Thin film composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nanofiltration membranes, and particularly relates to a thin-film composite nanofiltration membrane as well as a preparation method and application thereof. The composite nanofiltration membrane comprises a porous ultrafiltration supporting base membrane and a polyamide separation layer constructed on the porous ultrafiltration supporting base membrane, and the polyamide separation layer is obtained by polycondensation of a polyacyl chloride monomer and a polyamine monomer on the porous ultrafiltration supporting base membrane in the presence of an additive, the additive is tertiary amine based on an adamantane structure and a derivative thereof. Uniformly mixing a polyamine monomer, an additive and water to obtain a water-phase solution; uniformly mixing a multi-acyl chloride monomer with an alkane solvent to obtain an organic phase solution; the aqueous phase solution and the organic phase solution are sequentially applied to a porous ultrafiltration supporting base membrane, and the thin-film composite nanofiltration membrane is obtained through interfacial polymerization reaction and drying. The membrane composite nanofiltration membrane is thin and compact, has high water flux, high salt interception and monovalent and divalent anion separation performance, and can be used for low-cost and efficient desalination.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membranes, and in particular relates to a thin film composite nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] With global warming, population growth and economic development, human demand for water quality and quantity has increased dramatically. Global water shortage and water pollution are potential threats to human health and social development. The rational use and protection of water resources is a long-term and arduous task. Compared with traditional separation processes, membrane separation technology has the advantages of high separation efficiency, low energy consumption and low secondary pollution. It has good application prospects in treating urban sewage and efficiently obtaining drinking water from groundwater, seawater, etc.

[0003] Nanofiltration membranes can achieve efficient interception of small molecules and multivalent salt ions with molecular weights between 200-1000Da, so they have broad application prospects in seawater desalination, water softening, removal of pollutants and heavy metal ions in wastewater, etc. The most widely studied and applied nanofiltration membranes are thin-film composite nanofiltration membrane structures prepared based on interfacial polymerization processes, which are mainly prepared by constructing a cross-linked polyamide separation selection layer on an ultrafiltration porous base membrane using polyacyl chlorides and polyamines at the oil-water interface polymerization reaction. Although the cross-linked polyamide selection layer can achieve efficient interception of organic molecules and multivalent salts, the water flux is usually low, and the trade-off effect between flux and interception limits the improvement of the comprehensive performance of nanofiltration membranes.

[0004] Since enlarging the pore size is an effective way to reduce the mass transfer resistance in the nanofiltration membrane separation process and improve the membrane flux and selectivity. At present, there are literature reports that by adding an intermediate layer such as COF, MOF, etc. between the base membrane and the polyamide layer to adjust the pore size, the flux and selectivity can be effectively improved, but the preparation process of materials such as COF and MOF is relatively complicated, and the introduction of the above materials in some nanofiltration membranes will lose the retention rate of the membrane to a certain extent (J. Membr. Sci. 576 (2028) 131.); Another method is to add additives such as glycerol, phytate, polyvinyl alcohol to the aqueous solution, and use the hydrogen bond interaction or electrostatic interaction between the additive and the monomer to reduce the diffusion rate of the polyamine monomer, thereby enlarging the pore size and improving the separation flux and selectivity of the membrane (J. Membr. Sci. 657 (2022) 120673.), but there is also a problem of affecting the cross-linking degree of the polyamide layer and affecting the membrane retention performance to a certain extent.

[0005] Therefore, further seeking methods to optimize the polymerization system and developing new technologies to prepare thin-film composite nanofiltration membranes with high retention, high flux and high selectivity are of great research significance for promoting the application of nanofiltration membranes in the field of water treatment. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a thin film composite nanofiltration membrane with high retention rate, high water flux and high selectivity, so as to solve the problems of mutual restriction between water flux and retention rate and difficulty in efficient separation of monovalent and divalent anions in existing thin film composite nanofiltration membranes in water treatment and desalination.

