Rapidly dissolving granular hydrated calcium hypochlorite

A rapidly dissolving granular hydrated calcium hypochlorite product is comprised of hydrated calcium hypochlorite particles having at least 95 percent of the particles within a size range of from about 300 to about 850 microns. The product has a packed bulk density of less than about 1.05 grams per cubic centimeter. When dispersed on the surface of a body of water, such as a swimming pool, at least 3 feet deep, about 70 weight percent or higher of the particles dissolve within one minute.

This invention relates to calcium hypochlorite products used in sanitizing 
applications. More specifically, this invention relates to rapidly 
dissolving particles of hydrated calcium hypochlorite. 
The use of calcium hypochlorite product in the sanitizing and disinfection 
of water bodies is well known. Commercially employed granular hydrated 
calcium hypochlorite particles of the prior art, when dispersed in water, 
for example, by casting or sprinkling the granular particles on the 
surface of a swimming pool, dissolve somewhat slowly and, in addition, 
leave undissolved particles as a residue on the bottom of the pool. This 
residue was found to be undissolved product which, in addition to being 
unsightly, as it dissolves raises the pH in the dissolution zone and can 
result in promoting the precipitation of calcium carbonate, CaCO.sub.3. 
Insoluble CaCO.sub.3 particles require removal, for example, by vacuuming 
the pool or by the filter system. 
Among the properties which affect the solubility of calcium hypochlorite in 
water are the particle size. It has been generally recognized that the 
particle size range is an important factor in the dissolving rate for 
calcium hypochlorite. For example, U.S. Pat. No. 2,693,454, published Nov. 
2, 1954, by E. C. Soule teaches that quick dissolving, quick acting and 
non-sludging bleach mixtures are obtained using, as one ingredient, 
anhydrous calcium hypochlorite having an available chlorine concentration 
upwards of 60 percent and a water content not over about 2 percent in a 
semi-granular form. The particles should pass a 30 mesh screen and remain 
as a 60 mesh screen and not contain more than about 20 percent of fines 
which pass a 100 mesh screen. 
H. L. Robson, in U.S. Pat. No. 2,959,554, Nov. 8, 1960 describes bleach 
solutions containing anhydrous calcium hypochlorite having an available 
chlorine content of 70 to 76 percent in granular form which passes through 
a 30 mesh and is retained on a 70 mesh screen, with the weight percent 
passing a 100 mesh screen should not exceed 10 to 12 percent and the 
weight coarser than 30 mesh should be less than 5 percent. 
The screen analyses for anhydrous calcium hypochlorite containing about 70 
percent available chlorine employed in the bleaching compositions of A. 
Long et al in U.S. Pat. No. 3,639,284 is as follows: 
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Screen Granular 
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On 16 mesh 8 
On 20 mesh 35 
On 30 mesh 33 
On 40 mesh 16 
On 50 mesh 5 
On 70 mesh 1.3 
On 100 mesh -- 
Through 70 mesh 1.7 
Through 100 mesh -- 
Total 100.0 
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The bulk density of the commercial anhydrous calcium hypochlorite granules 
employed by Long et al had a minimum (loose packed) density of about 0.79 
and a maximum (shaken) density of about 0.83. 
Hydrated calcium hypochlorite particles may be produced by known processes 
such as those described in U.S. Pat. No. 3,544,267 issued on Dec. 1, 1970, 
to G. R. Dychdala or U.S. Pat. No. 3,669,894 issued on June 13, 1972, to 
J. P. Faust. 
Particles of solid, hydrated calcium hypochlorite products produced by 
commercial processes contain from about 55 to about 75 percent and 
preferably from about 65 to about 72 percent by weight of calcium 
hypochlorite Ca(OCl).sub.2, and from about 4 to about 10 percent and 
preferably from about 5 to about 8 percent by weight of water, the balance 
being inert materials usually resulting from the process of manufacture, 
e.g. sodium chloride, calcium hydroxide, calcium chloride and calcium 
carbonate. 
The hydrated calcium hypochlorite particles produced in any commercial 
process are then separated to provide particles having a selected size 
range. Any suitable separation method may be used including, for example, 
screening and air classification. In the separation process, the oversized 
particles are reduced in size, for example, by crushing, and the 
undersized particles are compacted. Both the crushed particles and the 
compacted particles are fed back through the separation apparatus along 
with additional particles of hydrated Ca(OCl).sub.2 from the commercial 
process. 
The dissolving rate of the above calcium hypochlorite compositions, 
however, is not sufficiently fast when dispersed on the surface of a water 
body such as a swimming pool to prevent the accumulation of undissolved 
materials on the bottom. 
It is an object of the present invention to provide a granular hydrated 
calcium hypochlorite which dissolves rapidly in water and, when dissolved, 
leaves reduced amounts of undissolved material. 
This and other objects of the invention are accomplished by a rapidly 
dissolving granular hydrated calcium hypochlorite product comprised of 
hydrated calcium hypochlorite particles having at least 95 percent of said 
particles within a size range of from about 300 to about 850 microns. 
More in detail, the novel granular product of the present invention is 
comprised of hydrated calcium hypochlorite particles having a selected 
particle size range which rapidly dissolve when dispersed in a swimming 
pool and substantially reduce the amount of undissolved product on the 
bottom of the pool. The product is obtained by the separation of 
commercially produced hydrated calcium hypochlorite on at least two 
screens. The first screen retains particles greater than about 850 microns 
and passes particles equal to or smaller than about 850, preferably 
smaller than 800 microns. The larger particles are fed to a crushing 
device and the size reduced. Hydrated calcium hypochlorite particles 850 
microns or less in size are passed to a second screen which retains 
particles larger than about 300, preferably larger than about 350 microns. 
Suitably, the particle size range for the granular hydrated calcium 
hypochlorite product of the present invention has at least 95%, preferably 
at least 97%, and more preferably at least 98% of the particles within the 
size range of from about 300 to about 850 microns. The selection of this 
particle size range for hydrated calcium hypochlorite surprisingly results 
in a reduced quantity of undersized particles and a subsequent reduction 
of the amount of hydrated calcium hypochlorite which must be compacted. 
Lowering the amount of compacted hydrated calcium hypochlorite particles 
results in a faster dissolving product. The presence of compacted material 
is reflected by an increase in the packed bulk density. Suitably the 
packed bulk density of the product of the present invention is less than 
about 1.05, for example from about 0.90 to about 1.03, and preferably from 
about 0.95 to about 1.02 grams per cubic centimeter as determined by the 
method of paragraph 4.3.7 in Federal Specification 0-C-114 B, Amendment-2, 
Mar. 9, 1977 entitled Calcium Hypochlorite, Technical. When added to a 
body of water such as a swimming pool, the novel granular hydrated calcium 
hypochlorite product of the present invention dissolves rapidly and 
results in a substantial reduction in the amount of undissolved product 
which reaches the bottom of the pool. For example, when the product of the 
present invention is dispersed on the surface of a water body at least 3 
feet deep, at least about 70 and preferably about 72 percent by weight of 
the particles dissolve within one minute.

