Solids crystallization

Parallel-feed operation is illustrated in Fig. 3.12c. Fresh feed is added to each stage, and product is withdrawn from each stage. The vapor from each stage is still used to heat the next stage. This arrangement is used mainly when the feed is almost saturated, particularly when solid crystals are the product. 

The word is also used to denote a unit in a solid crystal of an electrovalent compound such as NaCl in which each Na is electrically attracted by the surrounding six Cl" and each Cl" is electrically attracted by the surrounding six Na. The structure of such crystals is termed ionic to indicate that the crystal is not an aggregate of independent molecules. 

Antimony Trioxide. Antimony(III) oxide (antimony sesquioxide) [1309-64-4] Sb203, is dimorphic, existing in an orthorhombic modification valentinite [1317-98-2] is colorless (sp gr 5.67) and exists in a cubic form and senarmontite [12412-52-17, Sb O, is also colorless (sp gr 5.2). The cubic modification is stable at temperatures below 570°C and consists of discrete Sb O molecules. The molecule is similar to that of P40 and As O and consists of a bowed tetrahedron having antimony atoms at each corner united by oxygen atoms lying in front of the edges. This solid crystallizes in a diamond lattice with an Sb O molecule at each carbon position. 

Totally enclosed impellers are designed with the blades between two support shrouds or plates. These impellers are for totally clean liquids because tolerances are tight at the eye and the housing, and there is no room for suspended solids, crystals or sediment, see Figure 6-18. 

The slurry seal with the evacuation line is designed to handle/evacuate suspended solids, crystals, sediment, and dirt in the pumpage. The seal s springs are located out of the fluid. The o-rings move and rub across a clean surface as the faces wear. The o-rings are placed away from the heat generated by the faces. 

Crystallization is an important separation proeess that purifies fluids by forming solids. Crystallization is also a partiele formation proeess by whieh moleeules in solution or vapour are transformed into a solid phase of regular lattiee strueture, whieh is refleeted on the external faees. Crystallization may be further deseribed as a self-assembly moleeular building proeess. Crystallo-graphie and moleeular faetors are thus very important in affeeting the shape (habit), purity and strueture of erystals, as eonsidered in detail by, for example, Mullin (2001) and Myerson (1999). In this ehapter the internal erystal strueture and external partiele eharaeteristies of size and shape are eonsidered, whieh are important indieators of produet quality and ean affeet downstream proeessing, sueh as solid-liquid separation markedly. Larger partieles separate out from fluids more quiekly than fines and are less prone to dust formation whilst smaller partieles dissolve more rapidly. 

The change in dissolved solute between inlet and outlet of the vessel is matched by the gain in solid crystal mass. Thus, on a unit volume basis... 

Molecular sieve beds do not suffer any chemical degradation and can be regenerated indefinitely. Care should be taken to minimize mechanical damage to the solid crystals as this may decrease the bed s effectivenes . The main causes of mechanical damage are sudden pressure and/or temperature changes when switching from absorption to regeneration cycles. 

Erist chen, n. Uttle crystal. Kristall-chloroform, n. chloroform of crystallization. -druse, /. crystal druse, crystal cluster. -ebene, /. crystal plane, crystal face, -ecke,/. (solid) crystal angle, kristallelektrisch. a. piezoelectric, kristallen, a. crystalline. 

C) Preparation of Doxapram Hydrochloride [3,3-Diphenyl-1-Ethyl-4-(2-Morpholino-Ethylj-2-Pyrrolidinone Hydrochloride Monohydrate] A solution of 25 grams (0.076 mol) of 4-(2-chloroethyl)-3,3-diphenyl-1-ethyl-2-pyrrolidinone and 13.3 grams (0.153 mol) of morpholine in 500 ml of absolute ethanol was heated at 95°-120°C for 21 hours in a closed system and concentrated in vacuo. The residue was dissolved in 3(X) ml of two normal hydrochloric acid and extracted with 150 ml of ethyl acetate. A solid crystallized (13 g) during the extraction and was removed by filtration. MP 217°-219°C. The acid extracts were made basic with sodium hydroxide and extracted with ether, and the ether solution was concentrated in vacuo and the residue was suspended in six normal hydrochloric acid. Additional crystalline product formed and was recrystallized from two normal hydrochloric acid. Yield, 10 grams MP 217°-219°C. Total yield, 23 grams (70%). 

The isomer 2,4 -dioxy-3,3 -dichloro-diphenyl-(2-pyridyl)-methane is removed by thoroughly washing with 430 ml of 95°C boiling alcohol, obtaining 167 g of isomer-free product (yield 69%). The 3,3 -dichloro-4,4 -dioxy-diphenyl-(2-pyridyl)-methane is a white solid, crystallizing from 95% alcohol MP 212° to 215°C. 

