A preparation method of a ppta composite nanofiltration membrane with a hydrogel mosaic structure for optimizing pore size

Abstract

The application discloses a preparation method of a PPTA composite nanofiltration membrane with a pore size optimized by using a hydrogel mosaic structure. Compared with a PPTA composite nanofiltration membrane without the pore size optimized by the hydrogel mosaic structure, the PPTA nanofiltration membrane prepared by the application has a significantly improved pore size distribution and structural stability under the optimization of the hydrogel mosaic structure, and the permeation flux and the rejection are significantly improved. The pore size optimized nanofiltration membrane prepared by the application can be used in the field of membrane separation, for example, in the water treatment industry for drinking water purification, industrial water treatment, seawater desalination and wastewater treatment, and the water quality is improved to meet the requirements of different uses. The pore size optimized nanofiltration membrane can also be used in the fields of biopharmaceuticals and chemical dyes, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water treatment filtration membranes, and particularly relates to a preparation method of a PPTA composite nanofiltration membrane with a pore size optimized by a hydrogel mosaic structure. BACKGROUND

[0002] Water treatment filtration membranes are widely used in food processing, water treatment in the field of environmental protection, industrial production and other aspects as an important technology. The pore size of nanofiltration membranes is usually 0.5-2nm, so it can effectively remove multivalent ions, organic matter, trace pollutants and the like in water while allowing monovalent ions to pass through. At present, nanofiltration membranes have been widely used in the field of water treatment. PPTA nanofiltration membranes are widely used in the preparation of softened drinking water, and the nanofiltration technology is used for softening treatment of high-hardness island brackish water, and the water quality after treatment can reach the drinking water standard.

[0003] Nanofiltration membranes are special filtration membranes with high selectivity and high migration rate. The existing preparation methods of nanofiltration membranes are various, mainly including interfacial polymerization, blending, coating, layer-by-layer self-assembly and thermal-induced phase separation. The layer-by-layer self-assembly method is simple to operate, and various polyelectrolytes can be selected as film-forming materials to adjust the properties and functions of the membrane, and the thickness of the membrane is controllable. The thickness and performance of the membrane can be accurately controlled by controlling the number of deposited layers, but when the number of layers is too large, the separation performance and stability of the membrane will be affected. The nanofiltration membranes prepared by the interfacial polymerization method have the advantages of mild preparation conditions, high production efficiency, asymmetric pore size distribution, accurate control of surface performance and the like. In addition to the preparation of nanofiltration membranes, the interfacial polymerization method is also used for the preparation of composite membranes. At present, the pore size of the base membrane prepared by using PEG as a pore former is uneven, which is a major difficulty for the application of PPTA porous membranes in water treatment and the like. Therefore, developing a stable method for modifying the pore size has great significance for the application of PPTA membranes.

[0004] Nanofiltration membrane is the core of nanofiltration process, and the essence of preparing nanofiltration membrane is to construct nanoscale pores on the surface of support material by a certain way, so as to endow it with nanofiltration function. Interface polymerization technology is widely used due to its convenient, efficient and stable technical advantages. The nanofiltration membrane prepared by the interface polymerization technology is composed of a selective separation membrane and a base membrane, and has the characteristics of strong stability, high water flux and easy industrial production. The traditional interface polymerization technology is to use polyamine monomers and acyl chloride monomers dissolved in oil-water two phases to carry out condensation reaction on the surface of a microfiltration or ultrafiltration porous base membrane, so as to form a dense polyamide film with a thickness of 50-100 nm. The film is solidified on the surface of the base membrane and plays a selective separation role. However, the TFC nanofiltration membrane still faces the problem of membrane performance (permeability, selectivity, anti-fouling property, etc.), which will directly affect the separation efficiency and application cost of the nanofiltration membrane, and further determine the future application prospect of the nanofiltration membrane. Therefore, researchers have made great efforts and achieved many results in developing high-performance TFC nanofiltration membranes around the interface polymerization technology. SUMMARY

[0005] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments.

