Chemistry of inorganic compounds – Nitrogen or compound thereof – Carbon containing
Reexamination Certificate
2000-03-13
2001-09-18
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Carbon containing
C423S275000, C423S383000
Reexamination Certificate
active
06290925
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 199 14 616.0, filed Mar. 31, 1999, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to flowable cyanuric chloride which contains a hydrophilic silica as flow auxiliary, which cyanuric chloride exhibits an improved range of properties in comparison with prior art cyanuric chloride containing a pyrogenic silica. This invention furthermore relates to a process for the production of the improved flowable cyanuric chloride and to the use thereof.
BACKGROUND OF THE INVENTION
It is known that solid cyanuric chloride readily agglomerates when in finely divided form. In order to eliminate the consequent problems during storage and further processing, DE-AS 11 34 999 teaches the addition of flow auxiliaries to the finely divided cyanuric chloride, selected from the range of finely divided silicon dioxide, titanium dioxide, aluminium oxide, aluminium silicate and calcium silicate, in a quantity of 0.3 to 3 wt. %. Only one pyrogenically produced silica, namely AEROSIL® (Degussa-Hüls AG, Germany) is mentioned among the silicas stated in this document as flow auxiliaries. No suggestion is made to use silicas of other origins.
As is disclosed by DE-AS 28 39 384, using a hydrophobic pyrogenic or hydrophobic precipitated silica makes it possible not only to improve the flowability of cyanuric chloride, but also to counteract the unwanted hydrolysis of cyanuric chloride which occurs during storage and in-plant handling. Hydrolysis products formed during the storage and conversion of cyanuric chloride reduce the quality and/or yield of the reaction products.
In the process according to EP-A 0 416 584, an attempt was made to improve the flowability of solid cyanuric chloride by subjecting the cyanuric chloride to shear forces in a kneader or mixer while heating it to a temperature below the melting point. However, it was found (see Comparative Examples) that the reactivity of such products is reduced. Due to the inadequate storage stability of products treated in this manner, this process has not become established in practice, such that most commercial products still contain a hydrophilic pyrogenic silica or a hydrophobic pyrogenic or precipitated silica as a flow auxiliary.
A substantial disadvantage not only of all hydrophilic pyrogenic silicas as well as hydrophobic pyrogenic silicas but also of hydrophobic precipitated silicas is the high cost thereof, due to the production process. Specialist manufacturers are accordingly interested in lower cost alternatives, wherein these alternatives must exhibit an at least equivalent range of properties.
SUMMARY OF THE INVENTION
The object of the present invention is accordingly to provide a cyanuric chloride obtainable in an economic manner having a range of properties at least equal to that of current commercial products, but preferably surpassing current products in one respect or another. The range of properties substantially includes:
(i) a maximally high bulk density
(ii) good flowability corresponding to a rating of less than or equal to 3, preferably less than or equal to 2, and
(iii) maximally high reactivity, wherein this property should, where possible, not be impaired in comparison with untreated cyanuric chloride, but should preferably even be improved.
This object is achieved by a flowable cyanuric chloride having a flowability rating of less than or equal to 3, containing a hydrophilic silica as flow auxiliary, which cyanuric chloride is characterized in that the hydrophilic silica is a precipitated silica or silica gel having an average agglomerate diameter of less than or equal to 15 &mgr;m, determined using a Coulter Counter. Precipitated silicas are preferred as the flow auxiliary.
Preferred products have an average agglomerate diameter of less than 7 &mgr;m, preferably of less than 5 &mgr;m. It has furthermore been established that in particular hydrophilic precipitated silicas exhibiting DBP absorption of below 270 g/100 g provide a particularly good range of properties of the flowable cyanuric chloride. Precipitated silicas and silica gels exhibit various structures as a result of the production method used. The flow auxiliaries preferably comprise ground precipitated silicas, in particular steam or air jet ground precipitated silicas having an agglomerate diameter of less than 5 &mgr;m and DBP absorption in the range from 200 to 260 g/100 g. The precipitated silicas and silica gels in question conventionally comprise products having a BET surface area of at least 100 m
2
/g; products having a BET surface area in the range from 100 to 500 m
2
/g, are preferably used and a BET surface area from 150 to 300 m
2
/g, is particularly preferably used.
One particularly important criterion of the range of properties of the flowable cyanuric chloride is the bulk density achieved when using the flow auxiliary and under defined mixing conditions. It is of particular interest to achieve a maximally high bulk density with regard to the packaging volume of the flowable cyanuric chloride. Absolute bulk density is dependent not only upon the flow auxiliary content and mixing conditions, but also, as may be understood, upon the grain size distribution of the cyanuric chloride used. It has been found that a higher bulk density may be achieved when using flow auxiliaries according to the invention than when using a hydrophilic pyrogenic silica such as AEROSIL® 200. At an identical usage rate and under identical mixing conditions, the bulk density of a preferred flowable cyanuric chloride is comparable with that which is achieved using a hydrophobic precipitated silica, but surprisingly is higher than that obtainable using a hydrophilic pyrogenic silica.
Another criterion of the range of properties is flowability: the ratings are obtained from the results of using standardized flow funnels having outlet diameters in the range between 2.5 and 18 mm. A product which flows without stoppage from a 25 funnel having an outlet diameter of 8 mm or 5 mm receives a rating of 3 or 2, respectively. Products having a rating of 2 or less than 2 are preferred. Precipitated silicas and silica gels having an agglomerate diameter of greater than 15 &mgr;m do not yield any satisfactory flowability ratings.
The reactivity of the flowable cyanuric chloride constitutes the third criterion of the required range of properties. Reactivity is determined by hydrolyzing cyanuric chloride in an aqueous medium under defined conditions and measuring the time taken to reach a pH value of 7. A maximally high reactivity is desired, i.e. a short time until a pH value of 7 is achieved. While reactivity is distinctly reduced in comparison with untreated cyanuric chloride when hydrophobic precipitated or pyrogenic silica is used, the reactivity of flowable cyanuric chloride according to the invention substantially matches that of untreated cyanuric chloride and the reactivity of products according to the invention preferably exceeds that of the untreated cyanuric chloride. The reactivity of products according to the invention is within the range of that which is obtainable using a hydrophilic pyrogenic silica, but preferred products have a still higher reactivity.
One unexpected advantage of products according to the invention is that these products exhibit an extraordinarily low hydrolyzate content. The hydrolyzate content comprises toluene-insoluble products which are formed by hydrolysis of the cyanuric chloride. The hydrolyzate content is determined after a specified period of storage after production of the flowable cyanuric chloride. It has been found that the hydrolyzate content found when using the preferred precipitated silicas and silica gels is surprisingly substantially lower than that obtained when using hydrophobic silicas. This is surprising because hydrophobic silicas have hitherto been used specifically to provide an effective shell around the cyanuric chloride particles which are sensitive to hydrolysis and so to hinder hydrolysis.
Leutner Josef
Schmidt Manfred
Degussa - AG
Griffin Steven P.
Medina Maribel
Pillsbury & Winthrop LLP
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