Polyamide composite semipermeable membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of membranes, particularly relates to a polyamide composite semipermeable membrane, and further discloses a preparation method and application of the polyamide composite semipermeable membrane. In the polyamide composite semipermeable membrane, the yellow index of the polyamide membrane layer is required to be less than 30, and when an amido peak appears in the infrared absorption spectrum 1545 + / -10cm <-1 > range, the amido peak top frequency difference value before and after thermocuring treatment is detected to be greater than 2cm <-1 >, and the ratio X of the infrared intensity after thermocuring to the infrared intensity before thermocuring is less than 0.85. The polyamide composite semipermeable membrane has high flux and high salt rejection rate, also has high rejection performance on non-dissociative boron in a neutral region, and is more suitable for separation treatment of seawater.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and specifically relates to a polyamide composite semipermeable membrane which can achieve high flux and high salt rejection rate and has good interception ability for non-dissociated boron in the neutral region, and further discloses a preparation method and application thereof. Background Art

[0002] Membrane separation technology is a technology that can be used to remove substances (such as salts) dissolved in solvents (such as water), and the composite membrane of a porous carrier coated with a "thin film" polyamide layer is currently the most common type of separation membrane. Among them, the polyamide film is mainly obtained by interfacial polymerization of a polar solution containing multifunctional amines (generally containing m-phenylenediamine, isophthaloyl chloride, piperazine, aliphatic amine, polyetheramine, etc.) and a non-polar solution containing multifunctional acyl halides (generally containing trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, etc.). For example, the preparation method of the reverse osmosis membrane disclosed in patent US4277344A sequentially coats the immiscible solution containing the corresponding monomers on the surface of the carrier (polyester+polysulfone) to obtain a reverse osmosis membrane. These membranes are widely used in, for example, the situation of obtaining drinking water from seawater, alkaline water, water containing harmful substances, or the manufacture of industrial ultrapure water, wastewater treatment, and the recovery of valuable substances.

[0003] Boron is toxic to humans, animals and plants, and can cause neurological damage and growth inhibition, etc. Therefore, the World Health Organization has increasingly stringent requirements for boron content in water. However, seawater contains a large amount of boron, so boron removal is an important procedure in seawater desalination, and the requirements for the performance of removing trace boron contained in seawater are becoming increasingly stringent. Therefore, the art expects to achieve boron removal with the help of composite semipermeable membrane technology, and has also proposed a variety of methods to improve the boron removal performance of composite semipermeable membranes.

[0004] For example, Chinese patent CN102781560A discloses a method for improving performance by increasing the temperature of interfacial polymerization reaction and heat treating the obtained polyamide composite membrane. Another example is document (ZHAI X, MENG J, LI R, et al.Hypochlorite treatment on thin film composite RO membrane to improve boron removal performance [J]. Desalination, 2011, 274 (1-3): 136-143.) also discloses a method for contacting a composite semipermeable membrane obtained by interfacial polymerization with a free chlorine aqueous solution containing. However, when the membranes prepared by the above two methods are subjected to an operating pressure of 5.5 MPa and allow seawater of 25°C, pH 8, boron concentration of 5 ppm, and TDS concentration of 3.5 wt% to pass through, the membrane permeation flux is less than 36 LMH, and the boron removal rate is no more than about 95%. Another example is the literature (CHONG CY, LAU WJ, YUSOF N, et al. Studies on the properties of RO membranes for salt and boron removal: Influence of thermal treatment methods and rinsing treatmengs [J]. Desalination, 2018, 428: 218-226) also reported a method of changing the type of organic solvent to improve the deboronization of polyamide composite membranes after interfacial polymerization. Although the composite semipermeable membrane can improve the removal performance of boron while maintaining the flux, it is far from reaching the expected goal. Therefore, the art expects to develop a composite semipermeable membrane with higher boron blocking performance and higher flux. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to provide a polyamide composite semipermeable membrane, wherein the polyamide composite semipermeable membrane has high flux and high salt rejection rate, and also has good interception ability for boron that does not dissociate in the neutral region;

[0006] The second technical problem to be solved by the present invention is to provide a preparation method and application of the above-mentioned composite semipermeable membrane.

[0007] In order to solve the above technical problems, the present invention provides a polyamide composite semipermeable membrane, wherein the polyamide composite semipermeable membrane comprises a composite porous carrier and a polyamide membrane layer;

[0008] The polyamide composite semipermeable membrane has at least one of the following characteristics:

[0009] (a) the yellowness index of the polyamide film layer is less than 30; it should be noted that the so-called yellowness index is the degree to which the color tone of the polymer deviates from colorless or white to yellow, and is expressed as a positive value. The yellowness index of the polyamide separation layer can be measured using a colorimeter;

[0010] (b) The infrared absorption spectrum of the polyamide film layer before and after thermal curing was measured using the ATR method, and the infrared absorption spectrum at 1540±10 cm -1 The peak of the amide II absorption band of the amide group appears in the range of T 热固化处理前 The frequency of the peak of the amide II absorption band of the amide group is related to T 热固化处理后 The difference in frequency between the peaks of the amide II absorption bands of the amide group is 2 cm -1 above;

[0011] (c) During the heating process of the heat curing treatment, the infrared absorption spectrum of the surface of the polyamide film layer is measured, and the X value is calculated based on the following formula (1) to be less than 0.85:

[0012] X=Abs(T 热固化处理后 ) / Abs(T 热固化处理前 )(1);

[0013] Among them, Abs(T 热固化处理后 ) is measured at 1640 cm after thermal curing -1 The infrared absorption intensity of the peak at 热固化处理前 ) is the value at 1640 cm-1 measured when the polyamide composite film is not subjected to heat curing treatment. -1 The infrared absorption intensity of the peak.

