Positively charged acid and alkali resistant composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of membranes, and discloses a positively charged acid and alkali resistant 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 poly (triazinamine-urea) separation layer which are arranged in sequence, wherein the poly (triazinamine-urea) separation layer comprises a guanidyl structure as shown in a formula I and / or a formula II; and in the imgabs0 #, R1 and R2 are respectively and independently alkyl with 1 to 5 carbon atoms. The separation layer of the positively charged acid and alkali resistant composite nanofiltration membrane is poly (triazinamine-urea) and contains a guanidyl structure with a specific structure, the electropositivity of the surface of the nanofiltration membrane can be remarkably enhanced, and the interception effect of the nanofiltration membrane on divalent and high-valent metal cations is improved while it is guaranteed that the nanofiltration membrane has excellent acid and alkali stability.

Description

Technical Field

[0001] The present invention relates to the field of membranes, and in particular, to a positively charged acid and alkali resistant composite nanofiltration membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Electroplating is a process for regulating the surface properties of metals and non-metals through electrochemical technology to obtain ideal surface corrosion resistance, electrical conductivity, and decorative properties. Electroplating is widely used in China, generating a large amount of wastewater every year, accounting for about 20% of the total industrial wastewater discharge. Electroplating wastewater contains a large amount of toxic and harmful substances, among which wastewater containing heavy metal ions such as copper, nickel, chromium, and zinc accounts for about 40%. Moreover, the pickling and activation processes commonly used in the electroplating process make the above wastewater acidic. The comprehensive treatment of acidic electroplating wastewater is a requirement for environmental protection and an effective means for the resource recycling of industrial wastewater to reduce costs and increase efficiency. At present, the effective recovery of heavy metal ions in electroplating wastewater has become a key issue for the sustainable development of the electroplating industry.

[0003] Conventional chemical precipitation methods have problems such as a large amount of toxic sludge and low recovery rate of heavy metal resources. In contrast, membrane separation technology has the characteristics of high separation efficiency, no secondary pollution, low energy consumption, and convenient operation. It has been widely used to recover metal ions such as copper, nickel, chromium, and zinc in electroplating wastewater. Among them, nanofiltration separation has good application prospects in the above process. At present, it is generally believed that the nanofiltration separation performance is the result of the combined action of the size sieving effect and the Donnan effect. In addition to the density of the membrane itself, there is significant charge selectivity in the nanofiltration separation process. Polyamide thin film composite nanofiltration membranes are the most widely used commercial nanofiltration membranes. Hydrolysis of the acyl chloride groups on the membrane surface forms a large number of carboxyl groups, making the membrane surface negatively charged. Due to the influence of the Donnan effect, the membrane has a low removal rate of high-valent cations, resulting in a low recovery rate of metal ions such as copper, nickel, chromium, and zinc. Positively charged nanofiltration membranes can effectively intercept divalent and high-valent metal cations, better meeting the requirements of the above application scenarios.

[0004] In addition to the charge properties of the membrane, the treatment of acidic electroplating wastewater also has higher requirements for the acid resistance of the membrane. Under acidic conditions, the C=O bond in the structure of conventional polyamide nanofiltration membranes is susceptible to nucleophilic electron attack by H + , and the amide bond undergoes hydrolysis, resulting in the destruction of the membrane separation layer structure and a decrease in the retention performance. To ensure the structural stability of the nanofiltration membrane, the pH of the influent needs to be adjusted, which not only increases the dosage of chemicals but also makes the treatment process more complex.

[0005] Therefore, there is an urgent need to develop a positively charged nanofiltration membrane with a simple preparation method and excellent acid resistance to enhance the Donnan effect in the nanofiltration separation process and achieve the effective recovery of high-valent heavy metal cations. Summary of the Invention

[0006] The object of the present invention is to overcome the problems of poor acid-base stability of the existing nanofiltration membrane and low rejection rate of high-valent metal cations, and to provide a positively charged acid-base resistant composite nanofiltration membrane, a preparation method and an application thereof. The separation layer of the positively charged acid-base resistant composite nanofiltration membrane is poly(triazineamine-urea) and contains a guanidine group structure with a specific structure, which can significantly enhance the positive charge on the surface of the nanofiltration membrane. While ensuring that the nanofiltration membrane has excellent acid-base stability, the rejection effect of the nanofiltration membrane on high-valent cations is improved.

[0007] To achieve the above object, the first aspect of the present invention provides a positively charged acid-base resistant composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a poly(triazineamine-urea) separation layer arranged in sequence;

[0008] Wherein, the poly(triazineamine-urea) separation layer comprises a guanidine group structure represented by Formula I and / or Formula II;

[0009]

[0010] Wherein, R1 and R2 are each independently an alkyl group having 1 to 5 carbon atoms.

