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CN-122006507-A - Preparation method of nitrate selective low-pressure film

CN122006507ACN 122006507 ACN122006507 ACN 122006507ACN-122006507-A

Abstract

The invention relates to the technical field of water treatment and discloses a nitrate selective low-pressure membrane preparation method which comprises the following steps of support layer pretreatment, ion selective separation layer coating, functionalized ceramic-polymer composite layer preparation, composite layer deposition and solidification, low-pressure membrane formation and post-treatment; by constructing an ion selective separation layer formed by crosslinking quaternized chitosan derivatives and polyethyleneimine through glutaraldehyde on the surface of the support layer, the selective separation of nitrate relative to other anions is realized by utilizing the specific electrostatic adsorption and size screening effects of quaternized groups on nitrate ions. The structure can preferentially allow nitrate ions to permeate under low-pressure driving, and simultaneously retain mineral ions beneficial to human bodies in water, so that the problem of unbalanced water quality of effluent of the traditional desalination membrane is solved, and the health and taste of drinking water are improved.

Inventors

  • LIU CHENG
  • WU YANTONG

Assignees

  • 江苏问水环境有限公司

Dates

Publication Date
20260512
Application Date
20260414

Claims (10)

  1. 1. The preparation method of the nitrate selective low-pressure film is characterized by comprising the following steps of: step one, pretreatment of a supporting layer, namely selecting a flexible porous polymer base film as the supporting layer, and carrying out hydrophilization modification, cleaning and drying on the supporting layer; Coating an ion selective separation layer, namely uniformly coating a layer of ion selective separation layer solution on the surface of the pretreated support layer through slit coating; Preparing a functionalized ceramic-polymer composite layer, and preparing a composite coating liquid containing functionalized ceramic nano particles, a cross-linking agent and a film-forming polymer; depositing and curing the composite layer, depositing the composite coating liquid prepared in the step three on the surface of the ion selective separation layer formed in the step two, and crosslinking and curing the composite coating liquid in an ultraviolet light or heat curing mode to form a surface functional layer; Step five, low-pressure film forming and post-treatment, namely performing low-pressure hot-press shaping on the multi-layer composite film obtained in the step four at a specific temperature and under a specific tension, and then performing water retention treatment to obtain the nitrate selective low-pressure film; The ion selective separation layer solution is prepared from the following raw materials, by weight, 20-35 parts of quaternized chitosan derivative, 10-18 parts of polyethyleneimine, 5-10 parts of pore-forming agent, 3-8 parts of cross-linking agent and 50-70 parts of deionized water, wherein the cross-linking agent is glutaraldehyde, and the use concentration of the cross-linking agent is 2-5%.
  2. 2. The method for preparing a nitrate selective low-pressure membrane according to claim 1, wherein the step one, the pretreatment of the support layer comprises the steps of immersing a flexible porous polymer base membrane in a mixed aqueous solution containing sodium hydroxide and ammonium persulfate for hydrophilization treatment, treating at 50-70 ℃ for 0.5-2 hours, maintaining the solution at a low speed of 30-60r/min during the treatment, taking out the base membrane after the treatment, repeatedly flushing the base membrane with deionized water until effluent is neutral, and then placing the base membrane in a forced air drying oven for drying at 40-60 ℃ for 1-3 hours to obtain the pretreated support layer, wherein the flexible porous polymer base membrane is a polyvinylidene fluoride porous membrane or a polytetrafluoroethylene stretched porous membrane, the thickness of which is 80-150 microns, and the average pore diameter of which is 0.1-0.5 microns.
  3. 3. The method for preparing a nitrate selective low-pressure membrane according to claim 2, wherein in the hydrophilization treatment mixed aqueous solution, the concentration of sodium hydroxide is 1-3mol/L, the concentration of ammonium persulfate is 0.1-0.5mol/L, the volume ratio of the sodium hydroxide to the ammonium persulfate is 1:1, and the bath ratio of the flexible porous polymer base membrane to the mixed aqueous solution is 1g:20-50mL.
  4. 4. The method for preparing a nitrate selective low-pressure membrane according to claim 1, wherein in the second step, the ion selective separation layer coating operation is specifically that after the prepared ion selective separation layer solution is filtered and defoamed, the solution is injected into a trough of a slit coater, a coating gap is controlled to be 100-300 micrometers, the coating speed is controlled to be 0.5-2.0m/min, a wet membrane coating with the thickness of 10-30 micrometers is formed on the surface of a pretreated supporting layer, then the coated membrane is immediately transferred into a curing chamber with the relative humidity of 60-80%, and the solution is left to stand and crosslink for 2-6 hours at the temperature of 25-40 ℃ to enable glutaraldehyde to fully crosslink quaternized chitosan and polyethyleneimine to form the ion selective separation layer.
