Crystals production

Since zeolites are metastable crystallization products tliey are subject to Ostwald s mle which states tliat metastable phases are initially foniied and gradually transfonii into tlie tlieniiodynaniically most stable product. The least stable zeolitic phase (tliat witli tlie lowest framework density) is tlierefore foniied first and consumed with furtlier syntliesis time at tlie expense of a more stable phase due to a continuous crystallization/redissolution equilibrium. 

This procedure is used to separate crystallized product from solvent or to remove crap and solids from a liquid. Figure 8 shows the proper apparatus to use. The collecting flask is called a side arm flask and to that extended nipple (tee heel) is attached a vacuum source. The thing that is shoved through the rubber stopper is called a Buchner funnel and is usually made of white porcelain or, preferably, PP. The Buchner funnel, when viewed from above, can be seen to have lots of pin holes in the bottom surface of its reservoir. Over this surface is layered a single sheet of rounded filter paper or paper towel. 

Seemingly the presence of an aromatic substituent in the 4-position of the selenazole ring is necessary for obtaining well-crystallized products compounds with an alkyl group in the 4-position are amorphous and quite difficult to obtain as crystals. 

Essentially all the ammonium sulfate fertilizer used in the United States is by-product material. By-product from the acid scmbbing of coke oven gas is one source. A larger source is as by-product ammonium sulfate solution from the production of caprolactam (qv) and acrylonitrile, (qv) which are synthetic fiber intermediates. A third but lesser source is from the ammoniation of spent sulfuric acid from other processes. In the recovery of by-product crystals from each of these sources, the crystallization usually is carried out in steam-heated sa turator—crystallizers. Characteristically, crystallizer product is of a particle size about 90% finer than 16 mesh (ca 1 mm dia), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable, however, as a feed material to mixed fertilizer granulation plants, and this is the main fertilizer outlet for by-product ammonium sulfate. 

Several features of the hypothetical system in Eigure 2 can be used to illustrate proper selection of crystallizer operating conditions and limitations placed on the operation by system properties. Suppose a saturated solution at temperature is fed to a crystallizer operating at temperature T. Because the feed is saturated, the weight fraction of in the feed is given as shown in Eigure 2. The maximum crystal production rate from such a process depends on the value of and is given by... 

Mass and Energy Balances. The formulation of mass and energy balances follows procedures outlined ia many basic texts (2). The use of solubihties to calculate crystal production rates from a cooling crystallizer was demonstrated by the discussion of equations 1 and 2. Subsequent to determining the yield, the rate at which heat must be removed from such a crystallizer can be calculated from an energy balance ... 

Fig. 17. Effect of classified-product removal on population densities within a crystallizer and in the crystallizer product.

TABLE 18-6 Growth Rates and Kinetic Equations for Some Industrial Crystallized Products... 

For large-scale continuous crystal production, several alternate types of crystallizer vessel are available (Figure 3.3). 

Alternative microcrystallizer configurations are being developed that seek to avoid the mixing problems asociated with conventional agitated vessels and offer the potential of consistent precipitation of high quality crystal products. 

Thus, methods are now becoming available such that process systems can be designed to manufacture crystal products of desired chemical and physical properties and characteristics under optimal conditions. In this chapter, the essential features of methods for the analysis of particulate crystal formation and subsequent solid-liquid separation operations discussed in Chapters 3 and 4 will be recapitulated. The interaction between crystallization and downstream processing will be illustrated by practical examples and problems highlighted. Procedures for industrial crystallization process analysis, synthesis and optimization will then be considered and aspects of process simulation, control and sustainable manufacture reviewed. 

Figure 9.6 EJfect of process system on crystal product characteristics after Bennett, 1962)...

Hostomsky, J., 1987. Particle size distribution of agglomerated crystal product from a continuous crystallizer. Collection of Czechoslovakian Chemical Communications, 52, 1186-1197. 

Three liters of 5% formaldehyde solution (2,625 cc water and 375 cc 40% formalin) containing 50 g of nitrofurantoin is refluxed for about 5 minutes, then filtered hot and cooled. The crystallized product is filtered and washed with 1% formaldehyde solution. It is air dried and then further dried at 65°C. There is obtained 33 g of 3-hydroxymethyl-1 -(5-nitrofur-furylideneamino) hydantoin. 

The 3-(methylhydroxyethylamino)-2-hydroxypropyltheophylline-nicotinate separates, while still being warm, in the form of shiny, thin, small sheets. After cooling, the crystallization product is sucked off from the mother liquor and recrystallized from 85% isopropyl alcohol. 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Hemozoin, also known as malaria pigment, is, in teims of its chemical composition, identical to (3-hematin. Hemozoin is formed as a crystallization product of heme under the acidic conditions present in the food vacuole of malarial parasites. In the crystal, the heme molecules are linked into dimers through reciprocal iron-carboxylate bonds to one of the propionate side chains of each porphyrin. The dimers form chains linked by hydrogen bonds. 

The Ru(II)-BINAP complex,2 [Et2NH2]+[Ru2Cl5(BINAP)2]-,3 is prepared as a toluene solvate in nearly pure form by this procedure. Typical crystallized product shows no other signals in the phosphorus NMR and gives a good combustion analysis. The material is quite stable and can be routinely handled in air. Storage under nitrogen will extend its shelf life, however. 

Attempts to prepare related hpp complexes of tantalum were only partially successful. Reaction of 2 equivalents of either (hpplSiMes or in situ generated Li[hpp] with Tads afforded a solid that analyzed correctly for the compound (hpp)2TaCl3. X-ray structural analysis of the crystallized product identified the coordination isomer [Ta(hpp)4][TaCl6], with a distorted dodecahedral cation and a regular octahedral anion (Figure 28). °... 

Circulating liquor crystallisers and circulating magma crystallisers are used for the large-scale production of a wide range of crystal products. 

In addition to crystal size and size distribution, the shape of the crystal product might also be important. The term crystal habit is used to describe the development of faces of the crystal. For example, sodium chloride crystallizes from aqueous solution with cubic faces. On the other hand, if sodium chloride is crystallized from an aqueous solution... 

The crystallized product must be dried at 110° for one to one and a half hours otherwise benzene, possibly benzene of crystallization, will be retained by the solid indefinitely. 

During the secondary drying, the water will be removed which interacts with the solids such that the water cannot crystallize. The water can be bound to the surface of crystals in a crystallized product, or can be included in amorphous product. Pikal et al. [1.59] have listed four statements concerning secondary drying ... 

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