A method for preparing nanofiltration membrane based on pyrone acidic molecular additive regulation

Abstract

The present invention relates to the technical field of nanofiltration membrane preparation, and in particular to a method for preparing nanofiltration membrane based on the regulation of pyrone acidic molecule additives. The method of the present invention comprises the following steps: adding pyrone acidic molecules to a piperazine aqueous solution to obtain a piperazine mixed aqueous solution; soaking a support layer in the piperazine mixed aqueous solution to obtain a support layer attached with piperazine and pyrone acidic molecules; contacting the support layer attached with piperazine and pyrone acidic molecules with a trimesoyl chloride solution for interfacial polymerization to obtain a primary nanofiltration membrane; and soaking the primary nanofiltration membrane in water after heat treatment to obtain a nanofiltration membrane. The method provided by the present invention is simple and easy to implement, has a low cost, and is conducive to the large-scale industrial production of high-efficiency nanofiltration membranes. The nanofiltration membrane prepared by the method of the present invention has a high permeation flux while having an excellent solute retention rate.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane preparation, and in particular to a method for preparing a nanofiltration membrane based on the regulation of pyrone acidic molecular additives. Background Art

[0002] With the rapid growth of population and the rapid development of industrialization around the world, water shortage and water pollution have gradually become the focus of global attention. In order to solve the problems of water shortage and water pollution, it is necessary to develop water treatment technology to deeply treat sewage and wastewater for reuse and to desalinate seawater and brackish water to alleviate the water crisis. Among the many water purification technologies, nanofiltration membrane has the advantages of high efficiency, low energy consumption, simple operation, and the ability to remove multivalent salts and organic molecules with a molecular weight greater than 200Da, and is widely used in the field of water purification.

[0003] Nanofiltration membranes are usually prepared by interfacial polymerization, that is, when an aqueous solution containing piperazine comes into contact with an oil solution containing trimesoyl chloride, a polymerization reaction occurs at the oil / water interface, thereby obtaining a polyamide (PA) separation layer on the porous support layer (ultrafiltration membrane or microfiltration membrane). However, direct interfacial polymerization often results in the PA separation layer being too dense due to the excessively fast reaction rate of piperazine and trimesoyl chloride, resulting in a permeation flux of the nanofiltration membrane itself of usually 10L / m 2 h bar, and there is an obvious "trade-off" effect between membrane flux and solute retention rate, that is, the flux and solute retention rate restrict each other. Therefore, improving the permeation flux of nanofiltration membranes while maintaining the excellent solute separation performance of nanofiltration membranes has always been one of the hot topics in the water treatment industry. Summary of the invention

[0004] Based on the above content, the present invention provides a method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecular additive. The nanofiltration membrane prepared by the method of the present invention has a high permeation flux and an excellent solute retention rate.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecular additive, comprising the following steps:

[0007] adding pyrone acidic molecules to the piperazine aqueous solution to obtain a piperazine mixed aqueous solution;

[0008] soaking the support layer in the piperazine mixed aqueous solution to obtain a support layer with piperazine and pyrone acid molecules attached thereto;

[0009] The support layer with piperazine and pyrone acid molecules attached thereto is brought into contact with a trimesoyl chloride solution for interfacial polymerization to obtain a primary nanofiltration membrane;

[0010] The primary nanofiltration membrane is heat-treated and then immersed in water to obtain a nanofiltration membrane.

[0011] The second technical solution of the present invention is a nanofiltration membrane prepared according to the above-mentioned method for preparing nanofiltration membrane based on the regulation of pyrone acidic molecular additives.

[0012] A third technical solution of the present invention is the application of the above-mentioned nanofiltration membrane in sewage treatment or seawater desalination.

[0013] A fourth technical solution of the present invention is a method for improving the permeation flux of a nanofiltration membrane, which adopts the above-mentioned method for preparing a nanofiltration membrane by regulating the pyrone acidic molecular additive.