[0006] As one aspect of the present application, a preparation method of a PPTA composite nanofiltration membrane with pore size optimized by hydrogel mosaic structure is provided, which comprises the following steps,

[0007] Step 1: A poly-p-phenylene terephthalamide nanofiltration membrane base membrane is subjected to a pressure of 2.5N-4.0MPa, and is immersed in a 4N-10wt% precursor solution, and the treatment time is 2-8min, to obtain a PPTA porous membrane; the precursor solution comprises a titanate or silicate;

[0008] Step 2: The PPTA porous membrane obtained in step 1 is placed in an 80-95% ethanol solution for hydrolysis, to obtain a pore size modified PPTA porous membrane;

[0009] Step 3: A layer of silane coupling agent solution is coated on the surface of the pore size modified PPTA porous membrane obtained in step 2;

[0010] Step 4: Piperazine-2-carboxylic acid and sodium hydroxide are dissolved in water to obtain an aqueous solution, and trimesoyl chloride and n-heptane are mixed to obtain an oil solution; the membrane treated in step 3 is sequentially immersed in the aqueous solution, the oil solution and the aqueous solution for interface polymerization reaction; and then washed and dried, to obtain a PPTA composite nanofiltration membrane with pore size optimized by hydrogel mosaic structure.

[0011] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with pore size optimized by hydrogel mosaic structure, the poly-p-phenylene terephthalamide nanofiltration membrane base membrane uses PET non-woven fabric as a support layer.

[0012] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, the precursor solution is a tetraethyl titanate anhydrous ethanol solution, and the concentration of the precursor solution is 5-8 wt%.

[0013] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 2, the hydrolysis time is 3-5 h.

[0014] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 3, the silane coupling agent includes one of KH-550, KH-570, and KH-602.

[0015] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 3, the concentration of the silane coupling agent solution is 0.5-1 wt%.

[0016] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 4, the membrane treated in step 3 is sequentially immersed in a water phase solution for 2-3 min, an oil phase solution for 2-3 min, and a water phase solution for 2-3 min.

[0017] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 4, the molar ratio of piperazine-2-carboxylic acid to sodium hydroxide is 1:1, and the mass concentration of piperazine-2-carboxylic acid is 0.5-1 wt%.

[0018] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 4, the concentration of trimesoyl chloride is 0.1-0.2 wt%.

[0019] As a preferred scheme of the preparation method of the PPTA composite nanofiltration membrane with optimized pore size by using the hydrogel mosaic structure, in step 4, the washing includes washing with ethanol.

[0020] The present invention has the following beneficial effects: Compared to PPTA composite nanofiltration membranes without mosaic structure pore size optimization, the pore size distribution and structural stability of the PPTA nanofiltration membrane prepared by the present invention are significantly improved due to the optimized hydrogel mosaic structure, and both permeation flux and retention are significantly improved. The nanofiltration membrane with optimized pore size prepared by the present invention can be used in the field of membrane separation, for example, in the water treatment industry for drinking water purification, industrial water treatment, seawater desalination, and wastewater treatment, improving water quality to meet the needs of various applications. It can also be used in the biopharmaceutical field and the chemical dye industry, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, wherein:

[0022] Figure 1 This is a picture of the PPTA composite nanofiltration membrane prepared in Example 4. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0024] Example 1:

[0025] A method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure comprises the following steps:

[0026] (1) Prepare a PPTA (poly(p-phenylene terephthalamide)) base film supported by PET non-woven fabric according to a standardized process (refer to "Preparation and Characterization of Poly(p-phenylene terephthalamide) Porous Membranes", Wang Chun, 2014). The base film thickness is 300 μm.

[0027] (2) The PPTA base film was fixed in a pressurizing device, the nitrogen pressurizing pressure was set to 4.0 MPa, and an anhydrous ethanol solution of tetraethyl titanate with a tetraethyl titanate concentration of 5.0 wt% was pressed into the membrane pool. The solution penetration time was 6 min to obtain a PPTA porous membrane;

[0028] (3) placing the completely permeated PPTA porous membrane obtained in step (2) in a hydrolyzate solution prepared by 80% anhydrous ethanol and 20% deionized water for 3 hours, wherein the water in the hydrolyzate penetrates into the membrane pores and hydrolyzes tetraethyl titanate. As the hydrolysis proceeds, TiO2 hydrogel is formed in the membrane pores;

[0029] (4) After the reaction in step (3) is completed, a layer of 0.5 wt% KH550 silane coupling agent aqueous solution is uniformly coated on the surface of the base film;

[0030] (5) 0.5wt% piperazine-2-carboxylic acid (CPIP) and equimolar ratio of sodium hydroxide were dissolved in pure water to obtain the aqueous solution required for interfacial polymerization (IP) reaction, and 0.1wt% trimesoyl chloride (TMC) was added to n-heptane to obtain the oil phase solution required. The base film was immersed in the aqueous solution for 2 min and then in the oil phase solution for 3 min, and the interfacial polymerization (IP) reaction on the surface of the base film was completed.

