Seawater desalination method and seawater desalination system

Abstract

The invention relates to a seawater desalination method and a seawater desalination system. The seawater desalination method comprises the following steps: filtering seawater to obtain a filtrate, wherein the filtration membrane used in the filtering process is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material; the filtrate is subjected to a reverse osmosis process to obtain reverse osmosis produced water, wherein the reverse osmosis membrane used in the reverse osmosis process comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, wherein the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer; and the reverse osmosis produced water is subjected to a disinfection process to obtain desalinated water. The seawater desalination method can not only improve the desalination efficiency of seawater, but also does not require pretreatment of seawater, has a simple process, small footprint, low cost, and good anti-pollution performance, and can ensure the long-term operation stability of the seawater desalination system.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to a seawater desalination method and a seawater desalination system. Background Art

[0002] In the reverse osmosis membrane desalination method, seawater is usually pretreated to remove impurities such as silt, colloids, particles, suspended matter and microorganisms to ensure the normal operation of the subsequent membrane system. Traditional pretreatment methods mainly include coagulation, sedimentation, filtration, etc. However, due to the hydraulic retention time requirements, monomer processing capacity and membrane permeation flux limitations, the pretreatment processes such as coagulation, sedimentation and filtration have high requirements for the floor space and long construction periods. At the same time, the high cost of adding more chemicals and flocculants, as well as the electricity and membrane replacement fees will also increase the investment cost of the desalination method. In addition, there are problems such as poor resistance to pollution shock and poor system operation stability.

[0003] Therefore, the existing seawater desalination methods and systems still have problems such as long process flow, poor resistance to pollution impact, large footprint, and poor system operation stability. Summary of the invention

[0004] Based on this, it is necessary to provide a seawater desalination method and a seawater desalination system to address the above problems. The seawater desalination method can not only improve the desalination efficiency of seawater, but also does not require pretreatment of seawater, has a simple process, small footprint, low cost, and good anti-pollution performance, and can ensure the long-term operation stability of the seawater desalination system.

[0005] A seawater desalination method comprises the following steps:

[0006] Filtering the seawater to obtain a filtrate, wherein the filtration membrane used in the filtration is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material;

[0007] The filtrate is subjected to reverse osmosis treatment to obtain reverse osmosis water, wherein the reverse osmosis membrane used in the reverse osmosis treatment comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer;

[0008] The reverse osmosis produced water is disinfected to obtain desalinated water.

[0009] In one embodiment, the polymer film further contains ferrocene-modified magnesium titanate particles.

[0010] In one embodiment, the mass fraction of the ferrocene-modified magnesium titanate particles in the polymer film is 1%-5%;

[0011] And / or, the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.05%-0.5%.

[0012] In one of the embodiments, the mass fraction of the photocatalyst in the polymer film is 0.5%-8%.

[0013] In one embodiment, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 40%-70%.

[0014] In one embodiment, the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.1%-3%.

[0015] In one of the embodiments, the mass fraction of the positively charged crystalline polymer in the porous polymer layer is 5%-20%.

[0016] In the seawater desalination method of the present invention, a polymer membrane containing a photocatalyst is used as a filter membrane, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material. The porous polymer nanosphere containing the graphitized titanium-based framework material has a rich nanochannel structure, which provides a space for a nano-confined catalytic reaction to occur, so that the filter membrane can allow seawater to be quickly filtered while efficiently catalyzing and degrading organic pollutants in the seawater, thereby improving the removal efficiency of pollutants, so that the pollutants can be effectively prevented from clogging the filter membrane without pre-treatment such as coagulation and precipitation of the seawater, and the filter membrane has good anti-pollution performance, thereby ensuring the normal progress of the filtration treatment, thereby achieving the purpose of greatly reducing the amount of pre-treatment equipment, the floor space occupied and the operating cost of the treatment device, and improving the desalination efficiency of seawater; at the same time, the polyamide layer of the reverse osmosis membrane contains a layered ionic covalent organic framework material, and the layered ionic covalent organic framework material can cooperate with the polyamide layer, so that the reverse osmosis membrane has both high Water flux and desalination rate, at the same time, the charge carried by the layered ionic covalent organic framework material itself can be anchored in the functional separation layer through electrostatic and hydrogen bonding, preventing it from falling off during long-term use, and ensuring the long-term operation stability of the reverse osmosis membrane; moreover, by setting the porous polymer layer of the reverse osmosis membrane to contain positively charged crystalline polymer, on the one hand, it can avoid or alleviate the concentration polarization caused by the high concentration of salt ions enriched at the interface between the reverse osmosis membrane and seawater during the seawater desalination process, and can effectively ensure that the reverse osmosis membrane has a high desalination rate and water flux during long-term use; on the other hand, it can be used as a protective layer of the functional separation layer to intercept residual pollutants at the front end and prevent fouling of the reverse osmosis membrane, further ensuring the long-term operation stability of the reverse osmosis membrane, and the positive charge of the porous polymer layer of the positively charged crystalline polymer itself can repel trace metal cations in seawater, further improving the anti-pollution performance of the reverse osmosis membrane and improving the desalination efficiency of seawater.

