Boron-removal seawater desalination reverse osmosis membrane and preparation method therefor

Abstract

Disclosed in the present invention are a boron-removal seawater desalination reverse osmosis membrane and a preparation method therefor. In the present invention, a seawater reverse osmosis membrane preparation process is adjusted: firstly, Span-type substances are introduced during interfacial polymerization, and hydrophilic groups contained in the Span-type substances are used to promote diffusion of amine monomers to an organic phase, thereby broadening an interfacial polymerization region, improving the polymerization process, and increasing the flux of the reverse osmosis membrane; secondly, grafting is performed by means of secondary heat treatment, an acrylamide solution is applied after primary heat treatment, high-temperature heating is used to promote fusion crosslinking between acrylamide monomers and a polyamide layer, and heat treatment further promotes the shrinkage of the polyamide layer, enhancing the compactness of the polyamide layer, reducing the occurrence of concentrated pores, and achieving the objective of better boric acid molecule retention. The boron-removal seawater desalination reverse osmosis membrane prepared by the method of the present invention has certain permeability and good desalination performance, and has a boric acid removal rate of 91% or more.

Description

A boron-removing seawater desalination reverse osmosis membrane and a preparation method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of seawater desalination, and particularly relates to a boron-removing seawater desalination reverse osmosis membrane and a preparation method thereof. BACKGROUND

[0002] At present, under the rapid population growth and social development, the demand of human beings for water resources is increasing, and the problem of water resource shortage is becoming increasingly serious. Seawater is an important part of marine resources and an important supplement and reserve of freshwater resources, but it contains a large amount of salt, calcium and magnesium ions, microorganisms and the like, and direct drinking will cause harm to human health, so it needs to be treated to form freshwater resources. For coastal areas lacking water, seawater desalination has become one of the important ways to obtain freshwater resources. By 2023, the global seawater desalination market size has reached 200 billion US dollars, and with the further growth of population, the shortage of water resources will be aggravated, and the demand for seawater desalination in the future will further increase.

[0003] At present, the main seawater desalination technologies on the market are divided into two categories: thermal method (distillation method) and membrane method (reverse osmosis). The membrane method is mainly a membrane separation technology, which uses a reverse osmosis membrane as a separation medium to desalinate seawater. It is a highly selective semi-permeable membrane that allows water molecules to pass through while retaining salt ions and other impurities. In the seawater desalination process, a high-pressure pump is used to apply high pressure to filter the pretreated seawater to produce freshwater, which can effectively remove inorganic salts, heavy metal ions, organic matter, bacteria and other harmful components in seawater, and become a stable source of freshwater.

[0004] At present, membrane seawater desalination still faces many difficulties, such as the reverse osmosis membrane used being easily contaminated, oxidized by residual chlorine, having a high unit cost, and having a low removal rate of boron and other neutral small molecules. Boron, as a trace element necessary for biological growth, is widely present in seawater. The content of boron in seawater is 0.3 mg / L to 9.6 mg / L, with an average content of 4.6 mg / L. The World Health Organization (WHO) has set the safe drinking standard for boron at no more than 0.5 mg / L per liter of water. Therefore, boron needs to be removed to meet the drinking standard during seawater desalination. Most reverse osmosis membranes on the market have a low boron removal rate, which cannot meet the drinking demand. In water, when the pH value of the aqueous solution is lower than 9.3, boron mainly exists in the form of H3BO3, which passes through the reverse osmosis membrane in a similar way to water molecules; when the pH value of the aqueous solution is higher than 9.3, it exists in the form of B(OH) - , the hydrated ion radius increases and is negatively charged, and the removal rate increases, but the increase in pH value will cause scaling on the surface of the reverse osmosis membrane and damage to the polyamide layer, resulting in loss of desalination effect. Therefore, how to achieve good boron removal when the pH value of the aqueous solution is lower than 9.3 has become one of the research directions of reverse osmosis membranes for seawater desalination.

[0005] At present, many studies have focused on the research of boron removal reverse osmosis membranes, mainly by reducing the concentration of polyamide layer holes in seawater reverse osmosis membranes, reducing the size of the holes, improving the densification of the polyamide layer, and increasing the removal performance of boron molecules.

[0006] In the patent document with application number CN2023107317666, carbon nitride sol is introduced into the aqueous solution to prepare a seawater desalination reverse osmosis membrane that balances water flux and boron removal rate. However, the preparation process requires alkaline treatment of the carbon nitride sol, which is time-consuming and complicated.

[0007] In the patent document with application number CN2019104552297, before heat treatment of the polyamide reverse osmosis membrane, different polyacyl chlorides are introduced again to form polyamides of different dimensions and molecular weights, further adjusting the micro-nano structure of the membrane, adjusting the pore size and channel polarity, filling the defects of the reverse osmosis membrane, and further enhancing the boron removal and desalination performance of the reverse osmosis membrane. However, this document does not disclose the main structure of the grafting monomer that can improve the grafting effect, nor does it mention the coating method that can improve the densification of the polyamide layer and solve the corresponding technical problems.