[0014] In the polyamide composite semipermeable membrane of the present invention, when the polyamide membrane layer is in contact with a reagent that can react with an amino group or a carboxyl group, the yellow index of the polyamide membrane layer is preferably below 30. The yellow index is related to the content of azo compounds or azo groups in the polyamide separation layer. If the yellow index in the polyamide separation layer is higher than 30, fewer chemical bonds are generated after thermal curing, resulting in more free amine groups generating azo groups, a low degree of crosslinking of the membrane, and a reduced interception capacity for non-dissociated boron in the neutral region.

[0015] The polyamide composite semipermeable membrane of the present invention uses the ATR method to measure the infrared absorption spectrum of the separation layer during the heating process (thermal curing step), and determines the infrared absorption spectrum of 1540±10cm -1 The peak of the amide II absorption band of the amide group appears in the range of . 热固化处理前 The frequency of the peak of the amide II absorption band of the amide group is related to T 热固化处理后 The difference in frequency between the peaks of the amide II absorption band of the amide group is preferably 2 cm -1This is because the amide II absorption band of the amide group is considered to be related to hydrogen bonding. The reason why the peak position of the amide II absorption band of the amide group shifts depending on the temperature of thermal curing is that the hydrogen bonds formed at 20°C are cut by the DA reaction during the thermal curing process to generate new chemical bonds. The structural change at this time is observed as a peak shift. If the peak shift is 2 cm -1 The above results indicate that the DA reaction generates new chemical bonds, the cross-linking degree of the membrane is greatly improved, and the retention capacity of non-dissociated boron in the neutral region is enhanced.

[0016] The polyamide composite semipermeable membrane of the present invention preferably has an X value calculated by the following formula (1) less than 0.85 when the infrared absorption spectrum of the surface of the separation functional layer during the heating process (thermal curing step) is measured based on the ATR method;

[0017] X=Abs(T 热固化处理后 ) / Abs(T 热固化处理前 )(1);

[0018] Among them, Abs(T 热固化处理后 ) is measured at 1640 cm at the thermal curing temperature -1 The infrared absorption intensity, Abs(T 热固化处理前 ) is measured without heat curing treatment at 1640 cm -1 The infrared absorption intensity is 1000cm -1 ~1900cm -1 The measured data were baseline corrected and the 1250cm -1 The infrared absorption intensity at is set to 1 and the value after standardization.

[0019] The polyamide composite semipermeable membrane of the present invention is considered to be 1640±10cm -1 The infrared absorption intensity at and the peak shift mentioned above are also related to the formation of new chemical bonds. If the X value is less than 0.85, it indicates that the DA reaction generates sufficient new chemical bonds, which increases the cross-linking degree of the membrane and enhances the interception capacity of non-dissociated boron in the neutral region.

[0020] Specifically, the polyamide composite semipermeable membrane, the polyamide membrane layer is prepared by polymerization of an amine monomer and an acyl halide monomer; wherein,

[0021] The amino monomer comprises a mixture of a multifunctional amino monomer and a dienophile-containing amino monomer;

[0022] The acyl halide monomer comprises a mixture of a multifunctional acyl halide monomer and a conjugated diene acyl halide monomer.

[0023] Specifically, the polyamide composite semipermeable membrane:

[0024] The multifunctional amine monomer includes one or more of m-phenylenediamine, p-phenylenediamine, piperazine, aliphatic amine or polyetheramine; and / or,

[0025] The dienophile amine-containing monomer comprises at least one of but-2-ene-1,4-diamine, 4,5-diaminopyrimidine or 5-aminopyrimidine; more preferably but-2-ene-1,4-diamine; and / or,

[0026] The polyfunctional acyl halide monomer includes an aromatic or alicyclic polyfunctional acyl halide monomer, preferably one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid chloride, naphthalene dicarboxylic acid chloride, cyclopropane tricarboxylic acid chloride, cyclobutane tetracarboxylic acid chloride, cyclopentane tricarboxylic acid chloride, cyclopentane tetracarboxylic acid chloride, cyclohexane tricarboxylic acid chloride, cyclopentane dicarboxylic acid chloride, cyclobutane dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride, and tetrahydrofuran dicarboxylic acid chloride; and / or,

[0027] The conjugated diene halide-containing monomer includes at least one of 2,4-hexadienoyl chloride, 1-cyclopentadiene chloride or 1-cyclopentadiene chloride-5-methyl substituted cyclopentadiene; more preferably 2,4-hexadienoyl chloride.

[0028] As a scheme that can be implemented, the multifunctional acyl halide monomer is not particularly limited, and aromatic or alicyclic multifunctional acyl halide monomers and combinations thereof can be used. Specifically, non-limiting examples of the aromatic multifunctional acyl halide include: trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid chloride and phthaloyl dicarboxylic acid chloride; non-limiting examples of alicyclic multifunctional self-acyl halides include: cyclopropane tricarboxylic acid chloride, cyclobutane tetracarboxylic acid chloride, cyclopentane tricarboxylic acid chloride, cyclopentane tetracarboxylic acid chloride, cyclohexane tricarboxylic acid chloride, cyclopentane dicarboxylic acid chloride, cyclobutane dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride and tetrahydrofuran dicarboxylic acid chloride. In the present application scheme, trimesoyl chloride (TMC) is selected as a preferred multifunctional acyl halide monomer.