[0031] (6) The nanofiltration membrane was washed with anhydrous ethanol, then clamped on a shaping plate for drying treatment, and after completion, immersed in pure water for 12 h to prepare a new nanofiltration membrane with an IP layer polymerized on the basis of optimized pore size; the above experiment was repeated multiple times and corresponding performance tests were carried out. The test results show that the average pore size of the nanofiltration membrane base film with hydrogel inlay structure prepared in this embodiment is 0.16μm, the pore size distribution range is 0.12-0.27μm, the water permeation flux of the PPTA composite nanofiltration membrane is 135Lm -2 h -1 MPa -1 , the water flux attenuation rate after 10 times of measurement is 12%, and the water flux attenuation rate after 15 times of measurement is 16%. The 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 are 90% and 81% respectively under room temperature and pressure of 0.45MPa.

[0032] Step (1) The water permeation flux of the PPTA base film is 326Lm -2 h -1 MPa -1 , the 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 are 24% and 22% respectively under room temperature and pressure of 0.45MPa.

[0033] Example 2:

[0034] A preparation method of a PPTA composite nanofiltration membrane with hydrogel inlay structure for optimizing pore size, comprising the following steps:

[0035] (1) A PPTA (poly-p-phenylene terephthalamide) base film supported by a PET non-woven fabric was prepared according to a standardized process, and the thickness of the base film was 300μm;

[0036] (2) The PPTA base film was fixed in a pressurizing device, and the nitrogen pressurizing pressure was set to 4.0MPa. A titanium tetraethoxide anhydrous ethanol solution with a titanium tetraethoxide concentration of 8.0wt% was pressurized into the membrane pool, and the solution permeation time was 6min to obtain a PPTA porous membrane.

[0037] (3) Put the completely permeated PPTA porous membrane obtained in step (2) into a hydrolysis solution of 80% anhydrous ethanol and 20% deionized water for 3 hours, water in the hydrolysis solution permeates into the membrane pores and hydrolyzes tetraethyl titanate, and TiO2 hydrogel is formed in the membrane pores as the hydrolysis proceeds;

[0038] (4) After the reaction in step (3) is completed, evenly coat a layer of 0.5wt% KH550 silane coupling agent aqueous solution on the surface of the base membrane;

[0039] (5) Dissolve 0.5wt% piperazine-2-carboxylic acid (CPIP) and an equimolar ratio of sodium hydroxide in pure water to obtain an aqueous solution required for interfacial polymerization (IP) reaction, and add 0.1wt% trimesoyl chloride (TMC) to n-heptane to obtain an oil phase solution required. Soak the base membrane into the aqueous solution for 2 minutes first, and then soak it into the oil phase solution for 3 minutes, and the interfacial polymerization (IP) reaction on the surface of the base membrane is completed.

[0040] (6) Wash the nanofiltration membrane with anhydrous ethanol, then clamp it on a shaping plate for drying treatment, and after completion, soak it in pure water for 12 hours to prepare a new nanofiltration membrane with an IP layer polymerized on the basis of optimized pore size; repeat the above experiment multiple times and perform corresponding performance tests, and the test results show that the average pore size of the nanofiltration membrane base membrane with hydrogel inlay structure prepared in this embodiment is 0.275μm, the pore size distribution range is 0.24N0.354μm, and the water permeation flux of the PPTA composite nanofiltration membrane after optimizing the pore size is 116Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements is 11%, and the water flux attenuation rate after 15 measurements is 15%. The 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 are 92% and 83% respectively at room temperature and a pressure of 0.45MPa, and the nanofiltration membrane also has good solvent resistance.

[0041] Compared with Example 1, the solution concentration of the precursor used in Example 2 is higher, which provides sufficient reaction raw materials for the subsequent condensation reaction, and the modification of the large pores in the base membrane is more sufficient, so the water permeation flux is lower than that of Example 1.

