A nanofiltration membrane for water treatment to remove hardness and its preparation method

Abstract

This invention discloses a water treatment nanofiltration membrane for removing hardness, comprising: a non-woven fabric as a support layer; a microporous ultrafiltration layer as a base membrane; and a separation functional layer coated on the surface of the base membrane. It also discloses a method for preparing the water treatment nanofiltration membrane for removing hardness. If the separation functional layer is composed of a copolymer crosslinking resin of furfural and melamine, the preparation method includes: step S1, mixing furfural and melamine in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and adding 1-10% catalyst to the aqueous solution to obtain a final solution; step S2, uniformly coating the final solution onto the surface of the ultrafiltration substrate; step S3, controlling the heating temperature between 60-120℃, allowing the coating to crosslink, cure, and dry, forming a stable separation functional layer. This invention is resistant to strong acids and alkalis and can effectively intercept calcium and magnesium ions.

Description

Technical Field

[0001] This invention relates to a nanofiltration membrane for water treatment that removes hardness and its preparation method. Background Technology

[0002] The photovoltaic (PV) production process involves numerous chemical cleaning, etching, and acid / alkali adjustment processes, which generate wastewater containing heavy metals, acids, alkalis, solvents, and other harmful substances. Direct discharge of this wastewater without treatment will cause serious environmental pollution. Therefore, membrane technology for PV wastewater treatment has become an effective solution. PV wastewater treatment often requires the addition of calcium carbonate to remove fluoride ions. Calcium ions increase water hardness, significantly increasing the risk of scaling in subsequent membrane-treated water reuse. Removing hardness from the water is a crucial step in PV wastewater treatment. Nanofiltration membranes, as a highly efficient separation technology, can effectively remove calcium and magnesium ions from water, effectively reducing water hardness, minimizing scaling risks, and ensuring the purity of reused water. With the continuous development of nanofiltration membrane technology, membrane materials for calcium ion removal from PV wastewater are gradually evolving towards higher efficiency, durability, and lower cost, showing broad application prospects.

[0003] However, currently available nanofiltration membranes are mainly based on polyamide structures for their separation layers, which are not resistant to strong acids, strong alkalis, and strong oxidizing environments. To ensure long-term performance stability, the concentration of oxidizing substances in the influent must be below 0.1 ppm, the acid concentration below 0.2%, and the alkali concentration below 0.004%. Due to the special characteristics of photovoltaic wastewater—strong acid, concentrated alkali, and high oxidation—conventional nanofiltration membranes cannot be used directly and require complex pretreatment processes, increasing treatment costs.

[0004] Therefore, a water treatment nanofiltration membrane capable of removing hardness that can withstand strong acids and alkalis is provided, along with its preparation method. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing nanofiltration membranes for water treatment and their preparation method, which are resistant to strong acids and alkalis and can effectively intercept calcium and magnesium ions.

[0006] The technical solution to achieve the above objectives is:

[0007] One embodiment of the present invention is a water treatment nanofiltration membrane for removing hardness, comprising:

[0008] Non-woven fabric is used as the support layer;

[0009] Using a microporous ultrafiltration layer as the base membrane; and

[0010] Separation functional layer coated on the surface of the base film.

[0011] Preferably, the materials of the nonwoven fabric include, but are not limited to, polypropylene, polyvinyl chloride, and polyphenylene sulfide.

[0012] Preferably, the microporous ultrafiltration layer material includes, but is not limited to, polysulfone, polyethersulfone, polyethylene, polypropylene and polyvinylidene fluoride, wherein the micropore size is between 3 and 30 nanometers and the ultrafiltration layer thickness is between 5 and 50 micrometers.

[0013] Preferably, the separation functional layer has a thickness of 1-100 nanometers and its structure is composed of a copolymer crosslinked resin of furfural and melamine, wherein the molar ratio of furfural to melamine ranges from 1:1 to 5:1.

[0014] Preferably, the separation functional layer has a thickness of 1-100 nanometers and its structure is composed of a copolymer crosslinked resin of furfural, melamine and formaldehyde, wherein the molar ratio of furfural to melamine ranges from 1:1 to 5:1 and the molar ratio of formaldehyde to melamine ranges from 4:1 to 2:1.

[0015] A method for preparing a water treatment nanofiltration membrane for hardness removal according to the second aspect of the present invention, wherein the separation functional layer is composed of a copolymer crosslinking resin of furfural and melamine, the preparation method includes:

[0016] Step S1: Furfural and melamine are mixed in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and 1-10% catalyst is added to the aqueous solution to obtain the final solution;

[0017] Step S2: The final solution is uniformly coated on the surface of the ultrafiltration mold.

[0018] Step S3: Control the heating temperature between 60-120℃, the coating cross-links, cures and dries, forming a stable separation functional layer.

