Salt separator based on solar energy-thermal gradient as well as preparation method and application of salt separator

Abstract

The invention relates to a solar energy-thermal gradient-based salt separator as well as a preparation method and application thereof. The salt separator sequentially comprises an absorption layer, an adhesive layer and an evaporation layer, the absorption layer comprises a substrate and a photo-thermal conversion material layer sprayed on the surface of one side of the substrate; the substrate is arranged close to the adhesive layer; the photo-thermal conversion material layer completely covers the substrate; the evaporation layer is a hydrophilic film layer; the area of the surface of the side, close to the adhesive layer, of the evaporation layer is larger than the projection area of the absorption layer on the evaporation layer. The structure of the salt separator is designed, so that a temperature gradient can be generated at a controllable position, and salt separation and crystallization are realized by utilizing the solubility difference of different salts at different temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly to a salt separator based on solar - thermal gradient, its preparation method and application. Background Art

[0002] While modern industries produce numerous products, they also generate a large amount of high - salt wastewater, which not only imposes a heavy burden on the environment but also leads to further waste of resources. Realizing the reuse of salt resources is the key to environmental protection and sustainable resource development. However, the fractional separation of salts is the core factor affecting salt recovery efficiency and economy. Currently, although traditional technologies such as chemical precipitation, cooling crystallization, and evaporation crystallization are effective in separating single salts from mixed high - salt wastewater and have been widely applied, these methods require a large amount of energy and chemicals, making the cost of salt resource recovery high.

[0003] CN114956236A discloses an interfacial evaporation brine separation structure where the photothermal conversion interface is not in contact with water. It mainly separates the thin water layer or droplets in the brine rapidly under sunlight through the combined design of photothermal conversion materials and heat conductors, and collects the precipitated salts. Water does not directly contact the photothermal conversion materials, avoiding the pollution of the material surface by crystalline salts, prolonging the service life of the photothermal conversion layer, and the deposition and recovery of salts are achieved through gravity and external forces. However, the absorption rate of the nanomaterials used in its photothermal conversion layer is about 80%, the utilization of solar energy is insufficient, and the design of columnar and inclined structures needs to consider the uniformity of heat distribution, otherwise it may affect the precipitation effect of crystalline salts. At the same time, it can only separate brine and cannot achieve the separation and recovery of different salts.

[0004] CN106830465A discloses a method for treating saline wastewater, which separates and recovers sodium sulfate and sodium chloride in the wastewater through a multi - step process (pretreatment - advanced oxidation treatment - desalination and purification - deep concentration - freeze crystallization). This technology mainly operates under low temperature and normal pressure, the operating environment is relatively safe, and the energy required is mainly the latent heat of ice crystal formation, greatly reducing the energy demand for unit wastewater treatment. And the separated water can be directly used as makeup water for circulating cooling water, effectively achieving "zero discharge" of wastewater, with significant economic and social benefits. However, its freeze concentration and freeze crystallization equipment need to use special materials, the initial investment is large, the requirements for refrigeration equipment are high, indirectly increasing power consumption, and the system also involves multiple process units, the operation and maintenance are more complex, and it can only separate two salts with different prices, namely sodium chloride and sodium sulfate.

[0005] Therefore, there is an urgent need for an economical and efficient method that can simultaneously achieve high - efficiency purification and reuse of salts to address the challenges between water resources and energy. Summary of the Invention

[0006] To solve the above technical problems, the present invention designs the structure of the salt separator, and by combining the use of a photothermal conversion material and an evaporation material, a temperature gradient can be generated at a controllable position, and salt separation crystallization is achieved by utilizing the difference in solubility of different salts at different temperatures.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a salt separator based on solar - thermal gradient, which sequentially includes an absorption layer, an adhesive layer, and an evaporation layer;

[0009] The absorption layer includes a substrate and a photothermal conversion material layer sprayed on one side surface of the substrate; the substrate is disposed close to the adhesive layer;

[0010] The photothermal conversion material layer completely covers the substrate;

[0011] The evaporation layer is a hydrophilic film layer;

[0012] The area of the surface of the evaporation layer close to the adhesive layer is larger than the projected area of the absorption layer on the evaporation layer.