[0042] Example 3:

[0043] A preparation method of a PPTA composite nanofiltration membrane with a hydrogel inlay structure for optimizing pore size, comprising the following steps:

[0044] (1) Prepare a PPTA (poly-p-phenylene terephthalamide) base membrane with PET non-woven fabric as support according to a standardized process, and the thickness of the base membrane is 300μm;

[0045] (2) The PPTA base film is fixed in the pressure device, the nitrogen pressure is set to 4.0 MPa, the tetraethyl titanate concentration is 8.0wt%, the tetraethyl titanate anhydrous ethanol solution is pressed into the membrane pool, the solution penetration time is 6 min, and the PPTA porous membrane is obtained;

[0046] (3) The completely penetrated PPTA porous membrane obtained in step (2) is placed in a hydrolysis liquid composed of 80% anhydrous ethanol and 20% deionized water for 3h, water in the hydrolysis liquid penetrates into the membrane pores and hydrolyzes tetraethyl titanate, and TiO2hydrogel is formed in the membrane pores as the hydrolysis proceeds;

[0047] (4) A layer of 0.5wt% KH550 silane coupling agent aqueous solution is uniformly coated on the surface of the base film after the reaction in step (3) is completed;

[0048] (5) 0.5wt% piperazine-2-carboxylic acid (CPIP) and equimolar sodium hydroxide are dissolved in pure water to obtain the aqueous solution required for interfacial polymerization (IP) reaction, and 0.1wt% trimesoyl chloride (TMC) is added to n-heptane to obtain the required oil phase solution. The base film is sequentially immersed in the corresponding solutions in the order of water phase-oil phase-water phase, that is, the base film is sequentially immersed in the water phase solution for 2 min, then in the oil phase solution for 3 min, and then in the water phase solution for 2 min, and the interfacial polymerization (IP) reaction on the surface of the base film is completed;

[0049] (6) The nanofiltration membrane is washed with anhydrous ethanol, then clamped on a shaping plate for drying treatment, and after completion, immersed in pure water for 12h to prepare a new nanofiltration membrane with an IP layer polymerized on the basis of optimized pore size; The above experiment is repeated several times and the corresponding performance test is carried out, and the test shows that the nanofiltration membrane base film with hydrogel inlay structure prepared in this embodiment has an average pore size of 0.253μm, a pore size distribution range of 0.22-0.36μm, and a permeation flux of the PPTA composite nanofiltration membrane after optimization of the pore size is 216Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements is 11%, and the water flux attenuation rate after 15 measurements is 16%. The 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 are 95% and 87% respectively at room temperature and a pressure of 0.45MPa.

[0050] The present embodiment is based on embodiment 2, and the preparation process of interfacial polymerization is carried out in the order of water phase-oil phase-water phase infiltration to prepare the IP layer. Due to the additional water-oil interaction, the IP layer is more fully polymerized on the surface of the base film, and the liquid passes through the wrinkle structure, which is one of the main reasons why the composite nanofiltration membrane prepared in the present embodiment has better rejection and water permeation flux compared with embodiment 1 and embodiment 2.

[0051] Embodiment 4:

[0052] A preparation method of a PPTA composite nanofiltration membrane with a hydrogel mosaic structure to optimize the pore size, comprising the following steps:

[0053] (1) Prepare a PPTA (poly-p-phenylene terephthalamide) base film supported by a PET non-woven fabric according to the standardized process, and the thickness of the base film is 300 μm;

[0054] (2) Fix the PPTA base film in a pressurized device, set the nitrogen pressurization pressure to 4.0 MPa, and press 8.0 wt% tetraethyl titanate in anhydrous ethanol solution into the membrane pool at room temperature, and the solution permeation time is 6 min to obtain a PPTA porous membrane;

[0055] (3) Put the completely permeated PPTA porous membrane obtained in step (2) into a hydrolysis solution of 95 wt% ethanol and 5 wt% deionized water for 3 h, and the water in the hydrolysis solution permeates into the membrane pores and hydrolyzes tetraethyl titanate, and TiO2 hydrogel is formed in the membrane pores as the hydrolysis proceeds;

[0056] (4) Uniformly coat a layer of 0.5 wt% KH550 silane coupling agent aqueous solution on the surface of the base film after the reaction in step (3) is completed;

[0057] (5) Dissolve 0.5 wt% piperazine-2-carboxylic acid (CPIP) and an equimolar ratio of sodium hydroxide in pure water to obtain the aqueous solution required for interfacial polymerization (IP) reaction, and add 0.1 wt% trimesoyl chloride (TMC) to n-heptane to obtain the required oil phase solution. In the order of water phase-oil phase-water phase, the base film is sequentially immersed in the corresponding solution, i.e. the base film is immersed in the water phase solution for 2 min, then in the oil phase solution for 3 min, and then in the water phase solution for 2 min, and the interfacial polymerization (IP) reaction on the surface of the base film is completed;