[0008] In the patent document with application number CN2022109986542, the reverse osmosis composite membrane is soaked in an ionic liquid solution containing hydroxyl-containing amino acid, catalyst and condensation promoter for a period of time, then heated, washed and dried to obtain a reverse osmosis composite membrane with surface grafted amino acid. Although this patent document discloses the use of polysulfone polymers, polyacyl chloride solutions, polyamine materials and corresponding process steps, it does not disclose the contact time of the polyamine monomer solution, the pore size of the base film, the structure of the grafting monomer and the coating method. This patent document mainly solves the technical problem of desalination rate and does not involve the technical problem of boron removal rate.

[0009] In the literature (Thin film nanocomposite reverse osmosis membrane incorporated with UiO-66 nanoparticles for enhanced boron removal[J].Journal of Membrane Science 580 (2019) 101-109), it is mentioned that the addition of UiO-66 nanoparticles can improve the polyamide layer, making it have a narrow pore structure and improving the boron removal effect of the membrane. However, the synthesis of nanoparticles and their dispersion in actual production are relatively costly, and excessive addition will reduce the boron removal effect.

[0010] Therefore, the application starts from the existing process, and a high-deboronization seawater reverse osmosis membrane preparation method is provided by optimizing the existing process, so as to promote the further application of the reverse osmosis membrane in the seawater desalination field. SUMMARY

[0011] To solve the above technical problems, the application provides a de-boronization seawater desalination reverse osmosis membrane and a preparation method thereof.

[0012] The application is implemented by the following technical solutions.

[0013] The application provides a preparation method of a de-boronization seawater desalination reverse osmosis membrane, including the following steps.

[0014] S1: a base film prepared and soaked in water is contacted with a solution A, and the excess liquid is removed to obtain a base film containing a polyamine;

[0015] S2: the base film containing the polyamine obtained in step S1 is contacted with a solution B to obtain a base film containing a polyamide layer;

[0016] S3: heating is performed to volatilize the solution and form an initial reverse osmosis membrane;

[0017] S4: a solution C is coated on the surface of the initial reverse osmosis membrane, and then heating is performed;

[0018] S5: cleaning is performed using a solution D;

[0019] S6: water washing is performed, and then the base film is immersed in a solution E for pore preservation treatment;

[0020] S7: a solution F is coated on the surface of the membrane;

[0021] S8: heating and drying treatment are performed to obtain a de-boronization seawater desalination reverse osmosis membrane.

[0022] Preferably, the base film material in S1 includes one or more of polysulfone, sulfonated polysulfone, polyarylsulfone, polyethersulfone, polyphenylene sulfone, sulfonated polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene and polyethylene;

[0023] The base film pore size includes 20-40 nm, the base film is scraped on a polyester non-woven fabric, and the thickness includes 5.0-5.5 mil;

[0024] The solution A is a solution containing a polyamine, the polyamine includes a monomer containing two amino groups, and includes one or more of m-phenylenediamine, N,N-dimethyl-m-phenylenediamine, 1,3-propanediamine, melamine, piperazine, ethylenediamine, diethylenetriamine, triethylenetetramine, p-phenylenediamine, o-phenylenediamine and m-phenylenediamine;

[0025] The content of the polyamine monomer includes 0.1-10wt% based on the total weight of the solution A.

[0026] Preferably, the solution A includes an acid-binding agent, and the acid-binding agent includes one or more of triethylamine / camphorsulfonic acid complex system, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate and potassium hydrogen phosphate, wherein the ratio of triethylamine and camphorsulfonic acid is 1:2, and the total content is 3wt%;

[0027] The contact time of the base film with the solution A includes 10-60 seconds, and the contact temperature includes 15-45℃.

[0028] Preferably, it is characterized in that: in step S2, the base film containing the polyamine obtained in step S1 is immersed in a solution B containing an acyl chloride monomer and a Span substance additive, and the acyl chloride monomer includes one or more of trimesoyl chloride, cyanuric chloride, dansyl chloride, isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, oxalyl chloride, adipoyl chloride, oxalyl chloride, succinyl chloride, biphenyl tetracarboxylic chloride.

[0029] The solvent of the solution B includes one or more of n-hexane, n-heptane, cyclohexane, Isopar M, Isopar H, Isopar L, Isopar E or Isopar G.

[0030] The content of the acyl chloride monomer includes 0.05-1wt% based on the total weight of the solution B.

[0031] The contact time of the base film with the solution B includes 10-60 seconds, and the contact temperature includes 15-45℃.

[0032] The Span substance is a non-ionic surfactant, and the Span substance includes one or more of Span 20, Span 40, Span 60, Span 65, Span 80 and Span 85.

[0033] The content of the Span includes 0.01-3wt% based on the total weight of the solution B.

[0034] Preferably, it is characterized in that: in step S3, the heating temperature range includes 60-80℃, and the heating time includes 1-5 minutes.

[0035] Preferably, in S4, the initial reverse osmosis membrane is coated with a solution C containing an acrylamide grafting monomer on the membrane surface by a slit coating method at room temperature, and then heated and cross-linked in a 60-80℃ environment.

[0036] The solution C includes an initiator, a cross-linking agent, a grafting monomer and a reaction catalyst tetramethyl ethylenediamine, and the initiator includes one or both of potassium persulfate and ammonium persulfate.

