Preparation method of pH-responsive loose nanofiltration membrane

Abstract

The application discloses a preparation method of a pH response loose nanofiltration membrane, which hydrolyzes SMA in an alkaline environment to obtain carboxyl-terminated SMA, takes the carboxyl-terminated SMA and a polymer membrane material as main materials, blends into a homogeneous casting solution by adding a pore-forming agent and an organic solvent, then deposits sodium alginate with rich oxygen-containing groups (-OH, -COOH and =O) on the membrane surface, and forms a three-dimensional interconnected hydrogel network through the crosslinking of the carboxyl (-COOH) and the sodium alginate coating on the surface of the calcium ion (Ca 2+ The rapid ion exchange occurs, and finally, the three-dimensional interconnected hydrogel network is obtained through the crosslinking of the carboxyl (-COOH) and the sodium alginate coating on the surface of the calcium ion (Ca 2+ ) double crosslinking base membrane. The application has the advantages of simple operation, excellent composite membrane performance, high water flux, strong binding force, pH response characteristics, and good development prospect in the water treatment process for drinking water.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, specifically to a method for preparing a pH-responsive loose nanofiltration membrane. Background Technology

[0002] Nanofiltration (NF) is a green separation and purification technology widely used in the concentration of small molecules and the removal of salts. It is a pressure-driven membrane process with pore sizes between 0.5 and 2 nm, effectively retaining most multivalent ions and heavy metals in water. Because the separation performance of NF membranes falls between that of reverse osmosis and ultrafiltration, they are also known as "loose" reverse osmosis membranes and "dense" ultrafiltration membranes. Since nanofiltration membranes have better permeability than reverse osmosis membranes, sufficient water flux can be obtained at low operating pressures. They are commonly used for desalination (hard water softening, seawater desalination pretreatment), small molecule removal (removal of heavy metal ions and small molecule pollutants), concentration and purification of processed products (dye desalination, milk desalination), and substance separation (separation of monovalent and multivalent ions, separation of macromolecules and small molecules).

[0003] Commercial polyamide nanofiltration membranes are formed by a rapid cross-linking reaction between m-phenylenediamine (MPD) or piperazine (PIP) and trimesoyl chloride (TMC) on the base membrane surface, resulting in a dense polyamide cross-linked structure with tightly linked benzene rings. This cross-linked molecular structure endows nanofiltration membranes with highly efficient removal capabilities for polyvalent salts and heavy metals, but it suffers from poor water permeability, high operating pressure, and low water flux. Therefore, although commercial nanofiltration membranes possess unique separation characteristics, their water flux is generally low, typically around 10 L / m³. 2 Below h·bar, its application is greatly limited.

[0004] Based on the above, it is necessary to design a new nanofiltration membrane to solve the aforementioned technical problems. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing a pH-responsive loose nanofiltration membrane. The nanofiltration membrane prepared by this method has strong interlayer bonding and the separation layer has pH-responsive characteristics. Compared with the traditional interfacial polymerization method for preparing polyamide nanofiltration membranes, this application can obtain a nanofiltration membrane with a pH-responsive separation structure on the surface through a one-step reaction. This nanofiltration membrane has excellent permeability and pH responsiveness, thereby solving at least one of the technical problems involved in the background art.

[0006] To solve the above-mentioned technical problems, this application is implemented as follows:

[0007] This application provides a method for preparing a pH-responsive loose nanofiltration membrane, comprising the following steps:

[0008] Step 1: Prepare an alkaline solution with a sodium hydroxide mass fraction of 5%, and immerse styrene maleic anhydride in the alkaline solution for hydrolysis for more than 12 hours to obtain carboxyl-terminated styrene maleic anhydride.

[0009] Step 2: Dissolve carboxyl-terminated styrene maleic anhydride, pore-forming agent and polymer membrane material in an organic solvent, stir to prepare homogeneous membrane building solution, and allow the homogeneous membrane building solution to stand under vacuum to remove bubbles for later use.

[0010] Step 3: Use the phase inversion method to prepare a surface carboxylated ultrafiltration membrane from the deaerated homogeneous casting solution.

[0011] Step 4: The sodium alginate aqueous solution is filtered under negative pressure on the surface of the ultrafiltration base membrane to obtain a sodium alginate coated nanofiltration membrane.

[0012] Step 5: Immerse the sodium alginate-coated nanofiltration membrane in a calcium chloride aqueous solution for a certain period of time to obtain a pH-responsive loose nanofiltration membrane through a double crosslinking reaction.