[0017] Therefore, the seawater desalination method of the present invention can not only improve the desalination efficiency of seawater, but also does not require pretreatment of seawater, occupies a small area, has low cost, and has good anti-pollution performance, and can ensure the long-term operation stability of the seawater desalination system.

[0018] A seawater desalination system, comprising:

[0019] A filtering device, wherein the filtering membrane used in the filtering device is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material;

[0020] A reverse osmosis device, the reverse osmosis device is connected to the filtration device, the reverse osmosis membrane used in the reverse osmosis device comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer;

[0021] A disinfection device, wherein the reverse osmosis device is connected to the disinfection device.

[0022] In one of the embodiments, a safety filter is further provided between the filtering device and the reverse osmosis device.

[0023] In one of the embodiments, the seawater desalination system further includes an energy recovery device, and the energy recovery device is connected to the reverse osmosis device.

[0024] The seawater desalination system of the present invention can not only improve the desalination efficiency of seawater, but also does not require pretreatment of seawater, has a simple process, occupies a small area, has low cost, has good anti-pollution performance, and can operate efficiently and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A process flow chart of a seawater desalination method provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific implementation methods or embodiments, and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the combinations include any two related listed items, any more related listed items, or all related listed items.

[0029] like Figure 1 As shown, the seawater desalination method provided by the present invention comprises the following steps:

[0030] Filtering the seawater to obtain a filtrate, wherein the filtration membrane used in the filtration is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material;

[0031] The filtrate is subjected to reverse osmosis treatment to obtain reverse osmosis water, wherein the reverse osmosis membrane used in the reverse osmosis treatment comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer;

[0032] The reverse osmosis produced water is disinfected to obtain desalinated water.

[0033] Specifically, in the present invention, seawater is filtered and treated. In the process, a polymer membrane containing a photocatalyst is used as a filter membrane, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material. The porous polymer nanosphere containing a graphitized titanium-based framework material has a rich nanochannel structure. On the one hand, the permeability of the filter membrane can be effectively enhanced to achieve rapid filtration of seawater; on the other hand, a space for a nano-confined catalytic reaction can be provided, so that pollutants in the seawater are fully in contact with the graphitized titanium-based framework material and efficiently degraded, thereby effectively improving the removal efficiency of pollutants. Therefore, without pre-treatment of the seawater such as coagulation and precipitation, a large amount of pollutants in the seawater can be effectively avoided from clogging the filter membrane, having good anti-pollution performance, ensuring the normal progress of the filtration treatment, and thus achieving the purpose of greatly reducing the amount of pre-treatment equipment, the floor space and the operating costs of the treatment device, while improving the desalination efficiency of seawater.

[0034] In addition, since the graphitized titanium-based framework material is located in the porous polymer nanospheres, it can effectively prevent the risk of poisoning of the graphitized titanium-based framework material due to the encapsulation of a large amount of pollutants in the graphitized titanium-based framework material, further ensuring the photocatalytic efficiency of the graphitized titanium-based framework material and ensuring the efficient operation of the seawater desalination system.

[0035] It can be understood that compared with traditional filtration membranes, the filtration membrane used in the filtration treatment of the present invention can simultaneously perform pretreatment functions such as coagulation, sedimentation, and filtration on seawater, reduce the pretreatment process flow, and effectively improve the permeability of the filtration membrane. At the same time, it has excellent organic pollutant removal effects, and can effectively prevent pollutants from clogging the filtration membrane without pretreatment such as coagulation and sedimentation, thereby greatly reducing the amount of pretreatment equipment, floor space, and operating costs of the treatment device.

[0036] The filtrate obtained above is subjected to reverse osmosis treatment. In the process, the polyamide layer of the reverse osmosis membrane contains a layered ionic covalent organic framework material. The layered ionic covalent organic framework material has abundant ordered voids, can provide additional water transmission channels, and its two-dimensional structure can reduce the tortuous transmission path, can effectively reduce the resistance of the seawater reverse osmosis membrane, and greatly improve the water permeation flux; and the layered ionic covalent organic framework material has good compatibility with the polyamide layer, can avoid the generation of interface gaps, and effectively ensure the desalination effect of the reverse osmosis membrane; and the charge carried by the layered ionic covalent organic framework material itself can anchor it in the functional separation layer through electrostatic and hydrogen bonding, prevent it from falling off during long-term use, and ensure the long-term operation stability of the reverse osmosis membrane.

