The present invention relates to a method and an apparatus for removing hydrogen peroxide contained in water in a waste water treatment and a pure water or ultrapure water production process, and a pure water producing apparatus.
Conventionally, hydrogen peroxide is widely used as an oxidizing agent together with a chemical solution such as an acid or an alkali in cleaning and surface treatment of electronic components. Since hydrogen peroxide has an oxidizing power, it is necessary to appropriately manage and remove hydrogen peroxide so that hydrogen peroxide does not flow into a device with low oxidation resistance such as an ion exchange resin device constituting a water treatment system. In general, degradation by oxidizing agents causes irreparable fatal damage to water treatment facilities. In particular, it is known that an ion exchange resin in an electrodeionization (EDI) device tends to be deteriorated when an oxidizing agent is present. For example, it is known that, in an ultrapure water production system, a part of the ion exchange resin contained in the ultrapure water production system is oxidatively decomposed to cause elution of an organic substance when hydrogen peroxide is contained in water to be processed.
Since hydrogen peroxide has a high sterilizing power due to having an oxidizing power, it is necessary to remove hydrogen peroxide in advance and then discharge waste water when the waste water containing hydrogen peroxide is discharged from a pure water system to a waste water system outside the system, because hydrogen peroxide may affect biological treatment facilities contained in the waste water treatment system. In addition, in a pure water and ultrapure water production system, an ultraviolet oxidation device for decomposing total organic carbon (TOC) components is sometimes used, and it is known that a minute amount of hydrogen peroxide is contained in the processed water after the ultraviolet oxidation is performed.
Conventionally, as a method of reducing hydrogen peroxide in water to be processed, there are a method of adding a reducing agent, a method of contacting with activated carbon, a method of contacting a resin on which metal is supported, and the like. In the method of adding a reducing agent, a reducing agent such as sodium sulfite, sodium hydrogen sulfite, or sodium thiosulfate is added to the water to be processed which contains hydrogen peroxide. Since the reaction rate of the reducing agent and hydrogen peroxide is very large, it is possible to reliably decompose and remove hydrogen peroxide according to this method, but it is difficult to control the amount of the reducing agent added, and it is also necessary to add an excessive amount of the reducing agent in order to reliably remove hydrogen peroxide, so that the reducing agent increases the amount of ions in the liquid and may cause deterioration in water quality.
In the method of contacting with activated carbon, usually, a packed tower of activated carbon is installed to pass water to be processed, but since the reaction rate is low, there is a problem that the space velocity of passing water cannot be increased and the device becomes large. In addition, there is a concern that the activated carbon itself is also oxidized due to decomposition of hydrogen peroxide, resulting in collapse of particles.
As the method of contacting a resin on which metal is supported, for example, a method has been proposed in which water to be processed which contains hydrogen peroxide is brought into contact with a catalyst resin in which a palladium catalyst or a platinum catalyst is supported on an ion exchange resin [Patent Literature 1]. In this method, hydrogen peroxide is decomposed by the reaction shown in the following formula.
2H2O2→2H2O+O2
Although not a document relating to decomposition and removal of hydrogen peroxide, Patent Literature 2 discloses that, with regard to an ion exchanger packed in a concentration chamber of an electrodeionization device, the ion exchanger is packed in the concentration chamber so that a volume of the ion exchanger taken out from the concentration chamber after a deionization treatment in a deionization chamber becomes 103% to 125% of a volume of the concentration chamber.
Although the method of decomposing and removing hydrogen peroxide by a catalyst resin in which a catalyst made of palladium, platinum or the like is supported on an ion exchange resin has a larger decomposition rate of hydrogen peroxide than the method of contacting with activated carbon, it is desired to further improve the decomposition rate. In addition, in the method using a catalyst resin, it is known that the decomposition rate of hydrogen peroxide decreases with time, and it is desired that hydrogen peroxide can be stably decomposed over a long period of time.
It is an object of the present invention to provide a hydrogen peroxide removing method and an apparatus capable of rapidly and stably treating hydrogen peroxide in a wide concentration region in water to be processed for a long period of time, and a pure water producing apparatus equipped with the hydrogen peroxide removing apparatus. It is another object of the present invention to provide a method and an apparatus for removing hydrogen peroxide which can also be applied to waste water treatment.
The method for removing hydrogen peroxide according to the present invention is a method for removing hydrogen peroxide contained in water to be processed, comprising the step of passing the water to be processed through a hydrogen peroxide removal chamber which is provided between an anode and a cathode and in which a metal catalyst with hydrogen peroxide decomposition ability is at least partially filled, while applying a DC voltage between the anode and the cathode.
The hydrogen peroxide removing apparatus according to the present invention is a hydrogen peroxide removing apparatus for removing hydrogen peroxide contained in water to be processed, comprising: an anode and a cathode; and a hydrogen peroxide removal chamber provided between the anode and the cathode and at least partially filled with a metal catalyst with hydrogen peroxide decomposition ability, wherein a DC voltage is applied between the anode and the cathode.
The pure water producing apparatus according to the present invention is a pure water producing apparatus comprising: the hydrogen peroxide removing apparatus according to the present invention; and an ultraviolet oxidation device provided at a preceding stage of the hydrogen peroxide removing apparatus.
According to the present invention, while passing water to be processed through a hydrogen peroxide removal chamber in which a metal catalyst with hydrogen peroxide decomposition ability is at least partially filled, a DC (direct-current) voltage is applied between the anode and the cathode, so that removal of the reaction product by contact of hydrogen peroxide with the metal catalyst is quickly performed, and the decomposition and removal performance of hydrogen peroxide can be stably maintained high over a long period of time. In particular, in the present invention, it is preferable that an ion exchanger is filled in the hydrogen peroxide removal chamber so that the metal catalyst is supported on at least a part of the ion exchanger. By supporting the metal catalyst on an ion exchanger, when a DC voltage is applied between the anode and the cathode while passing the water to be processed through the hydrogen peroxide removal chamber, decomposition of hydrogen peroxide and electric regeneration of the ion exchanger proceed in parallel, and the decomposition and removal performance of hydrogen peroxide can be stably maintained higher over a long period of time.
