Patent Application
20160215402
Embodiments described herein relate generally to an electrolytic apparatus, an electrode unit of the electrolytic apparatus and an electrolyzed water production method.
As electrolytic apparatus for producing alkali ion water, ozone water, hypochlorous acidic water or the like, an electrolytic apparatus comprising a three-chamber electrolytic tank (electrolytic cell) is conventionally used. The three-chamber cell includes an electrolytic container divided into three chambers, that is, an anode chamber, an intermediate chamber and a cathode chamber by diaphragms. As the diaphragms, a cation-exchange membrane such as Nafion (trademark) is employed on the cathode side and an anion-exchange membrane containing a quaternary ammonium salt, quaternary phosphonium salt or the like on the anode side. In the anode chamber and the cathode chamber, an anode and a cathode which have a porous structure are provided, respectively.
In such an electrolytic apparatus, for example, a salt water is poured into the intermediate chamber, and water is poured into the cathode chamber and the anode chamber on the right and left sides. Thus, the salt water in the intermediate chamber is electrolyzed by the anode and the cathode to produce hypochlorous acid solution from gaseous chlorine produced in the anode chamber and sodium hydroxide solution in the cathode chamber. Hypochlorous acid thus produced can be utilized as sterilizing solution and sodium hydroxide solution as a cleaning solution.
In such a three-chamber cell, the anion-exchange membrane is deteriorated easily with chlorine or hypochlorous acid. To avoid this, a technology has been proposed, in which a nonwoven fabric with over-wraps and cuts is inserted between the anode of a porous structure prepare by punching or the like and the anion-exchange membrane, to reduce deterioration of the ion-exchange membrane by chlorine. Further, such a technique is also known that a porous membrane is provided so as not to close numerous pores of the electrode.
However, in the electrolytic apparatus having the above-described structure, the deterioration of the nonwoven fabric, and accordingly deterioration of the diaphragms occur after a very long time of operation.
Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, an electrolytic apparatus comprises a diaphragm consisting of a water-permeable porous membrane having a water permeation per cm2 of 0.0024 to 0.6 mL/min at a differential pressure of 20 kPa; a first electrode proposed to oppose the diaphragm; and a second electrode opposing the first electrode via the diaphragm, wherein a difference in hydraulic pressure acting on both sides of the porous membrane is within ±20 kPa.
Throughout the embodiments, common structural members are designated by the same reference symbols, and the explanation therefor will not be repeated. Further, the drawings are schematic diagrams designed to assist the reader to understand the embodiments easily. Thus, there may be sections where the shape, dimensions, ratio, etc. are different from those of the actual devices, but they can be re-designed as needed with reference to the following explanations and publicly known techniques.
The electrolytic apparatus 10 comprises a power supply 30 that applies voltage to the first and second electrodes 20 and 22 of the electrolytic cell 11, an ammeter 32, a voltmeter 34 and a control device 36 that controls the members. The anode chamber 16 and the cathode chamber 18 may be each provided with a fluid path for fluid. The electrolytic apparatus 10 comprises an electrolyte supplier 50 which supplies an electrolyte, for example, a saturated solution of sodium chloride (a salt water), to the intermediate chamber 19 of the cell 11 and a water supplier 51 which supplies a solution to be electrolyzed, for example, water, to the anode chamber 16 and the cathode chamber 18.
The electrolyte supplier 50 comprises a salt water tank 52 to produce a saturated solution of sodium chloride (a salt water), a supply pipe 50a which conveys saturated salt water from the salt water tank 52 to a lower portion of the intermediate chamber 19, a liquid feed pump 54 provided in the supply pipe 50a and a liquid discharge pipe 50b which sends the electrolyte which has flowed through the inside of the intermediate chamber 19 from an upper portion of the intermediate chamber 19 to the salt water tank 52. A regulating valve 53 is provided in the liquid discharge pipe 50b.
