Technical Field
[0001]
The present invention relates to an electrolysis device
and an apparatus for producing electrolyzed ozone water,
configured to use unpurified water containing a small amount
of ions of alkaline earth metals such as calcium and magnesium
as raw water and to perform electrolysis by a
membrane-electrode assembly which is constituted by a solid
polymer electrolyte separation membrane formed from a cation
exchange membrane, and an anode and a cathode which are
respectively adhered to both surfaces of the solid polymer
electrolyte separation membrane, and also to the electrolysis
device and the apparatus for producing electrolyzed ozone water,
which are capable of preventing localized deposition of scale
which is mainly formed of hydroxide of the alkaline earth metal,
at a contact interface between the cathode and the solid polymer
electrolyte separation membrane.
Background Art
2
[0002]
Water treatment using an electrolytic reaction is widely
performed, for example, in order to perform production of
functional water, ozone water, and electrolyzed water,
sterilization, decomposition and removal of a harmful
substance through electrolysis. A reaction tank used in the
above process generally has a structure in which an anode, a
cathode, and an ion exchange membrane or a porous separation
membrane which is interposed between the anode and the cathode
are accommodated in a housing. Such a reaction tank is referred
to as an electrolytic bath or an electrolysis cell. This type
of electrolytic bath or electrolysis cell is configured by a
separation membrane, an anode chamber formed by being separated
by the separation membrane, a cathode chamber formed by being
separated by the separation membrane, an anode provided in the
anode chamber, and a cathode provided in the cathode chamber.
As this type thereof, a two-chamber type electrolysis device
or a three-chamber type electrolysis device is known.
As the two-chamber type electrolysis device, there are
a diaphragm process type electrolysis device, a cation exchange
membrane type electrolysis device, and a solid polymer
electrolyte type electrolysis device which is a special type.
The diaphragm process type electrolysis device uses a
porous membrane as a separation membrane. The cation exchange
membrane type electrolysis device uses a cation exchange
3
membrane as the separation membrane. The solid polymer
electrolyte type electrolysis device configures an
electrolysis device in which the anode and the cathode are
adhered to both surfaces of the cation exchange membrane, and
thus it is possible to perform electrolysis of pure water having
small electric conductivity, by using the cation exchange
membrane as a solid polymer electrolyte. As the three-chamber
type electrolysis device, a device in which a cation exchange
membrane and an anion exchange membrane as a separation
membrane configured to separate an anode chamber and a cathode
chamber from each other are provided between the anode chamber
and the cathode chamber, and an intermediate chamber is formed
between the cation exchange membrane and the anion exchange
membrane is employed. In the electrolysis devices, various
types of functional water and ozone water are generated.
[0003]
Generally, in a waste liquid treatment process or a
producing process of functional water such as so-called alkali
ion water, unpurified water containing ions of alkaline earth
metal, such as a calcium ion and a magnesium ion is used as
a raw material. In electrolysis using such unpurified water,
while electrolysis is in progress, firstly, pH of a catholyte
is increased on the surface of the cathode, and thus ions of
alkaline earth metal in which a small amount of calcium in raw
water is the main component are deposited on the surface of
4
the cathode, as non-conductive scale, that is, hydroxide, oxide,
and carbonate thereof. As a result, continuing electrolysis
often becomes difficult.
[0004]
Thus, in PTL 1 and PTL 2 , a method of using acid as a
cathode chamber liquid is proposed. However, the
configurations in PTL 1 and PTL 2 are complicated, and safety
management in operation is burdened. In PTL 3, a method in
which an auxiliary tank and a plurality of electrode sets are
installed in an apparatus for producing electrolyzed water,
and are switched and used for each predetermined time, and thus
deposit in a cathode is suppressed is proposed. However, this
method causes the size and cost of the apparatus to be increased.
Further, in PTL 4, a method in which an operation is suspended
for each predetermined time and sediment is removed by acid
washing and the like is described in detail. However, the work
is complicated. In PTL 5, a method in which an electrolysis
cell which does not include a separation membrane is caused
to have acidity by using hydrochloric acid, and thus deposit
in a cathode is prevented is proposed. However, because a
strongly-acidic chemical liquid such as hydrochloric acid is
used, this method may be disadvantageous in an aspect of
securing of safety or cost, and using of strong acid may be
not accepted in accordance with the purpose of the use.
[0005]
5
In PTL 6, a method in which an anode and a cathode of
an electrolysis cell are reversed to each other when
electrolytic properties are deteriorated, and recovery of
performance is achieved by passing through a reverse current
is proposed. In this case, when such a reverse current flows,
the cathode temporarily acts as the anode, and thus the metal
constituent is eluted. Many of ions themselves of the eluted
metal are not preferable as ions contained in a treatment liquid
for each of Cr, Ni, and the like. In addition, the ions are
permeated into a solid polymer electrolyte membrane, and thus
ion transfer capability thereof is significantly degraded.
For this reason, valve metal having high corrosion resistance
may be used in the cathode. However, in this case, expensive
precious metal coating and the like may be performed on the
surface of the valve metal, and, if the coating is not performed,
lowering very high electrolysis overvoltage is required. In
addition, deterioration of an electrode catalyst or an
electrode base by cathodic reduction of the anode which
temporarily functions as the cathode, or hydrogen
embrittlement occurring by cathodic reduction is also
concerned.
[0006]
Further, according to PTL 7, a method of producing
hypochlorite, in which electrolysis of a chloride aqueous
solution is performed without separation membrane by using a
6
cathode in which a coated film which is formed on a conductive
base and has low hydrogen overvoltage is covered with a
reduction prevention coated film, is proposed. As the
reduction prevention coated film, an organic cation exchange
membrane body, an inorganic cation exchange membrane body, or
a mixture thereof is used. However, in an electrolysis method
performed without a separation membrane, that is, a method in
which a matter generated on the anode is directly brought into
contact with the cathode, the reduction prevention coated film
functions to prevent reduction of ions of hypochlorous acid,
which occurs by the cathode, but does not function to prevent
precipitation of cathode deposition which is mainly formed of
hydroxide of alkaline earth metal, on the cathode. In an
electrolysis method and an electrolysis device using a
separation membrane as in the present invention, a reduction
prevention film for preventing reduction of ions of
hypochlorous acid which is a product in an anode, as described
in PTL 7, is not required.
[0007]
In the electrolysis method and the electrolysis device
using a separation membrane in the related art, in a case where
unpurified water containing ions of alkaline earth metal is
used as a raw material, metal ions ionized as cations is
concentrated on the surface of a cathode, and pH is increased
by OH- ions generated on the cathode. As a result, scale which
7
is mainly formed of hydroxide precipitates as a cathode
deposition. Operation inhibition by the formation of the
scale causes a problem. However, in a method of suppressing
formation of scale, which has been conventionally proposed,
a negative aspect in that corresponding cost and labors are
required, or a portion of capability is to be abandoned is large.
Thus, improvement is desired.
[0008]
Ozone water exhibits an advantageous effect of
sterilization and the like when ozone in the ozone water is
decomposed. However, after the ozone is decomposed, only
stable oxygen remains. Thus, the ozone water attracts
attentions as a treatment agent having a very low environmental
load. Currently, the ozone water is used for decomposing an
organic matter, for example, used for sterilization or
decolorization, deodorization, or the like. Henceforth,
further wide use of the ozone water, for example, for preventing
infection diseases is expected.