[0013] The substrate used in the present invention has heat conduction performance. A photothermal conversion material is sprayed on one side surface thereof, and the photothermal conversion material layer completely covers the substrate. The photothermal conversion material can absorb solar energy and convert the solar energy into heat and transfer it to the substrate. The other side of the substrate is connected to the evaporation layer through the adhesive layer, and it is controlled that the area of the surface of the evaporation layer close to the adhesive layer is larger than the projected area of the absorption layer on the evaporation layer, so that a temperature gradient can be generated at a controllable position, and salt separation crystallization is achieved by utilizing the difference in solubility of different salts at different temperatures.

[0014] As a preferred technical solution of the present invention, the geometric centers of the absorption layer, the adhesive layer, and the evaporation layer overlap.

[0015] Preferably, the absorption layer, the adhesive layer, and the evaporation layer have the same shape.

[0016] Preferably, the projected area of the absorption layer on the evaporation layer is equivalent to the projected area of the adhesive layer on the evaporation layer.

[0017] Preferably, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is (2.25 - 25):1. For example, it can be 2.25:1, 4:1, 6.25:1, 9:1, 16:1, or 25:1, but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0018] By defining the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer as (2.25 - 25):1, the present invention can generate a temperature gradient at a controllable position, so as to accelerate crystallization under the synergistic action of the evaporation promoted by the heat converted by the photothermal conversion material and the formed temperature gradient, and separate different salts in space. If the ratio of the projected area is less than 2.25:1, the salt solution will crystallize when it just diffuses to the evaporation layer, resulting in local drying of the salt separator, thus unable to leave space for salt separation. At the same time, if the ratio of the projected area is too small, it will lead to waste of solar energy. If the ratio of the projected area is greater than 25:1, more heat is required to promote evaporation and salt concentration, and it is difficult to crystallize when the concentration of the salt solution is not enough.

[0019] As a preferred technical solution of the present invention, the shape of the substrate is circular.

[0020] Preferably, the thickness of the substrate is 50 - 500 μm, for example, it can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm or 500 μm, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0021] Preferably, the material of the substrate includes any one or a combination of at least two of metal sheets, silica gel sheets or ceramic sheets. Typical but non-limiting combinations include: a combination of metal and silica gel sheets, a combination of metal and ceramic sheets, a combination of silica gel sheets and ceramic sheets, and a combination of metal, silica gel sheets and ceramic sheets.

[0022] Preferably, the metal sheet includes any one or a combination of at least two of copper sheets, aluminum sheets or iron sheets. Typical but non-limiting combinations include: a combination of copper sheets and aluminum sheets, a combination of copper sheets and iron sheets, a combination of aluminum sheets and iron sheets, and a combination of copper sheets, aluminum sheets and iron sheets.

[0023] Preferably, the radius of the absorption layer is 20 - 200 mm, for example, it can be 20 mm, 50 mm, 100 mm, 150 mm or 200 mm, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0024] Preferably, the solar energy absorption rate of the absorption layer is 92 - 98%, for example, it can be 92%, 94%, 96% or 98%, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0025] As a preferred technical solution of the present invention, the material of the photothermal conversion material layer includes any one or a combination of at least two of carbon black, graphene, carbon nanotubes, gold nanoparticles, silver nanoparticles, MoS2 or graphite. 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[0026] Preferably, the thickness of the photothermal conversion material layer is 5 - 50 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0027] The present invention defines the thickness of the photothermal conversion material layer as 5 - 50 μm, which can effectively balance the light absorption efficiency and heat conduction performance. If the thickness of the photothermal conversion material layer is less than 5 μm, the photothermal conversion material cannot fully absorb solar energy, resulting in a decrease in the photothermal conversion efficiency. At the same time, the heat conduction path is short, and the heat is easily dissipated into the environment, reducing the evaporation efficiency. Further, when the thickness is too small, the coating may be uneven, resulting in local differences in photothermal conversion performance; if the thickness of the photothermal conversion material layer is greater than 50 μm, the heat conduction path becomes longer, and the heat is difficult to quickly transfer to the evaporation interface, reducing the evaporation efficiency. At the same time, when the thickness is too large, the usage amount of the photothermal conversion material increases, resulting in an increase in cost.

