An acid-catalyzed cross-linked high-flux acid-resistant nanofiltration membrane and a preparation method thereof

Abstract

This invention relates to an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane and its preparation method, comprising the following steps: Step 1, mixing a multifunctional amine substance, a surfactant, an acid catalyst, and water, and stirring until homogeneous to obtain an aqueous solution; the multifunctional amine substance includes one or more of polyethyleneimine, branched polyethyleneimine, polyethylene aniline, and polyaniline; Step 2, dissolving trimesoyl chloride monomer in n-hexane and stirring until dissolved to obtain an organic solution; Step 3, immersing the ultrafiltration base membrane first in the aqueous solution for treatment, and then immersing it in the organic solution for interfacial polymerization to generate a nascent polyamine membrane layer; Step 4, heat treatment: subjecting the generated nascent polyamine membrane layer to heat treatment to obtain an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane; the membrane structure of this invention is stable, exhibiting excellent acid resistance, high permeability, and desalination rate.

Description

Technical Field

[0001] This invention relates to the field of membrane separation and water treatment technology, specifically to a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking and its preparation method. Background Technology

[0002] Nanofiltration membrane technology can remove heavy metal ions from acidic wastewater and has significant advantages in acid recycling. Therefore, it is increasingly being used in the field of resource recovery of acidic wastewater.

[0003] However, traditional commercial nanofiltration membranes, such as polyamide nanofiltration membranes, typically have a selective layer prepared by interfacial polymerization of piperazine and trimesoyl chloride. In strong acid environments, the electron-withdrawing effect of the carbonyl group in the polyamide bond causes the electron cloud to concentrate towards the carbonyl oxygen, making the H on the amide N electron in an electron-deficient state, which makes it easy for nucleophilic substitution reactions to occur, leading to molecular rearrangement. Therefore, in long-term applications, they are somewhat sensitive to strong acids, making it difficult for polyamide nanofiltration membranes to reach a stable state in acidic solvents such as polar aprotic and protic solvents, thus limiting their application in the treatment of acidic wastewater.

[0004] To address these issues, researchers have developed acid-resistant nanofiltration membranes using sulfonyl chlorides or cyanuric chlorides as organic phase monomers resistant to strong acids. However, due to the low reactivity and low density of chlorine-containing functional groups of strong acid-resistant monomers such as sulfonyl chlorides and cyanuric chlorides, these acid-resistant nanofiltration membranes exhibit low crosslinking degree, large average pore size, low flux or low rejection rate, resulting in poor membrane performance.

[0005] Therefore, it is crucial to develop a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking and its preparation method, which can ensure excellent acid resistance while also having high flux and high rejection rate. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane and its preparation method, which not only has good acid resistance, but also has high flux and high rejection rate.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0009] Step 1, Preparation of aqueous solution: Mix the multifunctional amine, surfactant, and acid catalyst with water and stir until homogeneous to obtain an aqueous solution;

[0010] The multifunctional amine substances include one or more of polyethyleneimine, branched polyethyleneimine, polyethylene aniline, and polyaniline;

[0011] Step 2, Preparation of organic phase solution: Dissolve the trimesoyl chloride monomer in n-hexane and stir to dissolve, thus obtaining the organic phase solution;

[0012] Step 3, interfacial polymerization reaction: The ultrafiltration membrane is first immersed in an aqueous solution for treatment. After treatment, the aqueous solution is discarded and the residual solution is removed. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction is completed, a nascent polyamine membrane layer is generated.

[0013] Step 4, heat treatment: The generated nascent polyamine membrane layer is heat treated to obtain a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking.

[0014] As a further technical solution, the method for preparing the ultrafiltration membrane includes the following steps:

[0015] The polymer is dissolved in an organic solvent and stirred under a magnetic stirrer. After standing to remove bubbles, a homogeneous casting solution is formed. The homogeneous casting solution is then coated onto a nonwoven support material using a flatbed film scraper and then quickly placed in a coagulation bath for curing to form an ultrafiltration base membrane layer, thus obtaining the ultrafiltration base membrane.