[0014] The present invention discloses the following technical effects:

[0015] The method provided by the invention is simple and easy to implement, has low required cost, and is conducive to realizing large-scale industrial production of high-efficiency nanofiltration membranes.

[0016] The nanofiltration membrane prepared by the method of the present invention has excellent solute rejection rate and high permeation flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 Fourier-total reflection infrared spectra of nanofiltration membranes M1, M2, M3, M4, and M5 prepared in Comparative Example 1 and Examples 2-5 of the present invention.

[0019] Figure 2 These are scanning electron micrographs of cross sections of nanofiltration membranes M1, M2, M3, M4, and M5 prepared in Comparative Example 1 and Examples 2-5 of the present invention.

[0020] Figure 3 Pure water permeation flux and Na2SO4 retention rate of nanofiltration membranes M1, M2, M3, M4, and M5 prepared in Comparative Example 1 and Examples 2-5 of the present invention.

[0021] Figure 4 The permeation flux and solute retention rate of the nanofiltration membrane M5 prepared in Example 5 of the present invention for Na2SO4, MgCl2, CaCl2 and NaCl solutions. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] The "room temperature" described in the present invention, unless otherwise specified, refers to 20 to 30°C.

[0028] The first aspect of the present invention provides a method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecular additive, comprising the following steps:

[0029] adding pyrone acid molecules to the piperazine aqueous solution and mixing them evenly to obtain a piperazine mixed aqueous solution;

[0030] soaking the support layer in the piperazine mixed aqueous solution to obtain a support layer with piperazine and pyrone acid molecules attached thereto;

[0031] The support layer with piperazine and pyrone acid molecules attached thereto is brought into contact with a trimesoyl chloride solution for interfacial polymerization to obtain a primary nanofiltration membrane;

[0032] The primary nanofiltration membrane is heat-treated and then immersed in water to obtain a nanofiltration membrane.

[0033] In some embodiments of the present invention, the pyrone acidic molecule is at least one of chelidonic acid, γ-pyrone-2-carboxylic acid, 2-pyrone-5-carboxylic acid, 4,6-dimethylcoumaric acid, 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid, 6-carboxycoumarin, 4-phenylpyrone-2-carboxylic acid, coumarin-3-carboxylic acid, 6-bromocoumarin-3-carboxylic acid, 7-hydroxycoumarin-3-carboxylic acid, 6-chloro-7-methyl-4-oxo-4H-1-phenylpyran-2-carboxylic acid, 7-methoxy-2-oxo-2H-1-phenylpyran-4-acetic acid and 7-hydroxy-4-methyl-3-coumarin acetic acid. The structural formulas of the above pyrone acidic molecules are shown in formulas A to M:

[0034]

[0035] Further preferably, the pyrone acidic molecule is at least one of chelidonic acid, γ-pyrone-2-carboxylic acid, 2-pyrone-5-carboxylic acid, 4,6-dimethylcoumaric acid, 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid, 6-carboxycoumarin, 4-phenylpyrone-2-carboxylic acid, coumarin-3-carboxylic acid, 6-bromocoumarin-3-carboxylic acid, 7-hydroxycoumarin-3-carboxylic acid and 6-chloro-7-methyl-4-oxo-4H-1-phenylpyran-2-carboxylic acid.

[0036] The present invention does not impose any particular limitation on the source of the raw materials used to prepare the nanofiltration membrane, and commercially available products known to those skilled in the art may be used.

[0037] In some embodiments of the present invention, the mass concentration of the piperazine aqueous solution is 0.001% to 2.0%.

[0038] In some embodiments of the present invention, the mass concentration of the piperazine aqueous solution is 0.01% to 2.0%.

[0039] In some embodiments of the present invention, the mass concentration of the piperazine aqueous solution is 0.1% to 1.5%.

[0040] In some embodiments of the present invention, the mass concentration of the piperazine aqueous solution is 0.1% to 1%.