[0058] (6) The nanofiltration membrane obtained in step (5) is washed with anhydrous ethanol, and then clamped on a shaping plate for drying treatment, and after completion, immersed in pure water for 12 h to obtain a new type of nanofiltration membrane with an IP layer polymerized on the basis of pore size optimization; the above experiment is repeated multiple times and corresponding performance tests are carried out. After testing, the average pore size of the nanofiltration membrane base film prepared in this embodiment with a hydrogel inlaid structure is 0.253 μm, the pore size distribution range is 0.22-0.36 μm, and the water permeation flux of the PPTA composite nanofiltration membrane after optimization of the pore size is 252 Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements is 7%, and the water flux attenuation rate after 15 measurements is 12%. The 30-minute rejection rates of 1 g / L Na2SO4 and 1 g / L MgSO4 are 96.5% and 88.6% respectively under room temperature and pressure of 0.45 MPa, and the nanofiltration membrane exhibits good solvent resistance and acid and alkali corrosion resistance.

[0059] In this embodiment, the ratio of the hydrolysis reaction solution is improved based on Example 3, the proportion of pure water in the reaction solution is reduced to slow down the hydrolysis rate of the precursor, and the gel particles formed by condensation are more uniform, and the stacking and aggregation of the gel particles are reduced. Therefore, how to effectively and uniformly distribute the gel particles in the pore is one of the key links of this experiment.

[0060] Comparative Example 1:

[0061] Compared with Example 4, no pore size modification is performed, and interface polymerization is directly performed on the PPTA porous membrane, i.e., the process of steps (2) and (3) is not performed, and the remaining preparation methods (steps 1, 4, and 6) are the same as those of Example 4.

[0062] After corresponding performance tests, the average pore size of the nanofiltration membrane prepared in this embodiment is 0.483 μm, the pore size distribution range is 0.21-0.68 μm, and the permeation flux of the PPTA composite nanofiltration membrane after optimization of the pore size is 232 Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements is 38%, and the water flux attenuation rate after 15 measurements is 44%. The 30-minute rejection rates of 1 g / L Na2SO4 and 1 g / L MgSO4 are 36% and 34% respectively under room temperature and pressure of 0.45 MPa.

[0063] Since the PPTA porous membrane is not modified with a hydrogel inlaid structure, the large pores originally present on the base film still exist after interface polymerization, although the water permeation flux is good, the rejection performance is poor.

[0064] Comparative Example 2:

[0065] Comparing with Example 4, in which the precursor solution is not pressed into the pores of the PPTA porous membrane by using the pressurized way in step (2), but the PPTA porous membrane is directly immersed into the 8wt% tetraethyl titanate-absolute ethanol solution, i.e. step (2) is not pressurized, and the rest of the preparation method is the same as Example 4.

[0066] Through corresponding performance test, the average pore size of the nanofiltration membrane base membrane prepared in this example is 0.453μm, the pore size distribution range is 0.22-0.65μm, and the permeation flux of the PPTA nanofiltration membrane after optimizing the pore size is 195Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 times of measurement is 37%, the water flux attenuation rate after 15 times of measurement is 42%, and the 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 under the test of room temperature and pressure 0.45MPa are 43% and 37% respectively.

[0067] Because the precursor solution is not pressed into the pores of the PPTA porous membrane by using the pressurized way of bubble point pressure, the condensed TiO2 gel particles only float on the surface of the membrane and do not penetrate into the pores of the membrane to achieve the purpose of optimizing the pore size. Moreover, because part of the gel particles are solidified on the surface of the membrane, the surface of the membrane is uneven, which has adverse effects on the subsequent interfacial polymerization operation.

[0068] In addition, it is found through experimental exploration that the pressurized pressure should be close to or slightly greater than the minimum pore size pressure, and too small pressure cannot press the precursor solution into the pore size.

[0069] Comparative Example 3:

[0070] Comparing with Example 4, the hydrolysis solution (95% absolute ethanol and 5% deionized water mixture) in step (3) is replaced by pure deionized water, and the rest of the conditions and preparation process are the same as Example 4.