[0016] As a further technical solution, the polymer is one or more of polysulfone, polyethersulfone, polytetrafluoroethylene, polyvinylidene fluoride, and polyetheretherketone, with polysulfone being preferred.

[0017] As a further technical solution, the organic solvent is one or more of dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and tetramethyl sulfoxide, preferably dimethylformamide.

[0018] As a further technical solution, the concentration of the multifunctional amine in the aqueous solution is 1wt%-3wt%, the concentration of the surfactant is 0.1-3.0wt%, and the concentration of the acid catalyst is 0.05-0.5wt%.

[0019] As a further technical solution, the surfactant is mainly sodium dodecyl sulfate;

[0020] As a further technical solution, the acid catalyst is mainly one or more of a carboxylic acid catalyst or a sulfonic acid monomer catalyst; a carboxylic acid catalyst is preferred.

[0021] As a further technical solution, the carboxylic acid catalyst includes one or more of 1,2-benzoic acid, 1,3-benzoic acid, 1,4-benzoic acid, 1,2-phenylacetic acid, 1,3-phenylacetic acid, 1,4-phenylacetic acid, 1,2-phenylpropionic acid, 1,3-phenylpropionic acid, and 1,4-phenylpropionic acid.

[0022] The sulfonic acid catalyst includes one or more of p-benzenesulfonic acid, o-benzenesulfonic acid, and m-benzenesulfonic acid.

[0023] As a further technical solution, the concentration of pyromellitic chloride monomer in the organic phase solution is 0.1wt%-0.3wt%.

[0024] As a further technical solution, the immersion time of the ultrafiltration membrane in the aqueous solution is 30s-120s.

[0025] As a further technical solution, the immersion time of the ultrafiltration membrane in the organic phase solution is 10s-30s.

[0026] As a further technical solution, the heat treatment temperature is 50-90℃ and the heat treatment time is 3-8 minutes.

[0027] As a further technical solution, the acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane is stored in a deionized aqueous solution for later use.

[0028] A high-flux acid-resistant nanofiltration membrane prepared by the aforementioned preparation method comprises an ultrafiltration base membrane, a polyamide separation layer disposed on the ultrafiltration base membrane, wherein the ultrafiltration base membrane comprises a nonwoven support layer and an ultrafiltration base membrane layer disposed on the nonwoven support layer.

[0029] As a further technical solution, the polyamide release layer has a thickness of 0.16-0.21 μm, a crosslinking density of 81.2-88.6%, a porosity of 3.8-4.3%, and a tensile strength of 2397-2508 Kgf / cm². 2 ， The elongation at break is 89-91%.

[0030] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0031] Because the partial double bond configuration (NCO) in the amide bond is subject to the delocalization effect of lone pairs, the lone pairs provided by nitrogen to the carbonyl group make the oxygen in the carbonyl group highly nucleophilic. This makes the highly nucleophilic carbonyl oxygen and nitrogen atom easily protonated under acidic conditions. In this invention, polyamines are used as multifunctional amines. Compared with piperazine amide bonds in traditional technology, the delocalization effect of the lone pairs of nitrogen is more stable. Therefore, the polyamide separation layer formed by the reaction of polyamines and trimesoyl chloride in this invention has better acid resistance.

[0032] The present invention adds sodium dodecyl sulfate, a surfactant, to an aqueous solution, which can improve the affinity of the interface between the aqueous and organic phases, accelerate the reaction process of the multifunctional amine in the organic phase, thereby increasing the degree of crosslinking of the reaction, enhancing the mechanical properties of the polyamide film, and increasing its durability in acidic solutions.

[0033] This invention introduces an acid catalyst into an aqueous solution, which can lower the activation energy of the reaction, increase the reaction rate, and thus improve the conversion rate of polyamide per unit time. It also hinders the diffusion of multifunctional amines into the organic phase solution far from the interface, allowing the reaction to proceed within a limited area, ultimately forming a thin and compact polyamide separation layer, improving the membrane's permeability and desalination rate. Furthermore, the acid catalyst of this invention is preferably a carboxylic acid catalyst, especially a carboxylic acid catalyst containing a benzene ring, which is far superior to other types of acid catalysts.