[0013] As a preferred improvement of this application, in step one, the styrene maleic anhydride is a polymer with an anhydride content of 10% or more.

[0014] As a preferred improvement of this application, the feature is that, in step one, the styrene maleic anhydride is immersed in an alkaline solution for 24 hours for hydrolysis.

[0015] As a preferred improvement of this application, the characteristic feature is that, in step two, the pore-forming agent is one or a mixture of polyethylene glycol or polyvinylpyrrolidone.

[0016] As a preferred improvement of this application, the polymer membrane material in step two is any one of polyethersulfone, polysulfone, and polyvinylidene fluoride.

[0017] As a preferred improvement of this application, in step two, the organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

[0018] As a preferred improvement of this application, in step two, the mass percentages of the polymer membrane material, the carboxyl-terminated styrene maleic anhydride, the pore-forming agent, and the organic solvent are 15-20%, 0.5-8%, 2-12%, and 63-80%, respectively.

[0019] As a preferred improvement of this application, in step four, the sodium alginate aqueous solution has a mass fraction of 0.5%-10%.

[0020] As a preferred improvement of this application, in step five, the sodium alginate-coated nanofiltration membrane is immersed in a calcium chloride aqueous solution for 15 minutes.

[0021] As a preferred improvement of this application, in step five, the mass fraction of the calcium chloride aqueous solution is 1%-5%.

[0022] The beneficial effects of this application are as follows:

[0023] (1) Compared with the prior art, the preparation method provided in this application is simple to operate and the composite membrane has excellent performance;

[0024] (2) Because the bonding ability between the separation layer and the support layer is enhanced by blending styrene maleic anhydride (SMA) with the matrix, the prepared composite nanofiltration membrane has the characteristics of high water flux, strong bonding force and pH response.

[0025] (3) It has good development prospects in water treatment processes for drinking water purposes. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] This application provides a method for preparing a pH-responsive loose nanofiltration membrane, comprising the following steps:

[0028] Step 1: Prepare an alkaline solution with a sodium hydroxide mass fraction of 5%, and immerse styrene maleic anhydride in the alkaline solution for hydrolysis for more than 12 hours to obtain carboxyl-terminated styrene maleic anhydride.

[0029] Step 2: Dissolve carboxyl-terminated styrene maleic anhydride, pore-forming agent and polymer membrane material in an organic solvent, mechanically stir to prepare homogeneous membrane building solution, and allow the homogeneous membrane building solution to stand under vacuum to remove bubbles for later use.

[0030] Step 3: Use the phase inversion method to prepare a surface carboxylated ultrafiltration membrane from the deaerated homogeneous casting solution.

[0031] Step 4: The sodium alginate aqueous solution is filtered under negative pressure on the surface of the ultrafiltration base membrane to obtain a sodium alginate coated nanofiltration membrane.

[0032] Step 5: Immerse the sodium alginate-coated nanofiltration membrane in a calcium chloride aqueous solution for a certain period of time to obtain a pH-responsive loose nanofiltration membrane through a double crosslinking reaction.

[0033] In step one, the styrene-maleic anhydride is a polymer with an anhydride content of 10% or more. The styrene-maleic anhydride is immersed in an alkaline solution for 24 hours for hydrolysis.

[0034] In step two, the pore-forming agent is one or a mixture of polyethylene glycol and polyvinylpyrrolidone. The polymer membrane material is any one of polyethersulfone, polysulfone, and polyvinylidene fluoride. The organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

[0035] The polymer membrane material contains carboxyl-terminated styrene maleic anhydride, a pore-forming agent, and an organic solvent at mass percentages of 15-20%, 0.5-8%, 2-12%, and 63-80%, respectively.

[0036] In step four, the sodium alginate aqueous solution has a mass fraction of 0.5%-10%.

[0037] In step five, the sodium alginate-coated nanofiltration membrane is immersed in a calcium chloride aqueous solution for 15 minutes. Specifically, the calcium chloride aqueous solution has a mass fraction of 1%-5%.

[0038] It should be further noted that sodium alginate (SA), with its surface rich in oxygen-containing groups (-OH, -COOH, and =O), is deposited on the nanofiltration membrane surface. Both hydroxyl (-OH) and carboxyl (-COOH) groups can react with Ca. 2+ Rapid ion exchange occurs, ultimately through calcium ions (Ca). 2+ The carboxyl groups and sodium alginate coating on the surface of the double cross-linked nanofiltration membrane form a three-dimensional interconnected hydrogel network, thus obtaining a pH-responsive loose nanofiltration membrane.