[0011] The second aspect of the present invention provides a preparation method of a positively charged acid-base resistant composite nanofiltration membrane, characterized in that the preparation method comprises:

[0012] S1. Prepare a porous support layer on the bottom layer;

[0013] S2. The membrane layer obtained in step S1 is successively brought into first contact with an aqueous phase containing a polyamine and a guanidine group compound containing an amino group, and second contact with an organic phase containing a polyisocyanate compound and a triazine compound containing a C-Cl bond, and after heat treatment, the positively charged acid-base resistant composite nanofiltration membrane is obtained.

[0014] The third aspect of the present invention provides a positively charged acid-base resistant composite nanofiltration membrane prepared by the above preparation method.

[0015] The fourth aspect of the present invention provides an application of the above positively charged acid-base resistant composite nanofiltration membrane in the field of water treatment separation.

[0016] Through the above technical solution, the positively charged acid-base resistant composite nanofiltration membrane, the preparation method and the application thereof provided by the present invention obtain the following beneficial effects:

[0017] The poly(triazineamine-urea) separation layer of the positively charged acid- and alkali-resistant composite nanofiltration membrane provided by the present invention contains a guanidine group structure with a specific structure, which can significantly enhance the positive charge on the surface of the nanofiltration membrane. The enhancement of the Donnan effect enables the nanofiltration membrane to have excellent structural stability in strong acid and strong alkali environments, while improving the retention effect of the nanofiltration membrane on high-valent metal cations, and can achieve the efficient recovery of heavy metal ions in acidic or alkaline wastewater.

[0018] In the preparation method of the positively charged acid- and alkali-resistant composite nanofiltration membrane provided by the present invention, a guanidine compound containing an amino group in its structure is added to the aqueous solution of polyamine and participates in the interfacial polymerization reaction together, so that the guanidine group can be uniformly introduced into the poly(triazineamine-urea) separation layer. The operation of the present invention is simple, the required reagents are easily available, and it does not involve complex synthesis processes. The process is well compatible with the continuous film-making equipment currently used in industry and is easy to scale up industrially. Detailed implementation mode

[0019] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0020] The first aspect of the present invention provides a positively charged acid- and alkali-resistant composite nanofiltration membrane, characterized in that the composite nanofiltration membrane includes a bottom layer, a porous support layer, and a poly(triazineamine-urea) separation layer arranged in sequence;

[0021] Among them, the poly(triazineamine-urea) separation layer includes a guanidine group structure represented by formula I and / or formula II;

[0022]

[0023] Among them, R1 and R2 are each independently an alkyl group with 1 to 5 carbon atoms.

[0024] In the present invention, the poly(triazineamine-urea) separation layer of the positively charged acid- and alkali-resistant composite nanofiltration membrane contains a guanidine group structure with a specific structure, which can significantly enhance the positive charge on the surface of the nanofiltration membrane. The enhancement of the Donnan effect enables the nanofiltration membrane to have excellent structural stability in strong acid and strong alkali environments, while improving the retention effect of the nanofiltration membrane on high-valent metal cations, and can achieve the efficient recovery of heavy metal ions in acidic or alkaline wastewater.

[0025] In the present invention, the poly(triazineamine-urea) separation layer of the composite nanofiltration membrane contains a guanidine structure. When the guanidine group is ionized, the positive charge is delocalized on the three nitrogen atoms, forming a stable planar guanidine cation, thereby enhancing the positive charge of the membrane surface. During the nanofiltration separation process, the membrane's retention rate for divalent metal cations is improved due to the enhanced Donan effect, making it suitable for recovering heavy metals from acidic or alkaline wastewater.

[0026] In the present invention, * refers to the bonding position where the guanidine structure is connected to the poly(triazineamine-urea) separation layer.

[0027] Furthermore, R1 and R2 are each independently a C1-C3 alkyl group.

[0028] According to the present invention, the surface Zeta potential of the composite nanofiltration membrane is 0 mV to 35 mV.

[0029] In the present invention, when the surface Zeta potential of the composite nanofiltration membrane meets the above range, the positive charge on the surface of the composite nanofiltration membrane can effectively intercept divalent and high-valent metal cations. At the same time, the guanidine compound containing amino groups in the structure is not added excessively, so that the separation layer maintains a sufficient cross-linking density, thereby ensuring high retention of divalent and high-valent metal cations.

[0030] Furthermore, the surface Zeta potential of the composite nanofiltration membrane is 10 mV to 25 mV.

[0031] According to the present invention, the average pore size of the composite nanofiltration membrane is 0.1-0.4 nm.

[0032] In the present invention, when the average pore size of the composite nanofiltration membrane satisfies the above range, the composite nanofiltration membrane has a good interception effect on divalent and high-valent metal cations, thereby achieving efficient recovery.

[0033] Furthermore, the average pore size of the composite nanofiltration membrane is 0.1-0.25 nm.

[0034] In the present invention, there is no specific limitation on the bottom layer and the porous support layer, and they can be made of various existing materials that have a certain strength and can be used for nanofiltration and reverse osmosis membranes.

[0035] In the present invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0036] In the present invention, the porous support layer material may be at least one of polyethersulfone, polysulfone, polyarylether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride and polyaryletherketone.

