Note: Descriptions are shown in the official language in which they were submitted.
~t7~7
C-7746
PROCESS FOR MANUFACTURE OF CALCIUM HYPOCHLORITE
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This invention relates to the manufacture
of calcium hypochlorite. Calcium hypochlorite is
S a co~nercial bleaching and sanitizing agent used
particularly in the disinfection of swl~ning pool waters.
~nong the processes employed commercially
- for the production of calcium hypochlorite are several
which produce neutral calcium hypochlorite, Ca(OCl)2,
in the anhydrous form, or as a hydrated product containiny
at least 4 percent of water. These widely employed
processes have ef~iciently produced calcium hypochlorite
compositions o~ hiyh quality.
As energy costs have rapidly increased, ways
lS have been sought to lower energy requirements ~or producing
calcium hypochlorite, for example, by improving the drying
of the product so that the loss of available chlorine
during the drying stage is reduced.
In the past, methods for improving neutral
; 20 calcium hypochlorite processes have included those which
` attempted to eliminate impurities such as calcium
chloride from the product.
; U.S. Patent No. 1,713,650, issued May 21, 1929,
i~ to A. Georye and R. B. MacMullin, neutral calcium hypo-
chlorite is treated with a sodi~n hypochlorite solution in
an amount approximately equivalent to the calcium chloride
present to reduce the calcium chloride concentration by
converting it to neutral calcium hypochlorite.
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In a similar process, as described in U.S.
: Patent No. 1,713,654, issued May 21, 1929, to J. A. Guyer,
the calcium chloride content in the neutral calci~n
hypochlorite is reduced by forming lime upon reaction with
sodium hydroxide.
Alkali metal salts such a.s sodium hypochlorite,
sodium hydroxide, sodium carbonate, or trisodium phos-
phate are used to reduce the calcium chloride concen-
txation in a process for producing calci'um hypochlorite
by reacting lime with hypochlorous acid. ~he process,
,as described in U~S. Patent No. 3,134,641, issued
May 26, lg64, to R. D. Gleichert, is carried out while
maintaining the pH of 10 to 10.5 in the reaction mixture.
While it is desirable, as shown by the above
' 15 processes, to minimize the concentration of calcium
chloride or other undesirable impurities, their elimi-
nation alone does not result in reduced energy requirements.
Thus there is a need at the present time for an improved
process for the produc~ion of calcium hypochlorite having
lower energy requirements for drying.
' It is an object o the present invention to
provide a process ~or khe production of ~alcium hypo~
chlorite,having a reduced loss of available chlorine
duriny its dryincJ.
Another object of the present invention is
to provide a process for the production of calcium
hypochlorite having improved filterability o~ the
slurry form.
A further object of the present invention is
to provid,e a process for the production of calcium
hypochlorite having lower energy requirements.
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These and other objects of the invention will
be apparent from the following detailed description o~
the invention.
The novel process for the production of
` 5 granular calcium hypochlorite compositions comprises:
a) reacting neutral calcium hypo-
chlorite with an alkaline solution
comprised of an alkali metal hypo-
- chlorite and an alkali metal
hydroxide to produce a slurry
comprised of neutral calcium
hypochlorite and a residual
amount of hemibasic calcium
hypochlorite, and
lS b) recovering a wet cake of the neutral
calcium hypochlorite and the residual
amount of hemibasic calcium hypo-
chlorite and drying -the wet cake to
produce granular calci~m hypochlorite
compositions.
More in detail, the novel process o the
present invention employs as one reactant a slurxy of
neutral calci.-um hypochlorite, u~ually in the dihydrate
form. The qlurry is substant:ially fre~ o~ components
Z5 which provide active residual alkalinity. Active
residual alkalinity as used in the present specification
is defined as the presence of Ca(OH)2, hemibasic
calcium hypochlorite, or dibasic calcium hypochlorite in
the reactants or products. Neutral calcium hypochlorite
slurries may be prepared by any of several processes
including, for example, the triple salt process, the
'~ reaction of hypochlorous acid with a lime slurry, and
the chlorination of dibasic calcium hypochlorite. In a
: preferred embodiment, the neutral calcium hypochlorite
slurry is produced by the triple salt process. The triple
: salt process reacts ~ chlorinated lime slurry comprised of
,~ calcium hypochlori.te and calcium chloride with a slurry
of triple salt crys~als having the formula Ca(OCl)2 -
NaOCl NaCl 12H20. The lime slurry may be prepared,
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for example, by mixing lime having an active lime content
of from about 85 to about 100, and preferably from
about 90 to about 97 percent by weight with water to
produce an a~ueous lime slurry containing from about l0
to about 50, and preferably from about 15 to about 45
percent by weight of active lime. Active lirae is de~ined
by the amount of Ca~OH)2 in the lime.
