Note: Descriptions are shown in the official language in which they were submitted.
~74~41
C-9200
HYDRATED CALCIUM HYPOCHLORITE TABLETS CONTAINING
LIME COMPOUNDS AS LUBRICANTS
AND SOLUBILITY RETARDANTS
This invention relates to chlorine-containing
products for the sanitation of water bodies. More
particularly the invention relates to tablets of
hydrated calcium hypochlorite and the preparation
thereof.
Calcium hypochlorite is a well known source
of "available chlorine" for sanitation purposes, for
example, in disinfecting water bodies such as swimming
pools or waste streams. Calcium hypochlorite is added
to the water to maintain a small residual of "available
chlorine~, which is generally sufficient to insure
prompt destruction of bacterial contamination, so that
the water is safe for swimming, bathing or disposal
from sanitation treatment facilities.
Anhydrous calcium hypochlorite compositions
having Ca(OCl)2 concentrations of about 70 percent by
weight have been commercially available in granular or
ta~let form to be added to the water body to provide
the desired levels of available chlorine.
~, -" v
~4~41
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U.S. Patent 4,192,763 issued March 11, 1980
to P. W. W. Buchan describes a method of forming
tablets by mixing calcium hypochlorite with chloride of
lime and zinc stearate as a tabletting lubricant and
pressing the mixture into a tablet. The tablets,
containing from 5 to 15 percent chloride of lime and a
minor amount of zinc stearate as a lubricating agent,
have a decreased rate of dissolution in water.
Anhydrous calcium hypochlorite is used as water or
moisture results in an accelerated decomposition rate
for mixtures containing the hygroscopic chloride of
lime.
A similar method of decreasing the solubility
of calcium hypochlorite is described in Japanese Patent
Publication No. 90404-1980 published on July 9, 1980.
Mixtures of calcium chloride and calcium hydroxide and
anhydrous calcium hypochlorite are formed into tablets
in which CaC12 is present at 3-4 percent by weight
and the calcium hydroxide/calcium chloride weight ratio
is 0.5 to 3Ø These amounts of
CaC12 ~ Ca(OH)2 are required to provide reduced
solubility for the tablets. The presence of water or
moisture, however, would seriously effect the stability
of these tablets.
Hydrated calcium hypochlorite compositions
have been developed having a water content of-4 percent
by weight or greater which are more resistant to
ignition and exothermic decomposition than the
anhydrous product. Tabletting of calcium hypochlorite
having a water content of above 3 percent by weight
cannot be accomplished efficiently in commercial
tabletting apparatus as caking of the punches results
in excessive wear of the equipment. Frequent shutdowns
for maintenance of the equipment are required and
product control with respect to both the uniformity and
the appearance of the tablets is difficult to maintain.
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One object of the present invention is to
provide tablets of hydrated calcium hypochlorite
compositions which can be produced commercially while
minimizing costs and equipment wear.
Another object of the present invention is to
provide a process for producing hydrated calcium
hypochlorite ta~lets which are stable and have extended
shelf life.
An additional object of the present invention
is to provide a tablet of hydrated calcium hypochlorite
composition having controlled active chlorine release
properties for santizing water supplies.
These and other objects of the present
invention are accomplished in tablets for sanitizing
water bodies consisting essentially of hydrated calcium
hypochlorite admixed with a lime compound in amounts of
from about 0.1 to about 3 percent by weight of the
hydrated calcium hypochlorite.
The FIGURE is a graph illustrating the effect
of calcium hyclroxide on the solubility of hydrated
calcium hypochlorite tablets in water.
Granules of solid, hydrated calcium
hypochlorite contain from about 55 to about 75 percent
and preferably from about 65 to about 72 percent by
weight of calcium hypochlorite, Ca(OCl)2; from about
4 to about 10 percent, and preferably from about 5.5 to
about 8.5 percent by weight of water; and from about 1
to about 3 percent by weight of calcium hydroxide, the
balance being inert material usually resulting from the
process of manufacture, e.g. sodium chloride, calcium
chloride, and calcium carbonate. The hydrated calcium
hypochlorite has a specific gravity of about 2.1 to
about 2.2. Hydrated calcium hypochlorite particles of
the type used in the present invention may be produced
by known processes sùch as those described in U.S.
Patent No. 3,544,267, issued on December 1, 1970 to G.
R. Dychdala or U.S. Patent No. 3,669,894, issued on
June 13, 1972 to J. P. Faust~
4~4~
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Granules of hydrated calcium hypochlorite
used in the tablets of the present invention are those
which are normally produced commercially and have a
particle size in the range of from about 150 to about
2,000 microns.
~he lime compound employed is calcium oxide,
commercially available as quick lime; calcium hydroxide,
commercially available as hydrated lime; and mixtures
thereof.
The hydrated calcium hypochlorite particles
are admixed with particles of a lime compound to
produce mixtures containing amounts of the lime
compound in the range of from about 0.1 to about 3
percent, and preferably from about 0.5 to about 2
percent by weight of the hydrated calcium
hypochlorite. Larqer amounts may be used if desired,
however, they do not provide substantial increases in
benefits with respect to cost.
As stated above, calcium hypochlorite may
contain process calcium hydroxide as an integral part
of the composition as calcium hydroxide is one of the
raw materials commonly used in producing calcium
hypochlorite. The presence, however, of process
calcium hydroxide or lime in the calcium hypochloritè
suprisingly does not provide the beneficial results
which are accomplished when calcium oxide or calcium
hydroxide are admixed with the hydrated calcium
hypochlorite granules in the amount disclosed above.