Examples of the metal catalyst with hydrogen peroxide decomposition ability in the present invention include, for example, iron, manganese, nickel, gold, silver, copper, chromium, aluminum, and compounds thereof in addition to platinum group metal catalysts such as palladium and platinum. Among them, the platinum group metal catalyst is more suitably used because of its high catalytic activity for hydrogen peroxide decomposition. The platinum group metal catalyst is a catalyst containing one or more metals selected from ruthenium, rhodium, palladium, osmium, iridium and platinum. The platinum group metal catalyst may be one containing any one of these metal elements alone or a combination of two or more of them. Among these, platinum, palladium, and platinum-palladium alloys have high catalytic activity and are suitably used as the platinum group metal catalysts.
The present invention can exhibit more superiority by using an anion exchanger on which a platinum group metal catalyst is supported as the metal catalyst when hydrogen peroxide is removed from water to be processed which contains a carbonic acid component which serves as a load on the anion exchanger. Then, when the hydrogen peroxide removal chamber is compartmentalized by an anion exchange membrane on the anode side thereof, the anion component, i.e., the carbonic acid component, adsorbed to the anion exchanger in the hydrogen peroxide removal chamber from the water to be processed is desorbed from the anion exchanger by electric regeneration and is then discharged in a form of anion from the hydrogen peroxide removal chamber via the anion exchange membrane on the anode side. In other words, according to the present invention, not only the processed water from which hydrogen peroxide has been removed is generated but also the water quality of the processed water can be improved.
In addition, in the present invention, since the regeneration state of the ion exchanger on which the platinum group metal catalyst is supported can be maintained by continuously applying the DC voltage, it is also possible to operate by setting a space velocity (SV) to be equal to or higher than 100 h−1. The space velocity SV is a unit representing how many times the volume of the water to be processed is treated per unit time corresponding to the volume of the ion exchanger which is filled in the hydrogen peroxide removal chamber and on which the platinum group metal catalyst is supported. Specifically, the SV value can be determined by dividing the flow rate (L/h) of the water to be processed by the volume (L) of the ion exchanger on which the platinum group metal catalyst is supported. Enabling the operation at two times and three times the normal SV value is advantageous because it allows the amount of catalyst, which supports noble metal and is expensive, to be reduced by one-half or one-third in order to perform the treatment of the same amount of the water to be processed.
In the hydrogen peroxide removing apparatus according to the present invention, a deionization chamber in which an ion exchanger is filled may be provided adjacent to the hydrogen peroxide removal chamber at the cathode side or the anode side of the hydrogen peroxide removal chamber via an intermediate ion exchange membrane, and the processed water treated in the hydrogen peroxide removal chamber may be passed through the deionization chamber. With this configuration, it is possible to simultaneously perform the removal of hydrogen peroxide from the water to be processed and the deionization of the water to be processed. By using the processed water discharged from the deionization chamber, it becomes possible to produce high-purity pure water and ultrapure water.
In the present invention, it is preferable that a first cation exchange membrane and a first anion exchange membrane which are superposed on each other are arranged between the hydrogen peroxide removal chamber and the cathode so that the first cation exchange membrane is on the side facing the cathode and the first anion exchange membrane is on the side facing the hydrogen peroxide removal chamber. In this configuration, when a DC voltage is applied between the anode and the cathode, a dissociation reaction of water proceeds at an interface between the first cation exchange membrane and the first anion exchange membrane, and hydroxide ions (OH−) are supplied from the first anion exchange membrane to the hydrogen peroxide removal chamber. As a result, the electric resistance between the anode and the cathode becomes small, so that a large current can be flowed through the hydrogen peroxide removal chamber at a low voltage, and regeneration of the ion exchanger in the hydrogen peroxide removal chamber can be promoted. When the first cation exchange membrane and the first anion exchange membrane are superposed, they may be simply superposed on each other, or may be configured as a bipolar membrane by arranging a catalyst which promotes the dissociation reaction of water at the interface between them.
Further in the present invention, it is preferable that a packing ratio which is a value obtained by dividing, by a volume of the hydrogen peroxide removal chamber, a volume in a free state of the ion exchanger taken out from the hydrogen peroxide removal chamber after applying a DC voltage between the anode and the cathode and passing the water to be processed through the hydrogen peroxide removal chamber is 95% or more and 125% or less. By filling the ion exchanger into the hydrogen peroxide removal chamber so as to have such a packing ratio, it is possible to further reduce the effective electric resistance of the hydrogen peroxide removal chamber while smoothly passing the water to be processed into the hydrogen peroxide removal chamber, and it is possible to further reduce the value of the DC voltage applied to the hydrogen peroxide removing apparatus. Therefore, by setting the packing ratio of the ion exchanger within the above range, it is possible to reduce the applied DC voltage and to reduce the power consumption per water to be processed of a unit flow rate supplied to the hydrogen peroxide removal chamber.
The above-described packing ratio of the ion exchanger to be filled in the hydrogen peroxide removal chamber is measured after applying a DC voltage between the anode and the cathode to pass the water to be processed through the hydrogen peroxide removal chamber. In this state, the ion exchanger contains sufficient water and is in a state in which the regenerated form and the salt form are mixed with respect to the ionic form. For example, the volume of the ion exchanger which is an ion exchange resin varies depending on the water content and whether the ion form is a regenerated form or a salt form. The volume of the ion exchanger becomes maximum when the ion exchanger sufficiently contains water to swell and the ion form is a regenerated form. Therefore, by filling the hydrogen peroxide removal chamber with an ion exchanger having a relatively small water content and/or an ion exchanger in a salt form with regard to its ionic form, and then applying a DC voltage and passing of water to be processed so as to increase the volume of the ion exchange volume, it is possible to fill the hydrogen peroxide removal chamber with the ion exchanger so that the packing ratio exceeds 100%.
