DESCRIPTION
TITLE OF THE INVENTION: METHOD AND APPARATUS FOR PRODUCING
PURIFIED HYPOCHLOROUS ACID AQUEOUS SOLUTION, AND PURIFIED
5 HYPOCHLOROUS ACID AQUEOUS SOLUTION
TECHNICAL FIELD
[0001] The present invention relates to a method and an apparatus for
producing a high-purity hypochlorous acid aqueous solution, and a purified
10 hypochlorous acid aqueous solution.
BACKGROUND ART
[0002] Since 2020, coronaviruses have been spreading around the world
and threatening people’s lives. Hypochlorous acid water has shown activity
15 even against coronaviruses and is expected to provide sterilization performance
by spatial spraying, but there are concerns about the effects on the human body
and corrosion of sprayers due to impurities contained in hypochlorous acid water.
[0003] As production methods for hypochlorous acid (HOCl), (1) a method
of injecting chlorine gas into water (see Formula (I)), (2) a method of adding
20 (inorganic, organic) acids to a sodium hypochlorite solution (NaOCl) (see
Formula (II) and (II’)), and (3) a method of subjecting dilute hydrochloric acid
(HCl: Non-diaphragm method), chlorides such as sodium chloride and the like
(NaCl and the like: Diaphragm method) to electrolysis (see Formula (III) and (III’)
are widely known. A problem common to such production methods is that the
25 presence ratio (molar ratio) of acidic substances such as hydrogen chloride and
the like or acid and alkaline neutralizers to hypochlorous acid is generally 1:1 or
more. Therefore, unnecessary impurity ions are included in equivalent
2
amounts or more.
H2O+Cl2 → HCl+HOCl Formula (I)
NaOCl+HCl → HOCl+NaCl Formula (II)
NaOCl+CH3COOH → HOCl+CH3COONa Formula (II’)
5 HCl+H2O → HOCl+H2 Formula (III)
2NaCl+3H2O → HCl+HOCl+2NaOH+H2 Formula (III’)
[0004] Moreover, slightly acidic hypochlorous acid water produced by
dilute hydrochloric acid in (3) described above (Formula (III)) shows slight acidity
due to the neutralization reaction of hydrochloric acid with a salt of alkaline
10 metals, alkaline earth metals such as carbonates and the like that are hardness
components in source water (see Formula (IV)), so that the hardness in the
source water needs to be generally 30 mg/L or more.
2HCl+Ca(CO3)2 → CaCl2+2HCO3 Formula (IV)
[0005] Generally, hypochlorous acid is an unstable substance and is said
15 to deactivate immediately, but actually it does not deactivate rapidly unless
supply of external energy such as heat, ultraviolet light, and the like, or alter of
the chemical equilibrium with coexisting ions, so that it shows a gradual decay
curve due to the disproportionation reaction. In a case that unnecessary
impurity ions such as hydrogen chloride, which is a factor lowering the pH,
20 undecomposed salt derived from the source liquid, and the like are included in
a large amount, these are factors accelerating the deactivation (decomposition)
of hypochlorous acid. Chlorine is most stable in its chlorine ion (Cl-
) state, and
through the disproportionation reaction, hypochlorous acid (HOCl) gradually
becomes hydrogen chloride (HCl), and chlorous acid (HClO2), chloric acid
25 (HClO3) (see the following Formula (V) and (VI)). Then, when the pH of the
solution is 5 or less, the activity of hydrogen chloride (HCl) increases, and the
disproportionation reaction is accelerated.
3
2HOCl → HCl+HClO2 Formula (V)
HOCl+HClO2 → HCl+HClO3 Formula (VI)
[0006] A method of separating hypochlorous acid from alkaline metal
chlorides or alkaline earth metal chlorides by an evaporation method to address
5 these problems is disclosed in Patent document 1. Specifically, in Patent
document 1, thin-film distillation is performed at 60°C, and hypochlorous acid
water including 0.46 mol/L hypochlorous acid, 0.48 mol/L sodium chloride, and
0.04 mol/L chlorine is used to obtain hypochlorous acid water including a 55%
yield of hypochlorous acid, and having the concentrations of sodium chloride
10 and chlorine of 0.003 mol/L or less and 0.003 mol/L or less, respectively.
[0007] Moreover, Patent document 2 discloses producing hypochlorous
acid water not substantially including impurity ions other than hypochlorous acid
using a 2-diaphragm, 3-chamber electrolytic tank separating an anode chamber,
a cathode chamber and a middle chamber by diaphragms, respectively, which
15 middle chamber is provided between the anode chamber and the cathode
chamber and includes non-electrolyte.
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
25 [0009] Tests by the present inventors have revealed that, when separating
hypochlorous acid from ions by an evaporation method, the concentration of
sodium chloride being a source liquid could be reduced to 1/10,000 or less (for
4
example, NaCl 1,000 mg/L to 0.02 mg/L=1/50,000). However, with the method
of Patent document 1, there are concerns about the effect of the evaporation
temperature for evaporation, the decomposition of hypochlorous acid due to the
phase change from liquid to gas, the decrease in the pH of a hypochlorous acid
5 solution due to the presence of chlorine gas, and the like.
