Deeply modified coating and deeply modified coating composite separation membrane

Abstract

This invention relates to deeply modified coatings and deeply modified coating composite separation membranes. The deeply modified coating is prepared using a surface tension gradient-driven Marangoni convection process and is used to deeply modify the surface and pores of an ultrafiltration or microfiltration substrate membrane. Further crosslinking with a crosslinking agent enhances the coating's stability. The deeply modified coating composite separation membrane has a three-layer structure, with the deeply modified coating as the middle layer, and also includes a bottom substrate membrane and a top dense ultrathin separation layer. The deeply modified coating significantly enhances the adsorption capacity of the substrate membrane for amine monomers and ultimately improves the desalination performance of the composite separation membrane.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and specifically relates to a deep-modified coating and a deep-modified coating composite separation membrane. Background Technology

[0002] Water scarcity has severely impacted the sustainable development of human society. Membrane-based water treatment technologies have proven to be an effective solution. Composite separation membranes combining nanofiltration and reverse osmosis are core materials for high-precision water treatment. Taking seawater desalination as an example, reverse osmosis membrane-based separation processes have become the mainstream technology. Over the past two decades, their application scale has grown rapidly, currently accounting for more than two-thirds of global seawater desalination capacity. High-performance membrane materials represent a perfect combination of selectivity and permeability, which is of great significance for reducing carbon footprint and promoting sustainable development.

[0003] Interfacial polymerization is a classic process for preparing the dense top separation layer in composite separation membranes. It typically involves the polymerization reaction of two active monomers, each dissolved in one of two immiscible phases, at the phase interface on an ultrafiltration or microfiltration substrate membrane. As the site of the interfacial polymerization reaction, the substrate membrane's adsorption capacity for amine monomers significantly impacts the overall performance of the composite separation membrane. Therefore, coating modification techniques for the substrate membrane have been extensively researched and developed. Conventional coating modifications only modify the substrate surface, thus their effect on improving the substrate membrane's amine monomer adsorption capacity is limited. Due to the porous nature of ultrafiltration or microfiltration substrate membranes, deep modification strategies targeting the pores of the substrate membrane hold promise for significantly enhancing its amine monomer adsorption capacity, thereby substantially improving the performance of the composite separation membrane. Summary of the Invention

[0004] The purpose of this invention is to provide a deep-modified coating and a deep-modified coating composite separation membrane that improve the adsorption capacity of the amine monomer of the substrate membrane by deep modification of the substrate membrane surface and pores, thereby significantly improving the performance of the composite separation membrane.

[0005] The technical solution of the present invention, namely the deep modified coating, is characterized in that the deep modified coating is prepared by a Marangoni convection process driven by surface tension gradient. The solute in the coating solution adheres to the surface of the substrate and the pores under the drive of the surface tension gradient. The solute adhering to the surface of the substrate and the pores is further cross-linked by a cross-linking agent to enhance the stability of the coating.

[0006] Preferably, the bottom membrane is a single porous polymer membrane or a combination of a porous polymer membrane and a nonwoven fabric, with a pore size of 10–500 nm.

[0007] Preferably, the preparation steps of the deep-modified coating include:

[0008] (1) Immerse the substrate in the first solution for 0.5 to 5 hours to thoroughly wet the substrate, and then fix the substrate wetted by the first solution in the plate frame;

[0009] (2) The second solution is coated on the surface of the substrate for 10 min to 5 h to allow for convection and displacement with the first solution, and then the surface of the film is dried with an air knife.

[0010] (3) Optionally, the crosslinking solution is applied to the membrane surface for 1 to 30 minutes to allow the crosslinking reaction to occur and enhance the stability of the coating, and then the membrane surface is thoroughly cleaned with deionized water.

[0011] Preferably, the solvent for the first solution is one or a combination of methanol, ethanol, n-propanol and isopropanol; the solvent for the second solution is water.

[0012] Preferably, the solutes used in the first and second solutions have a size of less than 10 nm and are organic molecules or inorganic nanoparticles, preferably one or more combinations of polyols, polyphenols, polyamines, polyacids, polysulfonic acids and zero-dimensional materials.

[0013] Preferably, the deep-modified coating is prepared according to any of the aforementioned methods for deep-modified coatings.

[0014] Another technical solution of the invention, the deep-modified coating composite separation membrane, is characterized in that the deep-modified coating composite separation membrane structure includes a dense ultrathin separation layer at the top, a deep-modified coating in the middle, and a bottom membrane.

