Preparation method of high-flux nanofiltration membrane

Abstract

The invention relates to a preparation method of a high-flux nanofiltration membrane, in particular to a method for preparing a high-flux nanofiltration membrane by taking aminated ferroferric oxide nanospheres as a nano support for interfacial polymerization reaction and adding a polyhydroxy compound containing an organic carbon chain into a water-phase solution to adjust the diffusion behavior of a water-phase monomer in the interfacial polymerization reaction. The aminated ferroferric oxide nanospheres participate in an interfacial polymerization reaction to increase the integrity and compaction resistance of a polyamide structure, and provide an additional water channel, so that the nanofiltration membrane with a thin and compact polyamide functional layer is obtained, and the prepared nanofiltration membrane has high rejection rate and high water flux. The membrane preparation process is simple and convenient, industrial production is easy to realize, and the application prospect is wide.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanofiltration and relates to a method for preparing a high-flux nanofiltration membrane. Background Art

[0002] With the development of society, people pay more and more attention to the safety and health of water use, and membrane separation technologies represented by nanofiltration technology have received increasing attention. The core of nanofiltration technology is the nanofiltration membrane. Generally, it is considered that the pore size of the nanofiltration membrane is at the nanometer level, which can operate stably in various complex water quality scenarios, can achieve the selective separation of inorganic salts with different valences, and can also concentrate and purify high-value-added products. Nanofiltration membranes with low operating costs and high ion selectivity have many application cases in the fields of medicine, municipal administration, etc., and are an important method for realizing the separation and purification of substances.

[0003] At present, most nanofiltration membranes are prepared by the interfacial polymerization method. This method uses an ultrafiltration membrane or a microfiltration membrane as the reaction substrate membrane, and an interfacial polymerization reaction occurs between the aqueous monomer and the oil-phase monomer solution at the two-phase interface to prepare a dense polyamide separation layer on the substrate membrane, realizing the removal of inorganic salts and the selective separation of ions with different valences. The commonly used aqueous monomer and oil-phase monomer of the current nanofiltration membrane are piperazine (PIP) and trimesoyl chloride (TMC). The structure of the nanofiltration membrane prepared by them has good 1 / 2 valence ion selectivity and has gradually become the main reaction monomers for the preparation of nanofiltration membranes.

[0004] Interfacial polymerization is a self-limiting reaction. That is, during the interfacial polymerization reaction, initially, a polyamide polymer chain segment with a low cross-linking degree is formed at the two-phase interface, which will hinder the diffusion of subsequent reaction monomers to the two-phase interface, prolonging the reaction time of interfacial polymerization. Therefore, a polyamide separation layer with a high cross-linking degree cannot be obtained during the initial reaction, resulting in a relatively loose and thick structure of the polyamide separation layer. Based on this, it is particularly crucial to adjust the diffusion rate of reaction monomers during the interfacial polymerization reaction. By accelerating the diffusion rate of the aqueous monomer or increasing the concentration of the aqueous monomer during the interfacial reaction, a polyamide functional layer with a high cross-linking degree can be obtained, which can improve the desalination rate of the nanofiltration membrane but will lead to a decrease in water flux; using magnetite nanospheres as a nano scaffold to provide additional water channels can increase the flux of the nanofiltration membrane. However, because the unaminated magnetite nanospheres do not undergo an interfacial polymerization reaction and have a weak binding ability with the polyamide structure, they are prone to falling off during long-term operation, which is not conducive to the long-term operation stability of the nanofiltration membrane.

[0005] Based on this, how to improve the flux of the composite nanofiltration membrane on the premise of enhancing the cross-linking degree of the polyamide functional layer and maintaining a high desalination rate is of great significance and value for the production and popularization of nanofiltration membranes, and is helpful for the faster development and wider application of nanofiltration membranes. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing a high-flux nanofiltration membrane. By using amino-functionalized iron oxide nanoparticles as a nano-scaffold during the interfacial polymerization reaction, and adding a polyhydroxy compound containing an organic carbon chain as an additive to the aqueous solution to promote the interfacial polymerization reaction, the amino-functionalized iron oxide nanoparticles will participate in the interfacial polymerization reaction to increase the integrity and compaction resistance of the polyamide structure, and provide additional water channels, thereby obtaining a nanofiltration membrane with a thin and dense polyamide functional layer.

[0007] To achieve the object of the present invention, the following technical solutions are used in the present invention.