[0034] This invention utilizes an acid catalyst to react polyamines with trimesoyl chloride to form a polyamide separation layer. This membrane layer is generated under extreme conditions, exhibiting a stable structure and possessing not only excellent acid resistance but also high permeability and desalination rate. It can be used in the treatment of acid solutions and valuable metal-containing acid solutions. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments.

[0036] In this invention, the coagulation bath (non-solvent water bath) refers to deionized water;

[0037] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0038] Example 1

[0039] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0040] S1. Preparation of ultrafiltration membrane

[0041] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0042] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0043] S2, Preparation of polyamide separation layer

[0044] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate, acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.1 wt%.

[0045] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0046] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0047] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0048] S3, Save:

[0049] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0050] Example 2

[0051] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0052] S1. Preparation of ultrafiltration membrane

[0053] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0054] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0055] S2, Preparation of polyamide separation layer

[0056] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate, acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.15 wt%.

[0057] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0058] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0059] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0060] S3, Save:

[0061] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0062] Example 3

[0063] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0064] S1. Preparation of ultrafiltration membrane

[0065] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0066] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0067] S2, Preparation of polyamide separation layer

[0068] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate, acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.20 wt%.

[0069] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0070] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0071] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0072] S3, Save:

[0073] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0074] Example 4

[0075] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0076] S1. Preparation of ultrafiltration membrane

[0077] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0078] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0079] S2, Preparation of polyamide separation layer

[0080] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate, acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.25 wt%.

[0081] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0082] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0083] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0084] S3, Save:

[0085] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0086] Example 5

[0087] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0088] S1. Preparation of ultrafiltration membrane

[0089] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0090] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0091] S2, Preparation of polyamide separation layer

[0092] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate, acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.30 wt%.

[0093] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0094] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0095] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0096] S3, Save:

[0097] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0098] Comparative Example 1

[0099] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0100] S1. Preparation of ultrafiltration membrane

[0101] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0102] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0103] S2, Preparation of polyamide separation layer

[0104] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), acid catalyst 1,4-benzoic acid and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt% and the concentration of 1,4-benzoic acid is 0.15 wt%.

[0105] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0106] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0107] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0108] S3, Save:

[0109] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0110] Comparative Example 2

[0111] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0112] S1. Preparation of ultrafiltration membrane

[0113] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0114] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0115] S2, Preparation of polyamide separation layer

[0116] S2-1. Preparation of aqueous solution: Branched polyethyleneimine (BPEI), surfactant sodium dodecyl sulfate and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of BPEI is 1.5 wt% and the concentration of surfactant is 0.15 wt%.

[0117] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0118] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0119] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0120] S3, Save:

[0121] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0122] Comparative Example 3

[0123] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0124] S1. Preparation of ultrafiltration membrane

[0125] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0126] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0127] S2, Preparation of polyamide separation layer

[0128] S2-1. Preparation of aqueous solution: Piperazine (PIP), sodium dodecyl sulfate surfactant, 1,4-benzoic acid acid catalyst and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of piperazine is 1.5 wt%; the concentration of surfactant is 0.15 wt%; and the concentration of 1,4-benzoic acid is 0.15 wt%.

[0129] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0130] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0131] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0132] S3, Save:

[0133] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0134] Comparative Example 4

[0135] A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane includes the following steps:

[0136] S1. Preparation of ultrafiltration membrane

[0137] S1-1. Preparation of polysulfone casting solution: Mix polysulfone resin particles with N,N-dimethylformamide (DMF) solution and stir under heating to dissolve, thus preparing a 16wt% polysulfone casting solution.

[0138] S1-2, Coating the polysulfone-based membrane layer: 16 wt% polysulfone casting solution is used to form a film on the upper surface of the nonwoven fabric support layer using a one-step phase inversion method. That is, 16 wt% polysulfone casting solution is poured onto the nonwoven fabric support layer, and the coating thickness is adjusted and the appropriate speed is controlled to coat the nonwoven fabric support layer. After coating, the film is immersed in a coagulation bath for curing. The polysulfone casting solution is rapidly precipitated at the interface to form a porous layer structure, namely the polysulfone ultrafiltration base membrane layer, thus obtaining the polysulfone ultrafiltration base membrane.