[0037] At the same time, by providing the porous polymer layer of the reverse osmosis membrane with a positively charged crystalline polymer, on the one hand, the concentration polarization caused by the high concentration of salt ions enriched at the interface between the reverse osmosis membrane and the seawater can be avoided or alleviated during the seawater desalination process, and the high desalination rate and water flux of the reverse osmosis membrane can be effectively guaranteed during the long-term use of the reverse osmosis membrane. On the other hand, it can serve as a protective layer for the functional separation layer, intercepting residual pollutants at the front end and preventing fouling of the reverse osmosis membrane, further ensuring the long-term operation stability of the reverse osmosis membrane, and the positive charge of the porous polymer layer of the positively charged crystalline polymer itself can repel trace metal cations in seawater, further improving the anti-pollution performance of the reverse osmosis membrane and improving the desalination efficiency of seawater.

[0038] The reverse osmosis water obtained above is disinfected to kill bacteria in the water to ensure the hygiene and safety of the fresh water.

[0039] Therefore, the seawater desalination method of the present invention can not only improve the desalination efficiency of seawater, but also does not require pretreatment of seawater, has a simple process, small footprint, low cost, and good anti-pollution performance, and can ensure the long-term operation stability of the seawater desalination system.

[0040] As pollutants accumulate on the surface of the filter membrane, the transmembrane pressure difference during the desalination process will increase, affecting the anti-pollution performance of the filter membrane. In the present invention, the polymer membrane containing the photocatalyst also contains ferrocene-modified magnesium titanate particles. In this way, when the transmembrane pressure difference increases during the seawater filtration process, the increase in the pressure of the filter membrane will prompt the magnesium titanate in the filter membrane to generate charges to seize the protons of ferrocene, generating more negative charges, thereby enhancing the repelling effect on pollutants, further improving the anti-pollution performance of the filter membrane, and better ensuring the normal use of the filter membrane.

[0041] Optionally, the mass fraction of the ferrocene-modified magnesium titanate particles in the polymer membrane is 1%-5%, wherein the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.05%-0.5%. Such a setting is conducive to further improving the anti-pollution performance of the filter membrane and better ensuring the normal filtration process.

[0042] It is understood that the ferrocene-modified magnesium titanate particles are used in the present invention to perform pressure-sensitive modification on the polymer film containing the photocatalyst. In one embodiment, the ferrocene-modified magnesium titanate particles are heated and then sprayed onto the surface of the polymer film containing the photocatalyst.

[0043] Optionally, the mass fraction of the photocatalyst in the polymer film is 0.5%-8%. Such an arrangement can further improve the photocatalytic degradation efficiency of the filter membrane for pollutants in seawater, better improve the removal efficiency of pollutants in seawater, and better avoid the blockage of the filter membrane by pollutants without pre-treatment such as coagulation and precipitation of seawater, thereby better ensuring the normal operation of the filtration process.

[0044] Optionally, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 40%-70%. Such an arrangement can better improve the photocatalytic degradation efficiency of pollutants and further improve the removal efficiency of pollutants by the filter membrane.

[0045] In the present invention, the porous polymer nanospheres containing graphitized titanium-based framework materials can be prepared by referring to the following method. Specifically, the graphitized titanium-based framework materials are added to an ethanol solvent, and then cyanuric chloride, dinitrobenzene and sodium hydroxide are added, mixed and reacted for 20h-25h, and then terephthalaldehyde is added and heated at a temperature of 110°C-130°C for 65h-80h to obtain porous polymer nanospheres containing graphitized titanium-based framework materials; wherein the molar ratio of the cyanuric chloride, the dinitrobenzene, the sodium hydroxide and the terephthalaldehyde is 1:3:3:1-4, preferably 1:3:3:1.5.

[0046] It should be noted that in the present invention, the graphitized titanium-based framework material can be prepared in the following manner. Specifically, trimesic acid, tetraethoxytitanium and N,N-dimethylformamide are mixed to obtain a mixed solution, the mixed solution is placed at a temperature of 120°C-150°C for reaction for 45h-50h, then washed and dried, and then heat treated at a temperature of 800°C-1000°C for 4h-6h to obtain a graphitized titanium-based framework material, wherein the mass fraction of trimesic acid in the mixed solution is 2%-3%, and the mass fraction of tetraethoxytitanium in the mixed solution is 2%-4%, preferably 3%.