[0041] In some embodiments of the present invention, the mass concentration of the piperazine aqueous solution is 0.5% to 0.8%.

[0042] In some embodiments of the present invention, the mass concentration of pyrone acidic molecules in the piperazine mixed aqueous solution is 0.001% to 10.0%.

[0043] In some embodiments of the present invention, the mass concentration of pyrone acidic molecules in the piperazine mixed aqueous solution is 0.01% to 5.0%.

[0044] In some embodiments of the present invention, the mass concentration of pyrone acidic molecules in the piperazine mixed aqueous solution is 0.1% to 1.0%.

[0045] In some embodiments of the present invention, the mass concentration of pyrone acidic molecules in the piperazine mixed aqueous solution is 0.2% to 0.6%.

[0046] The present invention has no special requirements on the method of uniformly mixing the pyrone acidic molecules into the piperazine aqueous solution, and any mixing method well known to those skilled in the art can be used, such as stirring mixing, ultrasonic mixing, etc.

[0047] In some embodiments of the present invention, after taking out the support layer to which a certain amount of piperazine and pyrone acidic molecules are attached, the present invention also preferably includes a step of wiping the surface thereof to remove water droplets on the surface.

[0048] In some embodiments of the present invention, the support layer is immersed in the piperazine mixed aqueous solution for a period of 0.01 to 24 hours.

[0049] In some embodiments of the present invention, the support layer is immersed in the piperazine mixed aqueous solution for 5 to 10 hours.

[0050] In some embodiments of the present invention, the support layer is immersed in the piperazine mixed aqueous solution for 5 to 8 hours.

[0051] In the present invention, the support layer is immersed in the piperazine mixed aqueous solution to obtain a support layer attached with piperazine and pyrone acidic molecules; the present invention has no special requirements on the volume of the piperazine mixed aqueous solution containing pyrone acidic molecules, as long as the support layer (flat ultrafiltration membrane) can be completely immersed.

[0052] In some embodiments of the present invention, the mass concentration of the trimesoyl chloride solution is 0.001-0.1%.

[0053] In some embodiments of the present invention, the mass concentration of the trimesoyl chloride solution is 0.005-0.05%.

[0054] In some embodiments of the present invention, the mass concentration of the trimesoyl chloride solution is 0.01-0.05%.

[0055] In some embodiments of the present invention, the solvent of the trimesoyl chloride solution is n-hexane.

[0056] In some embodiments of the present invention, the time of the interfacial polymerization is 5 to 120 seconds.

[0057] In some embodiments of the present invention, the interfacial polymerization time is 10 to 100 seconds.

[0058] In some embodiments of the present invention, the time of the interfacial polymerization is 10 to 50 seconds.

[0059] In some embodiments of the present invention, the interfacial polymerization time is 10 to 20 seconds.

[0060] In the present invention, the support layer attached with piperazine and pyrone acidic molecules is contacted with a solution of trimesoyl chloride to perform interfacial polymerization to obtain a primary nanofiltration membrane; the primary nanofiltration membrane includes a support layer and a PA separation layer. The contact method is preferably to drop a certain concentration of trimesoyl chloride solution onto the surface of the support layer attached with piperazine and pyrone acidic molecules, and the dropping rate is preferably 1 mL / s. In the present invention, the temperature of the interfacial polymerization is preferably room temperature, and the time is preferably 15 s. In the present invention, piperazine and trimesoyl chloride undergo interfacial polymerization to form a PA separation layer.

[0061] In some embodiments of the present invention, the heat treatment is carried out at a temperature of 20 to 90° C. and for a time of 0.01 to 12 h.

[0062] In some embodiments of the present invention, the heat treatment is carried out at a temperature of 40 to 70° C. and for a time of 0.1 to 6 hours.

[0063] In the present invention, the heat treatment is preferably carried out in an oven. The heat treatment is beneficial to improving the crosslinking degree of the PA separation layer formed by interfacial polymerization.

