Polythiourea composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, and discloses a polythiourea composite nanofiltration membrane as well as a preparation method and application thereof. The composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polythiourea separation layer which are arranged in sequence, wherein the polythiourea separation layer comprises a structural unit A from polyamine and a structural unit B from a polyisothiocyano compound; wherein the structural unit A and the structural unit B are connected through a structure shown in a formula I, Ar1 is a residue obtained after a reaction of a compound containing polyisothiocyano groups, and Ar2 is a residue obtained after a reaction of polyamine. The separation layer structure of the polythiourea composite nanofiltration membrane contains C = S bonds, a large number of hydrogen bonds can be formed, the polythiourea composite nanofiltration membrane has excellent chemical stability, the structural stability of the composite nanofiltration membrane in a strong acid environment is remarkably improved on the premise that the separation performance of the composite nanofiltration membrane is guaranteed, and the acid resistance of the composite nanofiltration membrane is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular, to a polysulfourea composite nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] Nanofiltration is a membrane separation technology between ultrafiltration and reverse osmosis, the pore size of nanofiltration membrane is 1-2 nm, and the molecular weight cut-off is 200-1000 Da. Nanofiltration separation technology is widely used in fresh water softening, seawater softening, drinking water purification, water quality improvement, oil-water separation, wastewater treatment and recycling, and grading, purification and concentration of chemical products such as dyes, antibiotics, polypeptides and polysaccharides.

[0003] At present, commercial nanofiltration membranes are prepared by interfacial polymerization, and interfacial polymerization of polyamine aqueous phase and polyacyl chloride organic phase is carried out on the surface of porous ultrafiltration membrane to obtain an ultra-thin and dense polyamide separation layer. Under acidic conditions, C=O bond is easily attacked by nucleophilic electrons of H + , and the amide bond is hydrolyzed, resulting in the destruction of the structure of the membrane separation layer and the decrease of the rejection performance. The literature (M Liu, Z Chen, S Yu. Thin-film composite polyamide reverse osmosis membranes with improved acid stability and chlorine resistance by coating N-isopropylacrylamide-co-acrylamide copolymers. Desalination, 2011, 270: 248-257) conducted a study on the acid resistance of polyamide reverse osmosis membrane, which was continuously tested in a mixed solution of hydrochloric acid and sodium chloride for 60 days, and the water flux of the membrane was greatly improved, and the desalination rate was significantly decreased. The pH range of nanofiltration membrane with polyamide as separation layer material is 2-11, which cannot be used in strong acidic environment, which greatly limits its application in the field of acid wastewater treatment.

[0004] In actual industrial production process, the purification of acid, the concentration of metal ions in acidic solution, environmental remediation and resource recycling and other fields have great market demand for acid-resistant nanofiltration membranes. Researchers in this field have also made many efforts in the design and preparation of new acid-resistant nanofiltration membranes. Zhang Kaixong team of Institute of Urban Environment, Chinese Academy of Sciences prepared high-performance acid-resistant nanofiltration membranes by introducing catalyst terephthalic acid in the interface polymerization process to solve the problem of performance decline of traditional nanofiltration membranes in acidic environment. Shaolu team of Harbin Institute of Technology also prepared a new type of polyurethane composite nanofiltration membrane. The membrane significantly enhances the screening performance of various dyes and heavy metal ions while improving the flux, and can be stably operated for more than 500 hours in strong acid conditions. In addition, the Acidstab NF series acid-resistant nanofiltration membrane of Warton Technology can also be operated in 20% hydrochloric acid, nitric acid and sulfuric acid, with a molecular weight cut-off of about 200 Da. SUMMARY

[0005] The purpose of the present application is to overcome the problem of poor structural stability of existing composite nanofiltration membranes in strong acid environment, and to provide a polysulfide composite nanofiltration membrane and a preparation method thereof, as well as the application of the polysulfide composite nanofiltration membrane and the polysulfide composite nanofiltration membrane prepared by the method in the field of water treatment. The separation layer structure of the polysulfide composite nanofiltration membrane contains C=S bonds, which can form a large number of hydrogen bonds, so that it has excellent chemical stability, significantly improves the structural stability of the composite nanofiltration membrane in strong acid environment, and improves the acid resistance of the composite nanofiltration membrane.

[0006] To achieve the above purpose, the first aspect of the present application provides a polysulfide composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polysulfide separation layer arranged in sequence.