[0028] Preferably, the material of the adhesive layer includes any one or a combination of at least two of thermally conductive silicone, thermally conductive epoxy resin adhesive, or thermally conductive polyurethane adhesive. Typical but non-limiting combinations include: a combination of thermally conductive silicone and thermally conductive epoxy resin adhesive, a combination of thermally conductive silicone and thermally conductive polyurethane adhesive, a combination of thermally conductive epoxy resin adhesive and thermally conductive polyurethane adhesive, and a combination of thermally conductive silicone, thermally conductive epoxy resin adhesive, and thermally conductive polyurethane adhesive.

[0029] Preferably, the thickness of the adhesive layer is 5 - 50 μm. For example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 50 μm, but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0030] As a preferred technical solution of the present invention, the material of the evaporation layer includes any one or a combination of at least two of quartz glass fiber filter membrane, polytetrafluoroethylene membrane, or polyethersulfone membrane. Typical but non-limiting combinations include: a combination of quartz glass fiber filter membrane and polytetrafluoroethylene membrane, a combination of quartz glass fiber filter membrane and polyethersulfone membrane, a combination of polytetrafluoroethylene membrane and polyethersulfone membrane, and a combination of quartz glass fiber filter membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

[0031] By defining the material of the evaporation layer in the present invention, the evaporation layer has a high porosity, good hydrophilicity, and water transmission ability, which is beneficial to the progress of brine separation.

[0032] Preferably, the thickness of the evaporation layer is 0.1 - 2 mm. For example, it can be 0.01 mm, 0.05 mm, 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, or 2 mm, but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0033] Preferably, the radius of the evaporation layer is 30 - 500 mm. For example, it can be 30 mm, 50 mm, 100 mm, 200 mm, 350 mm, or 500 mm, but is not limited to the listed values. Other unlisted values within the above numerical range are equally applicable.

[0034] As a preferred technical solution of the present invention, the salt separator further includes a water guiding component; the water guiding component is connected to the surface of the evaporation layer away from the adhesive layer.

[0035] Preferably, the water guiding component is connected to the center of the surface of the evaporation layer away from the adhesive layer.

[0036] In the present invention, high-salt wastewater is introduced to the center of the salt separator through a water guiding component and then diffused to the edge of the salt separator. During this process, the evaporation promoted by the heat converted by the photothermal conversion material and the formed temperature gradient work together to accelerate crystallization and separate different salts spatially.

[0037] Preferably, the material of the water guiding component includes any one or a combination of at least two of cotton swabs, fiber rods or nylon ropes. Typical but non-limiting combinations include: the combination of cotton swabs and fiber rods, the combination of cotton swabs and nylon ropes, the combination of fiber rods and nylon ropes, and the combination of cotton swabs, fiber rods and nylon ropes.

[0038] In a second aspect, the present invention provides a preparation method of a salt separator based on solar-thermal gradient according to the first aspect, and the preparation method includes the following steps:

[0039] (1) Spraying a photothermal conversion material layer on one side surface of the substrate, and the photothermal conversion material layer completely covers the substrate to obtain an absorption layer;

[0040] (2) Bonding the other side surface of the substrate with a hydrophilic film layer using an adhesive to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer to obtain the salt separator.

[0041] In the present invention, a photothermal conversion material layer is first sprayed on one side surface of the substrate, and the photothermal conversion material layer completely covers the substrate to obtain an absorption layer, so that the absorption layer can absorb solar energy and convert solar energy into heat. Then, the other side surface of the substrate is bonded with a hydrophilic film layer using an adhesive to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer to obtain the salt separator. The preparation method of the salt separator of the present invention is simple and can achieve salt separation crystallization by utilizing the difference in solubility of different salts at different temperatures.

[0042] As a preferred technical solution of the present invention, the preparation method further includes: connecting the water guiding component to the side surface of the hydrophilic film layer away from the adhesive.

[0043] Preferably, the water guiding component is connected to the center of the side surface of the hydrophilic film layer away from the adhesive.

