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Crystallization is commonly used for separation and purification of of organic and inorganic chemicals. Often used as an alternative to distillation, it is more energy efficient and gentler for heat-sensitive products. Interest in the technology is growing with the demand for higher-quality products with better flowability, particle-size distribution, morphology and shape, as well as for new products, such as nanoparticles and time-release formulations.
For example, processors are looking at melt crystallization, a novel alternative to conventional crystallization processes, as a way to boost product purity without increasing costs, says Wayne Genck, president of Genck International (Richton Park, HI.). And, increasingly, melt crystallization is the only choice for processing pharmaceuticals, fats and oils, foods and beverages, and fine chemicals because it avoids or minimizes the use of solvents (CE, January 2000, pp. 30-33).
Melt crystallization is also used in petrochemical plants and petroleum refineries, to crystallize, for example, wax from lubricants. Armstrong Engineering Associates, (West Chester, Pa.) participates in this segment with scraped-surface heat-exchanger-crystallizers for solution and melt processing in capacities ranging from 5,000 to 550 million tons/yr. Joseph Armstrong, one of the company's owners, says it does a lot work with fats and oil, and is interested in para-xylene (PX), a precursor to polyethylene terephthalate (PET). Within the next 6-8 months, the company will extend its capabilities for organic chemicals when it introduces what Armstrong describes as "something between a product enhancement and a new product."
BEFS Prokem (Mulhouse, France) has recently completed pilot tests of a new design of its static crystallizers for the purification of soft materials, like paraffins, fatty acids and alcohols. Normally such compounds are purified by crystallization from solvents, often using a high ratio of solvent to product. This not only leads to the inclusion of an additional impurity, but the cost of solvent recovery can be more than the production plant, says Andor Papp, marketing director at BEFS.
The company has overcome the problem of the soft material slipping down by sweating - the most important purification step in melt crystallization - by using specially designed internals. The new design has been tested at the pilot scale (200-kg batches), reducing the oil content of the product to...