[0007] The polysulfide separation layer comprises structural unit A from a polyamine and structural unit B from a polyisothiocyanate compound.

[0008] The structural unit A and the structural unit B are connected by the structure shown in formula I Wherein, Ar1 is the residue after reaction of a compound containing polyisothiocyanate, and Ar2 is the residue after reaction of a polyamine.

[0009] The second aspect of the present application provides a preparation method of a polysulfide composite nanofiltration membrane, wherein the preparation method comprises the following steps:

[0010] S1, preparing a porous support layer on the bottom layer;

[0011] S2, contacting the membrane layer obtained in step S1 with an aqueous phase containing a polyamine for the first time;

[0012] S3, the membrane layer obtained in step S2 is subjected to a second contact with an organic solution containing a polyisothiocyanate compound, and after heat treatment, the polysulfourea composite nanofiltration membrane is obtained.

[0013] The third aspect of the present application provides a polysulfourea composite nanofiltration membrane prepared by the above preparation method.

[0014] The fourth aspect of the present application provides an application of the above polysulfourea composite nanofiltration membrane in the field of water treatment.

[0015] Through the above technical solution, the polysulfourea composite nanofiltration membrane, the preparation method and the application thereof provided by the present application have the following beneficial effects:

[0016] The C=S bond in the polysulfourea composite nanofiltration membrane provided by the present application can form a large number of hydrogen bonds, so that the polysulfourea composite nanofiltration membrane has excellent chemical stability. Under the premise of ensuring the separation performance of the composite nanofiltration membrane, the structural stability of the composite nanofiltration membrane in a strong acid environment is significantly improved, and the acid resistance of the composite nanofiltration membrane is improved.

[0017] Further, in the polysulfourea separation layer of the composite nanofiltration membrane provided by the present application, there are both flexible segments and aromatic rigid segments. By adjusting the molecular structure of the polysulfourea in the polysulfourea separation layer, the composite nanofiltration membrane can have excellent desalination rate and excellent acid permeability, and can simultaneously realize efficient metal ion removal and waste acid recovery.

[0018] The preparation method of the composite nanofiltration membrane provided by the present application is simple, the cost is controllable, is compatible with the existing continuous interface polymerization membrane preparation equipment, is easy to scale up production, has great commercial value and industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The surface SEM morphology diagram of the composite nanofiltration membrane prepared in Example 1.

[0020] Figure 2 The surface sulfur element distribution of the composite nanofiltration membrane prepared in Example 1.

[0021] Figure 3 The surface infrared spectrum diagram of the composite nanofiltration membrane prepared in Example 1. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood to include values approximately near these ranges and values within these ranges. For ranges of values, the endpoints of the ranges are included within the range. The endpoints of the ranges and the values are approximate values and should be understood to include values approximately near these ranges and values within these ranges.

[0023] The first aspect of the present invention provides a polythiourea composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polythiourea separation layer arranged sequentially;

[0024] The polythiourea separation layer comprises structural unit A from polyamines and structural unit B from polyisothiocyanate compounds;

[0025] Structural unit A and structural unit B are connected by the structure shown in Equation I. Ar1 is the residue of the compound containing polyisothiocyanate after the reaction, and Ar2 is the residue of the polyamine after the reaction.

[0026] In this invention, the C=S bonds in the polythiourea composite nanofiltration membrane can form a large number of hydrogen bonds, giving the composite nanofiltration membrane containing C=S bonds excellent chemical stability. Under the premise of ensuring the separation performance of the composite nanofiltration membrane, the structural stability of the composite nanofiltration membrane in a strong acid environment is significantly improved, and the acid resistance of the composite nanofiltration membrane is improved.

[0027] In this invention, the polyisothiocyanate compound refers to a compound containing at least two isothiocyanate groups (-N=C=S).

[0028] According to the present invention, the polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylene polyamine and polyetheramine, more preferably polyethyleneimine or polyethylene polyamine.

[0029] According to the present invention, the polyisothiocyanate compound is selected from at least one of 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, 1,2-phenyl diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate.

[0030] Furthermore, the polyisothiocyanate compound is selected from 1,4-phenyl diisothiocyanate and / or 1,3,5-triisothiocyanophenyl.

[0031] In this invention, the use of the above-mentioned specific types of polyisothiocyanate compounds enables the polythiourea separation layer of the composite nanofiltration membrane to contain both flexible segments and aromatic rigid segments. By controlling the molecular structure of polythiourea in the polythiourea separation layer, the composite nanofiltration membrane can achieve both excellent desalination rate and excellent acid permeability, thus simultaneously realizing efficient metal ion removal and waste acid recovery.

