Process for the production of lithium hypochloride

A process for producing lithium hypochlorite which admixes an aqueous hypochlorous acid solution, having a concentration of 35 percent or greater by weight of HOCl, with an aqueous slurry of lithium hydroxide at a temperature in the range of from about 0.degree. to about 20.degree. to produce a solution of substantially pure lithium hypochlorite. The lithium hypochlorite solutions produced can be dried directly or concentrated by cooling. The solid lithium hypochlorite produced is a highly pure source of available chlorine.

This invention is related to the production of concentrated lithium 
hypochlorite. More particularly, this invention is related to the 
production of concentrated lithium hypochlorite from pure concentrated 
solutions of hypochlorous acid. 
Lithium hypochlorite has found application as a swimming pool sanitization 
agent. Current commercial processes for the manufacture of lithium 
hypochlorite produce a low assay product of approximately 29% by weight of 
LiOCl by the chlorination of lithium hydroxide. The impurities in the 
commercial product include chlorates, carbonates, sulfates, and chlorides 
of potassium, sodium, or lithium. The process is in addition complex and 
costly. 
Various other processes for the manufacture of LiOCl of a higher degree of 
purity have been described. U.S. Pat. Nos. 1,481,039 and 1,481,040 teach a 
method for the production of LiOCl with a low level of impurities by 
chlorination of LiOH. The conformed LiOCl is removed by alcohol extraction 
to form an alkyl hypochlorite, which is then treated with excess LiOH to 
recover the LiOCl. 
U.S. Pat. No. 3,498,924, issued Mar. 3, 1970 to Walsh et al. describes the 
reaction of dilute hypochlorous acid solutions with sodium hydroxide. 
According to the patent, anhydrous sodium hypochlorite, sodium 
hypochlorite hydrate, and basic sodium hypochlorites can be produced. The 
authors contemplate the formation of solid products of potassium 
hypochlorite, lithium hypochlorite, and alkaline earth metal hypochlorites 
by this reaction. 
Surprisingly, now it has been discovered that solid lithium hypochlorite 
can be produced directly and with ease for use in sanitizing and bleaching 
applications. 
It is an object of the present invention to provide a process for producing 
lithium hypochlorite which substantially reduces the presence of 
impurities such as chlorates, carbonates, sulfates, and chlorides. 
Another object of the present invention is to provide a process for 
producing lithium hypochlorite which eliminates the need for extraction 
with an organic solvent. 
An additional object of the present invention is to provide a process for 
producing lithium hypochlorite which reduces the amount of expensive 
lithium hydroxide required. 
A further object of the present invention is to provide a process for 
producing lithium hypochlorite which readily dries the lithium 
hypochlorite product to desired moisture contents at reduced energy 
requirements and with a minimum of product loss. 
A still further object of the present invention is to provide a process for 
producing lithium hypochlorite which reduces the number of processing 
steps required. 
The novel process for producing lithium hypochlorite comprises admixing a 
hypochlorous acid solution having a concentration of 35 percent or greater 
by weight of HOCl with an aqueous slurry of lithium hydroxide at a 
temperature in the range of from about 0.degree. to about 20.degree. to 
produce a solution of lithium hypochlorite. 
The novel process of the present invention employs as the starting material 
a concentrated solution of hypochlorous acid, HOCl. A process for 
producing the concentrated solution of hypochlorous acid is carried out in 
a suitable reactor such as one provided with means for spraying discrete 
droplets of an aqueous solution of an alkali metal hydroxide into the 
reactor; means for feeding gaseous chlorine into the reactor; means for 
withdrawing solid alkali metal chloride product from the reactor; and 
means for withdrawing a gaseous mixture comprised of hypochlorous acid, 
chlorine monoxide, unreacted chlorine and water vapor from the reactor. 
The reactor, reactant feed lines, or both are provided with suitable 
heating means for maintaining the reaction at a temperature sufficiently 
high to vaporize the hypochlorous acid product and water and to dry the 
alkali metal chloride particles. 
