Chemistry: physical processes – Physical processes – Crystallization
Patent
1996-03-14
1998-09-22
Straub, Gary P.
Chemistry: physical processes
Physical processes
Crystallization
23313R, 585812, 585813, B01D 902, C07C 714
Patent
active
058108920
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and an apparatus for purifying chemical substances that are initially molten, crystallize out with heat absorption, and after being conveyed through a washing column can be removed as a purified product.
It is a known method in which the crystals are formed, and then washed in to utilize "melt crystallization" to "washing columns" to remove the residual molten substance adhering to the crystals, in order then to obtain purified crystals which can then be melted. The wash columns provided in such melt crystallization (BIWIC 1990--Bremen International Workshop for Industrial Crystallization, Sep. 12-13, 1990 in Bremen) basically operate satisfactorily. Their action is impaired, however, by the fact that they are supplied, for example, with crystalline particles in the form of a crystal slurry from scrape chillers. The size distribution of the crystalline particles produced in the scrape chillers is very broad, and the shape of the particles is not uniform. There are also numerous agglomerates. Separation of the particles is therefore greatly reduced by the residual melt, enriched in contaminants, that adheres to these particles. Because of the nonuniform particle shapes, the washing columns, in which flow occurs around the particles, are overtaxed. Methods for purifying chemical substances have already been disclosed (DE 40 41 669 C1and corresponding to U.S. Pat. No. 5,149,455) in which molten substances were first made into drops and allowed to solidify into tablets. In these known methods, however, the tablets are not washed in washing columns, but rather are subjected to a sweating operation in a hot gas stream; the temperature of the hot gas stream and its flow velocity being matched to the size and properties of the tablets so that the tablets, lying on a permeable conveyor support surface, are subjected to the sweating operation only in the region of that conveyor support surface, so that the melting tablet surfaces drip through the permeable support surfaces and the remaining tablets are carried off perpendicular to the drip direction.
The underlying object of the invention is therefore to propose a method and an apparatus with which the output of washing columns in melt crystallization systems can be improved.
SUMMARY OF THE INVENTION
Proceeding from the consideration that this object can only be achieved if the most uniform possible charging of the washing columns, with reference to the suspension, is provided, the invention consists in the fact that at least a part of the chemical substances is brought, after melting, into the form of monodispersed particles; and that those particles are then used to supply the washing column, together with molten substance or also without it.
With this procedure the washing columns can be supplied with practically monodispersed particles of adjustable and adequate size, which produces the critical advantage that a highly uniform flow around all particles takes place, and thus also an intensive and much more efficient purification. In a development of the invention, it is preferable if the particles are not completely solidified, meaning, for example, as a rule are solid only on the outside but on the inside are not completely consolidated before they are delivered to the washing column. The result is to produce good mass separation for the subsequent purification. Specifically, the desired mass separation or mass exchange that leads to purification takes place while the particles are being moved in the column on the basis of density difference and/or positive conveyance. Washing columns can operate very effectively in this manner and production can be increased, and not only in the conventional sense for separating out the adhering residual molten substance, but also in order to ensure actual separation and the best possible purification and removal of residues.
To implement the new method, an apparatus that is characterized by a granulating device, downstream from a melting apparatus and upstream f
REFERENCES:
patent: 2321117 (1943-01-01), Wilcock
patent: 2884471 (1959-04-01), Leston et al.
patent: 3272893 (1966-09-01), Mogensen
patent: 5013498 (1991-05-01), Froeschke
patent: 5149445 (1992-09-01), Schermutzki et al.
Konig Axel
Ulrich Joachim
Santrade Ltd.
Straub Gary P.
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