Nanofiltration membrane, preparation method thereof and water purifier containing nanofiltration membrane

Abstract

The invention provides a nanofiltration membrane, a preparation method thereof and a water purifier containing the nanofiltration membrane. The nanofiltration membrane comprises a supporting layer, an adsorption layer arranged on one side of the supporting layer, a base membrane layer arranged on the other side of the supporting layer and a separation layer arranged on the base membrane layer, the adsorption layer takes activated carbon and an amine substance as main materials, carboxyl in the activated carbon and amino in the amine substance are cross-linked through an amido bond, and the preparation method of the adsorption layer comprises the following steps: coating one side of the support layer with the amine substance and the activated carbon in sequence, and then carrying out a cross-linking reaction with a cross-linking agent to obtain the adsorption layer. And forming the adsorption layer on one side of the supporting layer. The nanofiltration membrane provided by the invention has good effects of removing heavy metals and disinfecting by-products.

Description

Technical Field

[0001] The present invention particularly relates to a nanofiltration membrane and a preparation method thereof and a water purifier containing the same. Background Art

[0002] In 2022, the new version of GB5749 was released, in which the requirements for disinfection by-product indicators were further improved, and some disinfection by-products were changed from unconventional indicators to conventional indicators. This shows that the problem of existing disinfection by-products in drinking water is becoming more and more serious, and experts are paying more and more attention to this aspect, which is enough to show the urgency of removing disinfection by-products in drinking water. Chloroform, as a typical representative of disinfection by-products, is also imminent for its removal in drinking water. At the same time, my country's tap water contains ppb-level heavy metal ions. Long-term drinking of water containing heavy metal ions will cause heavy metals to accumulate in human organs, which is extremely harmful to the human body. Therefore, the less heavy metal ions contained in drinking water, the better. At present, reverse osmosis technology, activated carbon adsorption technology, etc. are mostly used to remove disinfection by-products and heavy metals in drinking water.

[0003] The removal rate of heavy metals by reverse osmosis technology is as high as 99%, and the removal rate of chloroform is about 60%. The removal effect is good, but while removing disinfection byproducts and heavy metals, it will also remove mineral elements in drinking water that are beneficial to the human body. The traditional nanofiltration method can retain minerals in the water body during use, and has a certain effect on removing heavy metals, but it cannot completely remove heavy metals in the water body, and the removal rate of chloroform is basically 0. In order to enhance its ability to adsorb heavy metals or chloroform, the nanofiltration membrane base or modified layer is generally modified to form an adsorption layer, but there are two disadvantages in doing so: on the one hand, the adsorption layer will adsorb heavy metals and chloroform in the wastewater, reducing the efficiency of the adsorption layer; on the other hand, after adsorbing heavy metals and chloroform, the nanofiltration membrane itself is easily blocked due to the small pores of the membrane, resulting in a decrease in membrane flux and affecting the permeability of the membrane itself. Other methods for removing chloroform or heavy metals include ion exchange, electrodialysis, activated carbon adsorption, etc. They have problems such as poor removal effect and high cost.

[0004] Therefore, preparing a filter membrane that can simultaneously remove heavy metal ions and chloroform is a problem that needs to be solved urgently in the art. Summary of the invention

[0005] The present invention mainly aims to overcome the defect that it is difficult to remove both heavy metal ions and disinfection byproducts in the prior art, and provides a nanofiltration membrane and a preparation method thereof and a water purifier containing the same. The nanofiltration membrane provided by the present invention has good effects of removing heavy metals and disinfection byproducts.

[0006] The present invention provides a nanofiltration membrane, which comprises a support layer, an adsorption layer disposed on one side of the support layer, a base film layer disposed on the other side of the support layer, and a separation layer disposed on the base film layer; the adsorption layer uses activated carbon and amine substances as main materials, and carboxyl groups in the activated carbon and amino groups in the amine substances are cross-linked by amide bonds.

[0007] The preparation method of the adsorption layer comprises the following steps: sequentially coating an amine substance and activated carbon on one side of the support layer, and then performing a cross-linking reaction with a cross-linking agent to form the adsorption layer on one side of the support layer.

[0008] In the present invention, in the preparation method of the adsorption layer, the mass ratio of the cross-linking agent to the amine substance can be 1:(10 - 100), such as 1:50 or 1:90.

[0009] In the present invention, the mass ratio of the activated carbon to the amine substance can be 1:(1 - 5), such as 1:2 or 1:4.

[0010] In the present invention, the activated carbon can be activated carbon from conventional sources in the art, preferably coconut shell activated carbon.

[0011] In the present invention, the BET specific surface area of the activated carbon can be ≥1000 m 2 / g, such as 1050 m 2 / g.

[0012] In the present invention, the iodine value of the activated carbon can be ≥1000 mg / g, such as 1100 mg / g.

[0013] In the present invention, the diameter of the activated carbon can be 10 μm - 50 μm, such as 10 μm.

[0014] In the present invention, the amine substance can be a polyamine, such as at least one of polyethyleneimine, chitosan, aspartic acid, polyvinylimidazole, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

[0015] In the present invention, the molecular weight of the amine substance can be 7000 - 100000 g / mol, such as 10000 g / mol.

[0016] In some specific embodiments, the main materials of the adsorption layer are activated carbon and polyethyleneimine.