[0029] Specifically, the polyamide composite semipermeable membrane, the porous carrier comprises a substrate and a composite porous support layer;

[0030] Preferably, the substrate comprises a fabric formed of at least one of polyester or aromatic polyamide, and polyester having high mechanical properties and thermal stability is particularly preferred, including long-fiber nonwoven fabric or short-fiber nonwoven fabric, and more preferably short-fiber nonwoven fabric;

[0031] Preferably, the porous support layer comprises a polysulfone membrane layer, a polyethersulfone layer, a polyphenylene sulfone layer, a polyphenylene sulfide layer, a polyphenylene ether layer, a polyphenylene sulfide sulfone layer, a polyamide layer, a polyimide layer, a polyester layer, a vinyl polymer layer or a cellulose polymer layer.

[0032] As an operative mode, the porous carrier may be a polysulfone-based membrane, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyphenylene ether, polyphenylene sulfide sulfone, polyamide, polyimide, polyester, vinyl polymer, cellulose polymer, etc. formed on a non-woven fabric, wherein the vinyl polymer is selected from polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, etc., and the cellulose polymer is selected from cellulose acetate, cellulose nitrate, etc., and may be a blend of one or more thereof. The application method on the surface of the porous carrier may be coating, immersion, spraying, etc.

[0033] The present invention also discloses a method for preparing the polyamide composite semipermeable membrane, comprising the following steps:

[0034] (1) preparing a polyamide membrane layer by interfacial polymerization reaction of the selected amino monomer and acyl halide monomer on the surface of the porous support;

[0035] (2) The polyamide film layer is subjected to a heat curing treatment to obtain the polyamide film layer.

[0036] Specifically, the method for preparing the polyamide composite semipermeable membrane, the step (1) comprises the step of subjecting a first solution containing the multifunctional amine monomer and the dienophile amine monomer to an interfacial polymerization reaction with a second solution containing the multifunctional acyl halide monomer and the conjugated diene acyl halide monomer;

[0037] Preferably, the mass ratio of the amino monomer to the acyl halide monomer is 4-40:1;

[0038] Preferably, the mass ratio of the dienophile amine monomer to the multifunctional amine monomer is (0.1-2): (0.95-1.05); preferably, the mass ratio is (0.2-0.5): (0.95-1.05);

[0039] Preferably, the mass ratio of the conjugated diene acyl halide monomer to the multifunctional acyl halide monomer is (0.05-2): (0.95-1.05); preferably, the mass ratio is (0.1-1): (0.95-1.05);

[0040] Preferably, in the first solution, the mass concentration of the total amount of the dienophile amine monomer and the multifunctional amine monomer is 0.5-20wt%, preferably 1-10wt%, more preferably 2.5-5wt%;

[0041] Preferably, in the second solution, the total mass concentration of the conjugated diene acyl halide monomer and the multifunctional acyl halide monomer is 0.01-5wt%, preferably 0.05-0.5wt%;

[0042] Preferably, the first solution comprises a polar solvent, preferably an alcohol solvent and / or water;

[0043] Preferably, the second solution comprises a non-polar solvent, preferably an alkane.

[0044] In the second solution, the multifunctional acyl halide monomer is dissolved in a non-polar solvent, and the non-polar solvent (oil phase) is preferably a hydrocarbon solvent. Non-limiting examples of suitable hydrocarbon solvents include: alkanes (any one of n-hexane, octane, nonane, decane, etc. or a combination of at least two), isoparaffins (any one of Isopar E, Isopar G, Isopar L, etc. or a combination of at least two) and aromatics (any one of mesitylene, m-xylene, toluene, etc. or a combination of at least two), and n-decane and Isopar G are more preferred.

[0045] In a specific embodiment, the first solution of the dienophile-containing amine monomer and the multifunctional amine monomer can be prepared by dissolving the multifunctional amine monomer in a polar solvent, such as methanol, water, etc., and water is more preferred in consideration of cost and safety; then adding the dienophile-containing amine monomer and stirring thoroughly.

[0046] In a specific embodiment, the second solution of the dienophilic acyl halide monomer and the multifunctional acyl halide monomer is prepared by preferentially dissolving the multifunctional acyl halide monomer in a non-polar solvent, wherein the non-polar solvent is preferably n-decane, isoparaffin Isopar L, etc., more preferably n-decane, and then adding the dienophilic acyl halide monomer and stirring thoroughly.

[0047] Specifically, the method for preparing the polyamide composite semipermeable membrane comprises the steps of subjecting a first solution containing the multifunctional amine monomer and the dienophilic amine monomer to an interfacial polymerization reaction with a second solution containing the multifunctional acyl halide monomer to obtain a polyamide membrane layer, and coating a third solution containing the dienophilic amine monomer on the surface of the polyamide membrane layer to modify the polyamide membrane layer;

[0048] Preferably, the mass ratio of the amino monomer to the acyl halide monomer is 4-40:1;

[0049] Preferably, the mass ratio of the dienophile amine monomer to the multifunctional amine monomer is (0.1-2): (0.95-1.05); preferably, the mass ratio is (0.2-0.5): (0.95-1.05);

[0050] Preferably, the mass ratio of the conjugated diene acyl halide monomer to the multifunctional acyl halide monomer is (0.05-2): (0.95-1.05); preferably, the mass ratio is (0.1-1): (0.95-1.05);

[0051] Preferably, in the first solution, the mass concentration of the total amount of the dienophile amine monomer and the multifunctional amine monomer is 0.5-20wt%, preferably 1-10wt%, more preferably 2.5-5wt%;

[0052] Preferably, in the second solution, the mass concentration of the multifunctional acyl halide monomer is 0.01-5wt%, preferably 0.05-0.5wt%;

[0053] Preferably, in the third solution, the mass concentration of the dienophilic amine-containing monomer is 0.5-2wt%;

[0054] Preferably, the first solution comprises a polar solvent, preferably an alcohol solvent and / or water;

[0055] Preferably, the second solution comprises a non-polar solvent, preferably an alkane;

[0056] Preferably, the third solution comprises a non-polar solvent, preferably an alkane.