Typical illustrative specifications or an
acceptable lime and for a pre~erred lime are
~s follows:
Component Acceptable Preferred
Ca(OH)2 min.% 95.0 98
CaCo3 max.~ 1.0 0.8
: MgO max.% 0.8 0.5
SiO2 max.~ 0.5 0~Z
Fe2O3 ~ A1~03 max.%0.3 0.1
CaSO4 max.~ 0-3 0 05
The average particle size of lime employed in
the process generally is substantially all 325 me~h (wet
screen analysis) but particles up to about -200 mesh may
be employed if desired. ~rhe lime slurry is fed to a
reactor to which i~ al~o added chlorine in ei~her ga~eou~
or liquid ~orm. The reactor may be any suitable
chlorination apparatus provided with agitation means for
maximum contact between chlorine and the lime slurry.
; A particularly suitable reactor is an evaporator-
chlorinator of the type used in the chlorination process
described in U.S. Patent No. 3,241,912, issued to
B. H. Nicolaisen on March 22, 1966. During the chlorina-
tion, the temperature within the reactor is maintained
within the range from about 0 to about 30C. and prefer-
; ably from about 20 to about 25C. Chlorination of the
lime slurry forms calcium hypochlorite and calcium
chlorid~ in accordance with Equation (1).
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(1) Ca(OH)2 + Cl2 ~ 1/2 Ca(ClO)2 ~ H2O ~ l/2 CaC12
Chlorination of the lime slurry is continued
until substantially all of the active lime, Ca(OH)2 is
reacted. The chlorinated lime slurry pxoduced is
comprised of calcium hypochlorite and calcium chloride.
The slurry is alkaline having a total residual alkalinity
which includes inacti~e residual alXalinity provided by
lime impurities such as calcium carbonate and magnesia
and an active residual alkalinity as defined above.
The active residual alkalinity in the slurry is less
than ~2percent by weight.
The chlorinated lime slurry produced is reacted
: with a slurry of triple salt cryscals, Ca(OCl)2 NaOCl -
NaCl 12H20. Triple salt crystals are produced by
lS the chlorination of a slurry of hydrated lime and a
sodium hypochlorite solution where the reaction mixture
is cooled to a temperature below about -18C. The
crystals are separated from the reaction mixture, ~or
example, by filtering. The crystals recovered are
essentially neutral and have an active alkalinlty
content of less than 0.05percent by weight. The
triple salt cry~tals are admixed with the chlorinated
lime slurry in amount~ which provide su~flcient concen-
krations o~ sodium hypochlorite to react with the calcium
~ 25 chloride present in the chlorinated lime slurry and
,; reduce its concentration to less than about 0.5 percent
by weight. So~i~D~-hypochlorite present in the triple
salt crystals reac~s with calcium chloride to produce a
neutral calci~m ~ypochlorite slurry comprised o~ said
` - 30 calcium hypochlorite dihydrate, CatOCl)2 2H2O and
~'; a solution containing sodium chloxide.
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; This neutral slurry is admixed with an alkaline
solution comprised of an alkali metal hypochlorite and
an alkali metal hydroxide. Any suitable alkali metal
hypochlorite may be used, for example, sodium hypo-
- 5 chlorite, potassium hypochloxite, or lithium hypochlorite,
wi~h sodium hypochlorite being preferred. Similarly,
alkali metal hydroxides which may be employed include
sodium hydroxide, potassium hydroxide, or lithium
hydroxide with sodium hydroxide beiny preferred. In
order to simplify the disclosure, the alkaline solution
of the invention will be described hereafter in terms
of sodium hypochlorite and sodium hydroxide. To prevent
undesired dilution of the reaction mixture, the
concentration of the sodiwm hypochlorite is maintained
in the range of from about 20 to about 32 and preferably
from about 22 to about 30 percent by weight. The amount
of sodium hydroxide present in the alkaline solution
is sufficient to produce a residual amount of hemibasic
calcium hypochlorite by reaction of the alkaline solution
with neutral calcium hypochlorite in the slurry~
Suitable amounts include from about 2 to about ?J0, and
preferably from about 4 to about 20 percent b~ weight
of sodium hydroxide. While the sodium hydroxid~ may
be added to the hypochlorite solution a~ a solid, it
is preferred to use a concentrated aqueous solution
containing, for example, 50 percent by weight of NaOH.
The reaction is carried out at temperatures
in the range of from about 22 to about 30C., preferably
at from about 25 to about 28C.
The reaction mixture should be agitated in
; a manner which thoroughly admixes the alkaline solution
with the slu\rry. This results in the production of
small, fine crystals of hemibasic calcium hypochlorlte
which are thoroughly dispersed throughout the reac-tion
mixture.
The reaction between the sodium hypochlorite
solution containing sodium hydroxide and the calcium
hypochlorite in the neutral slurry proceeds in accordance
wi-th Equations (2) and ~3).