According to the present invention, hydrogen peroxide can be stably removed from water to be processed, which contains hydrogen peroxide in a wide concentration range, over a long period of time. As a result, for example, it becomes possible to perform stable operation of the entire water treatment facility to which water to be processed which contains hydrogen peroxide is supplied.
Next, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described in the drawings.
Next, the operation of the hydrogen peroxide removing apparatus shown in
There is no particular limitation on the supply water to be passed through concentration chambers 22, 24 and the electrode chambers (i.e., anode chamber 21 and cathode chamber 25), and each of the independent supply water may be used, and the same supply water may be branched and used. Further, the water to be processed or the processed water discharged from hydrogen peroxide removal chamber 23 may be fed as supply water, or the supply water of another system containing no hydrogen peroxide may be fed. In addition, although the flows of the supply water and the water to be processed in the electrode chambers, concentration chambers 22, 24 and hydrogen peroxide removal chamber 23 have mutually co-current relationship in the drawing, but water may be flowed so as to be countercurrent between adjacent chambers.
In the configuration shown in
In the hydrogen peroxide removing apparatus according to the present invention, as described above, a DC voltage is applied between anode 11 and cathode 12 to perform removal of hydrogen peroxide and deionization while electrically regenerating an ion exchanger, e.g., a granular ion exchange resin, in hydrogen peroxide removal chamber 23. In order to reduce the voltage applied between anode 11 and cathode 12, it is effective that the ion exchanger is densely filled in hydrogen peroxide removal chamber 23 within a range in which water permeation is not suppressed. In addition, it is known that ion exchangers, particularly ion exchange resins, vary in particle size depending on their water content and ionic form. When the ionic form is in a regenerated form, that is, in a state in which a hydroxide ion is adsorbed to the ion exchange group in case of a anion exchanger and a hydrogen ion is adsorbed to the ion exchange group in case of a cation exchanger, the particle diameter becomes larger than when the ionic form is other than the regenerated form (e.g., a state in which chloride ions or sodium ions are adsorbed), that is, when the ion exchange group is in a salt form. When the water content of the ion exchanger is large, the particle size becomes large. The ion exchanger, particularly the ion exchange resin, has elasticity, deforms when pressure is applied, and has a property of returning to its original shape when the application of pressure is terminated. Therefore, assuming that there is no deformation of hydrogen peroxide removal chamber 23, it is preferable that the ion exchanger is filled in hydrogen peroxide removal chamber 23 in a condition in which the particle diameter is small, and then the ion exchanger is expanded by passing water or electric regeneration so that the ion exchanger is densely filled in hydrogen peroxide removal chamber 23. However, if the ion exchanger is too densely present in hydrogen peroxide removal chamber 23, water passage into hydrogen peroxide removal chamber 23 is inhibited, which is not preferable.
Therefore, in the hydrogen peroxide removing apparatus, it is preferable that a packing ratio, which is a value obtained by dividing, by a volume of hydrogen peroxide removal chamber 23, a volume in a free state of an ion exchanger taken out from hydrogen peroxide removal chamber 23 after applying a DC voltage between anode 11 and cathode 12 to pass the water to be processed through hydrogen peroxide removal chamber 23 is 95% or more and 125% or less. The packing ratio is more preferably 102% or more and 125% or less. Here, the volume of the ion exchanger in the free state is an apparent volume including a void between particles in a state in which the ion exchanger is not restrained by hydrogen peroxide removal chamber 23. As described below, in the hydrogen peroxide removing apparatus according to the present invention, in addition to an ion exchanger on which a metal catalyst is supported, an ion exchanger on which a metal catalyst is not supported may be filled in hydrogen peroxide removal chamber 23 in some cases. Since the effect obtained by setting the packing ratio to 95% or more and 125% or less is considered to be caused by a physical degree of adhesion between the ion exchangers, the packing ratio in a case where the ion exchanger on which the metal catalyst is supported and the ion exchanger on which the metal catalyst is not supported coexist is determined based on the entire volume in the free state of the ion exchangers taken out from hydrogen peroxide removal chamber 23. Hereinafter, various hydrogen peroxide removing apparatuses based on the present invention will be described, but in any of them, the packing ratio of the ion exchanger in hydrogen peroxide removal chamber 23 is preferably set to 95% or more and 125% or less.
In the hydrogen peroxide removing apparatus of the first embodiment, an ion exchanger on which a metal catalyst is not supported can be filled in hydrogen peroxide removal chamber 23, in addition to an anion exchanger on which the platinum group metal catalyst is supported (Cat. AER). Hereinafter, such examples will be described with reference to
In the hydrogen peroxide removing apparatus shown in
In the hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
In the hydrogen peroxide removing apparatus shown in
Also in the hydrogen peroxide removing apparatuses described using
As described above, the anode chamber can also function as a concentration chamber without providing a concentration chamber adjacent to the anode chamber, and similarly, the cathode chamber can also function as a concentration chamber without providing a concentration chamber adjacent to the cathode chamber. In the hydrogen peroxide removing apparatus shown in
Next, a hydrogen peroxide removing apparatus according to the second embodiment of the present invention will be described. In the hydrogen peroxide removing apparatus of the first embodiment, a deionization chamber may be provided between anode 11 and cathode 12 so as to be adjacent to hydrogen peroxide removal chamber 23 via an intermediate ion exchange membrane on the cathode side or the anode side of hydrogen peroxide removal chamber 23, and the processed water obtained by passing the water to be processed through the hydrogen peroxide removal chamber may be passed through the deionization chamber. The deionization chamber is filled with an ion exchanger. In this configuration, it is possible to simultaneously perform removal of hydrogen peroxide from the water to be processed and deionization, and it becomes possible to produce pure water of high purity as well as ultrapure water. The intermediate ion exchange membrane may be an anion exchange membrane or a cation exchange membrane, and may be a composite membrane such as a bipolar membrane.
