Note: Descriptions are shown in the official language in which they were submitted.
WO92/21610 2 1 1 0 2 9 8 PCT/US92Jo375s ~
.
PROCESS FOR PRODUCIN~ CALCIUM HYPOCHLORITE FROM
CONCENTRATED HYPOC~LOROUS ACID SOLUTIONS
This invention relates to the manufacture of
calcium hypochlorite. More particularly, this
invention relates to an improved process for the
manufacture of calcium hypochlorite using hypochlorous
s acid as a reactant.
It has long been a desire to produce calcium
hypochlorite by the reaction of lime with a
hypochlorous acid solution to eliminate or minimize the
concentration of chloride ions in solutions or slurries
of calcium hypochlorite and thus avoid the formation of
effluents containing both hypochlorite and chloride
ions.
In one approach, an aqueous hypochlorite solution
was prepared in or e~tracted with an organic solvent
such as ethyl alcohol, carbon tetrachloride, or methyl
ethyl ketone. Suitable examples of this approach are
found in U.S. Patent No. 1,481,03g, issued January 15,
1924 to M. C. Taylor et al; and U.S. Patent No.
3,578,393, issued May 11, 1971 to J. A. Wojtowicz et al.
The use of organic solvents in producing
hypochlorous acid solutions not only increases process
costs but the prese~ce of organic materials as
impurities in the calcium hypochlorite product is
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, ,,
undesira~le as calcium hypochlorite is decomposed by a
large variety of organic materials.
U.S. Patent No. 2,429,531, issued October 21, 1947
by E. C. Soule et al teach a process for producing
calcium hypochlorite by the neutralization or reaction
of hypochlorous acid with a basic calcium hypochlorite
such as dibasic calcium hypochlorite and/or hemibasic
hypochlorite. Soule et al found that the direct
reaction of lime with hypochlorous acid produced dilute
concentrations of calcium hypochlorite in low yields.
The reasons for this is the formation of considerable
quantities of chlorate. The formation of the ~hlorate
is attributed to the o~idation of hypochlorite ion.
Additionally, the use of aqueous solutions of
hypochlorous acid in the preparation of calcium
hypochlorite is taught, for e~ample, in U.S. Patent
Nos. 3,134,641, issued May 26, 1964 ~y R. D. Gleichert;
4,146,578, issued March 27, 1979 by J. P. Brennan et
al; 4,147,761, issued April 3, 1979 by J. A. Wojtowicz
et al; and 4,416,864, issued November 22, l9B3 by J. A.
Wojtowicz. However, in these processes the
hypochlorous acid solutions employed were not used as
the sole chlorinating agent and the use of an
additional chlorinating agent such as chlorine or an
alkali metal hypochlorite was required.
Processes employing hy~ochlorous acid and these
additional chlorinating agents produce a calcium
hypochlorite product containing substantial amounts of
chloride ions. In addition, to recover the product, a
separation step is required which removes the solid
calcium hypochlorite product containing chloride ions
from a solution containins dissolved chloride ions and
hypochlorite ions. The volume of effluent containing
chloride and hypochlorite ions is greater than that
.
.
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.
which can be recycled to the process. Thus, the excess
effluent requires an additional application or if this
is not available, it must be treated to reduce or
remove the hypochlorite ions present prior to
disposal. Further, the hypochlorite ion concentrations
are relatively low and if they are to be recovered, the
solutions require concentration.
To remove chloride ions from a calcium hypochlorite
product Murakami et al, in U. S Patent No.4,355,014,
issued October l9, 1982 propose to wash the product
with large volumes of water. This method, however, is
not commercially feasible as it reduces the product
yield by dissolving calcium hypochlorite while
generating large volumes of solutions containing low
15 concentrations of dissolved chloride and hypochlorite
ions.