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2NaOH ~ Ca~Cl0)2 -~ Ca(OH)~ ~ 2NaC10 ~2)
1/2Ca(OH)2 ~ Ca(OCl)2 ~ Ga(~Gl)2 1/2ca(0H)2 (3)
After the reaction is completed, the slurry
comprised of neutral calcium hypochlorite dihydrate,
sodium chloride, and a residual amount of hemi~aqic
calcium hypochlorite is subjected to a solid-liquid
separation ~echnique such as filtering or centrifuging
to recover a moist cake of neutral calcium hypochlorite,
hemibasic calcium hypochlorite, and sodium chloride.
Where the moist cake~ is separated by filtering, the
hemibasic calcium hypochlorite crystals presente~
increase the rate of filtration of the slurry over that
of slurries produced in conventional processes for
producing neutral calcium hypochlorite. The residual
amount of hemibasic calcium hypochlorite present in the
moist cake is in the range of ~rom about 1 to about 4,
and preferably from about 1.5 to about 2.5 percent
by weighk. The moist cake is conveyed to a dr~er which
is any suitable apparatus capahle of reducing the moisture
; 20 content of the calcium hypochlorite cake to the desired
level without causiny excessive decomposition of the
calcium hypochlorite particles. During ~i:Lteriny,
a iltrate i9 xecovered which comprises a sodium chloride
; soiution containing hypochlorite value~. This filtrate
; 25 may be recycled, ~or example, for use in the production
o triple salt crystals.
By insreasing the filtration rate, the process
of the present invention provides increased productivity
and permits a greater amount of calcium hypochlorite
cake to he dried per unit of time resulting in a
lower energy cost per unit of product.
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During the drying process, the calcium hypo-
chlorite cake undergoes substantially less decompo~ition
than neutral calcium hypochlorite cakes produced, for
example, by conventional processes, resultins in a
higher available chlorine content in the dried product.
After drying, a calcium hypochlorite composi-
tion is obtained comprised of from about 60 to about 70
percent by weight of neutral calcium hypochlorite,
from about 1o to about 20 , and preferably from about
13 to about 16 percent by weight of hemibasic calcium
hypochlorite to provide a total calcium hypochlorite
concentration in the dry product of from about 65
to about 85, and preferably from about 70 to about 80
percent by weight. The water content is in the range
of from about 0.5 to about 10 and preferably from
about 5.0 to about 7.5 percent by weight. The
remainder of the dry calcium hypochlorite composition
is predominantly sodium chloride. The product is
then placed in suitable containers, with or without
prior size classification or other processing such as
pelletizincJ, prior to use, for example, in the sanltation
of water supplies.
The novel process o~ the invention may be
- conducted ~ a continuous proc~ss by proclucirly the
neutral hypochlorite slurry while simultaneously
introducing controlled amounts of the alkaline solution
! of the alkali metal hypochlorite and alkali metal
hydroxide. When operated as a batch process, for example,
a chlorinated lime slurry is reacted in a first stage
with a triple salt slurry to produce a slurry of
neutral calcium hypochlorite dihydrate. This neutral
calcium hypochlorite slurry is then reacted in a second
stage to produce the calcium hypochlorite slurry comprised
of neutral calcium hypochlorite, a residual amount of
hemibasic calcium hypochlorite, and sodium chloride.
The separation and drying of the calcium hypochlorite
cake i5 carried out as described above.
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In a preferred embodiment, the slurry of triple
salt crystals is admixed with the chlorinated lime
slurry in amounts which provide insufficient concentra~
- tions of sodium hypochlorite to completely react with
the calcium chloride present in the chlorinated lime
slurry. Sodium hypochlorite present in the trlple
; salt crystals reacts with calcium chloride to produce
`; neutral calcium hypochlorite. Unreacted calcium chlorideconcentrations are in the range of from about 2
~ 10 about 5 and preferably from about 2.5 to about 3.5
: percent by weight. The remaining calcium chloride
concentration in the neutral calcium hypochlorite
'; slurry is reacted with the sodium hypochlorite in the
alkaline solution to produce ad~itional neutral calcium
hypochlorite and reduce the concentration of CaC12 to
. less than about 0.5 percent by weight. The sodium
hydroxide present in the alkaline solution reacts with
neutral calcium hypochlorite present to produce the
residual amoun~`bf`hemibasic calcium hypochlorite as
. 20 described above.
. The fo~lowing examples are presented to
illustrate the invention more fully. ~11 parts and
` percentages are by weight unless otherwise speci~ied.