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
The hydroxide ion utilized for regeneration of the ion exchanger in hydrogen peroxide removal chamber 23 in the hydrogen peroxide removing apparatus of the first embodiment is generated by a dissociation reaction of water occurring at a point where the anion exchange resin and the cation exchange membrane come into contact with each other or at a point where the anion exchange resin and the cation exchange resin come into contact with each other. Since the area where the ion exchange resin and the ion exchange membrane come into contact with each other and the area where the ion exchange resins come into contact with each other are small, the amount of generated hydroxide ions used for regeneration of the ion exchanger in hydrogen peroxide removal chamber 23 is also small. If a large amount of hydroxide ions can be supplied into hydrogen peroxide removal chamber 23, the regeneration efficiency of the ion exchanger can be further improved, and the effective electric resistance of hydrogen peroxide removal chamber 23 can be further reduced. Therefore, in the hydrogen peroxide removing apparatus according to the third embodiment, a superposition in which a cation exchange membrane and an anion exchange membrane are superposed on each other is arranged between hydrogen peroxide removal chamber 23 and cathode 12 so that the cation exchange membrane is located on a side facing cathode 12 and the anion exchange membrane is located on a side facing hydrogen peroxide removal chamber 23. With this configuration, when a DC voltage is applied between anode 11 and cathode 12, the dissociation reaction of water proceeds at the interface between the cation exchange membrane and the anion exchange membrane due to the potential difference generated by the current, and the hydroxide ions are supplied from the anion exchange membrane to the hydrogen peroxide removal chamber. As a result, the electric resistance between anode 11 and cathode 12 becomes smaller, so that a large current can be flowed through the hydrogen peroxide removal chamber at a low voltage, and regeneration of the ion exchanger in hydrogen peroxide removal chamber 23 can be promoted. When the cation exchange membrane and the anion exchange membrane are superposed, they may be simply superposed on each other, or may be configured as a bipolar membrane by arranging a catalyst which promotes the dissociation reaction of water at an interface between them.
Next, the operation of the hydrogen peroxide removing apparatus shown in
In the hydrogen peroxide removing apparatus shown in
In the configuration shown in
Also in the hydrogen peroxide removing apparatus shown in
In the configuration shown in
In order to prevent the weak acid component from being mixed into the processed water discharged from hydrogen peroxide removal chamber 23, it is also effective to superpose anion exchange membrane 81 on cation exchange membrane 33. When anion exchange membrane 81 is superposed on cation exchange membrane 33, the weak acid component diffused to the side of hydrogen peroxide removal chamber 23 via cation exchange membrane 33 permeates through anion exchange membrane 81. At this time, the weak acid component is converted from a neutral molecule to an anion by ion exchange inside anion exchange membrane 81, and thus becomes an ionic form which is easily captured in the Pd-supported anion exchange resin (Pd AER) inside hydrogen peroxide removal chamber 23. As a result, incorporation of a weak acid component into the processed water is reduced.
Also in the hydrogen peroxide removing device of the third embodiment, as in the apparatus of the first embodiment, an ion exchanger on which a metal catalyst is not supported can be filled in hydrogen peroxide removal chamber 23, in addition to the anion exchanger (Cat. AER) on which the platinum group metal catalyst is supported. Hereinafter, such examples will be described.
In the hydrogen peroxide removing device shown in
In the hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
In the hydrogen peroxide removing apparatus shown in
Also in the hydrogen peroxide removing apparatuses described with reference to FIGS. 18 to 23, since hydrogen peroxide removal chamber 23 has a multilayered bed configuration, the amount of the expensive platinum group metal catalyst to be used can be reduced as compared with the case where only the catalyst-supported anion exchange resin (Cat. AER) is filled in hydrogen peroxide removal chamber 23, the cost can be reduced.
As described above, the anode chamber can also function as a concentration chamber without providing the concentration chamber adjacent to the anode chamber, and similarly, the cathode chamber can also function as a concentration chamber without providing the concentration chamber adjacent to the cathode chamber. In the hydrogen peroxide removing apparatus shown in
Next, a hydrogen peroxide removing apparatus according to a fourth embodiment of the present invention will be described. The hydrogen peroxide removing apparatus is one obtained by arranging, between hydrogen peroxide removal chamber 23 and cathode 12, a superposition in which a cation exchange membrane and an anion exchange membrane are superpose on each other in order to increase the amount of hydroxide ions supplied to hydrogen peroxide removal chamber 23 so that the cation exchange membrane is on the side of cathode 12 and the anion exchange membrane is on the side of hydrogen peroxide removal chamber 23, in the hydrogen peroxide removing apparatus of the second embodiment described above. In this case, the intermediate ion exchange membrane itself partitioning hydrogen peroxide removal chamber 23 and deionization chamber 28 may be a superpotition in which the anion exchange membrane and the cation exchange membrane are superposed on each other so that the anion exchange membrane is on the side of hydrogen peroxide removal chamber 23. Alternatively, when at least an anion exchange resin is filled in deionization chamber 28, the intermediate ion exchange membrane may be used as an anion exchange membrane, and deionization chamber 28 may be partitioned on the side thereof facing cathode 12 by a superposition in which an anion exchange membrane and a cation exchange membrane are superposed on each other so that the anion exchange membrane is on the side of hydrogen peroxide removal chamber 23. Also in this embodiment, it is preferable that the packing ratio of the ion exchanger in hydrogen peroxide removal chamber 23 is set to 95% or more and 125% or less.