  5. 5. The method for preparing a nitrate selective low-pressure membrane according to claim 4, wherein the quaternized chitosan derivative has a quaternized substitution degree of not less than 60% and a molecular weight of 10-50 kilodaltons in the ion selective separation layer solution, the pore-forming agent is polyvinylpyrrolidone or polyethylene glycol, and the crosslinking agent glutaraldehyde is slowly added dropwise, and the solution is kept in an ice bath and a stirring state of 200-400r/min in the dropwise adding process.
  6. 6. The method for preparing a nitrate selective low-pressure film according to claim 1, wherein in the third step, the functionalized ceramic-polymer composite coating liquid is prepared by the following method: Preparing functionalized ceramic nano particles, namely selecting silicon dioxide or aluminum oxide ceramic nano particles with the particle size of 20-50 nanometers, dispersing the silicon dioxide or aluminum oxide ceramic nano particles in ethanol solution containing a silane coupling agent, performing ultrasonic dispersion for 30-60 minutes under the ultrasonic power of 300-600W, performing reflux reaction for 3-6 hours at the temperature of 60-80 ℃, performing centrifugal separation after the reaction is finished, washing with ethanol for three times, and performing vacuum drying for 4-8 hours at the temperature of 80 ℃ to obtain the functionalized ceramic nano particles with amino or epoxy functional groups grafted on the surfaces; The preparation of the composite coating liquid comprises the steps of adding 15-25 parts by weight of polyurethane aqueous dispersion or acrylic ester emulsion serving as a film forming polymer into a stirring container with temperature control, controlling the temperature to be 25-35 ℃, stirring at the rotating speed of 300-600r/min, sequentially adding 5-10 parts by weight of functionalized ceramic nano particles, 1-3 parts by weight of polyfunctional aziridine crosslinking agent, 0.5-2 parts by weight of wetting leveling agent and 20-30 parts by weight of deionized water, and after the addition, increasing the stirring rotating speed to 800-1200r/min and continuously stirring for 1-2 hours to obtain the functionalized ceramic-polymer composite coating liquid.
  7. 7. The method for preparing the nitrate selective low-pressure film according to claim 6, wherein the mass concentration of the silane coupling agent in the ethanol solution is 1% -5%, the mass ratio of the ceramic nano particles to the silane coupling agent is 10:1-5:1, the mass fraction of the functionalized ceramic nano particles in the composite coating liquid is 2% -8%, and the wetting leveling agent is polyether modified polysiloxane leveling agent.
  8. 8. The method for preparing the nitrate selective low-pressure film according to claim 1, wherein in the fourth step, the deposition and curing of the composite layer are specifically performed by uniformly applying a functionalized ceramic-polymer composite coating solution to the surface of the cured ion selective separation layer by a precise doctor blade or spraying method, controlling the thickness of the wet film to be 20-50 micrometers, immediately transferring the coated film material into an ultraviolet curing machine or a drying tunnel, and when the film material is cured by ultraviolet light, using an ultraviolet light source with the wavelength of 365nm, the light intensity is 80-200mW/cm < 2 >, the irradiation time is 30-90 seconds, and when the film material is cured by heat, performing heat treatment at 80-110 ℃ for 10-30 minutes, so that the composite layer is completely crosslinked and cured to form the surface functional layer.
  9. 9. The method for preparing the nitrate selective low-pressure film according to claim 1, wherein the step five is characterized in that the low-pressure film forming and post-treatment comprises the steps of placing the wet composite film with the three-layer structure obtained in the step four between steel belts of a continuous hot press, carrying out low-pressure hot press shaping treatment for 1-5 minutes under the conditions of 100-130 ℃ and 0.5-2.0MPa and 1-3m/min of pressure, immersing the film into a water holding tank containing 0.1% -1.0% of glycerol aqueous solution after the low-pressure hot press shaping, immersing for 4-12 hours at 25-40 ℃ to enable the film to be fully hydrated, finally taking out, and draining surface moisture to obtain the final nitrate selective low-pressure film.
  10. 10. The method for preparing the nitrate selective low-pressure film according to claim 9, wherein the low-pressure hot-press shaping in the fifth step adopts a sectional temperature control and gradient pressurizing process, specifically comprises the steps of firstly placing the coated and cured composite film in a first hot-press area, pre-treating for 30-90 seconds under the conditions of 100-110 ℃ and 0.5-1.0MPa, then transferring the film to a second hot-press area, and carrying out main treatment for 60-120 seconds under the conditions of 120-130 ℃ and 1.5-2.0 MPa.