[0017] In some specific embodiments, the main materials of the adsorption layer are activated carbon and polyvinylimidazole.

[0018] In the present invention, the material of the support layer can be a non-woven fabric material commonly used in the art. Preferably, it is polyethylene terephthalate (PET) and / or polybutylene terephthalate (PBT).

[0019] In the present invention, the base film layer can be formed by doctor blading a casting solution conventional in the art. The casting solution preferably comprises a film-forming material, a pore-forming agent and an organic solvent.

[0020] Among them, the film-forming material is preferably selected from one of polysulfone, polyethersulfone, polypropylene, polyvinylidene fluoride, polyvinyl chloride and polyimide.

[0021] Among them, the number-average molecular weight of the film-forming material is preferably 50,000-200,000.

[0022] Among them, the organic solvent is preferably N,N-dimethylformamide or N,N-dimethylacetamide.

[0023] Among them, the pore-forming agent preferably comprises a mixture of polyvinylpyrrolidone and polyethylene glycol. The polyvinylpyrrolidone is preferably PVPK15; the polyethylene glycol is preferably PEG600.

[0024] In the present invention, the separation layer can be prepared by a conventional method in the art. The preparation method specifically comprises the following steps: coating an aqueous solution on the surface of the base film layer; then coating an oil-phase solution on the surface of the aqueous solution, and then drying to obtain the separation layer;

[0025] Among them, the temperature of the coating is preferably 5-40°C, more preferably 20-30°C; among them, the aqueous solution preferably comprises an aqueous monomer and a solvent; the aqueous monomer is more preferably at least one of piperazine, m-phenylenediamine and p-phenylenediamine; the solvent is more preferably water; among them, the oil-phase solution preferably comprises an oil-phase monomer and a solvent, and the oil-phase monomer is more preferably trimesoyl chloride and / or terephthaloyl chloride; the solvent is more preferably n-hexane;

[0026] Among them, the temperature of the drying is preferably 60-90°C, such as 80°C;

[0027] Among them, the time of the drying is preferably 10-30 s, such as 20 s.

[0028] The present invention also provides a method for preparing a nanofiltration membrane, which comprises the following steps:

[0029] S1. Coating an amine substance and activated carbon on one side of the support layer in sequence, and then performing a crosslinking reaction with a crosslinking agent to form an adsorption layer on one side of the support layer; the activated carbon and the amine substance in the adsorption layer are crosslinked by an amide bond;

[0030] S2. Preparing a base film layer on the other side of the support layer, and then performing interfacial polymerization on the surface of the base film layer to form a separation layer, thus obtaining the nanofiltration membrane.

[0031] In the present invention, the material of the support layer may be a non-woven fabric material commonly used in the art. Preferably, it is polyethylene terephthalate (PET) and / or polybutylene terephthalate (PBT).

[0032] In the present invention, the amine substance may be a polyamine. Preferably, it is at least one of polyethyleneimine, chitosan, aspartic acid, polyvinylimidazole, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine. More preferably, it is polyethyleneimine and / or chitosan.

[0033] In the present invention, the molecular weight of the amine substance may be 7000 - 100000 g / mol, such as 10000 g / mol.

[0034] In S1, the amine substance may react in the form of an amine substance solution.

[0035] Among them, the solvent of the amine substance solution is preferably water.

[0036] Among them, the concentration of the amine substance in the amine substance solution is preferably 1 wt% - 10 wt%, such as 2 wt%.

[0037] In S1, after coating the amine substance, it is preferably dried until there are no obvious water droplets on the surface before coating the activated carbon.

[0038] In the present invention, the activated carbon may be activated carbon from conventional sources in the art. Preferably, it is coconut shell activated carbon.

[0039] In the present invention, the BET specific surface area of the activated carbon may be ≥1000 m 2 / g, such as 1050 m 2 / g.

[0040] In the present invention, the iodine value of the activated carbon may be ≥1000 mg / g, such as 1100 mg / g.

[0041] In the present invention, the diameter of the activated carbon may be 10 μm - 50 μm, such as 10 μm.

[0042] In S1, the method of coating the activated carbon may be electrostatic spraying.

[0043] In S1, after coating the activated carbon, drying may also be carried out. The temperature of the drying is preferably 30°C - 80°C, such as 60°C. The time of the drying is preferably 5 h - 24 h, such as 10 h.

[0044] In the present invention, the mass ratio of the activated carbon to the amine substance may be 1:(1 - 5), such as 1:2 or 1:4.

[0045] In the present invention, the crosslinking agent can be a substance that can react between amine substances or between "amine substances and the support layer", preferably a polyacyl chloride or a polyaldehyde. The polyacyl chloride is preferably trimesoyl chloride, and the polyaldehyde is preferably glutaraldehyde.

[0046] In S1, the crosslinking agent can carry out the crosslinking reaction in the form of a crosslinking agent solution.

[0047] Among them, the solvent of the crosslinking agent solution is preferably one or more of n-hexane, isoparaffin, methanol, and ethanol.

[0048] Among them, the concentration of the crosslinking agent in the crosslinking agent solution is preferably 1 wt% - 5 wt%, for example, 2 wt%.

[0049] In S1, the temperature of the crosslinking reaction is preferably 15°C - 50°C, for example, 25°C.

[0050] In S1, the time of the crosslinking reaction is preferably 0.1 h - 5 h, for example, 20 min.