In the hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing device shown in
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
The anion exchanger used in the hydrogen peroxide removing apparatus according to the present invention is not particularly limited, regardless of whether it is used for supporting a metal catalyst or not, and a monolithic porous anion exchanger or an anion exchange resin is suitably used as the anion exchanger. Further, there is no particular limitation on the anion exchange membrane, and, for example, a homogeneous anion exchange membrane or a heterogeneous anion exchange membrane is suitably used as the anion exchange membrane. Furthermore, there is no particular limitation on the cation exchanger, and a monolithic porous cation exchanger or a cation exchange resin is suitably used as the cation exchanger. Still further, there is no particular limitation on the cation exchange membrane, and, for example, a homogeneous cation exchange membrane or a heterogeneous cation exchange membrane is suitably used as the cation exchange membrane. In addition, the intermediate ion exchange membrane is not particularly limited, and for example, a homogeneous anion exchange membrane or a heterogeneous anion exchange membrane, a homogeneous cation exchange membrane or a heterogeneous cation exchange membrane, a bipolar membrane, or the like is suitably used as the intermediate ion exchange membrane.
Although there is no particular limitation on the resin serving as a matrix of the anion exchange resin or the cation exchange resin, a resin containing an organic polymer having a three dimensional network structure is preferred as the matrix, and examples of the organic polymer serving as a matrix include a copolymer of styrene-divinylbenzene (i.e., styrene-based), a copolymer of acrylic-divinylbenzene (i.e., acrylic-based), and so on.
Further, examples of types of the anion exchanger include a weakly-basic anion exchanger, a strongly-basic anion exchanger, and so on. Examples of types of the cation exchanger include a weakly-acidic cation exchanger, a strongly-acidic cation exchanger, and so on. An ion exchanger supporting a platinum group metal catalyst used in the present invention is one in which particles of a platinum group metal catalyst are supported on the above cation exchanger or anion exchanger.
There is no particular limitation on the method for producing an ion exchanger on which the platinum group metal catalyst is supported and which is used in the present invention. An ion exchanger on which a platinum group metal catalyst is supported can be obtained by supporting particles of a platinum group metal on an ion exchanger by a known method. For example, there is a method in which an anion exchanger is immersed in an aqueous hydrochloric acid solution of palladium chloride to adsorb chloropalladate anions to the anion exchanger by ion exchange, and then contacted with a reducing agent to support palladium metal nanoparticles on the anion exchanger. Alternatively, there is a method in which an anion exchanger is packed in a column, an aqueous hydrochloric acid solution of palladium chloride is passed through the column to adsorb chloropalladate anions to the anion exchanger by ion exchange, and then a reducing agent is passed through the column to support palladium metal nanoparticles on the anion exchanger. There is no particular limitation on the reducing agent used in these processes, and the reducing agents include: alcohols such as methanol, ethanol, and isopropanol; carboxylic acids such as formic acid, oxalic acid, citric acid, and ascorbic acid; ketones such as acetone and methyl ethyl ketone; aldehydes such as formaldehyde and acetaldehyde; sodium borohydride; hydrazine; and so on.
The water to be processed supplied to the hydrogen peroxide removing apparatus according to the present invention is not particularly limited as long as it contains hydrogen peroxide. The concentration of hydrogen peroxide can include, for example, 1 μg/L or more, 5 μg/L or more, 10 μg/L or more, 100 μg/L or more, and 1000 μg/L or more. Further, the water to be processed may contain a carbonic acid component. Here, the carbic acid component refers to H2CO3, HCO3−, CO32−. The carbonic acid component is generated, for example, when decomposition and removal of TOC components is performed by an ultraviolet oxidation device. In this description, the total amount of these carbonic acid components is referred to as “total carbonic acid,” and the concentration thereof is expressed as CO2-converted concentration (as CO2). The concentration of the total carbonic acid of the water to be processed is not particularly limited, and examples thereof include those having 0.01 mg/L (as CO2) or more, 0.1 mg/L (as CO2) or more, and 1.0 mg/L (as CO2) or more. There is no particular limitation on the electric conductivity of the water to be processed, and examples thereof include those having 0.1 μS/cm or more, and 1 μS/cm or more. Further, the water to be processed may contain salt components such as sodium. The concentration of sodium contained in the water to be processed is not particularly limited, and examples thereof include 1 μg/L or more, 10 μg/L or more, 100 μg/L or more, and so on.
In the present invention, there is no particular limitation on the passing-water space velocity of the water to be processed with respect to the filling volume of the ion exchanger on which the platinum group metal catalyst is supported, as long as hydrogen peroxide can be removed, and examples thereof include 10 h−1 or more, 100 h−1 or more, and 200 h−1 or more. Further, there is no particular limitation on the removal ratio of hydrogen peroxide removed from the water to be processed, and examples thereof include 60% or more, 80% or more, 90% or more, and 95% or more.
In the present invention, it is preferable that the thickness of hydrogen peroxide removal chamber 23 is set to 9 mm or more and 30 mm or less. Here, the thickness of hydrogen peroxide removal chamber 23 is a size of hydrogen peroxide removal chamber 23 along the direction of voltage application when a DC voltage is applied between anode 11 and cathode 12, and the thickness direction of hydrogen peroxide removal chamber 23 is generally orthogonal to the flow direction of the water to be processed in hydrogen peroxide removal chamber 23. If the thickness of hydrogen peroxide removal chamber 23 is too small, the flow rate of the water to be processed which can be processed becomes too small. On the other hand, if the thickness of hydrogen peroxide removal chamber 23 is too large, the DC voltage to be applied between anode 11 and cathode 12 becomes excessively high, and since the amount of hydroxide ions and hydrogen ions generated by dissociation of water is insufficient as compared with the amount of the ion exchanger, electric regeneration of the ion exchanger in hydrogen peroxide removal chamber 23 is not sufficiently performed.