[0019] Preferably, in step S1, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes, but is not limited to, sulfuric acid, benzenesulfonic acid and trifluoroformic acid, and the Lewis acid includes, but is not limited to, zinc nitrate and aluminum nitrate.

[0020] Preferably, in step S2, the ultrafiltration bottom mold is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane.

[0021] In step S2, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating.

[0022] A method for preparing a water treatment nanofiltration membrane for hardness removal according to the third aspect of the present invention, wherein the separation functional layer is composed of a copolymer crosslinking resin of furfural, melamine and formaldehyde, the preparation method includes:

[0023] Step S4: Mix furfural, melamine and formaldehyde in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and add an appropriate amount of sodium hydroxide to the aqueous solution to adjust the solution.

[0024] Step S5: After heating at 80°C for 10-20 hours, cool to room temperature and add 1-10% catalyst to the resulting solution to obtain the final solution.

[0025] Step S6: The final solution is uniformly coated onto the surface of the ultrafiltration mold.

[0026] Step S7: Control the heating temperature between 60-120℃, the coating cross-links, cures and dries, forming a stable separation functional layer.

[0027] Preferably, in step S4, the pH of the solution is adjusted to 9-10;

[0028] In step S5, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes, but is not limited to, sulfuric acid, benzenesulfonic acid and trifluoroformic acid, and the Lewis acid includes, but is not limited to, zinc nitrate and aluminum nitrate;

[0029] In step S6, the ultrafiltration bottom mold is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane.

[0030] In step S6, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating.

[0031] The beneficial effects of this invention are as follows: This invention uses non-woven fabric as the support layer, selects non-woven fabric materials resistant to strong acids and alkalis, uses a microporous ultrafiltration layer as the base membrane, and selects acid and alkali resistant materials, so that the nanofiltration membrane can withstand strong acid, strong alkali and strong oxidizing environments, ensuring the long-term performance stability of the nanofiltration membrane. Moreover, the separation functional layer structure coated on the surface of the base membrane is composed of furfural and melamine, or furfural, melamine and formaldehyde, which greatly improves the performance of removing calcium and magnesium ions and can effectively intercept calcium and magnesium ions. Attached Figure Description

[0032] Figure 1 This is a flowchart of a method for preparing a water treatment nanofiltration membrane for removing hardness according to the present invention;

[0033] Figure 2 This is another flowchart of a method for preparing a water treatment nanofiltration membrane for removing hardness according to the present invention;

[0034] Figure 3 This is a chemical structure diagram of furfural in this invention;

[0035] Figure 4 This is the chemical structure diagram of melamine in this invention. Detailed Implementation

[0036] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] The invention will now be further described with reference to the accompanying drawings.

[0038] A water treatment nanofiltration membrane for removing hardness includes: a nonwoven fabric as a support layer; a microporous ultrafiltration layer as a base membrane; and a separation functional layer coated on the surface of the base membrane.

[0039] In the embodiments, the materials of the nonwoven fabric include, but are not limited to, polypropylene, polyvinyl polypropylene, and polyphenylene sulfide.

[0040] In the embodiments, the microporous ultrafiltration layer material includes, but is not limited to, polysulfone, polyethersulfone, polyethylene, polypropylene and polyvinylidene fluoride, wherein the micropore size is between 3 and 30 nanometers and the ultrafiltration layer thickness is between 5 and 50 micrometers.

[0041] In the embodiments, the thickness of the separation functional layer is 1-100 nanometers, and the structure is composed of a copolymer crosslinking resin of furfural and melamine, wherein the molar ratio of furfural to melamine ranges from 1:10 to 10:1, preferably from 1:1 to 5:1. Furfural can be replaced with furfuryl alcohol. The chemical structure of furfural is as follows: Figure 3 As shown, the chemical structure of melamine is as follows: Figure 4 As shown.

[0042] In the embodiments, the thickness of the separation functional layer is 1-100 nanometers, and the structure is composed of a copolymer crosslinking resin of furfural, melamine and formaldehyde, wherein the molar ratio of furfural to melamine ranges from 1:10 to 10:1, preferably from 1:1 to 5:1, and the molar ratio of formaldehyde to melamine ranges from 4:1 to 2:1.

[0043] like Figure 1 As shown, a method for preparing a water treatment nanofiltration membrane for hardness removal, wherein the separation functional layer is composed of a copolymer crosslinking resin of furfural and melamine, the preparation method includes:

[0044] Step S1: Furfural and melamine are mixed in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and 1-10% catalyst is added to the aqueous solution to obtain the final solution.

[0045] In the examples, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes, but is not limited to, sulfuric acid, benzenesulfonic acid and trifluoroformic acid, and the Lewis acid includes, but is not limited to, zinc nitrate and aluminum nitrate.

[0046] Step S2: The final solution is uniformly coated onto the surface of the ultrafiltration mold.