[0051] After the crosslinking reaction in S1, it is preferably washed and dried.

[0052] In the present invention, the mass ratio of the crosslinking agent to the amine substance can be 1:(10 - 100), for example, 1:50 or 1:90.

[0053] In S2, the preparation method of the base film layer can be conventional in the art, preferably by coating a casting solution on the surface of the support layer, thereby forming the base film layer.

[0054] The casting solution preferably includes a film-forming material, a pore-forming agent, and an organic solvent.

[0055] Among them, the film-forming material is preferably selected from one of polysulfone, polyethersulfone, polypropylene, polyvinylidene fluoride, polyvinyl chloride, and polyimide.

[0056] Among them, the number-average molecular weight of the film-forming material is preferably 50,000 - 200,000.

[0057] Among them, the organic solvent is preferably N,N-dimethylformamide or N,N-dimethylacetamide.

[0058] Among them, the pore-forming agent preferably includes a mixture of polyvinylpyrrolidone and polyethylene glycol. The polyvinylpyrrolidone is preferably PVPK15; the polyethylene glycol is preferably PEG600.

[0059] In S2, the method of interfacial polymerization can be conventional in the art, and preferably includes the following steps: coating an aqueous solution on the surface of the base film layer; then coating an oil-phase solution on the surface of the aqueous solution, and then drying to obtain a separation layer;

[0060] Among them, the temperature of the coating is preferably 5°C - 40°C, more preferably 20°C - 30°C; among them, the aqueous solution preferably includes an aqueous monomer and a solvent; the aqueous monomer is more preferably at least one of piperazine, m-phenylenediamine, and p-phenylenediamine; the solvent is more preferably water; among them, after coating the aqueous solution, it is preferably waited until the volatilization is complete before coating the oil-phase solution, for example, 3 minutes.

[0061] Among them, the oil-phase solution preferably includes an oil-phase monomer and a solvent, and the oil-phase monomer is more preferably trimellitic acid chloride and / or terephthaloyl chloride; the solvent is more preferably n-hexane;

[0062] Among them, after coating the oil-phase solution, it is preferably allowed to react for a period of time before drying, for example, 30 seconds.

[0063] Among them, the temperature of the drying is preferably 60°C - 90°C, for example, 80°C;

[0064] Among them, the time of the drying is preferably 10 seconds - 30 seconds, for example, 20 seconds.

[0065] The present invention also provides a nanofiltration membrane prepared by the preparation method as described above.

[0066] The present invention also provides a water purifier, which includes the nanofiltration membrane as described above.

[0067] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0068] The reagents and raw materials used in the present invention are all commercially available.

[0069] The positive and progressive effects of the present invention are as follows:

[0070] The nanofiltration membrane provided by the present invention has good effects of removing heavy metals and disinfection by-products, and can also maintain good flux and removal effects after being used for a period of time. Brief Description of the Drawings

[0071] Figure 1 It is a filtration schematic diagram of the nanofiltration membrane prepared by the present invention. (Reference numerals: 1 - influent water; 2 - wastewater; 3 - product water; 4 - separation layer; 5 - base film layer; 6 - support layer; 7 - adsorption layer) Detailed Description of the Embodiments

[0072] The present invention will be further described below by way of examples, but the present invention is not thereby limited to the scope of the described examples. For the experimental methods without specific conditions indicated in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0073] Example 1

[0074] (1) Aqueous solution of polyethyleneimine (molecular weight 10000 g / mol) with a concentration of 2 wt% was scrape-coated on one side of the polyester non-woven fabric. After scraping, it was left to dry until there were no obvious water droplets on the surface of the polyester support layer.

[0075] (2) Coconut shell activated carbon powder (BET = 1050 m 2 / g, iodine value = 1100 mg / g, particle size 10 μm) was sprayed by electrostatic spraying on the side of the support layer where the amine aqueous solution had been scrape-coated, so that the activated carbon was evenly attached to this side of the support layer. Then the electrostatically sprayed non-woven fabric was placed in an oven and dried at 60 °C for 10 h; among them, the mass ratio of activated carbon to polyethyleneimine was 1:2.

[0076] (3) After drying, the non-woven fabric was put into a 2 wt% n-hexane solution of trimellitic acid chloride and reacted at 25 °C for 20 min, then washed and dried, to obtain an adsorption layer distributed on one side; among them, the mass ratio of trimellitic acid chloride to polyethyleneimine was 1:50.

[0077] (4) A base film layer was prepared by scraping a film on the other side of the support layer; the casting solution used had a main film-forming material of polysulfone with a number-average molecular weight of 50,000 - 200,000; the organic solvent was N,N-dimethylformamide; the pore-forming agent was a mixture of PVPK15 and PEG600.

[0078] (5) An interfacial polymerization reaction was carried out on the surface of the base film layer to form a separation layer, and then it was washed, moisturized, and dried to obtain a nanofiltration membrane.