The water supplier 51 comprises a water supply source (not shown) which supplies water, a water supply pipe 51a which conveys water to lower portions of the anode chamber 16 and the cathode chamber 18 from the water supply source, a first liquid discharge pipe 51b which discharges from the upper portion of the anode chamber 16 the water which has flowed through the anode chamber 16, a second liquid discharge pipe 51c which discharges from the upper portion of the cathode chamber 18 the water which flowed through the cathode chamber 18, a regulating valve (throttle valve) 55a provided in the first liquid discharge pipe 51b and a regulating valve 55b provided in the second liquid discharge pipe 51c.
The hydraulic pressures in the anode chamber 16, the cathode chamber 18 and the intermediate chamber 19 and the differences between these hydraulic pressures can be adjusted by regulating the flow of the liquid feed pump 54 to supply an electrolyte to the intermediate chamber 19, or by adjusting the flow of water or the flow of the electrolyte with regulating valves 53, 55a and 55b.
The operation of the electrolytic apparatus 10 configured as described above, which actually electrolyzes salt water to produce an acidic solution (hypochlorous acid solution and hydrochloric acid) and alkaline water (sodium hydroxide) will now be described.
As shown in
Meanwhile, chlorine ions electrolytically dissociated in the salt water in the intermediate chamber 19 are attracted towards the first electrode 20, pass through the first diaphragm 24a and flow into the anode chamber 16. Then, the chlorine ions give electrons to the anode with the first electrode 20 to produce gaseous chlorine. After that, the gaseous chlorine reacts with water in the anode chamber 16 to produce hypochlorous acid and hydrochloric acid. The acidic solution thus produced (hypochlorous acidic water and hydrochloric acid) is discharged from the anode chamber 16 through the first liquid discharge pipe 51b.
Next, the electrode unit 12 provided in the electrolytic cell 11 will be described in detail.
The first electrode 20 has a porous structure in which, for example, numerous through-holes 13 are formed in a matrix 21 of a metal plate having a rectangular shape. The matrix 21 includes a first surface 21a and a second surface 21b opposing and substantially parallel to the first surface 21a. The gap between the first surface 21a and the second surface 21b, that is, the thickness of the electrode, is T1. The first surface 21a opposes the first diaphragm 24a and the second surface 21b opposes the anode chamber 16.
The through-holes 13 are formed over the entire area in the first electrode 20. The through-holes 13 are opened from the first surface 21a through to the second surface 21b. The through-holes 13 may be each formed to have a tapered or curved inner surface so that the diameter of the opening on the first surface 21a side is larger than that on the second surface 21b side. In this manner, it is possible to reduce the concentration of stress to the first diaphragm 24a, caused by the through-holes 13 of the first electrode 20. The through-holes 13 may have various forms such as rectangular, circular and elliptical. Moreover, the through-holes 13 may not be regularly arranged, but may be at random.
For the matrix 21 of the first electrode 20, a valve metal such as titanium, chromium or aluminum, or an alloy of these, or a conductive metal can be used. It may be desirable, depending on the electrolytic reaction, to form an electrolytic catalyst (catalyst layer) on the first surface 21a and the second surface 21b of the first electrode 20. When used as an anode, it is desirable to use a precious metal catalyst such platinum or an oxide catalyst such as iridium oxide, as the matrix itself of the electrode. The first electrode 20 may be formed so that the quantity of electrolytic catalyst per unit area differs from one surface to the other. Thus, a side reaction and the like can be inhibited; or, by covering the surface (second surface 21b) opposing the first diaphragm 24a of the first electrode 20 with an electrical insulating film, it is possible to reduce the side reaction.
As shown in
The first diaphragm 24a comprises a water-permeable continuous porous membrane 24. In this embodiment, the porous membrane 24 is formed into, for example, a rectangular shape having a size substantially equal to that of the first electrode 20 and is arranged between the first surface 21a of the first electrode 20 and the first surface 23a of the second electrode 22. The porous membrane 24 is located to oppose the first surface 21a of the first electrode 20, thus covering the entire first surface 21a and the through-holes 13.