[0009]
In an ozone water generation cell by an electrolysis
process, generally, a so-called membrane-electrode assembly
is configured as a function unit. The membrane-electrode
assembly has a structure in which an anode for generating ozone,
such as a diamond electrode, a cathode formed of stainless steel
or the like, and a cation exchange membrane interposed between
8
the anode and the cathode are strongly adhered to each other.
If a direct current is applied between the anode and the cathode
in the membrane-electrode assembly, oxygen and ozone are
generated on the surface of the anode in a form of a gas, and
a considerable amount of the ozone gas is dissolved in the
surrounding raw water. Thus, water in which an ozone gas is
dissolved, that is ozone water, is generated.
[0010]
One problem in the above process is that generation
efficiency of ozone water is much lower than a theoretical value
for ozone gas generation.
The inventors found that the amount of dissolved ozone
gas, which determines ozone water generation efficiency,
strongly depends on a flow rate of raw water in the vicinity
of the electrode. However, it is considered that this
phenomenon suggests the followings: a point that local ozone
concentration in water is rapidly locally saturated in the
ozone evolution site; and a point that fine ozone gas bubbles
just after evolution stay in a gas generation site, and rapidly
grow to be larger gas bubbles, and as a result, it becomes
difficult for the ozone gas to efficiently dissolve.
[0011]
Considering the above problems and afterward
marketability, the inventors proposed an electrolysis cell
which was to solve the above problems, and had a structure in
9
which a plurality of through hole were provided in a
membrane-electrode assembly, and raw water passed through the
holes in unidirection. The inventors applied for a patent (PTL
8) which disclosed that it is possible to improve ozone water
generation efficiency by the proposed electrolysis cell.
[0012]
According to an apparatus for producing electrolyzed
ozone water in PTL 8, an anolyte (acidic ozone water which is
an anode product) in an anode chamber and a catholyte (alkali
hydroxide which is a cathode product) generated in a cathode
chamber are mixed, and integrally flow out. Thus, the
catholyte is mixed with the acidic ozone water which is the
anolyte generated on the anode, and pH on the surface of the
cathode is lowered from alkalinity to the vicinity of
neutrality. Thus, an occurrence of a situation in which scale
which is mainly formed of hydroxide of alkaline earth metal
precipitates on the surface of the cathode is considerably
suppressed.
[0013]
However, the followings are understood in the apparatus
for producing electrolyzed ozone water in PTL 8. That is, a
rigid material such as precious metal, nickel, stainless steel,
and titanium is used in the cathode. Almost all of scale which
is mainly formed of hydroxide of alkaline earth metal, such
as calcium hydroxide and magnesium hydroxide, which
10
precipitates in the vicinity of a contact interface between
the cathode and a solid polymer electrolyte separation membrane
without coming into contact with acidic ozone water which is
an anolyte generated on the anode side is not stored in the
cathode, and does not pass through multiple through holes
formed in the cathode. Almost all of the scale is deposited
at the contact interface between the cathode and the solid
polymer electrolyte separation membrane. Thus, continuing
electrolysis may be interfered.
In addition, the followings are understood. The cathode
is formed from a rigid material, and does not have flexibility.
Thus, even though the cell is formed as a solid polymer type
electrolysis cell by compressing from both sides thereof, the
cathode, the anode, and the solid polymer separation membrane
are not sufficiently adhered to each other, and a cell voltage
is increased.
Citation List
Patent Literature
[0014]
[PTL 1] JP 2002-173789A
[PTL 2] JP 2005-177671A
[PTL 3] JP 2011-050807A
[PTL 4] JP 10-130876A
[PTL 5] JP 2008-200667A
11
[PTL 6] JP 2008-150665A
[PTL 7] JP 08-104991A
[PTL 8] JP 2011-246799A
Summary of Invention
Technical Problem
[0015]
An object of the present invention is to solve the above
problems in the method of the related art, and to provide an
electrolysis device and an apparatus for producing
electrolyzed ozone water. The electrolysis device and the
apparatus for producing electrolyzed ozone water performs
electrolysis in a membrane-electrode assembly configured by
a solid polymer electrolyte separation membrane formed from
a cation exchange membrane, and an anode and a cathode which
are respectively adhered to both surfaces of the solid polymer
electrolyte separation membrane. In a case where unpurified
water containing a small amount of ions of alkaline earth metal
such as calcium and magnesium is used as a raw material,
localized deposition of scale which is mainly formed of
hydroxide of the alkaline earth metal, at a contact interface
between the cathode and the solid polymer electrolyte
separation membrane can be prevented.
[0016]
The present invention relates to an electrolysis device
12
and an apparatus for producing electrolyzed ozone water which
performs electrolysis by using unpurified water containing a
small amount of ions of alkaline earth metal such as calcium
and magnesium, as a raw material. More specifically, a device
which uses unpurified water as raw water and solves problems
occurring by deposit of hydroxide on a cathode in an apparatus
for producing electrolyzed ozone water, an apparatus for
producing functional water, an apparatus for producing
electrolyzed water, a sterilizer, an apparatus for treating
waste water, and the like is proposed. According to the
electrolysis device and the apparatus for producing
electrolyzed ozone water in the present invention, solving
similar problems for other purposes can be expected.
Further, the inventors examined various flow passage
structures passing through a membrane-electrode assembly in
order to improve flow of raw water (tap water) which flows in
the vicinity of an electrode. As a result, the inventors
developed an electrolysis cell for producing ozone water which
shows ozone water production efficiency much higher than that
in the electrolysis cell of the related art, has an electrolytic
voltage lower than that in the electrolysis cell of the related
art, has high power efficiency which is a product of a
percentage of an actual electrolytic voltage and current
efficiency, and thus has small amount of consumed energy. The
inventors verified effectiveness.
13
Solution to Problem
[0017]
To achieve the above object, a first solution in the
present invention includes an electrolysis cell formed in a
manner that a membrane-electrode assembly is compressed from
both sides so as to adhere an anode, a cathode, and a solid
polymer electrolyte separation membrane formed from a cation
exchange membrane to each other, the membrane-electrode
assembly being configured by the solid polymer electrolyte
separation membrane formed from the cation exchange membrane,
and the anode and the cathode which are respectively adhered
to both surfaces of the solid polymer electrolyte separation
membrane; means for supplying raw water consisting of
unpurified water containing alkaline earth metal, to at least
one of the anode and the cathode; and means for mixing an anolyte
generated on the anode with a catholyte generated on the cathode,
wherein a porous conductive metal material which has
flexibility and in which multiple fine voids are provided is
used as the cathode, and scale which is mainly formed of
hydroxide of the alkaline earth metal is stored in the fine
void in the cathode so as to prevent localized deposition of
the scale which is mainly formed of hydroxide of the alkaline
earth metal at a contact interface between the cathode and the
solid polymer electrolyte separation membrane.
14
[0018]
According to a second solution in the present invention,
in the above apparatus for producing electrolyzed water, an
electrolysis cell having a monopolar stack structure is
configured in a manner that at least new one membrane-electrode
assembly which has the same structure as a structure of the
membrane-electrode assembly is further connected to an outside
of the cathode and/or the anode in the membrane-electrode
assembly, so as to bring the cathodes into contact with each
other and/or bring the anodes into contact with each other in
the membrane-electrode assemblies is further configured.
[0019]
According to a third solution in the present invention,
in the above apparatus for producing electrolyzed water, an
electrolysis cell having a bipolar stack structure is
configured in a manner that at least new one different
membrane-electrode assembly which has the same structure as
a structure of the membrane-electrode assembly is further
connected to an outside of the cathode and/or the anode in the
membrane-electrode assembly, so as to bring the cathode and
the anode into contact with each other in the
membrane-electrode assemblies is further configured.