[0079] The method of interfacial polymerization was as follows: The material obtained in step (3) was placed in an organic glass frame, clamped well, and placed upright in a fume hood. Wait for about 10 min for the water on its surface to evaporate; at room temperature, about 30 mL of an aqueous solution of piperazine prepared was poured into the organic glass frame, preferably poured from the corner position of the organic glass frame, and left to stand for 5 min; the excess aqueous phase solution was poured into the waste liquid bucket, then the membrane was erected, and wait for about 3 min for the aqueous phase to basically evaporate completely; about 15 mL of a n-hexane solution of trimellitic acid chloride prepared was poured into the organic glass frame as the oil phase, and it must be poured from the corner position of the organic glass frame, reacted for 30 s, and the excess oil phase solution was poured into the waste liquid bucket; shake the membrane vigorously to make the oil phase volatilize quickly, and place it in an oven and treat it at 80 °C for 20 s.

[0080] Example 2

[0081] (1) Scrape and coat an aqueous solution of 2 wt% polyethyleneimine (molecular weight 10000 g / mol) on one side of the polyester non-woven fabric. After scraping and coating, air-dry until there are no obvious water droplets on the surface of the polyester support layer;

[0082] (2) Spray coconut shell activated carbon powder (BET = 1050 m2 / g, iodine value = 1100 mg / g, particle size 10 μm) by electrostatic spraying on the side of the support layer where the amine aqueous solution has been scraped and coated, so that the activated carbon adheres evenly to this side of the support layer. Then, place the electrostatically sprayed non-woven fabric in an oven and dry at 60 °C for 10 h; among them, the mass ratio of activated carbon to amine substances is 1:4;

[0083] (3) After drying, put the non-woven fabric into a 25 °C n-hexane solution of 2 wt% trimellitic acid chloride and react for 20 min, then wash and air-dry to obtain an adsorption layer distributed on one side; among them, the mass ratio of trimellitic acid chloride to amine substances is 1:50;

[0084] (4) Scrape a film on the other side of the support layer to prepare a base film layer; the film-forming solution used has a main film material of polysulfone with a number average molecular weight of 50,000 - 200,000; the organic solvent is N,N-dimethylformamide; the pore-forming agent is a mixture of PVPK15 and PEG600;

[0085] (5) Conduct an interfacial polymerization reaction on the surface of the base film layer to form a separation layer, then wash, moisturize, and dry it to obtain a nanofiltration membrane;

[0086] The method of interfacial polymerization is as follows: Place the material obtained in step (3) in an organic glass frame, clamp it well, and place it vertically in a fume hood. Wait for about 10 min for the water on its surface to evaporate; Pour about 30 mL of an aqueous solution of piperazine prepared as the aqueous phase into the organic glass frame, pour it in as much as possible from the corner position of the organic glass frame, and let it stand for 5 min; Pour the excess aqueous phase solution into the waste liquid bucket, then stand the membrane upright and wait for about 3 min for the aqueous phase to basically evaporate completely; Pour about 15 mL of a n-hexane solution of trimellitic acid chloride prepared as the oil phase into the organic glass frame, and it must be poured in from the corner position of the organic glass frame. React for 30 s, then pour the excess oil phase solution into the waste liquid bucket; Shake the membrane vigorously to make the oil phase evaporate quickly, and place it in an oven and treat it at 80 °C for 20 s.

[0087] Example 3

[0088] (1) Scrape and coat an aqueous solution of 2 wt% polyethyleneimine (molecular weight 10000 g / mol) on one side of the polyester non-woven fabric. After scraping and coating, air-dry until there are no obvious water droplets on the surface of the polyester support layer;

[0089] (2) Spray coconut shell activated carbon powder (BET = 1050 m2 / g, iodine value = 1100 mg / g, particle size of 10 μm) on one side of the support layer that has been coated with an amine aqueous solution by electrostatic spraying, so that the activated carbon adheres evenly to this side of the support layer. Then, place the electrostatically sprayed non-woven fabric in an oven and dry it at 60 °C for 10 h; among them, the mass ratio of activated carbon to amine substance is 1:2;

[0090] (3) After drying is completed, place the non-woven fabric in a 2 wt% solution of trimellitic acid chloride in n-hexane and react at 25 °C for 20 min, then wash and air-dry to obtain an adsorption layer distributed on one side; among them, the mass ratio of trimellitic acid chloride to amine substance is 1:90;

[0091] (4) Prepare a base film layer by casting a film on the other side of the support layer; the casting solution used has a film main material of polysulfone with a number average molecular weight of 50,000 - 200,000; the organic solvent is N,N-dimethylformamide; the pore-forming agent is a mixture of PVPK15 and PEG600;

[0092] (5) Perform an interfacial polymerization reaction on the surface of the base film layer to form a separation layer, then wash, moisturize, and dry it to obtain a nanofiltration membrane;

[0093] The method of interfacial polymerization is as follows: Place the material prepared in step (3) in an organic glass frame, clamp it with clips, and place it vertically in a fume hood. Wait for about 10 min for the water on its surface to evaporate; Pour about 30 mL of an aqueous solution of piperazine prepared as the aqueous phase into the organic glass frame, pour it in as much as possible from the corner position of the organic glass frame, and let it stand for 5 min; Pour the excess aqueous phase solution into the waste liquid bucket, then stand the membrane upright and wait for about 3 min for the aqueous phase to basically evaporate completely; Pour about 15 mL of a solution of trimellitic acid chloride in n-hexane prepared as the oil phase into the organic glass frame, and it must be poured in from the corner position of the organic glass frame. React for 30 s, pour the excess oil phase solution into the waste liquid bucket; Shake the membrane vigorously to make the oil phase evaporate quickly, and place it in an oven and treat it at 80 °C for 20 s.

