High-water-flux thin-layer composite nanofiltration membrane and preparation method thereof

Abstract

The invention belongs to the technical field of separation membranes, and particularly relates to a high-water-flux thin-layer composite nanofiltration membrane and a preparation method thereof. The preparation method of the high-water-flux thin-layer composite nanofiltration membrane comprises the following steps: (1) preparing a polyamine monomer aqueous solution containing phosphate with a certain concentration, and standing for a period of time; and (2) fully infiltrating the surface of a porous bottom membrane with the aqueous solution obtained in the step (1), after the surface of the bottom membrane is aired, adding an organic phase solution of polyacyl chloride with a certain concentration into the surface of the bottom membrane, carrying out interfacial polymerization reaction to generate a polyamide active separation layer, and carrying out washing and post-treatment to obtain the high-water-flux thin-layer composite nanofiltration membrane. The thin-layer composite nanofiltration membrane comprises a porous bottom membrane and a polyamide active separation layer. The provided thin-layer composite nanofiltration membrane has the characteristics of high water flux, high antibiotic rejection rate and high univalent salt transmittance.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membranes, and more specifically, it is a high water flux thin film composite nanofiltration membrane and a preparation method thereof. Background Technique

[0002] Nanofiltration is a pressure-driven membrane separation technology with pore sizes between reverse osmosis and ultrafiltration. The molecular weight cut-off range is 200 Da - 1000 Da, covering ions to organic molecules. Therefore, it is suitable for the selective screening of different species, with high separation accuracy. Application fields include seawater desalination pretreatment, ion screening, drug purification, hard water softening, wastewater treatment, resource recovery, etc. Size screening and charge repulsion are the main mechanisms of nanofiltration membrane separation. The negative charge on the membrane surface has a good retention effect on divalent and multivalent anions, while the retention rate of monovalent ions is relatively low. Therefore, it is suitable for ion screening and desalination of organic molecules. The thin film composite membrane is the most widely used nanofiltration membrane structure form, which is composed of non-woven fabric, porous substrate membrane, and ultra-thin separation layer, and has the advantages of mild reaction conditions, simple preparation process, and low operating pressure. The variety of porous substrate membranes and ultra-thin separation layers enriches the separation performance window of nanofiltration membranes, and more new membrane materials and application scenarios are being developed in large quantities. Among them, the ultra-thin separation layer is formed by the polycondensation reaction of aqueous monomers and organic monomers at the oil-water interface. The aqueous monomers are usually polyamines or alcohols, etc., and the organic monomers are polyacyl chlorides. However, the uncontrollable diffusion and reaction behavior between monomers during the interfacial polymerization process restrict the further improvement of nanofiltration membrane performance. Moreover, the low flux and high monovalent ion retention rate of traditional commercial nanofiltration membranes limit the application of nanofiltration membranes in drug purification and concentration, such as antibiotic desalination, high-salt wastewater treatment, etc. Therefore, it is urgent to develop high-performance nanofiltration membranes with high water flux and strong screening ability. Existing literature and patents have reported methods such as introducing nanomaterials, surfactants, polymer polymers, hydrophilic intermediate layers, etc. during the interfacial polymerization process to improve the flux and selectivity of nanofiltration membranes, but there are often problems such as complex processes, harsh preparation conditions, high costs, and unsatisfactory separation stability. Summary of the Invention

[0003] To overcome the deficiencies of the prior art, the present invention provides a high water flux thin film composite nanofiltration membrane and a preparation method thereof, and its beneficial effects are that the provided thin film composite nanofiltration membrane has the characteristics of high water flux, high antibiotic retention rate, and high monovalent salt transmittance.

[0004] The technical solution adopted by the present invention to solve its technical problems is:

[0005] A preparation method of a high water flux thin film composite nanofiltration membrane, the preparation method includes the following steps:

[0006] (1) Prepare an aqueous solution of polyamine monomers containing phosphate and let it stand for a period of time;

[0007] (2) The surface of the porous substrate membrane is fully wetted with the aqueous solution described in step (1). After the surface of the substrate membrane is dried, an organic phase solution containing polyfunctional acyl chloride is added to the surface of the substrate membrane for interfacial polymerization reaction to form a polyamide active separation layer, and then it is washed and post-treated to obtain the high water flux thin film composite nanofiltration membrane.

[0008] The mass percentage of the polyamine monomer in the aqueous solution is 0.01 wt% - 5 wt%;

[0009] The polyamine is one or more of piperazine, m-phenylenediamine, polyethyleneimine, o-phenylenediamine, p-phenylenediamine, and hexamethylenediamine.