As the porous membrane 24, a continuous inorganic oxide porous membrane which contains a chemically stable inorganic oxide is used. Various types of inorganic oxides can be used here, for example, titanium oxide, silicon oxide, aluminum oxide, niobium oxide, tantalum oxide and nickel oxide. Of these, titanium oxide, silicon oxide and aluminum oxide are preferable.
When using the first electrode 20 for the anode, titanium oxide and aluminum oxide are preferable as the inorganic oxide for the porous membrane 24, since these materials easily becomes to have a positive zeta potential in an acidic region and therefore exhibit an anion exchange function. When using for the cathode, as an inorganic oxide of the porous membrane 24, titanium oxide, aluminum oxide and silicon oxide are preferable as the inorganic oxide for the porous membrane 24, since these materials easily becomes to have a negative zeta potential in an alkaline region and therefore exhibit an anion exchange function.
Besides the organic oxides, porous polymers and the like, containing chlorine- or fluorine-based halogenated polymer may be used as well for the porous membrane 24.
The porous membrane 24 has a pore size of 10 to 200 nm and is water-permeable. The porous membrane 24 has a water permeability per cm2 of, for example, 0.012 to 0.24 mL/min at a differential pressure of 20 kPa. Further, the hydraulic pressures of the anode chamber 16 and the intermediate chamber 19, which sandwich the porous membrane 24 are set to be approximately equal to each other, and adjusted so that the difference in pressure is within ±6 kPa in terms of hydraulic pressure.
Conventionally, for such a first diaphragm, an anion exchange membrane which is water-impermeable and penetrates only anion is used. But in this embodiment, it was found out that if a water-permeable porous membrane 24 is used at a specific hydraulic differential pressure, electrolyzed water free from excessive electrolyte, which has properties better than that obtained with use of an ion exchange membrane can be produced.
The porous membrane 24 will be described in detail.
As schematically shown in
As shown in
As shown in
On the other hand, the porous membrane 24 passes excessive Na ion also, and therefore there is apprehension that salinity mixes in the electrolyzed water produced in the anode chamber 16. As shown in
It is conventionally considered that the production efficiency and the mixing of salt content have a relationship of tradeoff as described. That is, in the porous membrane 24 of an anion exchange membrane without ion-selective permeability, when the production efficiency improves if a large number of chlorine ions penetrate from the intermediate chamber 19, but at the same time, sodium ions penetrate and therefore the mixing of salt content increases. However, it has been found here that the relationship is not completely a mutual tradeoff as conventionally considered, but it has a range in which the improvement in production efficiency and the reduction in mixing of salt content are established at the same time within a limited hydraulic pressure condition range as described above.
The indexes are shown in the lowest column of Table shown in
In practice, as the porous membrane 24, a material having a pore size of 10 to 200 nm and a water permeability of 0.6 to 12 mL/min/cm2/MPa (a water permeation of 0.012 to 0.24 mL/min at a hydraulic differential pressure of 20 kPa per cm2) is used, and the difference in hydraulic pressure between the intermediate chamber 19 and the anode chamber 16 (that is, the difference in hydraulic pressure between both sides of the porous membrane 24) is set within a range of ±6 kPa. In this manner, the function of the embodiment can be realized.
Moreover, the values discussed above are those of desirable ranges, and the practical ranges may be set as: a pore size of 2 to 500 nm, a water permeability of 0.12 to 30 mL/min/cm2/MPa (a water permeation of 0.0024 to 0.6 mL/min at a hydraulic differential pressure of 20 kPa per cm2), and a range of the difference in hydraulic pressure between the intermediate chamber 19 and the anode chamber 16 (that is, the hydraulic differential pressure between both sides of the porous membrane 24) of ±20 kPa.