[0094] Example 4

[0095] (1) Coat an aqueous solution of 2 wt% polyethyleneimine (molecular weight of 10,000 g / mol) on one side of the polyester non-woven fabric. After coating is completed, let it dry until there are no obvious water droplets on the surface of the polyester support layer;

[0096] (2) Spray coconut shell activated carbon powder (BET = 1050 m2 / g, iodine value = 1100 mg / g, particle size of 10 μm) on one side of the support layer that has been coated with an amine aqueous solution by electrostatic spraying, so that the activated carbon adheres evenly to this side of the support layer. Then, place the electrostatically sprayed non-woven fabric in an oven and dry it at 60 °C for 10 h; among them, the mass ratio of activated carbon to amine substance is 1:2;

[0097] (3) After drying is completed, place the non-woven fabric into a n-hexane solution of 2 wt% glutaraldehyde and react at 25 °C for 10 h, then wash and air-dry to obtain an adsorption layer distributed on one side; wherein, the mass ratio of glutaraldehyde to the amine substance is 1:50;

[0098] (4) Cast a film on the other side of the support layer to prepare a base film layer; the casting solution used has a film main material of polysulfone with a number average molecular weight of 50,000 - 200,000; the organic solvent is N,N-dimethylformamide; the pore-forming agent is a mixture of PVPK15 and PEG600;

[0099] (5) Perform an interfacial polymerization reaction on the surface of the base film layer to form a separation layer, then wash, moisturize, and dry it to obtain a nanofiltration membrane;

[0100] The method of interfacial polymerization is as follows: Place the material prepared in step (3) in an organic glass frame, clamp it with clips, and place it upright in a fume hood. Wait for about 10 min for the water on its surface to evaporate; Pour about 30 mL of an aqueous solution of piperazine prepared as the aqueous phase into the organic glass frame, pour it in as much as possible from the corner position of the organic glass frame, and let it stand for 5 min; Pour the excess aqueous phase solution into the waste liquid bucket, then stand the membrane upright, and wait for about 3 min for the aqueous phase to basically evaporate completely; Pour about 15 mL of a n-hexane solution of trimesoyl chloride prepared as the oil phase into the organic glass frame, and it must be poured in from the corner position of the organic glass frame. React for 30 s, then pour the excess oil phase solution into the waste liquid bucket; Shake the membrane vigorously to make the oil phase evaporate quickly, and place it in an oven at 80 °C for 20 s.

[0101] Example 5

[0102] (1) Coat a 2 wt% aqueous solution of polyvinylimidazole (molecular weight 10,000 g / mol) on one side of the polyester non-woven fabric. After coating is completed, air-dry until there are no obvious water droplets on the surface of the polyester support layer;

[0103] (2) Spray coconut shell activated carbon powder (BET = 1050 m 2 / g, iodine value = 1100 mg / g, particle size 10 μm) on the side of the support layer coated with the amine aqueous solution by electrostatic spraying, so that the activated carbon adheres evenly to this side of the support layer, and then place the electrostatically sprayed non-woven fabric in an oven at 60 °C and dry for 10 h; wherein, the mass ratio of activated carbon to the amine substance is 1:2;

[0104] (3) After drying is completed, place the non-woven fabric into a n-hexane solution of 2 wt% trimesoyl chloride and react at 25 °C for 20 min, then wash and air-dry to obtain an adsorption layer distributed on one side; wherein, the mass ratio of trimesoyl chloride to the amine substance is 1:50;

[0105] (4) A base membrane layer is prepared by casting a film on the other side of the support layer; the casting solution used has a main film material of polysulfone with a number average molecular weight of 50,000 - 200,000; the organic solvent is N,N-dimethylformamide; the pore-forming agent is a mixture of PVPK15 and PEG600;

[0106] (5) An interfacial polymerization reaction is carried out on the surface of the base membrane layer to form a separation layer, which is then washed, moisturized, and dried to obtain a nanofiltration membrane;

[0107] The method of interfacial polymerization is as follows: Place the material prepared in step (3) in an organic glass frame, clamp it well, and place it upright in a fume hood. Wait for about 10 minutes for the water on its surface to evaporate; Pour about 30 mL of an aqueous solution of piperazine prepared as the aqueous phase into the organic glass frame, and pour it in as much as possible from the corner position of the organic glass frame, and let it stand for 5 minutes; Pour the excess aqueous phase solution into the waste liquid bucket, then stand the membrane upright, and wait for about 3 minutes for the aqueous phase to basically evaporate completely; Pour about 15 mL of a hexane solution of trimesoyl chloride prepared as the oil phase into the organic glass frame, and it must be poured in from the corner position of the organic glass frame. React for 30 seconds, pour the excess oil phase solution into the waste liquid bucket; Shake the membrane vigorously to make the oil phase evaporate quickly, and place it in an oven at 80 °C for 20 seconds.

[0108] Comparative Example 1

[0109] A base membrane layer is prepared by casting a film on either side of the polyester non-woven fabric, and an interfacial polymerization reaction with the same steps as in Example 1 is carried out on the surface of the base membrane layer to form a separation layer. The membrane sheet is washed, moisturized, and dried to obtain a nanofiltration membrane.