[0020]
According to a fourth solution in the present invention,
in the above apparatus for producing electrolyzed water, the
15
cathode is formed by at least one porous conductive metal
material selected by a group formed from a metal foam, a
metallic fiber cloth, and a fibrous metal molded body.
[0021]
According to a fifth solution in the present invention,
in the above apparatus for producing electrolyzed water, in
a case where the cathode is positioned in an outermost layer
of the electrolysis cell, the cathode is supported by a rigid
cathode substrate formed of a plate material, a mesh, or
perforated punching metal.
[0022]
According to a sixth solution in the present invention,
there is provided an apparatus for producing electrolyzed ozone
water which produces ozone water by performing electrolysis
of unpurified water containing ions of alkaline earth metal
by using the above apparatus for producing electrolyzed water.
Advantageous Effects of Invention
[0023]
According to the present invention, in an electrolysis
device and an apparatus for producing electrolyzed ozone water
having a structure in which an anolyte generated on an anode
and a catholyte generated on a cathode are mixed by using a
membrane-electrode assembly configured by a solid polymer
electrolyte separation membrane formed from a cation exchange
16
membrane, and the anode and the cathode which are respectively
adhered to both surfaces of the solid polymer electrolyte
separation membrane, a porous metal material having
flexibility and having multiple fine voids therein is used as
the cathode. Thus, sufficient contact with acidic ozone water
which is the anolyte generated on the anode is possible, and
generating hydroxide of the alkaline earth metal is suppressed.
Further, scale which is mainly formed of hydroxide of the
alkaline earth metal is stored in the fine voids in the cathode,
and thus localized deposition of the scale which is mainly
formed of hydroxide of the alkaline earth metal, at a contact
interface between the cathode and the solid polymer electrolyte
separation membrane is prevented. Thus, even though various
means according to the related art, as described above, are
not employed, deposit of hydroxide and the like on the surface
of the cathode is suppressed, and thus an increase in
electrolytic voltage is suppressed. As a result, it is
possible to stably perform electrolysis operation for a long
term. The reason is considered as follows. Cathode deposit
is not concentrated on an opposing surface to the anode, that
is, on an electrolytic reaction surface having low solution
resistance, but dispersed in the entirety of the cathode. Thus,
a situation in which sediment of hydroxide and the like directly
covers a cathode catalytic surface which is a reaction surface
does not occur. Accordingly, it is difficult to inhibit the
17
hydrogen generation reaction on the cathode.
[0024]
That is, it is predicted that hydroxide of alkaline earth
metal is stored in fine voids in the cathode with time, because
of the following points. One point is as follows. A small
amount of ions of alkaline earth metal in raw water, for example,
Ca2+ is drawn to the surface of the cathode, and thus a cathode
reaction, that is, Ca2++2H2O+2e-^Ca(OH) 2+H2 occurs. Further,
a cathode reaction is performed on a small amount of ions of
alkali metal which is contained together in many cases, for
example, Na+, that is, Na++H2O+e-^NaOH+ (1/2) H2, and thus the
surface of the cathode has alkalinity. However, in the porous
medium in the cathode, the ions are mixed and brought into
contact with acidic ozone water which is an anolyte generated
on the anode is performed, and thus has properties near to
neutrality. Another point is that the inner and outer portions
of the porous medium may have an equipotential. Actually,
sediment on the cathode is provided on the back surface in
addition to a portion thereof opposing the anode, and is
substantially uniformly distributed on the entirety of the
inner surface and outer surface of the cathode. This is
confirmed by performing visual observation or observation with
a magnifier on the cathode after electrolysis is performed for
a long term. As described above, the contact interface itself
between the solid polymer electrolyte separation membrane
18
(cation exchange membrane) and the cathode is not directly and
preferentially covered with a deposition layer of Ca(OH)2, and
electrolysis continues.
[0025]
That is, according to the present invention, effects as
follows are confirmed.
1) A porous conductive metal material formed by a
material having high flexibility is used as the cathode, and
thus adhesiveness between the solid polymer electrolyte
separation membrane (cation exchange membrane) and the anode
is ensured. In addition, a contact area is increased by a
micro-unevenness, and thus an actual current density is
reduced.
Regarding this point, according to the present invention,
as will be described later, it is confirmed that large
dependency in that “a voltage increase rate by scaling is
proportional to the square or the cube of current density” is
shown.
2) Deposition of calcium is not concentrated at a contact
portion between the solid polymer electrolyte separation
membrane (cation exchange membrane) and the cathode, that is,
at a functional portion for hydrogen generation, but is
dispersed in the porous cathode thus. Thus, it is difficult
to inhibit a cathodic reaction.
3) A porous conductive metal material having multiple
19
fine voids therein is used as the cathode, and thus the fine
voids in the cathode function as a storage for a certain type
relating to scale, and there is an effect of delaying an
occurrence of a lifting phenomenon in which a film by scale
formed at an interface between the cathode and the solid polymer
electrolyte separation membrane (cation exchange membrane) is
therefore separated from the cathode.
Brief Description of Drawings
[0026]
Fig. 1 is a sectional view illustrating one example of
a solid polymer type electrolysis cell which is one example
of an electrolysis device in the related art.
Fig. 2 is a sectional view illustrating one example of
an electrolysis device according to the present invention.
Fig. 3 is a sectional view illustrating another example
of the electrolysis device according to the present invention.
Fig. 4 is a sectional view illustrating still another
example (monopolar stack structure) of the electrolysis device
according to the present invention.
Fig. 5 is a sectional view illustrating still another
example (bipolar stack structure) of the electrolysis device
according to the present invention.
Description of Embodiments
20
[0027]
Hereinafter, regarding the conventional electrolysis
device which is the premise of the present invention, and an
embodiment of an electrolysis device according to the present
invention, an apparatus for producing electrolyzed ozone water
will be described with reference to the drawings.
As described above, ozone water exhibits an advantageous
action such as sterilization, when ozone in the ozone water
is decomposed. After the ozone is decomposed, only stable
oxygen remains. Thus, the ozone water attracts attentions as
a treatment agent having a very low environmental load.
Currently, the ozone water is used for decomposing an organic
matter, for example, used for sterilization or decolorization,
deodorization, or the like. Henceforth, further wide use of
the ozone water, for example, for preventing infection diseases
is expected.
In an ozone water generation cell by an electrolysis
method, generally, a so-called membrane-electrode assembly is
configured as a function unit. The membrane-electrode
assembly has a structure in which an anode for generating ozone,
such as a diamond electrode, a cathode formed of stainless steel
or the like, and a solid polymer electrolyte separation
membrane which is formed from a cation exchange membrane and
is interposed between the anode and the cathode are strongly
adhered to each other. If a DC current is applied between the
21
anode and the cathode in the membrane-electrode assembly,
oxygen and ozone are generated on the surface of the anode in
a form of a gas, and a considerable amount of the ozone gas
is dissolved in the surrounding raw water. Thus, water in which
an ozone gas is dissolved, that is, ozone water is generated.
[0028]
One problem in the above process is that generation
efficiency of ozone water is much lower than a theoretical value
when an ozone gas is generated.
The inventors found that the amount of dissolved ozone
gas, which determines ozone water generation efficiency,
strongly depends on a flow rate of raw water in the vicinity
of the electrode. However, it is considered that this
phenomenon suggests the followings: a point that ozone
concentration in water is rapidly locally saturated in an ozone
generation site; and a point that fine ozone gas bubbles just
after evolution stay in the gas evolution sites, and rapidly
grow to be larger gas bubbles, and as a result, it becomes
difficult for the ozone gas to efficiently dissolve.