[0037] According to the present invention, there is no particular limitation on the thickness of the bottom layer, the porous support layer, and the poly(triazineamine-urea) separation layer, which can be a conventional choice in the art. However, in order to enable these three layers to play a better synergistic cooperation role and make the obtained composite nanofiltration membrane better combine excellent desalination rate 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; the thickness of the poly(triazineamine-urea) separation layer is 40-300 nm, preferably 50-200 nm.

[0038] In a second aspect of the present invention, a method for preparing a positively charged acid- and alkali-resistant composite nanofiltration membrane is provided, characterized in that the preparation method includes:

[0039] S1. Prepare a porous support layer on the bottom layer;

[0040] S2. The membrane layer obtained in step S1 is successively brought into first contact with an aqueous phase containing a polyamine and a guanidine compound containing an amino group, and into second contact with an organic phase containing a polyisocyanate compound and a triazine compound containing a C-Cl bond, and after heat treatment, the positively charged acid- and alkali-resistant composite nanofiltration membrane is obtained.

[0041] In the present invention, by adding a guanidine compound containing an amino group in the aqueous solution of the polyamine to participate in the interfacial polymerization reaction together, the guanidine group can be uniformly introduced into the poly(triazineamine-urea) separation layer. The operation of the present invention is simple, the required reagents are easily available, and it does not involve complex synthesis processes. The process has good compatibility with the continuous film-making equipment currently used in the industry and is easy to scale up industrially.

[0042] In the present invention, the role of the polyamine in the aqueous phase is to form a dense separation layer with a cross-linked structure by interfacial polymerization with the polyisocyanate compound and the triazine compound, and the role of the guanidine compound containing an amino group in the structure is to react with the polyisocyanate compound and the triazine compound to introduce the guanidine group into the poly(triazineamine-urea) separation layer.

[0043] In the present invention, there is no particular limitation on the method for preparing the porous support layer on the bottom layer, and it can be prepared by a conventional method in the art. Preferably, the phase inversion method is adopted. Specifically, a polymer solution of the porous support layer material is coated on one surface of the bottom layer, and the porous support layer is obtained through phase inversion.

[0044] In the present invention, the phase inversion method preferably can be: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20% by weight, degassing at 20-40 °C for 10-180 min; then coating the polymer solution on the bottom layer to obtain an initial film, and immediately soaking it in water at a temperature of 10-30 °C for 10-60 min to obtain the support layer polymer porous membrane through the phase inversion layer.

[0045] Among them, the solvent can be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0046] According to the present invention, in step S2, the polyamine is selected from at least one of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, and polyethylenepolyamine; preferably selected from polyethyleneimine and / or polyethylenepolyamine.

[0047] According to the present invention, the concentration of the polyamine in the aqueous phase is 0.1-5 wt%.

[0048] In the present invention, when the concentration of the polyamine in the aqueous phase is controlled to meet the above range, the prepared composite nanofiltration membrane can have both excellent retention and permeation performance. Specifically, when the polyamine concentration is too low, the retention performance of the formed poly(triazineamine-urea) separation layer is poor; when the polyamine concentration is too high, the permeation performance of the formed poly(triazineamine-urea) separation layer is poor.

[0049] Furthermore, the concentration of the polyamine in the aqueous phase is 0.3-2 wt%.

[0050] According to the present invention, the guanidine compound containing an amino group has the structure shown in formula 1 and / or formula 2:

[0051]

[0052] Among them, R1 and R2 are each independently an alkyl group with 1-5 carbon atoms, preferably an alkyl group with 1-3 carbon atoms.

[0053] In the present invention, the guanidine compound containing an amino group is selected from at least one of the compound shown in formula 1, the salt of the compound shown in formula 1, the compound shown in formula 2, and the salt of the compound shown in formula 2. Preferably, the compound salt refers to the hydrochloride salt of the compound shown in formula 1 or formula 2.

[0054] In a specific embodiment of the present invention, the guanidine compound containing an amino group is selected from at least one of polyaminopropyl biguanide, 1-(4-aminobutyl)guanidine, 1-amino-4-butylguanidine dihydrochloride, and 1,3-diaminoguanidine hydrochloride, preferably polyaminopropyl biguanide and / or 1-(4-aminobutyl)guanidine.

[0055] According to the present invention, the concentration of the guanidine compound containing an amino group in the aqueous phase is 0.05-1 wt%.

[0056] In the present invention, when the concentration of the guanidine compound containing an amino group in the aqueous phase is controlled to meet the above range, the prepared nanofiltration membrane can simultaneously have a high surface Zeta potential and a high crosslinking degree of the poly(triazineamine-urea) separation layer, ensuring that the nanofiltration membrane can effectively retain divalent and higher-valent metal cations. Specifically, when the concentration of the guanidine compound containing an amino group in the aqueous phase is too low, the enhancement effect of the guanidine structure on the surface positive charge of the composite nanofiltration membrane is not obvious; if the concentration of the guanidine compound containing an amino group in the aqueous phase is too high, too much guanidine compound will consume more polyisocyanate compounds and triazine compounds, resulting in insufficient polyisocyanate compounds and triazine compounds for reacting with polyamines, leading to a lower crosslinking degree of the poly(triazineamine-urea) separation layer and deteriorating the retention performance of the nanofiltration membrane.

