Process for the production of cyanuric chloride moldings

Details Process for the production of cyanuric chloride moldings Process for the production of cyanuric chloride moldings

2000-06-15

2001-04-24

Silbaugh, Jan H. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With severing, removing material from preform mechanically,...

To form particulate product

C264S144000, C264S157000, C264S212000, C264S330000, C264S299000, C264S316000

Reexamination Certificate

active

06221294

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 196 42 449.6, filed Oct. 15, 1996, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a new product form of solid cyanuric chloride, namely moldings, especially those in tablet or flake form, and a process for producing cyanuric chloride moldings, especially tablets and flakes.
BACKGROUND OF THE INVENTION
It is known to convert cyanuric chloride obtained in the form of vapor by trimerization of cyanogen chloride directly or via liquid cyanuric chloride into solid cyanuric chloride in finely particulate form:
The deposition of pulverulent cyanuric chloride by desublimation of cyanuric chloride in vapor form can be carried out in externally cooled chambers or by introducing cyanuric chloride vapor together with an inert gas and/or an inert cooling liquid vaporizing during the deposition process, into a deposition chamber—see for example DE-PS 12 66 308 and U.S. Pat. No. 4,591,493. In the preparation of finely particulate cyanuric chloride from liquid cyanuric chloride the latter is injected through a nozzle into a deposition chamber and cooled with cycled inert cooling gases or by indirect cooling in the deposition chamber until the spray droplets deposit in crystalline form—see for example DE 28 43 379. A common feature of these processes is a considerable technical expenditure on deposition chambers and devices for recycling and purifying the process gases and waste gases.
In the previously evaluated processes as well as processes based on the same principles, cyanuric chloride is always obtained in finely particulate form, in general having a maximum grain diameter of substantially less than 250 &mgr;m. Such finely particulate products are of course advantageous as regards their high reactivity, but have a number of disadvantages that make a different product form desirable for many purposes.
The handling, including conveyance, storage and metering, of finely particulate cyanuric chloride presents special problems since finely particulate substances usually lead to the formation of dusts that have corrosive and irritant properties and require suction purification equipment. In addition cyanuric chloride is sensitive to hydrolysis, and the resultant hydrolysis products can contaminate not only the cyanuric chloride itself but also following product produced therefrom. Finely particulate cyanuric chloride is particularly susceptible to hydrolysis on account of its large surface area. As a result solid deposits are also readily formed in the dust removal equipment and dust-conveying lines. Technically complicated and costly measures and/or equipment are necessary in order to avoid and eliminate resultant malfunctions.
A further disadvantage of finely particulate cyanuric chloride is the unsatisfactory flowability. Although the latter can admittedly be improved by adding flow auxiliaries, for example silicic acids, nevertheless the flow auxiliary reduces the product purity of the cyanuric chloride and possibly also of products prepared therefrom. According to EP-A 0 416 584 the flowability of solid cyanuric chloride prepared by desublimation or spray crystallization can also be improved without adding a flow auxiliary by a shear treatment of the cyanuric chloride in a kneader or mixer, especially at 60 to 120° C.; the finely pulverulent nature of the cyanuric chloride is not however affected by this process, for the mean grain size of typical embodiments is in the range from about 10 to 40 &mgr;m.
As well as the finely particulate form, cyanuric chloride is also commercially available in liquid form. The preparation of cyanuric chloride in liquid form is known for example from DE-PS 23 32 636. The liquid cyanuric chloride product form requires however storage and transporting vessels and containers that can be heated above the melting point of cyanuric chloride. Although such equipment is economical for users having a large and regular demand for cyanuric chloride, this is not the case however for users having a small and/or irregular demand for cyanuric chloride.
SUMMARY OF THE INVENTION
The object of the present invention is accordingly to provide a new solid product form for cyanuric chloride that exhibits the disadvantages of finely particulate cyanuric chloride at least to a considerably lesser extent. In particular the new product form should be easier to handle in order to reduce operational malfunctions and/or health and work safety problems.
This object is achieved by providing cyanuric chloride moldings, especially tablets and flakes. Such moldings conveniently have a thickness in the range from 0.5 to 3 mm, though thicker or thinner moldings are not excluded. Flakes are preferably between about 0.5 and 2 mm thick and tablets between 1 and 3 mm thick. The diameter of ellipsoidal tablets is preferably in the range from 2 to 10 mm, especially 3 to 6 mm. Flakes include flat moldings having the aforementioned thickness, roughly strip-shaped flakes having a width of between 5 and 10 mm and a length of between 10 and 50 mm, or irregularly broken flakes of similar size. Preferred moldings are substantially free of pulverulent cyanuric chloride. The term “substantially free” is understood to mean that a small amount of dust, preferably less than 5 wt. %, especially less than 2 wt. %, formed by abrasion of the moldings and/or by cyanuric chloride that has sublimated on the surface of the moldings, is not excluded.
The product form according to the invention can be bagged and removed from drums and containers without any problem, in other words substantially without dust formation. In the conveyance within a production plant there are no longer any deposits and blockages of pipelines that can be eliminated only with a great deal of effort. On account of the smaller surface compared to finely particulate cyanuric chloride, the danger of caking and hydrolysis is substantially reduced. The moldings according to the invention are also characterized by a higher purity compared to pulverulent cyanuric chloride since the hydrolyzate content is lower and flow auxiliaries are unnecessary. Although the disadvantages of finely particulate cyanuric chloride have been known for a long time and a considerable technical effort and expenditure was necessary in order reliably to be able to process the product despite the disadvantages, it was surprising that the moldings according to the invention, especially tablets and flakes, were not considered before now as a suitable product form for cyanuric chloride. A process for producing cyanuric chloride moldings according to the invention, especially tablets and flakes, comprises the droplet or strip-like application of cyanuric chloride in molten form on to a surface, dissipation of the latent heat of melting of the cyanuric chloride by cooling the surface and/or contacting the melt applied to the surface with a cooling gas, and removing the solidified moldings from the surface.
The surface on which the cyanuric chloride melt is applied may be formed in any suitable way. It may comprise a smooth or structured surface, preferably a smooth surface cooled from the rear side. The surface may also be flat or in the form of a corrugated surface. In the case of a stationary arrangement of a flat cooled surface, additional equipment is required in order to remove the moldings from the surface, for example blade-like removal devices. Equipment known per se is used to cool the rear side of the surface, especially spraying the rear side of the surface with a liquid or gaseous medium or causing such a medium to flow thereover. Instead of removing the latent heat of fusion through the surface, it is also possible to remove this by means of a cooling gas inert with respect to cyanuric chloride, for example cooled air or nitrogen, with which the melt applied to the surface is contacted. In the last mentioned embodiment a cooling gas may for example be fed directly on to the surface, or the surface is transported thro

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