Preparation method of novel guanidine-based composite nanofiltration flat membrane

Abstract

The application belongs to the technical field of membrane water treatment, and relates to a novel guanidine-based composite nanofiltration flat membrane, a preparation method thereof and application thereof. The preparation method of the guanidine-based composite nanofiltration flat membrane is characterized in that: a polymerization reaction occurs between the amino group of 1,3-diamino guanidine and the acyl chloride group of trimesoyl chloride, and a dense separation layer is formed on the surface of the polyether sulfone ultrafiltration membrane. Under suitable reaction conditions, the guanidine-based composite nanofiltration membrane obtained by the application can realize effective separation of multivalent ions in a wide pH range, the rejection rate of the guanidine-based composite nanofiltration membrane for a 1000ppm MgSO4 solution is as high as 96% or more, and the guanidine-based composite nanofiltration membrane can realize continuous and stable operation in an alkaline ion mixed solution with a pH of 8-9. The guanidine-based composite nanofiltration membrane has the advantages of fewer preparation steps, simple operation, low cost, continuous operation, wide suitable pH range and strong stability.

Description

Technical Field

[0001] This invention belongs to the field of membrane water treatment technology, and relates to a novel guanidine-based composite nanofiltration flat sheet membrane, its preparation method and application. Background Technology

[0002] Nanofiltration is a membrane separation technology driven by pressure difference, with pore sizes of approximately 0.5-2.0 nm. Nanofiltration membranes have charged groups on their surface or within the membrane, and their Donnan effect enables them to separate charged particles, especially divalent and high-valence ions, exhibiting high rejection rates.

[0003] Due to electrostatic interactions, the rejection rate of nanofiltration membranes for multivalent ions decreases with increasing pH, resulting in limited separation efficiency under alkaline conditions. In recent years, numerous studies have introduced amino or imidazole groups into nanofiltration membranes to protonate them and enhance their rejection of Mg2+. 2+ The retention of divalent ions is significant; however, these functional groups have relatively low acid dissociation constants (p0.05). Ka <10), making complete protonation difficult under alkaline conditions. The guanidinium group has the highest p-value. Ka The pH value is 13.8, which allows the membrane to maintain a protonated state over a relatively wide pH range. Introducing guanidine groups to improve the membrane's pH... Ka No Chinese patents have been reported that enable it to operate under a wide range of pH conditions. Existing patent research on introducing guanidine groups into membranes focuses more on the antibacterial and antifouling properties of the membranes. For example, Chinese patent CN113509849A discloses a composite modified membrane based on aminated graphene oxide, polydopamine, and a guanidine antibacterial agent, as well as its preparation method and application. However, existing patents have cumbersome operating procedures and do not specifically address nanofiltration membranes capable of retaining multivalent ions over a wide pH range. 1,3-Diaminoguanidine hydrochloride contains abundant guanidine and amino groups; therefore, directly introducing guanidine groups into the membrane surface can enhance the positive charge of the membrane surface under alkaline conditions, achieving Mg... 2+ Effective retention of isovalent positively charged multivalent ions over a wide pH range. Summary of the Invention

[0004] The purpose of this invention is to provide a method for introducing a dense separation layer rich in guanidine groups to prepare a Mg-retaining agent that is highly efficient under a wide range of pH conditions. 2+ Composite nanofiltration membranes containing polyvalent ions.

[0005] To achieve the above objectives, the present invention has shown that 1,3-diaminoguanidine hydrochloride contains abundant guanidine and amino groups. Therefore, directly introducing guanidine groups into the membrane surface can enhance the positive charge of the membrane surface under alkaline conditions, thereby achieving Mg 2+ Effective retention of isovalent positively charged multivalent ions over a wide pH range.