[0057] Specifically, in the preparation method of the polyamide composite semipermeable membrane, in the step (1), the temperature of the interfacial polymerization reaction is 10-50°C, and the reaction time is 0.5-30min. In the entire interfacial polymerization reaction, once the polar solution and the oil phase solution come into contact with each other, the amine monomer and the acyl halide undergo interfacial polymerization at the water-oil interface to form a polyamide membrane, the interfacial polymerization reaction temperature is 10-50°C, more preferably 20-30°C, the interfacial polymerization reaction time can be less than one second, but the water-oil phase contact time is about 0.5-5 minutes, more preferably 0.5-2 minutes, and then the excess liquid can be removed by any method such as air knife, drying, hanging drop, drying, etc.

[0058] Specifically, in the method for preparing the polyamide composite semipermeable membrane, in the step (2), the temperature of the heat curing treatment step is 25-120° C., preferably 40-80° C., and the time is 1-20 min, preferably 2-10 min.

[0059] Specifically, in the method for preparing the polyamide composite semipermeable membrane, in the step (1), the interfacial polymerization reaction step further comprises the step of selectively adding one or more of a phase transfer catalyst, an acid binding agent, a solubilizing agent, a complexing agent or a moisturizing agent.

[0060] As a feasible scheme, in order to promote the interfacial polymerization reaction, regulate the reaction rate and the performance of the composite membrane, the temperature of the water phase or oil phase involved in the reaction can be adjusted, and a phase transfer catalyst (such as dodecyltrimethylammonium chloride), an acid binding agent (such as sodium hydroxide, camphorsulfonic acid and triethylamine salt), a solubilizing agent (such as toluene), a complexing agent (such as phosphate compounds), a humectant (such as glycerol), etc. can be added.

[0061] The invention also discloses the application of the polyamide composite semipermeable membrane or the polyamide composite semipermeable membrane prepared by the method in the field of water treatment, especially seawater treatment.

[0062] The invention also discloses a water treatment process, comprising the step of using the polyamide composite semipermeable membrane or the polyamide composite semipermeable membrane prepared by the method for treatment.

[0063] The polyamide composite semipermeable membrane of the present invention comprises a porous carrier and a composite polyamide membrane layer, wherein the polyamide membrane layer is prepared by an interfacial polymerization reaction of an amine monomer and an acyl halide monomer on the surface of the porous carrier.

[0064] In order to achieve high flux and high salt rejection rate, and at the same time have good interception ability for the non-dissociated boron in the neutral region, in the polyamide composite semipermeable membrane described in the present application, the amine monomer forming the polyamide membrane layer includes a mixture of a multifunctional amine monomer and an amine monomer containing a dienophile, and the acyl halide monomer includes a mixture of a multifunctional acyl halide monomer and a conjugated diene acyl halide monomer. In the polyamide composite semipermeable membrane of the present invention, the polyamide membrane layer is required to have a yellow index less than 30 and an infrared absorption spectrum of 1545±10cm -1 When an amide peak appears within the range, the difference in the amide peak frequency before and after thermal curing is greater than 2 cm -1 The ratio of the infrared intensity after heat curing to the infrared intensity before heat curing is X<0.85. The polyamide composite semipermeable membrane has high flux and high salt interception rate, and also has high interception performance for non-dissociated boron in the neutral region, and is more suitable for separation and treatment of seawater.

[0065] In the polyamide composite semipermeable membrane described in the present application, the formed polyamide membrane layer is based on the traditional preparation of the polyamide system based on the polymerization of multifunctional amine monomers and multifunctional acyl halide monomers. During the heat curing treatment, the adjacent monomers of the amine monomers and acyl halide monomers containing dienophiles in the polymer network can undergo DA reaction, and the byproduct acid of the interfacial polymerization can be used as a DA reaction catalyst to accelerate the formation of new covalent bonds, thereby increasing the crosslinking degree of the polymer. After the polyamide composite semipermeable membrane is heat cured, DA crosslinking reactions can occur simultaneously within the molecule and between molecular chains. At the same time, the DA reaction consumes the byproduct acid generated during the interfacial polymerization as a catalyst for the reaction, further promoting the forward progress of the interfacial polymerization, and promoting the DA reaction to occur under milder conditions. At the same time, the consumption of acid will promote the formation of interfacial polymerization amide bonds. The two work together to improve the crosslinking degree of the polyamide composite membrane, improve the interception capacity of the composite membrane diaphragm, especially the interception capacity of non-dissociated boron in the neutral region. DETAILED DESCRIPTION

[0066] In order to achieve high flux and high salt rejection rate, and at the same time have good retention ability for non-dissociated boron in the neutral region, the present invention provides a polyamide composite semipermeable membrane including a porous carrier and a composite polyamide membrane layer, wherein the polyamide membrane layer is prepared by interfacial polymerization reaction of amine monomers and acyl halide monomers on the surface of the porous carrier.

[0067] In the polyamide composite semipermeable membrane described in the present application, the amine monomer forming the polyamide membrane layer includes a mixture of multifunctional amine monomers and dienophilic amine monomers, and the acyl halide monomer includes a mixture of multifunctional acyl halide monomers and conjugated diene acyl halide monomers.

[0068] In one feasible embodiment, the multifunctional amine-based monomer includes one or more of m-phenylenediamine, p-phenylenediamine, piperazine, aliphatic amine or polyetheramine.