As schematically shown in
Further, as schematically shown in
The porous membrane 24 may be a multilayer film of a plurality of porous membranes of different pore sizes. In this case, by adjusting the diameter of the pores of a membrane on the second electrode 22 side to be larger than that of a membrane on the first electrode 20 side, ions can migrate more easily, and also the concentration of the stress by the through-holes of the electrode can be reduced.
As shown in
As shown in
As to the electrolytic apparatus 10 of this embodiment, it is desirable to electrolyze an electrolyte containing chlorine ion. For example, when the electrolytic apparatus 10 is to produce hypochlorous acid solution, a salt water is poured into the intermediate chamber 19, and water is poured into the anode chambers 16 on both right and left sides and the cathode chamber 18, and thus the salt water of the intermediate chamber 19 is electrolyzed by the first electrode (anode) 20 and the second electrode (cathode) 22. In this manner, hypochlorous acid solution is produced from the gaseous chlorine produced in the anode chamber 16, and sodium hydroxide solution is produced in the cathode chamber 18. The hypochlorous acid solution thus produced is utilized as a bactericidal solution, and the sodium hydroxide solution is utilized as a cleaning solution.
According to the electrolytic apparatus, cell and electrode unit configured as described above, the continuous porous membrane 24 containing a chemically stable inorganic oxide is formed to cover the first surface 21a of the first electrode 20 and the through-holes 13. With this configuration, the distance between the first electrode 20 and the second electrode 22 can be maintained to keep the flow of liquid uniform. Thus, the electrolytic reaction can occur uniformly at the interfaces between electrodes. Because of the uniform electrolytic reaction occurring, the deteriorations of the catalysts and the electrode metals occur uniformly. In addition to this, with use of the chemically stable inorganic oxide, the life of the diaphragms and the cell can be significantly prolonged. Further, since it is possible to make the electrolytic reaction to occur uniformly, the reaction efficiency of the electrolytic apparatus can be improved, and also the deterioration of the electrodes and diaphragms can be inhibited.
The first electrode 20 of a porous structure is formed to have through-holes with a tapered or curved side which enlarges towards the first surface side. With this structure, the contact angle between the opening of each through-hole and the porous membrane 24 is an obtuse angle, thereby making it possible to reduce the concentration of stress on the porous membrane 24.
Further, the first diaphragm 24a is constituted by the porous membrane 24 only, and therefore the device structure is simplified though the ion selectivity may be reduced. Here, the life can be further extended and low-cost production can be realized.
As described above, a long-life electrolytic apparatus which can retain the electrolytic performance for a long time can be.
Note that in the first embodiment, the second electrode 22 has a porous structure with a great number of through-holes, but it is not limited to this. For example, a plate electrode without a through-hole may be employed. Similarly, the first electrode 20 is not limited to a porous structure but may be of a plate shape.
Next, an electrolytic cell and an electrolytic apparatus according to another embodiment will be described. Note that in the other embodiments described below, the same referential symbols are given to the same structural elements as the first embodiment above, and the detailed explanations therefor are omitted. The portions different from those of the first embodiment will be mainly discussed.
As the third diaphragm 24c, a material may be selected from various electrolyte membranes and porous membranes with nano-pores. An example of the electrolyte membranes is a polymer electrolyte membrane, and more specifically, an anion-exchange solid polyelectrolyte membrane, that is, an anion-exchange membrane or a hydrocarbon-based membrane. An example of the anion-exchange membrane is A201 of Tokuyama, Inc. Usable examples of the porous membranes with nano-pores are porous ceramics such as porous glass, porous alumina and porous titanium, and porous polymers such as porous polyethylene and porous propylene. With the third diaphragm 24c described above, the ion selectivity can be improved. Moreover, although an anion-exchange membrane deteriorates easily with gaseous chlorine or the like, it is possible with the structure that the highly durable porous membrane 24 is interposed between itself and the first electrodes 20 to prevent the deterioration of the ion exchange membrane nearly completely. Thus, with the structure that the porous membrane 24, which is the first diaphragm 24a, and the third diaphragm 24c constituted by the anion-exchange membrane are stacked, the electrolytic apparatus 10 with excellent durability and shielding ability to salinity can be realized though the production efficiency may not be increased.
