Method of producing perborate

Details Method of producing perborate Method of producing perborate

1991-12-09

1994-02-01

Theisen, Mary Lynn

Plastic and nonmetallic article shaping or treating: processes

Forming articles by uniting randomly associated particles

With subsequent cutting, grooving, breaking, or comminuting

252 99, 264141, 423277, C01B 1512

Patent

active

052830241

DESCRIPTION:

BRIEF SUMMARY
The present invention is relative to the production of sodium perborate tetrahydrate and its further processing to monohydrate.
Sodium perborate has found many applications on account of its ability to be reliably handled and on account of its chemical stability as oxidation agent, e.g. as a mild disinfection agent, but especially as a bleaching agent, especially in the washing of textiles Sodium perborate, commonly designated only as perborate, has long been a component of most of the powdery household detergents in Europe The most significant ones in a technical sense in this connection are primarily the so-called sodium perborate tetrahydrate and the so-called sodium perborate monohydrate, which are actually, according to current knowledge, the hexahydrate and the anhydrous form of ring-shaped disodium diperoxodiborate. However, the customary designations of perborate tetrahydrate (empirical formula NaBO.sub.3 .multidot.4 H.sub.2 O) and perborate monohydrate (NaBO.sub.3 .multidot.H.sub.2 O) will continue to be used in the following. The characterization about the available oxygen content which is customary in practice will also be valid in the following connection In accordance therewith, all perborates are designated as sodium perborate monohydrate which contain more than 15% by weight available oxygen (theoretical value for NaBO.sub.3 .multidot.H.sub.2 O:16.0% by weight AO).
When producing perborates, one generally begins with sodium borate solutions and obtains the tetrahydrate therefrom, after the addition of hydrogen peroxide, by means of cooling in crystalline form. The monohydrate is produced therefrom by means of dewatering, preferably with warm air in a fluid bed.
A great number of methodological variations have been suggested with the goal of improving the yield and the quality of perborates; however, only a few of them have proven themselves in practice. A problem which has not yet been solved to general satisfaction is the abrasion stability of perborate monohydrate. Very porous and readily decomposing grains form on account of the rapid exiting of water in the customary drying methods, with the result that a large part of the drying product accumulates as dust. However, abrasion-resistant material is of particular interest for use in detergents, which material should also correspond in its grain size approximately to that of a detergent, that is, approximately 0.3 to 2 mm.
None of the methods previously suggested for the production of an especially abrasion-stable monohydrate is free of disadvantages. Thus, the work is performed with especially high air temperatures of 180.degree. to 210.degree. C. in a fluid bed in the method of DE 19 30 286. However, such high temperatures are also problematic for thermally relatively resistant per compounds like the perborates, and, in addition, the use of such high temperatures is expensive from a technical heating standpoint In the method according to DE 20 40 507, the monohydrate is moistened on the surface after the customary production once again, preferably in a revolving tube, and redried. The method thus requires two additional method stages. The methods according to DE 22 58 319 and DE 24 47 780 dry the tetrahydrate at high relative air moistures. However, this causes the drying to last correspondingly longer and requires larger apparatuses and more energy. Finally, in the method according to EP 194,952, the temperature of the fluid bed is regulated in such a manner during the drying that it is above the melting temperature of the tetrahydrate. There is also the danger here of a chemical decomposition of the perborate. All the above-named methods for improving the abrasion stability of perborate monohydrate scale [become encrusted] in the drying stage of tetrahydrate. In most instances, a fine-grained component which was already present in the tetrahydrate therefore also remains in the monohydrate and must be removed from it if necessary.
On the other hand, it was also determined that an abrasion-stable monohydrate can be obtained in a simpler m

REFERENCES:
patent: 2900668 (1959-08-01), Hubner et al.
patent: 3227790 (1966-01-01), Bretschneider et al.
patent: 4405486 (1983-09-01), Eoga
patent: 4904458 (1990-02-01), Dugua et al.

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