[0139] S2, Preparation of polyamide separation layer

[0140] S2-1. Preparation of aqueous solution: Piperazine (PIP), surfactant sodium dodecyl sulfate and water are mixed and stirred evenly under magnetic stirring to obtain an aqueous solution; in the aqueous solution, the concentration of piperazine is 1.5 wt% and the concentration of surfactant is 0.15 wt%.

[0141] S2-2, Preparation of organic phase solution: Dissolve pyromellitic chloride monomer in an organic solvent of n-hexane, stir to dissolve, and obtain an organic phase solution; the concentration of pyromellitic chloride monomer in the organic phase solution is 0.15 wt%;

[0142] S2-3, Interfacial polymerization reaction: The polysulfone ultrafiltration membrane is first immersed in an aqueous solution for 60 seconds, the aqueous solution is poured off, and the droplets remaining on the polysulfone ultrafiltration membrane are removed with an air gun to ensure that the polysulfone ultrafiltration membrane is uniformly impregnated with the aqueous solution. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction time is 20 seconds, the impregnation is stopped, and a nascent polyamide layer is generated.

[0143] S2-4, Heat treatment: The polysulfone ultrafiltration membrane with the generated nascent polyamide layer is heat-treated at 60℃ for 4 min to form a polyamide separation layer, thus obtaining a high-flux acid-resistant nanofiltration membrane with acid catalytic crosslinking.

[0144] S3, Save:

[0145] The prepared acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane was stored in a deionized aqueous solution for later use.

[0146] Example 1: Quality Inspection

[0147] The thickness of the polyamide separation layer, crosslinking density, porosity, and mechanical properties of the nanofiltration membranes prepared in each embodiment and comparative example were measured, and the results are shown in Table 1.

[0148] 1. Method for determining the thickness of the polyamide separation layer: The membrane thickness shall be determined in accordance with the national standard GB / T 32373-2015 Reverse Osmosis Membrane Test Method;

[0149] 2. Crosslinking density determination: The nonwoven fabric layer of the nanofiltration membrane is completely peeled off, leaving the separation layer and support layer. The membrane is then laid flat on a glass slide with the support layer facing upwards and the separation layer in contact with the glass slide. Based on the difference in solubility between the separation layer and the support layer, the support layer is dissolved and removed using the organic solvent N,N-dimethylformamide (DMF). After vacuum drying to remove the DMF from the separation layer, the surface of the separation layer is sputtered and peeled using X-ray photoelectron spectroscopy. The molar percentage content of oxygen and nitrogen in the separation layer is then measured, and the degree of crosslinking of the membrane is calculated accordingly.

[0150] 3. Porosity determination method: The membrane porosity is determined by gravimetric method. The membrane is immersed in pure water for a period of time, then removed, its surface moisture is removed, and its wet weight M1 is measured. The membrane is then dried and its dry weight M2 is measured. The membrane porosity P is calculated using the following formula:

[0151] P = (M1 - M2) / (ρ * S * D) * 100%

[0152] Where: ρ - density of pure water (g / cm³) 3 S - membrane area (cm²) 2 ); D - film thickness (cm).

[0153] 4. Determination of mechanical properties (tensile strength and elongation at break): Mechanical properties were determined according to the national standard GB / T 1040.3-2006, Test Method for Tensile Properties of Plastics.

[0154] Table 1

[0155]

[0156] The data in Table 1 shows that:

[0157] A comparison of the data from Example 2 and Comparative Examples 1-2 shows that the addition of surfactants can improve the affinity of the interface between the aqueous and organic phases, accelerate the reaction process of multifunctional amines in the organic phase, and reduce the activation energy of the reaction under the action of acid catalysts, thereby increasing the reaction rate during polymerization. While forming a thinner polyamide separation layer, the crosslinking density, porosity, and mechanical properties of the membrane are also increased to some extent.