[0047] In one embodiment, the polymer membrane is selected from polyacrylonitrile membrane, polysulfone membrane, polyvinylidene fluoride membrane, polyethylene membrane or polypropylene membrane.

[0048] In one embodiment, the preparation method of the polymer film containing the photocatalyst is as follows: the photocatalyst is added to the polymer film liquid, and the polymer film is prepared by phase inversion or direct curing followed by punching.

[0049] Optionally, the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.1%-3%. Such a configuration is conducive to further improving the water flux and desalination rate of the reverse osmosis membrane and better ensuring the long-term operation stability of the reverse osmosis membrane.

[0050] In one embodiment, the method for preparing the polyamide layer comprises the following steps: preparing an aqueous solution by preparing an amine monomer and water; preparing an oil solution by preparing a layered ionic covalent organic framework material, an acyl chloride monomer and an alkane solvent; placing the aqueous solution and the oil solution in sequence on the same surface of a support membrane, and forming a polyamide layer by heat treatment, wherein the polyamide layer contains a layered ionic covalent organic framework material.

[0051] The amine monomer is selected from at least one of benzene diamine, o-phenylenediamine, m-phenylenediamine, trimesine, ethylenediamine, propylenediamine, butylene diamine, hexamethylenediamine and piperazine; the acyl chloride monomer is selected from at least one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, adipoyl chloride and biphenyl dichloride; and the support membrane is selected from polyacrylonitrile membrane, polysulfone membrane, polyvinylidene fluoride membrane, polyethylene membrane or polypropylene membrane.

[0052] It should be noted that, in the present invention, the layered ionic covalent organic framework material can be prepared by referring to the following method. Specifically, the layered ionic covalent organic framework material is prepared by reacting triaminoguanidine hydrochloride and trimesic acid aldehyde in tetrahydrofuran at 110°C-125°C for 4 to 5 days, followed by washing and drying.

[0053] The layered ionic covalent organic framework material in the present invention is preferably prepared by referring to the above method.

[0054] Optionally, the mass fraction of the positively charged crystalline polymer in the porous polymer layer is 5%-20%. Such an arrangement can better avoid or alleviate the concentration polarization caused by the high concentration of salt ions enriched at the interface between the reverse osmosis membrane and the seawater during the seawater desalination process, better ensure the desalination rate and water flux of the reverse osmosis membrane, and better ensure the long-term operation stability of the reverse osmosis membrane, thereby improving the desalination efficiency of seawater.

[0055] In one embodiment, the porous polymer layer comprises a positively charged crystalline polymer and a porous polymer, and the porous polymer is selected from at least one of polysulfone and polyethersulfone.

[0056] In one embodiment, a positively charged crystalline polymer and a porous polymer are prepared into a mixed solution, and then the mixed solution is coated on the surface of a polyamide layer containing a layered ionic covalent organic framework material, and cured to obtain a porous polymer layer, wherein the porous polymer layer contains a positively charged crystalline polymer.

[0057] It should be noted that, in the present invention, the positively charged crystalline polymer can be prepared by referring to the following method. Specifically, the positively charged crystalline polymer is prepared by polymerization reaction of p-toluenesulfonylphenylpropene and chloroplatinic acid under the action of an alkyl aluminum catalyst, wherein the molar ratio of p-toluenesulfonylphenylpropene to chloroplatinic acid is 4:1-5:1. The positively charged crystalline polymer obtained in this way can avoid or alleviate the concentration polarization caused by the enrichment of high-concentration salt ions at the interface between the reverse osmosis membrane and seawater during the desalination process, effectively ensure that the reverse osmosis membrane has a high desalination rate and water flux during long-term use, prevent the fouling of the reverse osmosis membrane by residual pollutants at the front end, and improve the anti-pollution performance of the reverse osmosis membrane. In addition, under high-pressure operating conditions, the non-covalent bonds (including metal-π bonds, hydrogen bonds, and weak coordination bonds) in the positively charged crystalline polymer molecules can undergo reversible dissociation, increase the interface gap between the positively charged crystalline polymer and the porous polymer layer, and effectively prevent the porous polymer layer containing the positively charged crystalline polymer from becoming dense due to high pressure, thereby affecting the water flux of the reverse osmosis membrane.

[0058] Therefore, the positively charged crystalline polymer in the present invention is preferably prepared by the above-mentioned preparation method.

[0059] In one embodiment, before the filtrate is subjected to reverse osmosis treatment, the filtrate is further subjected to filtration treatment to further improve the seawater desalination efficiency and better ensure the stable operation of the reverse osmosis treatment.

