Pure water production apparatus and pure water production method

Abstract

An object of the present disclosure is to provide a pure water production device suitable for providing pure water having a high purity from seawater, fresh water, muddy water, wastewater, sewage, or the like while suppressing or avoiding energy consumption, and a pure water production method using the pure water production device.SOLUTION: The water collecting device includes a plate-like filter which has an upper surface and a lower surface and is a crystal structure having a plurality of channels communicating from the lower surface to the upper surface, and a water collecting device which is provided on the upper surface side of the plate-like filter and condenses and collects water evaporated from the upper surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a pure water production apparatus and a pure water production method. [Background technology]

[0002] Water with few impurities and high purity is called pure water. Pure water is widely used for experiments, drinking, semiconductor cleaning, parts cleaning, and other industrial purposes. Multi-stage flash distillation is a well-known technology for producing pure water. Multi-stage flash distillation is a method of obtaining fresh water by heating and evaporating seawater and condensing the resulting steam.

[0003] Another known pure water production technology is the membrane desalination process using reverse osmosis membranes. Patent Document 1 discloses a pure water production device using reverse osmosis membranes. There is also a desalination method that uses sunlight. This method involves evaporating seawater using sunlight and condensing the resulting steam to obtain water. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7487812 Summary of the Invention [Problem to be solved by the invention]

[0005] Multi-stage flash distillation tends to consume a lot of energy, and can cause problems such as salt accumulation and corrosion of the equipment. Membrane desalination processes use reverse osmosis membranes, which requires high pressure and has low productivity. Desalination methods using sunlight have the problem of not being able to produce water of sufficient purity.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a pure water production apparatus and a pure water production method that are suitable for providing highly pure water while reducing energy consumption. [Means for solving the problem]

[0007] The pure water manufacturing apparatus according to the present disclosure includes a plate-shaped filter having a crystalline structure with an upper surface and a lower surface and a plurality of channels extending from the lower surface to the upper surface, and a water collection device provided on the upper surface side of the plate-shaped filter.

[0008] Other features of the present disclosure are set forth below. [Effects of the Invention]

[0009] Highly pure water can be provided while suppressing energy consumption. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of a pure water production apparatus. [Figure 2] FIG. 1 is a diagram showing an example of the crystal structure of δ-type manganese dioxide. [Figure 3] FIG. 1 is a diagram showing an example of use of a pure water production apparatus. [Figure 4] FIG. 1 is a diagram showing the results of thermogravimetry-differential thermal analysis (TG-DTA). [Figure 5] FIG. 10 is a diagram showing another example of use of the pure water production apparatus. [Figure 6] FIG. 10 is a diagram showing a modified example of the storage section. [Figure 7] FIG. 1 is a diagram showing an example of a pure water production apparatus equipped with a heating device. [Figure 8] FIG. 1 is a diagram showing an example of a pure water production apparatus equipped with a pressure reducing device. [Figure 9] FIG. 1 is a diagram showing an example of a pure water production apparatus equipped with an air flow device. [Figure 10] FIG. 1 is a diagram showing an example of a pure water production system equipped with a cooling device. DETAILED DESCRIPTION OF THE INVENTION

[0011] The pure water production apparatus and the pure water production method will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0012] Embodiment FIG. 1 is a diagram showing an example of a pure water production system according to an embodiment. This pure water production system includes a plate filter 10. The plate filter 10 has an upper surface 10a and a lower surface 10b. Due to its crystalline structure, the plate filter 10 has multiple channels 10c that connect the lower surface 10b to the upper surface 10a. The multiple channels 10c are used to mechanically filter out impurities contained in the liquid, and therefore have a relatively narrow diameter or width.

[0013] Various materials can be used for the plate filter 10 that provides such narrow channels 10c. For example, layered manganese oxide having a delta crystal structure (hereinafter sometimes referred to as δ-type manganese dioxide) represented by the following formula (1) can be used for the plate filter 10. AxMnO2·nH2O ··· Formula (1)

[0014] In formula (1), A represents an element capable of maintaining a delta-type crystal structure, and x is, for example, a number between 0.00 and 0.50. According to one example, A is, for example, a semimetal, a metal element, or the like, and is one or more metal elements having monovalent or divalent cations. For example, A is one or more elements selected from alkali metals and alkaline earth metals, and exists in the crystal as alkali metal ions or alkaline earth metal ions. According to yet another example, A is one or more elements selected from alkali metals. Specifically, A is one or more elements selected from sodium (Na) and potassium (K). For example, A can be potassium. A may be composed of one element, or two or more elements.