[0037] The concentration of tetramethylethylenediamine is 0.01-0.1 wt%, the concentration of initiator is 0.1-1.0 wt%, and the concentration of crosslinking agent is 0.1-3.0 wt%, based on the total weight of solution C;

[0038] The crosslinking agent includes one or both of N,N-dimethylacrylamide and N,N-methylenebisacrylamide.

[0039] The slit coating method includes: solution C only contacts one side of the polyamide layer of the initial reverse osmosis membrane, does not contact the non-woven fabric side of the initial reverse osmosis membrane, and reacts by slowly penetrating into the polyamide layer, the process is divided into two parts, the first part, the coating stage is carried out at room temperature, after coating, waiting for 5-20 seconds, the second part, placing in a 60-80°C oven for heating reaction, the heating time is 2-20 minutes, and the coating amount is 0.01-1.00 L / m 2 .

[0040] Preferably, the grafting monomer body is an acrylamide structure, and the main features include containing a group capable of active initiation to form a free radical, and the structure is as follows:

[0041] The R1 feature can be a single group or a linear or branched molecular structure composed of multiple groups, and the R1 feature includes one or more of hydrogen, phenyl, methyl, ethyl, propyl, isopropyl, tert-butyl, hydroxyethyl, hydroxymethyl, hydroxypropyl, hydroxyphenyl, dimethylamine, 2-methylpropane sulfonic acid, acrylate methyl acetate, and pyridine.

[0042] The R2 includes one of hydrogen, methyl, hydroxyl, and hydroxyethyl.

[0043] The grafting monomer includes one or more of acrylamide, N-propyl acrylamide, N-methyl-2-acrylamide, N-phenyl acrylamide, dimethylamine acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide, N-ethyl acrylamide, N-isopropyl acrylamide, N-tert-butyl acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, N-(pyridin-2-yl) acrylamide, N’N-vinyl bisacrylamide, N-phenyl methyl acrylamide, N-methyl methyl acrylamide, N-isopropyl methyl acrylamide, N-(4-hydroxyphenyl) methyl acrylamide, and N-(2-hydroxypropyl) methyl acrylamide.

[0044] The concentration of the grafting monomer is 0.5-10 wt%, based on the total weight of solution C.

[0045] Preferably, the solution D used in the step S5 comprises a weak base solution, the weak base solution comprises sodium carbonate, the cleaning temperature comprises 50-80℃, the weak base solution concentration comprises 5-10wt%, and the cleaning time comprises 1-10 minutes.

[0046] The pure water used in the step S6 is washed, the washing temperature comprises 20-30℃, and the cleaning time comprises 3-10 minutes.

[0047] The solution D comprises a glycerol solution, the temperature of the immersion solution D comprises 20-30℃, and the time comprises 1-5 minutes.

[0048] Preferably, after the residual solution D on the membrane surface is blown dry in the step S7, a dialdehyde cross-linking agent is immersed and coated, the dialdehyde cross-linking agent comprises glutaraldehyde and glyoxal, the immersion and coating time comprises 10-30 seconds; then a solution F is coated on the membrane surface, the solution F comprises a polyvinyl alcohol solution, and the coating time comprises 10-30 seconds.

[0049] Based on the total weight of the solution D, the concentration of the dialdehyde cross-linking agent comprises 0.01-0.5wt%, and the concentration of the polyvinyl alcohol solution comprises 1-3wt%.

[0050] The heating and drying treatment temperature in the step S8 comprises 80-90℃, and the time comprises 3-10 minutes.

[0051] A desalination reverse osmosis membrane for desalination of seawater prepared by the preparation method.

[0052] The beneficial effects of the present application are as follows:

[0053] The desalination reverse osmosis membrane for desalination of seawater prepared by the present application has certain permeation performance and good desalination performance, the flux reaches 32L / (m 2 .h) or more, the desalination rate reaches 99.8% or more, and the boron removal rate is 91% or more. DETAILED DESCRIPTION

[0054] The technical solutions of the present application are further described below, but the scope of protection is not limited to the description.

[0055] A preparation method of a desalination reverse osmosis membrane for desalination of seawater, comprising the following steps:

[0056] S1: a base film prepared and soaked in pure water is contacted with a solution A, and the excess liquid is removed to obtain a base film containing a polyamine;

[0057] S2: the base film containing the polyamine obtained in the step S1 is contacted with a solution B, an interfacial polymerization reaction occurs, a polyamide layer is formed on the base film by the reaction, and a base film containing the polyamide layer is obtained;

[0058] S3: heating to evaporate the solution, and further cross-linking the polyamide layer to form an initial reverse osmosis membrane;

[0059] S4: applying a surface coating solution C to the initial reverse osmosis membrane, and then heating to promote cross-linking reactions between the acrylamide species and amino groups on the polyamide layer, and to promote further reactions between unreacted amino and acyl chloride groups to increase the density of the polyamide layer;

[0060] S5: cleaning with a low concentration solution D to remove unreacted polyamine, polyacyl chloride, and acrylamide monomers, as well as initiators and cross-linking agents;

[0061] S6: water washing, and then immersing in a solution E for base membrane pore maintenance treatment;

[0062] S7: applying a solution F to the surface of the membrane to protect the membrane surface and ensure the stability of the membrane structure during subsequent drying;

[0063] S8: heating and drying treatment to obtain a desalination reverse osmosis membrane for boron removal from seawater.