[0006] This invention provides a method for preparing a guanidine-based composite nanofiltration flat sheet membrane, comprising the following steps:

[0007] 1) Pretreatment of PES ultrafiltration membrane: After ultrasonication, the PES wet membrane is immersed in deionized water for at least 12 hours, and visible water on the surface is removed with a rubber roller;

[0008] 2) Preparation of reaction solution: The aqueous phase solution is prepared with 2-2.5 wt% 1,3-diaminoguanidine hydrochloride, and the oil phase solution is prepared with 0.1-0.3 wt% trimesoyl chloride;

[0009] 3) Preparation of guanidine-based composite nanofiltration membrane: Place the aqueous solution obtained in step 2), i.e., the 1,3-diaminoguanidine hydrochloride solution, on the surface of the PES ultrafiltration membrane described in step 1), shake well, quickly adjust the pH to 11.2-11.5, react for 1 minute, pour out the solution and absorb the visible water on the membrane surface, add the oil phase solution obtained in step 2), react for 1-2 minutes, then pour out the oil phase solution and place it in an oven to dry; "quickly" means adjusting the pH immediately, for example within 10 seconds, preferably within 5 seconds;

[0010] After cooling to room temperature, rinse the surface of the guanidine-based composite nanofiltration membrane with deionized water to obtain the guanidine-based composite nanofiltration sheet membrane.

[0011] Preferably, in step 1), the PES wet film is a PES film immersed in a sodium bisulfite solution.

[0012] Preferably, in step 1), the rubber roller is rolled 1-2 times.

[0013] Preferably, in step 2), the aqueous solution is a guanidine salt aqueous solution, which is prepared and used immediately.

[0014] Preferably, in step 2), the oil phase solution uses n-hexane as the solvent.

[0015] Preferably, in step 3), the pH is adjusted using a 10wt% NaOH solution.

[0016] Preferably, in step 3), the room temperature is 20°C.

[0017] Preferably, in step 3), the TMC is ultrasonicated for 1-3 minutes before use, and the ultrasonic water temperature is kept constant at 20 ℃, with a fluctuation of no more than 1 ℃.

[0018] Preferably, in step 3), after pouring out the aqueous solution and absorbing the visible water on the membrane surface, TMC is added, and this process is controlled within 1 minute.

[0019] Accordingly, the present invention provides a guanidine-based composite nanofiltration sheet membrane, which forms a separation layer on the surface of a PES ultrafiltration membrane. The separation layer is a dense separation layer of the nanofiltration membrane prepared by interfacial polymerization of the amino group of 1,3-diaminoguanidine and the acyl chloride group of trimesoyl chloride.

[0020] This invention introduces the guanidine group into the separation layer of a polyamide nanofiltration membrane by interfacial polymerization of the amino group of 1,3-diaminoguanidine with the acyl chloride group of TMC, thereby effectively enhancing the protonation of the membrane surface.

[0021] The guanidine-based composite nanofiltration sheet membrane described in this invention is used for the efficient retention of divalent and high-valent ions such as MgSO4. The guanidine-based composite nanofiltration membrane prepared by this invention has a retention rate of over 96% for 1000 ppm MgSO4 solution, while the retention rate for monovalent ions such as 1000 ppm NaCl solution is only 42%, and it can operate continuously and stably in alkaline ion mixed solutions with a pH of 8-9.

[0022] Specifically, the preparation method of the novel guanidine-based composite nanofiltration flat sheet membrane of the present invention includes the following steps:

[0023] 1) Pretreatment of polyethersulfone (PES) ultrafiltration membrane: After sonication for several minutes, soak in continuously replenished deionized water for at least 12 hours, remove visible water from the surface with a rubber roller, and place in a self-made reaction device (the size can be selected as needed, such as a square frame with an inner diameter of 6×6cm).

[0024] 2) Preparation of reaction solution: The aqueous phase solution is prepared with 2-2.5 wt% 1,3-diaminoguanidine hydrochloride, and the oil phase solution is 0.2 wt% trimesoyl chloride (TMC).

[0025] 3) Preparation of guanidine-based composite nanofiltration membrane: Place 10 mL of the guanidine salt aqueous solution obtained in step 2) on the surface of the PES membrane described in step 1), shake well, adjust the pH to 11.2-11.5 within 5 seconds, pour out the solution after 1 minute, and absorb the visible water on the membrane surface. Add 5-10 mL of TMC solution and react for 1-2 minutes, then pour out the solution and place in a 60℃ oven for 5 minutes. After cooling to room temperature, rinse the membrane surface with deionized water to obtain the guanidine-based composite nanofiltration membrane.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention uses 1,3-diaminoguanidine hydrochloride, which has a significant price advantage compared to other polyamino monomers, thus reducing preparation costs.