[0044] Preferably, the spraying pressure is 0.2 - 0.5 mPa, for example, it can be 0.2 mPa, 0.3 mPa, 0.4 mPa or 0.5 mPa, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0045] Preferably, the spraying distance is 150 - 300 mm, for example, it can be 150 mm, 200 mm, 250 mm or 300 mm, but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0046] Preferably, the spraying speed is 10 - 300 mm / s. For example, it can be 10 mm / s, 50 mm / s, 100 mm / s, 200 mm / s or 300 mm / s. However, it is not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0047] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0048] (1) Under a pressure of 0.2 - 0.5 mPa, at a speed of 10 - 300 mm / s, spray a photothermal conversion material layer on one side surface of the substrate at a distance of 150 - 300 mm from the substrate, and the photothermal conversion material layer completely covers the substrate to obtain an absorption layer;

[0049] (2) Use an adhesive to bond the other side surface of the substrate to the hydrophilic film layer to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer, and connect the water guiding component to the center of the side surface of the hydrophilic film layer away from the adhesive to obtain the salt separator.

[0050] In the third aspect, the present invention provides an application of the salt separator based on solar - thermal gradient according to the first aspect in the treatment of high - salt wastewater or seawater desalination.

[0051] The salt separator provided by the present invention can achieve salt separation and crystallization by utilizing the difference in solubility of different salts at different temperatures. It has significant advantages such as high efficiency, energy conservation, environmental protection, good effluent water quality and simple operation in the treatment of high - salt wastewater or seawater desalination. These advantages make the salt separator have broad application prospects and market value in the treatment of high - salt wastewater or seawater desalination.

[0052] Compared with the prior art, the present invention has at least the following beneficial effects:

[0053] The present invention designs a salt separator driven by solar thermal gradient, which can generate a temperature gradient at a controllable position and achieve salt separation and crystallization by utilizing the difference in solubility of different salts at different temperatures. It realizes the spatial separation and efficient recovery of different monovalent salts in high - salt wastewater. At the same time, the purification rate of sodium chloride can reach more than 13.35%. It can not only achieve resource utilization and economic benefits, but also reduce environmental pollution and wastewater discharge, providing a green and efficient solution for the treatment of high - salt wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic structural diagram of the salt separator provided in Embodiment 1 of the present invention.

[0055] Among them, 1 - absorption layer, 2 - adhesive layer, 3 - evaporation layer, 4 - water guiding component. Detailed implementation manners

[0056] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation manners. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] Example 1

[0058] This example provides a salt separator based on solar - thermal gradient, as Figure 1 shown. The salt separator successively includes an absorption layer 1, an adhesive layer 2, an evaporation layer 3, and a water - guiding component 4; the geometric centers of the absorption layer 1, the adhesive layer 2, the evaporation layer 3, and the water - guiding component 4 overlap; the absorption layer 1 includes a circular copper sheet with a thickness of 300 μm and a circular carbon black layer with a thickness of 25 μm sprayed on one side surface of the copper sheet; the copper sheet is arranged close to the adhesive layer 2; the carbon black layer completely covers the copper sheet; the radius of the absorption layer 1 is 80 mm; the solar energy absorption rate of the absorption layer 1 is 96%; the adhesive layer 2 is a circular heat - conductive silica gel (Jienuoli - N22737) with a thickness of 20 μm and a radius of 80 mm; the evaporation layer 3 is a circular quartz glass fiber filter membrane with a thickness of 1 mm and a radius of 200 mm; the ratio of the area of the side surface of the evaporation layer 3 close to the adhesive layer 2 to the projected area of the absorption layer 1 on the evaporation layer 3 is 6.25:1; the water - guiding component 4 made of cotton swab is connected to the center of the side surface of the evaporation layer 3 far from the adhesive layer 2.

[0059] This example also provides a preparation method for a salt separator based on solar - thermal gradient. The preparation method includes the following steps:

[0060] (1) Under a pressure of 0.4 mPa, at a speed of 150 mm / s, spray a carbon black layer on one side surface of the copper sheet at a distance of 200 mm from the copper sheet, and the carbon black layer completely covers the copper sheet to obtain the absorption layer;

[0061] (2) Use heat - conductive silica gel to bond the other side surface of the copper sheet to the quartz glass fiber filter membrane to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer, and connect the water - guiding component made of cotton swab to the center of the side surface of the quartz glass fiber filter membrane far from the heat - conductive silica gel to obtain the salt separator.