[0032] According to the present invention, the content of structural unit A on the membrane surface is 20-40 wt%, and the content of structural unit B on the membrane surface is 60-80 wt%.

[0033] In this invention, when the contents of structural unit A and structural unit B meet the above-mentioned range, it indicates that the reaction between structural unit A from the polyamine and structural unit B from the polyisothiocyanate compound is sufficient, which can ensure that the surface of the composite nanofiltration membrane, especially the surface of the polythiourea separation layer, is free of defects, thereby ensuring that the composite nanofiltration membrane has excellent separation performance.

[0034] Furthermore, the content of structural unit A on the membrane surface is 25-35 wt%, and the content of structural unit B on the membrane surface is 65-75 wt%.

[0035] According to the present invention, the sulfur content in the composite nanofiltration membrane is 1-5 at.%.

[0036] In this invention, when the content of S element in the composite nanofiltration membrane meets the above-mentioned range, the density of C=S bonds in the polythiourea composite nanofiltration membrane is appropriate, and hydrogen bonds can be formed with H atoms in the polythiourea molecular structure, so that the composite nanofiltration membrane has excellent chemical inertness. Under the premise of ensuring excellent separation performance of the composite nanofiltration membrane, the structural stability of the composite nanofiltration membrane in a strong acid environment is significantly improved.

[0037] Furthermore, the sulfur content in the composite nanofiltration membrane is 2-4 at.%.

[0038] According to the present invention, the average pore size of the composite nanofiltration membrane is 0.2-0.6 nm.

[0039] In this invention, when the average pore size of the composite nanofiltration membrane meets the above-mentioned range, it indicates that the separation layer of the polythiourea composite nanofiltration membrane has a suitable cross-linking density. When used for the separation of high-valence heavy metal ions and waste acid in acidic environments, it can better repel high-valence heavy metal ions, thereby improving the recovery rate of high-valence heavy metal ions.

[0040] Furthermore, the average pore size of the composite nanofiltration membrane is 0.3-0.5 nm.

[0041] According to the present invention, the molecular weight cutoff of the composite nanofiltration membrane is 300-600 Da.

[0042] In this invention, when the molecular weight cutoff of the composite nanofiltration membrane meets the above-mentioned range, it indicates that the pore size of the polythiourea composite nanofiltration membrane is moderate, enabling the composite nanofiltration membrane to achieve high water flux while efficiently separating heavy metal ions and recovering acid.

[0043] Furthermore, the composite nanofiltration membrane has a molecular weight cutoff of 300-400 Da.

[0044] In this invention, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials with certain strength that can be used for nanofiltration and reverse osmosis membranes.

[0045] In this invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0046] In this invention, the porous support layer material can be at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0047] According to the present invention, the thickness of the bottom layer, the porous support layer, and the polythiourea separation layer is not particularly limited and can be a conventional choice in the art. However, in order to enable these three layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent magnesium-lithium separation coefficient and high water flux, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; and the thickness of the polythiourea separation layer is 10-500 nm, preferably 50-300 nm.

[0048] A second aspect of the present invention provides a method for preparing a polythiourea composite nanofiltration membrane, wherein the preparation method includes the following steps:

[0049] S1. Prepare a porous support layer on the bottom layer;

[0050] S2. The membrane obtained in step S1 is brought into first contact with an aqueous phase containing polyamines.

[0051] S3. The membrane layer obtained in step S2 is brought into a second contact with an organic solution containing polyisothiocyanate compounds, and after heat treatment, the polythiourea composite nanofiltration membrane is obtained.

[0052] In this invention, an organic solution containing polyisothiocyanate compounds is brought into contact with a porous support layer impregnated with an aqueous phase containing polyamines. An interfacial polymerization reaction occurs on the surface of the porous support layer, and after heat treatment, a composite nanofiltration membrane containing a polythiourea separation layer with a specific structure, as described in the first aspect of this invention, is obtained. This composite nanofiltration membrane can significantly improve the structural stability of the composite nanofiltration membrane in a strong acid environment and improve the acid resistance of the composite nanofiltration membrane while ensuring the separation performance of the composite nanofiltration membrane.