[0008] A method for preparing a high-flux nanofiltration membrane, comprising the following steps:

[0009] (1) Dispersing amino-functionalized iron oxide nanoparticles in water to obtain a uniformly dispersed solution of amino-functionalized iron oxide nanoparticles;

[0010] (2) Preparation of the aqueous solution: Mixing an aqueous monomer, a polyhydroxy compound containing an organic carbon chain, and water to obtain an aqueous solution;

[0011] (3) Preparation of the organic phase solution: Mixing an organic solvent and an acyl chloride monomer to obtain an organic phase solution;

[0012] (4) Preparation of the nanofiltration membrane: Pouring the nanoparticle dispersion solution prepared in step (1) onto the surface of an ultrafiltration substrate membrane to adsorb the nanoparticles on the surface of the ultrafiltration substrate membrane. Then pour the aqueous solution onto the ultrafiltration substrate membrane, remove the excess aqueous solution on the surface of the ultrafiltration substrate membrane, and then pour the organic phase solution prepared in step (3) onto the ultrafiltration substrate membrane for interfacial polymerization reaction. After the reaction is completed, remove the organic phase solution on the membrane surface, perform heat treatment, and then wash with water.

[0013] Preferably, in step (1), the amino-functionalized iron oxide nanoparticles are centrifuged, and the bottom nanoparticles are dispersed in water to obtain a uniformly dispersed solution of amino-functionalized iron oxide nanoparticles;

[0014] Preferably, in step (1), the mass ratio of the amino-functionalized iron oxide nanoparticles to water ranges from 1:500 to 1:3000, and the rotation speed is 7000 - 10000 rpm;

[0015] Preferably, in step (1), the amino-functionalized iron oxide nanoparticles are ultrasonically dispersed, the ultrasonic time is 30 - 180 min, the ultrasonic frequency is 10 kHz - 40 kHz, and the ultrasonic power is 200 - 450 W;

[0016] Preferably, in step (1), the particle size of the amino-functionalized iron oxide nanoparticles is 20 - 30 nm.

[0017] Preferably, in step (2), the aqueous phase monomer is one or more of polyethyleneimine, piperazine, diethylenetriamine, and tetraethylenepentamine, and the concentration of the aqueous phase monomer is 0.1-5.0 wt%, preferably 0.5-3.0 wt%.

[0018] Preferably, in step (2), the polyhydroxy compound containing an organic carbon chain is one or more of N-methyl-D-glucamine, N-acetyl-D-mannosamine, and glucoctamine.

[0019] Preferably, in step (2), the concentration of the polyhydroxy compound containing an organic carbon chain is 0.05-0.5 wt%, preferably 0.1-0.4 wt%.

[0020] Preferably, in step (3), the organic solvent is selected from one or more of n-hexane, cyclohexane, n-octane, cyclooctane, and methylcyclopentane. Preferably, in step (3), the acyl chloride monomer is one or more of polytriisophthaloyl chloride, phthaloyl chloride, terephthaloyl chloride, glutaroyl chloride, suberoyl chloride, and 3-methyladipoyl chloride.

[0021] Preferably, in step (3), the concentration of the acyl chloride monomer is 0.05-1.0 wt%, preferably 0.1-0.8 wt%.

[0022] Preferably, in step (4), the adsorption amount of the aminated magnetite nanospheres on the surface of the ultrafiltration base membrane is 0.2-2.0 mg / cm 2 Preferably 0.5-1.5 mg / cm 2 ;

[0023] Preferably, in step (4), the nanospheres are adsorbed on the surface of the ultrafiltration base membrane by negative pressure suction.

[0024] Preferably, in step (4), the ultrafiltration base membrane is soaked in the aqueous phase for 0.5-5 min, and the excess aqueous phase solution on the surface of the ultrafiltration base membrane is removed by an air knife.

[0025] Preferably, in step (4), the oil phase solution on the membrane surface is removed by an air knife.

[0026] Preferably, in step (4), the interfacial polymerization reaction time is 15-120 s, preferably 30-90 s.

[0027] Preferably, in step (4), after heat treatment in an oven, the membrane surface is washed with water from hydrophobic to hydrophilic.

[0028] Preferably, the heat treatment temperature is 40°C to 100°C, preferably 50°C to 70°C, and the heat treatment time is 30 s to 180 s.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. The present invention uses amino-functionalized magnetite nanospheres as the nano-scaffold for interfacial polymerization, and at the same time adds an amphiphilic substance with lipophilic and hydrophilic structures to the aqueous solution to prepare a polyamide nanofiltration membrane. The amino groups on the surface of the amino-functionalized magnetite nanospheres will participate in the interfacial polymerization reaction, increasing the binding force between the nanospheres and the polyamide structure, improving the overall stability of the separation layer structure, enhancing the compaction resistance performance of the nanofiltration membrane. At the same time, the hollow structure of the nanospheres can provide additional water channels, increasing the water flux of the nanofiltration membrane.