[0069] In one possible embodiment, the dienophilic amine group-containing monomer includes at least one of but-2-ene-1,4-diamine, 4,5-diaminopyrimidine or 5-aminopyrimidine.

[0070] In a feasible embodiment, the multifunctional acyl halide monomer includes an aromatic or alicyclic multifunctional acyl halide monomer, preferably one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid chloride, naphthalene dicarboxylic acid chloride, cyclopropane tricarboxylic acid chloride, cyclobutane tetracarboxylic acid chloride, cyclopentane tricarboxylic acid chloride, cyclopentane tetracarboxylic acid chloride, cyclohexane tricarboxylic acid chloride, cyclopentane dicarboxylic acid chloride, cyclobutane dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride, and tetrahydrofuran dicarboxylic acid chloride.

[0071] In one feasible embodiment, the conjugated diene halide-containing monomer includes at least one of 2,4-hexadienoyl chloride, 1-cyclopentadiene chloride or 1-chloro-5-methyl-substituted cyclopentadiene.

[0072] In the polyamide composite semipermeable membrane described in the present application, the formed polyamide membrane layer is based on the traditional preparation of the polyamide system based on the polymerization of multifunctional amine monomers and multifunctional acyl halide monomers. During the heat curing treatment, the adjacent monomers of the amino monomers containing dienophiles and the acyl halide monomers containing dienophiles in the polymer network can undergo DA reaction. At the same time, the by-product acid of the interfacial polymerization can act as a DA reaction catalyst to accelerate the formation of new covalent bonds, thereby increasing the cross-linking degree of the polymer. The specific reaction is shown below.

[0073]

[0074] After the polyamide composite semipermeable membrane of the present invention is obtained by interfacial polymerization, its structure will change before and after ultraviolet light irradiation. Taking but-2-ene-1,4-diamine and 2,4-hexadienoyl chloride as examples, the partial structure of the polyamide is shown below.

[0075]

[0076] It can be seen that after the polyamide composite semipermeable membrane of the present invention is subjected to heat curing treatment, DA cross-linking reactions can occur simultaneously within the molecule and between the molecular chains. The DA reaction consumes the by-product acid generated during the interfacial polymerization as a catalyst for the reaction, thereby promoting the DA reaction to occur under milder conditions. At the same time, the consumption of the acid promotes the formation of interfacial polymerization amide bonds. The two work together to improve the cross-linking degree of the polyamide composite membrane, improve the retention capacity of the composite membrane, especially the retention capacity of non-dissociated boron in the neutral region.

[0077] In a feasible implementation scheme, the polyamide composite semipermeable membrane of the present invention may also contain an azo compound in its polyamide membrane layer. The azo compound is an organic compound containing an azo group (-N=N-), which exists and remains in the separation functional layer after the polyamide membrane layer is contacted with a reagent that can react with an amino group or a carboxyl group.

[0078] In a feasible embodiment, in the polyamide composite semipermeable membrane of the present invention, when the separation functional layer is in contact with a reagent that can react with an amino group or a carboxyl group, the yellow index of the separation functional layer is preferably below 30. The yellow index is related to the content of azo compounds or azo groups in the polyamide separation layer. If the yellow index in the polyamide separation layer is higher than 30, fewer chemical bonds are generated after thermal curing, resulting in more free amine groups generating azo groups, a low degree of crosslinking of the membrane, and a reduced interception capacity for non-dissociated boron in the neutral region.

[0079] In a feasible embodiment, the polyamide composite semipermeable membrane of the present invention uses the ATR method to measure the infrared absorption spectrum of the separation layer during the heating process (thermal curing step), and determines the infrared absorption spectrum of the separation layer at 1540±10cm -1 The peak of the amide II absorption band of the amide group appears in the range of T 热固化处理前 The frequency of the peak of the amide II absorption band of the amide group is related to T 热固化处理后 The difference in frequency between the peaks of the amide II absorption band of the amide group is preferably 2 cm -1 This is because the amide II absorption band of the amide group is believed to be related to hydrogen bonding. The reason why the peak position of the amide II absorption band of the amide group shifts depending on the temperature of thermal curing is that the hydrogen bonds formed at 20°C undergo DA reaction during the thermal curing process to generate new chemical bonds and are cut off. The structural change at this time is observed as a peak shift. If the peak shift is 2 cm -1 The above results indicate that the DA reaction generates new chemical bonds, the cross-linking degree of the membrane is greatly improved, and the retention capacity of non-dissociated boron in the neutral region is enhanced.

[0080] In addition, in a feasible embodiment, when the infrared absorption spectrum of the surface of the separation functional layer of the polyamide composite semipermeable membrane of the present invention is measured by the ATR method during the heating process (thermal curing step), the X value calculated by the following formula is preferably less than 0.85;

[0081] X=Abs(T 热固化处理后 ) / Abs(T 热固化处理前 );

[0082] Abs(T 热固化处理后 ) is measured at 1640 cm at the thermal curing temperature -1 The infrared absorption intensity, Abs(T 热固化处理前 ) is measured without heat curing treatment at 1640 cm -1 The infrared absorption intensity is 1000cm -1 ~1900cm -1 The measured data were baseline corrected and the 1250cm -1 The infrared absorption intensity at is set to 1 and the value after standardization.

[0083] The polyamide composite semipermeable membrane of the present invention is considered to have a thermal conductivity of 1640 ± 10 cm -1 The infrared absorption intensity at and the peak shift mentioned above are also related to the formation of new chemical bonds. If the X value is less than 0.85, it indicates that the DA reaction generates sufficient new chemical bonds, which increases the cross-linking degree of the membrane and enhances the retention capacity of non-dissociated boron in the neutral region.