[0110] Comparative Example 2

[0111] (1) Coat an aqueous solution of 2 wt% polyethyleneimine (molecular weight 10,000 g / mol) on one side of the polyester non-woven fabric. After coating, let it dry until there are no obvious water droplets on the surface of the polyester support layer;

[0112] (2) Spray coconut shell activated carbon powder (BET = 1050 m 2 / g, iodine value = 1100 mg / g, particle size 10 μm) on the side of the support layer where the amine aqueous solution has been coated by electrostatic spraying, so that the activated carbon adheres evenly to this side of the support layer. Then place the electrostatically sprayed non-woven fabric in an oven at 60 °C and dry it for 10 h;

[0113] (3) After drying, place the non-woven fabric in a 2 wt% hexane solution of trimesoyl chloride and react at 25 °C for 20 minutes, wash and dry it to obtain a support layer with an adsorption layer distributed on one side, that is, a nanofiltration membrane.

[0114] Comparative Example 3

[0115] (1) Prepare a base film layer by scraping a film on one side of the non-woven fabric. Coat an aqueous solution of 2 wt% polyethyleneimine (molecular weight 10,000 g / mol) on the base film layer. After coating, air-dry until there are no obvious water droplets on the surface;

[0116] (2) Spray coconut shell activated carbon powder (BET = 1050 m 2 / g, iodine value = 1100 mg / g, particle size 10 μm) on the side of the support layer where the amine aqueous solution has been coated by electrostatic spraying, so that the activated carbon adheres evenly to this side of the support layer. Then place the electrostatically sprayed non-woven fabric in an oven and dry at 30 °C for 24 h;

[0117] (3) After drying, put the non-woven fabric into a 2 wt% solution of trimellitic acid chloride in n-hexane and react at 25 °C for 20 min. Wash and air-dry to obtain a support layer with an adsorption layer distributed on one side;

[0118] (4) Perform an interfacial polymerization reaction on the surface of the support layer to form a separation layer. Wash, moisturize, and dry the membrane to obtain a nanofiltration membrane.

[0119] (5) Take a flat nanofiltration membrane with a diameter of 53 mm and place it in a test fixture to test its heavy metal adsorption performance. Use a 25 ppb cadmium nitrate (Cd(NO3)2) solution as the spike solution, control the wastewater ratio to 2:1. The initial heavy metal removal rate of the membrane is 99.9%, and the initial flow rate is 15.8 LMH / Bar. After the membrane passes 4 L of the spike solution (converted to a nanofiltration filter element with a nanofiltration membrane area of 2 m2, the corresponding water passing volume is 4 t, which is 2 times the life of a general nanofiltration filter element), the heavy metal removal rate of the membrane is 99.3%, and the flow rate is 9.5 LMH / Bar. After the membrane passes 8 L of the spike solution (converted to a nanofiltration filter element with a nanofiltration membrane area of 2 m2, the corresponding water passing volume is 8 t, which is 4 times the life of a general nanofiltration filter element), the heavy metal removal rate of the membrane is 95.3%, and the flow rate is 5.6 LMH / Bar. This shows that the nanofiltration membrane has excellent heavy metal removal effect within its service life, but as the amount of spike solution increases, its removal rate decreases slightly and the flow rate decreases significantly;

[0120] (6) Take a flat nanofiltration membrane with a diameter of 53 mm and place it in a test fixture to test its disinfection by-product adsorption performance. Use a 300 ppb chloroform solution as the spike solution, control the wastewater ratio to 2:1. The initial chloroform removal rate of the membrane is 99.9%. The initial flow rate is 15.7 LMH / Bar. After the membrane passes 4 L of the spike solution (converted to a nanofiltration filter element with a nanofiltration membrane area of 2 m 2 2, the corresponding water passing volume is 4 t, which is 2 times the life of a general nanofiltration filter element), the chloroform removal rate of the membrane is 99.9%, and the flow rate is 11.6 LMH / Bar. After the membrane passes 8 L of the spike solution (converted to a nanofiltration filter element with a nanofiltration membrane area of 2 m 2The nanofiltration filter element has a water passing volume of 8t, which is 4 times the lifespan of a general nanofiltration filter element. After that, the chloroform removal rate of the membrane sheet is 43.5%, and the flow rate is 8.9 LMH / Bar. This indicates that the nanofiltration membrane has excellent and stable removal effects on disinfection by-products in the initial stage within its lifespan. However, as the volume of the spiked solution increases, its removal rate decreases significantly, and the flow rate attenuates significantly.

[0121] Effect Example

[0122] Place a nanofiltration membrane with a diameter of 53mm into the test tooling, control the wastewater ratio to be 2:1, and conduct the following effect tests on it:

[0123] (1) TDS (Total Dissolved Solids) rejection rate

[0124] TDS (Total Dissolved Solids) rejection rate = 1 - TDS of filtered water / TDS of spiked solution

[0125] (2) Flux

[0126] At a test temperature of 25°C and a certain external pressure condition, pre-pressurize the membrane for 30 minutes to make it reach a stable state; then, use pure water to test the filter membrane. The test data is repeated three times and the average value is taken. The flux (J) of the filter membrane is calculated by the following formula:

[0127] J = V / (A × Δt × P)

[0128] where, V (L) is the volume of the permeate, A (m 2 ) is the effective area of the test filter membrane, Δt (h) is the running time, and P (bar) is the pressure in front of the membrane.