[0039] The preparation method of the pH-responsive loose nanofiltration membrane provided in this application will be described in detail below with reference to specific embodiments 1-4.

[0040] Example 1

[0041] Example 1 provides a method for preparing a pH-responsive loose nanofiltration membrane, the specific steps of which are as follows:

[0042] 1) Preparation of casting solution: 20g of polyethersulfone, 5g of carboxyl-terminated styrene maleic anhydride and 5g of polyethylene glycol-800 were added to 70g of DMAC organic solution, heated to 80℃ and stirred to obtain a homogeneous casting solution.

[0043] 2) Vacuum settling and degassing: The above casting solution is kept under heating and vacuum is applied, and stirring is stopped to perform degassing treatment;

[0044] 3) Preparation of the base membrane: The above casting solution was used to prepare an ultrafiltration base membrane by phase inversion method, and then placed in deionized water for later use;

[0045] 4) Pre-preparation of nanofiltration membrane: Prepare a 2% sodium alginate aqueous solution and apply it to the surface of the ultrafiltration membrane by negative pressure suction.

[0046] 5) Preparation of loose nanofiltration membrane: Prepare a calcium chloride aqueous solution with a mass fraction of 0.5%, immerse the ultrafiltration base membrane from step 4 in the calcium chloride aqueous solution, and obtain a loose nanofiltration membrane after crosslinking for 15 minutes.

[0047] Example 2

[0048] Example 2 provides a method for preparing a pH-responsive loose nanofiltration membrane, the specific steps of which are as follows:

[0049] 1) Preparation of casting solution: 20g of polyethersulfone, 5g of carboxyl-terminated styrene maleic anhydride and 5g of polyethylene glycol-800 were added to 70g of DMAC organic solution, heated to 80℃ and stirred to obtain a homogeneous casting solution.

[0050] 2) Vacuum settling and degassing: The above casting solution is kept under heating and vacuum is applied, and stirring is stopped to perform degassing treatment;

[0051] 3) Preparation of the base membrane: The above casting solution was used to prepare an ultrafiltration base membrane by phase inversion method, and then placed in deionized water for later use;

[0052] 4) Pre-preparation of nanofiltration membrane: Prepare a 5% sodium alginate aqueous solution and apply it to the surface of the ultrafiltration base membrane by negative pressure suction.

[0053] 5) Preparation of loose nanofiltration membrane: Prepare a calcium chloride aqueous solution with a mass fraction of 1%, immerse the ultrafiltration base membrane from step 4 in the calcium chloride aqueous solution, and obtain the loose nanofiltration membrane after crosslinking for 15 minutes.

[0054] Example 3

[0055] Example 3 provides a method for preparing a pH-responsive loose nanofiltration membrane, the specific steps of which are as follows:

[0056] 1) Preparation of casting solution: 20g polyethersulfone, 5g carboxyl-terminated styrene maleic anhydride and 5g polyvinylpyrrolidone were added to 70g DMAC organic solution, heated to 80℃ and stirred to obtain homogeneous casting solution.

[0057] 2) Vacuum settling and degassing: The above casting solution is kept under heating and vacuum is applied, and stirring is stopped to perform degassing treatment;

[0058] 3) Preparation of the base membrane: The above casting solution was used to prepare an ultrafiltration base membrane by phase inversion method, and then placed in deionized water for later use;

[0059] 4) Pre-preparation of nanofiltration membrane: Prepare a 3% sodium alginate aqueous solution and apply it to the surface of the ultrafiltration base membrane by negative pressure suction.

[0060] 5) Preparation of loose nanofiltration membrane: Prepare a calcium chloride aqueous solution with a mass fraction of 1%, immerse the ultrafiltration base membrane from step 4 in the calcium chloride aqueous solution, and obtain the loose nanofiltration membrane after crosslinking for 15 minutes.

[0061] Example 4

[0062] Example 4 provides a method for preparing a pH-responsive loose nanofiltration membrane, the specific steps of which are as follows:

[0063] 1) Preparation of casting solution: 20g polyethersulfone, 5g carboxyl-terminated styrene maleic anhydride and 5g polyvinylpyrrolidone were added to 70g DMAC organic solution, heated to 80℃ and stirred to obtain homogeneous casting solution.

[0064] 2) Vacuum settling and degassing: The above casting solution is kept under heating and vacuum is applied, and stirring is stopped to perform degassing treatment;

[0065] 3) Preparation of the base membrane: The above casting solution was used to prepare an ultrafiltration base membrane by phase inversion method, and then placed in deionized water for later use;

[0066] 4) Pre-preparation of nanofiltration membrane: Prepare a 2% sodium alginate aqueous solution and apply it to the surface of the ultrafiltration membrane by negative pressure suction.