[0010] Moreover, with the method of Patent document 2, there is a problem
that, when trying to increase the concentration of hypochlorous acid, the pH
decreases, resulting in an aqueous solution with a high total chlorine ion content,
and the concentration of hypochlorous acid decreases during storage.
10 Moreover, when, to reduce the amount of hydrogen chloride in the aqueous
solution, sodium hydroxide, sodium hydrogen carbonate, and the like are used
to neutralize hydrogen chloride, undecomposed chlorides such as NaCl and the
like increase.
[0011] Therefore, a problem of the present invention is to provide a high15 purity purified hypochlorous acid aqueous solution with a very small content of
impurity ions relative to the concentration of hypochlorous acid.
MEANS TO SOLVE THE PROBLEM
[0012] As a result of the present inventors studying the above-described
20 problems, it has been found that, when a hypochlorous acid-containing water
solution was subjected to vacuum evaporation, by setting a temperature in the
above-mentioned vacuum evaporation to 40°C or less, a high-purity purified
hypochlorous acid aqueous solution with a very small content of impurity ions
relative to the concentration of hypochlorous acid could be provided.
25 [0013] In other words, the present invention relates to:
[1] A method for producing a purified hypochlorous acid aqueous
solution, which comprises a step of extracting hypochlorous acid by subjecting
5
a hypochlorous acid-containing water solution as a source liquid to vacuum
evaporation at a temperature of 40°C or less,
[2] The method according to [1] described above, wherein pH of the
hypochlorous acid-containing water solution being the source liquid is between
5 5.0 and 8.6, preferably between 5.0 and 7.5, more preferably between 5.0 and
6.5, and further preferably between 5.8 and 6.3,
[3] The method according to [1] or [2] described above, wherein a
temperature of the vacuum evaporation is between 10°C and 40°C,
[4] The method according to [3] described above, wherein the
10 temperature of the vacuum evaporation is between 10°C and 30°C, preferably
between 10°C and 15°C,
[5] The method according to any one of [1] to [4] described above,
wherein a concentration of hypochlorous acid in the hypochlorous acidcontaining water solution being the source liquid is 10,000 ppm or less,
15 preferably between 20 ppm and 10,000 ppm, more preferably between 20 ppm
and 1,000 ppm, and further preferably between 500 ppm and 800 ppm,
[6] A vacuum evaporation apparatus comprising a heater, an
evaporation can, and a condenser to purify a hypochlorous acid-containing
water solution, characterized in that the vacuum evaporation apparatus
20 comprises a mechanism to control an evaporation temperature to between 10°C
and 40°C, preferably between 10°C and 30°C, and more preferably between
10°C and 15°C,
[7] The vacuum evaporation apparatus according to [6] described
above, comprising an after-condenser after the condenser, and
25 [8] A purified hypochlorous acid aqueous solution obtained by
vacuum evaporation, wherein a pH is 6.5 or less, preferably between 5.8 and
6.5, a concentration of hypochlorous acid in the aqueous solution is between 40
6
ppm and 10,000 ppm, preferably between 50 ppm and 1,000 ppm, and a
concentration of impurity ions in the aqueous solution is 5.0 ppm or less,
preferably 0.05 ppm or less.
5 EFFECTS OF THE INVENTION
[0014] The present invention makes it possible to provide a high-purity
purified hypochlorous acid aqueous solution with a very small content of impurity
ions relative to the concentration of hypochlorous acid by manufacturing a
purified hypochlorous acid aqueous solution with the temperature of the vacuum
10 evaporation of a hypochlorous acid-containing water solution being set to 40°C
or less.
[0015] Moreover, such a purified hypochlorous acid aqueous solution is
slow in deactivating hypochlorous acid being the main component of disinfection,
making it possible to suppress the side reaction (effect) such as irritation on
15 living organisms, corrosion, and the like to the equivalent level or less relative to
that of tap water.

CLAIMS:
1. A method for producing a purified hypochlorous acid aqueous
solution, which comprises a step of extracting hypochlorous acid by subjecting
5 a hypochlorous acid-containing water solution as a source liquid to vacuum
evaporation at a temperature of 40°C or less.
2. The method according to claim 1, wherein a pH of the
hypochlorous acid-containing water solution being the source liquid is between
10 5.0 and 8.6.
3. The method according to claim 1, wherein a temperature of the
vacuum evaporation is between 10°C and 40°C.
15 4. The method according to claim 3, wherein the temperature of the
vacuum evaporation is between 10°C and 30°C.
5. The method according to any one of claims 1 to 4, wherein a
concentration of hypochlorous acid in the hypochlorous acid-containing water
20 solution being the source liquid is 10,000 ppm or less.
6. A vacuum evaporation apparatus comprising a heater, an
evaporation can, and a condenser to purify a hypochlorous acid-containing
water solution, characterized in that the vacuum evaporation apparatus
25 comprises a mechanism to control an evaporation temperature to between 10°C
and 40°C.
7. The vacuum evaporation apparatus according to claim 6,
comprising an after-condenser after the condenser.
8. A purified hypochlorous acid aqueous solution obtained by
5 vacuum evaporation, wherein a pH is 6.5 or less, a concentration of
hypochlorous acid in the aqueous solution is between 40 ppm and 10,000 ppm,
and a concentration of impurity ions in the aqueous solution is 5.0 ppm or less.