[0064] In some embodiments of the present invention, the soaking time in water is 0.5 to 30 days.

[0065] In some embodiments of the present invention, the soaking time in water is 0.5 to 15 days.

[0066] The nanofiltration membrane prepared in the present invention is immersed in deionized water, so as to remove the pyrone acid molecules that may be attached to the support layer.

[0067] In some embodiments of the present invention, the support layer is an ultrafiltration membrane or a microfiltration membrane.

[0068] The second aspect of the present invention provides a nanofiltration membrane prepared according to the above-mentioned method for preparing a nanofiltration membrane based on the regulation of pyrone acidic molecular additives; comprising a PA separation layer and a support layer; the thickness of the PA separation layer is 5 to 200 nm; the effective area is preferably 1 to 50 cm 2 .

[0069] A third aspect of the present invention provides an application of the above-mentioned nanofiltration membrane in sewage treatment or seawater desalination.

[0070] A fourth aspect of the present invention provides a method for increasing the permeation flux of a nanofiltration membrane, using the above-mentioned method for preparing a nanofiltration membrane based on pyrone acidic molecular additives.

[0071] The present invention provides a method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecule additive, firstly, a certain amount of piperazine is added to deionized water to fully dissolve it, and a piperazine aqueous solution is obtained. Then a certain amount of pyrone acidic molecules is added to the above piperazine aqueous solution to completely mix and dissolve it, and then a supporting layer (commercial flat ultrafiltration membrane supported by non-woven fabric) is placed in a mixed piperazine aqueous solution containing a certain concentration of pyrone acidic molecules, so that a certain amount of pyrone acidic molecules and piperazine are attached to the surface, and then interfacial polymerization is carried out with a certain concentration of trimesoyl chloride to obtain a primary nanofiltration membrane; and the primary nanofiltration membrane is heat-treated to obtain a nanofiltration membrane based on the regulation of pyrone acidic molecules. The present invention creatively introduces pyrone acid molecules into the piperazine aqueous solution, so that part of the piperazine molecules are converted into protonated piperazine. Due to the synergistic effects such as hydrogen bonds and electrostatic effects between piperazine and protonated piperazine and pyrone acid molecules, the diffusion rate of piperazine and protonated piperazine to the oil / water interface is effectively reduced. At the same time, due to the low reactivity of protonated piperazine and trimesoyl chloride, the crosslinking degree of polymerization at the oil / water interface can be significantly reduced. The above multiple factors work together to help form a thinner, looser, and more hydrophilic PA separation layer, which maximizes the permeation flux of the nanofiltration membrane while ensuring the solute selective separation performance of the membrane, and obtains a nanofiltration membrane with high efficiency separation performance. Further, the present invention optimizes the PA layer structural parameters by regulating the type and addition amount of pyrone acid molecules, the heat treatment time, temperature, and the concentration of the reaction monomer (generally speaking, with the increase of heat treatment time, the increase of temperature, and the increase of monomer concentration, the thickness and crosslinking degree of the PA layer significantly increase), ensuring that high permeation flux is obtained while maintaining excellent solute selective separation performance. The results of the embodiment show that the permeation flux of the nanofiltration membrane obtained by the method of the present invention can reach 30.6L m -2 h -1 bar -1 , the solute rejection rate of Na2SO4 can reach 95.2%. At the same time, the method provided by the present invention is simple and easy to implement, the required cost is low, and it is conducive to the large-scale industrial production of high-efficiency nanofiltration membranes.

[0072] The present invention is further described below by way of examples.

[0073] Example 1

[0074] The commercialized flat ultrafiltration membrane supported by non-woven fabric was cut into appropriate sizes to obtain the flat ultrafiltration membrane support layer M0, which was then immersed in deionized water for testing and the next step of modification.