[0031] 2. When a polyhydroxy compound containing an organic carbon chain is added to the aqueous phase as an aqueous phase additive, the hydroxyl groups are easy to combine with the aqueous phase monomers to form hydrogen bonds, while the organic carbon chains are more soluble in organic solvents. Therefore, its amphiphilic property can increase the thickness of the interfacial polymerization reaction region, contributing to the faster formation of an initial low cross-linking degree polyamide network structure and obtaining a nanofiltration membrane with a high cross-linking degree. Detailed implementation manners

[0032] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0033] The test methods used in the examples and comparative examples of the present invention are as follows:

[0034] 1. Water flux and salt rejection rate are two important indicators for evaluating the performance of the prepared composite nanofiltration membrane. Water flux: Under certain operating pressure conditions, the volume of water passing through a unit membrane area per unit time, with the unit of LMH. The test conditions adopted for the performance of the nanofiltration membrane in the present invention are as follows: The feed liquid is an aqueous sodium sulfate solution with a concentration of 2000 ppm, the solution pH is 7.0 ± 0.5, the test temperature is 25 °C, and the test pressure is 0.61 MPa. Salt rejection rate: The ratio of the difference between the inorganic salt concentration (C f ) of the feed liquid and the inorganic salt concentration (C p ) of the permeate to the concentration (C f ) of the feed liquid, and the calculation formula is R = (C f - C p ) / C f * 100%.

[0035] 2. Long-term operation performance test

[0036] The long-term operation performance reflects the stability of the nanofiltration membrane during long-term operation. This long-term performance test focuses on investigating the change in the water flux of the nanofiltration membrane and uses it to evaluate the compaction resistance performance of the nanofiltration membrane prepared by the present invention. The specific test conditions are as follows.

[0037] (1) The feed liquid is an aqueous sodium sulfate solution with a concentration of 2000 ppm, the solution pH is 7.0 ± 0.5, the test temperature is 25 °C, the test pressure is 0.61 MPa. After pre-pressing for 2 h, the initial water flux F1 of the nanofiltration membrane is measured.

[0038] (2) After continuously operating for 100 h at 0.61 MPa, the water flux F at the end of the test is measured. 2 , and the flux decay rate of the nanofiltration membrane under long-term operating conditions is calculated, which is the ratio of the difference in water flux to the initial water flux. The calculation formula is R F = (F 1 - F 2 ) / F 2 * 100%.

[0039] Examples 1 - 4

[0040] (1) First, the amino-functionalized Fe₃O₄ nanospheres are centrifuged. During centrifugation, the mass ratio of the nanospheres to ultrapure water is 1:2000, and the centrifuge speed is 9000 rpm.

[0041] (2) The centrifuged amino-functionalized Fe₃O₄ nanospheres are taken for ultrasonic treatment. The ultrasonic time is 90 min, the ultrasonic frequency is 30 kHz, and the ultrasonic power is 300 W.

[0042] (3) Piperazine, N-methyl-D-glucosamine, and water are mixed to obtain an aqueous solution, where the concentration of piperazine is 1.0 wt%, and the concentration of N-methyl-D-glucosamine is shown in Table 1.

[0043] (4) Trimellitic acid chloride and n-hexane are mixed to obtain an oil-phase solution, and the concentration of trimellitic acid chloride is 0.2 wt%.

[0044] (5) The dispersion of amino-functionalized Fe₃O₄ nanospheres is poured onto the surface of the ultrafiltration substrate membrane. The nanospheres are adsorbed on the surface of the ultrafiltration substrate membrane by negative pressure suction. The adsorption amount of amino-functionalized Fe₃O₄ nanospheres on the substrate membrane surface is shown in Table 1. Then, the aqueous solution is poured onto the ultrafiltration substrate membrane and soaked for 2 min. After taking it out, it is dried with an air knife to remove the excess aqueous solution. Then, the oil-phase solution is poured onto the surface of the ultrafiltration substrate membrane, and the interfacial polymerization reaction is carried out for 60 s. After that, the excess oil-phase solution is removed using an air knife. Finally, the ultrafiltration substrate membrane after the interfacial polymerization reaction is placed in an oven for heat treatment for 2 min, and the interfacial polymerization reaction temperature is 70 °C. After completion, the membrane surface is rinsed with deionized water until it is in a hydrophilic state to obtain a high-flux nanofiltration membrane.