[0071] Through corresponding performance test, the average pore size of the nanofiltration membrane base membrane prepared in this example is 0.453μm, the pore size distribution range is 0.22-0.65μm, and the permeation flux of the PPTA nanofiltration membrane after optimizing the pore size is 195Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 times of measurement is 22%, the water flux attenuation rate after 15 times of measurement is 27%, and the 30-minute rejection rates of 1g / L Na2SO4 and 1g / L MgSO4 under the test of room temperature and pressure 0.45MPa are 33% and 27% respectively.

[0072] Because the reaction solution is replaced by pure water, the concentration ratio of the reactants is increased, thereby increasing the reaction rate of the precursor with water, causing the gel particles to stack and aggregate seriously, and the aggregated TiO2 large particles form a blockage in the pore diameter, thereby seriously reducing the water permeation flux.

[0073] In addition, it is found through experiments that the proportion of pure water in the hydrolysis solution is crucial to whether the gel particles can be uniformly distributed in the membrane pores. Too high a water proportion will cause the pore to be blocked.

[0074] Comparative Example 4:

[0075] Compared with Example 4, KH590 silane coupling agent is selected in step (4), and the rest of the conditions and preparation process are the same as those of Example 4.

[0076] Through corresponding performance tests, the nanofiltration membrane base film prepared in this embodiment has an average pore diameter of 0.29 μm, a pore diameter distribution range of 0.20-0.43 μm, and a permeation flux of the PPTA nanofiltration membrane after optimization of the pore diameter is 173 Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements is 13%, and the water flux attenuation rate after 15 measurements is 24%. The 30-minute rejection rates of 1 g / L Na2SO4 and 1 g / L MgSO4 are 82% and 71% respectively under room temperature and pressure of 0.45 MPa

[0077] It is found that the silane coupling agent without amino groups causes insufficient bonding between the IP layer and the PPTA porous layer, which also causes the core performance of the nanofiltration membrane produced in this embodiment to decrease. In addition, it is found through experiments that the silane coupling agent containing amino groups has better adaptability to the PPTA porous membrane and can better connect the membrane layer and the IP layer.

[0078] Comparative Example 5:

[0079] (1) A PPTA (poly-p-phenylene terephthalamide) base film supported by a PET non-woven fabric is prepared, and the base film has a thickness of 300 μm;

[0080] (2) Equal-molar deionized water is added to a tetraethyl titanate anhydrous ethanol solution with a tetraethyl titanate concentration ratio of 5.0 wt%, and the reaction is allowed to stand for 0.5 h;

[0081] (3) The reaction solution in step (2) is filtered to obtain TiO2 hydrogel;

[0082] (4) The gel particles in step (3) are uniformly coated on the surface of the base film, and then air-dried for 2 h;

[0083] (5) 0.5wt% piperazine-2-carboxylic acid (CPIP) and equimolar ratio of sodium hydroxide were dissolved in pure water to obtain the aqueous solution required for interfacial polymerization (IP) reaction, and 0.1wt% trimesoyl chloride (TMC) was added to n-heptane to obtain the oil phase solution required. The treated base film was immersed in the aqueous solution for 2 min and then in the oil phase solution for 3 min, and the interfacial polymerization (IP) reaction on the surface of the base film was completed.

[0084] (6) The nanofiltration membrane was washed with anhydrous ethanol, then clamped on a shaping plate for drying treatment, and after completion, immersed in pure water for 12 h to prepare a new nanofiltration membrane with an IP layer polymerized on the basis of optimized pore size; the above experiment was repeated multiple times and corresponding performance tests were conducted. Through corresponding performance tests, the average pore size of the nanofiltration membrane base film prepared in this embodiment was 0.573 μm, the pore size distribution range was 0.21-0.68 μm, and the permeation flux of the PPTA nanofiltration membrane after optimization of the pore size was 205 Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 measurements was 32%, and the water flux attenuation rate after 15 measurements was 47%. The 30-minute rejection rates of 1 g / L Na2SO4 and 1 g / L MgSO4 were 35% and 32% respectively at room temperature and a pressure of 0.45 MPa.

[0085] The TiO2 gel particles were treated on the surface of the base film in a coating manner without penetrating into the pores of the membrane to achieve the purpose of optimizing the pore size. Moreover, the bonding of the gel particles on the surface was not firm, which caused adverse effects on the subsequent interfacial polymerization operation and preparation, resulting in low rejection rate and poor durability.