[0062] Example 2

[0063] This embodiment provides a desalination device based on solar-thermal gradient. The desalination device sequentially includes an absorption layer, an adhesive layer, an evaporation layer, and a water guiding component; the geometric centers of the absorption layer, the adhesive layer, the evaporation layer, and the water guiding component overlap; the absorption layer includes a circular silica gel sheet with a thickness of 50 μm and a circular silver nanoparticle layer with a thickness of 5 μm sprayed on one side surface of the silica gel sheet; the silica gel sheet is disposed close to the adhesive layer; the silver nanoparticle layer completely covers the silica gel sheet; the radius of the absorption layer is 20 mm; the absorptivity of the absorption layer for solar energy is 98%; the adhesive layer is a circular thermally conductive epoxy resin adhesive (Thermos-S828D) with a thickness of 5 μm and a radius of 20 mm; the evaporation layer is a circular polytetrafluoroethylene film (Qingxintong - environmentally friendly hydrophilic PTFE film) with a thickness of 0.01 mm and a radius of 100 mm; the ratio of the area of the side surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 25:1; the water guiding component made of a fiber rod is connected to the center of the side surface of the evaporation layer away from the adhesive layer.

[0064] This embodiment also provides a preparation method for a desalination device based on solar-thermal gradient. The preparation method includes the following steps:

[0065] (1) Under a pressure of 0.5 mPa, at a speed of 300 mm / s, a silver nanoparticle layer is sprayed on one side surface of the silica gel sheet at a distance of 300 mm from the silica gel sheet, and the silver nanoparticle layer completely covers the silica gel sheet to obtain the absorption layer;

[0066] (2) The other side surface of the silica gel sheet is bonded to the polytetrafluoroethylene film using the thermally conductive epoxy resin adhesive to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer, and the water guiding component made of a fiber rod is connected to the center of the side surface of the polytetrafluoroethylene film away from the thermally conductive epoxy resin adhesive to obtain the desalination device.

[0067] Example 3

[0068] This embodiment provides a salt separator based on solar-thermal gradient. The salt separator sequentially includes an absorption layer, an adhesive layer, an evaporation layer, and a water guiding component; the geometric centers of the absorption layer, the adhesive layer, the evaporation layer, and the water guiding component overlap; the absorption layer includes a circular ceramic sheet with a thickness of 500 μm and a circular MoS2 layer with a thickness of 50 μm sprayed on one side surface of the ceramic sheet; the ceramic sheet is arranged close to the adhesive layer; the MoS2 layer completely covers the ceramic sheet; the radius of the absorption layer is 200 mm; the solar absorptivity of the absorption layer is 92%, the adhesive layer is a circular thermally conductive polyurethane adhesive (Enshijie NS-483) with a thickness of 50 μm, and its radius is 200 mm; the evaporation layer is a circular polyethersulfone membrane (Delv Technology - PES microporous membrane) with a thickness of 2 mm, and its radius is 300 mm; the ratio of the area of the side surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 2.25:1; the water guiding component made of nylon rope is connected to the center of the side surface of the evaporation layer far from the adhesive layer.

[0069] This embodiment also provides a preparation method of a salt separator based on solar-thermal gradient. The preparation method includes the following steps:

[0070] (1) Under a pressure of 0.2 mPa, at a speed of 100 mm / s, spray the MoS2 layer on one side surface of the ceramic sheet at a distance of 150 mm from the ceramic sheet. The MoS2 layer completely covers the ceramic sheet to obtain the absorption layer;

[0071] (2) Use the thermally conductive polyurethane adhesive to bond the other side surface of the ceramic sheet to the polyethersulfone membrane, so as to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer, and connect the water guiding component made of nylon rope to the center of the side surface of the polyethersulfone membrane far from the thermally conductive polyurethane adhesive to obtain the salt separator.

[0072] Example 4

[0073] This embodiment provides a salt separator based on solar-thermal gradient. The difference from Example 1 is only that, except that the radius of the evaporation layer is 96 mm, that is, the ratio of the area of the side surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 1.44:1, the rest are the same as those in Example 1.

[0074] Example 5

[0075] This embodiment provides a salt separator based on solar-thermal gradient. The difference from Example 1 is only that, except that the radius of the evaporation layer is 500 mm, that is, the ratio of the area of the side surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 39:1, the rest are the same as those in Example 1.

[0076] Example 6

[0077] This embodiment provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the material of the evaporation layer is replaced by zinc oxide film from quartz glass fiber filter membrane, the rest are the same as those in Embodiment 1.