[0075] Comparative Example 1

[0076] Prepare 100 mL of a piperazine aqueous solution with a mass concentration of 0.5 wt% and a 0.03 wt% n-hexane solution of trimesoyl chloride (the mass concentration ratio of the aqueous phase solution to the oil phase solution is 50:3) respectively; immerse the flat ultrafiltration membrane support layer M0 prepared in Example 1 in the piperazine aqueous solution for 6 hours, then wipe off the excess aqueous solution on its surface until there are no obvious water drops, and obtain a flat ultrafiltration membrane support layer attached with piperazine; then, drop the n-hexane solution of trimesoyl chloride onto the surface of the flat ultrafiltration membrane support layer attached with piperazine and perform interfacial polymerization for 15 seconds to obtain a primary nanofiltration membrane containing a PA separation layer. Then, place the primary nanofiltration membrane containing a PA separation layer in an oven at 60°C for 0.5 hours, and then place it in a pure water environment for 12 hours, thereby obtaining a nanofiltration membrane blank control sample M1 without the addition of pyrone acid molecules.

[0077] Example 2

[0078] 100 mL of a piperazine aqueous solution with a mass concentration of 0.5 wt % and a n-hexane solution of 0.03 wt % of trimesoyl chloride were prepared respectively (the concentration ratio of the piperazine aqueous solution to the trimesoyl chloride solution was 50:3), 0.25 g of chelidonic acid was added to the piperazine aqueous solution and fully dissolved to obtain a piperazine mixed aqueous solution with a chelidonic acid mass concentration of 0.25 wt %; the flat ultrafiltration membrane support layer M0 obtained in Example 1 was immersed in the piperazine mixed aqueous solution with a chelidonic acid mass concentration of 0.25 wt % obtained above for 6 h, and then the excess aqueous solution on its surface was wiped clean until there were no obvious water droplets, to obtain a flat ultrafiltration membrane support layer attached with piperazine and chelidonic acid; then, the n-hexane solution of trimesoyl chloride was dripped onto the surface of the flat ultrafiltration membrane support layer attached with piperazine and chelidonic acid for 15 s of interfacial polymerization to obtain a primary nanofiltration membrane containing a PA separation layer. Then, the primary nanofiltration membrane containing the PA separation layer was placed in an oven at 60° C. for 0.5 h, and then immersed in pure water for 12 h, thereby obtaining a nanofiltration membrane M2.

[0079] Example 3

[0080] The only difference from Example 2 is that the amount of chelidonic acid added is 0.5 g, that is, a piperazine mixed aqueous solution with a chelidonic acid mass concentration of 0.5 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; a nanofiltration membrane M3 is obtained.

[0081] Example 4

[0082] The only difference from Example 2 is that the amount of chelidonic acid added is 0.6 g, that is, a piperazine mixed aqueous solution with a chelidonic acid mass concentration of 0.6 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; a nanofiltration membrane M4 is obtained.

[0083] Example 5

[0084] The only difference from Example 2 is that the amount of chelidonic acid added is 0.75 g, that is, a piperazine mixed aqueous solution with a chelidonic acid mass concentration of 0.75 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; a nanofiltration membrane M5 is obtained.

[0085] Example 6

[0086] The only difference from Example 2 is that chelidonic acid is replaced by γ-pyrone-2-carboxylic acid, and the added amount of γ-pyrone-2-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of γ-pyrone-2-carboxylic acid of 0.5 wt% is obtained, and the remaining steps and parameters are the same as in Example 2; nanofiltration membrane M6 is obtained.

[0087] Example 7

[0088] The only difference from Example 2 is that chelidonic acid is replaced by 2-pyrone-5-carboxylic acid, and the added amount of 2-pyrone-5-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 2-pyrone-5-carboxylic acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; nanofiltration membrane M7 is obtained.

[0089] Example 8

[0090] The only difference from Example 2 is that chelidonic acid is replaced by 4,6-dimethylcoumaric acid, and the added amount of 4,6-dimethylcoumaric acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 4,6-dimethylcoumaric acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; nanofiltration membrane M8 is obtained.