Any alkali metal hydroxide capable of reacting with gaseous chlorine to 
form hypochlorous acid may be employed as a reactant in the process of 
this invention. Typical examples of suitable alkali metal hydroxides 
include sodium hydroxide, potassium hydroxide, lithium hydroxide and 
mixtures thereof. Sodium hydroxide is the preferred reactant since the 
resulting sodium chloride by-product is more easily disposed of than the 
other alkali metal chlorides. As gaseous mixtures having high 
concentrations of hypochlorous acid and chlorine monoxide are desired, 
highly concentrated aqueous solutions of the alkali metal hydroxide are 
used. Suitable concentrations include those in the range of from about 40 
to about 80, and preferably from about 45 to about 60 percent by weight of 
alkali metal hydroxide. 
The alkali metal hydroxide solution is sprayed from at least one atomizer 
preferably positioned at or near the top of the reactor. The atomizer is 
preferably positioned along the central axis of a cylindrical reactor, to 
provide minimum contact between the atomized droplets and the walls. The 
atomizer may be directed up, down, sideways or any other orientation that 
meets the above conditions. Droplet sizes are selected which permit a 
substantially complete reaction of the droplets of alkali metal hydroxide 
with chlorine, the vaporization of hypochlorous acid and water produced 
and the production of substantially dry alkali metal chloride particles 
having low concentrations of chlorate. 
The dry alkali metal chloride particles produced, while smaller than the 
original droplets, are preferably sufficiently large enough to prevent a 
significant portion of the particles from being entrained in the gaseous 
mixture of hypochlorous acid produced. 
Typical atomizing techniques of the pneumatic, hydraulic, and spinning disc 
type, among others, which are suitable for use in the process of this 
invention, are described in the monograph entitled "Atomization and Spray 
Graining" by W. R. Marshall, Jr., Chemical Engineering Progress Monograph 
Series, No. 2, Volume 50, 1954. A gas, such as chlorine gas, under 
pressure may be used to atomize droplets of aqueous alkali metal hydroxide 
by premixing before discharge from the nozzle, or the liquid droplets and 
chlorine gas are mixed after discharge from their respective nozzles. The 
chlorine gas which reacts with the alkali metal hydroxide is fed directly 
to the reactor. 
The process of for producing concentrated hypochlorous acid employs a large 
excess of chlorine gas above the stoichiometric amount of alkali metal 
hydroxide as illustrated by the following equation: 
EQU Cl.sub.2 +NaOH.fwdarw.HOCl+NaCl (1). 
Suitable excess amounts of chlorine gas include those in which the molar 
ratio of chlorine to alkali metal hydroxide is equal or greater than about 
20:1. For example, excess amounts of chlorine may include molar ratios 
from 20:1 to about 200:1, preferably from about 25:1 to about 100:1, and 
more preferably from about 30:1 to about 50:1. 
These large excesses of chlorine gas result in increased yields of 
hypochlorous acid as the formation of chlorate is minimized and its 
concentration in the alkali metal chloride particles is less than about 10 
percent by weight, and preferably less than about 6 percent by weight. In 
addition, the use of large excesses of chlorine gas provide an improved 
method of maintaining the reaction temperature. In a continuous process, 
the gaseous mixture of hypochlorous acid vapor, water vapor, chlorine gas, 
and chlorine monoxide gas produced in the reactor is removed from the 
reactor and passed through a solids separator to remove any fine particles 
of alkali metal chloride which may be present. The solids-free gaseous 
mixture is then liquified to produce an aqueous solution of hypochlorous 
acid having, for example, from about 40 to about 60, and preferably from 
about 45 to about 50 percent by weight of HOCl. The liquefaction may be 
carried out, for example, by condensing the gaseous mixture at 
temperatures in the range of from about -5.degree. to about +10.degree. C. 
The concentrated hypochlorous acid solution is substantially free of ionic 
impurities such as alkali metal, chloride, and chlorate ions. For example, 
concentrations of the chloride ion are less than about 50 parts per 
million; the alkali metal ion concentration is less than about 50 parts 
per million; and the chlorate ion concentration is no higher than about 
100 parts per million. 