[0078] Embodiment 7

[0079] This embodiment provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the thickness of the carbon black layer is 1 μm, the rest are the same as those in Embodiment 1.

[0080] Embodiment 8

[0081] This embodiment provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the thickness of the carbon black layer is 100 μm, the rest are the same as those in Embodiment 1.

[0082] Comparative Example 1

[0083] This comparative example provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the radius of the evaporation layer is 80 mm; the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 1:1, the rest are the same as those in Embodiment 1.

[0084] Comparative Example 2

[0085] This comparative example provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the carbon black layer does not completely cover the copper sheet, where the radius of the copper sheet is 80 mm, the radius of the carbon black layer is 40 mm, and the centers of the copper sheet and the carbon black layer overlap, the rest are the same as those in Embodiment 1.

[0086] Comparative Example 3

[0087] This comparative example provides a salt separator based on solar - thermal gradient. The difference from Embodiment 1 is only that, except that the material of the evaporation layer is replaced by a copper sheet from quartz glass fiber filter membrane, the rest are the same as those in Embodiment 1.

[0088] Since the copper sheet cannot conduct water, the salt separator provided in this comparative example cannot separate the brine.

[0089] Comparative Example 4

[0090] This comparative example provides a salt separator. The salt separator includes a stainless steel with a thermal conductivity of 15 W / (m·K) and dimensions of 8 cm × 4 cm × 0.2 cm as a heat conductor. On the right side of the upper surface of the heat conductor, an area of 5 × 4 cm is selected for magnetron sputtering to load a photothermal conversion layer. The photothermal conversion material (metal ceramic ZrC nanoparticles) does not completely cover the surface of the heat conductor, and the uncovered part is left as the position of the contact evaporation surface of water. The 3 × 4 × 0.2 cm heat conductor on the left is made into a columnar arrangement structure with a spacing of 3 mm by an etching method, and the diameter of the column is 2.5 mm.

[0091] The salt separator provided in this comparative example can only separate brine and cannot achieve the separation and recovery of different salts.

[0092] Prepare brine: Use sodium chloride / sodium nitrate solution to simulate high-salt wastewater, where the NaCl concentration is 200 g / L and the NaNO3 concentration is 50 g / L. Divide the evaporation layer into 6 annuli with equal width along its radial direction. The edge of the photothermal conversion material is located within the fourth annulus from the center to the edge. The radii are named annulus 1, annulus 2, annulus 3, annulus 4, annulus 5, and annulus 6 from small to large. Among them, the function of annulus 1 is to guide the high-salt wastewater to the evaporation layer and concentrate the high-salt wastewater. Annulus 1 will not crystallize. After the experiment, annulus 2 - annulus 6 are cut off respectively, and the crystalline salts on them are eluted. The concentrations of different anions in the eluate are measured by an ion chromatograph, and finally the mass ratios of different salts in each annulus are calculated. Among them, the purification rate of NaCl (%) = the purity of obtained NaCl (%) - the purity of NaCl in the original high-salt wastewater (%).

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] Among them, the purification rates of NaCl in annulus 5 and annulus 6 are negative values, that is, the crystallized and purified substance at annulus 5 and annulus 6 is NaNO3.

[0098] It can be seen from the test results that:

[0099] (1) As can be seen from Examples 1 to 3, by designing the structure of the salt separator, the present invention can generate a temperature gradient at the fourth annular zone. When using the salt separator of the present invention to separate and recover NaCl and NaNO3, the separation of the two can be achieved by utilizing the difference in solubility of NaCl and NaNO3 at different temperatures. The purification rate of NaCl can reach more than 13.35%, and the purification rate of NaNO3 can reach more than 13.01%. That is, the salt separator of the present invention can achieve spatial separation and efficient recovery of different monovalent salts in high-salt wastewater.

[0100] (2) As can be seen from Examples 1 to 4-5, in the salt separator of Example 1, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 6.25:1. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 15.19%, and the purification rate of NaNO3 at Ring 6 is 14.54%. Compared with Example 1, in the salt separator of Example 4, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 1.44:1. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 10.25%, and the purification rate of NaNO3 at Ring 6 is 11.22%. In the salt separator of Example 5, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 39:1. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 11.56%, and the purification rate of NaNO3 at Ring 6 is 10.8. This shows that by limiting the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer to (2.25-25):1, the present invention can generate a temperature gradient at a controllable position, so as to accelerate crystallization under the synergistic action of the evaporation promoted by the heat converted by the photothermal conversion material and the formed temperature gradient, separate different salts in space, and too large or too small ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer will affect the separation effect.