[0015] In formula (1), x represents the number of moles of A per mole of Mn atoms, and its value can be 0.00 to 0.50, 0.06 to 0.40, or 0.10 to 0.33. By setting a lower limit for the numerical range of x, the layered structure of δ-type manganese dioxide can be stabilized, the amount of water absorbed can be increased, and durability against repeated use can be improved. On the other hand, by setting an upper limit for the numerical range of x, gaps between the layers of δ-type manganese dioxide can be secured, and the amount of water absorbed can be increased. When x is 0, the δ-type manganese dioxide does not have the element A in the interlayer region. When x is 0.01 or more, the δ-type manganese dioxide has the element A in the interlayer region. According to one example, by setting x to 0.01 or more, the layered structure of the δ-type manganese dioxide can be stabilized.

[0016] In formula (1), n ​​represents the number of moles of water molecules per mole of Mn atoms, and its value is between 0.00 and 1.00. When n is 0.00, this means that δ-type manganese dioxide has no water molecules in the interlayer region; the larger n, the more water molecules there are in the interlayer region. When δ-type manganese dioxide has two regions with different n values, water molecules diffuse within the layers due to the concentration gradient of water molecules between the regions. A large n value increases this concentration gradient, allowing for faster intralayer diffusion of water molecules.

[0017] Figure 2 shows an example of the crystal structure of δ-type manganese dioxide. This δ-type manganese dioxide is a hexagonal crystal with a layered structure in which oxygen octahedral units of MnO6 are arranged in layers. An interlayer region S1 exists between layers L1 and L2, and an interlayer region S2 exists between layers L2 and L3. Elements that maintain the δ-type crystal structure and water molecules can be contained in the interlayer regions S1 and S2. By heating δ-type manganese dioxide, water molecules present in the interlayer regions S1 and S2 can be desorbed. Conversely, by cooling to room temperature, the same amount of water molecules are absorbed into the interlayer regions S1 and S2. Water desorption from the interlayer regions and absorption into the interlayer regions are reversibly repeated by heating and cooling. The interlayer distance continuously changes as water enters and leaves the interlayer region. Setting the interlayer distance change rate to 15% or less or 10% or less suppresses internal strain associated with the water molecule concentration gradient and improves the durability of the material. The lower limit of the rate of change in the interlayer distance is not particularly limited, but is, for example, 1%.

[0018] The interlayer regions S1 and S2 shown in FIG. 2 are an example of the multiple channels 10c in FIG. 1. The interlayer distances d1 and d2, which are the widths of these interlayer regions S1 and S2, vary as described above, but are, for example, approximately 7 Å (0.7 nm). The height of the space provided as the channel 10c is essentially about 4-5 Å. Taking into account errors and variations, the channel 10c is provided with a width of 11 Å or less in at least a portion. If a different material is used for the plate-like filter 10, the width of the channel 10c will also be a corresponding width.

[0019] In another example, the material of the plate-like filter 10 is Birnessite, in which case the layer (or wall) spacing is about 7 Å, and the spatial height provided as the channel 10c is 4-5 Å.

[0020] In another example, the material of the plate-like filter 10 is layered Buserite, in which two layers of water molecules are inserted. In this case, the layer (or wall) spacing is about 10 Å, and the spatial height provided as the channel 10c is 7-8 Å. Note that layered Buserite does not contain Mg in the channel.2+ It may contain:

[0021] In another example, the material of the plate-shaped filter 10 is tunnel-shaped Todorokite. In this case, the layer (or wall) spacing is about 10 Å, and the spatial height provided as the channel 10c is 7-8 Å. Note that the tunnel-shaped Todorokite contains Mg 2+ It may contain: Various materials that absorb (hydrate) and dehydrate (dehydrate) water through channels can be used for the plate filter 10. More specifically, various materials that produce a filtering effect by absorbing, transmitting, and desorbing water can be used. Therefore, the material for the plate filter 10 is not limited to δ-type manganese dioxide.