[0015] Preferably, the dense, ultrathin separation layer at the top is made of polyamide or polysulfonamide, with a thickness of 10–300 nm, and is prepared by an interfacial polymerization process, including the following steps:

[0016] (1) A polyamine aqueous solution is coated on the surface of a substrate film with a deep-modified coating for 1 to 30 minutes, and then the film surface is dried with an air knife. The polyamine aqueous solution contains an aqueous phase additive.

[0017] (2) An alkane solution of polyacrylamide chloride or polysulfonyl chloride is coated onto the surface of the above-mentioned film for 0.5 to 10 min to undergo an interfacial polymerization reaction, wherein the alkane solution contains an alkane phase additive;

[0018] (3) The surface of the nascent membrane is rinsed with an alkane solvent and then transferred to an oven for heat treatment to finally obtain a deeply modified coating composite separation membrane.

[0019] As a preferred option, the aqueous phase additive used in the preparation of the separation layer synergistically enhances the adsorption capacity of polyamines on the substrate by working with the deep-modified coating. One or more of the following are selected: triethylamine, sodium alkyl sulfate, sodium alkylbenzene sulfonate, alkyl ammonium bromide, sodium hydroxide, camphor sulfonic acid, fatty alcohol polyoxyethylene ether, and fatty acid polyoxyethylene ester.

[0020] As a preferred option, the alkane phase additive used to prepare the separation layer is used to accelerate the interfacial polymerization reaction process, and one or more combinations of acetone, dimethyl carbonate, and ethyl acetate are selected.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) In this invention, the deep-modified coating is prepared on the substrate film through a simple solvent convection process, and the stability of the coating can be improved through further cross-linking reaction. The operation is simple and the practicality is strong.

[0023] (2) In this invention, the deep-modified coating enhances the adsorption capacity of the base film for amine monomers, thereby promoting the diffusion-reaction process in the interfacial polymerization process, and ultimately significantly improves the desalination performance of the deep-modified coating composite separation membrane.

[0024] (3) The deep-modified coating in this invention has a good promoting effect on the reaction of various interfacial polymerization reaction systems, namely different polyamines and different polyacryl chlorides or polysulfonyl chlorides.

[0025] (4) The preparation strategy of the deep modified coating described in this invention can provide a reference for the preparation of functional coatings in other fields.

[0026] (5) The interfacial polymerization process described in this invention can synergistically enhance the adsorption capacity of the base membrane for amine monomers with the deep-modified coating, thereby improving the performance of the composite separation membrane. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the deep-modified coating composite separation membrane of the present invention;

[0028] Figure 2 This is a schematic diagram of the deep-modified coating preparation process based on Marangoni convection according to the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments and accompanying drawings:

[0030] This invention discloses a method for preparing a deeply modified coated composite separation membrane for sieving mono / divalent anions. The deeply modified coated composite separation membrane comprises a bottom polyvinylidene fluoride substrate, a middle tannic acid-amino carbon quantum dot deeply modified coating, and a top polyamide separation layer. Please refer to the schematic diagram for the structural representation. Figure 1 .

[0031] The polyvinylidene fluoride substrate has a static water contact angle of 110–140° and a pore size of 50–450 nm, preferably 100 nm.

[0032] The aminated carbon quantum dots have a size of 1–10 nm and are prepared by citric acid pyrolysis.

[0033] Specifically, the preparation steps of the aminated carbon quantum dots include:

[0034] (1.1) Anhydrous citric acid is placed in a high-pressure reactor and heated at 200°C for 0.5 to 3 hours, preferably 1 hour, to obtain a brownish-yellow liquid;

[0035] (1.2) After the reaction solution is cooled, deionized water is added and the solution is transferred to a dialysis bag for dialysis for 24 hours to remove oligomers;

[0036] (1.3) The solution obtained in the dialysis bag was freeze-dried for 48 hours, and the brownish-yellow solid obtained was the aminated carbon quantum dots.

[0037] Examples 1-3 are tannic acid-amino carbon quantum dot deep-modified coatings, and the preparation steps include:

[0038] (2.1) Immerse the bottom film in ethanol (corresponding to) Figure 2 The substrate is immersed in solvent 2) for 0.5-5 hours, preferably 1 hour, to fully wet the substrate, and then the substrate wetted with ethanol is fixed in the plate frame.