[0007] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0008] The present invention provides a thin film composite nanofiltration membrane, comprising a porous ultrafiltration support base membrane and a polyamide separation layer arranged on the surface of the porous ultrafiltration support base membrane;

[0009] The polyamide separation layer is obtained by polycondensation of polyacyl chloride monomers and polyamine monomers on the surface of the porous ultrafiltration support base membrane; the polycondensation is carried out in the presence of an additive, and the additive is selected from hexamethylenetetramine or a derivative of hexamethylenetetramine.

[0010] The additive is a tertiary amine (hexamethyltetramine) based on adamantane structure and its derivatives.

[0011] Preferably, the structure of the additive is as follows:

[0012]

[0013] Preferably, the porous ultrafiltration supporting base membrane is selected from polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polysulfone ultrafiltration membrane, sulfonated polysulfone ultrafiltration membrane, vinylidene chloride ultrafiltration membrane or polyimide ultrafiltration membrane; the pore size of the porous ultrafiltration supporting base membrane is 5-100 nm.

[0014] Furthermore, the porous ultrafiltration supporting base membrane is selected from polyethersulfone ultrafiltration membrane.

[0015] Furthermore, the porous ultrafiltration supporting base membrane is constructed on a non-woven fabric substrate.

[0016] Furthermore, the thickness of the polyamide separation layer is preferably less than 60 nm, more preferably less than 30 nm, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, but is not limited to the thickness listed above.

[0017] Preferably, the polyacyl chloride monomer is selected from one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and adipoyl chloride.

[0018] Preferably, the polyamine monomer is selected from one or more of piperazine, m-phenylenediamine, diethyltriamine and polyethyleneimine.

[0019] The present invention uses hexamethylenetetramine additives to control and prepare a thin film composite nanofiltration membrane with both high water flux and high retention rate. The hexamethylenetetramine additive can undergo a quaternization reaction with a polyacyl chloride monomer. Since such additives contain a rigid body structure, a wrinkled structure appears on the membrane surface after participating in the reaction, thereby increasing the water flux of the membrane. Different from the prior art in which the diffusion rate of the polyamine monomer is reduced by adding additives, the present invention adds hexamethylenetetramine additives to control the interfacial polymerization reaction, thereby finely controlling the pore size of the membrane surface, thereby increasing the water flux of the nanofiltration membrane having the polyamide separation layer, and at the same time, while ensuring that the polyvalent anions have a high retention rate, the retention rate of monovalent anions is reduced, so that the membrane has high monovalent and divalent anion separation performance.

[0020] The present invention also provides a method for preparing the above-mentioned thin film composite nanofiltration membrane, comprising the following steps:

[0021] S11: preparing an aqueous phase solution and an organic phase solution; the aqueous phase solution comprises a polyamine monomer, an additive and an aqueous solution, and the organic phase solution comprises a polyacyl chloride monomer and a hydrocarbon solvent;

[0022] S12: applying the aqueous solution to the porous ultrafiltration support base membrane, so that the aqueous solution infiltrates the surface of the porous ultrafiltration support base membrane;

[0023] S13: applying the organic phase solution to the porous ultrafiltration support base membrane infiltrated with the aqueous phase solution in step S12, so that the organic phase solution infiltrates the surface of the porous ultrafiltration support base membrane, and performing an interfacial polymerization reaction to obtain a polyamide separation layer;

[0024] S14: Drying to obtain the thin film composite nanofiltration membrane.

[0025] The present invention adds additives to an aqueous solution containing polyamine monomers, and allows the aqueous solution and an organic solution containing polyacyl chloride monomers to sequentially infiltrate a porous ultrafiltration support base membrane, the polyamine monomers in the aqueous solution and the additives diffuse and aggregate toward the oil-water interface (i.e., the porous ultrafiltration support base membrane), and undergo interfacial polymerization reaction with the polyacyl chloride monomers in the interfacial organic solution, thereby forming a polyamide separation layer on the surface of the porous ultrafiltration support base membrane.

[0026] Preferably, the concentration of the polyamine monomer in the aqueous phase solution is 0.5-10 g / L, and the molar ratio of the polyamine monomer to the additive is 1-300:1; the concentration of the polyacyl chloride monomer in the organic phase solution is 0.5-10 g / L.