[0067] 5) Preparation of loose nanofiltration membrane: Prepare a calcium chloride aqueous solution with a mass fraction of 0.2%, immerse the ultrafiltration base membrane from step 4 in the calcium chloride aqueous solution, and obtain the loose nanofiltration membrane after crosslinking for 15 minutes.

[0068] The product performance obtained in Examples 1-4 is shown in Table 1 below.

[0069] Table 1 shows the performance parameters of the pH-responsive loose nanofiltration membrane in the examples.

[0070]

[0071] The above experiments show that the prepared pH-responsive loose nanofiltration membrane has a high rejection rate for various dyes, reaching the nanofiltration level. It has a high bonding force between the support layer and the functional layer, and a high permeability to monovalent ions and divalent cations. It can be used in the field of dye desalination. In addition, the composite membrane has excellent permeability and pH response capability. The membrane structure remains intact for a long time under an operating pressure of 0.3 MPa, proving that this method is a feasible way to prepare a pH-responsive loose nanofiltration membrane.

[0072] The beneficial effects of this application are as follows:

[0073] (1) Compared with the prior art, the preparation method provided in this application is simple to operate and the composite membrane has excellent performance;

[0074] (2) Because the bonding ability between the separation layer and the support layer is enhanced by blending styrene maleic anhydride (SMA) with the matrix, the prepared composite nanofiltration membrane has the characteristics of high water flux, strong bonding force and pH response.

[0075] (3) It has good development prospects in water treatment processes for drinking water purposes.

[0076] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0077] Furthermore, it should be noted that the scope of the methods and systems in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions in a substantially simultaneous manner or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0078] The embodiments of this application have been described above, but this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many changes under the guidance of this application without departing from the spirit and scope of the claims, but all such changes should fall within the protection scope of this application.

Claims

1. A method for preparing a pH-responsive loose nanofiltration membrane, characterized in that, Includes the following steps: Step 1: Prepare an alkaline solution with a sodium hydroxide mass fraction of 5%, and immerse styrene maleic anhydride in the alkaline solution for hydrolysis for more than 12 hours to obtain carboxyl-terminated styrene maleic anhydride. Step 2: Dissolve carboxyl-terminated styrene-maleic anhydride, pore-forming agent, and polymer membrane material in an organic solvent, stir to prepare a homogeneous membrane building solution, and allow the homogeneous membrane building solution to stand under vacuum to remove bubbles for later use; the mass percentages of the polymer membrane material, carboxyl-terminated styrene-maleic anhydride, pore-forming agent, and organic solvent are 15-20%, 0.5-8%, 2-12%, and 63-80%, respectively. Step 3: Use the phase inversion method to prepare a surface carboxylated ultrafiltration membrane from the deaerated homogeneous casting solution. Step 4: The sodium alginate aqueous solution is filtered under negative pressure on the surface of the ultrafiltration base membrane to obtain a sodium alginate coated nanofiltration membrane. Step 5: Immerse the sodium alginate-coated nanofiltration membrane in a calcium chloride aqueous solution for a certain period of time. Through the double cross-linking reaction of calcium ions with the carboxyl groups on the surface of the ultrafiltration base membrane and the sodium alginate coating to form a three-dimensional interconnected hydrogel network, a pH-responsive loose nanofiltration membrane is obtained.

2. The method according to claim 1, characterized in that, In step one, the styrene maleic anhydride is a polymer with an anhydride content of 10% or more.

3. The method according to claim 1, characterized in that, In step one, the styrene maleic anhydride is immersed in an alkaline solution for 24 hours for hydrolysis.

4. The method according to claim 1, characterized in that, In step two, the pore-forming agent is one or a mixture of polyethylene glycol or polyvinylpyrrolidone.

5. The method according to claim 1 or 4, characterized in that, In step two, the polymer membrane material is any one of polyethersulfone, polysulfone, and polyvinylidene fluoride.

6. The method according to claim 5, characterized in that, In step two, the organic solvent is N,N-dimethylacetamide or N,N-dimethylformamide.

7. The method according to claim 1, characterized in that, In step four, the sodium alginate aqueous solution has a mass fraction of 0.5%-10%.

8. The method according to claim 1, characterized in that, In step five, the sodium alginate-coated nanofiltration membrane is immersed in a calcium chloride aqueous solution for 15 minutes.

9. The method according to claim 1, characterized in that, In step five, the calcium chloride aqueous solution has a mass fraction of 1%-5%.

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