[0010] The mass percentage of the phosphate in the aqueous solution is 0.01 wt% - 10 wt%;

[0011] The phosphate is one or more combinations of trisodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, sodium pyrophosphate, potassium pyrophosphate, sodium metaphosphate, potassium metaphosphate, sodium polyphosphate, and potassium polyphosphate.

[0012] The solvent in the organic phase solution is one or more combinations of alkane solvents or Isopar G. Isopar G is an isoparaffinic solvent oil, which is a highly branched synthetic hydrocarbon composed of C9 - C11 isoparaffins and is prepared by hydrotreating petroleum-derived raw materials in the presence of a catalyst.

[0013] The polyfunctional acyl chloride is one or more combinations of trimesoyl chloride, isophthaloyl chloride, glutaroyl chloride, adipoyl chloride, and suberoyl chloride;

[0014] The mass percentage of the polyfunctional acyl chloride in the organic phase solution is 0.05 wt% - 3 wt%.

[0015] The porous substrate membrane material is a polymer-based or ceramic-based porous membrane;

[0016] The pore size range of the porous substrate membrane is 5 nm - 500 nm.

[0017] The porous substrate membrane is a polysulfone ultrafiltration membrane or a microfiltration membrane.

[0018] The time for the polyamine monomer aqueous solution to wet the surface of the porous substrate membrane is 30 s - 300 s;

[0019] The washing solvent of the thin film composite nanofiltration membrane is the same as the organic phase solvent that dissolves the polyfunctional acyl chloride during interfacial polymerization, and the washing time is 10 s - 300 s.

[0020] The interfacial polymerization reaction time is 30 s - 180 s; the post-treatment temperature is 30 °C - 90 °C, and the heat treatment time is 5 min - 60 min.

[0021] A high water flux thin film composite nanofiltration membrane, the thin film composite nanofiltration membrane comprising a porous substrate membrane and a polyamide active separation layer.

[0022] The beneficial effects of the high water flux thin film composite nanofiltration membrane and its preparation method of the present invention are:

[0023] The preparation method of the present invention uses an inorganic phosphate additive added to an aqueous solution to prepare a nanofiltration membrane with high water flux and high antibiotic rejection rate, which has the characteristics of small process modification, environmental friendliness, and low cost. During the preparation of the nanofiltration membrane, the phosphate group in the inorganic phosphate forms a hydrogen bond interaction with the polyamine monomer, effectively regulating the diffusion of the polyamine monomer. The prepared nanofiltration membrane has an increased pore size, a reduced thickness, and enhanced surface negative charge, and has the advantages of high water flux, high antibiotic rejection rate, and low monovalent salt rejection rate compared with traditional commercial nanofiltration membranes. Description of the Drawings

[0024] The present invention will be further described in detail below in conjunction with the drawings and specific implementation methods.

[0025] Figure 1 It is a schematic diagram of the comparison of the water permeation flux of the thin film composite nanofiltration membranes prepared in Example 3 and Comparative Example 1 of the present invention in desalination;

[0026] Figure 2 It is a schematic diagram of the comparison of the Zeta potential changes of the thin film composite nanofiltration membranes prepared in Example 3 and Comparative Example 1 of the present invention. Specific Embodiments

[0027] Example 1:

[0028] A high water flux thin film composite nanofiltration membrane is prepared by the following method:

[0029] Step (1), prepare an aqueous solution containing 0.2 wt% trisodium phosphate dodecahydrate and 0.2 wt% piperazine, and let it stand for 3 h;

[0030] Step (2), fully soak the surface of the polyethersulfone ultrafiltration membrane with the aqueous solution described in step (1) for 1 min. After the surface of the substrate membrane is dried, add a n-hexane solution of 0.2 wt% trimesoyl chloride to the substrate membrane for an interfacial polymerization reaction for 30 s to generate a polyamide active separation layer, and then wash with n-hexane, heat-treat at 60 °C for 30 min, and soak in deionized water to obtain the high water flux thin film composite nanofiltration membrane.

[0031] After testing, the thin-film composite nanofiltration membrane prepared in this example has a water flux of 50 L m-2 h-1, a Na2SO4 rejection rate of 97.2%, and an NaCl rejection rate of 8.3% at a test temperature of 25°C and an operating pressure of 4 bar; the rejection rate of rifamycin at 50 ppm is 99.2%.