Thus, prior art processes for producing calcium
hypochlorite by the reaction of lime with hypochlorous
acid suffer from several disadvantages including the
20 production of a calcium hypochlorite product containing
substantial amounts of chloride ions; the requirement
of a separation step of the product from an effluent
solution containing dissolved chloride and hypochlorite
ions, and the use or disposal of escess volumes of
25 effluents containing chloride and hypochlorite ions.
Now a novel process for producing calcium
hypochlorite has been discovered that employs
concentrated solutions of hypochlorous acid to produce
a calcium hypochlorite product in the absence of
30 supplementary chlorinating agents such as chlorine or
an alkali metal hypochlorite. The process is free of
effluents containing mi~tures of chloride ions and
hypochlorite ions which reguire disposal. In addition,
the calcium hypochlorite product is of a high assay and
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2110298
high purity and does not contain chloride ions formed - --
by the use of chlorine or an alkali metal hypochlorite
as chlorinating agents. Further, the process requires
reduced amounts of fresh water and produces calcium
hypochlorite slurries having higher concentrations of
solids which can be dried at reduced energy
requirements and thus reduced energy costs. ~;
These and other advantages are accomplished in a
_ process for producing calcium hypochlorite which
consists essentially of reacting lime or a lime slurry
containing greater than 30% by weight of Ca(OH)2 with
a chlorinating agent consisting of a hypochlorous acid
solution containing at least about 35 percent by weight
of HOCl to produce a slurry of calcium hypochlorite
dihydrate crystals in a solution of calcium
hypochlorite, the slurry containing at least 30% of
Ca(OCl)2 and being substantially free of alkali metal
and chloride ions.
More in detail, the novel process of the present
invention employs as one reactant a concentrated
hypochlorous acid solution containing at least 35
percent by weight of HOCl. The method of producing
these high purity concentrated HOCl solutions is that
in which a gaseous misture, having high concentrations -~
of hypochlorous acid vapors and chlorine monoside gas
and controlled amounts of water vapor is produced. The
gaseous misture can be produced by the process
described by J. P. Brennan et al in U.S. Patent No.
4,197,761. `-
The gaseous mi~ture having high concentrations of ;
hypochlorous acid vapors and chlorine monoside gas and
controlled amounts of water vapor may also contain
varying amounts of chlorine gas. To remove any solid
particles, such as alkali metal chloride particles,
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which may be entrained, the gaseous mizture may be
passed through a separation means. To produce the
concentrated solutions of hypochlorous, the gaseous
misture is converted to hypochlorous acid, for e~ample,
by condensing the gaseous mi~ture at low temperatures
such as those in the range of from about -5C to about
l20C and preferably from about 0C to about ~10C.
Condensation of the gaseous mi~ture is operated at
autogenous pressures for the temperatures employed.
The concentrated solutions of hypochlorous acid
contain from about 35 percent to about 75 percent of
HOCl, preferably from about 40 to about 60 percent,
more preferably from about 42 to about S5, and most
preferably from about 45 to about 50 percent by weight
of HOCl. The hypochlorous acid solutions are
substantially free of ionic impurities such as chloride
ions, and alkali metal ions and have low concentrations
of dissolved chlorine. For e~ample, concentrations of
the chloride ion are less than about 50 par~s per
million; the alkali metal ion concentration is less
than about 50 parts per million. The dissolved
chlorine concentration in the hypochlorous acid
solution is less than about 3 percent, and preferably
less than about 1 percent by weight.
In the process of the present invention, the
concentrated hypochlorous acid is initially reacted
with lime.
The lime employed can be any suitable lime having
an active lime content of from about 85 to about 99,
and preferably from about 90 to about 98 percent, where
active lime is defined as the weight percent of
Ca(OH)2 in the lime. The lime employed usually
contains impurities such as iron compounds, silica,
aluminum salts, magnesium salts, manganese, unburned
WO92/21610 PcT~us9~/o3?s9 ~-
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limestone (calcium carbonate and magnesium carbonate)
and other compounds in trace quantities. These
impurities represent ~rom about l to about 15, and
preferably from about 2 to about 8 percent by weight of
the lime. More preferred are limes having low
concentrations of heavy metal compounds such as those
of iron and manganese.