The organic fractions are combined and washed successively with N,N-dimethyl-1,3-propane-diamine, dilute hydrochloric acid, saturated sodium bicarbonate solution and saturated sodium chloride solution. The organic fraction is dried over anhydrous magnesium sulfate. The solvent is then evaporated off. Upon trituration of the residue with methanol, a solid crystallizes, 5-(p-toluovl)-1 -methvlpvrrole-2-acetonitrile, which is removed by filtration and purified by recrystallization from benzene. 

To 5 grams of N,N -bis[1-methyi-3-(2,2,6-trimethylcyclohexyl)propyl]-N,N -dimethyl-1,6-hexanediamine dissolved in 100 ml of methanol, at 4°C, were added 100 ml methanol containing 10 grams of methyl chloride. The solution was heated in a closed vessel at 60°C for 15 hours. The colorless solution was concentrated and the resulting white solid crystallized from ethanol-acetonitrile-ether to obtain N,N -bis[1-methyl-3-(2,2,6-trimethylcyclo-hexyOpropyl] -N,N -dimethyl-1,6-hexanediamine bis(methochloride) hemihydrate. 

In batch operations, mixing takes place until a desired composition or concentration of chemical products or solids/crystals is achieved. For continuous operation, the feed, intermediate, and exit streams will not necessarily be of the same composition, but the objective is for the end/exit stream to be of constant composition as a result of the blending, mixing, chemical reaction, solids suspension, gas dispension, or other operations of the process. Perfect mixing is rarely totally achieved, but represents the instantaneous conversion of the feed to the final bulk and exit composition (see Figure 5-26). 

We have pointed out above that the volume of the solid crystal is not a useful basis for comparing different salts in the same solvent. It is, however, quite satisfactory, when we are comparing the apparent volumes of the same salt in different solvents, as is being done in Fig. 59. 

Illustration.—If we have a saturated solution of a salt in contact with solid crystals of salt, the whole is in equilibrium at an assigned temperature and pressure. If thermodynamic potentials of the solution and crystals respectively, and if we suppose a further very small mass of salt, 8m, to pass into solution, there will be ... 

Liquid crystals have a degree of order characteristic of solid crystals, but they can flow like viscous liquids. They are mesophases, intermediate between solids and liquids their properties can be modified by electric fields and changes in temperature. 

Rundle and co-worker performed x-ray diffraction studies on solid phenylmag-nesium bromide dietherate and on ethylmagnesium bromide dietherate, which they obtained by cooling ordinary ethereal Grignard solutions until the solids crystallized. They found that the structures were monomeric ... 

Sugar dissolving in coffee involves dispersal of molecules. Sugar molecules are distributed more widely in solution than they are in the solid crystal. 

In 1895, Rdntgen experimentally discovered "x-rays" and produced the first picture of the bones of the human hand. This was followed by work ty von Laue in 1912 who showed that solid crystals could act as diffraction gratings to form symmetrical patterns of "dots" whose arrangement depended upon how the atoms were arranged in the solid. It was soon... 

Between 1865 and 1887, Dmitri 1. Mendeleev developed the chemical theory of solutions. According to this theory, the dissolution process is the chemical interaction between the solutes and the solvent. Upon dissolution of salts, dissolved hydrates are formed in the aqueous solution which are analogous to the solid crystal hydrates. In 1889, Mendeleev criticized Arrhenius s theory of electrolytic dissociation. Arrhenius, in turn, did not accept the idea that hydrates exist in solutions. 

R = reflux ratio, g reflux/g product Tp = product temperature, °C Tp = saturated-feed temperature, °C Cp = specific heat of solid crystals, cal/(g °c) and X = heat of fusion, cal/g. 

Although the crystals are likely to be pure, the mass of crystals will retain some liquid when the solid crystals are separated from the residual liquid. If the adhering liquid is dried on the crystals, this will contaminate the product. In practice, the crystals will be separated from the residual liquid by filtration or centrifuging. Large uniform crystals separated from a low-viscosity liquid will retain the smallest proportion of liquid. Nonuniform crystals separated from a viscous liquid will retain a higher proportion of liquid. It is common practice to wash the crystals in the filter or centrifuge. This might be with fresh solvent, or in the case of melt crystallization, with a portion of melted product. 

Batch crystallization. Crystallization is extremely common in the production of fine and specialty chemicals. Many chemical products are in the form of solid crystals. Also, crystallization has the advantage that it can produce a product with a high purity and can be more effective than distillation from the separation of heat-sensitive materials. Crystallization has already been discussed in Chapter 10 and has two main steps. Firstly the solute to be crystallized is dissolved in a suitable solvent, unless it is already dissolved, for example, solute dissolved in a solvent from a previous a reaction step. Secondly, the solid is then deposited in the form of crystals from the solution by cooling, evaporation and so on. 

Crystallization is extremely common in the production of fine and specialty chemicals. Many chemical products are in the form of solid crystals. Also, crystallization has the advantage that it can produce a product with a high purity and can be more effective than distillation from the separation of heat-sensitive materials. Batch crystallization is ... 

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