[0027] Furthermore, the concentration of the polyamine monomer in the aqueous solution is 1-5 g / L, such as 2 g / L, 3 g / L, 4 g / L, including but not limited to the concentrations listed above.

[0028] Furthermore, the molar ratio of the polyamine monomer to the additive is 10-40: 1. If the content of the additive in the aqueous solution is too low or too high, the flux of the nanofiltration membrane will be affected. Under the premise of ensuring the rejection rate of the nanofiltration membrane, in order to obtain a high-flux nanofiltration membrane, the amount of the additive needs to be controlled within a suitable range, for example, the molar ratio of the polyamine monomer to the additive in the aqueous solution is controlled to be 10-200: 1.

[0029] Preferably, in step S11, the aqueous solution is selected from water or a mixed solution of water and an organic solvent, and the organic solvent can be selected from one or more of ethanol, methanol, n-hexane, butanol, and acetone; wherein the mass concentration of the organic solvent in the mixed solution is preferably 0.5wt%-10wt%, more preferably 1wt%-5wt%.

[0030] Preferably, the hydrocarbon solvent is selected from one or more of n-hexane, cyclohexane and benzene.

[0031] Preferably, the aqueous phase solution is applied to the porous ultrafiltration supporting base membrane by coating, casting, spraying or dipping; the organic phase solution is applied to the porous ultrafiltration supporting base membrane by coating, casting, spraying or dipping.

[0032] Furthermore, the aqueous phase solution and the organic phase solution are applied to the porous ultrafiltration supporting base membrane by means of casting.

[0033] Preferably, in step S13, the aqueous solution is allowed to infiltrate the surface of the porous ultrafiltration support base membrane for 10-180 s, more preferably 30-120 s.

[0034] Preferably, in step S13, the organic phase solution is allowed to infiltrate the surface of the porous ultrafiltration support base membrane for 10-180 seconds.

[0035] Preferably, in step S13, the temperature of the interfacial polymerization reaction is 15-50°C and the humidity is 30-70RH%. The interfacial polymerization reaction temperature needs to be controlled at 15-50°C. Within a certain temperature range, increasing the temperature can promote the formation of a thinner film, but if the reaction temperature is too high, it will lead to excessive crosslinking, thereby reducing the flux of the membrane.

[0036] Preferably, in step S14, the drying temperature is 20-80° C. and the drying time is 5-30 min.

[0037] Specifically, in step S13, after the aqueous phase solution fully infiltrates the surface of the porous ultrafiltration support base membrane, the residual aqueous solution on the surface is absorbed until there is no visible water stain, and then an organic phase solution containing polyacyl chloride monomers is applied to the membrane surface to make the membrane surface fully infiltrated with the polyacyl chloride monomer organic oil phase solution, and wait for the polyamine monomer and the polyacyl chloride monomer to complete the interfacial polymerization reaction at the two-phase boundary.

[0038] The present invention also provides application of the thin film composite nanofiltration membrane in desalted water treatment.

[0039] Preferably, the thin film composite nanofiltration membrane can be used in the fields of seawater desalination pretreatment, salt separation or industrial wastewater desalination treatment.

[0040] The technical solution of the present invention has the following advantages over the prior art:

[0041] 1. The present invention introduces tertiary amine compounds to polymerize polyamine monomers and polyacyl chloride monomers on the surface of a porous ultrafiltration support base membrane to obtain a polyamide separation layer with special pores, so that the thin film nanofiltration membrane containing the polyamide separation layer has the excellent properties of high retention, high flux and high selectivity; and the present invention can adjust the separation performance of the thin film composite nanofiltration membrane for different salts by changing the type of polyamine monomers.