[0057] Further, the concentration of the guanidine compound containing an amino group in the aqueous phase is 0.1-0.5 wt%.

[0058] According to the present invention, the polyisocyanate compound is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, toluene-2,6-diisocyanate, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, 3,3'-dichloro-4,4'-diisocyanatobiphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine ethyl ester diisocyanate, 1,4-cyclohexylene diisocyanate, and 4-chloro-6-methyl-m-phenylene diisocyanate; preferably selected from 1,4-phenylene diisocyanate and / or 1,3-phenylene diisocyanate.

[0059] According to the present invention, the triazine compound containing a C-Cl bond is a triazine compound containing at least two C-Cl bonds; preferably selected from one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine, and 2,4-dichloro-6-phenyl-1,3,5-triazine.

[0060] In a specific embodiment of the present invention, the triazine compound containing a C-Cl bond is cyanuric chloride.

[0061] According to the present invention, the concentration of the polyisocyanate compound in the organic phase is 0.01-0.1 wt%.

[0062] Further, the concentration of the polyisocyanate compound in the organic phase is 0.03-0.05 wt%.

[0063] According to the present invention, the concentration of the triazine compound containing a C-Cl bond in the organic phase is 0.05 - 0.2 wt%.

[0064] Further, the concentration in the organic phase is 0.1 - 0.15 wt%.

[0065] In the present invention, when the concentrations of the polyisocyanate compound and the polyisocyanate compound in the organic phase are controlled within the above ranges, the synergistic cooperation effect of the two can be fully exerted, and the prepared poly(triazineamine-urea) separation layer is thin and dense, taking into account good retention performance and high water flux.

[0066] According to the present invention, the amounts of the aqueous phase and the organic phase are such that the mass ratio of the polyamine, the guanidyl compound containing an amino group, the triazine compound containing a C-Cl bond, and the polyisocyanate compound is 10 - 30:3 - 40:1 - 5:1.

[0067] In the present invention, when the mass ratio of the polyamine, the guanidyl compound containing an amino group, the polyisocyanate compound, and the triazine compound containing a C-Cl bond meets the above range, on the one hand, the poly(triazineamine-urea) separation layer containing guanidyl groups in the obtained structure has sufficient crosslinking density and a relatively high surface Zeta potential to obtain high ion retention performance; on the other hand, the thickness of the poly(triazineamine-urea) separation layer is relatively thin, and a relatively high water flux can be obtained.

[0068] Further, the amounts of the aqueous phase and the organic phase are such that the mass ratio of the polyamine, the guanidyl compound containing an amino group, the polyisocyanate compound, and the triazine compound containing a C-Cl bond is 10 - 20:4 - 20:2 - 3:1. In the present invention, there is no particular limitation on the type of the solvent in the organic phase as long as it can dissolve the polyacyl chloride. Preferably, the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, and paraffin solvent oils (Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M).

[0069] In the present invention, there are no special limitations on the interfacial polymerization conditions of polyamines, polyisocyanate compounds and triazine compounds, as well as the reaction conditions of polyisocyanate compounds, triazine compounds and guanidyl compounds containing amino groups, and they can be carried out according to the conventional conditions in the art. However, in order to enable these three layers to play a better synergistic cooperation effect and make the obtained composite nanofiltration membrane better possess excellent ion selective separation performance and higher water flux, preferably, the time of the first contact is 5 - 100 s, preferably 10 - 60 s; the time of the second contact is 10 - 200 s, preferably 20 - 120 s; the heat treatment conditions include: the heat treatment temperature is 40 - 150 °C, preferably 50 - 120 °C; the heat treatment time is 0.5 - 10 min, preferably 1 - 5 min.

[0070] In the present invention, the time of the first contact is 5 - 100 s. If the time of the first contact is too short, the amount of water phase infiltration is insufficient, and the separation layer formed by the subsequent interfacial polymerization reaction may be defective; if the contact time is longer than the preferred value, the amount of water phase infiltration is excessive, and the separation layer formed by the subsequent interfacial polymerization reaction may be too thick and have poor permeability. Preferably, the time of the first contact is 10 - 60 s.

[0071] In the present invention, the time of the second contact is 10 - 200 s. When the time of the second contact is controlled within the above range, it can ensure that polyamines and guanidyl compounds containing amino groups can fully contact and react with polyisocyanate compounds and triazine compounds to form a poly(triazineamine-urea) separation layer containing guanidyl structure. When the time of the second contact is too short, the two-phase reaction is insufficient, and the separation layer formed by the interfacial polymerization reaction may be defective; if the time of the second contact is too long, the separation layer formed by the interfacial polymerization reaction may be too thick, and the permeability of the nanofiltration membrane decreases. Preferably, the time of the second contact is 20 - 120 s.