[0053] In this invention, there is no particular limitation on the method for preparing the porous support layer on the bottom layer. Conventional methods in the art can be used for preparation, with phase inversion method preferred. Specifically, a polymer solution of porous support layer material is coated on one surface of the bottom layer, and the porous support layer is obtained through phase inversion.

[0054] In this invention, the phase inversion method is preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20 wt%, degassing at 20-40°C for 10-180 min; then coating the polymer solution onto the bottom layer to obtain an initial film, and then immersing it in water at a temperature of 10-30°C for 10-60 min, thus forming the phase inversion layer of the support layer polymer porous membrane.

[0055] The solvent may be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0056] According to the present invention, the polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylene polyamine and polyetheramine, more preferably polyethyleneimine or polyethylene polyamine.

[0057] According to the present invention, the concentration of the aqueous phase containing the polyamine is 0.05wt%-5wt%.

[0058] In this invention, controlling the concentration of the aqueous phase containing polyamines to meet the above-mentioned range ensures that the porous support layer is fully wetted by the aqueous monomers during the interfacial polymerization process, without wasting monomers, thus ensuring effectiveness and economy.

[0059] Furthermore, the concentration of the aqueous phase containing the polyamine is 0.1 wt% to 2.5 wt%.

[0060] According to the present invention, the compound containing a polyisothiocyanate is selected from at least one of 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, 1,2-phenyl diisothiocyanate, 2,6-toluene diisothiocyanate, and 1,3-propane diisothiocyanate, preferably selected from 1,4-phenyl diisothiocyanate and / or 1,3,5-triisothiocyanobenzene.

[0061] In one specific embodiment of the present invention, the compound containing polyisothiocyanate is 1,4-phenyl diisothiocyanate and 1,3,5-triisothiocyanobenzene. There is no particular limitation on the ratio of the two, as long as the total amount of the compound containing polyisothiocyanate meets the limitations of the present invention. For example, the mass ratio of 1,4-phenyl diisothiocyanate to 1,3,5-triisothiocyanobenzene is 0.1-10:1.

[0062] According to the present invention, the concentration of the organic solution containing the polyisothiocyanate compound is 0.025 wt% to 1 wt%.

[0063] In this invention, controlling the concentration of the organic solution containing polyisothiocyanate compounds to meet the above-mentioned range ensures that the two monomers react fully during the interfacial polymerization process, resulting in a uniform and dense polythiourea separation layer without wasting monomers, thus ensuring effectiveness and economy.

[0064] Furthermore, the concentration of the organic solution containing the polyisothiocyanate compound is 0.05wt%-0.5wt%.

[0065] In this invention, there is no particular limitation on the type of organic solution in step S3, as long as it can dissolve the polyisothiocyanate compound. Preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0066] According to the present invention, the mass ratio of the polyamine to the polyisothiocyanate compound is 0.1-50:1.

[0067] In this invention, when the mass ratio of polyamine to polyisothiocyanate is controlled to meet the above-mentioned range, it can ensure that the polyamine and polyisothiocyanate react fully, and the polythiourea separation layer prepared by the interfacial polymerization of the two has few defects. It can maintain a high water flux while ensuring a high retention efficiency for high-valence metal ions, thereby obtaining an ideal separation efficiency.

[0068] Furthermore, the mass ratio of the polyamine to the polyisothiocyanate compound is 0.5-20:1.

[0069] According to the present invention, the ratio of the volume of the aqueous phase to the membrane area of ​​the membrane layer obtained in step S1 is 0.1-0.5 mL / cm². 2 The preferred concentration is 0.2-0.4 mL / cm³. 2 .

[0070] According to the present invention, the ratio of the volume of the organic solution to the membrane area of ​​the membrane obtained in step S2 is 0.05-0.3 mL / cm². 2 Preferably 0.1-0.2 mL / cm 2 .

[0071] In this invention, there are no particular limitations on the interfacial polymerization conditions between the polyamine and the polyisothiocyanate compound; they can be carried out according to conventional conditions in the art. However, in order to enable the three layers to play a better synergistic role and to enable the resulting composite nanofiltration membrane to better combine excellent acid resistance, acid permeability, high water flux, and desalination rate, preferably, the first contact time is 5-100s, more preferably 10-60s; and the second contact time is 10-200s, more preferably 20-120s.

[0072] In this invention, there is no particular limitation on the temperature of the first contact and the second contact; for example, it can be room temperature (20-30°C).