[0022] The water collection device shown in FIG. 1 will be described. The water collection device is provided on the upper surface 10a side of the plate-shaped filter 10. FIG. 1 illustrates a structure 14 covering the upper surface 10a of the plate-shaped filter 10 as an example of a water collection device. The structure 14 is shaped so that the space in contact with the upper surface 10a is an enclosed space 16. The structure 14 has a transparent portion 14a that transmits light above the upper surface 10a. The transparent portion 14a is made of, for example, glass. The structure 14 also has a storage portion 14b that stores water condensed in the enclosed space 16. In the example of FIG. 1, the storage portion 14b is provided below the upper surface 10a. In the example of FIG. 1, at least the storage portion 14b of the structure 14 is made of a material with good thermal conductivity, such as metal.

[0023] FIG. 3 is a diagram showing an example of use of the water purifying apparatus of FIG. 1. The lower surface 10b of the plate-shaped filter 10 is brought into contact with a water-containing liquid. In the example of FIG. 3, seawater is shown as the water-containing liquid. The water-containing liquid is not limited to seawater, but may be freshwater, muddy water, wastewater, sewage, or the like. Any configuration may be provided to maintain contact between the lower surface 10b and seawater. For example, a support for fixing the water purifying apparatus at a certain height, a float for floating the water purifying apparatus, or the like may be provided. In the example of FIG. 3, as a result of the contact of not only the lower surface 10b but also the reservoir 14b with seawater, the reservoir 14b is maintained at a seawater temperature of, for example, about 20°C.

[0024] The lower surface 10b of the plate-shaped filter 10 is in contact with seawater, and water enters the channels 10c of the plate-shaped filter 10 from the lower surface 10b. Seawater contains H2O, Na + , Cl - However, only water enters the channel 10c due to the following two filtering effects. The first filtering effect is produced by the presence of monovalent or divalent cations in the plate-shaped filter 10. For example, if Na cations are contained in the delta-type manganese dioxide that is the plate-shaped filter 10, the Na + In other words, if the chemical potential of the sodium ions in the δ-type manganese dioxide is set to be higher than that of the Na ions in seawater, the Na ions in the seawater can be prevented from penetrating into the plate-like filter 10. + This means that the Na in seawater does not enter the plate filter 10. This means that the chemical potential is adjusted. + does not enter the plate filter 10, the Cl in seawater is - The inventors have confirmed this through experiments. Specifically, dried K-MnO2 powder was placed in an aqueous solution containing 4% NaCl for 24 hours, washed, dried, and then analyzed for composition. In ICP analysis before quenching, K 0.27 MnO2, whereas EDS analysis after quenching revealed K 0.09 Na 0.1 MnO2. Therefore, K+ From Na + Ion exchange to Cl occurred. - Furthermore, when the dried Na-MnO2 powder was placed in an aqueous solution containing 4% NaCl for 24 hours, washed, dried, and then analyzed for composition, ICP analysis before quenching showed that K 0.04 Na 0.25 MnO2, whereas EDS analysis after quenching revealed K 0.03 Na 0.12 Therefore, the addition of seawater resulted in the formation of Cl in both materials. - It was found that there was no penetration.

[0025] Regarding the first filtering effect, although an example in which the plate-shaped filter 10 contains Na cations has been described here, by making the plate-shaped filter 10 contain alkali metal ions or alkaline earth metal ions, it is possible to effectively remove Na cations from seawater. + and Cl - This can prevent the penetration of the alkali metal ions into the plate-shaped filter 10. Examples of alkali metal ions include Na cations and K cations, and an example of alkaline earth metal ions is Mg ions.

[0026] The second filtering effect is obtained by mechanical filtering by the channel 10c. Because bacteria and viruses in seawater are at least several tens of nanometers in size, by setting the diameter or width of the channel 10c to, for example, Å or several nanometers, bacteria and viruses cannot enter or pass through the channel 10c.

[0027] These two filtering effects allow only water to enter the plate filter 10, and Na + , Cl - The first filtering effect is not essential. For example, when fresh water, muddy water, wastewater, sewage, etc. are brought into contact with the plate filter, unlike seawater, NaCl, etc. + and Cl -It is considered that there is no need to suppress the penetration of organic matter into the plate-shaped filter, or that the suppression is low. In such cases, water can be purified only by the second filtering effect (mechanical filtering) of the multiple channels 10c with a relatively narrow width formed by the crystalline structure. A plate-shaped filter that does not have the first filtering effect and only exerts the second filtering effect removes organic matter using the sub-nano-sized channels, and can therefore purify water to a level that is suitable for drinking.