[0029]
Considering the above problems and afterward
marketability, the inventors proposed an electrolysis cell
which was to solve the above problems, and had a structure in
which a plurality of through hole were provided in a
membrane-electrode assembly, and raw water passed through the
22
holes in unidirection. The inventors applied for a patent (PTL
8) which disclosed that it is possible to improve efficiency
more.
Further, the inventors examined various flow passage
structures passing through a membrane-electrode assembly in
order to improve flow of raw water (tap water) which flows in
the vicinity of an electrode. As a result, the inventors
developed an electrolysis cell for producing ozone water that
shows ozone water production efficiency much higher than that
in the electrolysis cell of the related art, has an electrolytic
voltage lower than that in the electrolysis cell of the related
art, has high power efficiency which is a product of a ratio
of the theoretical voltage over an actual electrolytic voltage
and current efficiency, and thus demands small amount of
consumed energy. The inventors verified effectiveness.
[0030]
Further, as will be described later, the inventors found
that a very useful and remarkable phenomenon is exhibited in
the process of developing the invention of the above technology.
The phenomenon is that a porous metal material which has
flexibility and multiple fine voids therein is used as a cathode
material of an electrolysis cell, and scale which is mainly
formed of hydroxide of the alkaline earth metal is stored in
the fine voids in the cathode, and thus it is possible to prevent
localized deposition of the scale which is mainly formed of
23
the hydroxide of the alkaline earth metal, on the surface of
the cathode.
The present invention is developed on the premise of a
cell structure in which an anode chamber and a cathode chamber
are not separated from each other in order to cause the
electrolysis cell to be compact, and on the premise that
chemicals are not used by emphasizing easiness of an operation
maintenance.
In the present invention, the followings are found. A
porous metallic material is used as a cathode body, and thus
inhibition of electrolysis by hydroxide (scale) which is
deposited in a cathode in a case where electrolysis is performed
by using unpurified water containing a small amount of ions
of alkaline earth metal such as calcium and magnesium, for
example, general tap water, as raw material is significantly
reduced.
That is, according to the present invention, it is
possible to continuously use an ozone generation device having
high efficiency, for a long term without employing other
measures for preventing deposition of scale.
[0031]
Fig. 1 illustrates a conventional apparatus for
producing electrolyzed ozone water, which is disclosed in PTL
8. 1 indicates an electrolysis cell, and 2 indicates a
membrane-electrode assembly. In the membrane-electrode
24
assembly 2 , an anode 4 is adhered onto one side surface of a
solid polymer electrolyte separation membrane 3 formed from
a cation exchange membrane. The anode 4 is formed in a manner
that an anodic catalyst for ozone generation is held by a
structure body having a predetermined shape and predetermined
physical properties. A cathode 5 is adhered onto the other
side surface of the solid polymer electrolyte separation
membrane 3 formed from the cation exchange membrane. The
cathode 5 is formed in a manner that a cathodic catalyst for
hydrogen generation is held by a structure body having a
predetermined shape and predetermined physical properties.
A plurality of through holes 6, 7, and 8 having a diameter
of 0.1 mm or more are provided over the entire surface of the
solid polymer electrolyte separation membrane 3, the anode 4,
and the cathode 5. The plurality of through holes 6, 7 , and
8 are formed over the entire surface of the anode 4, the cathode
5, and the solid polymer electrolyte separation membrane 3.
Thus, a raw liquid and an electrolysis product are transitioned
from the anode side to the cathode side, or from the cathode
side to the anode side through the through holes 6, 7, and 8.
In order to smoothly perform transition of the raw liquid and
the electrolysis product from the anode side to the cathode
side, or from the cathode side to the anode side, the through
holes 6, 7, and 8 in the anode 4, the cathode 5, and the solid
polymer electrolyte separation membrane 3 are respectively
25
provided at the corresponding portions.
[0032]
9 indicates an anode chamber provided on the front
surface of the anode 4. 10 indicates a cathode chamber provided
on the front surface of the cathode 5. 11 indicates a pipe
for supplying raw water to the anode chamber 9 of the
electrolysis cell 1. 12 indicates a pipe for allowing ozone
water generated by electrolysis in the cathode chamber 10 of
the electrolysis cell 1 to flow out. 13 indicates an inflow
port for supplying the raw water to the anode chamber 9 of the
electrolysis cell 1. 14 indicates an outflow port for allowing
the ozone water in the cathode chamber 10 of the electrolysis
cell 1 to flow out.
[0033]
Regarding water to be treated, which is raw water, the
inflow port 13 of raw water and the pipe 11 for supplying the
raw water are connected to the anode chamber 9 in a direction
which is perpendicular or oblique to the surfaces of the anode
4, the solid polymer electrolyte separation membrane 3, and
the cathode 5. In addition, the outflow port 14 of ozone water
and the pipe 12 for allowing the ozone water to flow out are
connected to the cathode chamber 10 in a direction which is
perpendicular or oblique to the surfaces of the anode 4, the
solid polymer electrolyte separation membrane 3, and the
cathode 5.
26
The electrolysis cell 1 can be placed in an oblique
direction, in addition to a direction perpendicular to a
direction in which raw water flows. In a case where the
electrolysis cell is provided in the oblique direction, it is
possible to enlarge the electrolysis area, and to further
increase its current efficiency and the amount of generated
ozone.
[0034]
As described above, according to the conventional
apparatus for producing electrolyzed ozone water, which is
disclosed in PTL 8, an anolyte (ozone water which is an anodic
product) in the anode chamber 9 and a catholyte (alkali
hydroxide which is a cathodic product) generated in the cathode
chamber 10 are mixed, and integrally flow out. Thus, the
catholyte is mixed with ozone water which is the anolyte
generated on the anode side. pH on the surface of the cathode
transits from the alkaline side to the neutral side. Thus,
deposition of hydroxide of alkaline earth metal on the surface
of the cathode is suppressed to a certain degree.
[0035]
However, according to the conventional apparatus for
producing electrolyzed ozone water, which is disclosed in PTL
8, the followings are understood. That is, a rigid material
such as precious metal, nickel, stainless steel, and titanium
is used in the cathode 2 . Almost all of scale which is mainly
27
formed of hydroxide of alkaline earth metal, such as calcium
hydroxide and magnesium hydroxide, which precipitates in the
vicinity of the solid polymer electrolyte separation membrane
3 is not stored in the cathode, and does not pass through
multiple through holes 8 formed in the cathode 5. Almost all
of the scale is deposited at a contact interface between the
cathode 5 and the solid polymer electrolyte separation membrane
3. Thus, continuing electrolysis may be interfered.
In addition, it is understood that the cathode 5 is formed
from a rigid material, which does not have flexibility, and
therefore, even though the cell is formed as a solid polymer
type electrolysis cell by compressing from both sides thereof,
scale preferentially precipitates in a gap between the cathode
and the separation membrane, which is generated by the cathode,
the anode and the solid polymer separation membrane being not
adhered to each other. Thus the cell voltage increases.
[0036]
Fig. 2 illustrates an embodiment of the electrolysis
device according to the present invention. In one embodiment
of the present invention illustrated in Fig. 2 , in the
electrolysis device of the related art illustrated in Fig. 1,
a porous conductive material which has flexibility and has
multiple fine voids therein is used as the cathode 5. Scale
which is mainly formed of hydroxide of the alkaline earth metal
is stored in the fine voids in the cathode, and thus localized
28
deposition of the scale which is mainly formed of hydroxide
of the alkaline earth metal, at a contact interface between
the cathode and the solid polymer electrolyte separation
membrane is prevented.