[0072] In the present invention, the heat treatment temperature is 40 - 150 °C; the heat treatment time is 0.5 - 10 min. When the heat treatment conditions are controlled within the above range, it can ensure that the water-phase monomers (polyamines and guanidyl compounds containing amino groups) and the organic-phase monomers (polyisocyanate compounds and triazine compounds) fully react, further improve the crosslinking degree of the separation layer, and at the same time dry the organic solvent. If the heat treatment temperature is too low and the heat treatment time is too short, the organic solvent volatilizes insufficiently; if the heat treatment temperature is too high and the heat treatment time is too long, the permeability of the obtained composite nanofiltration membrane will deteriorate and the separation performance will decrease.

[0073] Furthermore, the heat treatment temperature is 50 - 120 °C; the heat treatment time is 1 - 5 min.

[0074] In the present invention, in step S2, the ratio of the volume of the aqueous phase containing polyamine and amino group-containing guanidine compound to the membrane area of the membrane layer obtained in step S1 is 0.1 - 0.5 mL / cm 2 , preferably 0.2 - 0.4 mL / cm 2 .

[0075] In the present invention, in step S2, the ratio of the volume of the organic phase containing polyisocyanate compound and C-Cl bond-containing triazine compound to the membrane area of the membrane layer obtained in step S1 is 0.05 - 0.3 mL / cm 2 , preferably 0.1 - 0.25 mL / cm 2 .

[0076] The third aspect of the present invention provides a positively charged acid and alkali resistant composite nanofiltration membrane prepared by the above preparation method.

[0077] The fourth aspect of the present invention provides an application of the above positively charged acid and alkali resistant composite nanofiltration membrane in the field of water treatment separation.

[0078] To enable those skilled in the art to better understand the features and effects of the present invention, the technical solutions and effects of the present invention will be described in detail below in conjunction with specific embodiments.

[0079] In this article, for the sake of simplicity of description, all possible combinations of all technical features in the embodiments are not described. The described embodiments are partial embodiments of the present invention, not all embodiments, and are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0080] Unless otherwise defined, all technical and scientific terms used herein belong to the general definitions in the field of this application.

[0081] In the following examples and comparative examples, the water flux of the composite nanofiltration membrane is measured by the following method: The composite nanofiltration membrane is installed in a membrane cell, pre-pressed at 1.5 MPa for 1 h, and then the water permeation amount of the composite nanofiltration membrane within a certain time is measured under the conditions of a pressure of 2.0 MPa and a temperature of 25°C. The water flux is calculated by the following formula: J = Q / (A·t), where J is the water flux, Q is the water permeation amount (L), A is the effective filtration membrane area of the composite nanofiltration membrane (m 2 ), and t is the time (h).

[0082] The desalination rate of the composite nanofiltration membrane was tested as follows: The composite nanofiltration membrane was installed in a membrane cell and pre-pressed at 1.5 MPa for 1 h. Subsequently, the concentration changes of salts in the raw aqueous solution with an initial concentration of 2000 ppm and the permeate were tested within 1 h under the conditions of a pressure of 2.0 MPa and a temperature of 25 °C. The desalination rate was calculated by the following formula: R = (Cf - Cp) / Cf × 100%, where R is the desalination rate, Cf is the concentration of nickel chloride or copper chloride in the stock solution, and Cp is the concentration of nickel chloride or copper chloride in the permeate.

[0083] The acid resistance test method of the composite membrane: The composite nanofiltration membrane sheet was immersed in a 20 wt% HCl solution, taken out and washed after 30 days, and then the changes in the desalination rate and water flux of the composite nanofiltration membrane were tested.

[0084] The Zeta potential of the nanofiltration membrane was measured based on the streaming potential and streaming current measurement method. The model of the Zeta potential analyzer used was SurPASS 3, and it was measured according to the streaming potential method in the test method for the surface Zeta potential of nanofiltration membranes (GB / T 37617-2019).

[0085] Thickness measurement: The cross-sectional morphology of the membrane sheet was observed using a Hitachi S-4800 high-resolution field emission scanning electron microscope (FESEM), and then the thickness of the membrane was obtained.

[0086] In addition, in the following examples and comparative examples:

[0087] Branched polyethyleneimine (weight average molecular weight of 25000 g / mol) and polyethylenepolyamine were purchased from InnoChem Technology Co., Ltd. Polyaminopropyl biguanide and 1-(4-aminobutyl)guanidine were purchased from Sinopharm Chemical Reagent Co., Ltd. Polyhexamethylene biguanide hydrochloride, 1-amino-4-butylguanidine dihydrochloride, cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, and toluene-2,6-diisocyanate were purchased from Xilong Scientific.

[0088] The support layer was prepared by the phase inversion method. The specific steps are as follows:

[0089] A certain amount of polysulfone (number average molecular weight of 80000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18 wt%. It was degassed at 25 °C for 120 min. Then, the polysulfone solution was coated on a polyester non-woven fabric (with a thickness of 75 μm) using a doctor blade to obtain an initial membrane. Immediately, it was immersed in water at 25 °C for 60 min, so that the polysulfone layer on the surface of the polyester non-woven fabric was phase-transformed into a porous membrane. Finally, it was washed 3 times to obtain a bottom-layer porous support layer with a total thickness of 115 μm.