In the second embodiment, the other structure of the electrolytic apparatus 10 is the same as that of the first embodiment described above.
As shown in
As shown in
A plurality of first holes 40 are formed in the first surface 21a of the matrix 21 to open on the first surface 21a. Moreover, a plurality of second holes 42 are formed in the second surface 21b to open on the second surface 21b. The first holes 40 made on the porous membrane 24 side, have a diameter R1 of the opening, which is smaller than the diameter R2 of the openings of the second holes 42. Further, the first holes 40 are more in number than the second holes 42. The depth of the first holes 40 is T2 and the depth of the second holes 42 is T3. In this embodiment, the holes are made to satisfy: T2<T3.
The second holes 42 are formed into, for example, a rectangular shape to be arranged in a matrix on the second surface 21b. The circumferential wall which defines each second hole 42 may be formed to have a tapered or curved surface so that the diameter enlarges toward the second surface side from the bottom of the hole to the opening. The interval between adjacent second holes 42, that is, the width of a linear portion 60a is set to W2. Note that the second holes 42 are not limited to a rectangular shape, but may take various other forms. Moreover, the second holes 42 may not necessarily be arranged regularly, but may be at random.
The first holes 40 are formed into, for example, a rectangular shape and are arranged in a matrix on the first surface 21a. The wall surface which defines each first hole 40 may be formed to have a tapered or curved surface so that the diameter enlarges toward the first surface 21a from the bottom of the hole to the opening. In this embodiment, a plurality of, for example, sixteen first holes 40 are provided to oppose one second hole 42. The sixteen first holes 40 each are communicated to the second hole 42 and form the through-holes made through the matrix 21 together with the second hole 42. A mesh linear portion 60b is formed between adjacent first holes 40, and the width W1 of the linear portion 60b is set less than the width W2 of the linear portion 60a between the second holes 42. With this structure, the number in density of the first holes 40 in the first surface 21a is sufficiently larger than that of the second holes 42 in the second surface 21b.
Note that the first holes 40 are not limited to a rectangular shape, but may take some other form. Further, the first holes 40 may not necessarily be arranged regularly, but may be at random. Furthermore, all the first holes 40 may not necessarily be communicated with the second holes 42, but there may be some first holes not communicated with a second hole 42.
The porous membrane 24 is formed on the first surface 21a of the first electrode 20 so as to cover the entire surface of the first surface 21a and the first holes 40. The porous membrane 24 employs a porous membrane similar to that of the first embodiment described above.
As shown in
A plurality of first holes 44 are formed in the first surface 23a of the matrix 23 to open on the first surface 23a. Further, a plurality of second holes 46 are formed in the second surface 23b to open on the second surface 23b. These holes are made so that the opening diameter of the first holes 40 made on the first membrane 24a side is larger than that of the second holes 42, the first holes 40 are more in number than the second holes 42, and the depth of the first holes 40 is more than that of the second holes 42.
A plurality of, for example, sixteen first holes 44 are provided to oppose one second hole 46. These nine first holes 44 are each communicated to the second hole 42 and form the through-holes made through the matrix 23 together with the second hole 46. A narrow mesh linear portion is formed between adjacent first holes 44 and a wide mesh and lattice-like linear portion is formed between adjacent second holes 46. The number in density of the first holes 44 in the first surface 23a is sufficiently larger than that of the second holes 46 in the second surface 23b.
The porous membrane 24, which serves as the first diaphragm 24a, is inserted between the first electrode 20 and the second electrode 22 so as to oppose the entire first surface 21a of the first electrode 20 and also the entire first surface 23a of the second electrode 22.
In the third embodiment, the other structure of the electrolytic apparatus 10 is the same as that of the first embodiment described above. It is desirable for the electrolytic apparatus 10 of this embodiment to electrolyze an electrolyte containing chlorine ion.
