A flat plate nanofiltration membrane preparation method based on chemical bubble to improve membrane flux

Abstract

This invention belongs to the field of membrane water treatment, and particularly relates to a nanofiltration flat sheet membrane and its preparation method based on chemical bubbles to increase membrane flux. The nanofiltration flat sheet membrane preparation method of this invention includes pretreatment of a PES ultrafiltration membrane, preparation of aqueous and oil phase reaction solutions, and a method for preparing a nanofiltration membrane with increased membrane flux through bubble formation, thereby obtaining a nanofiltration membrane with increased membrane flux through bubble formation. On the surface of the PES ultrafiltration membrane, a polymerization reaction occurs between the amino group of 1,3-diaminoguanidine and the acyl chloride group of trimesoyl chloride under alkaline conditions, simultaneously generating a large number of continuous nanobubbles. This promotes the polymerization reaction to proceed within numerous released bubbles, thereby forming a porous surface structure, increasing the effective filtration surface of the membrane, and optimizing the water molecule transport path. The dense surface layer of the high-molecular-weight polyamide can achieve the retention of multivalent ions, while the porous structure reduces membrane resistance and increases membrane flux. The advantages of this invention are that compared with traditional methods of introducing physical bubbles such as ultrasound and heat, it eliminates cumbersome steps and is simple to operate and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of membrane water treatment technology, and relates to a method for preparing nanofiltration flat sheet membranes, and more particularly to a nanofiltration flat sheet membrane based on chemical bubbles to improve membrane flux and its preparation method. Background Technology

[0002] Nanofiltration membranes, with pore sizes typically ranging from 0.5 to 2 nm, are functionally selective semi-permeable membranes that allow certain low-molecular-weight compounds and other small molecules or low-valence ions to pass through. They are named for the nanometer-sized substances they can retain. They are now widely used in wastewater treatment in fields such as seawater desalination, metal recovery, pharmaceuticals, food processing, and textiles.

[0003] The trade-off effect between water flux and rejection rate in nanofiltration membranes limits their ability to maintain high flux while retaining high rejection. Introducing nanobubbles during nanofiltration membrane fabrication can effectively loosen the membrane structure, thereby increasing membrane flux. Compared to the cumbersome steps of introducing physical bubbles through ultrasound, heat, etc., the reaction of guanidine compounds under alkaline conditions to release a large number of chemical nanobubbles can simply and efficiently improve membrane flux.

[0004] Existing research on membrane preparation using guanidine compounds mostly focuses on antibacterial and antifouling properties. Chinese patent application CN110433675A discloses a guanidine-functionalized graphene oxide / polysulfone ultrafiltration membrane and its preparation method. The ultrafiltration membrane prepared by this invention can improve the pure water flux of the membrane to a certain extent, has high antimicrobial performance, and increased antifouling performance. However, the steps are complicated and not easy to operate. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing nanofiltration flat sheet membranes that introduces nanobubbles during interfacial polymerization to achieve a high membrane rejection rate while simultaneously loosening the separation layer structure to improve membrane flux.

[0006] 1,3-Diaminoguanidine hydrochloride contains both guanidine and amino groups. The guanidine groups react under alkaline conditions to generate numerous nanobubbles. Furthermore, the amino groups can react with the acyl chloride groups of trimesoyl chloride to form a dense amide layer. During interfacial polymerization of the nanofiltration membrane, the membrane interface is continuously impacted by the generated nanobubbles while forming polyamide, causing the dense separation layer to become porous. The introduction of nanobubbles increases the effective filtration area of ​​the membrane, optimizes the water molecule transport path, and achieves both high retention and high flux in the nanofiltration membrane. This invention is based on the above research.

[0007] This invention provides a method for preparing a nanofiltration flat sheet membrane based on chemical bubbles to improve membrane flux, comprising the following steps:

[0008] 1) Pretreatment of PES ultrafiltration membrane: Immerse the commercial PES ultrafiltration membrane in regularly replaced deionized water for at least 12 hours, remove visible water from the membrane surface with a rubber roller, and fix it in a square reaction device with an inner diameter of 6 × 6 cm.

[0009] 2) Preparation of reaction solution: The aqueous phase solution is 2.5-3 wt% 1,3-diaminoguanidine hydrochloride, the oil phase is 0.1-0.3 wt% trimesoyl chloride (TMC), and the solvent is n-hexane;

[0010] 3) Preparation method of nanofiltration membrane with increased bubble flux: Adjust the pH of the 10 mL diaminoguanidine hydrochloride solution prepared in step 2) to 11.2-11.5 with NaOH, shake well, and then place it on the surface of the PES membrane described in step 1). Shake evenly, pour out the solution after a certain period of time, and roll the visible water on the membrane surface with a rubber roller; add 5-10 mL TMC and react for 1-4 min, pour out the solution and place it in a 60 ℃ oven for 5 min to obtain the nanofiltration membrane with increased bubble flux.

[0011] Preferably, the dried nanofiltration membrane is cooled and cleaned, for example, cooled to room temperature, and then the membrane is removed and rinsed with deionized water.