[0032] Example 2:

[0033] A high water flux thin-film composite nanofiltration membrane is prepared by the following method:

[0034] Step (1): Prepare an aqueous solution containing 1 wt% trisodium phosphate dodecahydrate and 0.2 wt% piperazine, and let it stand for 3 h;

[0035] Step (2): Fully immerse the surface of the polyethersulfone ultrafiltration membrane with the aqueous solution described in step (1) for 1 min. After the surface of the bottom membrane is dried, add a 0.2 wt% solution of trimesoyl chloride in n-hexane to the bottom membrane for an interfacial polymerization reaction for 30 s to form a polyamide active separation layer, and then wash with n-hexane, heat-treat at 60°C for 30 min, and soak in deionized water to obtain the high water flux thin-film composite nanofiltration membrane.

[0036] After testing, the thin-film composite nanofiltration membrane prepared in this example has a water flux of 56 L m-2 h-1, a Na2SO4 rejection rate of 97.0%, and an NaCl rejection rate of 7.6% at a test temperature of 25°C and an operating pressure of 4 bar; the rejection rate of rifamycin at 50 ppm is 99.0%.

[0037] Example 3:

[0038] A high water flux thin-film composite nanofiltration membrane is prepared by the following method:

[0039] Step (1): Prepare an aqueous solution containing 2 wt% trisodium phosphate dodecahydrate and 0.2 wt% piperazine, and let it stand for 3 h;

[0040] Step (2): Fully immerse the surface of the polyethersulfone ultrafiltration membrane with the aqueous solution described in step (1) for 1 min. After the surface of the bottom membrane is dried, add a 0.2 wt% solution of trimesoyl chloride in n-hexane to the bottom membrane for an interfacial polymerization reaction for 30 s to form a polyamide active separation layer, and then wash with n-hexane, heat-treat at 60°C for 30 min, and soak in deionized water to obtain the high water flux thin-film composite nanofiltration membrane.

[0041] After testing, the thin-film composite nanofiltration membrane prepared in this example has a water flux of 68 L m-2 h-1, a Na2SO4 rejection rate of 96.8%, and an NaCl rejection rate of 6.3% at a test temperature of 25°C and an operating pressure of 4 bar; the rejection rate of rifamycin at 50 ppm is 98.8%.

[0042] Example 4:

[0043] A high water flux thin film composite nanofiltration membrane is prepared by the following method:

[0044] Step (1): Prepare an aqueous solution containing 1 wt% sodium pyrophosphate and 0.2 wt% piperazine, and let it stand for 3 h;

[0045] Step (2): Fully soak the surface of the polyethersulfone ultrafiltration membrane with the aqueous solution described in step (1) for 1 min. After the surface of the bottom membrane is dried, add a n - hexane solution of 0.2 wt% trimesoyl chloride to the bottom membrane for an interfacial polymerization reaction for 30 s to form a polyamide active separation layer, and then obtain the high water flux thin film composite nanofiltration membrane after washing with n - hexane, heat treatment at 60 °C for 30 min, and soaking in deionized water.

[0046] After testing, the thin film composite nanofiltration membrane prepared in this example has a water flux of 62 L m - 2 h - 1, a Na2SO4 rejection rate of 97.2%, an NaCl rejection rate of 7.6%, and a rifamycin rejection rate of 99.0% at a test temperature of 25 °C and an operating pressure of 4 bar.

[0047] Example 5:

[0048] A high water flux thin film composite nanofiltration membrane is prepared by the following method:

[0049] Step (1): Prepare an aqueous solution containing 1 wt% sodium metaphosphate and 0.2 wt% piperazine, and let it stand for 3 h;

[0050] Step (2): Fully soak the surface of the polyethersulfone ultrafiltration membrane with the aqueous solution described in step (1) for 1 min. After the surface of the bottom membrane is dried, add a n - hexane solution of 0.2 wt% trimesoyl chloride to the bottom membrane for an interfacial polymerization reaction for 30 s to form a polyamide active separation layer, and then obtain the high water flux thin film composite nanofiltration membrane after washing with n - hexane, heat treatment at 60 °C for 30 min, and soaking in deionized water.

[0051] After testing, the thin film composite nanofiltration membrane prepared in this example has a water flux of 58 Lm - 2 h - 1, a Na2SO4 rejection rate of 97.0%, an NaCl rejection rate of 7.3%, and a rifamycin rejection rate of 99.2% at a test temperature of 25 °C and an operating pressure of 4 bar.