[0073] In this invention, there are no particular limitations on the heat treatment conditions, as long as the polyamine and polyisothiocyanate compounds can be fully polymerized, so that the obtained polythiourea composite nanofiltration membrane has excellent acid resistance, high water flux and desalination rate. For example, the heat treatment conditions include: heat treatment temperature of 40-150℃, preferably 50-120℃, and heat treatment time of 0.5-20min, preferably 1-10min.

[0074] A third aspect of the present invention provides a polythiourea composite nanofiltration membrane prepared by the above-described preparation method.

[0075] A fourth aspect of the present invention provides an application of the above-mentioned polythiourea composite nanofiltration membrane in the field of water treatment.

[0076] The present invention will be described in detail below through embodiments. In the following embodiments,

[0077] (1) Test method for water flux of composite nanofiltration membrane: The composite nanofiltration membrane is placed in a membrane tank and pre-pressurized at 1.5 MPa for 1 hour. Then, the water permeation rate of the composite nanofiltration membrane is measured within a certain time under the conditions of 1.5 MPa pressure and 25℃. The water flux is calculated by the following formula: J=Q / (A×t), where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the composite nanofiltration membrane (m²). 2 ), where t is time (h).

[0078] (2) Test methods for desalination rate and acid permeability of composite nanofiltration membrane: A mixed solution of 2000 ppm copper chloride and 5 wt% hydrochloric acid was used as the original solution. The composite nanofiltration membrane was loaded into the membrane tank and pre-pressurized at 1.5 MPa for 1 h. Subsequently, the test was carried out at a pressure of 1.5 MPa and a temperature of 25 °C, and the filtrate was collected. The desalination rate of the membrane for CuCl2 was calculated by the following formula: R=(Cf-Cp) / Cf×100%, where R is the desalination rate, %, Cf is the concentration of copper ions in the original solution, ppm, and Cp is the concentration of copper ions in the filtrate, ppm, both of which were determined by ion chromatography.

[0079] The acid permeability of the membrane can be calculated using the following formula: Wherein, P represents acid permeability, %. The concentration of hydrogen ions in the original solution is expressed in ppm. The concentration of hydrogen ions in the filtrate, in ppm, was determined by acid-base titration.

[0080] The desalination rate test method for the nanofiltration membranes prepared in Comparative Examples 1 and 2: A 2000 ppm copper chloride solution was used as the original solution. The composite nanofiltration membrane was loaded into the membrane tank and pre-pressurized at 1.5 MPa for 1 h. Subsequently, the test was conducted at a pressure of 1.5 MPa and a temperature of 25 °C, and the filtrate was collected. The desalination rate of the membrane for CuCl2 was calculated using the following formula: R = (Cf - Cp) / Cf × 100%, where R is the desalination rate (%), Cf is the concentration of copper ions in the original solution (ppm), and Cp is the concentration of copper ions in the filtrate (ppm), both determined by ion chromatography.

[0081] (3) Test method for acid resistance of composite nanofiltration membrane: The composite nanofiltration membrane is immersed in an aqueous solution containing 20 wt% hydrochloric acid. After 30 days, the membrane is taken out and cleaned. Under neutral conditions, the changes in desalination rate and water flux of the composite nanofiltration membrane are tested.

[0082] (4) The content of structural unit A and structural unit B in the composite nanofiltration membrane was determined by X-ray photoelectron spectroscopy (XPS, Escalab 250, Thermo Fisher, USA).

[0083] (5) The content of sulfur in the composite nanofiltration membrane was determined by X-ray photoelectron spectroscopy (XPS, Escalab 250, Thermo Fisher, USA).

[0084] (6) Test methods for the average pore size and molecular weight cutoff of composite nanofiltration membranes:

[0085] The membrane's molecular weight cutoff was obtained by filtering a PEG solution with a concentration of 100 ppm and calculating the molecular weights of the PEG, which were selected as 67, 200, 400, 600, and 800 Da. The concentrations of PEG in the raw and product water were determined using a total organic carbon analyzer (TOC, multi N / C 3100, Analytica Jena, Germany). The membrane's molecular weight cutoff was defined as the molecular weight of PEG corresponding to a 90% retention rate.

[0086] The Stokes radius of a PEG is calculated using the following formula:

[0087] r s =16.73×10 -3 ×M 0.557 (1)

[0088] Where, r s is the Stokes radius, and M is the molecular weight of PEG.

[0089] The average pore size of the membrane should be the PEG molecule size corresponding to a PEG rejection rate of 50%.