[0158] A comparison of the data from Examples 1-5 shows that as the concentration of the acid catalyst increases, the connection process between the acid catalyst molecules and BPEI during interfacial polymerization increases the density of the surfactant solution, thereby leaving an excess of unreacted linker solution, which slightly reduces the thickness of the polyamide separation layer.

[0159] The comparison between Comparative Examples 3 and 4 shows that when piperazine is used to replace polyurethane materials in the preparation of polyamide separation layer, whether or not an acid catalyst is added has no significant effect on the thickness, crosslinking density, and porosity of the polyamide separation layer of the membrane.

[0160] As can be seen from the comparison between Example 2 and Comparative Example 3, when piperazine of Comparative Example 3 is used to replace the polyurethane material of Example 2, the film thickness of the polyamide separation layer increases significantly, but the crosslinking density, porosity and mechanical properties decrease significantly.

[0161] Example 2: Performance Test

[0162] The acid resistance of the nanofiltration membranes prepared in the above embodiments and comparative examples was tested by acid immersion method, and the results are shown in Table 2.

[0163] Acid resistance test: The acid resistance test was conducted using the acid immersion method. The nanofiltration membranes prepared in the examples and comparative examples were immersed in 20% H2SO4 solution (25℃). Samples were taken after immersion in the acid for 0 (initial performance), 5, 10, 15, 20, 25 and 30 days, respectively. The membranes were rinsed with pure water until the pH of the pure water used for immersion was 7, and then the water permeation flux and salt rejection of the membranes were tested.

[0164] Water permeation flux and salt rejection were tested on a membrane testing platform.

[0165] The test methods for water permeation flux and salt rejection are as follows: A membrane test stand is used. The concentration of the original aqueous solution is 2000 ppm sodium sulfate aqueous solution. The operating pressure is 1.0 MPa, the temperature is 25℃, and the test duration is 30 min. The water permeation flux and salt rejection rate of the membrane are tested.

[0166] Table 2

[0167]

[0168]

[0169] The data in Table 2 shows that:

[0170] 1) Data from Examples 1-5 show that the acid-catalyzed crosslinked acid-resistant nanofiltration membrane provided by this invention has excellent initial performance; when the membrane is immersed for 0 days, its flux is 67-75 L / (m²). 2Within the range of h), the retention rate is in the range of 98.6%-99.4%, and after soaking for 30 days, its flux is 114-119 L / (m²). 2 Within the range of h), the rejection rate is in the range of 94.2%-98.2%, with only a slight variation. The overall rejection rate remains at a high level. Therefore, it can be proved that the membranes prepared in Examples 1-5 of the present invention have better acid resistance.

[0171] 2) A comparison of Examples 1-5 with Comparative Example 1 shows that when no surfactant is added to Comparative Example 1, the flux is 79.4 L / (m²). 2 The rejection rate was 97.8%. Compared with Examples 1-5, the initial flux of the membrane was slightly increased and the desalination rate was slightly decreased. Combined with the crosslinking density measurement in Table 1, it can be proved that the surfactant can improve the crosslinking degree of the membrane to a certain extent during the reaction.

[0172] 3) From the comparison between Examples 1-5 and Comparative Example 2, it can be seen that when Comparative Example 2 does not add an acid catalyst, compared with Examples 1-5 which add an acid catalyst, as the acid soaking time increases, its water permeation flux increases significantly, while the desalination rate decreases significantly. The membrane has almost no acid resistance. Therefore, it can be seen that the acid catalyst is one of the key factors affecting the acid resistance of the membrane.

[0173] 4) From the comparison between Examples 1-5 and Comparative Example 3, it can be seen that when piperazine is used as a multifunctional amine in Comparative Example 3 to participate in the reaction to form a polyamide separation layer, even in the presence of an acid catalyst, its stability in acidic solution is still very poor due to the delocalization effect of the lone electron pair of the N atom in the piperazine amide bond, which is extremely unstable. It is far less stable than the stability of polyamines as aqueous monomers. Therefore, it can be seen that the synthesis of polyamide separation layer by using polyamines as multifunctional amines is also one of the key factors affecting the acid resistance of the membrane.