[0091] Example 9

[0092] The only difference from Example 2 is that chelidonic acid is replaced by 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid, and the added amount of 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 0.5 wt% of 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid is obtained, and the remaining steps and parameters are the same as in Example 2; nanofiltration membrane M9 is obtained.

[0093] Example 10

[0094] The only difference from Example 2 is that chelidonic acid is replaced by 6-carboxycoumarin, and the added amount of 6-carboxycoumarin is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 6-carboxycoumarin of 0.5 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; nanofiltration membrane M10 is obtained.

[0095] Embodiment 11

[0096] The only difference from Example 2 is that chelidonic acid is replaced by 4-phenylpyrone-2-carboxylic acid, and the added amount of 4-phenylpyrone-2-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 0.5 wt% of 4-phenylpyrone-2-carboxylic acid is obtained, and the remaining steps and parameters are the same as those in Example 2; a nanofiltration membrane M11 is obtained.

[0097] Example 12

[0098] The only difference from Example 2 is that chelidonic acid is replaced by coumarin-3-carboxylic acid, and the added amount of coumarin-3-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a coumarin-3-carboxylic acid mass concentration of 0.5 wt % is obtained, and the remaining steps and parameters are the same as those in Example 2; nanofiltration membrane M12 is obtained.

[0099] Embodiment 13

[0100] The only difference from Example 2 is that chelidonic acid is replaced by 6-bromocoumarin-3-carboxylic acid, and the added amount of 6-bromocoumarin-3-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 6-bromocoumarin-3-carboxylic acid of 0.5 wt% is obtained, and the remaining steps and parameters are the same as those in Example 2; nanofiltration membrane M13 is obtained.

[0101] Embodiment 14

[0102] The only difference from Example 2 is that chelidonic acid is replaced by 7-hydroxycoumarin-3-carboxylic acid, and the added amount of 7-hydroxycoumarin-3-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 7-hydroxycoumarin-3-carboxylic acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as in Example 2; nanofiltration membrane M14 is obtained.

[0103] Embodiment 15

[0104] The only difference from Example 2 is that chelidonic acid is replaced by 6-chloro-7-methyl-4-oxo-4H-1-phenylpyran-2-carboxylic acid, and the added amount of 6-chloro-7-methyl-4-oxo-4H-1-phenylpyran-2-carboxylic acid is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 6-chloro-7-methyl-4-oxo-4H-1-phenylpyran-2-carboxylic acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as in Example 2; nanofiltration membrane M15 is obtained.

[0105] Example 16

[0106] The only difference from Example 2 is that chelidonic acid is replaced by 7-methoxy-2-oxo-2H-1-phenylpyran-4-acetic acid, and the amount of 7-methoxy-2-oxo-2H-1-phenylpyran-4-acetic acid added is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 7-methoxy-2-oxo-2H-1-phenylpyran-4-acetic acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as in Example 2; a nanofiltration membrane M16 is obtained.

[0107] Embodiment 17

[0108] The only difference from Example 2 is that chelidonic acid is replaced by 7-hydroxy-4-methyl-3-coumarin acetic acid, and the amount of 7-hydroxy-4-methyl-3-coumarin acetic acid added is 0.5 g, that is, a piperazine mixed aqueous solution with a mass concentration of 7-hydroxy-4-methyl-3-coumarin acetic acid of 0.5 wt % is obtained, and the remaining steps and parameters are the same as in Example 2; nanofiltration membrane M17 is obtained.

[0109] Effect verification example 1

[0110] (I) The permeability of M1, M2, M3, M4 and M5 was tested using cross-flow medium and low pressure filtration equipment, and the permeation flux and the retention rate of Na2SO4 were calculated as follows:

[0111] At 0.8 MPa, pure water was pre-pressed on the membrane to be tested for 30 min, then the pressure was reduced to 0.4 MPa, and 1 g / L Na2SO4 was used to continuously test for 1 h, and the permeate volume (L) was recorded.