[0012] The reaction apparatus used in this invention can be any conventional reaction apparatus in the art, and can be a reaction apparatus of various shapes capable of fixing nanofiltration membranes. Preferably, in step 1), the reaction apparatus is square with an inner diameter of 6 × 6 cm.

[0013] Preferably, in step 2), the solution temperature is controlled at 20 ℃, and the solution is prepared and used immediately.

[0014] Preferably, in step 3), the room temperature is 18-23°C, more preferably 20°C.

[0015] Preferably, in step 3), the TMC is ultrasonicated for 2-5 minutes before use, and the ultrasonic water temperature is kept constant at 20°C.

[0016] Preferably, in step 3), the aqueous solution is immersed on the membrane surface for 1-4 minutes.

[0017] This invention provides a nanofiltration membrane in which a loose and porous polyamide layer is formed on the surface of a PES ultrafiltration membrane by continuously generating nanobubbles.

[0018] This invention utilizes the reaction of 1,3-diaminoguanidine hydrochloride under alkaline conditions to generate uniform nanobubbles. The polymerization of these nanobubbles at the interface between the amino group and the acyl chloride group of TMC alters the structure of the nanofiltration membrane separation layer, making it porous and effectively increasing the effective filtration area and optimizing the water molecule transport pathway. This increases membrane flux without altering the rejection rate. Its dense polyamide layer effectively retains multivalent ions, achieving a rejection rate of over 92% for 1000 ppm MgSO4, with a water flux of 53.29-59.57 L / m³. 2 The efficiency (·h) was increased by 4.07 - 10.56 L / m compared to when a small number of nanobubbles were generated under the same conditions. 2 The efficiency of nanobubble release was increased by 10.60 - 20.33 L / m² compared to the same conditions. 2 ·h.

[0019] The nanofiltration membrane of the present invention improves water flux under conditions of high rejection rate.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention uses 1,3-diaminoguanidine hydrochloride, which can react to generate nanobubbles under alkaline conditions. The amino group can participate in the polymerization reaction to achieve simultaneous gas-generating polymerization, resulting in strong functionality.

[0022] 2. This invention incorporates chemical nanobubbles, which are generated by their own reaction, thus reducing the cumbersome steps associated with physical bubbles and other additives. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, each drawing described below is for a part of the embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the preparation process of a nanofiltration flat sheet membrane based on chemical bubbles to improve membrane flux, as proposed in this invention.

[0025] Figure 2 This is a SEM image of a commercial PES film under a scanning electron microscope at 20,000x magnification.

[0026] Figure 3 This is a SEM image of a nanofiltration flat sheet membrane with increased membrane flux based on chemical bubbles, as described in the present invention, under a scanning electron microscope at 20,000x magnification. Detailed Implementation

[0027] This invention provides a method for preparing nanofiltration flat-sheet membranes based on chemical bubbles to improve membrane flux. On the surface of a PES ultrafiltration membrane, a large number of continuous nanobubbles are generated simultaneously through a polymerization reaction between the amino groups of 1,3-diaminoguanidine and the acyl chloride groups of trimesoyl chloride under alkaline conditions. This process promotes the polymerization reaction within numerous released bubbles, forming a porous surface structure, increasing the effective filtration area of ​​the membrane, and optimizing the water molecule transport path. The high density of the polyamide allows for the retention of multivalent ions, while the porous structure reduces membrane resistance and increases membrane flux. The advantages of this invention are that compared to traditional methods of introducing physical bubbles such as ultrasound and heat, it eliminates cumbersome steps and is simple and easy to implement.

[0028] The technical solution will be clearly and completely described below through embodiments of this application. Obviously, the described embodiments are only some preferred embodiments of this application, and 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 protection scope of this application.

[0029] Example 1

[0030] like Figure 1 As shown, this invention discloses a method for preparing a nanofiltration flat sheet membrane with improved membrane flux based on chemical bubbles, comprising the following steps:

[0031] 1) Pretreatment of PES ultrafiltration membrane: Immerse the commercial PES ultrafiltration membrane in regularly replaced deionized water for at least 12 hours, roll it 1-2 times with a rubber roller to remove visible water from the membrane surface, and fix it in a reaction apparatus with an inner diameter of 6 × 6 cm; the commercial PES membrane is a wet membrane with a molecular weight cutoff of 100 kDa and an effective polymerization area of ​​36 cm². 2 ;

[0032] 2) Preparation of reaction solution: The aqueous phase solution is 2.5-3 wt% 1,3-diaminoguanidine hydrochloride, and the oil phase is 0.1-0.3 wt% trimesoyl chloride (TMC), with n-hexane as solvent;

[0033] 3) Preparation method of nanofiltration membrane with bubble-enhanced membrane flux: Adjust the pH of 10 mL of the diaminoguanidine hydrochloride solution prepared in step 2) to 11.2-11.5 with NaOH, shake well, and then place it on the surface of the PES membrane described in step 1). Shake evenly, and after a certain period of time, pour out the solution and roll the visible water on the membrane surface with a rubber roller; add 5-10 mL of TMC and react for 1-4 min, pour out the solution and place it in a 60 ℃ oven for 5 min. After the dried membrane cools to room temperature, remove the membrane and rinse it with deionized water to obtain the nanofiltration membrane with bubble-enhanced membrane flux. The aqueous phase solution is immersed on the membrane surface for 1-4 min, and all solutions are kept at 20 ℃.