That is, in the present invention, as illustrated in Fig.
2, the membrane-electrode assembly 2 is configured by the solid
polymer electrolyte separation membrane 3 that is formed from
a cation exchange membrane, the anode 4 and the cathode 5 which
are respectively adhered to both surfaces of the solid polymer
electrolyte separation membrane 3. The electrolysis cell 1
is made by compressing the membrane-electrode assembly 2 from
both surfaces thereof such that the solid polymer electrolyte
separation membrane 3 formed of the cation exchange membrane,
the anode 4, and the cathode 5 are adhered to each other.
[0037]
According to the present invention, as illustrated in
Fig. 2 , in at least any one of the anode 4 and the cathode 5,
raw water consisted of unpurified water containing alkaline
earth metal is allowed to flow into the anode chamber 9 through
the inflow port 13, by using the supply pipe 11, so as to perform
electrolysis. An anolyte which is ozone water generated in
the anode chamber 9 flows into the cathode chamber 10 through
the through hole 7 of the anode 4, the through hole 6 of the
solid polymer electrolyte separation membrane 3 formed from
the cation exchange membrane, and an internal space of the
29
porous conductive metallic material of the cathode 5. Then,
the anolyte is mixed with a catholyte, and a mixture thereof
flows out of the outflow pipe 12 through the outflow port 14.
The present invention is characterized in that a porous
conductive metallic material which has flexibility and has
multiple fine voids therein is used as the cathode, scale which
is mainly formed of hydroxide of the alkaline earth metal is
stored in the fine voids in the cathode, and thus localized
deposition of the scale, which is mainly formed of hydroxide
of the alkaline earth metal, at a contact interface between
the cathode and the solid polymer electrolyte separation
membrane is prevented.
[0038]
The electrolysis device in the present invention is
applied to an electrolysis device having a structure in which
anolyte and catholyte are mixed. As the electrolysis device
having this type of structure, an electrolysis device having
a structure as follows is exemplified.
(1) An electrolysis device in which raw water formed by
unpurified water containing alkaline earth metal is supplied
to any one of an anode chamber and a cathode chamber, and a
through hole is provided in a solid polymer electrolyte
separation membrane configured by an anode, a cathode, and a
cation exchange membrane.
(2) An electrolysis device, as illustrated in Fig. 2,
30
in which perforated metal such as expanded metal is used as
the anode 4, a through hole is provided in the solid polymer
electrolyte separation membrane 3 formed of a cation exchange
membrane, and a porous conductive metallic material is used
as the cathode 5.
(3) An electrolysis device, as illustrated in Fig. 3,
in which a flow passage 15 for an electrolyte is provided at
an upper portion and/or a lower portion of the
membrane-electrode assembly 2 , raw water formed by unpurified
water containing alkaline earth metal is supplied to any one
of the anode chamber 9 and the cathode chamber 1 0 , and an anolyte
and a catholyte are mixed through the flow passage 15 for an
electrolyte at the upper portion and/or the lower portion of
the membrane-electrode assembly 2.
(4) An electrolysis device in which one or a plurality
of membrane-electrode assemblies illustrated in Fig. 2 , 4, or
5 are arranged at an interval in the electrolysis device with
being inclined, so as to form a flow passage for a liquid at
an upper portion and/or a lower portion, and, in a case where
raw water formed by unpurified water containing alkaline earth
metal is supplied to any one of the anode chamber 9 and the
cathode chamber 10 in an orthogonal direction or an oblique
direction, similarly to that in Fig. 3, a flow passage 15 for
an electrolyte is formed at an upper portion and/or a lower
portion of the membrane-electrode assembly 2.
31
(5) An electrolysis device in which a solid polymer
electrolyte separation membrane formed from a cation exchange
membrane which is not subjected to hole machining is used as
a membrane-electrode assembly, raw water formed by unpurified
water containing alkaline earth metal is supplied to any one
or both of the anode chamber and the cathode chamber, and an
anolyte and a catholyte which are generated in the anode chamber
or the cathode chamber are mixed in the outside of the system,
or an electrolysis device in which the anode chamber and the
cathode chamber are linked to each other by a communication
tube, and thus the anolyte and the catholyte are mixed in the
system.
[0039]
Further, in the present invention, a structure in which
at least one selected from a group configured by the solid
polymer electrolyte separation membrane formed from the cation
exchange membrane, the anode, and the cathode is connected to
the outside of the cathode and/or the anode in the
membrane-electrode assembly such that solid polymer
electrolyte separation membranes formed from the cation
exchange membrane do not come into contact with each other,
and the outermost layer of the membrane-electrode assembly
functions as the anode or the cathode can be made.
[0040]
Fig. 4 illustrates an example of the above structure,
32
and illustrates still another embodiment in the present
invention. Fig. 4 illustrates an example in which a new
membrane-electrode assembly 21 having the same structure as
that of the membrane-electrode assembly 2 is connected to the
outside of the membrane-electrode assembly 2 illustrated in
Fig. 2 , so as to cause the cathode 5 in the membrane-electrode
assembly 2 to come into contact with a cathode 19 in the
membrane-electrode assembly 21, and thereby an electrolysis
cell having a monopolar stack structure is configured. 16
indicates a solid polymer electrolyte separation membrane of
the membrane-electrode assembly 21, which is formed from a
cation exchange membrane. 17 indicates an anode of the
membrane-electrode assembly 21. 18 indicates a through hole
provided in the anode 17. 19 indicates a cathode of the
membrane-electrode assembly 21. 20 indicates a through hole
provided in the solid polymer electrolyte separation membrane
16 of the membrane-electrode assembly 21, which is formed from
a cation exchange membrane. The cathode 5 and the cathode 19
may be configured by one cathode member.
By configured as above, a reaction area is increased to
be twice, and thus treatment capability is doubled for the same
projection area. In addition, in the configurations in Fig.
2 or 3, a structure body for mechanically supporting a cathode
material formed of a flexible porous medium from the back
surface is required. However, if the configuration
33
illustrated in Fig. 4 is employed, such a support member may
be omitted.
In this type of electrolysis cell configured by a
monopolar stack structure, it is possible that a cathode 19
of a new membrane-electrode assembly 21 having the same
structure as that of the membrane-electrode assembly 2 may not
come into contact with the outside of the cathode 5 in the
membrane-electrode assembly 2 , but the anode 4 in the
membrane-electrode assembly 2 may come into contact with the
anode 17 in the membrane-electrode assembly 21.
[0041]
Fig. 5 illustrates another embodiment of the present
invention, and illustrates an example in which a new
membrane-electrode assembly 21 having the same structure as
that of the membrane-electrode assembly 2 is connected to the
outside of the cathode 5 in the membrane-electrode assembly
2 illustrated in Fig. 2 , so as to cause the cathode 5 of the
membrane-electrode assembly 2 and the anode 17 of the
membrane-electrode assembly 21 to come into contact with each
other, and thereby an electrolysis cell having a bipolar stack
structure is configured.
With this electrolysis cell, similarly to the example
of the electrolysis device illustrated in Fig. 4, a reaction
area is increased to be twice. Thus, treatment capability of
twice for the same projection area is obtained. Also in the
34
example of the electrolysis device illustrated in Fig. 5, a
support member other than a cathode which functions as a
termination portion is not required except for a case where
the cathode 5 functions as the termination.