[0039] (2.2) Tannic acid-amino carbon quantum dots (corresponding to) Figure 2 Water (corresponding to solute 1) Figure 2 The medium solvent 1) dispersion is coated on the surface of the substrate film for a certain period of time, and then the film surface is dried with an air knife;

[0040] The tannic acid concentration in the tannic acid-amino carbon quantum dot aqueous dispersion is 0.05-0.3%, preferably 0.1%, and the amino carbon quantum dot concentration is 0.02-0.5%, preferably 0.1%.

[0041] The coating duration of the aqueous dispersion of tannic acid-amino carbon quantum dots is 30 min to 10 h, preferably 1 to 4 h.

[0042] The coating durations of the aqueous dispersions of tannic acid-amino carbon quantum dots in Examples 1-3 were 1 h, 2 h, and 4 h, respectively.

[0043] Comparative Example 1 is a conventional modified coating of tannic acid-amino carbon quantum dots. The difference between the preparation steps and those of Examples 1 to 3 is that the polyvinylidene fluoride substrate is wetted with water in step (2.1), and the coating duration of the aqueous dispersion of tannic acid-amino carbon quantum dots in step (2.2) is 2 hours. The other steps are the same.

[0044] The elemental composition of the coating surfaces and the surfaces after etching 20 nm of Examples 1-3 and Comparative Example 1 was tested using X-ray photoelectron spectroscopy (ThermoFisher ESCALAB 250Xi). The elemental composition is shown in Table 1. The percentages listed in the table are calculated based on the measured elements only. N is a characteristic element of carbon quantum dots, and O is a characteristic element of tannic acid.

[0045] Table 1. Elemental composition of the coating surface and the surface after etching 20 nm in Examples 1-3 and Comparative Example 1.

[0046]

[0047] The results showed that, compared with Control Example 1, although the coating time of the aqueous dispersion of tannic acid-amino carbon quantum dots was the same, the content of O and N elements on the surface and after etching 20 nm in Example 2 was significantly higher than that in Control Example 1, indicating the successful preparation of the deep modified coating. According to Examples 1-3, the content of O and N elements on the surface and after etching 20 nm increased with the extension of coating time, indicating that the degree of modification of the deep modified coating continued to increase.

[0048] The interfacial polymerization processes of Examples 4-6 and Comparative Example 2 were prepared based on Examples 1-3 and Comparative Example 1, respectively, and the specific steps included:

[0049] (3.1) A piperazine / sodium dodecylbenzenesulfonate aqueous solution was coated on the surface of the coating modified film (i.e., Examples 1-3 and Comparative Example 1) for 1-20 min, preferably 2 min, wherein the concentration of piperazine was 0.1-1.5%, preferably 0.6%, and the concentration of sodium dodecylbenzenesulfonate was 0.01-0.1%, preferably 0.05%, and then the film surface was dried with an air knife;

[0050] (3.2) A hexane solution of pyromellitic chloride is coated onto the surface of the above-mentioned film for 20-75 seconds to carry out an interfacial polymerization reaction. The coating time is preferably 45 seconds. The concentration of the pyromellitic chloride solution is 0.06-0.15%, preferably 0.1%.

[0051] (3.3) Rinse the surface of the nascent film with n-hexane, and then transfer it to an oven at 60°C to dry for 1 to 6 minutes, preferably 2 minutes.

[0052] The desalination performance of Examples 4-6 and Control Example 2 was tested. The test conditions were as follows: a mixed aqueous solution of 1 g / L sodium chloride and 1 g / L sodium sulfate as feed liquid, a test pressure of 0.6 MPa, and the desalination performance after two hours of stable operation is shown in Table 2.

[0053] Table 2 Desalination performance of Examples 4-6 and Control Example 2

[0054]

[0055] The results showed that, according to Examples 4-6, the flux and mono / divalent anion selectivity of the composite separation membrane increased with the extension of the coating time of the tannic acid-amino carbon quantum dot aqueous dispersion and eventually tended to stabilize. Compared with Control Example 2, the composite membrane prepared based on the tannic acid-amino carbon quantum dot deep modified coating had significantly higher flux and mono / divalent anion selectivity.

[0056] This invention discloses a method for preparing a deeply modified coated composite separation membrane for brackish water desalination. The deeply modified coated composite separation membrane comprises a plasma-treated polyethylene base membrane at the bottom, a 9,9-bis(4-aminophenyl)fluorene-sodium nitrite deeply modified coating in the middle, and a polyamide separation layer at the top. Please refer to the schematic diagram for the structural representation. Figure 1 .

