Yield from a Crystallization Process

Example 1 Yield from a Crystallization Process A 10,000-lh batch of a 32,5 percent MgS04 solution at 120°F is cooled without appreciable evaporation to 70°F, What weight of MgS04-7H20 crystals will be formed (if it is assumed that the mother liquor leaving is saturated) ... 

Table 10.7 shows that the temperature must be decreased to low values to obtain a reasonable yield from the crystallization process. It should also be noted that cooling to 40°C should be possible against cooling water, and perhaps even down to 30°C. Any cooler than this, and refrigeration of some kind is required. This increases the cost of the cooling significantly. 

Yields and material balances in crystallization. In most of the industrial crystallization processes, the solution (mother liquor) and the solid crystals are in contact for a long enough time to reach equilibrium. Hence, the mother liquor is saturated at the final temperature of the process, and the final concentration of the solute in the solution can be obtained from the solubility curve. The yield of crystals from a crystallization process can then be calculated knowing the initial concentration of solute, the final temperature, and the solubility at this temperature. 

To this point we have been interested in the scattered waves, or X rays from atoms that combine to yield the observed diffraction from a crystal. Because the waves all have the same wavelength, we could ignore frequency in our discussions. In X-ray crystallography, however, we are equally interested in understanding how the waves diffracted by a crystal can be transformed and summed, in a symmetrical process, to produce the electron density in a unit cell. 

In opt mazing any separation process it becomes necessary lo compute the product recovery efficiency of the operation as a fuuciion of design variables. For crystallization operations the ihsoretical maximum product recovery or yield from (he crystallizer is defiand by [ha following general relationship ... 

Some simple laboratory tests can be performed on the product magma from a crystallizer, or on the filtered and laboratory-dried crystals, to make an assessment of the potential downstream handling problems. Each test is capable of yielding a piece of useful information which, when added to that from the others, can give a useful picture of the slurry and crystal characteristics that will enable downstream process problems to be more clearly identified. The tests outlined below are not listed in any order of importance. 

The ratio of reactants had to be controlled very closely to suppress these impurities. Recovery of the acrylamide product from the acid process was the most expensive and difficult part of the process. Large scale production depended on two different methods. If soHd crystalline monomer was desired, the acrylamide sulfate was neutralized with ammonia to yield ammonium sulfate. The acrylamide crystallized on cooling, leaving ammonium sulfate, which had to be disposed of in some way. The second method of purification involved ion exclusion (68), which utilized a sulfonic acid ion-exchange resin and produced a dilute solution of acrylamide in water. A dilute sulfuric acid waste stream was again produced, and, in either case, the waste stream represented a... 

Gumylphenol. -Cumylphenol (PGP) or 4-(1-methyl-l-phenylethyl)phenol is produced by the alkylation of phenol with a-methylstyrene under acid catalysis. a-Methylstyrene is a by-product from the production of phenol via the cumene oxidation process. The principal by-products from the production of 4-cumylphenol result from the dimerization and intramolecular alkylation of a-methylstyrene to yield substituted indanes. 4-Cumylphenol [599-64-4] is purified by either fractional distillation or crystallization from a suitable solvent. Purification by crystallization results in the easy separation of the substituted indanes from the product and yields a soHd material which is packaged in plastic or paper bags (20 kg net weight). Purification of 4-cumylphenol by fractional distillation yields a product which is almost totally free of any dicumylphenol. The molten product resulting from purification by distillation can be flaked to yield a soHd form however, the soHd form of 4-cumylphenol sinters severely over time. PGP is best stored and transported as a molten material. 

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