[0090] Example 1

[0091] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine and polyaminopropyl biguanide (where R2 in Formula 2 is ethyl) in water to obtain a binary blended aqueous phase. The concentration of polyethyleneimine is 0.5 wt%, and the concentration of polyaminopropyl biguanide is 0.2 wt%.

[0092] Step 2: Prepare the organic phase solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic phase solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0093] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous phase solution prepared in Step 1 for 60 s at 25 °C, and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic phase solution prepared in Step 2 for 60 s at 25 °C, and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane N1. Among them, the mass ratio of polyethyleneimine, polyaminopropyl biguanide, cyanuric chloride, and 1,3-phenylene diisocyanate is 20:8:3:1.

[0094] The physicochemical properties of the composite membrane N1 are shown in Table 1.

[0095] Example 2

[0096] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine and polyaminopropyl biguanide in water to obtain a binary blended aqueous phase. The concentration of polyethyleneimine is 0.5 wt%, and the concentration of polyaminopropyl biguanide is 0.5 wt%.

[0097] Step 2: Prepare the organic phase solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic phase solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0098] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous phase solution prepared in Step 1 for 60 s at 25 °C, and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic phase solution prepared in Step 2 for 60 s at 25 °C, and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane N2. Among them, the mass ratio of polyethyleneimine, polyaminopropyl biguanide, cyanuric chloride, and 1,3-phenylene diisocyanate is 20:20:3:1.

[0099] The physicochemical properties of the composite membrane N2 are shown in Table 1.

[0100] Example 3

[0101] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine and polyaminopropyl biguanide in water to obtain a binary blended aqueous phase. The concentration of polyethyleneimine is 0.5 wt%, and the concentration of polyaminopropyl biguanide is 1 wt%.

[0102] Step 2: Prepare the organic phase solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic phase solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0103] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous phase solution prepared in Step 1 for 60 s at 25 °C and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic phase solution prepared in Step 2 for 60 s at 25 °C and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane N3. Among them, the mass ratio of polyethyleneimine, polyaminopropyl biguanide, cyanuric chloride and 1,3-phenylene diisocyanate is 20:40:3:1.

[0104] The physicochemical properties of the composite membrane N3 are shown in Table 1.

[0105] Example 4

[0106] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine and 1-(4-aminobutyl)guanidine (R1 is butyl in Formula 1) in water to obtain a binary blended aqueous phase. The concentration of polyethyleneimine is 0.5 wt%, and the concentration of 1-(4-aminobutyl)guanidine is 0.1 wt%.

[0107] [[ID=CH=22]]Step 2: Prepare the organic phase solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic phase solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0108] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous phase solution prepared in Step 1 for 60 s at 25 °C and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic phase solution prepared in Step 2 for 60 s at 25 °C and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane N4. Among them, the mass ratio of polyethyleneimine, 1-(4-aminobutyl)guanidine, cyanuric chloride and 1,3-phenylene diisocyanate is 20:4:3:1.

[0109] The physicochemical properties of the composite membrane N4 are shown in Table 1.

[0110] Example 5

[0111] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine and 1-amino-4-butylguanidine dihydrochloride (the hydrochloride of the guanidine compound shown in Formula 1 when R1 is butyl) in water to obtain a binary blended aqueous phase. The concentration of polyethyleneimine is 0.5 wt%, and the concentration of 1-amino-4-butylguanidine dihydrochloride is 0.2 wt%.

[0112] Step 2: Prepare the organic solution: Dissolve cyanuric chloride and toluene-2,6-diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of toluene-2,6-diisocyanate is 0.05 wt%.

[0113] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1, drain the liquid after contacting for 60 s at 25°C; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2, drain the liquid after contacting for 60 s at 25°C; then, put the membrane into an oven and heat it at 70°C for 5 min to obtain the composite nanofiltration membrane N5. Among them, the mass ratio of polyethyleneimine, 1-amino-4-butylguanidine dihydrochloride, cyanuric chloride, and toluene-2,6-diisocyanate is 20:8:3:1.

[0114] The physicochemical properties of the composite membrane N5 are shown in Table 1.

[0115] Example 6

[0116] Step 1: Prepare the aqueous solution: Dissolve polyethylenepolyamine and polyaminopropyl biguanide in water to obtain a binary blended aqueous phase. The concentration of polyethylenepolyamine is 0.3 wt%, and the concentration of polyaminopropyl biguanide is 0.2 wt%.

[0117] Step 2: Prepare the organic solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0118] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1, drain the liquid after contacting for 60 s at 25°C; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2, drain the liquid after contacting for 60 s at 25°C; then, put the membrane into an oven and heat it at 70°C for 5 min to obtain the composite nanofiltration membrane N6. Among them, the mass ratio of polyethylenepolyamine, polyaminopropyl biguanide, cyanuric chloride, and 1,3-phenylene diisocyanate is 12:8:3:1.