[0090] (7) The thickness of each layer in the composite nanofiltration membrane was measured by scanning electron microscopy. The scanning electron microscopy model was Hitachi S-4800.

[0091] In the following examples and comparative examples, branched polyethyleneimine (weight-average molecular weight 25000 g / mol), polyethylenepolyamine, 1,3,5-triaminobenzene, 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, and 1,3,5-benzenetricarboxyl chloride were all purchased from Innovent Biologics Inc. Other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0092] Preparation Example

[0093] The porous support layer of the composite nanofiltration membrane was prepared by phase inversion method. The specific steps are as follows: a certain amount of polyethersulfone (number average molecular weight of 80000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polyethersulfone solution with a concentration of 18 wt%. The solution was degassed at 25 °C for 120 min. Then, the polyethersulfone solution was coated onto a polyethylene nonwoven fabric with a thickness of 75 μm using a doctor blade to obtain a nascent membrane. The membrane was then immersed in water at a temperature of 25 °C for 60 min, so that the polyethersulfone nascent layer on the surface of the polyethylene nonwoven fabric underwent phase inversion to form a porous membrane. Finally, after three water washes, a bottom layer - porous support layer with a total thickness of 115 μm was obtained.

[0094] Example 1

[0095] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,4-phenylene diisothiocyanate at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N1. The mass ratio of branched polyethyleneimine to 1,4-phenylene diisothiocyanate was 5:1. The composite nanofiltration membrane N1 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 71 nm.

[0096] Figure 1 Here is a surface SEM image of the composite nanofiltration membrane N1, from... Figure 1 It can be seen that the polythiourea separation layer obtained by interfacial polymerization of polyethyleneimine and 1,4-phenyl diisothiocyanate has a dense and uniform surface, and no surface defects were observed in the SEM field of view.

[0097] Figure 2 The surface sulfur distribution of the composite nanofiltration membrane N1 is determined by... Figure 2It can be seen that the sulfur element is uniformly distributed on the surface of the polythiourea separation layer of the composite nanofiltration N1, indicating that the formed polythiourea separation layer has a uniform structure.

[0098] Figure 3 The surface infrared spectrum of the composite nanofiltration membrane N1 is shown below. Figure 3 It can be seen that the surface infrared spectrum shows obvious thiourea group characteristics, indicating that the interfacial polymerization of polyethyleneimine and 1,4-phenyl diisothiocyanate successfully prepared the polythiourea separation layer.

[0099] Example 2

[0100] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,3,5-triisothiocyanobenzene at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N2. The mass ratio of branched polyethyleneimine to 1,3,5-triisothiocyanobenzene was 5:1. The composite nanofiltration membrane N1 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 76 nm.

[0101] Example 3

[0102] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of IsoparE solution containing 0.1 wt% 1,4-phenylene diisothiocyanate and 0.1 wt% 1,3,5-triisothiocyanobenzene at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N3. The mass ratio of branched polyethyleneimine to the total mass of 1,4-phenylene diisothiocyanate and 1,3,5-triisothiocyanobenzene was 5:1. The composite nanofiltration membrane N3 had a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 74 nm.

[0103] Example 4

[0104] 400cm 2The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% polyethylenepolyamine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,4-phenylenediisothiocyanate at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N4. The mass ratio of polyethylenepolyamine to 1,4-phenylenediisothiocyanate was 5:1. The composite nanofiltration membrane N4 had a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 65 nm.

[0105] Example 5

[0106] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% 1,3,5-triaminobenzene at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,3,5-triisothiocyanobenzene at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N5. The mass ratio of 1,3,5-triaminobenzene to 1,3,5-triisothiocyanobenzene was 5:1. The composite nanofiltration membrane N5 had a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 63 nm.

[0107] Example 6

[0108] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.025 wt% 1,4-phenylene diisothiocyanate at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N6. The mass ratio of branched polyethyleneimine to 1,4-phenylene diisothiocyanate was 40:1. The composite nanofiltration membrane N6 had a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 60 nm.

[0109] Example 7

[0110] 400cm 2The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.01 wt% 1,4-phenylene diisothiocyanate at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N7. The mass ratio of branched polyethyleneimine to 1,4-phenylene diisothiocyanate was 100:1. The composite nanofiltration membrane N7 had a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 58 nm.