The second reactant in the novel process of the present invention is 
lithium hydroxide in the anhydrous or monohydrated form. The lithium 
hydroxide employed is, for example, a commercially available industrial 
grade, preferably having low concentrations of impurities such as lithium 
chloride. In the process, lithium hydroxide is employed as an aqueous 
slurry containing from about 10 to about 40%, preferably from about 15 to 
about 35, and more preferably from about 25 to about 35 percent by weight 
of LiOH. While lower concentrations of LiOH may be used, their use results 
in excessive amounts of filtrate for recycle or disposal. 
In the novel process of the present invention, the hypochlorous acid 
solution, having a concentration of 35 percent or greater by weight of 
HOCl, is admixed with a lithium hydroxide slurry to form a reaction 
mixture. The reaction mixture is preferably stirred or agitated to provide 
a homogeneous reaction mixture. During the process, the temperature of the 
reaction mixture is maintained for example, in the range of from about 
0.degree. C. to about 20.degree. C., and preferably from about 5.degree. 
C. to about 10.degree. C. Additional lithium hydroxide is added until the 
desired lithium hypochlorite concentration is attained The reaction 
mixture is monitored for excess alkalinity and when this decreases to 
about 1 percent or less, addition of HOCl is discontinued, and the product 
solution is recovered. 
The process of the invention is represented by the following equation: 
EQU LiOH+HOCl.fwdarw.LiOCl+H.sub.2 O (2) 
As shown in the above equation, only one mole of lithium hydroxide is 
required per mole of lithium hypochlorite. The lithium hypochlorite 
solution produced has a concentration of from about 15 to about 40, and 
preferably from about 25 to about 40 percent by weight of LiOCl. The 
product solutions contain small amounts of impurities such as lithium 
chlorate and lithium chloride which are formed during the reaction. 
The lithium hypochlorite solutions produced are highly pure and could be 
used directly in the sanitizing of water. However it is preferred to use 
solid forms of lithium hypochlorite. 
In one embodiment, solutions of lithium hypochlorite are concentrated by 
evaporation at sub-atmospheric pressures at temperatures in the range of 
from about 30.degree. to about 60.degree., and preferably from about 
40.degree. to about 50.degree. C. Suitable pressures are those which are 
about 10% or less of the vapor pressure of the solution at the 
concentration temperature. The concentration process is continued until a 
slurry of lithium hypochlorite containing at least 40 percent by weight, 
for example, from about 42 to about 50 percent by weight of LiOCl. Excess 
solution is removed by any suitable solid-liquid separation method such as 
filtration. 
In a preferred embodiment, the solutions of lithium hypochlorite are 
concentrated by cooling the solutions at about subzero temperatures, for 
example, at a temperature in the range of from about 0.degree. to about 
-20.degree. C., and preferably in the range of from about -5.degree. to 
about -15.degree. C. Crystals of lithium hypochlorite are separated from 
excess solution by any suitable solid-liquid separation method such as 
filtration. The crystals recovered may be dried in any suitable manner. 
In a more preferred embodiment, the crystals are allowed to melt to form a 
substantially pure solution of lithium hypochlorite. Melting of the pure 
lithium hypochlorite crystals takes place at ambient temperatures, 
however, gentle heating conditions may be employed if desired. 
The concentrated solution or slurry of LiOCl is dried using any suitable 
gentle drying method to produce solid lithium hypochlorite having the 
desired moisture content. For example, the concentrated LiOCl may be dried 
in a fluidized bed dryer, a spray dryer, a vacuum pan dryer, etc. where 
the drying temperature is in the range of from about 50.degree. C. to 
about 200.degree. C. The low concentrations of impurities in the lithium 
hypochlorite solutions or crystals minimizes the hygroscopicity of the 
product permitting ease of drying at reduced energy requirements. 
Concentrated solutions or slurries of LiOCl are preferably dried in a 
spray dryer employing inlet temperatures in the range of from about 
120.degree. to about 200.degree. C. 