[0119] The physicochemical properties of the composite membrane N6 are shown in Table 1.

[0120] Example 7

[0121] Step 1: Prepare the aqueous solution: Dissolve polyethylenepolyamine and 1-(4-aminobutyl)guanidine in water to obtain a binary blended aqueous phase. The concentration of polyethylenepolyamine is 0.3 wt%, and the concentration of 1-(4-aminobutyl)guanidine is 0.1 wt%.

[0122] Step 2: Prepare the organic solution: Dissolve cyanuric chloride and 1,4-phenylene diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,4-phenylene diisocyanate is 0.05 wt%.

[0123] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1 for 60 s at 25 °C and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2 for 60 s at 25 °C and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane N7. Among them, the mass ratio of polyethylenepolyamine, 1-(4-aminobutyl)guanidine, cyanuric chloride to 1,4-phenylene diisocyanate is 12:4:3:1.

[0124] The physicochemical properties of the composite membrane N7 are shown in Table 1.

[0125] Comparative Example 1

[0126] Step 1: Prepare the aqueous solution: Dissolve polyethyleneimine in water to obtain an aqueous solution. The concentration of polyethyleneimine is 0.5 wt%.

[0127] Step 2: Prepare the organic solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0128] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1 for 60 s at 25 °C and then drain the liquid; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2 for 60 s at 25 °C and then drain the liquid; then, put the membrane into an oven and heat it at 70 °C for 5 min to obtain the composite nanofiltration membrane D1. Among them, the mass ratio of polyethyleneimine, cyanuric chloride to 1,3-phenylene diisocyanate is 20:3:1.

[0129] The physicochemical properties of the composite membrane D1 are shown in Table 1.

[0130] Comparative Example 2

[0131] Step 1: Prepare an aqueous solution: Dissolve polyaminopropyl biguanide in water to obtain an aqueous solution. The concentration of polyaminopropyl biguanide is 0.2 wt%.

[0132] Step 2: Prepare an organic solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0133] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1, drain the liquid after contacting for 60 s at 25°C; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2, drain the liquid after contacting for 60 s at 25°C; then, put the membrane into an oven and heat it at 70°C for 5 min to obtain the composite nanofiltration membrane D2. Among them, the mass ratio of polyaminopropyl biguanide, cyanuric chloride to 1,3-phenylene diisocyanate is 8:3:1.

[0134] The physicochemical properties of the composite membrane D2 are shown in Table 1.

[0135] Comparative Example 3

[0136] Step 1: Prepare an aqueous solution: Dissolve polyethylenepolyamine in water to obtain an aqueous solution. The concentration of polyethylenepolyamine is 0.3 wt%.

[0137] Step 2: Prepare an organic solution: Dissolve cyanuric chloride and 1,3-phenylene diisocyanate in Isopar E to obtain an organic solution. The concentration of cyanuric chloride is 0.15 wt%, and the concentration of 1,3-phenylene diisocyanate is 0.05 wt%.

[0138] Step 3: Contact the upper surface of the 400 cm 2 polysulfone support layer with 100 mL of the aqueous solution prepared in Step 1, drain the liquid after contacting for 60 s at 25°C; then, contact the upper surface of the support layer with 50 mL of the organic solution prepared in Step 2, drain the liquid after contacting for 60 s at 25°C; then, put the membrane into an oven and heat it at 70°C for 5 min to obtain the composite nanofiltration membrane D3. Among them, the mass ratio of polyethylenepolyamine, cyanuric chloride to 1,3-phenylene diisocyanate is 12:3:1.

[0139] The physicochemical properties of the composite membrane D3 are shown in Table 1.

[0140] The thickness, surface Zeta potential, and average pore size of each layer of the composite membrane in the examples and comparative examples are shown in Table 1.

[0141] Table 1

[0142] Bottom layer / μm Porous support layer / μm Separation layer / nm Surface Zeta potential (mV) Average pore size (nm) Example 1 75 40 103 17.6 0.19 Example 2 75 40 107 21.3 0.23 Example 3 75 40 128 23.9 0.25 Example 4 75 40 112 15.4 0.2 Example 5 75 40 109 13.5 0.23 Example 6 75 40 105 15.3 0.18 Example 7 75 40 114 13.2 0.15 Comparative example 1 75 40 110 -25.6 0.21 Comparative example 2 75 40 463 28.2 0.53 Comparative example 3 75 40 97 -28.4 0.16

[0143] The water flux of the composite nanofiltration membranes prepared in the examples and comparative examples and the desalination rates for nickel chloride and copper chloride were tested, and the results are shown in Table 2.

[0144] The composite nanofiltration membranes prepared in the examples and comparative examples were immersed in a 20 wt% HCl aqueous solution for 30 days, and then the water flux of the composite nanofiltration membranes and the desalination rates for nickel chloride and copper chloride were tested, and the results are shown in Table 2.