[0042] 2. The present invention also provides a method for preparing the above-mentioned high-performance thin film nanofiltration membrane, by adding the additive hexamethylenetetramine to an aqueous solution containing a polyamine monomer, and under the control of the additive, causing the polyamine monomer in the aqueous solution and the polyacyl chloride monomer in the organic solution to undergo polymerization reaction at the interface, and the additive having multiple tertiary amine groups participates in the reaction and enters into the polymer grid to obtain the above-mentioned high-performance thin film nanofiltration membrane; the preparation method is simple and easy to operate, and the performance of the prepared nanofiltration membrane is controllable, and can be used for industrial mass production.

[0043] 3. The above high-performance thin film composite nanofiltration membrane can intercept up to 99.2% of Na2SO4 with a concentration of 1000ppm, and only 7.0% of NaCl solution with a concentration of 1000ppm, with a selectivity of 116, and a flux of up to 16.9Lm for pure water. -2 h -1 bar -1 This type of thin-film composite nanofiltration membrane with high selectivity, high flux and high selectivity has good application prospects in seawater desalination, salt separation, industrial wastewater desalination treatment, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a SEM image of the surface of the thin film composite nanofiltration membrane prepared in Example 1;

[0045] Figure 2 It is a comparison chart of the molecular weight cut-off of polyamide membrane with (Example 1) and without (Comparative Example 1);

[0046] Figure 3 The pore size comparison chart of the thin film composite nanofiltration membrane prepared with additives (Example 1) and without additives (Comparative Example 1). DETAILED DESCRIPTION

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0048] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0049] Example 1

[0050] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, which is prepared by a porous ultrafiltration support base membrane and a polyamide separation layer constructed on the porous ultrafiltration support base membrane, and the polyamide separation layer is prepared by interfacial polymerization of piperazine (PIP, a polyamine monomer) and trimesoyl chloride (TMC, a polyacyl chloride monomer) under the control of hexamethylenetetramine (HMTA, an additive). The specific preparation process is as follows:

[0051] (1) Preparation of aqueous phase solution and organic phase solution: Under the conditions of temperature of 25° C. and relative humidity of 60%, PIP was dissolved in pure water to prepare a piperazine aqueous solution with a concentration of 4 g / L, and then HMTA (the molar ratio of PIP to HMTA was 200:1) was added and mixed to obtain an aqueous phase solution; TMC was dissolved in n-hexane solution to prepare an organic phase solution with a concentration of 1.5 g / L.

[0052] (2) Preparation of polyamide separation layer: At room temperature, the surface of the polyethersulfone ultrafiltration bottom membrane was soaked with the aqueous solution prepared above for 120 seconds, the solution on the membrane surface was dried until no visible water stains were found, and then the membrane surface was soaked with the organic solution prepared above for 30 seconds to form a polyamide separation layer on the membrane surface, and then the membrane was soaked in n-hexane for 30 seconds to wash away the residual trimesoyl chloride monomer on the surface. Finally, the membrane was placed in an oven, heat treated at 60°C for 10 minutes, and then soaked in deionized water and stored in a refrigerator.

[0053] Figure 1 This is a SEM picture of the thin film composite nanofiltration membrane prepared in this example. It can be seen from the picture that the polyamide separation layer on the surface of the nanofiltration membrane is dense and has no obvious defects.

[0054] Example 2

[0055] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the amount of additives added. In this example, the molar ratio of PIP to HMTA is 40:1, and the rest is the same as Example 1.

[0056] Example 3

[0057] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the amount of additives added. In this example, the molar ratio of PIP to HMTA is 20:1, and the rest is the same as Example 1.

[0058] Example 4

[0059] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from embodiment 1 is the concentration of PIP in the aqueous solution. The concentration of PIP in the aqueous solution in this embodiment is 2 g / L, and the rest is the same as embodiment 1.

[0060] Example 5

[0061] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is that: after adding HMTA to the piperazine aqueous solution, the solution is placed in a 40°C water bath and heated for 3 minutes to obtain an aqueous phase solution; the concentration of TMC in the organic phase solution. In this example, the concentration of TMC in the organic phase solution is 3 g / L, and the rest is the same as Example 2.