[0064] The base membrane material in S1 includes one or more of polysulfone, sulfonated polysulfone, polyarylsulfone, polyethersulfone, polyphenylene sulfone, sulfonated polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, and polyethylene;

[0065] The base membrane pore size includes 20-40 nm, and the base membrane is coated on a polyester non-woven fabric, and the thickness includes 5.0-5.5 mil;

[0066] The solution A is a solution including a polyamine, and the polyamine includes a monomer containing two amino groups, including one or more of m-phenylenediamine, N,N-dimethyl-m-phenylenediamine, 1,3-propanediamine, melamine, piperazine, ethylenediamine, diethylenetriamine, triethylenetetramine, p-phenylenediamine, o-phenylenediamine, and m-phenylenediamine;

[0067] The content of the polyamine monomer based on the total weight of the solution A includes 0.1-10 wt%, preferably 3-6 wt%;

[0068] The solution A includes an acid-binding agent, and the acid-binding agent includes one or more of a triethylamine / camphor sulfonic acid complex system, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate, and potassium hydrogen phosphate, and the acid-binding agent is preferably a triethylamine / camphor sulfonic acid complex system, in which the ratio of triethylamine to camphor sulfonic acid is 1:2, and the total content is 3 wt%;

[0069] The contact time of the base membrane with the solution A includes 10-60 seconds, and the contact temperature includes 15-45°C.

[0070] The base film containing polyamine obtained in step S1 is immersed in solution B containing acyl chloride monomer and span additive in step S2. The process is mainly through the interfacial polymerization of polyamine monomer and acyl chloride monomer. Under the influence of span, the diffusion of amine monomer is promoted, the interfacial polymerization area is widened, a relatively thick and loose polyamide layer is formed, and the types of acyl chloride monomers include one or more of trimesoyl chloride, cyanuric chloride, dansyl chloride, isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, oxalyl chloride, adipoyl chloride, oxalyl chloride, succinyl chloride, and biphenyl tetracarboxylic chloride.

[0071] The solvent of the solution B includes one or more of n-hexane, n-heptane, cyclohexane, Isopar M, Isopar H, Isopar L, Isopar E, or Isopar G.

[0072] Based on the total weight of the solution B, the content of the acyl chloride monomer includes 0.05-1wt%, preferably 0.1-0.5wt%. When the concentration is lower than 0.1wt%, a better polyamide layer cannot be formed to meet the performance requirements of seawater desalination reverse osmosis membranes. When the concentration is higher than 1wt%, the prepared seawater desalination reverse osmosis membrane has low flux and cannot meet the actual application requirements.

[0073] The contact time of the base film with solution B includes 10-60 seconds, and the contact temperature includes 15-45℃.

[0074] The span is a non-ionic surfactant that can promote the compatibility of the water phase and the oil phase interface, promote the diffusion of amine monomers to the organic phase, expand the interfacial polymerization area, and then grow a relatively thick polyamide layer. The span includes one or more of Span 20, Span 40, Span 60, Span 65, Span 80, and Span 85.

[0075] Based on the total weight of the solution B, the content of the span includes 0.01-3wt%, preferably 0.1-1.5wt%. When the content of the span is higher than 3wt%, the prepared membrane has poor desalination, which does not meet the actual requirements. When the content of the span is lower than 0.01wt%, there is no improvement effect.

[0076] In step S3, heating treatment is performed to promote the volatilization of the organic solution and the further cross-linking and solidification of the polyamide layer to form a reverse osmosis membrane. The heating temperature range includes 60-80℃, and the heating time includes 1-5 minutes. Too high a heating temperature or too long a heating time can cause the tearing of the membrane surface microstructure, form concentrated pores, and cause the desalination and desboron performance of the membrane to decrease. Too low a temperature or too short a heating time cannot complete the formation of the dense polyamide layer within the effective time of the next process, and the desalination performance of the membrane is poor.

[0077] In the S4, the initial reverse osmosis membrane is coated with solution C containing acrylamide grafting monomers on the membrane surface by slit coating at room temperature, and then heated and cross-linked in an environment of 60-80°C. The heat cross-linking can promote the self-cross-linking of the polyamide layer and the grafting of acrylamide substances to the membrane surface and the polyamide layer, so as to improve the compactness of the polyamide layer and reduce the proportion of large pores.

[0078] The solution C includes an initiator, a cross-linking agent, a grafting monomer, and a reaction catalyst tetramethyl ethylenediamine. The initiator includes one or both of potassium persulfate and ammonium persulfate.

[0079] Based on the total weight of the solution C, the concentration of tetramethyl ethylenediamine is 0.01-0.1wt%, the concentration of the initiator is 0.1-1.0wt%, and the concentration of the cross-linking agent is 0.1-3.0wt%.

[0080] The cross-linking agent includes one or both of N,N-dimethyl acrylamide and N,N-methylene bisacrylamide.