[0129] (3) Heavy metal adsorption performance

[0130] Use a 25 ppb Cd(NO3)2 solution as the spiked solution, test the concentration of heavy metal ions in the solution passing through the filter membrane, and then calculate it according to the following method. After passing 8L of the spiked solution (converted to a nanofiltration membrane area of 2m 2 The nanofiltration filter element has a water passing volume of 8t, which is 4 times the lifespan of a general nanofiltration filter element), then use the same method for testing and calculation.

[0131] Heavy metal removal rate = 1 - Cd(NO3)2 concentration of filtered water / Cd(NO3)2 concentration of spiked solution

[0132] (4) Disinfection by-product adsorption performance

[0133] Use a 300 ppb chloroform solution as the spiked solution, test the concentration of chloroform in the solution passing through the filter membrane, and then calculate it according to the following method. After passing 8L of the spiked solution, after passing 8L of the spiked solution (converted to a nanofiltration membrane area of 2m 2The nanofiltration filter element has a corresponding water passing capacity of 8 t, which is 4 times the lifespan of a general nanofiltration filter element), and then the same method is used for testing and calculation.

[0134] Trichloromethane removal rate = 1 - concentration of trichloromethane in filtered water / concentration of trichloromethane in spiked solution

[0135]

[0136] The nanofiltration membrane provided by the present invention has good effects in removing heavy metals and disinfection by-products. Further, after being used for a period of time, it can still maintain good flux and the removal efficiency of heavy metals and disinfection by-products. The structural schematic diagram of the nanofiltration membrane and the water flow direction during its application are as Figure 1 shown.

[0137] The rejection rates of TDS of the nanofiltration membranes prepared in Examples 1 - 5 are all 80.7% and above; the adsorption rates of heavy metal ions in the initial state are all 99.9% and above; after passing 8 L of spiked solution, the adsorption rates of heavy metal ions are 92.3% and above, and can reach 99.9% in the better case; the adsorption rates of disinfection by-products in the initial state are all 99.9% and above; after passing 8 L of spiked solution, the adsorption rates of disinfection by-products are 90.5% and above, and can reach 99.9% in the better case. And during the process of removing heavy metals and disinfection by-products, the flow rate is relatively stable and there is no obvious attenuation. The activated carbon on the surface of the nanofiltration membrane provided by the present invention contains abundant carboxylic acid groups. During the drying process after electrostatic spraying, the carboxylic acid groups on the surface of the activated carbon react with the amino groups of amine substances, enabling the activated carbon to be well fixed on the amine substance coating; and the amine substances undergo a cross-linking reaction with the cross-linking agent, which can firmly fix the amine substances and the activated carbon on the support layer; it can maintain a long service life and significantly enhance the function of adsorbing heavy metals and disinfection by-products.

[0138] In Comparative Example 1, no adsorption layer was set. It can be seen from the effect data in Table 1 that although its ability to remove heavy metal ions remains good, the overall level is worse than that of the examples; and the removal effect on disinfection by-products is very poor. This may be because Comparative Example 1 has a base film layer and a separation layer, which can remove heavy metal ions to a certain extent, but since the substances in the adsorption layer have a significant impact on the removal of disinfection by-products, and no adsorption layer was set in Comparative Example 1, resulting in very poor effects.

[0139] In Comparative Example 2, no base film layer and separation layer were set, and the removal abilities of both heavy metals and disinfection by-products are very poor. This may be because the pore size of the support layer itself is relatively large, so the flux of the overall filter membrane is very high, and heavy metal ions and disinfection by-products cannot come into full contact with the adsorption layer, resulting in a very low removal efficiency.

[0140] In Comparative Example 3, the base film layer, the separation layer and the adsorption layer are arranged according to the structure of the present invention. From the effect data, it can be known that the nanofiltration membrane has excellent and stable removal effect on disinfection by-products in the initial stage within its service life. However, as the spiked solution increases, its removal rate decreases significantly and the flux attenuates significantly.

[0141] In the specific embodiments described above, the purpose, technical solution and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A nanofiltration membrane, characterized in that, It includes a support layer, an adsorption layer provided on one side of the support layer, a base film layer provided on the other side of the support layer, and a separation layer provided on the base film layer; the adsorption layer uses activated carbon and amine substances as the main materials, and the carboxyl group in the activated carbon and the amino group in the amine substances are crosslinked by amide bonds; The preparation method of the adsorption layer includes the following steps: sequentially coat the amine substance and the activated carbon on one side of the support layer, and then carry out a crosslinking reaction with a crosslinking agent to form the adsorption layer on one side of the support layer.

2. The nanofiltration membrane according to claim 1, wherein, In the preparation method of the adsorption layer, the mass ratio of the crosslinking agent to the amine substance is 1:(10 - 100), such as 1:50 or 1:90; And / or, the mass ratio of the activated carbon to the amine substance is 1:(1 - 5), such as 1:2 or 1:4; And / or, the molecular weight of the amine substance is 7000 - 100000 g / mol, such as 10000 g / mol; And / or, the main materials of the adsorption layer are activated carbon and polyethyleneimine; And / or, the material of the support layer is polyethylene terephthalate and / or polybutylene terephthalate; and / or, the BET specific surface area of the activated carbon is ≥ 1000 m 2 / g, such as 1050 m 2 / g; And / or, the iodine value of the activated carbon is ≥1000 mg / g, such as 1100 mg / g; And / or, the diameter of the activated carbon is 10 μm - 50 μm, such as 10 μm.