[0062] Example 6

[0063] This embodiment relates to the preparation of a thin film composite nanofiltration membrane. The only difference from Example 1 is that after adding HMTA to the piperazine aqueous solution, the mixture is placed in a 60°C water bath and heated for 3 minutes to obtain an aqueous phase solution. The rest is the same as Example 2.

[0064] Example 7

[0065] The pip was replaced with polyethyleneimine 70000 (PEI70000).

[0066] Example 8

[0067] The pip was replaced with polyethyleneimine 20000 (PEI20000).

[0068] Example 9

[0069] Replace pip with meta-phenylenediamine (MPD).

[0070] Example 10

[0071] This embodiment relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 7 is the type of polyamine monomer added and the concentration of TMC in the organic phase solution. The polyamine monomer added in this embodiment is polyethyleneimine 20000 (PEI20000), the concentration of TMC in the organic phase solution is 3 g / L, and the rest is the same as Example 1.

[0072] Embodiment 11

[0073] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the type of additive added. The additive added in this example is HMTA-1, and the rest is the same as in Example 1.

[0074] Example 12

[0075] This example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the type of additive added. The additive added in this example is HMTA-2, and the rest is the same as in Example 1.

[0076] Comparative Example 1

[0077] This comparative example involves the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is that no additive HMTA is added.

[0078] Comparative Example 2

[0079] This comparative example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the amount of additives added. In this comparative example, the molar ratio of PIP to HMTA is 5:1, and the rest is the same as Example 1.

[0080] Comparative Example 3

[0081] This comparative example involves the preparation of a thin film composite nanofiltration membrane, which is different from Example 1 only in that the preparation of the polyamide separation layer is carried out at 60° C., and the rest is the same as Example 1.

[0082] Comparative Example 4

[0083] This comparative example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the type of additive added. The additive added in this example is triethylamine, and the rest is the same as Example 1.

[0084] Comparative Example 5

[0085] This comparative example relates to the preparation of a thin film composite nanofiltration membrane, and the only difference from Example 1 is the type of additive added. The additive added in this example is tetramethylethylenediamine, and the rest is the same as Example 1.

[0086] Effect evaluation 1 Effect of hexamethylenetetramine additive on the pore size of polyamide separation layer in thin film composite nanofiltration membrane

[0087] The present invention takes Example 1 and Comparative Example 1 as examples to study the effect of the hexamethylenetetramine additive on the pore size of the polyamide separation layer in the thin film composite nanofiltration membrane.

[0088] Figure 2 This is a comparison of the molecular interception size of the polyamine monomer in the aqueous solution with and without the hexamethylenetetramine additive. It can be seen from the figure that the presence of the hexamethylenetetramine additive increases the molecular weight interception.

[0089] Figure 3 The pore size comparison diagram of the thin film composite nanofiltration membrane prepared in Example 1 and Comparative Example 1 shows that the pore size of the polyamide separation layer of the thin film composite nanofiltration membrane prepared in Example 1 is 0.63 nm, and the pore size of the polyamide separation layer prepared in Comparative Example 1 without the presence of hexamethylenetetramine additive is 0.61 nm. It can be seen that the presence of the hexamethylenetetramine additive increases the pore size of the polyamide separation layer. This is because the presence of the hexamethylenetetramine additive plays a place-occupying role in the interfacial polymerization process, leaving vacancies in the prepared polyamide separation layer, increasing the pore size, and thus achieving the separation of monovalent and divalent anions.

[0090] Effect evaluation 2 Study on water flux and retention rate of nanofiltration membrane

[0091] The water flux and the retention rate of different salts of the thin film composite nanofiltration membrane prepared in the above examples and comparative examples were tested. The specific operation was as follows: at a temperature of 25°C and an operating pressure of 2 bar,

[0092] (1) Test the permeation flux of pure water;

[0093] (2) Testing the flux and retention rate of 1000ppm Na2SO4 aqueous solution;

[0094] (3) Testing the flux and retention rate of 1000 ppm MgSO4 aqueous solution;

[0095] (4) Testing the flux and retention rate of 1000 ppm MgCl2 aqueous solution;

[0096] (5) Test the flux and retention rate of 1000 ppm NaCl aqueous solution.