[0081] The slit coating method includes that the solution C only contacts the side of the initial reverse osmosis membrane containing the polyamide layer and does not contact the side of the non-woven fabric of the initial reverse osmosis membrane, and the reaction is carried out by slowly penetrating into the polyamide layer. The process is divided into two parts. In the first part, the coating stage is carried out at room temperature. After coating, it is waited for 5-20 seconds. In the second part, it is placed in a 60-80°C oven for heating reaction. The heating time is 2-20 minutes. The coating amount is 0.01-1.00L / m 2 The main purpose of the process is to introduce monomers to react with the groups on the polyamide chain of the membrane surface, promote the compactness of the polyamide layer, and improve the boron removal and desalination effect. However, it needs to be noted that the concentration and time of the process should be controlled. Too long reaction time and reaction concentration may cause too much flux decline, while lower concentration and shorter time may not bring appropriate desalination and boron removal performance.

[0082] The main body of the grafting monomer is an acrylamide structure, which mainly includes a group capable of active initiation to form a free radical. The structure formula is as follows:

[0083] The R1 feature can be a single group or a linear or branched molecular structure composed of multiple groups. The R1 feature includes one or more of hydrogen, phenyl, methyl, ethyl, propyl, isopropyl, tert-butyl, hydroxyethyl, hydroxymethyl, hydroxypropyl, hydroxyphenyl, dimethylamine, 2-methylpropane sulfonic acid, acrylate methyl acetate, and pyridine.

[0084] The R2 includes one of hydrogen, methyl, hydroxyl, and hydroxyethyl.

[0085] The grafting monomer includes one or more of acrylamide, N-propyl acrylamide, N-methyl-2-acrylamide, N-phenyl acrylamide, dimethylamino acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide, N-ethyl acrylamide, N-isopropyl acrylamide, N-tert-butyl acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-(pyridin-2-yl) acrylamide, N'N-vinyl bisacrylamide, N-phenyl methyl acrylamide, N-methyl methacrylamide, N-isopropyl methacrylamide, N-(4-hydroxyphenyl) methacrylamide, and N-(2-hydroxypropyl) methacrylamide;

[0086] The grafting monomer concentration includes 0.5-10 wt%, preferably 1-5 wt%, based on the total weight of the solution C; when the grafting monomer concentration is lower than 0.5 wt%, the grafting effect is not obvious, and the membrane sheet has poor desalination and de-boron performance; when the grafting concentration is higher than 5 wt%, the grafting density is too high, the polyamide layer is relatively dense, and the membrane sheet has low flux, which is not conducive to actual use.

[0087] The solution D used in the step S5 includes a weak alkali solution, the weak alkali solution includes sodium carbonate, the cleaning temperature includes 50-80°C, the weak alkali solution concentration includes 5-10 wt%, and the cleaning time includes 1-10 minutes, preferably 3-8 minutes;

[0088] The pure water washing in the step S6 includes a water washing temperature of 20-30°C, and a cleaning time of 3-10 minutes;

[0089] The solution D includes a glycerol solution, the temperature for immersing in the solution D includes 20-30°C, and the time includes 1-5 minutes.

[0090] In the step S7, after the residual solution D on the membrane surface is blown dry, a dialdehyde cross-linking agent is immersed and coated, the dialdehyde cross-linking agent includes glutaraldehyde and glyoxal, the immersion and coating time includes 10-30 seconds; then a solution F is coated on the membrane surface, the solution F includes a polyvinyl alcohol solution, and the coating time includes 10-30 seconds;

[0091] The concentration of the dialdehyde cross-linking agent includes 0.01-0.5 wt% based on the total weight of the solution D, and the concentration of the polyvinyl alcohol solution includes 1-3 wt%;

[0092] The cross-linking agent mainly functions to cross-link and fix the polyvinyl alcohol on the membrane surface, or promote the cross-linking of the polyvinyl alcohol, and the polyvinyl alcohol functions as a protective layer to protect the stability of the polyamide chain in the subsequent heating process;

[0093] In the step S8, the heating and drying treatment temperature includes 80-90°C, and the time includes 3-10 minutes.

[0094] The technical solutions of the present application are further described in detail below in combination with examples, but are not limited to the present application. It should be noted that the reagents and raw materials used in the examples of the present application are commercially available unless otherwise specified.

[0095] Solution configuration and base membrane preparation:

[0096] Base membrane: polysulfone base membrane with a pore size range of 20-30 nm and a polyester non-woven cloth layer thickness of 5.2-5.3 mil;

[0097] Preparation of polyamine monomer solution: 35 g of m-phenylenediamine, 40 g of triethylamine, and 60 g of camphor sulfonic acid were dissolved in 865 g of pure water to prepare a polyamine monomer solution.

[0098] Preparation of polyacyl chloride monomer solution: 2 g of trimesoyl chloride was dissolved in 998 g of Isopar G solvent to prepare an acyl chloride monomer solution.

[0099] Preparation of grafting monomer solution: 5 g of potassium persulfate, 0.5 g of tetramethyl ethylenediamine, 10 g of N’N-methylene bisacrylamide, and 30 g of acrylamide monomer were dissolved in 954.5 g of pure water, stirred at room temperature, and then left to stand.

[0100] Preparation of crosslinking agent solution: 1.25 g of glutaraldehyde solution (40 wt%) was dissolved in 100 g of pure water, diluted with water to 1000 g, and then hydrochloric acid was added dropwise to adjust the pH to 2.5-3.5.

[0101] Preparation of polyvinyl alcohol solution: 15 g of polyvinyl alcohol powder was dissolved in 490 g of hot water at 90°C, stirred for 0.5 hours, diluted with 500 g of pure water at room temperature, and then used.