[0060] In one embodiment, in the step of subjecting the filtrate to reverse osmosis treatment, reverse osmosis concentrated water is also obtained. It should be noted that in the desalination process, the filtrate needs to be transported to the reverse osmosis device by means of a high-pressure pump for reverse osmosis treatment. It can be understood that the reverse osmosis concentrated water obtained in the reverse osmosis treatment step contains a relatively high pressure. For this reason, in the present invention, the reverse osmosis concentrated water is subjected to energy recovery to reduce the pressure of the reverse osmosis concentrated water, and the pressure of the reverse osmosis inlet water is increased by recovering the pressure of the reverse osmosis concentrated water.

[0061] In the present invention, the reverse osmosis produced water can be disinfected and sterilized by using liquid chlorine, chlorine dioxide, ozone or ultraviolet rays to obtain safe and hygienic desalinated water.

[0062] In one embodiment, the desalinated water obtained in the present invention can be used for domestic water, fish farming or water supply for related industries.

[0063] At the same time, the present invention also provides a seawater desalination system, which includes: a filtering device, the filtering membrane used in the filtering device is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material; a reverse osmosis device, the reverse osmosis device is connected to the filtering device, the reverse osmosis membrane used in the reverse osmosis device includes a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer; a disinfection device, the reverse osmosis device is connected to the disinfection device.

[0064] In the seawater desalination system of the present invention, porous polymer nanospheres containing graphitized titanium-based framework materials are used as photocatalysts in the filtration membrane, and the synergistic effect of the polyamide layer containing the layered ionic covalent organic framework material and the porous polymer layer containing the positively charged crystalline polymer in the reverse osmosis membrane is used, so that the seawater desalination system of the present invention can not only improve the desalination efficiency of seawater, but also does not need to pretreat the seawater, has a simple process, a small footprint, low cost, good anti-pollution performance, and can operate efficiently and stably.

[0065] Optionally, the polymer film further contains ferrocene-modified magnesium titanate particles, the mass fraction of the ferrocene-modified magnesium titanate particles in the polymer film is 1%-5%, and the mass fraction of ferrocene in the ferrocene-modified magnesium titanate particles is 0.05%-0.5%.

[0066] Optionally, the mass fraction of the photocatalyst in the polymer film is 0.5%-8%.

[0067] Optionally, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 40%-70%.

[0068] Optionally, the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.1%-3%.

[0069] Optionally, the mass fraction of the positively charged crystalline polymer in the porous polymer layer is 5%-20%.

[0070] It should be noted that, in the present invention, the filtering device is connected to the reverse osmosis device via a high-pressure pump.

[0071] Optionally, a safety filter is further provided between the filtering device and the reverse osmosis device for removing residual pollutants in the filtrate. Specifically, the outlet of the safety filter is connected to the inlet of the high-pressure pump.

[0072] Optionally, the seawater desalination system further comprises an energy recovery device, which is connected to the reverse osmosis device and is used to recover energy from the reverse osmosis concentrated water produced from the reverse osmosis device.

[0073] Specifically, in one embodiment, the water production side of the filtration device is connected to the water inlet side of the reverse osmosis membrane device, the water production side of the reverse osmosis membrane device is connected to the water inlet side of the disinfection device, the concentrate side of the reverse osmosis membrane device is connected to the high-pressure water inlet side of the energy recovery device, the low-pressure water outlet side of the energy recovery device is connected to the reverse osmosis concentrate treatment device and / or connected to the backwash water tank, and the water production side of the disinfection device is used to output fresh water for use.

[0074] The seawater desalination method and the seawater desalination system will be further described below by the following specific examples. However, it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0075] It should be noted that the preparation method of the graphitized titanium-based framework material and the porous polymer nanospheres containing the graphitized titanium-based framework material involved in the embodiments and comparative examples of the present invention is as follows: trimesic acid, tetraethoxytitanium and N,N-dimethylformamide are mixed to obtain a mixed solution, the mixed solution is placed at a temperature of 130°C for reaction for 48 hours, washed and dried, and then heat treated at a temperature of 900°C for 5 hours to obtain a graphitized titanium-based framework material, wherein the mass fraction of the trimesic acid in the mixed solution is 2%, and the mass fraction of the tetraethoxytitanium in the mixed solution is 3%; the graphitized titanium-based framework material obtained above is added to an ethanol solvent, and then cyanuric chloride, dinitrobenzene and sodium hydroxide are added to mix and react for 24 hours, and then terephthalaldehyde is added and reacted at 120°C for 72 hours to obtain porous polymer nanospheres containing graphitized titanium-based framework materials; wherein the molar ratio of the cyanuric chloride, the dinitrobenzene, the sodium hydroxide and the terephthalaldehyde is 1:3:3:1.5.