[0042]
The cathode used in the present invention is firstly
required to have flexibility. The reason is as follows. The
cathode is used in the membrane-electrode assembly, and thus,
if the cathode is highly rigid, when the membrane-electrode
assembly is compressed from both sides, the solid polymer
electrolyte separation membrane formed from a cation exchange
membrane, the anode, and the cathode may not be adhered to each
other, and a cell voltage may be increased. Accordingly, it
is necessary that the cathode has sufficient flexibility.
[0043]
The cathode used in the present invention is secondly
required to be made of a porous conductive metallic material
having multiple fine voids therein. If the cathode is
configured a rigid material such as a plate material, a mesh,
or perforated punching metal, which has been used
conventionally, almost all of scale which is mainly formed of
hydroxide of alkaline earth metal such as calcium and magnesium,
which precipitates on the surface of the solid polymer
electrolyte separation membrane formed from a cation exchange
membrane, is not stored in the cathode, and does not pass
35
through multiple through holes formed in the cathode. Hence,
almost all of the scale is rapidly deposited at a contact
interface between the cathode and the solid polymer electrolyte
separation membrane. Thus, continuing electrolysis is
interrupted.
[0044]
Further, the cathode used in the present invention is
thirdly required to be configured by a material which allows
a liquid such as an anolyte and a catholyte to smoothly flow
through. The reason is as follows. If acidic ozone water
which is generated in the anode chamber horizontally and
vertically moves in the internal space of the cathode and stays
in the membrane-electrode assembly, the acidic ozone water may
reach the contact interface between the cathode and the solid
polymer electrolyte separation membrane. Thus, forming scale
which is mainly formed of hydroxide of alkaline earth metal
is suppressed. As a result, an increase in cell voltage is
delayed.
Accordingly, a porous conductive metallic material is
used as the cathode material used in the present invention.
As the porous conductive metallic material, preferably, at
least one porous conductive metallic material selected from
a group configured by a metal foam, metallic fiber cloth, and
a fibrous metal molded body is provided. As the most preferable
specific material, a nickel foam, a SUS foam, and SUS non-woven
36
fabric are used. Precious metal and precious metal oxide may
be appropriately coated thereon as an electrode catalyst in
accordance with the use.
[0045]
Since the cathode in the present invention is used in
a membrane-electrode structured assembly, even though the
flexibility is required, the cathode is preferably supported
by a rigid cathode member so as to be capable of withstanding
external stress of deformation.
Thus, in the present invention, the cathode positioned
on the outermost layer of the membrane-electrode assembly is
preferably held by a rigid cathode member formed of a plate
material, a mesh, or perforated punching metal.
[0046]
As the cathode substrate, a substrate which is
appropriate in accordance with the purpose is selected from
iron and alloys thereof including stainless steel, nickel and
alloys thereof, copper and alloys thereof, aluminum and alloys
thereof, and titanium, zirconium, molybdenum, tungsten, and
silicon, and alloys or carbide thereof, carbon and allotropes
thereof, and the like. The substrate material can be selected
in accordance with the use in applying the present invention.
Precious metal and precious metal oxide may be appropriately
used as an electrode catalyst in accordance with the use, and
these substances may be coated.
37
[0047]
As an anode substrate of the anode, metal and alloys,
such as tantalum, niobium, titanium, zirconium, and silicon,
which forms a passivation film which is stable in treatment
water can be used. Conductive diamond, lead dioxide, precious
metal, and precious metal oxide can be appropriately selected
from a viewpoint of reaction catalytic activity and the like,
on the surface thereof in accordance with the use, and coated
on the anode substrate as an anode catalyst. As the anode,
an anode substrate of ferrite, amorphous carbon, graphite, and
the like may be singly used.
[0048]
As the solid polymer electrolyte separation membrane
formed from a cation exchange membrane in the present invention,
a cation exchange membrane which has been conventionally known
can be widely used. In particular, a perfluorosulfonic acid
type cation exchange membrane which has a sulfonic acid group
and has chemical stability is suitable.
[0049]
In the electrolysis devices, various types of functional
water and ozone water are generated.
In the present invention, functional water refers to
“water whose scientific evidence on a treatment and a function
is clarified or is to be clarified among aqueous solutions which
acquire a useful function having reproduction property by
38
artificial treatment”. As the functional water, various types
of functional water such as electrolyzed water and ozone water
are provided.
[0050]
The definition and the type of electrolyzed water are
defined as follows, according to the descriptions in the home
page of Functional Water Foundation.
[0051]
The electrolyzed water is a general term of aqueous
solutions obtained by performing electrolytic treatment on a
tap water, dilute salt water, or the like with a weak DC voltage.
Various types of water are obtained in accordance with a
difference of a device or an electrolysis condition. Based
on the purpose of use, the electrolyzed water is roughly divided
into sterilizing electrolyzed water (acidic electrolyzed
water such as strongly-acidic electrolyzed water and
slightly-acidic electrolyzed water, and electrolytic
hypo-water considered as a diluted solution of sodium
hypochlorite) used in sanitation management such as washing
and disinfection, and alkali electrolyzed water (alkaline
ionized water) having an obvious effect of improving
gastrointestinal symptoms by routine drinking.
[0052]
The acidic electrolyzed water is a general term of
electrolyzed water having pH of 6.5 or less and refers to acidic
39
electrolyzed water. The acidic electrolyzed water widely
shows strong sterilizing power in various pathogenic organisms
or drug resistant bacteria (MRSA and the like) thereof. The
acidic electrolyzed water is used in various fields such as
medicine, dentistry, food, or agriculture. The main
sterilization factor is hypochlorous acid produced by
electrolysis. Thus, when the strongly-acidic electrolyzed
water and slightly-acidic electrolyzed water are designated
as food additives, based on the determination of “not having
a concern of damaging health of a person” in 2002, the name
of “hypochlorous acid” is also assigned.
The strongly-acidic electrolyzed water
(strongly-acidic hypochlorous acid water) refers to
electrolyzed water mainly containing hypochlorous acid
(effective chlorine concentration of 20 to 60 ppm) produced
at the anode side in a manner that electrolysis of a salt
solution (NaCl) of 0.1 % or less is performed in a two-chamber
type electrolytic bath in which the anode and the cathode are
separated by a separation membrane, and whose pH is equal to
or less than 2.7. Strongly-alkaline electrolyzed water refers
to electrolyzed water showing strong alkalinity (pH 11 to 11.5)
simultaneously generated on the cathode side.
The slightly-acidic electrolyzed water is a hypochlorous
acid aqueous solution which has pH of 5 to 6.5 and has effective
chlorine of 10 to 30 ppm, and is produced in a manner that
40
hydrochloric acid water of 2% to 6% is subjected to electrolysis
in one-chamber type electrolysis device in which the anode and
the cathode are not separated by the separation membrane. The
slightly-acidic electrolyzed water thus produced has a feature
that the whole product is sterile water.
[0053]
The alkaline ionized water is a general term of
weakly-alkaline (pH 9 to 10) drinkable electrolyzed water which
is produced in a manner that electrolysis is performed on
drinkable water by using a household electrolyzed water
generator which is generally referred to as an alkaline ion
water conditioner. The household electrolyzed water
generator is the name of household medical equipment classified
in “tool or instrument type No. 83, medical substance
generators” in Order for Enforcement of Pharmaceutical Law.
Regarding effects of alkaline ionized water, the following
effects are confirmed as a result of rigorous comparative
clinical tests causing permission for the generator as medical
equipment. That is, the alkaline ionized water is effective
in “chronic diarrhea, indigestion, abnormal gastrointestinal
fermentation, antacid, and stomach acid hyperacidity”. An
effect for improving constipation was confirmed. Moreover,
its recognition in the Pharmaceutical Law is restated that “the
alkaline ionized water has an improved effect on
gastrointestinal symptoms” as the Pharmaceutical Law has been
41
revised (2005).