[0102] Example 1

[0103] The base membrane soaked in pure water was taken out and immersed in the polyamine solution for 30 seconds, and then the excess solution on the surface was removed after taking it out. It was then immersed in a 1 wt% Span 60 and polyacyl chloride monomer solution for 30 seconds to generate a polyamide layer through interfacial polymerization. It was then heated at 60°C for 2 minutes to promote further crosslinking of the reactants and volatilization of the organic phase solution. An N-hydroxyethyl acrylamide grafting monomer solution was coated on the membrane surface at a coating amount of 50 mL / m 2, after standing at room temperature for 15 seconds, the membrane was heated at 70°C for 10 minutes to promote the grafting process, then the membrane was cleaned with 10wt% sodium carbonate solution at 70°C for 5 minutes, with pure water at 25°C for 5 minutes, and immersed in 12wt% glycerol solution at 25°C for 2 minutes. Then the membrane was placed in an environment of 80-90°C for 8 minutes to dry the water in the membrane, and the final desalination reverse osmosis membrane was obtained.

[0104] Example 2

[0105] The preparation method is basically the same as that of Example 1, except that Span 20 is added to the polyacyl chloride monomer solution.

[0106] Example 3

[0107] The preparation method is basically the same as that of Example 1, except that Span 40 is added to the polyacyl chloride monomer solution.

[0108] Example 4

[0109] The preparation method is basically the same as that of Example 1, except that Span 80 is added to the polyacyl chloride monomer solution.

[0110] Examples 1-4 mainly investigate the influence of different Span substances on the performance of the membrane.

[0111] Example 5

[0112] The preparation method is basically the same as that of Example 1, except that the grafting monomer is acrylamide.

[0113] Example 6

[0114] The preparation method is basically the same as that of Example 1, except that the grafting monomer is N-isopropyl acrylamide.

[0115] Example 7

[0116] The preparation method is basically the same as that of Example 1, except that the grafting monomer is N-ethyl acrylamide.

[0117] Example 8

[0118] The preparation method is basically the same as that of Example 1, except that the grafting monomer is 2-acrylamide-2-methylpropane sulfonic acid.

[0119] Example 9

[0120] The preparation method is basically the same as that of Example 1, except that the grafting monomer is acrylamide-based propyl acrylate.

[0121] Example 10

[0122] The preparation method is substantially the same as that of Example 1, except that the grafting monomer is N-tert-butyl acrylamide.

[0123] Example 11

[0124] The preparation method is substantially the same as that of Example 1, except that the grafting monomer is N-(2-hydroxypropyl) methacrylamide.

[0125] Example 12

[0126] The preparation method is substantially the same as that of Example 1, except that the grafting monomer is methacrylamide.

[0127] Examples 5-12 mainly show the influence of different grafting monomers on the performance of the membrane.

[0128] Comparative Example 1

[0129] The base membrane immersed in pure water is taken out and placed in a polyamine solution for 30 seconds. After removal of the excess solution on the surface, the membrane is immersed in a polyacyl chloride monomer solution containing 1 wt% Span 60 for 30 seconds to generate a polyamide layer through interfacial polymerization. The membrane is heated at 60°C for 2 minutes to promote further crosslinking of the reactants and volatilization of the organic phase solution. The membrane is washed with a 10 wt% sodium carbonate solution at 70°C for 5 minutes, washed with pure water at 25°C for 5 minutes, immersed in a 12 wt% glycerol aqueous solution at 25°C for 2 minutes, and then immersed in a crosslinking agent solution for 10 seconds and a polyvinyl alcohol solution for 20 seconds on the membrane surface at room temperature. The membrane is then placed in an environment of 80-90°C for 8 minutes to dry the water in the membrane.

[0130] Comparative Example 2

[0131] The base membrane immersed in pure water is taken out and placed in a polyamine solution for 30 seconds. After removal of the excess solution on the surface, the membrane is immersed in a polyacyl chloride monomer solution containing 1 wt% Span 60 for 30 seconds to generate a polyamide layer through interfacial polymerization. The membrane is heated at 60°C for 2 minutes to promote further crosslinking of the reactants and volatilization of the organic phase solution. The membrane is washed with a 10 wt% sodium carbonate solution at 70°C for 5 minutes, washed with pure water at 25°C for 5 minutes, immersed in a 12 wt% glycerol aqueous solution at 25°C for 2 minutes, and then immersed in a crosslinking agent solution for 10 seconds and a polyvinyl alcohol solution for 20 seconds on the membrane surface at room temperature. The membrane is then placed in an environment of 80-90°C for 8 minutes to dry the water in the membrane.

[0132] The difference between Comparative Example 1 and Comparative Example 2 is that the polyacyl chloride solution in Comparative Example 2 contains 1 wt% Span 60.