Lime slurries employed in the novel process of the.
invention.contain greater than 30 percent by weight of
lo Ca(OH)2. For esample, the lime slurries contain from
about 32 to about 45%, preferably, from about 33 to
about 44~ and, ~ore preferably from about 35 to about
43 percent by weight of Ca(OH)2.
Reacting these thick slurries of lime substantially
15 eliminates the formation of liquid effluents requiring
reuse or disposal. In the process of the invention,
the concentrated lime slurries are added to and admi~ed
with the concentrated solutions of hypochlorous acid.
The reaction is carried out using vigorous agitation to
20 assure the production of a uniform or homogeneous
slurry of neutral calcium hypochlorite dihydrate. As
the process is preferably operated continuously,
control of the reaction can be accomplished, for
esample, by addinq the concentrated lime slurry to the
25 hypochlorous acid solution at a rate which maintains
the desired pH of the reaction misture. Suitably the
pH is maintained in the range of from about lO to about
10.8, and preferably at from about 10.2 to about 10.5.
Th.e reaction between the concentrated hypochlorous
30 acid solut.ion and the concentrated lime slurry is
carried out at a temperature in the range of from about
15 to about 30C, and preferably from about 20 to
about 25C. As the hypochlorous acid solution is
maintained at low temperatures, for e~ample, below
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about 10C, its use provides a portion of the cooling
reguired for this esothermic reaction.
A slurry of neutral calcium hypochlorite dihydrate
crystals is produced in the reaction which is e~pressed
by the equation:
2HOCl~+,Ca(OH)2 ~ > Ca(OCl)2.2H20 (1)-
The product is a dense slurry of calciumhypochlorite dihydrate solids suspended in an aqueous
solution of calcium hypochlorite. The slurry,
containing at least 30%, and preferably from about 35
to about 50 percent by weight of Ca(OCl)2, is dried
without a solid-liguid separation step has a suspended
solid content, from about 10 to about 30 percent, and
preferably from about 15 to about 30 percent by
weight. The slurry is substantially free of alkali
metal ions and contains less than about 4 percent by
weight of calcium salts such as lime, calcium chloride,
and calcium chlorate.
In a preferred embodiment, a portion of the slurry
of calcium hypochlorite dihydrate produced is used to
~wet" the lime and form the lime slurry. When mi~ed
with lime, the slurry of calcium hypochlorite dihydrate
reacts to produce crystals of dibasic calcium
hypochlorite in a reactiorl represented by the following
25 equation:
2Ca(OH)2 + Ca(OCl)2.2H2O -----> Ca(OCl)2.2Ca(OH)2 (2)
2H20
Reacting a portion of the slurry of calcium
hypochlorite dihydrate with the lime significantly
reduces the requirements for fresh water to be used in
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the process. The slurry of dibasic calcium
hypochlorite is then reacted with the concentrated
hypochlorous acid solution to produce a slurry of
neutral calcium hypochlorite dihydrate crystals.
This reaction is represented by the equation:
Ca(OCl)2.2Ca(OH)2 + 4HOCl ~ 3Ca(OCl)2 + 4H2O (3)
_ While the process of the present invention may be
conducted batchwise, it is preferably operated with the
hypochlorous acid solution and a slurry of lime,
dibasic calcium hypochlorite or mi~tures thereof, being
charged continuously to the reactor. The rate of
addition of reactants provides the reaction misture
with a slurry having a suspended solids concentration
in the range of at least about l0 percent, preferably
Of about l0 to about 30 percent and more preferably
about 15 to about 30 per~ent by weight.
A slurry of neutral calcium dihydrate crystals is
continuously recovered from the reaction mi~ture. The
slurry is substantially free of alkali metal ions, and
has very low concentrations of chloride ions, i.e. less
than about 3 percent, and preferably less than about 2
percent by weight.