[0101] (3) As can be seen from Examples 1 to 6, the material of the evaporation layer in the salt separator of Example 1 is a quartz glass fiber filter membrane. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 15.19%, and the purification rate of NaNO3 at Ring 6 is 14.54%. Compared with Example 1, the material of the evaporation layer of the salt separator in Example 6 is a zinc oxide film. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 12.32%, and the purification rate of NaNO3 at Ring 6 is 12.52%. This shows that by defining the material of the evaporation layer, the evaporation layer has a high porosity, good hydrophilicity and water transmission ability, which is beneficial to the salt water separation.

[0102] (4) As can be seen from Examples 1 to 7 - 8, the thickness of the carbon black layer in the salt separator of Example 1 is 25 μm, that is, the thickness of the photothermal conversion material layer is 25 μm. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 15.19%, and the purification rate of NaNO3 at Ring 6 is 14.54%. Compared with Example 1, the thickness of the carbon black layer in the salt separator of Example 7 is 1 μm, that is, the thickness of the photothermal conversion material layer is 1 μm. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 12.11%, and the purification rate of NaNO3 at Ring 6 is 12.44%. The thickness of the carbon black layer in the salt separator of Example 8 is 100 μm, that is, the thickness of the photothermal conversion material layer is 100 μm. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 12.14%, and the purification rate of NaNO3 at Ring 6 is 11.95%. This shows that by defining the thickness of the photothermal conversion material layer to be 5 - 50 μm, the light absorption efficiency and heat conduction performance can be effectively balanced. If the thickness of the photothermal conversion material layer is less than 5 μm, the photothermal conversion material cannot fully absorb solar energy, resulting in a decrease in the photothermal conversion efficiency. At the same time, the heat conduction path is short, and the heat is easily dissipated into the environment, reducing the evaporation efficiency. If the thickness of the photothermal conversion material layer is greater than 50 μm, the heat conduction path becomes longer, and the heat is difficult to quickly transfer to the evaporation interface, reducing the evaporation efficiency.

[0103] (5) It can be seen from Example 1 and Comparative Example 1 that in Comparative Example 1, the radius of the evaporation layer is 80 mm; that is, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is 1:1. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 5.12%, and the purification rate of NaNO3 at Ring 6 is 10.98%. This shows that by limiting the area of the surface of the evaporation layer close to the adhesive layer to be larger than the projected area of the absorption layer on the evaporation layer, the present invention can generate a temperature gradient at a controllable position and achieve salt separation crystallization by utilizing the difference in solubility of different salts at different temperatures.

[0104] (6) It can be seen from Example 1 and Comparative Example 2 that in Comparative Example 2, the radius of the copper sheet is 80 mm and the radius of the carbon black layer is 40 mm, that is, the photothermal conversion material layer does not completely cover the substrate. When using this salt separator to separate and recover NaCl and NaNO3, the purification rate of NaCl at Ring 4 is 9.25%, and the purification rate of NaNO3 at Ring 6 is 10.01%. This shows that by limiting the photothermal conversion material layer to completely cover the substrate, the present invention can enable the photothermal conversion material to convert the absorbed solar energy into heat and transfer it to the substrate, and ensure that the heat is sufficient to generate a temperature gradient at a controllable position of the salt separator, so as to achieve salt separation crystallization by utilizing the difference in solubility of different salts at different temperatures.

[0105] In summary, the present invention designs a salt separator driven by solar thermal gradient to promote the expansion of the solar water evaporation system in the direction of salt purification and reuse. This salt separator is realized through the good combination of specifically designed solar photothermal conversion materials and evaporation materials, can generate a temperature gradient at a controllable position, and achieve salt separation crystallization by utilizing the difference in solubility of different salts at different temperatures. The high-salt wastewater is led by the water guiding component to the center of the salt separator and then diffuses to the edge of the salt separator. During this process, the evaporation promoted by the heat converted from solar energy and the formed temperature gradient work together to simultaneously accelerate crystallization and separate different salts in space.