[0133] Comparative Example 3

[0134] The base membrane soaked in pure water was taken out and put into the polyamine solution for 30 seconds. After being taken out, the excess solution on the surface was removed, and the membrane was immersed in the polyacyl chloride monomer solution for 30 seconds to generate a polyamide layer through interfacial polymerization. The membrane was heated at 60°C for 2 minutes to promote further cross-linking of the reactants and volatilization of the organic phase solution. The membrane surface was coated with a solution containing N-hydroxyethyl acrylamide grafting monomers at a coating amount of 50 mL / m 2 After standing at room temperature for 15 seconds, the membrane was heated at 70°C for 10 minutes to promote the occurrence of the grafting process. Then, the membrane was cleaned with a 10 wt% sodium carbonate solution at 70°C for 5 minutes, a pure water solution at 25°C for 5 minutes, and a 12 wt% glycerol aqueous solution at 25°C for 2 minutes. The membrane was immersed in a cross-linking agent solution at room temperature for 10 seconds and a polyvinyl alcohol solution for 20 seconds, and then the membrane was blown dry by placing it in an environment of 80-90°C for 8 minutes to remove the water in the membrane, thereby obtaining the final seawater reverse osmosis membrane.

[0135] The difference between Comparative Example 1 and Comparative Example 3 is that Comparative Example 3 contains a grafting acrylamide monomer process.

[0136] Performance test

[0137] (1) Permeation and separation performance test

[0138] To test the performance of the prepared reverse osmosis membrane, the reverse osmosis membranes obtained in Examples 1-12 and Comparative Examples 1-3 were tested on a cross-flow membrane test bench. The test conditions were 32000 mg / L sodium chloride solution, 5 ppm boric acid, operating pressure 800 psi, temperature 25°C, and pH value 7. The test stabilization time was 40 minutes.

[0139] Alkaline cleaning conditions: 0.2 wt% sodium hydroxide cleaning for 10 hours, alkaline cleaning temperature 25°C, and pressure 200 psi.

[0140] The test results are shown in Table 1.

[0141] Table 1: Performance test table of reverse osmosis membranes

[0142] From the comparative example 1 to 3, only adding span type substance in the preparation process can significantly improve the flux of seawater reverse osmosis membrane, but the removal rate of sodium chloride and boric acid of the prepared membrane is reduced, because the span type substance is a non-ionic surfactant, the hydrophilic group and the like on it will affect the diffusion of amine monomer when the interfacial polymerization reaction occurs, and then a more loose structure of polyamide layer is formed, resulting in the increase of permeation performance and the decrease of desalination performance; only containing the thermal crosslinking grafting process, because the thermal crosslinking grafting on the membrane surface will make the polyamide layer more dense, the desalination and boron removal performance of the membrane sheet is significantly increased, but the permeation performance of the membrane sheet is reduced, therefore, the two methods are coupled in the application, from the example 1 to 12, the seawater reverse osmosis membrane with certain permeation performance and good desalination can be prepared, and the boron removal can be greater than 91%.

[0143] From the example 1 to 4, different span types will bring different performance changes, but the flux can be improved as a whole, and the subsequent thermal crosslinking grafting process can realize good desalination and boron removal performance; from the example 5 to 12, due to the double bond structure of acrylamide, acrylamide can be well connected with the polyamide layer, which promotes the polyamide layer to become dense and improves the desalination and boron removal performance of the membrane sheet, and due to the loose structure with good water channel formed by the addition of span type substance, the seawater desalination reverse osmosis membrane prepared by the application still has good boron removal performance after alkali washing, which shows that the polyamide layer has good density, so the prepared seawater reverse osmosis membrane has practical permeation and removal performance.

Claims

1. A method for preparing a boron-removed seawater desalination reverse osmosis membrane, characterized in that, The method comprises the following steps: S1: contact the prepared base film soaked in water with solution A, remove excess liquid, and obtain a base film containing polyamines; S2: contact the base film containing polyamines obtained in step S1 with solution B to obtain a base film containing a polyamide layer; S3: heat to volatilize the solution and form an initial reverse osmosis membrane; S4: coat solution C on the surface of the initial reverse osmosis membrane, and then heat; S5: clean with solution D; S6: wash with water, then immerse in solution E for base film pore maintenance treatment; S7: coat solution F on the surface of the membrane; S8: heat and dry to obtain a boron-removed seawater desalination reverse osmosis membrane.

2. The method of claim 1, wherein the method is characterized by: The base film material in S1 includes one or more of polysulfone, sulfonated polysulfone, polyaryl sulfone, polyether sulfone, polyphenylene sulfone, sulfonated polyether sulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, and polyethylene; The base film pore size includes 20-40 nm, the base film is coated on a polyester non-woven fabric, and the thickness includes 5.0-5.5 mil; Solution A is a solution containing polyamines, the polyamines include monomers containing two amino groups, and include one or more of m-phenylenediamine, N,N-dimethyl-m-phenylenediamine, 1,3-propanediamine, melamine, piperazine, ethylenediamine, diethylenetriamine, triethylenetetramine, p-phenylenediamine, o-phenylenediamine, and m-phenylene diamine; The content of the polyamine monomer based on the total weight of solution A includes 0.1-10 wt%.

3. The method for preparing a boron-removed seawater desalination reverse osmosis membrane according to claim 2, wherein solution A includes an acid-binding agent, and the acid-binding agent includes one or more of a triethylamine / camphorsulfonic acid complex system, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydrogen phosphate, and potassium hydrogen phosphate, wherein the ratio of triethylamine to camphorsulfonic acid is 1:2, and the total content is 3 wt%. The contact time of the base film with solution A includes 10-60 seconds, and the contact temperature includes 15-45°C.