[0086] Comparative Example 6:

[0087] Compared with Example 4, i.e. the 8wt% tetraethyl titanate-anhydrous ethanol solution in step (2) was changed to a 12wt% tetraethyl titanate-anhydrous ethanol solution, and the rest of the preparation method was the same as that of Example 4.

[0088] Through corresponding performance tests, the average pore size of the nanofiltration membrane base film prepared in this embodiment was 0.253 μm, the pore size distribution range was 0.14-0.32 μm, and the permeation flux of the PPTA nanofiltration membrane after optimization of the pore size was 75 Lm -2 h -1 MPa -1 , and the rejection rates of 1 g / L Na2SO4 and MgSO4 were 53% and 47% respectively.

[0089] Due to the use of too high concentration of precursor solution, the pore modification of PPTA porous membrane is excessive, not only the large pores are filled, but also the small pore channel space is squeezed, resulting in a serious decline in water permeation flux.

[0090] Comparative Example 7:

[0091] Compared with Example 4, the nitrogen pressure in step (2) is changed from 4.0 MPa to 5.0 MPa, and the rest of the preparation method is the same as Example 4.

[0092] After corresponding performance test, the average pore size of the nanofiltration membrane base film prepared in this embodiment is 0.23 μm, the pore size distribution range is 0.12-0.325 μm, the water permeation flux of the PPTA composite nanofiltration membrane after optimization of the pore size is 172 Lm -2 h -1 MPa -1 The water flux attenuation rate after 10 times of measurement is 18%, the water flux attenuation rate after 15 times of measurement is 23%, the rejection rates of 1 g / L Na2SO4 and 1 g / L MgSO4 are 87.5% and 73.6% respectively, and the solvent resistance is poor.

[0093] Due to the use of too large nitrogen pressure, the precursor solution rushes into the large pores of the PPTA porous membrane at a faster rate, although there is still a certain modification effect, but the large pressure will damage the ridge valley structure of the membrane pores, resulting in a certain decline in durability and solvent resistance.

[0094] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure, characterized by: The following steps are included: Step 1: Applying a pressure of 2.5-4.0 MPa to the poly (p-phenylene terephthalamide) nanofiltration membrane base film and immersing it in a 4-10 wt% precursor solution for 2-8 minutes to obtain a PPTA porous membrane; the precursor solution is an anhydrous ethanol solution of tetraethyl titanate, and the precursor solution concentration is 5-8 wt%; Step 2: placing the PPTA porous membrane obtained in step 1 in an 80-95% ethanol solution for hydrolysis to obtain a PPTA porous membrane with modified pore size; Step 3: coating a layer of silane coupling agent solution on the surface of the pore-modified PPTA porous membrane obtained in step 2; Step 4: dissolving piperazine-2-carboxylic acid and sodium hydroxide in water to obtain an aqueous phase solution, and mixing trimesoyl chloride and n-heptane to obtain an oil phase solution; immersing the membrane treated in step 3 in the aqueous phase solution, the oil phase solution, and the aqueous phase solution in turn to perform interfacial polymerization reaction; washing and drying to obtain a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure.

2. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1, characterized in that: The poly(p-phenylene terephthalamide) nanofiltration membrane base film uses PET non-woven fabric as a supporting layer.

3. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, characterized in that: In step 2, the hydrolysis time is 3 to 5 hours.

4. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, wherein: In step 3, the silane coupling agent includes one of KH-550, KH-570 and KH-602.

5. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 4, characterized in that: In step 3, the concentration of the silane coupling agent solution is 0.5-1 wt %.

6. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, characterized in that: In step 4, the membrane treated in step 3 is immersed in the aqueous solution for 2 to 3 minutes, the oily solution for 2 to 3 minutes, and the aqueous solution for 2 to 3 minutes.

7. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, characterized in that: In step 4, the molar ratio of piperazine-2-carboxylic acid to sodium hydroxide is 1:1; and the mass concentration of piperazine-2-carboxylic acid is 0.5-1 wt %.

8. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, characterized in that: In step 4, the concentration of trimesoyl chloride is 0.1-0.2 wt %.

9. The method for preparing a PPTA composite nanofiltration membrane with optimized pore size using a hydrogel mosaic structure according to claim 1 or 2, characterized in that: In step 4, the washing comprises washing with ethanol.

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