The hydrogen peroxide removing apparatus according to the present invention can be incorporated into, for example, a pure water producing apparatus or an ultrapure water producing apparatus. Hereinafter, a pure water producing apparatus and an ultrapure water producing apparatus incorporating a hydrogen peroxide removing apparatus according to the present invention will be described.
Note that, in
In the pure water producing apparatus, a carbonic acid removing means may be provided at a stage preceding the hydrogen peroxide removing apparatus. When the carbonic acid component in the water to be processed which is supplied to the hydrogen peroxide removing apparatus becomes small, it becomes possible to reduce the voltage applied to the hydrogen peroxide removing apparatus and to reduce the power consumption. As the carbonic acid removing means, a reverse osmosis membrane (RO) device, an additive of a basic agent to a reverse osmosis membrane device, and further, although not shown in
The ultrapure water producing apparatus shown in
In the ultrapure water producing apparatus, hydrogen peroxide removing apparatus 100 according to the present invention can also be arranged in a subsystem.
Next, the present invention will be described in more detail by way of Examples and Comparative Examples.
Using the apparatuses shown in
The concentration of total carbonic acid in the water to be processed was calculated from the measured inorganic carbon (IC) concentration using a TOC meter (Sievers™ M9e, manufactured by SUEZ Co., Ltd.) by the following method.
Total carbonic acid concentration [mg/L (as CO2)]=Inorganic carbon (IC) concentration [mg/L (as C)]×3.364
Here, 3.664 is a factor used for converting an amount of carbon (C) into a corresponding amount of total carbonic acid (CO2), which is calculated by the following formulae.
Molecular weight of CO2=44.01 [g/mol]
Atomic weight of C=12.01 [g/mol]
44.01 [g/mol]/12.01 [g/mol]=3.364
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide removing apparatus shown in
A hydrogen peroxide removing apparatus shown in
A device having the configuration shown in
The hydrogen peroxide removing apparatus shown in
<Influence of Total Carbonic Acid>
The effect of total carbon contained in the water to be processed was considered. As can be seen from Table 2, even if the concentration of total carbonic acid in the water to be processed increases, in Examples 1-1 and 1-2, the removal ratio of hydrogen peroxide is almost 100%, and the electrical resistivities in the processed water also exhibit high values of 18.1 MΩ·cm and 17.7 MSΩ·cm, respectively. In contrast, in Comparative Examples 1-1, 1-2, 1-3 and 1-4, the removal ratios of hydrogen peroxide were 7%, 99%, 17% and 58%, respectively, and the electrical resistivities of the processed water were 17.9 MΩ·cm, 16.8 MΩ·cm, 17.9 MΩ·cm and 0.6 MΩ·cm, respectively. In other words, in the results of Comparative Examples 1-1 and 1-3, when the total carbonic acid concentration of the water to be processed increased, the performance of removing hydrogen peroxide slightly improved, but it was still only an increase of 7%→17%, which is a low value. Here, from the results of Comparative Examples 1-2 and 1-4, it can be seen that, when the total carbonic acid concentration of the water to be processed increases, the removal ratio of hydrogen peroxide is remarkably lowered. On the other hand, from Examples 1-1 and 1-2, it can be seen that, according to the method based on the present invention, even if the total carbonic acid concentration of the water to be processed increases, a very good removal ratio of hydrogen peroxide can be obtained.
<Hydrogen Peroxide Concentration Dependency and Applied Current Dependency of Removal Ratio>
The dependencies of the hydrogen peroxide removal ratio on the concentration of hydrogen peroxide in the water to be processed and the applied current were studied. As shown in Table 3, even if the hydrogen peroxide concentration in the water to be processed changes, the removal ratios of hydrogen peroxide are almost 100% in Examples 1-2, 1-3, 1-4 and 1-5. On the other hand, in Comparative Examples 1-3 to 1-10, the removal ratios of hydrogen peroxide were greatly reduced, and in some cases, hydrogen peroxide could not be removed at all as in Comparative Example 1-5. From these results, it was confirmed that, in the hydrogen peroxide removing apparatus according to the present invention, removal of hydrogen peroxide can be stably achieved in a wide concentration range. In particular, it was also confirmed that the present invention can further exhibit superiority in removing hydrogen peroxide when the hydrogen peroxide concentration in the water to be processed is at a low concentration. Further, comparing the result of Comparative Example 1-3 with the result of Comparative Example 1-9, the removal ratio of hydrogen peroxide increased from 17% to 24% by increasing the applied current from 0.1 A to 1 A. However, in these comparative examples, the removal ratios are still low, and it is considered difficult to achieve a removal ratio close to 100% by increasing the current value.
<Influence of Flow Rate>
The flow rate of water to be processed was considered. As can be seen from Table 4, in Examples 1-5 and 1-6, the removal ratio of hydrogen peroxide was 100% even when the flow rate of water to be processed was changed. On the other hand, in the apparatus of the comparative examples, as can be seen by comparing the results of Comparative Examples 1-9 and 1-10 with those of Comparative Examples 1-11 and 1-12, even if the flow rate of the water to be processed was reduced by half, increasing the removal rate of hydrogen peroxide to nearly 100% as in the apparatus according to the present invention could not be achieved.
<Influence of Sodium in Water to be Processed>
A case in which sodium, a cationic component, is added to water to be processed was considered. Note that, by adding an aqueous NaOH solution, sodium was added to the water to be processed. As shown in Table 5, in Examples 1-7 and 1-8, even if sodium was contained in the water to be processed, the removal ratio of hydrogen peroxide was almost 100%. Further, in Example 1-8, even if sodium was contained in the water to be processed, a water quality as high as 15.1 MΩ·cm was obtained. On the other hand, in Comparative Examples 1-13, 1-14 and 1-15, the removal ratio of hydrogen peroxide was low.