[0106] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A salt separator based on solar-thermal gradient, characterized in that The salt separator sequentially includes an absorption layer, an adhesive layer, and an evaporation layer; The absorption layer includes a substrate and a photo-thermal conversion material layer sprayed on one surface of the substrate; the substrate is disposed close to the adhesive layer; The photo-thermal conversion material layer completely covers the substrate; The evaporation layer is a hydrophilic film layer; The area of the surface of the evaporation layer close to the adhesive layer is larger than the projected area of the absorption layer on the evaporation layer.

2. The salt separator according to claim 1, wherein, The geometric centers of the absorption layer, the adhesive layer, and the evaporation layer overlap; Preferably, the absorption layer, the adhesive layer, and the evaporation layer have the same shape; Preferably, the projected area of the absorption layer on the evaporation layer is equivalent to the projected area of the adhesive layer on the evaporation layer; Preferably, the ratio of the area of the surface of the evaporation layer close to the adhesive layer to the projected area of the absorption layer on the evaporation layer is (2.25 - 25):

1.

3. The salt separator according to claim 1 or 2, characterized in that The shape of the substrate is circular; Preferably, the thickness of the substrate is 50 - 500 μm; Preferably, the material of the substrate includes any one or a combination of at least two of metal sheets, silica gel sheets, or ceramic sheets; Preferably, the metal sheet includes any one or a combination of at least two of copper sheets, aluminum sheets, or iron sheets.

4. The salt separator according to any one of claims 1-3, characterized in that, The material of the photo-thermal conversion material layer includes any one or a combination of at least two of carbon black, graphene, carbon nanotubes, gold nanoparticles, silver nanoparticles, MoS2, or graphite; Preferably, the thickness of the photo-thermal conversion material layer is 5 - 50 μm; Preferably, the material of the adhesive layer includes any one or a combination of at least two of thermally conductive silica gel, thermally conductive epoxy resin adhesive, or thermally conductive polyurethane adhesive; Preferably, the thickness of the adhesive layer is 5 - 50 μm.

5. The salt separator according to any one of claims 1-4, characterized in that, The material of the evaporation layer includes any one or a combination of at least two of quartz glass fiber filter membranes, polytetrafluoroethylene membranes, or polyethersulfone membranes; Preferably, the thickness of the evaporation layer is 0.01 - 2 mm.

6. The salt separator according to any one of claims 1-5, characterized in that, The salt separator further includes a water guiding component; the water guiding component is connected to the surface of the evaporation layer away from the adhesive layer; Preferably, the water guiding component is connected to the center of the surface of the evaporation layer away from the adhesive layer; Preferably, the material of the water guiding component includes any one or a combination of at least two of cotton swabs, fiber rods, or nylon ropes.

7. A method for preparing a salt separator based on solar-thermal gradient according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) Spray a photo-thermal conversion material layer on one surface of the substrate, and the photo-thermal conversion material layer completely covers the substrate to obtain the absorption layer; (2) Use an adhesive to bond the other surface of the substrate to the hydrophilic film layer so as to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer to obtain the salt separator.

8. The preparation method according to claim 7, wherein The preparation method further includes: connecting the water guiding component to the surface of the hydrophilic film layer away from the adhesive; Preferably, the water guiding component is connected to the center of the surface of the hydrophilic film layer away from the adhesive; Preferably, the spraying pressure is 0.2 - 0.5 mPa; Preferably, the spraying distance is 150 - 300 mm; Preferably, the spraying speed is 10 - 300 mm / s.

9. The preparation method according to claim 7 or 8, characterized in that, The preparation method includes the following steps: (1) At a pressure of 0.2 - 0.5 mPa, at a speed of 10 - 300 mm / s, spray a photo-thermal conversion material layer on one side surface of the substrate at a distance of 150 - 300 mm from the substrate, and the photo-thermal conversion material layer completely covers the substrate to obtain an absorption layer; (2) Use an adhesive to bond the other side surface of the substrate to the hydrophilic film layer, so as to form an adhesive layer and an evaporation layer stacked in sequence on the absorption layer, and connect the water guiding component to the center of the side surface of the hydrophilic film layer away from the adhesive to obtain the desalting device.

10. Use of the desalting device based on solar-thermal gradient according to any one of claims 1 - 6 in high-salt wastewater treatment or seawater desalination.

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