[0097] The separation performance of the thin film composite nanofiltration membrane was evaluated using a cross-flow filtration device. The effective test membrane area was 7.1 cm 2 The cross flow rate was controlled at 30 L h -1, the test pressure is 2 bar. Before the test, the membrane is pre-pressurized until the pure water flux reaches a stable level.

[0098] Pure water permeation flux test: The pure water permeation flux (Permeance, L m -2 h -1 bar -1 ):

[0099] P=Δm / ρSPΔt (1)

[0100] Where Δm (Kg) is the mass of solvent permeate collected within Δt (s) (cross-flow time); ρ is the density of the permeate solvent in Kg / m 3 ; S is the effective filtration area of ​​the separation membrane, in m 2 ; ΔP is the transmembrane pressure, the unit is bar.

[0101] Solute separation test: Prepare 1000 mg L -1 The inorganic salt solution is used as the feed solution. The conductivity of the feed solution and the filtrate is measured by a conductivity meter and calculated. The retention rate (R) is calculated by formula 2:

[0102]

[0103] Among them, C p and C f Represent the concentration of solute in the permeate and feed solution (mgmL -1 ).

[0104] The above test results are shown in Table 1 below:

[0105] Table 1 Flux and rejection test results of various embodiments and comparative examples

[0106]

[0107] From Examples 1 to 3 and Comparative Examples 1 and 2, it can be seen that the additive can affect the flux and selectivity of the membrane when added in small amounts. When the ratio of PIP to HMTA is 200:1, the additive can still play a role. Adding an appropriate amount of additive can change the size of the membrane pore size and obtain a higher selectivity. When an excess of hexamethylenetetramine additive is added, compared with the thin film nanofiltration membrane prepared without additives in Comparative Example 1, the water flux and selectivity of the thin film composite nanofiltration membrane prepared in Example 3 are also improved, which is higher than the water flux and selectivity of the thin film composite nanofiltration membrane prepared in Comparative Example 1. It can be seen that in order to prepare a high-performance thin film composite nanofiltration membrane with both high flux and selectivity, the amount of hexamethylenetetramine additive added can be controlled in a suitable range, for example, the molar ratio of the polyamine monomer to the additive is controlled at 100-200:1.

[0108] It can be seen from Examples 1 and 4 that reducing the content of the polyamine monomer in the aqueous phase solution to a certain extent has a certain effect on the water flux and the salt retention rate. This is because the content of the polyamine will affect the cross-linking degree of the polyamide membrane.

[0109] It can be seen from Examples 2, 5 and 6 that heating the aqueous solution will reduce the water flux of the thin film composite nanofiltration membrane and increase the salt retention rate. This is because during the preparation of the aqueous solution, heating can promote the dissolution of additives in the aqueous phase, prepare a more uniform solution, increase the crosslinking degree of the polyamide membrane, and make it denser.

[0110] The thin film composite nanofiltration membranes prepared in Examples 1 to 6 have a high retention rate for Na2SO4 and MgSO4, but a relatively low retention rate for MgCl2; in Examples 7 to 10, polyethyleneimine is used as the monomer of the teramine, and the thin film composite nanofiltration membranes prepared have a high retention rate for MgSO4 and MgCl2, both of which can be as high as more than 95%, but the retention rate for Na2SO4 is much lower than the nanofiltration membranes prepared in Examples 1 to 6.

[0111] It can be seen from Example 1, Example 11 and Example 12 that when the quaternized HMTA is added as an additive to the water phase, the water flux and selectivity of the polyamide membrane are improved in the same manner.

[0112] It can be seen from Example 1 and Comparative Example 3 that although HMTA is also used as an additive in Comparative Example 3, the reaction temperature is too high, which makes the degree of interfacial polymerization reaction too high and the formed polyamide separation layer is too dense, which in turn reduces the water flux.