[0028] 2. This invention introduces p Ka The extremely high guanidine group allows it to operate under a wide range of pH conditions. The prepared guanidine composite nanofiltration membrane exhibits a rejection rate of over 96% for 1000 ppm MgSO4 solution. Attached Figure Description

[0029] 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.

[0030] Picture 1 This is a flowchart illustrating the preparation method of a novel guanidine-based composite nanofiltration sheet membrane proposed in this invention.

[0031] Picture 2 This is a SEM image of a commercial PES film under a scanning electron microscope at 20,000x magnification.

[0032] Picture 3 This is a SEM image of the guanidine-based composite nanofiltration membrane of the present invention under a scanning electron microscope at 20,000x magnification. Detailed Implementation

[0033] This invention provides a novel method for preparing a guanidine-based composite nanofiltration sheet membrane. The method involves a polymerization reaction between the amino group of 1,3-diaminoguanidine and the acyl chloride group of trimesoyl chloride, forming a dense separation layer on the surface of the polyethersulfone ultrafiltration membrane. Under optimal reaction conditions, guanidine hydrolysis is reduced, allowing a large amount of guanidine polymer to be retained on the membrane surface. This utilizes the extremely high p-value of the guanidine group. Ka The properties enable the guanidine-based composite nanofiltration membrane to effectively separate multivalent ions over a wide pH range. The advantages of this invention are that it involves fewer preparation steps, is simple to operate, has low cost, and the prepared polymeric composite nanofiltration membrane can operate continuously, has a wide suitable pH range, and exhibits strong stability.

[0034] 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.

[0035] Example

[0036] like Picture 1 As shown, this invention discloses a method for preparing a novel guanidine-based composite nanofiltration flat sheet membrane, comprising the following steps:

[0037] 1) Pretreatment of PES ultrafiltration membrane; 2) Preparation of reaction solution; 3) Preparation of guanidine-based composite nanofiltration membrane.

[0038] During the pretreatment of the PES ultrafiltration membrane, the wet PES membrane is ultrasonicated for several minutes and then immersed in continuously replenished deionized water for at least 12 hours. Visible surface moisture is removed by rolling with a rubber roller 1-2 times. The membrane is then placed in a self-made reaction apparatus and compacted for fixation. Preferably, the PES ultrafiltration membrane is a wet membrane, immersed in a 1 wt% sodium bisulfite solution. The ultrafiltration membrane has a molecular weight cutoff of 100 kDa. The effective reaction area of ​​the membrane is 36 cm². 2 .

[0039] When preparing the reaction solution, the aqueous phase solution is prepared using 2-2.5 wt% 1,3-diaminoguanidine hydrochloride, and the oil phase is prepared by ultrasonically dissolving 0.1-0.3 wt% trimesoyl chloride (TMC) in n-hexane. The guanidine salt aqueous solution is prepared fresh and used immediately.

[0040] To prepare the guanidine-based composite nanofiltration membrane, 10 mL of the obtained aqueous solution was placed on the surface of the pretreated PES ultrafiltration membrane and shaken well. The pH was rapidly adjusted to 11.2-11.5 within 5 seconds using 10 wt% NaOH. After 1 minute, the solution was poured out, and the visible water on the membrane surface was absorbed. 5-10 mL of sonicated TMC solution was added, and the reaction was repeated for 1-2 minutes. The solution was then poured out again. The aqueous solution was poured out, and the visible water on the membrane surface was absorbed before adding TMC. This process was preferably controlled within 1 minute. The membrane was placed in a 60 ℃ oven for 5 minutes. After cooling to room temperature, the membrane surface was rinsed with deionized water to obtain the guanidine-based composite nanofiltration membrane.

[0041] The main objective of this embodiment is to adopt a low-cost, high-p Ka Dense nanofiltration membranes capable of operating under a wide pH range were prepared by interfacial polymerization of guanidine salts and TMC. The amino group of the guanidine salt reacts with the acyl chloride group of TMC to form a dense nanofiltration membrane separation layer. The introduced guanidine group can remain protonated under alkaline conditions, thereby achieving effective separation of multivalent ions by the guanidine composite nanofiltration membrane under a wide pH range.