[0084] In a kind of feasibility embodiment, the polyamide composite semipermeable membrane prepared by the present invention can also optionally include hygroscopic polymer on at least a portion of its polyamide film surface.Feasible polymer includes polymer surfactant, polyacrylic acid, polyvinyl acetate, polyalkylene oxide compound, poly (oxazoline) compound, polyacrylamide and relevant reaction product, as generally described in US 7815987, US7918349, US 7905361 and US201 1 / 0220569.In some embodiments, these polymers can be blended and / or reacted, and can be coated from the same solution or otherwise applied to the polyamide film surface or applied successively.

[0085] In order to better understand the technical solution of the present invention, the content of the present invention is further described below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0086] In the following embodiments and comparative examples of the present invention, the porous carrier is a non-woven fabric coated with a polysulfone membrane (i.e., a polysulfone-based membrane) as an example to illustrate the relevant effects. The polysulfone-based membrane used can be a commercial product or self-made.

[0087] As an exemplary scheme, the present invention provides a feasible method for preparing the polysulfone-based membrane, which specifically includes: dissolving polysulfone (Ultrason S6010, BASF, Germany) in N,N-dimethylformamide to prepare a solution with a solid content of 18%, using a 250-micron thick wet film preparation device to coat the polysulfone solution on the surface of a non-woven fabric (Zhejiang Qinglan Membrane Technology Co., Ltd., R80), after staying in the air for 4-5 seconds, immersing the non-woven fabric in pure water at room temperature, completing phase inversion after immersion for 5 minutes, immersing the polysulfone-based membrane that has completed the phase inversion in pure water at room temperature, changing the water every 2 hours, and cutting for use after fully cleaning the residual solvent.

[0088] The following embodiments and comparative examples of the present invention, unless otherwise specified, are all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. and are reagent-grade raw materials.

[0089] Example 1

[0090] At 25°C, the cut polysulfone base film is attached to the plate frame, and the plate frame size is a rectangle with a side length of 16*12cm. According to the following preparation concentration, 1wt% of butane-2-ene-1,4-diamine and 4wt% of m-phenylenediamine (MPD), 6wt% of camphorsulfonic acid, and 3wt% of triethylamine are dissolved in water, and fully stirred to obtain an aqueous phase solution. The plate frame is immersed in the above-mentioned aqueous phase solution for 1 minute, and the excess water phase is squeezed out, and then the n-decane organic phase containing 0.16wt% of trimesoyl chloride (TMC) and 0.04wt% of sorbic acid chloride is poured onto the surface of the polysulfone base film, and reacted for 1 minute. At this time, the membrane surface temperature is controlled to 25°C, and then it is placed in a 60°C baking oven, reacted for 3min, and the surface is rinsed to hydrophilicity to obtain the target polyamide composite membrane, and then the prepared polyamide composite membrane is treated in a 0.2 wt% sodium nitrite aqueous solution at pH=3 for 1 minute at room temperature, and placed in pure water for standby use. The specific raw material composition parameters of this embodiment are shown in Table 1 below.

[0091] Embodiment 2-9

[0092] The present invention is as follows: Examples 2-9, which are prepared based on the scheme of the polyamide composite semipermeable membrane in Example 1, and the interfacial polymerization temperature and time, the type and concentration of the dienophile, the type and concentration of the diene, the thermal curing temperature and time of the polyamide composite membrane used for treatment are changed as shown in Table 1, and other operations are consistent with Example 1. After preparation, the membrane is placed in pure water for standby use.

[0093] Comparative Example 1

[0094] At 25°C, the cut polysulfone-based membrane is attached to the plate frame, the size of the plate frame is a rectangle with a side length of 16*12cm; 4wt% m-phenylenediamine, 6wt% camphorsulfonic acid, and 3wt% triethylamine are dissolved in water and stirred thoroughly to obtain an aqueous solution. The plate frame is immersed in the above aqueous solution for 1 minute, the excess aqueous phase is squeezed out, and then the organic phase of n-decane containing 0.16wt% trimesoyl chloride is poured onto the surface of the polysulfone-based membrane, and reacted for 1 minute. At this time, the membrane surface temperature is controlled to 25°C, and it is placed in a 70°C oven for 1 minute to obtain the target polyamide composite membrane, and then the prepared polyamide composite membrane is treated in a 0.2 wt% sodium nitrite aqueous solution at pH=3 at room temperature for 1 minute, and then placed in pure water for standby use. The specific raw material composition parameters of this embodiment are shown in Table 1 below.

[0095] Comparative Examples 2-5

[0096] The present invention has the following comparative examples 2-5, which are prepared based on the polyamide composite semipermeable membrane scheme in Example 1, and the polyamide composite membrane used for treatment is changed as shown in Table 1, and other operations are the same as in Example 1. After preparation, the membrane is placed in pure water for standby use.

[0097] Table 1 Polyamide composite semipermeable membrane system

[0098]

[0099] Experimental example

[0100] The polyamide composite membranes prepared in the above Examples 1-9 and Comparative Examples 1-5 were respectively subjected to performance tests, including membrane flux, salt rejection and boron removal performance tests.

[0101] In this experimental example, various properties of the polyamide composite membrane were determined by running the polyamide composite membrane for 24 hours at an operating pressure of 5.52 MPa, a supply temperature of 25°C, and seawater (salt concentration of about 3.2%) adjusted to pH 8.0. The water quality of the permeate and supply water before and after the membrane was measured to obtain the various properties of the membrane:

[0102] Salt rejection rate calculation method:

[0103] Desalination rate (%) = 100 × {1-(salinity of permeate water / salinity of supply water)};

[0104] The calculation method of flux is:

[0105] The membrane permeation water volume of the supply water (seawater) is converted into the water permeation volume (cubic decimeter) per square meter of membrane area per hour, and the membrane permeation flux (L / m 2 / h) indicates;

[0106] Calculation method of deboronization rate:

[0107] The boron concentration in the supply water and the permeate water was analyzed using an ICP emission analyzer (P-4010 manufactured by Hitachi, Ltd.), and the boron removal rate was calculated using the following formula:

[0108] Boron removal rate (%) = 100 × {1-(boron concentration in permeate water / boron concentration in feed water)}.