In an alternate embodiment, a mother liquor may be ~ ~-
recovered from the slurry of calcium hypochlorite by
separation of the calcium hypochlorite dihydrate
crystals. The mother liquor is a concentrated solution
containing at least 15 percent, and normally from about
20 to about 25 percent by weight of Ca(OCl)2. This
concentrated calcium hypochlorite solution having very
low concentrations of impurities may be used or sold as
a bleach solution or used in the preparation of the
WO92/21610 PCT~US92/03759
2110298
1 ime s lurry .
The slurry may be used directly in the treatment
of water systems such as swimming pools and the like,
but is generally dried and stored prior to use.
The slurry is dried by known means, for esample,
using a spray dryer, turbodryer or vacuum dryer where
the appropriate temperature ranges are employed to
reduce the water conten~ to the desired level. A
preferred method of dryiDg employs a fluidized spray
10 drier having a fluidized bed of granular particles into
which off-sized product is fed after being agglomerated
to adjust particle size.
The dried calcium hypochlorite product is then
placed in suitable containers, with or without prior
15 size classification or other processing such as
pelletizing, prior to use in water treatment or any
other application. During the drying of the product or
in a size classification operation, fine particles of
the dried calcium hypochlorite are recovered. In one
20 embodiment of the process, these fine particles of
dried calcium hypochlorite are admi~ed with a lime
solution. This permits the recovery of the calcium
hypochlorite ~alues without forming an effluent or
requiring other means of disposal of the fine particles.
The novel process of the present invention
employing highly concentrated solutions of hypochlorous
acid and thick lime slurries produces calcium
hypochlorite in a reaction mi~ture which does not
require the use of supplementary chlorinating agents
30 such as chlorine or an alkali metal hypochlorite and
the product is therefore substantially free of chloride
ions. The process does not produce effluents
containing chloride and hypochlorite ions which require
separation, treatment and disposal. The process can
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1o
thus be operated as a "closed loop~.
The preferred embodiment of the continuous process
of the invention is operated without solid-liquid
separating equipment, such as vacuum filters, which
significantly reduces both the capital costs and the
maintenance costs.
The hydrated calcium hypochlorite product which is
produced by the process of the present invention
contains at least 70 percent, for example, from about
75 to about 95 percent, and preferably from about 80 to
about 95 percent by weight of Ca(OCl)2. The hydrated
calcium hypochlorite has a water content in the ranqe
of 4 to about 20, and preferably from about 7 to about
20 percent by weight.
Hydrated calcium hypochlorite products produced by
commercial processes presently in operation have had to
lower the concentrations of Ca(OCl)2 in the product
to permit the water contents required for improved
safety and handling properties.
The process of the present invention produces
hydrated calcium hypochlorite having the water content
required for improved safety properties and yet having
very high assays of Ca~OCl)2.
Surprisingly, the high purity calcium hypochlorite
product produced by the process of the present
invention is substantially free of alkali metal
chlorides and contains less than about 4 percent,
preferably less than about 3 percent, and more
preferably less than about 2.5 percent by weight of
calci~m chloride.
To further illustrate the present invention, the
following example(s) are presented without any
intention of being limited thereby. All parts and
percentages are by weight unless otherwise indicated.
WO92/21~10 PCT/US92~037~9
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EXAMPLE 1
To a hypochlorinator reactor was continuously
charged a slurry of dibasic calcium hypochlorite
crystals having a total solids content of 30.7 percent
at a rate of 535 parts per hour. Simultaneously, at a
rate of 113 parts per hour was added an aqueous
hypochlorous acid solution having a concentration of
HOCl of 50-percent by weight. The reaction mi~ture was
agitated and maintained at a temperature of about
30~C. A slurry of calcium hypochlorite dihydrate was
produced which was conveyed to a filter which separated
a cake of calcium hypochlorite having a Ca(OCl)2
concentration of 37.9 percent by weight and a water
content of 56.9 percent from a calcium hypochlorite
mother liquor containing 20.9 percent by weiqht of
Ca(OCl)2. The calcium hypochlorite dihydrate cake
was dried by a convector heating dryer to a product
containing 85.1 percent by weight of Ca(OCl)2, a
water content of 4.7 percent by weight and a calcium
~0 chloride concentration of 1.4 percent by weight.