[0047] In this embodiment, the ultrafiltration substrate is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane.

[0048] In the embodiments, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating.

[0049] Step S3: Control the heating temperature between 60-120℃, the coating cross-links, cures and dries, forming a stable separation functional layer.

[0050] like Figure 2 As shown, a method for preparing a water treatment nanofiltration membrane for hardness removal, wherein the separation functional layer is composed of a copolymer crosslinking resin of furfural, melamine, and formaldehyde, the preparation method includes:

[0051] Step S4: Furfural, melamine and formaldehyde are mixed in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and an appropriate amount of sodium hydroxide is added to the aqueous solution to adjust the solution.

[0052] In the example, the pH of the solution was adjusted to 9-10.

[0053] Step S5: After heating at 80°C for 10-20 hours, cool to room temperature and add 1-10% catalyst to the resulting solution to obtain the final solution.

[0054] In the examples, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes, but is not limited to, sulfuric acid, benzenesulfonic acid and trifluoroformic acid, and the Lewis acid includes, but is not limited to, zinc nitrate and aluminum nitrate.

[0055] Step S6: The final solution is uniformly coated onto the surface of the ultrafiltration mold.

[0056] In this embodiment, the ultrafiltration substrate is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane.

[0057] In the embodiments, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating.

[0058] Step S7: Control the heating temperature between 60-120℃, the coating cross-links, cures and dries, forming a stable separation functional layer.

[0059] The comparative examples and Examples 1-4 demonstrate that the solution of the present invention can effectively improve the hardness removal effect of nanofiltration membranes.

[0060] Comparative Example: 8.0 g of furfuryl alcohol and 2.5 g of formaldehyde were mixed in 89.5 g of pure water. 50% NaOH solution was slowly added to adjust the pH to between 9.5 and 10. The solution was heated at 80°C for 10 hours and then cooled to room temperature. 5 g of trifluoroacetic acid was added to prepare a coating solution. The above coating solution was uniformly applied to the surface of a polysulfone ultrafiltration membrane (pore size 10 nm, thickness 30 μm, polypropylene nonwoven fabric support layer). The membrane was then placed in a 100°C oven for crosslinking polymerization for 180 seconds, followed by rinsing in pure water until the pH was neutral. The resulting membrane was tested for calcium chloride separation performance at a pressure of 100 psi, a calcium chloride aqueous solution concentration of 500 ppm, and a membrane surface flow rate >4 L / min. After stabilization for 30 min, the flux was measured to be 20 LMH, and the calcium chloride removal rate was 8.5%.

[0061] Example 1: 8.0 g of furfuryl alcohol and 10.3 g of melamine were mixed in 81.7 g of pure water, and 3.0 g of zinc chloride was added to prepare a coating solution. The above solution was uniformly coated onto the surface of a polysulfone ultrafiltration membrane, which was then placed in a 120°C oven for crosslinking polymerization for 180 seconds. Afterward, it was immersed in pure water and washed until the pH was neutral. The resulting membrane was tested for calcium chloride separation performance at a pressure of 100 psi and a calcium chloride aqueous solution concentration of 500 ppm. The measured flux was 16.8 LMH, and the calcium chloride removal rate was 62.1%.

[0062] Example 2: 3.0 g of furfuryl alcohol and 19.3 g of melamine were mixed in 77.7 g of pure water, and 3.0 g of zinc chloride was added to prepare a coating solution. The polysulfone ultrafiltration membrane was uniformly coated with this solution and placed in a 120°C oven for crosslinking polymerization for 180 seconds. It was then rinsed in pure water until the pH was neutral. The resulting membrane was tested for calcium chloride separation performance at a pressure of 100 psi and a calcium chloride aqueous solution concentration of 500 ppm. The measured flux was 9.1 LMH, and the calcium chloride removal rate was 85.8%.

[0063] Example 3: 5.0 g furfuryl alcohol, 12.8 g melamine, and 30.6 g formaldehyde solution (30%) were mixed to form 100 g of aqueous solution. 50% NaOH solution was slowly added to adjust the pH to between 9.5 and 10. The solution was heated at 80°C for 20 hours and then cooled to room temperature. 5 g trifluoroacetic acid was added to prepare a coating solution. The polysulfone ultrafiltration membrane was uniformly coated with the above coating solution and placed in a 100°C oven for crosslinking polymerization for 180 seconds. It was then immersed in pure water and washed until the pH was neutral. The resulting membrane was tested for calcium chloride separation performance at a test pressure of 100 psi and a calcium chloride aqueous solution concentration of 500 ppm. The measured flux was 7.7 LMH, and the calcium chloride removal rate was 80.3%. After immersing the resulting membrane in a 4% sodium hydroxide aqueous solution for 168 hours and washing with pure water until neutral, the calcium chloride removal rate was tested to be 80.4%, and the performance remained unchanged.