[0034] The obtained nanofiltration membrane was visualized using a scanning electron microscope at 20,000x magnification, as shown in the image. Figure 2 As shown.

[0035] The main purpose of this embodiment is to introduce nanobubbles while generating a dense separation layer through the interfacial polymerization of amino and acyl chlorides. The two are effectively combined to increase the loose structure inside the membrane, thereby achieving both high retention and high throughput.

[0036] This embodiment uses a customized cross-flow filtration device for membrane performance testing. The effective filtration area of ​​the device is 6.25 cm². 2 The crossflow velocity is 0.6 L / min, and the operating pressure is 0.6 MPa.

[0037] Comparative Example

[0038] In this embodiment, deionized water, 1000 ppm NaCl, and MgSO4 were used to evaluate the membrane flux and the retention performance of monovalent / multivalent ions.

[0039] The performance of the nanofiltration membrane with improved membrane flux based on chemical bubbles prepared in the examples was compared with that of Comparative Example 1 (nanofiltration membrane prepared by generating a small number of nanobubbles under the same conditions) and Comparative Example 2 (nanofiltration membrane prepared by fully releasing nanobubbles under the same conditions). The results are shown in Table 1.

[0040] Table 1. Performance comparison of nanofiltration membranes with chemically enhanced membrane flux and those with minimal or complete bubble generation.

[0041]

[0042] As shown in Table 1, the nanofiltration membrane with improved membrane flux due to chemical bubbles in Example 1, compared with the nanofiltration membrane prepared by generating a small number of nanobubbles under the same conditions (Comparative Example 1) and the nanofiltration membrane prepared by fully releasing nanobubbles under the same conditions (Comparative Example 2), has a basically the same rejection rate, but its membrane flux is significantly improved, increasing by 10.60 - 20.33 L / m compared with the nanofiltration membrane prepared by fully releasing nanobubbles under the same conditions. 2 ·h.

[0043] This invention utilizes the reaction of 1,3-diaminoguanidine under alkaline conditions to generate a large number of nanobubbles. These nanobubbles continuously impact the surface layer while the amino-acyl chloride forms the polyamide separation layer, loosening the membrane structure and increasing membrane flux without altering the retention performance of the separation layer. After the introduction of nanobubbles, the nanofiltration membrane achieves a retention rate of over 92% for 1000 ppm MgSO4, and the water flux is increased by 10.60 - 20.33 L / m compared to nanofiltration membranes with fully released nanobubbles. 2 The embodiments described above are merely specific implementations of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in this application without creative effort should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims in this application.

Claims

1. A method for preparing a nanofiltration flat sheet membrane, characterized by, Includes the following steps: 1) Pretreatment of PES ultrafiltration membrane: Immerse the PES ultrafiltration membrane in regularly replaced deionized water to remove visible water from the membrane surface and then fix it in the reaction device; 2) Preparation of reaction solution: The aqueous phase solution is 2.5-3 wt% of 1,3-diaminoguanidine hydrochloride, and the oil phase is 0.1-0.3 wt% of trimesoyl chloride; 3) Preparation method of nanofiltration membrane with bubble-enhanced membrane flux: Adjust the pH of the aqueous solution obtained in step 2) to 11.2-11.5 with NaOH, shake well, then place it on the surface of the PES ultrafiltration membrane obtained in step 1), shake well, then pour out the liquid and remove the visible solution on the membrane surface with a rubber roller; add TMC and react for 1-4 min, pour out the solution and dry it to obtain the PES ultrafiltration membrane with bubble-enhanced membrane flux.

2. The method for preparing a nanofiltration flat sheet membrane according to claim 1, characterized in that, In step 1), PES is a wet film, which is immersed in a 1wt% sodium bisulfite solution.

3. The method for preparing a nanofiltration flat sheet membrane according to claim 1, characterized by, In step 2), the oil phase solvent is n-hexane.

4. The method for preparing a nanofiltration flat sheet membrane according to claim 1, characterized by, In step 2), the aqueous solution is prepared and used immediately.

5. The method for preparing a nanofiltration flat sheet membrane according to claim 1, wherein, In step 3), the room temperature is 20 ℃.

6. The method for preparing a nanofiltration flat sheet membrane according to claim 1, wherein, In step 3), the TMC is used for 2-5 minutes of ultrasound before use, and the ultrasound water temperature is kept constant at 20 ℃.

7. The method for preparing a nanofiltration flat sheet membrane according to claim 1, characterized in that, In step 3), the aqueous solution is immersed on the membrane surface for 1-4 minutes.

8. A nanofiltration flat sheet membrane prepared by the preparation method according to claim 1, characterized in that, A loose polyamide layer is formed on the surface of the PES ultrafiltration membrane by continuously generating nanobubbles.

9. The application of the nanofiltration flat sheet membrane according to claim 8, characterized in that, The nanofiltration membrane described above increases membrane flux under conditions of high rejection rate.

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