[0174] 5) The comparison between Comparative Example 3 and Comparative Example 4 shows that when piperazine is used as a multifunctional amine to participate in the reaction to form a polyamide separation layer, the presence of an acid catalyst does not have a significant beneficial effect on the acid resistance of the membrane.

[0175] In summary, the acid catalyst, the polyamine as a multifunctional amine synthesis polyamide separation layer, and the addition of surfactants work together as a whole to give the prepared polyamide separation layer good acid resistance, acid stability, and high water permeability and salt rejection rate.

[0176] The embodiments described above are merely preferred embodiments of the present invention, and not an exhaustive list of all possible implementations of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane, characterized in that, Includes the following steps: Step 1, Preparation of aqueous solution: Mix the multifunctional amine, surfactant, and acid catalyst with water and stir until homogeneous to obtain an aqueous solution; The multifunctional amine substances include one or more of branched polyethyleneimine, polyethylene aniline, and polyaniline; The concentration of the multifunctional amine in the aqueous solution is 1–3 wt%, the concentration of the surfactant is 0.1–3.0 wt%, and the concentration of the acid catalyst is 0.05–0.5 wt%. The surfactant is sodium dodecyl sulfate; The acid catalyst includes a carboxylic acid catalyst; the carboxylic acid catalyst includes one or more of 1,2-benzoic acid, 1,3-benzoic acid, 1,4-benzoic acid, 1,2-phenylacetic acid, 1,3-phenylacetic acid, 1,4-phenylacetic acid, 1,2-phenylpropionic acid, 1,3-phenylpropionic acid, and 1,4-phenylpropionic acid. Step 2, Preparation of the organic phase solution: Trimethylbenzene chloride monomer is dissolved in n-hexane and stirred to obtain an organic phase solution; the concentration of trimethylbenzene chloride monomer in the organic phase solution is 0.1–0.3 wt%. Step 3, interfacial polymerization reaction: The ultrafiltration membrane is first immersed in an aqueous solution for treatment. After treatment, the aqueous solution is discarded and the residual solution is removed. Then, it is immersed in an organic solution for interfacial polymerization reaction. After the reaction is completed, a nascent polyamine membrane layer is generated. Step 4, heat treatment: The generated nascent polyamine membrane layer is heat treated to obtain a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking.

2. The method for preparing a high-flux acid-resistant nanofiltration membrane via acid catalytic crosslinking according to claim 1, characterized in that, The method for preparing the ultrafiltration membrane includes the following steps: The polymer is dissolved in an organic solvent and stirred under a magnetic stirrer. After standing to remove bubbles, a homogeneous casting solution is formed. The homogeneous casting solution is then coated onto a nonwoven support material using a flatbed film scraper and then quickly placed in a coagulation bath for curing to form an ultrafiltration base membrane layer, thus obtaining the ultrafiltration base membrane.

3. The method for preparing a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking according to claim 2, characterized in that, The polymer is one or more selected from polysulfone, polyethersulfone, polytetrafluoroethylene, polyvinylidene fluoride, and polyetheretherketone. The organic solvent is one or more of dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and tetramethyl sulfoxide.

4. The method for preparing a high-flux acid-resistant nanofiltration membrane via acid catalytic crosslinking according to claim 1, characterized in that, The immersion time of the ultrafiltration membrane in the aqueous solution is 30–120 s; The immersion time of the ultrafiltration membrane in the organic phase solution is 10–30 s; The heat treatment temperature is 50–90℃, and the heat treatment time is 3–8 minutes.

5. The method for preparing a high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking according to claim 1, characterized in that, The acid-catalyzed crosslinked high-flux acid-resistant nanofiltration membrane is stored in deionized aqueous solution for later use.

6. A high-flux acid-resistant nanofiltration membrane with acid-catalyzed crosslinking prepared by the preparation method according to any one of claims 1-5, characterized in that, It includes an ultrafiltration base membrane and a polyamide separation layer disposed on the ultrafiltration base membrane. The ultrafiltration base membrane includes a nonwoven support layer and an ultrafiltration base membrane layer disposed on the nonwoven support layer.

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