The hydrated hypochlorite granules are
admixed with commercially available quick lime or
hydrated lime to form a substantially homogeneous
mixture. Any suitable means of admixing or blendinq
the two components may be employed.
The mixture is then tabletted using
commercially available tabletting machines. In
producing tablets, it has unexpectedly been found that
a lubricating agent is not required as the lime
compound provides excellent lubricating properties in
the amounts used in the mixtures. Tablets produced
from the mixtures of the present invention are readily
released from the tabletting die. The novel tablets of
the present invention, having an available chlorine
content of from about 65 to about 70 percent, provide a
controlled rate of dissolution in water which is
substantially reduced over the rate of dissolution of
hydrated calcium hypochlorite.
Further illustrations are provided by the
following examples with no intention of being limited
thereby. All percentages and parts are by weight
unless otherwise indicated.
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EXAMPLE 1
Anhydrous calcium oxide was added to hydrated
calcium hypochlorite granules in an amount of 1.5
percent by weight of the hydrated calcium
hypochlorite. The compounds were blended in a
V-blender to provide a homogeneous mixture.
A stainless steel die [7.6 centimeters (3
inches) in diameter, No. 420C3 and a punch were placed
in a Wabash press and a sufficient amount of the
hydrated calcium hypochlorite-calcium oxide mixture was
added to produce six tablets at a tabletting pressure
of 20 tons~ The tablets (200 grams each) were released
from the tabletting press without sticking to the die
and the appearance of the tablets was excellent. No
cleaning of the die was required during the tabletting
operation.
Three of the tablets were placed in an
errosion type dissolver where the water flow rate was
7.5 gallons per minute and the temperature about
26.7C (800F). The tablets were allowed to
dissolve for 3.0 hours after which time the remainder
of the tablets was removed, dried for 4.0 hours and
weighed. The amount of dissolved Ca(OCl)2 was
calculated by subtracting the quantity of Ca(OCl)2
remaining after the test from the initial weight. The
tablets prepared with calcium oxide retained 68 percent
of their original weight.
Comparative Example A
The procedure of EXAMPLE 1 was repeated with
the exceptions that hydrated calcium hypochlorite was
tabletted in place of the mixture of hydrated calcium
hypochlorite and calcium oxide, and the stainless steel
die was coated with a sodium stearate solution as a
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lubricatiny agent. During the tabletting operation a
significant quantity of hydrated calcium hypochlorite
stuck to the die. The die had to be cleaned and coated
with sodium stearate solution after each tablet was
made otherwise the punch could not be removed.
The dissolving rate determination was
repeated with three of the tablets containing only
hydrated calcium hypochlorite. The tablets retained 42
percent of their original weight.
Using the novel tabletting composition of the
present invention, the tablets dissolved at a reduced
rate which was 38 percent slower than the hydrated
calcium hypochlorite tablets of Comparative Example A.
EXAMPLES 2-4
Four homogeneous mixtures were made
containing granular hydrated calcium hypochlorite and
calcium hydroxide (reagent grade) where the calcium
hydroxide was added in amounts of 0, 0.75, 1.5, and 3.0
weight percent~ The hydrated calcium hypochlorite had
the following analysis~
COMPONENT % BY WEIGHT
Ca(OCl)2 66.5-66.6
ca(C103)2 1.7-1.8
Ca(OH)2 1.8-2.0
CaC12 4.5-5.2
CaC03 1.37
NaCl 16.2-18.2
~2 6.8
Each mixture was tabletted at pressures of
17,000 pounds to produce tablets weighing 25.3 grams
and having a diameter of about 2.54 centimeters (1.00
inch), a height of about 2.37 centimeters (0.93 inch),
and a surface area of 29.05 square centimeters.
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--8--
Tablets of each mixture were placed in an open mesh
basket and immersed in a tank of water ha~ing a
temperature of 32C where the water was slowly
agitated. During the initial dissolution period of
about three hours, the tablets were removed at time
intervals of 0.5 to 1.0 hour, dried and weighed.
Tablets having 0 content of lime admixed dissolved at a
rate of 0.53 grams per square centimeter of surface
area per hour. Tablets having a Ca(OH)2 content of
0.75 percent by weight dissolved at a rate of 0.40
grams per square centimeters per hour. Tablets having
Ca(OH)2 contents of 1.5 and 3.0 percent by weight had
a dissolving rate of 0.32 and 0.243 grams per square
centimeters per hour, respectively. The results are
illustrated on the FIGURE.
EXAMPLES 5-7
Tablets weighing 275 grams and having a
diameter of about 7.6 centimeters (3 inches) were
produced from homogeneous mixtures of compacted
granular calcium hypochlorite and lime where the lime
was present in amounts of 0.5, 1.5 and 2.5 percent by
weight. the calcim hypochlorite granules had the
following analysis:
COMPONENT % BY W~IGHT
_
ca(OCl)2 69.5
Ca(OH)2 1.5
CaCO3 2.0
CaC12 ca 1.0
ca(ClO3)2 ca 1.0
NaCl ca 18.0
H2O 7.0
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The tablets were placed in a basket and
submerged in a swimming pool skimmer having a water
flow rate of 35 gallons per minute. The total time to
dissolve the tablets was measured and found to be:
% OF LIME DISSOLVING TIME (HRS.)
0.5 7~5
1.5 11.5
2.5 15.0
Comparative Example B
The procedure of EXAMPLES 5-7 was repeated
using tablets of hydrated calcium hypochlorite which
were identical to those used in EXAMPLES 5-7 except for
the omission of lime. These tablets had a dissolving
time of 6.0 hours.