4. The method of claim 1, wherein the method further comprises: In step S2, the base film containing polyamines obtained in step S1 is immersed in solution B containing an acyl chloride monomer and a Span additive, and the type of the acyl chloride monomer includes one or more of trimesoyl chloride, cyanuric chloride, dansyl chloride, isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, oxalyl chloride, adipoyl chloride, oxalyl chloride, succinyl chloride, and biphenyl tetracarboxylic chloride; ​ The solvent of solution B includes one or more of n-hexane, n-heptane, cyclohexane, Isopar M, Isopar H, Isopar L, Isopar E, or Isopar G; The content of the acyl chloride monomer based on the total weight of solution B includes 0.05-1 wt%. The contact time of the base film with solution B includes 10-60 seconds, and the contact temperature includes 15-45°C. The Span additive is a non-ionic surfactant, and the Span additive includes one or more of Span 20, Span 40, Span 60, Span 65, Span 80, and Span 85; The content of the Span based on the total weight of solution B includes 0.01-3 wt%.

5. The method of claim 1, wherein the method further comprises: The heating temperature range in step S3 includes 60-80℃, and the heating time includes 1-5 minutes. ​ 6. The method of claim 1, wherein the method further comprises: In S4, the initial reverse osmosis membrane is coated with solution C containing acrylamide grafting monomers on the membrane surface by slit coating at room temperature, and then heated and cross-linked in a 60-80℃ environment. ​ The solution C includes initiator, cross-linking agent, grafting monomer and reaction catalyst tetramethyl ethylenediamine, and the initiator includes one or both of potassium persulfate and ammonium persulfate. Based on the total weight of the solution C, the concentration of tetramethyl ethylenediamine is 0.01-0.1wt%, the concentration of the initiator is 0.1-1.0wt%, and the concentration of the cross-linking agent is 0.1-3.0wt%. The cross-linking agent includes one or both of N,N-dimethyl acrylamide and N,N-methylene bisacrylamide. The slit coating method step includes: solution C only contacts one side of the initial reverse osmosis membrane containing the polyamide layer, does not contact the non-woven cloth side of the initial reverse osmosis membrane, and reacts by slowly penetrating into the polyamide layer, the process is divided into two parts, the first part, the coating stage is carried out at room temperature, after coating, waiting for 5-20 seconds, the second part, heating reaction is carried out by putting into a 60-80 DEG C oven, the heating time includes 2-20 minutes; the coating amount includes 0.01-1.00L / m 2 .

7. A method of preparing a desalination reverse osmosis membrane for desalination of sea water as claimed in claim 6, wherein the main body of the grafting monomer is acrylamide structure, the main features include containing groups capable of active initiation to form free radicals, and the structure formula is as follows: The R1 feature can be a single group or a linear or branched molecular structure composed of multiple groups, and the R1 feature includes one or more of hydrogen, phenyl, methyl, ethyl, propyl, isopropyl, tert-butyl, hydroxyethyl, hydroxymethyl, hydroxypropyl, hydroxyphenyl, dimethylamine, 2-methylpropane sulfonic acid, acrylic acid methyl acetate and pyridine. The R2 includes one of hydrogen, methyl, hydroxyl and hydroxyethyl. The grafting monomer includes one or more of acrylamide, N-propyl acrylamide, N-methyl-2-acrylamide, N-phenyl acrylamide, dimethylamine acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide, N-hydroxypropyl acrylamide, N-ethyl acrylamide, N-isopropyl acrylamide, N-tert-butyl acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, N-(pyridine-2-yl) acrylamide, N’N-vinyl bisacrylamide, N-phenyl methyl acrylamide, N-methyl methyl acrylamide, N-isopropyl methyl acrylamide, N-(4-hydroxyphenyl) methyl acrylamide and N-(2-hydroxypropyl) methyl acrylamide. Based on the total weight of the solution C, the concentration of the grafting monomer is 0.5-10wt%.

8. The method of claim 1, wherein the method further comprises: The solution D used in step S5 includes a weak base solution, the weak base solution includes sodium carbonate, the cleaning temperature is 50-80℃, the concentration of the weak base solution is 5-10wt%, and the cleaning time is 1-10 minutes. ​ In step S6, pure water is used for washing, the washing temperature is 20-30℃, and the cleaning time is 3-10 minutes. Solution D includes a glycerol solution, the temperature for immersing in solution D is 20-30℃, and the time is 1-5 minutes.

9. The method of claim 1, wherein the method further comprises: 5 0.1% to 0.5% of a surfactant; and 0.1% to 0.5% of a biocide. 0 In step S7, after blowing dry the residual solution D on the membrane surface, a dialdehyde cross-linking agent is immersed and coated, the dialdehyde cross-linking agent includes glutaraldehyde and glyoxal, the immersion and coating time is 10-30 seconds; then solution F is coated on the membrane surface, the solution F includes a polyvinyl alcohol solution, and the coating time is 10-30 seconds. ​ Based on the total weight of the solution D, the concentration of the dialdehyde cross-linking agent is 0.01-0.5wt%, and the concentration of the polyvinyl alcohol solution is 1-3wt%. The heating drying treatment temperature in the step S8 includes 80-90℃, and the time includes 3-10 minutes.

10. A desalination reverse osmosis membrane prepared by the method of any one of claims 1-9.

Images