[0052] Comparative Example 1:

[0053] A high water flux thin film composite nanofiltration membrane is prepared by the following method:

[0054] Step (1): Prepare an aqueous solution of 0.2 wt% piperazine, and let it stand for 3 h;

[0055] Step (2): The surface of the polyethersulfone ultrafiltration membrane is fully wetted with the aqueous solution described in step (1) for 1 min. After the surface of the substrate membrane is dried, a 0.2 wt% solution of trimesoyl chloride in n-hexane is added to the substrate membrane for an interfacial polymerization reaction for 30 s to form a polyamide active separation layer, which is then washed with n-hexane, heat-treated at 60 °C for 30 min, and soaked in deionized water to obtain a comparative thin-film composite nanofiltration membrane without adding inorganic phosphate.

[0056] After testing, the thin-film composite nanofiltration membrane prepared in this example has a water flux of 28 Lm-2h-1, a Na2SO4 rejection rate of 96.8%, a NaCl rejection rate of 21%, and a rifamycin rejection rate of 99.0% at a test temperature of 25 °C and an operating pressure of 4 bar.

[0057] In addition, the inventors of this case also conducted experiments in the manner of the foregoing Examples 1-5 with other raw materials, process operations, and process conditions described in this specification, and also obtained a thin-film composite nanofiltration membrane with high water flux and high antibiotic rejection rate.

[0058] Figure 1 The water permeation flux is measured using a cross-flow nanofiltration membrane test device at 4 atmospheres with a 2000 ppm salt solution as the test solution.

[0059] Figure 2 The Zeta potential value is measured by a Zeta potential meter using the streaming potential method. The Zeta potential value reflects the charge property of the membrane surface. The larger the absolute value of the Zeta potential, the stronger the charge property of the membrane surface, and the stronger the repulsion of the membrane to solutes with the same charge.

Claims

1. A preparation method of a high water flux thin film composite nanofiltration membrane, characterized in that: The preparation method comprises the following steps: (1) Prepare an aqueous solution of polyamine monomers containing phosphates and let it stand for a period of time; (2) Fully infiltrate the surface of the porous substrate membrane with the aqueous solution described in step (1). After the surface of the substrate membrane dries, add an organic phase solution containing polyacyl chloride to the surface of the substrate membrane for interfacial polymerization reaction to generate a polyamide active separation layer, and then obtain the high water flux thin film composite nanofiltration membrane through washing and post-treatment.

2. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 1, characterized in that: The mass percentage of the polyamine monomers in the aqueous solution is 0.01 wt% - 5 wt%; The polyamine is one or more of piperazine, m-phenylenediamine, polyethyleneimine, o-phenylenediamine, p-phenylenediamine, and hexamethylenediamine.

3. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 1, characterized in that: The mass percentage of the phosphates in the aqueous solution is 0.01 wt% - 10 wt%; The phosphates are one or a combination of more than one of trisodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, sodium pyrophosphate, potassium pyrophosphate, sodium metaphosphate, potassium metaphosphate, sodium polyphosphate, and potassium polyphosphate.

4. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 1, characterized in that: The solvent in the organic phase solution is one or a combination of more than one of alkane solvents or Isopar G.

5. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 1, characterized in that: The polyacyl chloride is one or a combination of more than one of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, glutaroyl chloride, adipoyl chloride, and suberoyl chloride; The mass percentage of the polyacyl chloride in the organic phase solution is 0.05 wt% - 3 wt%.

6. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 1, characterized in that: The porous substrate membrane material is a polymer-based or ceramic-based porous membrane; The pore size range of the porous substrate membrane is 5 nm - 500 nm.

7. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 6, characterized in that: The porous substrate membrane is a polysulfone ultrafiltration membrane or microfiltration membrane.

8. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 7, characterized in that: The time for the aqueous solution of polyamine monomers to infiltrate the surface of the porous substrate membrane is 30 s - 300 s; The washing solvent of the thin film composite nanofiltration membrane is the same as the organic phase solvent that dissolves polyacyl chloride during interfacial polymerization, and the washing time is 10 s - 300 s.

9. The preparation method of a high water flux thin film composite nanofiltration membrane according to claim 8, characterized in that: The interfacial polymerization reaction time is 30 s - 180 s; the post-treatment temperature is 30 °C - 90 °C, and the heat treatment time is 5 min - 60 min.

10. A high water flux thin film composite nanofiltration membrane, characterized in that: The thin film composite nanofiltration membrane comprises a porous substrate membrane and a polyamide active separation layer.

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