Alkali metal ions could not be detected in the product.
The mother liquor was recycled to a crystallizer
reactor and admi~ed with additional lime to produce the
dibasic calcium hypochlorite slurry charged to the
hypochlorinator reactor.
EXAMPLE 2
A gaseous mixture containing an average
concentration of 23.7 parts by weight of chlorine
mono~ide, 65.5 parts by weight of C12, and 1.8 parts
by weight of water vapor was continuously passed
through a cyclone separator to remove any entrained
WO92~21610 PCT/US42/03759
21102~8
-~2-
solid particles of alkali metal chloride. The
solid-free gaseous mi~ture at a temperature of 85-90C
was passed through a vertical shell and tube heat
eschanger maintained at a temperature of about 0C and
a pressure of about 3-4 torr gauge to condense a
portion of the chlorine mono~ide and substantially all
of the water vapor to produce an aqueous hypochlorous
acid solution containing 40 to 55 percent by weight of
HOCl. The` hypochlorous acid solution had a pH of about
1 and the dissolved chlorine concentration was
determined to be about 1 percent by weight. The
concentrated hypochlorous acid solution was
continuously added to a hypochlorinator reactor at a
rate of 113 parts per hour. Also added to the reactor
was a slurry of dibasic calcium hypochlorite at a rate
of 373 parts per hour. The reaction mi~ture was
agitated and maintained at a temperature of about
30C. A slurry of calcium hypochlorite dihydrate was
produced which was conveyed to a filter which separated
a cake of calcium hypochlorite having a Ca(OCl)
concentration of 42.7 percent by weight and a water
content of ~3.8 percent from a calcium hypochlorite
mother liquor containing 20.8 percent by weight of
Ca(OCl)2. The calciùm hypochlorite dihydrate cake
was dried by a convector heating dryer to a product
containing 84.1 percent by weig~.t of Ca(OCl)2, a
water content of 7.8 percent by weight and a calcium
chloride concentration of 1.2 percent by weight.
Alkali metal ions could not be det~cted in the product.
The mother liquor was recycled to a crystallizer
reactor and admi~ed with additional lime to produce the
dibasic calcium hypochlorite slurry charged to the
hypochlorinator reactor.
WO92/21610 PCT/US92/03759
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EXAMPLE 3 ~;
. , ~;
A slurry of dibasic calcium hypochlorite crysta~s
- was continuously fed to a hypochlorinator reactor at a
rate controlled by pH. Simultaneous addition of
hypochlorous acid solution, containing 47% by wt. of
HOCl, at appro~imately 0.5 gallons/min. (gpm) produced
a paste slurry containing about 38% Ca~OCl)2, 0.3%
total alkalinity as Ca~OH)2, 1.3% chloride salts of
calcium and sodium, 0.5% Ca(ClO3)2 and 60% water
(by difference). Temperatures of the hypochlorinator
reactor were maintained between 20C and 25C by
circulating ~hilled brine through cooling coils
immersed in the reactor. Vigorous agitation was
maintained to assure rapid dispersion of the
hypochlorous acid and dibasic slurry into the paste
slurry. A portion of this paste was spray dried to
produce product, the analysis averaging 81.6%
Ca(OCl)2, 5.8% total alkalinity as Ca(OH)~, 1.8%
chloride salts of calcium and sodium, 2.5%
20 Ca(ClO3)2, and 8.5% H2O. The other portion of
~he paste was recycled to a dibasic calcium
hrpochlorite crystallizer at a rate of about 0.3 to 0.4
gpm.