[0028] Next, we will explain how water absorbed through the lower surface 10b of the plate-shaped filter 10 is desorbed as water vapor from the upper surface 10a. Because the lower surface 10b of the plate-shaped filter 10 is in contact with seawater, it is maintained at a seawater temperature of, for example, about 20°C. On the other hand, because sunlight that passes through the transparent portion 14a is irradiated onto the upper surface 10a, the temperature of the upper surface 10a rises to, for example, about 80°C. Since δ-type manganese dioxide has the property of desorbing water when heated, water can be desorbed from the upper surface 10a by increasing the temperature of the upper surface 10a. Water vaporizes on the upper surface 10a, providing water vapor into the sealed space 16.

[0029] Thus, when water evaporates from the upper surface 10a, a concentration gradient of water molecules is created within the plate filter 10. That is, the concentration of water molecules is lower on the upper side of the plate filter 10 and higher on the lower side. By making the water concentration lower on the upper surface 10a side of the plate filter 10 than on the lower surface 10b side, a difference in water concentration is created within the plate filter 10. This difference in concentration causes a flux of water molecules from the lower surface 10b to the upper surface 10a. That is, water that comes into contact with the lower surface 10b passes through multiple channels 10c formed by the crystalline structure of the plate filter 10 and reaches the upper surface 10a. In one example, at least a portion of the channels 10c has a width of 11 Å or less. By heating the upper surface 10a with sunlight and maintaining a state in which the water that reaches the upper surface 10a is released as water vapor from the upper surface 10a, the water flux within the plate filter is maintained, and seawater continues to be purified automatically without consuming any artificial energy such as power or power.

[0030] Figure 4 shows the results of thermogravimetry-differential thermal analysis (TG-DTA). Referring to Figure 4, we explain how δ-manganese dioxide absorbs and desorbs water in response to temperature changes. The horizontal axis of Figure 4 represents the temperature of δ-manganese dioxide. The vertical axis, TG, represents the mass change of the sample, and the vertical axis, DTA, represents the temperature difference between the sample and a reference material. These experimental results show that δ-manganese dioxide desorbs water when heated and absorbs water when cooled. This reversible reaction is called a water intercalation reaction. More specifically, starting from a TG of -6% at approximately 20°C, the temperature is increased until the weight decreases by about 7% at approximately 160°C, and all of the absorbed water is desorbed. Conversely, as the temperature is decreased (with some hysteresis), the weight increases, and δ-manganese dioxide absorbs water to its full capacity. Figure 4 shows that if δ-manganese dioxide is heated to approximately 80°C or 100°C by sunlight, a few percent of water will desorb. Even this level of water desorption can create a sufficient water concentration gradient in the plate filter. When the upper surface 10a is heated to, for example, 80°C, a difference in water concentration of several percent occurs between the upper surface 10a and the lower surface 10b. Therefore, water reaches the upper surface 10a from the lower surface 10b through the channel 10c and evaporates from the high-temperature upper surface 10a.

[0031] Next, the collection of water vapor in the sealed space 16 will be described. First, the area directly above the upper surface 10a is a region with high temperature and high water vapor partial pressure due to irradiation with sunlight and evaporation of water. On the other hand, as shown in FIG. 3, the reservoir 14b is in contact with seawater and is maintained at a seawater temperature of about 20°C, and water vapor condenses in the reservoir 14b, accumulating as liquid pure water. The example in FIG. 3 shows that the reservoir 14b, cooled by seawater, condenses the water vapor in the sealed space, accumulating as pure water 18. Pure water can also be called purified water.

[0032] When water condenses in reservoir 14b, the water vapor partial pressure in reservoir 14b decreases, and water vapor naturally migrates from the region directly above upper surface 10a, where the temperature and water vapor partial pressure are high, to reservoir 14b. The water vapor that reaches reservoir 14b is cooled and condenses, causing the water vapor partial pressure in reservoir 14b to decrease again, and the water vapor migrates to reservoir 14b. In this way, pure water can be collected in reservoir 14b by utilizing the temperature dependency of vapor pressure, i.e., the higher the temperature, the greater the amount of saturated water vapor, and the lower the temperature, the less saturated water vapor there is. Furthermore, the process of water evaporation on upper surface 10a and water condensation in reservoir 14b can be achieved by heating upper surface 10a with sunlight and cooling reservoir 14b with seawater, allowing the pure water production system to operate using only renewable energy.