[0054]
In the present invention, ozone water is an electrolysis
product which obtained in a manner that electrolysis is
performed on pure water, tap water, a sterilization treatment
liquid, waste water, a waste liquid and the like by using the
electrolysis cell according to the present invention, and
mainly contains an ozone gas. The ozone water may also contain
oxygen radicals such as OH radicals or super oxide anions,
hydrogen peroxide, and other oxidizing substances. As an
action of the ozone water, ozone gas itself acts as the main
oxidizing agent at low pH (acidic). At high pH (alkali), the
ozone gas is decomposed, and OH radical at this time is
consequently generated becoming the main oxidizing agent, so
as to exhibit a stronger oxidative power even in a case where
the total oxidation equivalent should remain the same..
[0055]
The present invention can be applied to an electrolysis
device for producing hydrogen or oxygen, for producing ozone
water, for producing alkaline ionized water, for producing
acidic water, for producing slightly-acidic water, and for
treating waste water, and the like.
As an operational practice of a cell according to this
invention, a procedure type in which a catholyte containing
ions of alkaline earth metal flows steadily is suitable. The
42
above effect is also obtained in a procedure type in which an
unpurified catholyte containing ions of alkaline earth metal
is replaced regularly.
Examples
[0056]
Next, the present invention will be described more
specifically by using examples and comparative examples.
However, the present invention is not limited thereto.
In order to confirm the effects of the invention, an ozone
water producing test was performed by using multiple types of
porous materials as a cathode. Similarly, an oxygen
generation electrolysis test was performed by using an
electrolysis cell in which a porous material is used as a
cathode. Further, the similar tests were performed on an
electrolysis cell having the same structure body which used
a general metallic material as a cathode material. Results
of the test were compared, and thus the effects of the present
invention were verified. Table 1 shows a cell type and
materials of a cathode and an anode, which are used in examples
and comparative examples.
[0057]
[Example 1]
A metallic material having a porous structure through
which liquid and gas can pass was used for cathodes. Solid
43
polymer electrolyte separation membranes formed from cation
exchange membranes were tightly disposed on both sides of the
cathodes, and in addition, anodes obtained by coating niobium
bases with conductive diamond were tightly disposed on an
outside of each of the solid polymer electrolyte separation
membranes so as to form an electrolysis cell having a monopolar
stack structure illustrated in Fig. 4. Thereby, a
membrane-electrode assembly (projection electrode area of 3.3
cm2, sum of two surfaces of the anode is 6.6 cm2) for confirming
the effects was configured.
A plurality of through holes having a diameter of 3 mm
are provided in the anode. A plurality of through holes having
a diameter of 2 mm are provided at the corresponding locations
of the solid polymer electrolyte separation membrane formed
from a cation exchange membrane.
Various materials are considered as porous metal for the
cathode. For an effect confirmation test, three types of
cathode materials, that is, a nickel foam which has a foam
polyhedral structure with internal voids, a SUS316L foam, and
non-woven fabric which uses SUS316L fiber having a diameter
of about 40 \im were selected as representative examples. As
a selection criterion from a viewpoint of practicality when
using general tap water and the like, it is desirable to select
a material that exhibits low liquid passing resistance with
a pressure loss of 0.5M Pa or less at a flow rate of passing
44
water of 1 L for each minute per an electrode projection area
of 1 cm2. In a case where porosity of the material is low,
pressure loss is increased and expecting a sufficient scale
suppression effect is not possible. If the porosity is too
high, it is difficult to maintain physical strength as a cathode.
Thus, the porosity is desirably to be in a range of 50% to 96%.
[0058]
In the membrane-electrode assembly configured in this
manner, as illustrated in Fig. 4, tap water as raw water was
supplied at a flow rate of 2 L for each minute in an electrolysis
cell accommodated in a housing, and was provided in an ozone
water production performance test and a long-term continuous
operation test. Ozone concentration in the generated ozone
water was measured by a UV absorption type ozone concentration
meter. As a power source, a commercial DC constant current
power source having capacity of 20A-40V was used. The
temperature of raw water was maintained at 20°C by a temperature
control system since an ozone generation efficiency largely
depends on the water temperature. In ozone water generation
electrolysis which uses unpurified water containing a small
amount of calcium or magnesium such as general tap water, an
influence of the dissolved elements remarkably appears as an
increase in electrolytic voltage which is a result of scale
formation during a continuous operation. If the electrolytic
voltage reaches a certain voltage, continuing electrolysis
45
becomes difficult. Thus, when the continuous operation test
is performed, a voltage between an anode and a cathode was
periodically monitored as the electrolytic voltage at a
predetermined interval. Considering the withstand voltage of
the anode material and the like, the test was terminated at
a time when the voltage reached 25 V. An electrolytic current
was set to 2 A. Table 2 shows results of the ozone water
production performance test. Table 3 shows results of the
long-term continuous electrolysis test, that is, cell voltage
increase characteristics.
[0059]
[Example 2]
An additional verification test which assumed production
of functional water such as production of an electrolytic
ionized water was performed. Non-woven fabric using SUS316
fiber described in Example 1 was used as a cathode. The cathode
was tightly disposed on one surface of a solid polymer
electrolyte separation membrane formed from a cation exchange
membrane. An anode obtained in a manner that expanded metal
made of pure titanium was coated with platinum was tightly
disposed on the opposite surface of the solid polymer
electrolyte separation membrane. Thus, a membrane-electrode
assembly having the same size (electrode projection area of
3.3 cm2) as that in Example 1 was configured. The back surface
of a porous structure body was mechanically supported by
46
expanded metal made of SUS304.
In this example, as illustrated in Fig. 3, an
electrolysis cell having a structure in which water to be
treated rapidly passed through a gap between a cell housing
and the membrane-electrode assembly without providing through
holes in the solid polymer electrolyte separation membrane
formed from a cation exchange membrane was obtained. Tap water
as raw water was supplied to the electrolysis cell configured
in this manner at a flow rate of 1 L for each minute, and was
provided in the long-term continuous operation test. An
electrolytic current was set to 1 A. Due to use of a member
prepared from expanded metal made of pure titanium coated with
platinum as the anode, the anodic over voltage was low, and
ozone was not generated in this test. Thus, the electrolytic
voltage was low at an initial time but it was gradually
increased as scale precipitates on the cathode similarly to
that in Example 1. The test was terminated when a voltage
between the anode and the cathode reached 20V, and the total
uptime until termination of electrolysis was recorded.
Table 3 shows the results.
[0060]
[Comparative Example 1]
A SUS304 plate having a plurality of through holes with
a diameter of 3 mm and a plain-stitched mesh made of SUS304
(#100) were used as a cathode. An anode and a solid polymer
47
electrolyte separation membrane formed from a cation exchange
membrane were tightly disposed, thereby a membrane-electrode
assembly in which the anode and the solid polymer electrolyte
separation membrane had the same size and the same structure
as those in Example 1 was obtained. An electrolysis cell using
the membrane-electrode assembly was provided for an ozone water
production electrolysis test and the long-term continuous
operation test under the same conditions as those in the
examples. Tables 2 and 3 show the results.
[0061]
[Comparative Example 2]
An electrolysis cell in which a membrane-electrode
assembly having the same configuration as that in Example 2
except that expanded metal made of stainless steel was used
as a cathode material was accommodated in a housing was provided
in the long-term continuous operation test under the same
conditions as those in Example 2 . Table 3 shows the results.