[0111] Example 8

[0112] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.05 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,3,5-triisothiocyanobenzene at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N8. The mass ratio of branched polyethyleneimine to 1,3,5-triisothiocyanobenzene was 0.5:1. The composite nanofiltration membrane N8 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 61 nm.

[0113] Example 9

[0114] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.025 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,3,5-triisothiocyanobenzene at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane N9. The mass ratio of branched polyethyleneimine to 1,3,5-triisothiocyanobenzene was 0.25:1. The composite nanofiltration membrane N9 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polythiourea separation layer thickness of 57 nm.

[0115] Comparative Example 1

[0116] 400cm 2The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% branched polyethyleneimine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of an IsoparE solution containing 0.2 wt% 1,3,5-benzenetricarboxylic acid chloride at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane D1. The mass ratio of branched polyethyleneimine to 1,3,5-benzenetricarboxylic acid chloride was 5:1. The composite nanofiltration membrane D1 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polyamide separation layer thickness of 131 nm.

[0117] Comparative Example 2

[0118] 400cm 2 The upper surface of the aforementioned polyethersulfone porous support layer was contacted with 100 mL of an aqueous solution containing 0.5 wt% polyethylenepolyamine at 25°C for 60 s, after which the solution was drained. The residual aqueous phase on the surface was then removed using a rubber roller. Next, the upper surface of the support layer was contacted with 50 mL of IsoparE solution containing 0.2 wt% 1,3,5-benzenetricarboxylic acid chloride at 25°C for 60 s, after which the solution was drained. The membrane was then placed in an oven and heat-treated at 70°C for 5 min to obtain the composite nanofiltration membrane D2. The mass ratio of polyethylenepolyamine to 1,3,5-benzenetricarboxylic acid chloride was 5:1. The composite nanofiltration membrane D2 has a bottom layer thickness of 75 μm, a porous support layer thickness of 40 μm, and a polyamide separation layer thickness of 115 nm.

[0119] The content of each structural unit, S element content, average pore size, molecular weight cutoff, and thickness of the composite nanofiltration membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0120] Table 1

[0121]

[0122] a - Corresponds to the content of structural units derived from polyacrylamide chlorides.

[0123] The acid resistance, water flux, desalination rate of CuCl2, and acid permeability of the composite nanofiltration membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 2.

[0124] Table 2

[0125]

[0126] In Examples 1 to 9 of this invention, the separation layer of the composite nanofiltration membrane is composed of polythiourea, which is prepared by interfacial polymerization using polyamines and 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, or mixtures thereof as monomers. Compared to the composite nanofiltration membranes described in Comparative Examples 1 and 2, the nanofiltration membrane of this invention, using polythiourea as its separation layer, exhibits superior acid resistance. Furthermore, this nanofiltration membrane also exhibits high water flux, high desalination efficiency, and good acid permeability. After being treated with 20 wt% hydrochloric acid solution for 30 days, the desalination rate of the composite nanofiltration membranes in Examples 1 to 9 remained stable, further demonstrating the excellent acid resistance of its separation layer. Therefore, the nanofiltration membrane of this invention is suitable for application in strongly acidic environments, providing a novel and effective solution for the efficient resource-based treatment and recycling of acidic wastewater.

[0127] In further research of this invention, Examples 6 to 9 analyzed the concentration of reactants in the interfacial polymerization reaction in detail. The concentration of reactants has a significant impact on the degree of crosslinking in the formation of the polythiourea separation layer. Experimental data show that although a polythiourea separation layer with good acid resistance can be obtained by carrying out the interfacial polymerization reaction under insufficient monomer concentration, the resulting polymer network density is low, which leads to the desalination efficiency of the composite nanofiltration membrane not reaching the ideal level, affecting the efficient recovery and utilization of metal ions.

[0128] The separation layer of the composite nanofiltration membranes prepared in Comparative Examples 1 and 2 was a polyamide separation layer. After contact with strong acid, the separation layer structure was completely destroyed, making it impossible to test the desalination rate of the nanofiltration membrane under conditions containing strong acid. Therefore, the desalination rates in Comparative Examples 1 and 2 were measured using a 2000 ppm copper chloride solution as the original solution.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polythiourea composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane comprises a bottom layer, a porous support layer, and a polythiourea separation layer arranged sequentially. The polythiourea separation layer comprises structural unit A from polyamines and structural unit B from polyisothiocyanate compounds; Structural unit A and structural unit B are connected by the structure shown in Equation I. Ar1 is the residue of the compound containing polyisothiocyanate after the reaction, and Ar2 is the residue of the polyamine after the reaction.