[0033] FIG. 5 shows another example of use of a pure water production system. In this example, the lower surface 10b of the plate filter 10 faces the sea surface without contacting it. Any support is provided to keep the lower surface 10b above the sea surface. The reservoir 14b contacts seawater. The gap between the lower surface 10b and the sea surface does not need to be an enclosed space. In this case, the gap between the lower surface 10b and the sea surface is saturated with water vapor pressure at approximately the seawater temperature, and water is absorbed from the lower surface 10b into the plate filter 10. As described above, the water absorbed by the plate filter 10 reaches the upper surface 10a due to the difference in concentration of water molecules within the plate filter 10 and is collected in the reservoir 14b. Because the lower surface 10b does not contact the sea surface, viruses, bacteria, and salt in the seawater can be prevented from entering the plate filter 10.

[0034] FIG. 6 shows a modified example of the reservoir 14b. In FIG. 6A, the reservoir 14c is positioned below the lower surface 10b. This ensures that the reservoir 14b and seawater come into contact with each other. FIG. 6B shows an example in which the reservoir 14d is positioned at the same level as the upper surface 10a. In this case, the reservoir 14d can still come into contact with seawater. Naturally, even if the reservoir is positioned higher than the upper surface 10a, it can still come into contact with seawater. FIG. 6C shows an example in which the reservoir 14e is spaced apart from the plate-shaped filter 10. By spaced apart the reservoir 14e from the plate-shaped filter, a sufficient contact area between the reservoir 14e and seawater can be ensured. The pure water collected in the reservoir can be removed from the pure water production system, for example, via a pipe connected to the reservoir.

[0035] The pure water production apparatus described above can produce a greater amount of pure water as the area of ​​the plate-shaped filter 10 is increased. Therefore, one possible application is to increase the area of ​​the plate-shaped filter 10 and install it offshore. As another example, a business operator can draw seawater, freshwater, muddy water, wastewater, sewage, etc. into a water treatment facility and use the pure water production apparatus according to the present disclosure there. In this case, it is anticipated that pure water will be provided in areas where there are no water pipes or in depopulated areas where repairs to water pipes are unlikely. As yet another example, by making the pure water production apparatus according to the present disclosure handy and easily portable, it becomes possible to secure water in emergencies such as disasters and wars.

[0036] The pure water production system of this embodiment can be modified in various ways. For example, the method for generating a concentration gradient of water molecules in the plate-like filter 10 is not limited to heating with sunlight, and the method for collecting pure water is not limited to using seawater as a cooling source. Therefore, we will now consider modified examples.

[0037] <Variation 1> A heating device can be used instead of sunlight to generate a concentration gradient of water molecules in the plate-like filter 10. FIG. 7 is a diagram showing an example of the configuration of a pure water production system according to Modification 1. This pure water production system includes a heating device 20 attached to the structure 14 as part of a water collection system. The heating device 20 is any heating device that heats the upper surface 10a. In one example, the heating device 20 includes an infrared heater 20a and a mounting portion 20b for screwing and fastening to the structure 14. By applying electricity to the infrared heater 20a via a power cable 20c, the temperature of the upper surface 10a can be increased by radiant heating. In one example, the pure water production system can be installed in a factory, and electricity can be generated from factory waste heat to power the heating device 20.

[0038] <Variation 2> A method for creating a concentration gradient of water molecules within the plate filter 10 is to reduce the pressure of the sealed space 16 rather than heating the upper surface of the plate filter. Figure 8 shows an example of the configuration of a pure water production system according to Modification 2. This pure water production system includes a pressure reducing device 30, which reduces the pressure of the sealed space 16, as part of the water collection device. In one example, the pressure reducing device 30 is a vacuum pump. By reducing the pressure of the sealed space 16 using the pressure reducing device 30, water on the upper surface 10a of the plate filter 10 evaporates, thereby creating a concentration gradient of water molecules within the plate filter 10. In this case, a filtering effect of extracting pure water from seawater can be achieved without heating the upper surface 10a. The configuration of Modification 2 allows for water purification even in areas with insufficient sunlight. As with Modification 1, operating the pressure reducing device 30 using power generated from factory waste heat can reduce costs. For example, if a pressure reducing device 30 is installed in the structure 14 having the transparent portion 14a shown in Figures 1 and 3, the upper surface 10a can be heated by sunlight during the day and the pressure reducing device 30 can be operated at night, making it possible to produce purified water all day long.