The solid lithium hypochlorite product produced is a highly pure source of 
available chlorine having a concentration of at least 55 percent by weight 
of LiOCl, and preferably, in the range of from about 75 to about 100 
percent by weight of LiOCl. These solid products contain at least 65% of 
available chlorine, and preferably from about 90 to 120% of available 
chlorine. 
As the process of the invention does not employ extraction with an organic 
solvent, the product is free of organic impurities. Further, the process 
employs a molar ratio of the costly lithium hydroxide to hypochlorous acid 
of about 1:1 in comparison to the processes commercially employed up to 
the present which require a molar ratio of at least 2:1. 
The addition of a potassium compound, such as solid KOH or a solution of 
KOCl to any LiOCl filtrate recovered results in the precipitation of solid 
KClO.sub.3 which is readily removed from the solution. The remaining 
filtrate may be utilized to suspend lithium hydroxide for further 
hypochlorination. 
Small amounts of this filtrate may be discarded depending upon the level of 
the chloride impurities present. It is envisioned that this same technique 
would be useful in the removal of deleterious Ca(ClO.sub.3).sub.2 from 
solutions generated in the manufacture of calcium hypochlorite.

To further illustrate the invention the following examples are provided 
without any intention of being limited thereby. All parts and percentages 
are by weight unless otherwise specified. 
EXAMPLE I 
A slurry of 15% LiOH (221 g.) was prepared by suspending 79 g of solid 
LiOH.H.sub.2 O in water. To this slurry, an aqueous hypochlorous acid 
solution containing 38 percent by weight HOCl was added until all of the 
lithium hydroxide had been converted to a solution of lithium 
hypochlorite. To this solution an additional 79 g of LiOH.H.sub.2 O was 
then added and the addition of the aqueous solution of HOCl was continued 
until the lithium hydroxide was completely converted to a solution of 
lithium hypochlorite. The solution of LiOCl was then subjected to vacuum 
evaporation at temperatures increasing from 35.degree. C. to 50.degree. C. 
Components and their concentrations are given in Table 1 below: 
TABLE I 
______________________________________ 
Component HOCl* LiOH* Slurry* 
Paste* 
______________________________________ 
HOCl 38 
LiOH 57 0.8 1.7 
LiOCl 25.0 48.1 
LiClO.sub.3 1.6 2.7 
LiCl 0.8 1.2 
H.sub.2 O 62 43 71.8 46.3 
______________________________________ 
*Wt. % 
EXAMPLE 2 
The process of Example 1 was repeated to produce a paste of lithium 
hypochlorite containing 40.6 percent by weight of LiOCl. The paste was 
filtered on a coarse fritted Buchner funnel to produce a filter cake 
containing 56.2 percent by weight of lithium hypochlorite. This filter 
cake was then dried in a fluid bed dryer at air temperatures ranging 
50.degree. C. to 60.degree. C. The product contained 24.8 percent by 
weight of moisture. There was little or no decomposition during the drying 
stage. The components and their concentrations are given in Table 2 below. 
TABLE II 
__________________________________________________________________________ 
Dried* 
Dried* 
Component 
HOCl* 
LiOH* 
Slurry* 
Paste* 
Felt* 
Cake* 
(50.degree. C.) 
(60.degree. C.) 
__________________________________________________________________________ 
44.4 
LiOH 57 0.7 1.2 1.5 
0.6 1.5 0.6 
LiOCl 25.4 40.6 
34.7 
56.2 
66.6 68.4 
LiClO.sub.3 1.9 3.8 4.8 
2.7 3.1 4.1 
LiCl 1.6 2.9 3.9 
2.3 3.0 2.1 
H.sub.2 O 
55.6 
43 70.4 51.5 
55.1 
38.2 
25.8 24.8 
__________________________________________________________________________ 
*Wt. % 
EXAMPLE 3 
The process of Example 2 was repeated to produce a cake containing 59.45% 
by weight of LiOCl. This cake was dried at a temperature of 83.degree. C. 
for 60 minutes to produce a product containing 75.0% LiOCl with a moisture 
content of 12.2% water. The lithium hypochlorite product produced 
corresponded to a mixture of LiOCl.H.sub.2 O and anhydrous LiOCl. The dry 
basis LiOCl was reduced from 88.5% to 85.4%, indicating very slight 
degradation of the product while drying. 