[0109] In this experimental example, a colorimeter was used to measure the yellowness index of each polyamide composite semipermeable membrane.

[0110] In this experimental example, the infrared absorption spectrum of the polyamide film layer before and after thermal curing was measured using the ATR method. The sample was dried in a vacuum oven at 40°C for 4 hours and then scanned using a Fourier transform attenuated total reflection infrared spectrometer. The number of scans was 100 and the resolution was 4 cm. -1 , obtain the infrared spectrum, and measure 1540±10cm -1 The peak of the amide II absorption band of the amide group appears in the range of T 热固化处理前 The frequency of the peak of the amide II absorption band of the amide group is related to T 热固化处理后 The difference in frequency between the peaks of the amide II absorption band of the amide group is 2 cm -1 above.

[0111] In this experimental example, the infrared absorption spectrum of the polyamide film surface was measured by the ATR method during the heating process of the thermal curing treatment. The X value was calculated to be less than 0.85 based on the following formula (1):

[0112] X=Abs(T 热固化处理后 ) / Abs(T 热固化处理前 )(1);

[0113] Among them, Abs(T 热固化处理后 ) is measured at 1640 cm after thermal curing -1 The infrared absorption intensity of the peak at 热固化处理前 ) is the value at 1640 cm-1 measured when the polyamide composite film is not subjected to heat curing treatment. -1 The infrared absorption intensity of the peak.

[0114] In this experimental example, the test results of the polyamide composite semipermeable membrane are shown in Table 2 below.

[0115] Table 2 Polyamide composite semipermeable membrane performance test results

[0116] serial number Flux / LMH Desalination rate / % Boron removal rate % X Value Yellow Index Example 1 36 99.86 96.6 0.54 20 Example 2 38 99.8 94.8 0.62 19 Example 3 35 99.8 94.3 0.64 21 Example 4 37.5 99.8 90.8 0.81 28 Example 5 39 99.75 91.7 0.73 17 Example 6 38 99.82 95.2 0.64 22 Example 7 42 99.71 87.4 0.98 34 Example 8 37 99.74 93.3 0.65 29 Example 9 37.6 99.79 94.2 0.6 24 Comparative Example 1 37 99.75 87.6 1 45 Comparative Example 2 36.4 99.76 88.4 0.98 40 Comparative Example 3 35 99.76 88 0.99 38 Comparative Example 4 34 99.78 88.8 0.99 42 Comparative Example 5 32 99.76 89 0.97 36

[0117] It can be seen that in the polyamide composite semipermeable membrane described in the present application, the polyamide membrane layer formed is based on the traditional preparation of the polyamide system based on the polymerization of multifunctional amine monomers and multifunctional acyl halide monomers. The dienophilic amine monomers and dienophilic acyl halide monomers in the polymer network help to improve the crosslinking degree of the polymer during the thermal curing treatment, thereby improving the retention capacity of the composite membrane, especially the retention capacity for non-dissociated boron in the neutral region. The flux, desalination rate and boron removal rate of the polyamide membrane layer are all improved, and the application performance is greatly improved.

[0118] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A polyamide composite semipermeable membrane, characterized in that: The polyamide composite semipermeable membrane comprises a composite porous carrier and a polyamide membrane layer; The polyamide composite semipermeable membrane has at least one of the following characteristics: (a) the yellowness index of the polyamide film layer is less than 30; (b) The infrared absorption spectrum of the polyamide film layer before and after thermal curing was measured using the ATR method, and the infrared absorption spectrum at 1540±10 cm -1 The peak of the amide II absorption band of the amide group appears in the range of T 热固化处理前 The frequency of the peak of the amide II absorption band of the amide group is related to T 热固化处理后 The difference in frequency between the peaks of the amide II absorption bands of the amide group is 2 cm -1 above; (c) During the heating process of the heat curing treatment, the infrared absorption spectrum of the surface of the polyamide film layer is measured, and the X value is calculated based on the following formula (1) to be less than 0.85: X=Abs(T 热固化处理后 ) / Abs(T 热固化处理前 )(1); Among them, Abs(T 热固化处理后 ) is measured at 1640 cm after thermal curing -1 The infrared absorption intensity of the peak at 热固化处理前 ) is the value at 1640 cm-1 measured when the polyamide composite film is not subjected to heat curing treatment. -1 The infrared absorption intensity of the peak.

2. The polyamide composite semipermeable membrane according to claim 1, characterized in that: The polyamide film layer is prepared by polymerization of an amine monomer and an acyl halide monomer; wherein, The amino monomer comprises a mixture of a multifunctional amino monomer and a dienophile-containing amino monomer; The acyl halide monomer comprises a mixture of a multifunctional acyl halide monomer and a conjugated diene acyl halide monomer.