From the results shown in Table 2 to Table 5 described above, it can be seen that, by means of the hydrogen peroxide removing apparatus and the hydrogen peroxide removing method according to the present invention, an electrical resistivity of the processed water of 1 MΩ·cm or more can be achieved and a removal ratio of hydrogen peroxide of 90% or more can be achieved.
The hydrogen peroxide removing apparatus shown in
The hydrogen peroxide concentration contained in the processed water discharged from hydrogen peroxide removal chamber 23 when the system was stabilized after about 1000 hours have elapsed since passing water and application of the DC voltage to the hydrogen peroxide removing apparatus was started was determined, and the removal ratio of hydrogen peroxide in this hydrogen peroxide removing apparatus was determined. At the same time, the electrical resistivity of the water to be processed and the value of the DC voltage applied at that time were determined. Based on the applied voltage and the current value, the power consumption per unit flow rate of the water to be processed was determined. The results are shown in Table 6. Further, after completing these measurements, the Pd-supported anion exchange resin (Pd AER) was taken out from hydrogen peroxide removal chamber 23 to determine its volume in a free state, which was 95 to 100% of the volume of hydrogen peroxide removal chamber 23.
A hydrogen peroxide removing apparatus similar to that in Example 2 was assembled in which hydrogen peroxide removal chamber 23 and concentration chamber 24 located on the cathode 12 side thereof were partitioned only by cation exchange membrane 33. The hydrogen peroxide removing apparatus of Example 3 has the structure shown in
The same water as in Example 2 was used, and the same measurements as in Example 2 were carried out so that the flow rate of the water to be processed into hydrogen peroxide removal chamber 23 was set at 56 L/h and the current flowing between anode 11 and cathode 12 became 0.66 A. The results are shown in Table 6. Further, after completion of the measurements, the Pd-supported anion exchange resin (Pd AER) was taken out from hydrogen peroxide removal chamber 23 to determine its volume in a free state, which was 95 to 100% of the volume of hydrogen peroxide removal chamber 23. Note that, in the hydrogen peroxide removing apparatus of Example 3, a dissociation reaction of water proceeds at an interface between the Pd-supported anion exchange resin (Pd AER) and cation exchange membrane 33, but hydrogen ions generated at this time are released into concentration chamber 24 adjacent to hydrogen peroxide removal chamber 23 and react with the carbonic acid component contained in the water in concentration chamber 24 to generate free carbonic acid. Since the free carbonic acid does not have a charge, it is not affected by the charge repulsion of cation exchange membrane 33 and diffuses from concentration chamber 24 into hydrogen peroxide removal chamber 23 via cation exchange membrane 33. Since this free carbonic acid is not in an ionic form, it is hardly adsorbed to the Pd-supported anion exchange resin (Pd AER) in hydrogen peroxide removal chamber 23, and it is caused to leak to the processed water side and reduce the water quality. In order for the carbonic acid component to be adsorbed on the Pd-supported anion exchange resin (Pd AER), it needs to be converted into carbonate ions or bicarbonate ions. On the other hand, in the hydrogen peroxide removing apparatus of Example 2, since anion exchange membrane 81 is superposed on cation exchange membrane 33 in which the free carbonic acid diffuses, the free carbonic acid is reliably converted into carbonate ions or bicarbonate ions when passing through anion exchange membrane 81 and then released into hydrogen peroxide removal chamber 23, so that water quality deterioration in the processed water hardly occurs.
A hydrogen peroxide removing apparatus similar to that in Example 2 was assembled in which hydrogen peroxide removal chamber 23 and concentration chamber 24 located on the cathode 12 side thereof were partitioned only by cation exchange membrane 33.
The same water as in Example 2 was used, and the same measurements as in Example 2 were carried out so that the flow rate of the water to be processed into hydrogen peroxide removal chamber 23 was 88 L/h and the current flowing between anode 11 and cathode 12 became 1.04 A. The results are shown in Table 6. Further, after completion of the measurements, the Pd-supported anion exchange resin (Pd AER) was taken out from hydrogen peroxide removal chamber 23 to determine its volume in a free state, which was 95 to 100% of the volume of hydrogen peroxide removal chamber 23. Note that, even in the hydrogen peroxide removing apparatus of Example 4, a dissociation reaction of water proceeds at an interface between the Pd-supported anion exchange resin (Pd AER) and cation exchange membrane 33, but hydrogen ions generated at this time diffuse into concentration chamber 24 via cation exchange membrane 33 to generate free carbonic acid.
Comparing Examples 2 to 4, the hydrogen peroxide removal ratio is substantially the same, and the electrical resistivity of the processed water is highest in Example 2. With regard to any of Examples 2 to 4, the DC voltage applied between anode 11 and cathode 12 was within a practicable range. However, while the applied voltage in Example 2 was 10.0 V, the applied voltage in Example 3 was about 1.5 times that of Example 1 at 14.6 V despite the current value was reduced than in Example 2. In Example 4, which had the same current value as in Example 2, the applied voltage was 29.2 V, which was about 3 times. With the applied voltage increased, in the power consumption per unit flow rate of the processed water, compared to a value of 0.11 Wh/L in Example 2, the value in Example 3 was 0.17 Wh/L which was about 1.5 times that of Example 2, and the value in Example 4 was 0.33 Wh/L which was about 3 times that of Example 2. The reason why the applied voltage can be lowered in Example 2 and the power consumption per amount of the processed water can be reduced in this way is considered to be that, in Example 2, a dissociation reaction of water occurs on the entire surface of the bonding interface between anion exchange membrane 81 and cation exchange membrane 33, so that a large amount of hydroxide ions used for electric regeneration of the ion exchanger is supplied to hydrogen peroxide removal chamber 23. On the other hand, in Examples 3 and 4, since the dissociation reaction of water proceeds only in a relatively narrow place in which the Pd-supported anion exchange resin (Pd AER) and cation exchange membrane 33 come into contact with each other, it can be considered that an increase in the applied voltage is caused. Further, it is considered that the reason why the electrical resistivity of the processed water is high in Example 2 is that the free carbonic acid diffusing from concentration chamber 24 into hydrogen peroxide removal chamber 23 is converted into carbonate ions or bicarbonate ions when diffusing through anion exchange membrane 81, and then captured by the Pd-supported anion exchange resin (Pd AER).