EXAMPLE 4 
The process of Example 2 was repeated and a portion of the product placed 
in constant temperature storage oven at 45.degree. C. and allowed to stand 
for 30 days at this temperature. The initial product analyzed 75.7% LiOCl 
by weight. The moisture content was 11%. At the end of thirty days, the 
product analyzed 73.7% LiOCl by weight. This corresponds to relative loss 
of sanitizing power of 2.7% over 30 days. This illustrates the 
surprisingly high stability of the lithium hypochlorite solid produced by 
this process. 
EXAMPLE 5 
A slurry of 20% lithium hydroxide (737 g) was prepared by suspending 263 g 
of solid LiOH.H2O in water. This slurry was then cooled to 0.degree. C. An 
aqueous hypochlorous acid solution containing 43.7% by weight HOCl was 
added to the LiOH slurry while maintaining a temperature below 20.degree. 
C. until the excess alkalinity of the lithium hypochlorite solution 
reached one percent. An additional 263 g of LiOH.H.sub.2 O was introduced 
to the LiOCl solution. The HOCl addition continued at a temperature below 
20.degree. C. until the LiOH was completely converted to LiOCl. The LiOCl 
solution was then vacuum evaporated at temperatures ranging from 
45.degree. C. to 50.degree. C. to produce a slurry containing 41.6% by 
weight of LiOCl. The slurry was vacuum filtered to produce a cake with a 
LiOCl concentration of 56.4% by weight. The filter cake was then dried in 
a fluid bed dryer for 20 to 25 minutes at an air temperature of 90.degree. 
C. 
TABLE III 
______________________________________ 
Com- 
ponent 
HOCl* LiOH* Solution* 
Slurry* 
Cake* Product* 
______________________________________ 
HOCL 46.0 
LiOCl 27.8 41.6 56.4 70.1 
LiClO.sub.3 1.1 2.1 3.4 5.2 
LiCl 1.2 2.2 3.1 8.2 
LiOH 57.0 1.0 1.5 1.8 3.2 
H.sub.2 O 
54.0 53.0 68.9 52.6 53.3 13.3 
______________________________________ 
*Wt. % 
EXAMPLE 6 
A slurry of 20% lithium hydroxide (13,274 g) was prepared by suspending 
4737 g of LiOH.H.sub.2 O in water. The slurry was then cooled to 
0..degree. C. While maintaining a temperature below 10.degree. C., an 
aqueous hypochlorous acid solution containing 47% by weight HOCl was added 
to the LiOH slurry until the excess alkalinity approached one percent. An 
additional 4737 g of LiOH.H.sub.2 O was introduced to the LiOCl solution. 
The HOCl addition was continued at a temperature below 20.degree. C. until 
the alkalinity of the solution was below 1%. The LiOCl solution was then 
spray dried at an inlet temperature ranging from 210.degree. C. to 
260.degree. C. and an atomizer air pressure of 20 to 25 lbs. The exit 
temperature of the dryer system ranged from 100.degree. C. to 130.degree. 
C. The dried solid LiOCl had the consistency of powder with an 18.7% water 
content. 
TABLE IV 
______________________________________ 
Component HOCl* LiOH* Solution* 
Product* 
______________________________________ 
HOCl 47.0 
LiOCl 29.1 57.2 
LiClO.sub.3 0.5 5.7 
LiCl 2.0 13.1 
LiOH 57.0 0.7 5.3 
H.sub.2 O 53.0 43.0 67.7 18.7 
______________________________________ 
*Wt. % 
EXAMPLE 7 
Deionized water (8537 g) and 4737 g of LiOH.H.sub.2 O were mixed in a 15 
gallon reactor. The slurry was cooled to 3.degree. C. and 48% HOCl was 
added at a rate to maintain the temperature between 0.degree. C. and 
15.degree. C. As the alkalinity decreased, solid LiOH.H.sub.2 O was added 
to the reactor. A total of 18,948 g of LiOH.H.sub.2 O was added to the 
reactor. The HOCl flow was shut off when the residual alkalinity of the 
LiOCl solution, as measured by a "drop test", was reduced to less than 1%. 