Description

Preparation method of nitrate selective low-pressure film Technical Field The invention relates to the technical field of water treatment, in particular to a preparation method of a nitrate selective low-pressure membrane. Background In recent years, due to the fact that the use amount of nitrogenous fertilizer is continuously increased, the land utilization type is changed from grazing to farming, the urban sewage discharge amount in low-land river areas is increased, the concentration of nitrate in the groundwater is continuously increased, the groundwater is a serious global environment problem, the exceeding of nitrate in the water has a certain carcinogenic rate, causes methemoglobin diseases and damages to human health, and also causes eutrophication of water, damages to aquatic ecosystems and aquatic organisms, and simultaneously releases a large amount of algae toxins to cause water supply peculiar smell, thereby seriously threatening urban water supply safety. At present, when nitrate treatment is carried out on drinking water, the adopted membrane separation method is generally insufficient in selectivity of nitrate ions, mineral ions beneficial to human bodies in water cannot be reserved while nitrate is efficiently removed, so that the quality of effluent is unbalanced, the health and taste of drinking water are affected, meanwhile, in long-term operation of the existing low-pressure membrane, the surface functional layer of the existing low-pressure membrane is poor in tolerance to organic pollutants and microorganisms, the problem of rapid flux attenuation caused by membrane pollution cannot be relieved, the operation stability is insufficient, and the membrane is frequently cleaned and has a shortened service life. Thus, a nitrate selective low pressure film production method has been proposed to solve the above-mentioned problems. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a nitrate selective low-pressure membrane preparation method, which solves the problems that the health, taste and running stability of drinking water are affected due to unbalanced water quality of effluent water proposed in the background art, the cleaning is frequent and the service life of the membrane is shortened. In order to achieve the purpose, the invention provides a preparation method of a nitrate selective low-pressure film, which comprises the following steps: step one, pretreatment of a supporting layer, namely selecting a flexible porous polymer base film as the supporting layer, and carrying out hydrophilization modification, cleaning and drying on the supporting layer; Coating an ion selective separation layer, namely uniformly coating a layer of ion selective separation layer solution on the surface of the pretreated support layer through slit coating; Preparing a functionalized ceramic-polymer composite layer, and preparing a composite coating liquid containing functionalized ceramic nano particles, a cross-linking agent and a film-forming polymer; depositing and curing the composite layer, depositing the composite coating liquid prepared in the step three on the surface of the ion selective separation layer formed in the step two, and crosslinking and curing the composite coating liquid in an ultraviolet light or heat curing mode to form a surface functional layer; Step five, low-pressure film forming and post-treatment, namely performing low-pressure hot-press shaping on the multi-layer composite film obtained in the step four at a specific temperature and under a specific tension, and then performing water retention treatment to obtain the nitrate selective low-pressure film; The ion selective separation layer solution is prepared from the following raw materials, by weight, 20-35 parts of quaternized chitosan derivative, 10-18 parts of polyethyleneimine, 5-10 parts of pore-forming agent, 3-8 parts of cross-linking agent and 50-70 parts of deionized water, wherein the cross-linking agent is glutaraldehyde, and the use concentration of the cross-linking agent is 2-5%. Preferably, the pretreatment of the support layer comprises the steps of immersing a flexible porous polymer base film in a mixed aqueous solution containing sodium hydroxide and ammonium persulfate for hydrophilization treatment, treating for 0.5-2 hours at 50-70 ℃, keeping the solution stirred at a low speed of 30-60r/min in the treatment process, taking out the base film after the treatment, repeatedly flushing the base film until effluent liquid is neutral by deionized water, then placing the base film in a blast drying box, and drying for 1-3 hours at 40-60 ℃ to obtain the pretreated support layer, wherein the flexible porous polymer base film is a polyvinylidene fluoride porous film or a polytetrafluoroethylene stretched porous film, the thickness is 80-150 microns, and the average pore diameter is 0.1-0.5 microns. Preferably, in the hydrophilization treatment mixed aqueous solution, the c