Also in the third embodiment configured as described above, the deterioration of the diaphragms can be inhibited, and therefore it is possible to realize an electrolytic apparatus with improved reaction efficiency and prolonged life as in the first embodiment.
Next, various examples and comparative example will be described.
As the porous membrane constituting the first diaphragm 24a, Y-9211T of Yuasa Membrane Systems Co. Ltd. was employed, as the second diaphragm 24b on the cathode side, a cation-exchange membrane, Nafion N117 (trademark) of E.I. du Pont de Nemours, was employed, and as the third diaphragm 24c on the cathode side, an anion-exchange membrane, AHA of Astom Co. was used to prepare an electrode unit and an electrolytic cell 11 shown in
The anode chamber 16 and the cathode chamber 18 of the electrolytic cell 11 were each formed from a vinyl-chloride container in which a straight pathway was formed. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 were provided. Pipes and a pump for supplying tap water to the anode chamber 16 and the cathode chamber 18 were connected to the electrolytic cell 11. Further, a saturated salt water tank, pipes and a pump for circulating saturated salt water to the holder (porous polystyrene material) of the electrode unit or the intermediate chamber, were connected to the electrolytic cell 11.
Then, the electrolytic apparatus 10 was operated for electrolysis at a voltage of 5.2 V and a current of 25 A. Here, hypochlorous acid solution having an effective chlorine concentration of 60 ppm was produced on the first electrode (anode) 20 side, and sodium hydroxide solution was produced on the second electrode (cathode) 22 side. Even after continuous operation for 2,000 hours, no substantial rise in voltage or change in the quality of produced solution was observed. Thus, a stable electrolytic treatment could be carried out.
An electrolytic apparatus was manufactured in the same manner as in Example 1 except that the third diaphragm 24c on a cathode side was not used. That is, the electrolytic apparatus shown in
As compared to Example 1, the concentration of sodium chloride contained in the hypochlorous acid solution increased by about 0.1%. Even after continuous operation for 3,000 hours, no substantial rise in voltage or change in the quality of produced solution was observed, thus achieving stable operation.
An electrolytic apparatus 10 was manufactured in the same manner as in Example 1 except that a polypropylene-based nonwoven fabric was employed as the porous membrane 24.
With the electrolytic apparatus 10, electrolysis was carried out at a voltage of 5 V and a current of 25 A, in which hypochlorous acid solution was produced on the anode side, and a sodium hydroxide solution was produced on the cathode side. After continuous operation for 1,000 hours, a significant rise in voltage and a decrease in effective chlorine concentration were observed. Thus, it was found that this device lacks a long-term stability.
The present invention is not limited to the embodiments described above but the constituent elements of the invention can be modified in various manners without departing from the spirit and scope of the invention. Various aspects of the invention can also be extracted from any appropriate combination of a plurality of constituent elements disclosed in the embodiments. Some constituent elements may be deleted in all of the constituent elements disclosed in the embodiments. The constituent elements described in different embodiments may be combined arbitrarily.
For example, the first electrode and the second electrode are not limited to rectangular shapes, but various other forms may be selected. Further, the material of each structural component is not limited to that employed in the embodiments or examples discussed, but various other materials may be selected as needed. The electrolytic cell of the electrode device is not limited to a three-chamber or two-chamber type, but it may as well be applied to single-chamber types or any electrolytic cells with electrodes in general. The electrolytes and product are not limited to salt or hypochlorous acid, but may be developed into various electrolytes and products.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-191567 | Sep 2014 | JP | national |
This application is a Continuation application of PCT Application No. PCT/JP2015/075242, filed Sep. 4, 2015 and based upon and claiming the benefit of priority from Japanese Patent Application No. 2014-191567, filed Sep. 19, 2014, the entire contents of all of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2015/075242 | Sep 2015 | US |
| Child | 15057539 | US |