[0057] The static water contact angle of the plasma-treated polyethylene substrate is 70–110°, preferably 90±5°, the surface porosity is 20–30%, the overall porosity is 40–50%, and the plasma treatment conditions are a power of 1–2 kW and a linear velocity of 2–6 m / min.

[0058] Examples 7-9 are 9,9-bis(4-aminophenyl)fluorene-sodium nitrite deep-modified coatings, and the preparation steps include:

[0059] (4.1) Immerse the substrate in isopropanol (corresponding to...) Figure 2 The isopropanol-soaked substrate is immersed in solvent 2) for 0.5 to 5 hours, preferably 1 hour, to fully wet the substrate, and then the substrate is fixed in the plate frame.

[0060] (4.2) 9,9-bis(4-aminophenyl)fluorene (corresponding to Figure 2 Water (corresponding to solute 1) Figure 2 A liquid solvent 1) solution is coated onto the surface of the substrate film for a certain period of time, and then the film surface is dried with an air knife;

[0061] The concentration of the 9,9-bis(4-aminophenyl)fluorene aqueous solution is 0.05-0.8%, preferably 0.3%, and 0.7-2 mL of concentrated hydrochloric acid is added to aid dissolution and the pH is adjusted to 2;

[0062] The coating duration of the aqueous solution of 9,9-bis(4-aminophenyl)fluorene is 10 min to 5 h, preferably 30 min to 2 h;

[0063] The coating durations of the 9,9-bis(4-aminophenyl)fluorene aqueous solution in Examples 7-9 were 30 min, 1 h, and 2 h, respectively.

[0064] (4.3) Apply an aqueous solution of sodium nitrite to the membrane surface for 2 to 10 minutes, preferably 5 minutes. The concentration of the aqueous solution of sodium nitrite is 0.1 to 10%, preferably 1%; the pH is 1 to 3, preferably pH = 2; and the temperature is 0 to 5°C. Then, thoroughly clean the membrane surface with deionized water and blow dry to obtain a 9,9-bis(4-aminophenyl)fluorene-sodium nitrite deep modified coating.

[0065] Comparative Example 3 is a conventional modified coating of 9,9-bis(4-aminophenyl)fluorene-sodium nitrite. The difference between the preparation steps and those of Examples 7-9 is that in step (4.1), the polyethylene substrate is wetted with water during plasma treatment, and in step (4.2), the aqueous coating of 9,9-bis(4-aminophenyl)fluorene lasts for 1 hour. The remaining steps are the same.

[0066] The elemental composition of the coated surfaces and the surfaces after etching 20 nm of Examples 7-9 and Comparative Example 3 was tested using X-ray photoelectron spectroscopy (ThermoFisher ESCALAB 250Xi). The elemental composition is shown in Table 3. The percentages listed in the table are calculated based on the measured elements only. N is a characteristic element of 9,9-bis(4-aminophenyl)fluorene and sodium nitrite.

[0067] Table 3. Elemental composition of the coating surfaces and the surfaces after 20 nm etching in Examples 7-9 and Comparative Example 3.

[0068]

[0069]

[0070] The results showed that, compared with Control Example 3, although the coating time of 9,9-bis(4-aminophenyl)fluorene aqueous solution was the same, the N content on the surface and after etching 20 nm in Example 8 was significantly higher than that in Control Example 3, indicating the successful preparation of the deep-modified coating. According to Examples 7-9, the N content on the surface and after etching 20 nm increased with the extension of coating time, indicating that the degree of modification of the deep-modified coating continued to increase.

[0071] The interfacial polymerization processes of Examples 10-12 and Comparative Example 4 were prepared based on Examples 7-9 and Comparative Example 3, respectively, and the specific steps included:

[0072] (5.1) Apply an aqueous solution of m-phenylenediamine to the surface of the coating-modified film (i.e., Examples 7-9 and Comparative Example 3) for 1-20 min, preferably 3 min, wherein the concentration of the m-phenylenediamine solution is 1-3.5%, preferably 2%, and then dry the film surface with an air knife;

[0073] (5.2) A hexane solution of pyromellitic chloride is coated onto the surface of the above-mentioned film for 30-90 seconds to carry out an interfacial polymerization reaction. The coating time is preferably 60 seconds. The concentration of the pyromellitic chloride solution is 0.1-0.25%, preferably 0.13%.

[0074] (5.3) Rinse the surface of the nascent film with n-hexane, and then transfer it to an oven at 60°C to dry for 2 to 10 minutes, preferably 5 minutes.