The novel product of the present invention is further illustrated by the 
following examples. All parts and percentages are by weight unless 
otherwise specified. 
EXAMPLES 1-4 
Granular hydrated calcium hypochlorite particles having reduced amounts of 
compacted material were passed through a controlled screening process. The 
hydrated calcium hypochlorite products recovered had the following 
composition and particle size range, each example represents the average 
product produced daily for the period of one month. 
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Exam- Exam- Exam- Exam- 
ple 1 ple 2 ple 3 ple 4 
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Average Ca(OCl).sub.2 
Composition 
% Ca(OCl).sub.2 70.33 69.70 69.64 69.09 
Total Alkali 3.59 3.36 3.41 3.60 
% CaCl.sub.2 0.43 0.84 0.70 0.89 
% NaCl 16.75 16.58 15.66 16.65 
% Ca(ClO.sub.3).sub.2 
1.34 1.13 1.25 1.35 
% CaCO.sub.3 2.39 1.93 2.34 2.42 
Packed bulk Density (g/cc) 
1.01 1.03 1.00 1.00 
% Screen Analysis 
Mesh Microns 
+20 &gt;850 0.16 0.17 0.18 0.21 
-20 to +50 
850 to 300 98.55 98.67 98.51 98.08 
-50 &lt;300 1.39 1.19 1.29 1.33 
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Five grams of the granular hydrated calcium hypochlorite product having a 
known available chlorine concentration were placed on the surface of a 
tank of water four feet deep. No circulation or agitation was present 
during the initial dissolution period. The granular hydrated calcium 
hypochlorite particles passed through the water for a period of one 
minute. At the end of this period, any undissolved particles were removed 
from the bottom of the tank. A pump was operated for five minutes to 
provide a homogeneous solution. The available chlorine concentration of 
this solution was then determined and the percentage of the product 
dissolved was calculated. For each example, this procedure was repeated 
daily for one month. The average percent of improved hydrated 
Ca(OCl).sub.2 particles dissolved is given in Table I below. 
COMATIVE EXAMPLES A, B, C, and D 
Commercial granular hydrated calcium hypochlorite particles were produced 
during the same time periods as those of Examples 1-4 having the following 
average compositions and sieve analysis: 
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Comparative 
Comparative 
Comparative 
Comparative 
Example A 
Example B 
Example C 
Example D 
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Average Ca(OCl).sub.2 
Composition 
% Ca(OCl).sub.2 
69.57 69.18 68.94 68.61 
Total Alkali 3.51 3.36 3.38 3.64 
% CaCl.sub.2 0.50 0.59 0.57 0.83 
% NaCl 16.51 16.38 15.87 16.53 
% Ca(ClO.sub.3).sub.2 
1.33 1.13 1.28 1.38 
% CaCO.sub.3 2.31 1.93 2.36 2.43 
Packed bulk Density (g/cc) 
1.08 1.08 1.06 1.08 
% Screen Analysis 
Mesh Microns 
+20 &gt; 850 61.42 63.95 65.88 62.20 
-20 to +50 
850 to 300 
37.02 34.57 33.20 39.45 
-50 &lt;300 1.34 1.53 0.98 1.33 
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Five grams of the commercial granular hydrated calcium hypochlorite of the 
above compositions were dispersed daily in the tank using the exact 
procedure of EXAMPLE 1 for the same time period. The average percent of 
commercial hydrated Ca(OCl).sub.2 particles which dissolved is shown in 
Table I below. 
TABLE I 
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Hydrated Ca(OCl).sub.2 Particles Dissolved 
Example 
% Particles 
Comparative 
% Particles 
No. Dissolved Example Dissolved 
% Difference 
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1 72.6 A 49.1 23.5 
2 74.5 B 50.0 24.5 
3 75.9 C 51.2 24.7 
4 76.8 D 52.3 24.5 
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Using the improved granular hydrated calcium hypochlorite product of the 
present invention, there was an average increase in the solubility rate of 
at least 23 percent over that of the commercial granular hydrated calcium 
hypochlorite of the prior art.