[0076] Example 1

[0077] Seawater (with a conductivity of 397600 μS / cm, a turbidity of 20.5 NTU, and a COD of 13.8 mg / L) is passed through a filtration device for treatment to obtain a filtrate, wherein the filtration membrane used in the filtration device is a polypropylene membrane containing a photocatalyst, the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material, the mass fraction of the photocatalyst in the polypropylene membrane is 0.5%, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanosphere is 40%, the polypropylene membrane further contains ferrocene-modified magnesium titanate particles, the mass fraction of the ferrocene-modified magnesium titanate particles in the polypropylene membrane is 1%, and the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.05%.

[0078] The filtrate obtained above is successively passed through a security filter and a high-pressure pump into a reverse osmosis membrane device for treatment to obtain reverse osmosis produced water and reverse osmosis concentrated water, wherein the reverse osmosis membrane used in the reverse osmosis device includes a polysulfone support membrane and a polyamide layer and a porous polysulfone layer sequentially stacked on the surface of the polysulfone support membrane, the polyamide layer contains a layered ionic covalent organic framework material, the porous polysulfone layer contains a positively charged crystalline polymer, the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.1%, the mass fraction of the positively charged crystalline polymer in the porous polysulfone layer is 5%, and the positively charged crystalline polymer is prepared by polymerization reaction of p-methylsulfonylphenylpropylene and chloroplatinic acid in a molar ratio of 5:1 under the action of an alkyl aluminum catalyst.

[0079] The reverse osmosis concentrated water obtained above is introduced into an energy recovery device for treatment; the reverse osmosis produced water obtained above is introduced into a disinfection device for sterilization treatment to obtain desalinated water.

[0080] After testing, the turbidity of the filtrate was 0.16NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 5.2μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 82%.

[0081] Example 2

[0082] The only difference between Example 2 and Example 1 is that the mass fraction of the photocatalyst in the polypropylene film is 4%, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 55%, the mass fraction of the ferrocene-modified magnesium titanate particles in the polypropylene film is 3%, and the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.25%; the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 1.5%, and the mass fraction of the positively charged crystalline polymer in the porous polysulfone layer is 12%, and the other conditions are the same.

[0083] After testing, the turbidity of the filtrate was 0.15NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 5.6μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 85%.

[0084] Example 3

[0085] Compared with Example 1, Example 3 differs only in that the mass fraction of the photocatalyst in the polypropylene film is 8%, the mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 70%, the mass fraction of the ferrocene-modified magnesium titanate particles in the polypropylene film is 5%, and the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.5%; the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 3%, and the mass fraction of the positively charged crystalline polymer in the porous polysulfone layer is 20%, and the other conditions are the same.

[0086] After testing, the turbidity of the filtrate was 0.11NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 4.8μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 83%.

[0087] Example 4

[0088] The only difference between Example 4 and Example 1 is that the mass fraction of the photocatalyst in the polypropylene film is 0.1%, and the other conditions are the same.

[0089] After testing, the turbidity of the filtrate was 0.25NTU and the COD was 0.8mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water is 6.3μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate is 78%.

[0090] Example 5

[0091] The only difference between Example 5 and Example 1 is that the mass fraction of the photocatalyst in the polypropylene film is 10%, and the other conditions are the same.

[0092] After testing, the turbidity of the filtrate was 0.64NTU and the COD was 0.7mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water is 6.1μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate is 76%.

[0093] Example 6

[0094] The only difference between Example 6 and Example 1 is that the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.05%, and the other conditions are the same.

[0095] After testing, the turbidity of the filtrate was 0.21NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 6.7μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 75%.

[0096] Example 7

[0097] The only difference between Example 7 and Example 1 is that the mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 5%, and the other conditions are the same.

[0098] After testing, the turbidity of the filtrate was 0.15NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 9.4μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 76%.

[0099] Example 8

[0100] The only difference between Example 8 and Example 1 is that the mass fraction of the positively charged crystalline polymer in the porous polysulfone layer is 2%, and the other conditions are the same.

[0101] After testing, the turbidity of the filtrate was 0.17NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 5.7μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 78%.

[0102] Example 9

[0103] The only difference between Example 9 and Example 1 is that the mass fraction of the positively charged crystalline polymer in the porous polysulfone layer is 25%, and the other conditions are the same.