[0075] The desalination performance of Examples 10-12 and Control Example 4 was tested. The test conditions were 2 g / L sodium chloride aqueous solution as feed liquid, test pressure of 1.5 MPa, and desalination performance after two hours of stable operation are shown in Table 4.

[0076] Table 4. Desalination performance of Examples 10-12 and Control Example 4

[0077]

[0078] The results showed that, according to Examples 10-12, the flux and rejection rate of the composite separation membrane for sodium chloride increased with the extension of the 9,9-bis(4-aminophenyl)fluorene coating time and eventually stabilized. Compared with Control Example 4, the composite membrane prepared based on the 9,9-bis(4-aminophenyl)fluorene-sodium nitrite deep modified coating had significantly higher flux and rejection rate.

[0079] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. A deep-modified coating, characterized in that, It is prepared by a surface tension gradient-driven Marangoni convection process, specifically including the following steps: (1) Immerse the substrate in the first solution for 0.5 to 5 hours to thoroughly wet the substrate, and then fix the wetted substrate in the plate frame; (2) The second solution is coated on the surface of the substrate for 10 min to 5 h to allow it to be convected and replaced with the first solution. Then the surface of the film is dried with an air knife. (3) Apply the crosslinking solution to the membrane surface for 1–30 min to allow the crosslinking reaction to occur and enhance the stability of the coating, and then thoroughly clean the membrane surface with deionized water; The solute in the coating solution in step (2) adheres to the surface of the substrate and the pores under the drive of the surface tension gradient. The solute adhering to the surface of the substrate and the pores is further cross-linked by the cross-linking agent to enhance the stability of the coating. The solutes used in the first and second solutions are smaller than 10 nm in size, and the solutes are one or more of polyols, polyphenols, polyamines, polyacids, and zero-dimensional materials.

2. The depth-modified coating according to claim 1, characterized in that, The base film is a single porous polymer film or a combination of a porous polymer film and a nonwoven fabric, with a pore size of 10–500 nm.

3. The depth-modified coating according to claim 1, characterized in that, The solvent for the first solution is one or a combination of methanol, ethanol, n-propanol and isopropanol; the solvent for the second solution is water.

4. A deeply modified coating composite separation membrane, characterized in that, It includes a top dense ultrathin separation layer, a middle deep-modified coating according to claim 1, and a bottom film layer; wherein the top dense polyamide ultrathin separation layer is made of polyamide or polysulfonamide, with a thickness of 10-300 nm, and is prepared by an interfacial polymerization process, including the following steps: (1) Apply an aqueous solution of polyamine to the surface of a substrate with a deep-modified coating for 1–30 min, and then dry the surface of the film with an air knife. The aqueous solution of polyamine contains an aqueous phase additive, which works synergistically with the deep-modified coating to improve the adsorption capacity of polyamine on the substrate. One or more of the following are selected: triethylamine, sodium alkyl sulfate, sodium alkylbenzene sulfonate, alkyl ammonium bromide, sodium hydroxide, camphor sulfonic acid, fatty alcohol polyoxyethylene ether, and fatty acid polyoxyethylene ester. (2) An alkane solution of polyacrylamide chloride or polysulfonyl chloride is coated onto the surface of the above-mentioned film for 0.5 to 10 min to undergo an interfacial polymerization reaction, wherein the alkane solution contains an alkane phase additive; (3) The surface of the nascent membrane is rinsed with an alkane solvent and then transferred to an oven for heat treatment to finally obtain a deeply modified coating composite separation membrane.

5. The deep-modified coating composite separation membrane according to claim 4, characterized in that, The alkane phase additives used in the preparation of the separation layer are used to accelerate the interfacial polymerization process, and one or more combinations of acetone, dimethyl carbonate, and ethyl acetate are selected.

6. The deep-modified coating composite separation membrane according to claim 4, characterized in that, The deep-modified coating composite separation membrane consists of a polyvinylidene fluoride base membrane at the bottom, a tannic acid-amino carbon quantum dot deep-modified coating in the middle, and a polyamide separation layer at the top.

7. The deep-modified coating composite separation membrane according to claim 4, characterized in that, The deep-modified coating composite separation membrane consists of a plasma-treated polyethylene base membrane at the bottom, a 9,9-bis(4-aminophenyl)fluorene-sodium nitrite deep-modified coating in the middle, and a polyamide separation layer at the top.

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