The LiOCl solution was poured into a container and refrigerated at a 
temperature of 2.degree.-5.degree. C. After 6 days the solution was fed 
directly to a spray dryer operated at an inlet temperature of 175.degree. 
C. and an outlet temperature of 98.degree. C. During the drying operation, 
a collection chamber filled with dry product. After one hour dried LiOCl 
crystals were removed from the collection chamber and analyzyed. The 
analysis is reported as Example 7a below. Dried LiOCl crystals were 
removed from the collection chamber after 2 hours of drying and again 
after 3 hours of drying. The analyses are reported below as Examples 7b 
and 7c respectively. 
______________________________________ 
Solution* 
______________________________________ 
LiOCl 31.4 
LiClO.sub.3 
1.3 
LiCl 0.8 
LiOH 0.5 
H.sub.2 O 
66.0 
______________________________________ 
Spray Dried LiOCl Crystals*: 
Example 7a Example 7b 
Example 7c 
______________________________________ 
LiOCl 75.13 76.43 74.84 
LiClO.sub.3 
5.39 5.32 5.70 
LiCl 6.15 6.58 6.64 
LiOH 0.00 2.02 1.73 
H.sub.2 O 
13.33 9.65 11.09 
______________________________________ 
*Wt. % 
EXAMPLE 8 
Deionized water (8537 g) and 4737 g of LiOH.H.sub.2 O were mixed in a 15 
gallon reactor. The slurry was cooled to 3.degree. C. and 48% HOCl was 
added at a rate to maintain the temperature between 0.degree. C. and 
15.degree. C. As the alkalinity decreased, solid LiOH.H.sub.2 O was added 
to the reactor. A total of 18,948 g of LiOH.H.sub.2 O was added to the 
reactor. The HOCl flow was shut off when the residual alkalinity of the 
LiOCl solution, as measured by a "drop test", was reduced to less than 1%. 
A container of the LiOCl solution was refrigerated at a temperature of 
2.degree.-5.degree. C. After 23 days the solution was stored in a freezer 
at -6.degree. C. After 6 days the frozen LiOCl crystal agglomerates were 
removed and exposed to ambient conditions for 24 hours. The crystal 
agglomerates, having sizes in the range of about 1.2 to 3.6 centimeters, 
were then readily separated by filtration from the mother liquor and both 
the crystals and the mother liquor were analyzed. The crystals were 
allowed to melt at room temperature and the concentrated solution formed 
was fed directly to the spray dryer. The spray dryer was operated at an 
inlet temperature of 145.degree.-160.degree. C. and an outlet temperature 
of 90.degree.-120.degree. C. During the drying operation, a collection 
chamber filled with dry product. After 70 minutes dried LiOCl crystals 
were removed from the collection chamber and analyzed. The analysis is 
reported as Example 8a below. Dried LiOCl crystals were removed from the 
collection chamber after 2.5 hours of drying and analyzed (Example 8b). At 
this time the dryer was shutdown, cleaned and restarted. After 2 
additional hours of drying the dried LiOCl crystals in the collection 
chamber were removed and analyzed (Example 8c). 
______________________________________ 
Original LiOCl LiOCl 
Analysis: 
Solution* Crystals* Filtrate* 
______________________________________ 
LiOCl 32.43 38.99 15.76 
LiClO.sub.3 
0.48 0.59 3.30 
LiCl 0.88 0.53 4.66 
LiOH 0.26 0.00 1.00 
H.sub.2 O 
65.95 59.89 75.23 
______________________________________ 
Spray Dried LiOCl Crystals*: 
Example 8a Example 8b 
Example 8c 
______________________________________ 
LiOCl 78.19 77.07 81.51 
LiClO.sub.3 
3.47 4.92 5.40 
LiCl 4.07 5.36 6.47 
LiOH 0.94 1.34 1.55 
H.sub.2 O 
13.33 11.31 5.07 
______________________________________ 
*Wt. %