3. A method for preparing a nanofiltration membrane, characterized in that, It includes the following steps: S1. Sequentially coat the amine substance and the activated carbon on one side of the support layer, and then carry out a crosslinking reaction with a crosslinking agent to form an adsorption layer on one side of the support layer; the activated carbon and the amine substance in the adsorption layer are crosslinked by amide bonds; S2. Prepare a base film layer on the other side of the support layer, and then carry out interfacial polymerization on the surface of the base film layer to form a separation layer, thus obtaining the nanofiltration membrane.

4. The preparation method of the nanofiltration membrane according to claim 3, characterized in that, The amine substance is a polyamine, such as at least one of polyethyleneimine, chitosan, aspartic acid, polyvinylimidazole, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine; And / or, the crosslinking agent is a polyacid chloride or a polyaldehyde, and the polyacid chloride is preferably trimesoyl chloride, and the polyaldehyde is preferably glutaraldehyde; And / or, in S1, the amine substance reacts in the form of an amine substance solution; wherein, the solvent of the amine substance solution is preferably water; the concentration of the amine substance in the amine substance solution is preferably 1 wt% - 10 wt%, such as 2 wt%; And / or, the mass ratio of the activated carbon to the amine substance is 1:(1 - 5), such as 1:2 or 1:4; And / or, in S1, the crosslinking agent carries out a crosslinking reaction in the form of a crosslinking agent solution; wherein, the solvent of the crosslinking agent solution is preferably one or more of n - hexane, isoparaffin, methanol, and ethanol; the concentration of the crosslinking agent in the crosslinking agent solution is preferably 1 wt% - 5 wt%, such as 2 wt%; And / or, the mass ratio of the crosslinking agent to the amine substance is 1:(10 - 100), such as 1:50 or 1:

90.

5. The preparation method of the nanofiltration membrane according to claim 3, characterized in that, In S1, the way of coating the activated carbon is electrostatic spraying; And / or, in S1, after coating the activated carbon, drying is also carried out; the temperature of the drying is preferably 30°C - 80°C, such as 60°C; the time of the drying is preferably 5h - 24h, such as 10h; And / or, in S1, the temperature of the cross-linking reaction is 15°C - 50°C, such as 25°C; And / or, in S1, the time of the cross-linking reaction is 0.1h - 5h, such as 20min; And / or, in S1, after the cross-linking reaction is completed, washing and drying are also carried out.

6. The method for preparing a nanofiltration membrane according to claim 3, wherein The molecular weight of the amine substance is 7000 - 100000 g / mol, such as 10000 g / mol; And / or, the material of the support layer is polyethylene terephthalate and / or polybutylene terephthalate; and / or, the BET specific surface area of the activated carbon is ≥ 1000 m 2 / g, such as 1050 m 2 / g; And / or, the iodine value of the activated carbon is ≥1000 mg / g, such as 1100 mg / g; And / or, the diameter of the activated carbon is 10μm - 50μm, such as 10μm.

7. The method for preparing a nanofiltration membrane according to claim 3, wherein In S2, the method for preparing the base film layer is to coat the casting solution on the surface of the support layer, and then the base film layer is formed; Wherein, the casting solution preferably includes a film-forming material, a pore-forming agent and an organic solvent; Wherein, the film-forming material is preferably selected from one of polysulfone, polyethersulfone, polypropylene, polyvinylidene fluoride, polyvinyl chloride and polyimide; Wherein, the number-average molecular weight of the film-forming material is preferably 50,000 - 200,000; Wherein, the organic solvent is preferably N,N-dimethylformamide or N,N-dimethylacetamide; Wherein, the pore-forming agent preferably includes a mixture of polyvinylpyrrolidone and polyethylene glycol; the polyvinylpyrrolidone is preferably PVPK15; the polyethylene glycol is preferably PEG600.

8. The method for preparing a nanofiltration membrane according to any one of claims 3-7, characterized in that, In S2, the interfacial polymerization includes the following steps: coating the aqueous solution on the surface of the base film layer; then coating the oil-phase solution on the surface of the aqueous solution, and then drying to obtain the separation layer; Wherein, the temperature of the coating is preferably 5°C - 40°C, more preferably 20°C - 30°C; Wherein, the aqueous solution preferably includes an aqueous monomer and a solvent; the aqueous monomer is more preferably at least one of piperazine, m-phenylenediamine and p-phenylenediamine; the solvent is more preferably water; Wherein, after coating the aqueous solution, it is preferably waited until volatilization is complete before coating the oil-phase solution, such as 3min; Wherein, the oil-phase solution preferably includes an oil-phase monomer and a solvent, the oil-phase monomer is more preferably trimesoyl chloride and / or terephthaloyl chloride; the solvent is more preferably n-hexane; Wherein, after coating the oil-phase solution, it is preferably allowed to react for a period of time before drying, such as 30s; Wherein, the temperature of the drying is preferably 60°C - 90°C, such as 80°C; Wherein, the time of the drying is preferably 10s - 30s, such as 20s.

9. A nanofiltration membrane, characterized in that, It is prepared by the preparation method described in any one of claims 3 - 8.

10. A water purifier, characterized in that, It includes the nanofiltration membrane described in any one of claims 1, 2 and 9.

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