[0045] The water flux, salt rejection rate, and long-term operation performance of the nanofiltration membranes prepared in Examples 1 - 4 are evaluated, and the results are shown in Table 1.

[0046] Comparative Examples 1 - 2

[0047] Comparative Example 1: The difference in the preparation method from Example 1 is that during the preparation of the nanofiltration membrane, amino-functionalized Fe₃O₄ nanospheres are not added, and N-methyl-D-glucosamine is not added to the aqueous solution.

[0048] Comparative Example 2: The difference in the preparation method from Example 1 is that in the process of preparing the nanofiltration membrane, the aminated Fe₃O₄ nanospheres are replaced by unaminated Fe₃O₄ nanospheres, and N-methyl-D-glucosamine is added to the aqueous solution.

[0049] Table 1 Process parameters and evaluation results of examples and comparative examples

[0050]

[0051] From the comparison of the performance of the nanofiltration membranes prepared in Examples 1 to 4 and Comparative Example 1, it can be seen that when aminated Fe₃O₄ nanospheres are adsorbed on the surface of the ultrafiltration substrate membrane and N-methyl-D-glucosamine is added to the aqueous solution, the thickness of the interfacial polymerization reaction region is increased, the formation of the polyamide network structure with low cross-linking degree in the initial stage is accelerated, the continuous diffusion of the subsequent aqueous monomers and oil-phase monomers into the interfacial polymerization region is restricted, a thinner and more compact-structured nanofiltration membrane is formed, and the compaction resistance performance of the nanofiltration membrane is improved.

[0052] From the comparison of the performance of the nanofiltration membranes prepared in Example 1 and Comparative Example 2, it can be seen that when aminated Fe₃O₄ nanospheres are adsorbed on the surface of the ultrafiltration substrate membrane, the flux decay rate after long-term operation is 11.7%, and when unaminated Fe₃O₄ nanospheres are adsorbed on the surface of the ultrafiltration substrate membrane, the flux decay rate of the nanofiltration membrane after long-term operation is 30.5%. The amino groups in the aminated Fe₃O₄ nanospheres will undergo an interfacial polymerization reaction with the oil-phase monomers during the interfacial polymerization reaction, increasing the integrity of the polyamide structure and enhancing the compaction resistance performance of the nanofiltration membrane. The unaminated Fe₃O₄ nanospheres do not have amino groups and cannot have a good combination with the polyamide structure during the interfacial polymerization reaction, so the nanofiltration membrane has poor compaction resistance performance.

[0053] Examples 5 to 8:

[0054] Examples 5 to 6: The difference in the preparation method from Example 1 is that in the process of preparing the nanofiltration membrane, the piperazine concentration is 0.8 wt%, and N-acetyl-D-mannosamine is used instead of N-methyl-D-glucosamine in the aqueous solution. The addition amount of N-acetyl-D-mannosamine is shown in Table 2.

[0055] Examples 7 to 8: The difference in the preparation method from Example 1 is that in the process of preparing the nanofiltration membrane, the piperazine concentration is 0.8 wt%, and N-octylglucamine is used instead of N-methyl-D-glucosamine in the aqueous solution. The addition amount of N-octylglucamine is shown in Table 2.

[0056] Comparative Example 3

[0057] Comparative Example 3: The difference in the preparation method from Comparative Example 1 is that in the process of preparing the nanofiltration membrane, the piperazine concentration is 0.8 wt%, the aminated Fe₃O₄ nanospheres are not adsorbed on the surface of the ultrafiltration substrate membrane, and no polyhydroxy compound is added to the aqueous solution.

[0058] Table 2 Process parameters and evaluation results of examples and comparative examples

[0059]

[0060] It can be seen from the comparison of the performance of the nanofiltration membranes prepared in Examples 5-8 and Comparative Example 3 that when amino-functionalized magnetite nanospheres are adsorbed on the surface of the ultrafiltration substrate membrane and N-acetyl-D-mannosamine or glucooctylamine is added to the aqueous solution, the amphiphilic structure is conducive to promoting the diffusion of the aqueous monomer to the water / oil two-phase interface, increasing the concentration of the aqueous monomer participating in the interfacial polymerization reaction at the interface, forming a thinner and more compact nanofiltration membrane, and improving the compaction resistance of the nanofiltration membrane.