2. The polythiourea composite nanofiltration membrane according to claim 1, wherein, The polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylene polyamine and polyetheramine, more preferably polyethyleneimine or polyethylene polyamine; Preferably, the polyisothiocyanate compound is selected from at least one of 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, 1,2-phenyl diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate, and more preferably from 1,4-phenyl diisothiocyanate and / or 1,3,5-triisothiocyanobenzene.

3. The polythiourea composite nanofiltration membrane according to claim 1 or 2, wherein, The content of structural unit A on the membrane surface is 20-40 wt%, preferably 25-35 wt%, and the content of structural unit B on the membrane surface is 60-80 wt%, preferably 65-75 wt%.

4. The polythiourea composite nanofiltration membrane according to any one of claims 1-3, wherein, The sulfur content in the composite nanofiltration membrane is 1-5 at.%, preferably 2-4 at.%.

5. The polythiourea composite nanofiltration membrane according to any one of claims 1-4, wherein, The composite nanofiltration membrane has an average pore size of 0.2-0.6 nm, preferably 0.3-0.5 nm; Preferably, the polythiourea composite nanofiltration membrane has a molecular weight cutoff of 300-600 Da, more preferably 300-400 Da.

6. The polythiourea composite nanofiltration membrane according to any one of claims 1-5, wherein, The thickness of the bottom layer is 30-150μm, preferably 50-120μm; Preferably, the thickness of the porous support layer is 10-100 μm, and more preferably 30-60 μm; Preferably, the thickness of the polythiourea separation layer is 10-500 nm, and more preferably 50-150 nm.

7. The polythiourea composite nanofiltration membrane according to any one of claims 1-6, wherein, The material of the bottom layer is selected from at least one of polyester nonwoven fabric, polyethylene nonwoven fabric and polypropylene nonwoven fabric; Preferably, the material of the porous support layer is selected from at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

8. A method for preparing a polythiourea composite nanofiltration membrane, characterized in that, The preparation method includes the following steps: S1. Prepare a porous support layer on the bottom layer; S2. The membrane obtained in step S1 is brought into first contact with an aqueous phase containing polyamines. S3. The membrane layer obtained in step S2 is brought into a second contact with an organic solution containing polyisothiocyanate compounds, and after heat treatment, the polythiourea composite nanofiltration membrane is obtained.

9. The preparation method according to claim 8, wherein, The polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, polyethylene polyamine and polyetheramine, more preferably polyethyleneimine or polyethylene polyamine; Preferably, the concentration of the aqueous phase containing polyamine is 0.05wt%-5wt%, more preferably 0.1wt%-2.5wt%.

10. The preparation method according to claim 8 or 9, wherein, The compound containing polyisothiocyanate is selected from at least one of 1,4-phenyl diisothiocyanate, 1,3,5-triisothiocyanobenzene, 1,2-phenyl diisothiocyanate, 2,6-toluene diisothiocyanate and 1,3-propane diisothiocyanate, preferably selected from 1,4-phenyl diisothiocyanate and / or 1,3,5-triisothiocyanobenzene; Preferably, the concentration of the organic solution containing the polyisothiocyanate compound is 0.025wt%-1wt%, more preferably 0.05wt%-0.5wt%.

11. The preparation method according to any one of claims 8-10, wherein, The mass ratio of the polyamine to the polyisothiocyanate compound is 0.1-50:1, preferably 0.5-20:1; Preferably, the ratio of the volume of the aqueous phase to the membrane area of ​​the membrane layer obtained in step S1 is 0.1-0.5 mL / cm². 2 ; Preferably, the ratio of the volume of the organic solution to the membrane area of ​​the membrane obtained in step S2 is 0.05-0.3 mL / cm². 2 .

12. The preparation method according to any one of claims 8-11, wherein, The duration of the first contact is 5s-100s, preferably 10s-60s; Preferably, the second contact time is 10s-200s, more preferably 20s-120s; Preferably, the heat treatment conditions include: a heat treatment temperature of 40-150℃, more preferably 50-120℃, and a heat treatment time of 0.5-20 min, more preferably 1-10 min.

13. A polythiourea composite nanofiltration membrane prepared by any one of claims 8-12.

14. The application of the polythiourea composite nanofiltration membrane according to any one of claims 1-7 and 13 in the field of water treatment.

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