[0039] <Variation 3> As a variation of the water collection device, an airflow device that generates airflow in a sealed space can be provided. FIG. 9 is a diagram showing an example of the configuration of a pure water production system according to Variation 3. In the example of FIG. 9, the airflow device 40 is a fan, but another example provides a different airflow device. If the water vapor partial pressure in the sealed space 16 increases and water condenses on the transparent portion 14a (glass), heating of the upper surface 10a by sunlight is prevented. Therefore, the airflow device 40 provides a gentle airflow in the sealed space 16, moving the moisture to a lower temperature area and condensing it. Here, a lower temperature area refers to an area where sunlight is not irradiated or where sunlight is sufficiently weak, an area that is intentionally cooled, etc. In the example of FIG. 9, the storage section 14b is an area where sunlight is not irradiated or where sunlight is sufficiently weak. If there is a lower temperature area in the same sealed space, moisture will preferentially condense there. Therefore, pure water can be stored in the storage section 14b. Note that the airflow path may be circular in plan view to circulate air within the sealed space.

[0040] In Modification 3, it is not necessary to bring reservoir 14b into contact with seawater to cool reservoir 14b. As described above, if water is condensed in reservoir 14b, the water vapor partial pressure is kept low, and water condensation in transparent portion 14a is suppressed. However, by providing airflow while bringing reservoir 14b into contact with seawater, the condensation of water in reservoir 14b can be promoted.

[0041] <Variation 4> As a modification of the water collection device, a cooling device for cooling the reservoir can be provided. FIG. 10 is a diagram showing an example of the configuration of a pure water production system according to Modification 4. In the example of FIG. 10, a cooling device 50 is fixed to the reservoir 14b. According to one example, the cooling device 50 includes a cooling portion 50a, a portion 50b for attachment to the structure 14, and a power cable 50c. According to another example, a cooling device that circulates a refrigerant may be employed. The advantages of providing a cooling device are that it promotes condensation of water and that the reservoir does not need to come into contact with seawater.

[0042] The pure water production apparatus according to the present disclosure can be modified in various ways in addition to the modifications 1 to 4. The above-described features can be combined in any way depending on the environment and purpose of use. [Explanation of symbols]

[0043] 10 Plate-shaped filter, 10a Upper surface, 10b Lower surface, 10c Channel, 14 Structure, 16 Sealed space, 20 Heating device, 30 Pressure reducing device, 40 Air flow device, 50 Cooling device

Claims

1. a plate-like filter having a crystal structure with an upper surface and a lower surface and a plurality of channels extending from the lower surface to the upper surface; a water collecting device provided on the upper surface side of the plate-shaped filter.

2. 2. The water purifying apparatus according to claim 1, wherein the plate-like filter is made of layered manganese oxide having a delta-type crystal structure.

3. 3. The water purifying apparatus according to claim 2, wherein the layered manganese oxide contains alkali metal ions or alkaline earth metal ions.

4. 4. The pure water producing apparatus according to claim 1, wherein the water collecting device has a structure that defines a space in contact with the upper surface as a sealed space.

5. 5. The pure water producing apparatus according to claim 4, wherein the structure has a transparent portion that transmits light above the upper surface.

6. 5. The pure water producing apparatus according to claim 4, wherein the water collecting device has a heating device for heating the upper surface.

7. 5. The pure water producing apparatus according to claim 4, wherein the water collecting device includes a pressure reducing device for reducing the pressure in the sealed space.

8. 5. The pure water producing apparatus according to claim 4, wherein the water collecting device comprises an airflow device that generates an airflow in the sealed space, and a reservoir that stores water condensed in the sealed space.

9. a plate-shaped filter having an upper surface and a lower surface, the lower surface of which is opposed to a liquid containing water in contact with or without contact therewith; By making the concentration of water lower on the upper surface side of the plate-like filter than on the lower surface side, water passes through a plurality of channels formed by the crystalline structure of the plate-like filter, at least a portion of which has a width of 11 Å or less, and reaches the upper surface; releasing the water that has reached the upper surface as steam from the upper surface; and condensing the water vapor to obtain liquid water.

10. The method for producing pure water according to claim 9, wherein the water vapor is condensed by cooling it with a cooling device.

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