avoid sucrose inversion and caramelization. Pan boiling and crystallization practices are very similar to the same unit process in the sugarcane refinery described earlier for cane sugar. Crystallization is continued until the crystals have reached the required size. This mixture of crystals and mother liquor, known as massecuite, is discharged into a mixer tank and from there it is sent to centrifugal separators. In... 

Properties White, crystalline powder or colorless lustrous crystals practically odorless. D 1.27 (25C) soluble in water, alcohol, and chloroform insoluble in ether sublimes approximately 200C partly decomposes. 

This structure factor calculation confirms the geometric argument of (001) extinction in a body-centered crystal. Practically, we do not have to calculate the structure extinction using Equation 2.11 for simple crystal structures such as BCC and face-centered cubic (FCC). Their structure extinction rules are given in Table 2.2, which tells us the detectable crystallographic planes for BCC and FCC crystals. From the lowest Miller indices, the planes are given as following. 

Example 7-6 illustrates the applicability of good crystallization practice to achieve continuous production of large-volume pharmaceutical compounds. It also illustrates a crystallization process that is inherently unfeasible by any method other than continuous operation. When carried out using fluidized bed crystallizers, ultrasonic crystal disraption is used, even at factory scale, to maintain a steady-state population of seed particles in this all-growth system. 

The isolation of terephthalic acid in a pure state from the products of oxidation is not easy because it cannot be distilled, nor is crystallization practical, on account of its insolubility in most solvents. It has, therefore, been found easier to esterify the crude yield after oxidation with methanol and purify the resultant dimethyl terephthalate by distillation and recrystallization. 

Bismuth fluoride (Bip3) is found in the form of white or gray dimorphic crystals, practically insoluble in water, but soluble in concentrated hydrofluoric acid with the formation of complexes. It volatilizes slowly with partial decomposition at high temperatures. Bismuth bromide (BiBr3) is found as yellowish crystals, soluble in aqueous alkali halides and dilute hydrochloric acid, but practically insoluble in alcohols. It is readily decomposed by water to give bismuth oxybromide BiOBr. Bismuth iodide (BiU) is a black fine crystalline solid with a metallic sheen, practically insoluble in water, but slowly decomposes in hot water. It dissolves in liquid ammonia, aqueous potassium iodide, hydriodic acid and hydrochloric acid, but not so much (ca. 3.5%) in absolute ethanol. When exposed to air for a prolonged time, it is slowly converted to bismuth iodate (Bi(I03)3). Bismuth fluoride of 98% purity costs US 24.30 ( 6200) per 25 g, bromide of 98% purity US 24.90 ( 6200), and iodide of 99% US 34.50 ( 8600). These halides are all corrosive and moisture-sensitive. 

Crystals. Practically tasteless, nip 194°. One gram dissolves in 3000 ml cold water, in 210 ntl boiling water. One part dissolves in 10 paris ale, 75 parts ether. Decolorizes KMri04 solns. 

Blackish-brown, orthorhombic, bipyramidal crystals. Practically insol in water, ethyl acetate sol in HNOs, HCl. 

Crystals. Practically inso] in water, ammonia, alkali hydroxides so] in hot alcohol, dil acids. 

Green to blue amorphous powder Or dark-green mono-clinic crystals. Practically tnsol in water, alcohol sol in dil acids, ammonia. 

Green crystals. Practically insol in cold water slightly sol in hot water sol m alcohol, glacial acetic acid, in alkali carbonates wirh reddish color, in coned HCl with a blue color which becomes red upon diluting with water-USE As a dye in alkali carbonate soln as a reagent for lead with which it forms a deep violet color-... 

Prismatic crystals, practically tasteless, mp 145-147. Practically insol in water One gram dissolves in about 3 liters of water. Sol in methanol, hot ethanol, ether, chloroform, acetone, benzene, aq solns nf alkali hydroxides, but not carbonates. 

Pamoate, C H ClN.Og, Equipose, Masmoran, Paxistil, Vistaril Pamoate. Crystals. Practically insol in water. 

Hydriodide, ClsHlsN03,HI, crystals. Practically insol in water. 

PHYSICAL PROPERTIES bright yellow powder or crystals practically odorless soluble in most organic solvents insoluble in water MP (108-110°C, 226.4 - 230°F) BP (decomposes) DN/SG (1.06) VD (data not available) VP (very low). 

In crystallization practice, however, it is usual to take the heat of crystallization as being equal in magnitude, but opposite in sign, to the heat of solution at infinite dilution, since this is the quantity most commonly available... 

If the concentration of a solution can be measured at a given temperature, and the corresponding equilibrium saturation concentration is known, then it is a simple matter to calculate the supersaturation (equations 3.67-3.69). Just as there are many methods of measuring concentration (section 3.9.2) so there are also many ways of measuring supersaturation, but not all of these are readily applicable to industrial crystallization practice. 

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