[0104] After testing, the turbidity of the filtrate was 0.18NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 6.1μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 77%.

[0105] Example 10

[0106] The only difference between Example 10 and Example 1 is that the polypropylene film containing the photocatalyst does not contain ferrocene-modified magnesium titanate particles, and the other conditions are the same.

[0107] After testing, the turbidity of the filtrate was 0.41NTU and the COD was 0.7mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water is 6.4μS / cm. The desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate is 79%.

[0108] Comparative Example 1

[0109] The only difference between Comparative Example 1 and Example 1 is that the filter membrane used in the filter device is a polypropylene membrane without a photocatalyst, and the other conditions are the same.

[0110] After testing, the turbidity of the filtrate was 1.55NTU and the COD was 8.6mg / L. The conductivity of the reverse osmosis water was 8.3μS / cm. The desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate is 65%.

[0111] Comparative Example 2

[0112] The only difference between Comparative Example 2 and Example 1 is that the photocatalyst is a graphitized titanium-based framework material, and the other conditions are the same.

[0113] After testing, the turbidity of the filtrate was 0.67NTU and the COD was 3.4mg / L. The conductivity of the reverse osmosis water was 7.8μS / cm. The desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 67%.

[0114] Comparative Example 3

[0115] The only difference between Comparative Example 3 and Example 1 is that titanium dioxide is used to replace the photocatalyst in Example 1, and the other conditions are the same.

[0116] After testing, the turbidity of the filtrate was 0.93NTU, the COD was 6.5mg / L, and the conductivity of the reverse osmosis water was 8.9μS / cm. The desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate is 67%.

[0117] Comparative Example 4

[0118] The only difference between Comparative Example 4 and Example 1 is that the polyamide layer of the reverse osmosis membrane used in the reverse osmosis treatment does not contain a layered ionic covalent organic framework material, that is, a common polyamide layer, and the other conditions are the same.

[0119] After testing, the turbidity of the filtrate was 0.20NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 6.1μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 63%.

[0120] Comparative Example 5

[0121] The only difference between Comparative Example 5 and Example 1 is that the porous polysulfone layer does not contain a positively charged crystalline polymer, and the other conditions are the same.

[0122] After testing, the turbidity of the filtrate was 0.14NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 6.3μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 62%.

[0123] Comparative Example 6

[0124] The only difference between Comparative Example 6 and Example 1 is that the structure of the reverse osmosis membrane does not contain a porous polysulfone layer, and the other conditions are the same.

[0125] After testing, the turbidity of the filtrate was 0.16NTU and COD was less than 0.5mg / L, which means that almost all pollutants in the seawater have been removed. The conductivity of the reverse osmosis water was 7.3μS / cm, and the desalinated water has reached the water quality requirements for reused water. At the same time, after calculation and analysis, the water recovery rate was 60%.

[0126] At the same time, it has been verified that under the conditions of the same seawater composition, the same seawater inlet temperature, the same seawater inlet flow rate, and the same inlet pressure, after the filter membrane in the filtration device of Comparative Example 1 is blocked, the desalination system of Comparative Example 2 can still continue to operate stably for 4 days, and the desalination system of Comparative Example 3 can continue to operate stably for 2 days. The reason is that in Comparative Examples 1 to 3, porous polymer nanospheres containing graphitized titanium-based framework materials are not used as photocatalysts, resulting in a significant reduction in the removal effect of pollutants during filtration treatment, thereby making the subsequent reverse osmosis system operation stability worse; while the desalination system of Comparative Example 4 can continue to operate stably for 12 days, because the polyamide layer of the reverse osmosis membrane in Comparative Example 4 does not contain a layered ionic covalent organic framework material, resulting in the water flux of the reverse osmosis membrane being unstable and severely attenuated with the operating time; the desalination system of Comparative Example 5 The system can continue to operate stably for 9 days, and the desalination system of comparative example 6 can continue to operate stably for 7 days. The reason is that since no porous polymer layer containing a positively charged crystalline polymer is provided on the polyamide layer of the reverse osmosis membrane in comparative examples 5 to 6, the reverse osmosis membrane is prone to concentration polarization and fouling during operation, thereby reducing the operational stability of the reverse osmosis membrane; the desalination systems of Examples 1 to 10 can continue to operate stably for more than 30 days, among which the desalination systems of Examples 8 to 9 can continue to operate stably for more than 35 days, and the desalination systems of Examples 1 to 7 can continue to operate stably for more than 45 days, and during the period when the desalination systems of Examples 1 to 10 continue to operate stably, no fouling occurs during the entire water production process, the flux of the filtration membrane and the reverse osmosis membrane does not change significantly, and the produced water flow rate and the produced water quality remain stable.