48
[0062]
Table 1: cell type, cathode material and anode material which are used in examples and
comparative examples
Type of Examples
/Comparative examples
Example 1
Example 2
Comparative
Example 1
Comparative
Example 2
1
2
3
-
1
2
-
Cell Anode
structurematerial
Fig. 4
Fig. 4
Fig. 4
Fig. 3
Fig. 4
Fig. 4
Fig. 3
BDD
BDD
BDD
Pt
coating
BDD
BDD
Pt
coating
Cathode material
Ni foam
SUS foam
SUS non-woven
fabric
SUS non-woven
fabric
Perforated SUS
plate
SUS mesh
SUS
expanded metal
Specifications
Pure Ni porous body (regular dodecahedron void
porosity: 93%, thickness: 1.6 mm
SUS316L porous body (regular dodecahedron void)
porosity: about 85%, thickness: 2.5 mm
SUS316L fiber , diameter of 40 |am
porosity: 90%, thickness: 1.5 mm
SUS316L fiber, diameter of 40 |om
porosity: 90%, thickness: 1.5 mm
SUS304 plate thickness: 2 mm
plurality of through holes: 3 mm dia.
SUS304 wire 0.12 mm dia.
#100 plain-stitched mesh
SUS304 plate thickness of 0.8 mm (0.8 T/W 0.8)
BDD is an abbreviation of a Boron-doped Diamond electrode.
49
[0063]
Table 2: ozone water production performance test results
Type of
Examples/
Comparative
Examples
Example 1
Comparative
Example 1
1
2
3
1
2
Cathode Material
Ni foam
SUS foam
SUS
non-woven fabric
Perforated SUS
plate
SUS mesh
Ozone Concentration (ppm)
Applied Current
0.5 A1.0 A1.5 A2.0 A2.5 A3.0 A
0.25
0.27
0.24
0.21
0.23
0.52
0.58
0.57
0.55
0.53
0.82
0.86
0.89
0.83
0.82
1.11
1.10
1.23
1.11
1.10
1.43
1.36
1.59
1.41
1.42
1.77
1.61
1.97
1.74
1.73
Performance at Applied Current of 2A
Current
efficiency
(%)
22.3
22.1
24.7
22.3
22.1
Initial
electrolytic
voltage (V)
9.8
12.4
9.5
10.7
10.5
Initial
Initial
power
electrolytic
efficiency
power (W)
(%)
19.6
24.8
19.0
21.4
21.0
3.4
2.7
3.9
3.1
3.2
50
[0064]
Table 3: long-term continuous electrolysis test result - cell voltage increase
characteristics
Type of Examples/Comparative
Examples
Example 1
Example 2
Comparative Example 1
Comparative Example 2
1
2
3
-
1
2
-
Cathode Material
Ni foam
SUS foam
SUS non-woven fabric
SUS non-woven fabric
Perforated SUS plate
SUS mesh
SUS expanded metal
Time to Reach 20 V
(hr)
217
158
196
224
32
36
31
Time to Reach 25 V
(hr)
249
180
219
-
38
47
-
51
[0065]
From the results of the above examples and the
comparative examples, the followings are inferred.
(1) Effect on performance
In the electrolysis cell according to the present
invention, which uses a porous conductive metallic material
as the cathode material, it was estimated that catalytic
activity of the cathode would be high, and as a result ozone
water production efficiency would be reduced by cathodic
reduction of dissolved ozone. However, contrary to the
expectation, it was confirmed in the result of the test that
ozone water production efficiency was as equivalently high as
that with the electrolysis cell using SUS304 plate as the
cathode material. In relation, consumed power of the trial
cell was in the same level as that of a small PC, and therefore,
a battery operation was sufficiently possible. The remarkable
effect of the present invention was exhibited in the continuous
electrolysis test in which the time for the electrolytic
voltage to reach the upper limit of 25V in continuous
electrolysis is extended by 3.8 to 7.2 times. After the voltage
reached 25 V, maintenance such as washing by acid allows scale
to be removed and thus electrolysis can be restarted. However,
large elongation in the operation time till maintenance is
still highly advantageous in practice. Therefore, in a use
having low frequency such as hand washing, long-term operation
52
without maintenance becomes possible.
(2) Discussion on the effects
As described above, the inventors found that it was
possible to significantly reduce an influence of scaling of
calcium and the like which are dissolved in water when a porous
conductive metallic material was used as a cathode in the
electrolysis cell according to the proceeding invention of the
inventors. The mechanism is not clear yet at present, however,
it is roughly estimated that the mechanism corresponds to any
of the following effects or a result of combined actions
thereof.
1) Adhesiveness between the anode and the solid polymer
electrolyte separation membrane formed from a cation exchange
membrane is ensured by a substance with high flexibility, and
the micro contact area thereof is extended by micro roughness
of the substance, which results in a lower actual current
density. In a separate test the inventors confirmed a large
current dependency in that “a voltage increase rate due to
scaling is proportional to the second to the third power of
current density”.

CLAIMS
[Claim 1]
An electrolysis device comprising:
an electrolysis cell formed in a manner that a
membrane-electrode assembly is compressed from both sides so
as to adhere an anode, a cathode, and a solid polymer
electrolyte separation membrane formed from a cation exchange
membrane to each other, the membrane-electrode assembly being
configured by the solid polymer electrolyte separation
membrane formed from the cation exchange membrane, and the
anode and the cathode which are respectively adhered to both
surfaces of the solid polymer electrolyte separation membrane;
means for supplying raw water consisting of unpurified
water containing alkaline earth metal, to at least one of the
anode and the cathode; and
means for mixing an anolyte generated on the anode with
a catholyte generated on the cathode, wherein
a porous conductive metallic material which has
flexibility and in which multiple fine voids are provided is
used as the cathode, and
scale which is mainly formed of hydroxide of the alkaline
earth metal is stored in the fine void in the cathode so as
to prevent localized deposition of the scale which is mainly
formed of hydroxide of the alkaline earth metal at a contact
56
interface between the cathode and the solid polymer electrolyte
separation membrane.
[Claim 2]
The electrolysis device according to Claim 1, wherein
an electrolysis cell having a monopolar stack structure
is configured in a manner that at least new one
membrane-electrode assembly which has the same structure as
a structure of the membrane-electrode assembly is further
connected to an outside of the cathode and/or the anode in the
membrane-electrode assembly, so as to bring the cathodes into
contact with each other and/or bring the anodes into contact
with each other in the membrane-electrode assemblies.
[Claim 3]
The electrolysis device according to Claim 1, wherein
an electrolysis cell having a bipolar stack structure
is configured in a manner that at least new one different
membrane-electrode assembly which has the same structure as
a structure of the membrane-electrode assembly is further
connected to an outside of the cathode and/or the anode in the
membrane-electrode assembly, so as to bring the cathode and
the anode into contact with each other in the
membrane-electrode assemblies.
57
[Claim 4]
The electrolysis device according to any one of Claims
1 to 3, wherein
the cathode is formed by at least one porous conductive
metallic material selected by a group formed from a metal foam,
a metallic fiber cloth, and a fibrous metal molded body.
[Claim 5]
The electrolysis device according to any one of Claims
1 to 4, wherein
in a case where the cathode is positioned in an outermost
layer of the electrolysis cell, the cathode is supported by
a rigidsubstrate formed of a plate material, a mesh, or
perforated punching metal.
[Claim 6]
An apparatus for producing electrolyzed ozone water
which produces ozone water by performing electrolysis of
unpurified water containing ions of alkaline earth metal by
using the electrolysis device according to any one of Claims
1 to 5.