[0042] This embodiment uses a customized cross-flow filtration device to test membrane performance; the device has an effective filtration area of ​​6.25 cm². 2 The crossflow velocity is 0.6 L / min, and the operating pressure is 0.6 MPa.

[0043] In this embodiment, the membrane's retention performance was evaluated using 1000 ppm MgSO4, MgCl2, LiCl, and NaCl, respectively. This invention can operate under a wide range of pH conditions. The prepared guanidine-based composite nanofiltration membrane achieved a retention rate of over 96% for 1000 ppm MgSO4 solution.

[0044] Comparative Example

[0045] The retention performance of the guanidine-based composite nanofiltration membrane prepared in the examples was compared with that of the piperazine amide nanofiltration membrane prepared by the same method in Comparative Example 1. The results are shown in Table 1.

[0046] Table 1. Comparison between guanidine-based composite nanofiltration membranes and piperazine amide nanofiltration membranes prepared by the same method.

[0047]

[0048] As can be seen from the test results in Table 1, the guanidine composite nanofiltration membrane in the examples has a higher rejection rate than the piperazine amide nanofiltration membrane (Comparative Example 1) prepared by the same method, with a rejection rate of MgSO4 of over 96%.

[0049] This invention prepares a dense separation layer for nanofiltration membranes by interfacial polymerization of the amino group of 1,3-diaminoguanidine and the acyl chloride group of TMC on the surface of a PES ultrafiltration membrane, achieving a retention rate of over 96% for MgSO4 at 1000 ppm. Simultaneously, the introduction of guanidine groups enhances the protonation of the membrane surface, enabling long-term stable operation in mixed ion solutions at pH 8-9, achieving ion separation under alkaline conditions.

[0050] 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 guanidine-based composite nanofiltration flat sheet membrane, characterized in that, Includes the following steps: 1) Pretreatment of PES ultrafiltration membrane: After ultrasonication, the PES wet membrane is immersed in deionized water for at least 12 hours, and visible water on the surface is removed with a rubber roller; 2) Preparation of reaction solution: The aqueous phase solution is prepared with 2-2.5 wt% 1,3-diaminoguanidine hydrochloride, and the oil phase solution is prepared with 0.1-0.3 wt% trimesoyl chloride; 3) Preparation of guanidine-based composite nanofiltration membrane: Place the aqueous solution obtained in step 2) on the surface of the PES ultrafiltration membrane described in step 1), shake well, and rapidly adjust the pH to 11.2-11.5 within 10 seconds using a 10wt% NaOH solution. After 1 minute, pour out the aqueous solution and absorb the visible water on the membrane surface. Then, add the oil phase solution obtained in step 2), react for 1-2 minutes, pour out the oil phase solution, place it in an oven to dry, and after cooling to room temperature, rinse the surface of the guanidine-based composite nanofiltration membrane with deionized water to obtain the guanidine-based composite nanofiltration sheet membrane.

2. The method for preparing the guanidine-based composite nanofiltration flat sheet membrane according to claim 1, characterized in that, In step 1), the PES wet film is a wet film immersed in sodium bisulfite solution.

3. The method for preparing the guanidine-based composite nanofiltration sheet membrane according to claim 1, characterized in that, In step 2), the aqueous solution is prepared and used immediately, and the oil solvent is n-hexane.

4. The method for preparing the guanidine-based composite nanofiltration flat sheet membrane according to claim 1, characterized in that, In step 3), the room temperature is 20°C.

5. The method for preparing the guanidine-based composite nanofiltration sheet membrane according to claim 1, characterized in that, In step 3), the pyromellitic chloride solution is sonicated for 1–3 minutes before use, and the ultrasonic water temperature is kept constant at 20°C.

6. A guanidine-based composite nanofiltration sheet membrane, characterized in that, The guanidine-based composite nanofiltration sheet membrane prepared by the method described in any one of claims 1–5.

7. The application of the guanidine-based composite nanofiltration sheet membrane according to claim 6, characterized in that, The guanidine-based composite nanofiltration sheet membrane has a high rejection rate for multivalent ions, and the salt of the multivalent ions is MgSO4.

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