[0113] It can be seen from Example 1 and Comparative Examples 4 and 5 that although additives containing tertiary amines are also used in Comparative Examples 3 and 4, the water flux and selectivity of the polyamide membrane are not improved. This is because these additives have no body structure and cannot achieve the effect of hexamethylenetetramine in adjusting the pore size of the membrane.

[0114] In summary, the present invention introduces a suitable hexamethylenetetramine compound into the reaction system of preparing the polyamide separation layer from the polyamine monomer and the polyacyl chloride monomer, thereby preparing a dense polyamide separation layer with a large pore size, thereby obtaining a thin film composite nanofiltration membrane with both high flux and high selectivity, which can be used for the desalination treatment of saline aqueous solutions; in addition, by changing the type of polyamine monomer, the separation performance of the thin film composite nanofiltration membrane for different salts can be adjusted.

[0115] Obviously, the above embodiments are merely examples for 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 from these are still within the protection scope of the invention.

Claims

1. A thin film composite nanofiltration membrane, characterized in that: It comprises a porous ultrafiltration supporting base membrane and a polyamide separation layer arranged on the surface of the porous ultrafiltration supporting base membrane; The polyamide separation layer is obtained by polycondensation of polyacyl chloride monomers and polyamine monomers on the surface of the porous ultrafiltration support base membrane; the polycondensation is carried out in the presence of an additive, and the additive is selected from hexamethylenetetramine or a derivative of hexamethylenetetramine.

2. The thin film composite nanofiltration membrane according to claim 1, characterized in that: The structure of the additive is as follows:

3. The thin film composite nanofiltration membrane according to claim 1, characterized in that: The porous ultrafiltration supporting base membrane is selected from polyethersulfone ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polysulfone ultrafiltration membrane, sulfonated polysulfone ultrafiltration membrane, vinylidene chloride ultrafiltration membrane or polyimide ultrafiltration membrane; the pore size of the porous ultrafiltration supporting base membrane is 5-100nm.

4. The thin film composite nanofiltration membrane according to claim 1, characterized in that: The polyacyl chloride monomer is selected from one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and adipoyl chloride.

5. The thin film composite nanofiltration membrane according to claim 1, characterized in that: The polyamine monomer is selected from one or more of piperazine, m-phenylenediamine, diethyltriamine and polyethyleneimine.

6. A method for preparing the thin film composite nanofiltration membrane according to any one of claims 1 to 5, characterized in that: The steps include: S11: preparing an aqueous phase solution and an organic phase solution; the aqueous phase solution comprises a polyamine monomer, an additive and an aqueous solution, and the organic phase solution comprises a polyacyl chloride monomer and a hydrocarbon solvent; the aqueous solution is selected from water or a mixed solution of water and an organic solvent; S12: applying the aqueous solution to the porous ultrafiltration support base membrane, so that the aqueous solution infiltrates the surface of the porous ultrafiltration support base membrane; S13: applying the organic phase solution to the porous ultrafiltration support base membrane infiltrated with the aqueous phase solution in step S12, so that the organic phase solution infiltrates the surface of the porous ultrafiltration support base membrane, and performing an interfacial polymerization reaction to obtain a polyamide separation layer; S14: Drying to obtain the thin film composite nanofiltration membrane.

7. The preparation method according to claim 6, characterized in that: The concentration of the polyamine monomer in the aqueous phase solution is 0.5-10 g / L, and the molar ratio of the polyamine monomer to the additive is 1-300:1; the concentration of the polyacyl chloride monomer in the organic phase solution is 0.5-10 g / L.

8. The preparation method according to claim 6, characterized in that: The aqueous phase solution is applied to the porous ultrafiltration supporting base membrane by coating, casting, spraying or dipping; the organic phase solution is applied to the porous ultrafiltration supporting base membrane by coating, casting, spraying or dipping.

9. The preparation method according to claim 6, characterized in that: In step S13, the temperature of the interfacial polymerization reaction is 15-50° C., and the humidity is 30-70 RH%.

10. Use of the thin film composite nanofiltration membrane according to any one of claims 1 to 5 in desalinated water treatment.

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