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. EX~PLE 1
A solution of sodium hypochlorite (24 g) was
mixed with 9.0 g of a 50 percent solution of sodium
hydroxide to produce an al~aline sodium hypochlorite
. 5 solution containlng 22;19 percent NaOCl and 13.64 percent
NaOH. The alkaline solution (33 g) was blénded in a
reactor equipped with a variable speed agitator with a
neutral calcium hypochlorite slurry (490 g) contai~ing
less than 0.3 percent of calcium chloride, to ~orm a
~inal calcium hypochlorite slurry which contained 21.48
percent Ca(OCl)2 and 0.25 percent NaOCl and had an
. active residual alkalinity of 8.27 percent in the form o~
hemibasic calcium hypochlorite. This paste was filtered
:; to yield a calcium hypochlorite filter cake having a
moisture content of 45.69 percent and an available
: chlorine content of 38.79 percent. The cake was dried
. in a.vacuum oven at 100 mm Hg absolute pressure and
65C. to produce a hydrated granular calcium hypochlorite
product containing 6.6 percent water and 6~.48 percent
available chlqrine (wet basi~), indicating a 1058 on
drying o~ 6.34 percent o~ the available chlorine (dry
basi.s).
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`~! EXAMPLE 2
Triple salt crystals (500 g), having the
formula Ca(OCl)2 NaOCl NaCl 12H20 in which the
NaOCl concentration was 9.12 percent, were blended with
~ a chlorinated lime slurry haviny a calcium chloride
;. concentration of 15.23 percent. A first calcium
~ hypochlorite slurry was produced containing 28.29 percent
`- Ca(OCl)~ 2H2O and 3.21 percent CaC12. In a separate
reactor, a solution of sodium hypochlorite (197 g)
.. 10 was mixed with 2.73 g of a 50 percent solution of
sodium hydroxid~ to produce an alkaline sodium hypo-
chloritP solution containing 29.61 percent NaOCl and
2.29 percent NaOH. The alkaline solution (90 g) was
., blended with the first calcium hypochlorite slurry to
., 15 produce a slurry paste containing 28.42 perceIlt Ca(OC1~2
. and 0.56 percent CaC12 and having an alkalinity of 2.87
percent. in the form of hemibasic calcium hypochlorite,
Ca(OCl)2 1/2Ca(0~)2. The final paste was filtered
to yield a calcium hypochlorite filter cake having a
moisture content of 45.16 percent and an available
chlorine content of 43.25 percent. The cake wa~ dried
in a vacuum oven at 100 mm Hg absolute pressure and
65C. to produce a granular product contain.ing 8:2
percent water and 69.57 percent available chlorine
(wet basis), indicath~g a loss on drying o~ 3.91
percent of nvailable chlorine (dry basis).
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_OMPARATIVE EX~MPLE A
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. Triple salt crystals (500 g) of the formula
Ca(OCl)2 NaOCl NaCl 12H20 containing 10.53 percent
NaOCl were mixed with 333 g of a chlorinated lime slurry
:; 5 containing 13.04 percent CaC12 to produce a calcium
.. hypochIorite paste containing 22.98 percent Ca(OCl)2 and
O.22 p~rcent CaC12. The calcium hypochlorite paste
was filtered to p.rovide a filter cake having a moisture
content of 44.93 percen~ and an available chlorine
content 42~71 percent. The filter cake was dried
in a vacuum oven at 100 mm Hg absolute pxessure and
: 65C.. to produce a granular product containing 67.~9
percent of available chlorine (dry basis) indicating
a loss on drying of 12.46 percent of available chlorine
:~ 15 (dry basis).
Using the novel process of Examples l and 2
resulted in a reduction of 49% and 69% respectively in
the loss of available chlorine during drying when
compared with the prior art process o~ Comparati~e
: 20 Example A.
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` EXAMPLE 3
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~:~ A solution of sodium hypochlorite (187 g) was
mixed with 12.9 g of a 50 percent solution of sodium
hydroxide to produce an alkaline sodium hypochlorite
' 5 solution containing 30.38 percent NaOC1 and 4.66
~, percent NaOH. The alkaline solu~ion (122 g) was blended
in a reactor having a vaxiabl~ speed agitator with a
, chlorinated lime slurry (449 g) having a calcium chloride
concentration of 15.72 percent, and triple salt crystals
(500 g~, having the ~ormula Ca(OCl)2 NaOCl NaCl 12~20,
in which the NaOCl concentration was 10.93 percent. A
;v calcium hypochlorite paste was produced which contained
26.53 percent Ca(OCl)2 and 0.40 percent CaC12 and had
`~ an alkalinity of 2~34 percent in the form of hemibasic
calcium hypochlorite. The ~inal paste was filtered to
yield a calcium hypochlorite ~ilter cake having a moisture
content of 51.87 percent and an available chlorine
of 37~78 percent. The cake was dried in a vacuum oven
at 100 mm Hg absolute pressure and 65C. to produce a
granular product containing 73.22 percent available
chlorine (dry basis) indicating a loss on drying Oe
6.72 percent o~ available chlorine (dry basis).
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