3. The polyamide composite semipermeable membrane according to claim 2, characterized in that: The multifunctional amine monomer includes one or more of m-phenylenediamine, p-phenylenediamine, piperazine, aliphatic amine or polyetheramine; and / or, The dienophile amine-containing monomer comprises at least one of but-2-ene-1,4-diamine, 4,5-diaminopyrimidine or 5-aminopyrimidine; and / or, The polyfunctional acyl halide monomer includes an aromatic or alicyclic polyfunctional acyl halide monomer, preferably one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid chloride, naphthalene dicarboxylic acid chloride, cyclopropane tricarboxylic acid chloride, cyclobutane tetracarboxylic acid chloride, cyclopentane tricarboxylic acid chloride, cyclopentane tetracarboxylic acid chloride, cyclohexane tricarboxylic acid chloride, cyclopentane dicarboxylic acid chloride, cyclobutane dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride, and tetrahydrofuran dicarboxylic acid chloride; and / or, The conjugated diene halide-containing monomer includes at least one of 2,4-hexadienoyl chloride, 1-cyclopentadiene chloride or 1-cyclopentadiene chloride-5-methyl substituted cyclopentadiene.

4. The polyamide composite semipermeable membrane according to any one of claims 1 to 3, characterized in that: The porous carrier comprises a substrate and a composite porous support layer; Preferably, the substrate comprises a fabric formed of at least one of polyester or aromatic polyamide; Preferably, the porous support layer comprises a polysulfone membrane layer, a polyethersulfone layer, a polyphenylene sulfone layer, a polyphenylene sulfide layer, a polyphenylene ether layer, a polyphenylene sulfide sulfone layer, a polyamide layer, a polyimide layer, a polyester layer, a vinyl polymer layer or a cellulose polymer layer.

5. A method for preparing the polyamide composite semipermeable membrane according to any one of claims 1 to 4, characterized in that: The steps include: (1) preparing a polyamide membrane layer by interfacial polymerization reaction of the selected amino monomer and acyl halide monomer on the surface of the porous support; (2) The polyamide film layer is subjected to a heat curing treatment to obtain the polyamide film layer.

6. The method for preparing the polyamide composite semipermeable membrane according to claim 5, characterized in that: The step (1) comprises the step of subjecting a first solution containing the multifunctional amine monomer and the dienophile amine monomer to an interfacial polymerization reaction with a second solution containing the multifunctional acyl halide monomer and the conjugated diene acyl halide monomer; Preferably, the mass ratio of the amino monomer to the acyl halide monomer is 4-40:1; Preferably, the mass ratio of the dienophile amine monomer to the multifunctional amine monomer is (0.1-2): (0.95-1.05); preferably, the mass ratio is (0.2-0.5): (0.95-1.05); Preferably, the mass ratio of the conjugated diene acyl halide monomer to the multifunctional acyl halide monomer is (0.05-2): (0.95-1.05); preferably, the mass ratio is (0.1-1): (0.95-1.05); Preferably, in the first solution, the mass concentration of the total amount of the dienophile amine monomer and the multifunctional amine monomer is 0.5-20wt%, preferably 1-10wt%, more preferably 2.5-5wt%; Preferably, in the second solution, the total mass concentration of the conjugated diene acyl halide monomer and the multifunctional acyl halide monomer is 0.01-5wt%, preferably 0.05-0.5wt%; Preferably, the first solution comprises a polar solvent, preferably an alcohol solvent and / or water; Preferably, the second solution comprises a non-polar solvent, preferably an alkane.

7. The method for preparing the polyamide composite semipermeable membrane according to claim 5, characterized in that: The step (1) comprises the steps of subjecting a first solution containing the multifunctional amine monomer and the dienophilic amine monomer to an interfacial polymerization reaction with a second solution containing the multifunctional acyl halide monomer to obtain a polyamide film layer, and a step of coating a third solution containing the dienophilic amine monomer on the surface of the polyamide film layer to modify the film layer; Preferably, the mass ratio of the amino monomer to the acyl halide monomer is 4-40:1; Preferably, the mass ratio of the dienophile amine monomer to the multifunctional amine monomer is (0.1-2): (0.95-1.05); preferably, the mass ratio is (0.2-0.5): (0.95-1.05); Preferably, the mass ratio of the conjugated diene acyl halide monomer to the multifunctional acyl halide monomer is (0.05-2): (0.95-1.05); preferably, the mass ratio is (0.1-1): (0.95-1.05); Preferably, in the first solution, the mass concentration of the total amount of the dienophile amine monomer and the multifunctional amine monomer is 0.5-20wt%, preferably 1-10wt%, more preferably 2.5-5wt%; Preferably, in the second solution, the mass concentration of the multifunctional acyl halide monomer is 0.01-5wt%, preferably 0.05-0.5wt%; Preferably, in the third solution, the mass concentration of the dienophilic amine-containing monomer is 0.5-2wt%; Preferably, the first solution comprises a polar solvent, preferably an alcohol solvent and / or water; Preferably, the second solution comprises a non-polar solvent, preferably an alkane; Preferably, the third solution comprises a non-polar solvent, preferably an alkane.

8. The method for preparing a polyamide composite semipermeable membrane according to any one of claims 5 to 7, characterized in that: In the step (1), the temperature of the interfacial polymerization reaction is 10-50° C., and the reaction time is 0.5-30 min; and / or, In the step (2), the temperature of the heat curing step is 25-120° C. and the time is 1-20 min; and / or, In the step (1), the interfacial polymerization reaction step further comprises the step of selectively adding one or more of a phase transfer catalyst, an acid binding agent, a solubilizing agent, a complexing agent or a moisturizing agent.

9. Use of the polyamide composite semipermeable membrane according to any one of claims 1 to 4 or the polyamide composite semipermeable membrane prepared by the method according to any one of claims 5 to 8 in the field of water treatment, especially seawater treatment.

10. A water treatment process, characterized in that: The method comprises the step of treating the polyamide composite semipermeable membrane according to any one of claims 1 to 4 or the polyamide composite semipermeable membrane prepared by the method according to any one of claims 5 to 8.

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