[0127] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0128] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for desalination of seawater, characterized in that: The following steps are involved: Filtering the seawater to obtain a filtrate, wherein the filtration membrane used in the filtration is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material, and the polymer membrane also contains ferrocene-modified magnesium titanate particles; The filtrate is subjected to reverse osmosis treatment to obtain reverse osmosis water, wherein the reverse osmosis membrane used in the reverse osmosis treatment comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer; Disinfecting the reverse osmosis produced water to obtain desalinated water; The porous polymer nanospheres containing the graphitized titanium-based framework material are prepared by referring to the following method: adding the graphitized titanium-based framework material to an ethanol solvent, then adding cyanuric chloride, dinitrobenzene and sodium hydroxide to mix and react for 20h-25h, adding terephthalaldehyde and heating the mixture at a temperature of 110°C-130°C for a reaction of 65h-80h to obtain the porous polymer nanospheres containing the graphitized titanium-based framework material; the graphitized titanium-based framework material is prepared by referring to the following method: mixing trimesic acid, tetraethoxytitanium and N,N-dimethylformamide to obtain a mixed solution, placing the mixed solution at a temperature of 120°C-150°C for a reaction of 45h-50h, washing and drying, and then heat-treating the mixture at a temperature of 800°C-1000°C for 4h-6h to obtain the graphitized titanium-based framework material; The preparation method of the polymer film containing the photocatalyst is as follows: adding the photocatalyst to the polymer film liquid, and preparing it by phase inversion or direct curing followed by punching; The preparation method of the polyamide layer comprises the following steps: preparing an aqueous phase solution by preparing an amine monomer and water; preparing an oil phase solution by preparing a layered ionic covalent organic framework material, an acyl chloride monomer and an alkane solvent; placing the aqueous phase solution and the oil phase solution on the same surface of a support membrane in sequence, and forming a polyamide layer by heat treatment, wherein the polyamide layer contains a layered ionic covalent organic framework material; the layered ionic covalent organic framework material is prepared by reacting triaminoguanidine hydrochloride and trimesic acid aldehyde in tetrahydrofuran at 110° C.-125° C. for 4 to 5 days, and then washing and drying the layered ionic covalent organic framework material; The porous polymer layer includes a positively charged crystalline polymer and a porous polymer. The positively charged crystalline polymer and the porous polymer are prepared into a mixed solution, and then the mixed solution is coated on the surface of a polyamide layer containing a layered ionic covalent organic framework material, and the porous polymer layer is obtained after curing. The porous polymer layer contains the positively charged crystalline polymer.

2. The seawater desalination method according to claim 1, characterized in that: The mass fraction of the ferrocene-modified magnesium titanate particles in the polymer film is 1%-5%; And / or, the mass fraction of the ferrocene in the ferrocene-modified magnesium titanate particles is 0.05%-0.5%.

3. The seawater desalination method according to claim 1, characterized in that: The mass fraction of the photocatalyst in the polymer film is 0.5%-8%.

4. The seawater desalination method according to claim 3, characterized in that: The mass fraction of the graphitized titanium-based framework material in the porous polymer nanospheres is 40%-70%.

5. The seawater desalination method according to claim 1, characterized in that: The mass fraction of the layered ionic covalent organic framework material in the polyamide layer is 0.1%-3%.

6. The seawater desalination method according to claim 1, characterized in that: The mass fraction of the positively charged crystalline polymer in the porous polymer layer is 5%-20%.

7. A seawater desalination system used in the seawater desalination method according to any one of claims 1 to 6, characterized in that: The seawater desalination system comprises: A filtering device, wherein the filtering membrane used in the filtering device is a polymer membrane containing a photocatalyst, and the photocatalyst is a porous polymer nanosphere containing a graphitized titanium-based framework material; A reverse osmosis device, the reverse osmosis device is connected to the filtration device, the reverse osmosis membrane used in the reverse osmosis device comprises a support membrane and a polyamide layer and a porous polymer layer sequentially stacked on the surface of the support membrane, the polyamide layer contains a layered ionic covalent organic framework material, and the porous polymer layer contains a positively charged crystalline polymer; A disinfection device, wherein the reverse osmosis device is connected to the disinfection device.

8. The seawater desalination system according to claim 7, characterized in that: A safety filter is also provided between the filtering device and the reverse osmosis device.

9. The seawater desalination system according to claim 8, characterized in that: The seawater desalination system further comprises an energy recovery device, and the energy recovery device is connected to the reverse osmosis device.

Images