The dibasic crystallizer system consisted of a
25 cr~stallizer reactor, a lime slurry makeup tank, a
hypochlorinator reactor feed tank, and a hydroclone.
The dibasic slurry produced in the crystallizer was fed
to the hydroclone at a rate of about 9 gpm. The
thicker underflow dropped into the hypochlorinator
30 reactor feed tank. The thin hydroclone overflow fed
the lime slurry makeup tank where lime was added at a
rate of about 100 lbs/hr.
WO92/21610 PCT/VS92/03759
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A small amount of water was also added to the lime
slurry makeup tank for overall water balance control to
maintain 60% water in the paste slurry. This lime
slurry fed the dibasic crystallizer reactor along with
the recycled paste slurry to produce a dibasic calcium
hypochlorite slurry with a slight escess of free lime.
The temperature in the dibasic crystallizer reactor was
- maintained between 30C and 35~C by recirculating the
dibasic slurry through a shell and tube heat e~changer
using low pressure steam. The stream analyses in the
dibasic crystallizer system were.
Lime Dibasic Hypochlorinator
Slurrv Slurry Feed Slurry
%ca(OCl)2 12.8 19.1 23.5
%Ca(OH)2 (TA)*15.4 13.4 20.2
%CaC12/NaCl 1.1 1.2 1.1
%H2O (difference)70.7 64.3 55.2
~ Total alkalinity
A hypochlorinator was operated continuously by
feeding a concentrated solution of HOCl (47-50%) at a
rate of about 7 gallons per minute. Also fed to the
hypochlorinator was a concentrated slurry of hydrated
lime (40-42% Ca(OH)2) at a controlled rate such that
the pH of the paste slurry was maintained at about
10.2. The reactants were mi~ed using a high shear
mi~er (Lightning~ mi~er, Mi~ing Equipment Co.,
Rochester N.Y.). The paste slurry level in the
W092/21610 2110 2 9 8 PCT/US92/03759 ~-
-15-
hypochlorinator was controlled by continuously drawing
off a portion of the paste slurry to a storage vessel. ~ -
The analysis of the paste slurry averaged 35%
. ca(OCl)2, 0.2% Ca(OH)2, 0-5% CaC12, 0-5%
Ca(C103)2, and 63.8~ H20. From the storage vessel
the paste slurry was fed directly to a fluidized bed :~
spray dryer and dried to produce a calcium hypochlorite
product containing containing 78-80% (Ca(OCl)2 and
11-14% H20 (by difference).
EXAMPLE 5
The hypochlorinator of Esample 4 was operated
continuously by feeding a csncentrated solution of HOCl
(47-50%) at a rate of about 7.5 gallons per minute.
Also fed to the hypochlorinator was a dilute
chlorinated lime solution at a rate of about 1 gallon
per minute (~.5% Ca(OCl)2, 2% Ca(OH)2, 25CaC12,
0.2%CaC103 and the balance water). A concentrated
slurry of hydrated lime (38-41% Ca(OH)2) was
continuously added at a controlled rate such that the
pH of the paste slurry was maintained at about 10.2.
The reactants were mi~ed using a high shear mi~er
(Lightning~ mi~er, Mi~ing Equipment CQ., Rochester
N.Y.). The paste slurry level in the hypochlorinator
was controlled by continuously drawing off a portion of
the paste slurry to a storage vessel. The analysis of
the paste slurry averaged 33.5% (Ca(OCl)2, 0.3%
Ca(OH)2, 0.8% CaC12, 0-4% Ca(C103)2 and 65%
H20. From the storage vessel the paste slurry was
fed directly to a fluidized bed spray dryer and dried -
to produce a calcium hypochlorite product containing
78-80% (Ca(OCl)2 and 11-14% H20 (by difference).
During operation of the dryer, fine particles of
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calcium hypochlorite recovered from the e~haust were
fed to a scrubber containing a dilute solution of lime
and a chlorinated lime solution produced. This
- chlorinated lime solution was recycled to the
5 hypochlorinator. ~-