[0145] Table 2

[0146]

[0147]

[0148] As can be seen from Table 1 and Table 2,

[0149] (1) By adding a guanidine compound containing an amino group in its structure to the aqueous solution of polyamine and jointly participating in the interfacial polymerization reaction, the guanidine group can be uniformly introduced into the poly(triazineamine-urea) separation layer, significantly improving the Zeta potential of the membrane surface, and thus improving the rejection rate of the membrane for divalent copper ions and nickel ions.

[0150] (2) The above operation will not damage the acid-base stability of the poly(triazineamine-urea) separation layer. After the above nanofiltration membrane is treated in a 20 wt% HCl solution for 30 days, the desalination rates of the membrane for nickel chloride and copper chloride basically remain unchanged, indicating that the membrane can maintain good structural integrity.

[0151] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A positively charged acid and alkali resistant composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane comprises a bottom layer, a porous support layer, and a poly(triazineamine-urea) separation layer arranged in sequence; Among them, the poly(triazineamine-urea) separation layer contains a guanidine group structure shown in Formula I and / or Formula II; Among them, R1 and R2 are each independently an alkyl group with 1 to 5 carbon atoms.

2. The positively charged acid and alkali resistant composite nanofiltration membrane according to claim 1, wherein, R1 and R2 are each independently an alkyl group with 1 to 3 carbon atoms.

3. The positively charged acid- and alkali-resistant composite nanofiltration membrane according to claim 1 or 2, wherein, The surface Zeta potential of the composite nanofiltration membrane is 0 mV to 35 mV, preferably 10 mV to 25 mV.

4. The positively charged acid and alkali resistant composite nanofiltration membrane according to any one of claims 1-3, wherein, The average pore size of the composite nanofiltration membrane is 0.1 - 0.4 nm, preferably 0.1 - 0.25 nm.

5. The positively charged acid and alkali resistant composite nanofiltration membrane according to any one of claims 1-4, wherein The thickness of the bottom layer is 30 - 150 μm, preferably 50 - 120 μm; Preferably, the thickness of the porous support layer is 10 - 100 μm, preferably 30 - 60 μm; Preferably, the thickness of the poly(triazineamine-urea) separation layer is 40 - 300 nm, preferably 50 - 200 nm.

6. A preparation method of a positively charged acid and alkali resistant composite nanofiltration membrane, characterized in that, The preparation method includes: S1. Prepare a porous support layer on the bottom layer; S2. The membrane layer obtained in step S1 is successively brought into first contact with an aqueous phase containing a polyamine and a guanidine group compound containing an amino group, and into second contact with an organic phase containing a polyisocyanate compound and a triazine compound containing a C-Cl bond. After heat treatment, the positively charged acid- and alkali-resistant composite nanofiltration membrane is obtained.

7. The preparation method according to claim 6, wherein, In step S2, the polyamine is selected from at least one of polyethyleneimine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, and polyethylenepolyamine; Preferably, the concentration of the polyamine in the aqueous phase is 0.1 - 5 wt%; Preferably, the guanidine group compound containing an amino group has a structure shown in Formula 1 and / or Formula 2: Wherein, R1 and R2 are each independently an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms; Preferably, the concentration of the guanidine group compound containing an amino group in the aqueous phase is 0.05 - 1 wt%; Preferably, the polyisocyanate compound is selected from at least one of isophthaloyl diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, toluene-2,6-diisocyanate, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, 3,3'-dichloro-4,4'-diisocyanatobiphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine ethyl ester diisocyanate, 1,4-cyclohexylene diisocyanate, and 4-chloro-6-methyl-m-phenylene diisocyanate; Preferably, the triazine compound containing a C-Cl bond is a triazine compound containing at least two C-Cl bonds; preferably selected from cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine, and 2,4-dichloro-6-phenyl-1,3,5-triazine; Preferably, the concentration of the polyisocyanate compound in the organic phase is 0.01 - 0.1 wt%; Preferably, the concentration of the triazine compound containing a C-Cl bond in the organic phase is 0.05 - 0.2 wt%; Preferably, the amounts of the aqueous phase and the organic phase are such that the mass ratio of the polyamine, the amino group-containing guanidine compound, the C-Cl bond-containing triazine compound, and the polyisocyanate compound is 10-30:3-40:1-5:

1.

8. The preparation method according to claim 6 or 7, wherein The time of the first contact is 5-100 s, preferably 10-60 s; Preferably, the time of the second contact is 10-200 s, preferably 20-120 s; Preferably, the conditions of the heat treatment include: the heat treatment temperature is 40-150 °C, preferably 50-120 °C; the heat treatment time is 0.5-10 min, preferably 1-5 min.

9. A positively charged acid- and alkali-resistant composite nanofiltration membrane prepared by the preparation method according to any one of claims 6-8.

10. Use of the positively charged acid- and alkali-resistant composite nanofiltration membrane according to any one of claims 1-5 and 9 in the field of water treatment separation.

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