[0061] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A preparation method of a high-throughput nanofiltration membrane, characterized in that, it comprises the following steps: (1) Dispersing the aminated iron oxide nanoparticles in water to obtain a uniformly dispersed solution of aminated iron oxide nanoparticles; (2) Preparation of the aqueous solution: Mixing an aqueous monomer, a polyhydroxy compound containing an organic carbon chain, and water to obtain an aqueous solution; (3) Preparation of the oil-phase solution: Mixing an organic solvent and an acyl chloride monomer to obtain an oil-phase solution; (4) Preparation of the nanofiltration membrane: Pouring the nanoparticle dispersion prepared in step (1) onto the surface of an ultrafiltration substrate membrane to adsorb the nanoparticles on the surface of the ultrafiltration substrate membrane, then pouring the aqueous solution onto the ultrafiltration substrate membrane to remove the excess aqueous solution on the surface of the ultrafiltration substrate membrane, and then pouring the oil-phase solution prepared in step (3) onto the ultrafiltration substrate membrane for interfacial polymerization reaction. After the reaction is completed, the oil-phase solution on the membrane surface is removed, and after heat treatment, it is washed with water.

2. The preparation method according to claim 1, characterized in that, in step (1), the aminated iron oxide nanoparticles are centrifuged, and the bottom nanoparticles are dispersed in water to obtain a uniformly dispersed solution of aminated iron oxide nanoparticles; Preferably, in step (1), the mass ratio of the aminated iron oxide nanoparticles to water ranges from 1:500 to 1:3000, and the rotation speed is 7000 - 10000 rpm; Preferably, in step (1), the aminated iron oxide nanoparticles are ultrasonically dispersed, the ultrasonic time is 30 - 180 min, the ultrasonic frequency is 10 kHz - 40 kHz, and the ultrasonic power is 200 - 450 W; Preferably, in step (1), the particle size of the aminated iron oxide nanoparticles is 20 - 30 nm.

3. The preparation method according to claim 1 or 2, characterized in that, in step (2), the aqueous monomer is one or more of polyethyleneimine, piperazine, diethylenetriamine, and tetraethylenepentamine, and the concentration of the aqueous monomer is 0.1 - 5.0 wt%, preferably 0.5 - 3.0 wt%.

4. The preparation method according to any one of claims 1 - 3, characterized in that, in step (2), the polyhydroxy compound containing an organic carbon chain is one or more of N-methyl-D-glucosamine, N-acetyl-D-mannosamine, and glucosamine octylamine; Preferably, in step (2), the concentration of the polyhydroxy compound containing an organic carbon chain is 0.05 - 0.5 wt%, preferably 0.1 - 0.4 wt%.

5. The preparation method according to any one of claims 1 - 4, characterized in that, in step (3), the organic solvent is selected from one or more of n-hexane, cyclohexane, n-octane, cyclooctane, and methylcyclopentane; Preferably, in step (3), the acyl chloride monomer is one or more of trimesoyl chloride, phthaloyl chloride, terephthaloyl chloride, glutaroyl chloride, suberoyl chloride, and 3-methyladipoyl chloride; Preferably, in step (3), the concentration of the acyl chloride monomer is 0.05 - 1.0 wt%, preferably 0.1 - 0.8 wt%.

6. The preparation method according to any one of claims 1 - 5, characterized in that, In step (4), the adsorption amount of the amino-functionalized magnetite nanospheres on the surface of the ultrafiltration substrate membrane is 0.2-2.0 mg / cm 2 , preferably 0.5-1.5 mg / cm 2 ; Preferably, in step (4), the nanospheres are adsorbed on the surface of the ultrafiltration base membrane by means of negative pressure suction.

7. The preparation method according to any one of claims 1-6, characterized in that in step (4), the ultrafiltration base membrane is soaked in the aqueous phase for 0.5 to 5 minutes, and the excess aqueous phase solution on the surface of the ultrafiltration base membrane is removed by an air knife; Preferably, in step (4), the oil phase solution on the membrane surface is removed by an air knife.

8. The preparation method according to any one of claims 1-7, characterized in that in step (4), the interfacial polymerization reaction time is 15 to 120 s, preferably 30 to 90 s.

9. The preparation method according to any one of claims 1-8, characterized in that the heat treatment temperature is 40 °C to 100 °C, preferably 50 °C to 70 °C, and the heat treatment time is 30 s to 180 s.

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