[0064] Example 4: 5.0 g furfural, 12.8 g melamine, and 30.6 g formaldehyde solution (30%) were mixed to form 100 g of aqueous solution. 50% NaOH solution was slowly added to adjust the pH to between 9.5 and 10. The solution was heated at 80°C for 20 hours and then cooled to room temperature. 5 g trifluoroacetic acid was added to prepare a coating solution. The above coating solution was uniformly applied to the surface of a polyethylene microporous ultrafiltration membrane (pore size 30 nm, thickness 40 μm, polypropylene nonwoven fabric support layer). The membrane was then placed in an 80°C oven for crosslinking polymerization for 60 seconds, followed by immersion in pure water until the pH was neutral. The resulting membrane was tested for calcium chloride separation performance at a pressure of 100 psi and a calcium chloride aqueous solution concentration of 500 ppm. The measured flux was 13.8 LMH, and the calcium chloride removal rate was 76.1%. After immersion in a 4% sodium hydroxide aqueous solution for 168 hours and rinsing with pure water until neutral, the calcium chloride removal rate was 76.0%, and the performance remained unchanged.

[0065] From a material perspective, the nanofiltration membrane of this invention, whether it is the support layer, the ultrafiltration layer, or the separation functional layer, can withstand strong acids and concentrated alkalis, is not easily hydrolyzed, and has stable performance. In particular, it has a high removal rate for polyvalent cations (such as calcium and magnesium ions), is suitable for water hardening, improves the membrane treatment recycling rate, and has a good application prospect in high recovery rate or zero discharge wastewater treatment applications.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nanofiltration membrane for water treatment to remove hardness, characterized in that, include: Non-woven fabric is used as the support layer; Using a microporous ultrafiltration layer as the base membrane; as well as A separation functional layer coated on the surface of the base film; The thickness of the separation functional layer is between 1 and 100 nanometers, and the structure is composed of a copolymer crosslinked resin of furfural and melamine, wherein the molar ratio of furfural to melamine ranges from 1:1 to 5:

1. or The separation functional layer has a thickness between 1 and 100 nanometers and is composed of a copolymer crosslinked resin of furfural, melamine and formaldehyde. The molar ratio of furfural to melamine ranges from 1:1 to 5:1, and the molar ratio of formaldehyde to melamine ranges from 4:1 to 2:

1. If the separation functional layer is composed of a copolymer crosslinking resin of furfural and melamine, its preparation method includes: Step S1: Furfural and melamine are mixed in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and 1-10% catalyst is added to the aqueous solution to obtain the final solution; Step S2: The final solution is uniformly coated on the surface of the ultrafiltration mold. Step S3: Control the heating temperature between 60-120℃, the coating cross-links, cures and dries, forming a stable separation functional layer; In step S1, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes sulfuric acid, benzenesulfonic acid or trifluoroformic acid, and the Lewis acid includes zinc nitrate or aluminum nitrate. In step S2, the ultrafiltration bottom mold is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane. In step S2, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating. If the separation functional layer is composed of a copolymer crosslinking resin of furfural, melamine, and formaldehyde, its preparation method includes: Step S4: Mix furfural, melamine and formaldehyde in a certain proportion to prepare an aqueous solution with a concentration range of 1%-10%, and add an appropriate amount of sodium hydroxide to the aqueous solution to adjust the solution. Step S5: After heating at 80°C for 10-20 hours, cool to room temperature and add 1-10% catalyst to the resulting solution to obtain the final solution. Step S6: The final solution is uniformly coated onto the surface of the ultrafiltration mold. Step S7: Control the heating temperature between 60-120℃, the coating cross-links, cures, and dries to form a stable separation functional layer; In step S4, the pH of the solution is adjusted to 9-10; In step S5, the catalyst is a strong acid or a Lewis acid, wherein the strong acid includes sulfuric acid, benzenesulfonic acid or trifluoroformic acid, and the Lewis acid includes zinc nitrate or aluminum nitrate. In step S6, the ultrafiltration bottom mold is composed of a non-woven fabric as a support layer and a microporous ultrafiltration layer as a base membrane. In step S6, the coating method is one of dip coating, spray coating, printing, transfer coating, or slot coating.

2. The nanofiltration membrane for removing hardness in water treatment according to claim 1, characterized in that, Nonwoven fabrics are made of materials including polypropylene, polyvinyl polypropylene, or polyphenylene sulfide.

3. The water treatment nanofiltration membrane for removing hardness according to claim 1, characterized in that, Microporous ultrafiltration layer materials include polysulfone, polyethersulfone, polyethylene, polypropylene, or polyvinylidene fluoride, wherein the micropore size is between 3 and 30 nanometers and the ultrafiltration layer thickness is between 5 and 50 micrometers.

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