The packing ratio of ion exchanger in the hydrogen peroxide removal chamber was considered. Here, as described above, the packing ratio of the ion exchanger is a value obtained by dividing the volume in the free state of the ion exchanger taken out from the hydrogen peroxide removal chamber after applying a DC voltage between the anode and the cathode and then passing the water to be processed through the hydrogen peroxide removal chamber by the volume of the hydrogen peroxide removal chamber. A hydrogen peroxide removing apparatus having the same configuration as in Example 2 was used, and hydrogen peroxide removal chamber 23 was filled with a salt-form Pd-supported anion-exchange resin (Pd AER). By changing the filling amount, the hydrogen peroxide removing apparatuses of Example 5-1 and Example 5-2 were assembled. For the electrode chambers, concentration chambers 22, 24 and hydrogen peroxide removal chamber 23, water having a conductivity of 1.3 μS/cm, a hydrogen peroxide concentration of 97.5 μg/L, and a total carbonic acid concentration of 0.103 mg/L (as CO2) was supplied, and a voltage was applied between anode 11 and cathode 12 so that the current became 1.04 A. The flow rate of the water to be processed to hydrogen peroxide removal chamber 23 was set to 88 L/h.
For each of the hydrogen peroxide removing apparatuses of Example 5-1 and Example 5-2, the hydrogen peroxide concentration contained in the processed water discharged from hydrogen peroxide removal chamber 23 was determined when the system became stable after about 500 hours elapsed since passing water and application of a DC voltage to the hydrogen peroxide removing apparatus was started, and the hydrogen peroxide removal ratio in this hydrogen peroxide removing apparatus was determined. At the same time, the electrical resistivity of the processed water and the value of the DC voltage applied at that time were determined. The results are shown in Table 7. Further, after completing these measurements, the Pd-supported anion exchange resin (Pd AER) was taken out from hydrogen peroxide removal chamber 23 to obtain its volume in a free state, and the packing ratio was determined. The packing ratio was 110 to 115% in Example 5-1, and 95 to 100% in Example 5-2.
Comparing Example 5-1 and Example 5-2, the hydrogen peroxide removal ratio is substantially the same, and there is a slight difference in the electrical resistivity of the processed water. However, while the applied voltage is 6.5V in Example 5-1 having a high packing ratio, the applied voltage is 29.2V in Example 5-2 having a low packing ratio, which is about 4.5 times as large as that in Example 5-1. Compared to Example 2, it was possible to lower the applied voltage in Example 5-1 with a higher packing ratio. It was found that the applied voltage can be lowered by increasing the packing ratio within a range that does not interfere with the water flow of the water to be processed. Further, since the voltage is lowered and electric current flows easily, it is considered that the electrical resistivity of the processed water of Example 5-1 became slightly higher and had a good value.
The relationship between the packing ratio of the ion exchanger on which the platinum group metal catalyst was supported and the electric resistance of the hydrogen peroxide removal chamber was investigated. Here, a space of a 53.1 cm3 provided with a plate electrode of platinum on each of both sides was prepared to simulate a hydrogen peroxide removal chamber, and a salt-form Pd-supported anion exchange resin was filled in this space so as to correspond to a packing ratio, and ultrapure water having a temperature of 25° C. was passed through. Then, an AC voltage having a frequency of 1 kHz and a voltage of 1000 mV was applied between the plate electrodes using an LCR meter to measure the impedance between the plate electrodes, which was then evaluated as an electrical resistance at the time of applying a DC voltage when operating as a hydrogen peroxide removing apparatus. The results are shown in
Similarly to Example 5, the packing ratio of the ion exchanger in the hydrogen peroxide removal chamber was investigated. A hydrogen peroxide removing apparatus having the same configuration as in Example 4, which is shown in
For each of the hydrogen peroxide removing apparatuses of Example 7-1 and Example 7-2, the hydrogen peroxide concentration contained in the processed water discharged from hydrogen peroxide removal chamber 23 was determined when the system was stabilized after about 300 hours elapsed since passing water and application of a DC voltage to the hydrogen peroxide removing apparatus was started, and the hydrogen peroxide removal ratio in this hydrogen peroxide removing apparatus was determined. At the same time, the electrical resistivity of the processed water, the value of the DC voltage applied at that time, and the power consumption per amount of the processed water were determined. The results are shown in Table 8. Further, after completing these measurements, the Pd-supported anion exchange resin (Pd AER) was taken out from hydrogen peroxide removal chamber 23 to obtain its volume in a free state, and the result was found to be 110 to 115% in Example 7-1, and 95 to 100% in Example 7-2.
Comparing Example 7-1 and Example 7-2, the hydrogen peroxide removal ratio is substantially the same, and there is a difference in the electrical resistivity of the processed water. In Example 7-1 with the high packing ratio, the applied voltage becomes less than half of that of Example 7-2, and accordingly, the power consumption became low. Since the voltage is lowered and electric current flows easily, it is considered that the electrical resistivity of the processed water of Example 7-1 became higher than the case of Example 7-2 and had a good value.
Number | Date | Country | Kind |
---|---|---|---|
2020-107733 | Jun 2020 | JP | national |
2021-003462 | Jan 2021 | JP | national |
2021-003463 | Jan 2021 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2021/019568 | 5/24/2021 | WO |