[0112] The permeation flux J was calculated according to formula 1:

[0113] In formula 1, J is the permeation flux, L / m 2 h; V is the permeate volume, L; A is the nanofiltration membrane area, m 2 ; t is the penetration time, h.

[0114] The salt solution retention rate R is calculated according to formula 2:

[0115] In formula 2, R is the interception rate, %; C p is the mass concentration of the salt solution before the test, g / L; C f is the mass concentration of the salt solution after the test, g / L.

[0116] After testing, the pure water permeation flux and Na2SO4 retention rate of M1, M2, M3, M4 and M5 are shown in Table 1 and Figure 3 (Pure water permeation flux and Na2SO4 retention rate of nanofiltration membranes M1, M2, M3, M4, and M5).

[0117] Table 1 Permeation flux and Na2SO4 retention rate of M1, M2, M3, M4 and M5

[0118]

[0119] It can be seen from Table 1 that as the mass concentration of chelidonic acid in the piperazine aqueous solution increases to 0.6wt%, the permeation flux of the nanofiltration membranes M1 to M5 gradually increases while the Na2SO4 rejection rate is basically maintained at more than 95%. This is mainly because as the concentration of chelidonic acid increases, the portion of the piperazine molecule that is converted into protonated piperazine increases. On the one hand, the increase in the concentration of chelidonic acid inhibits the diffusion rate of piperazine and protonated piperazine to the oil / water interface. On the other hand, as the concentration of protonated piperazine increases, the cross-linking degree of polymerization at the oil / water interface continues to decrease, which is conducive to the formation of a thinner, looser, and more hydrophilic PA layer, so that the nanofiltration membrane increases the permeation flux while keeping the rejection rate basically unchanged.

[0120] (ii) The above method was used to test the permeation flux and solute retention rate of M5 for Na2SO4, CaCl2, MgCl2 and NaCl solutions. The results are shown in Table 2 and Figure 4 (Permeation flux and solute retention rate of nanofiltration membrane M5 for Na2SO4, MgCl2, CaCl2 and NaCl solutions) shown.

[0121] Table 2M5 Permeation flux and solute retention rate for Na2SO4, CaCl2, MgCl2 and NaCl solutions

[0122]

[0123] It can be seen from Table 2 that the solute rejection rate of nanofiltration membrane M5 shows a change of Na2SO4>MgCl2>CaCl2>NaCl, while the corresponding permeation flux shows a change of Na2SO4<MgCl2<CaCl2<NaCl. This is mainly related to the fact that the solute rejection of nanofiltration membrane is affected by the pore size screening theory and Donan effect at the same time. SO4 2- Ions with larger sizes and the most negative charges are easily retained by negatively charged nanofiltration membranes. Conversely, NaCl has the least charge and a smaller corresponding ion size, so it is easily permeated and has the largest corresponding flux.

[0124] Figure 1 The Fourier-total reflection infrared spectra of nanofiltration membranes M1, M2, M3, M4, and M5 prepared in Comparative Example 1 and Examples 2-5 of the present invention are shown in FIG. Figure 1 It can be seen that at 1630cm -1 The characteristic absorption peak of C=O of the amide bond appears between them, thus proving the successful preparation of the PA layer.

[0125] Figure 2 The cross-sectional scanning electron micrographs of the nanofiltration membranes M1, M2, M3, M4, and M5 prepared in Comparative Example 1 and Examples 2-5 of the present invention are shown. Figure 2 It can be seen that with the increase of chelidonic acid content, the thickness of PA layer gradually decreases, which is mainly attributed to the fact that the addition of chelidonic acid not only reduces the diffusion rate of piperazine and protonated piperazine into the oil phase, but also reduces the reaction activity with trimesoyl chloride, resulting in a decrease in the degree of crosslinking.

[0126] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a nanofiltration membrane based on the regulation of pyrone acidic molecular additives, characterized in that: The following steps are involved: adding pyrone acidic molecules to the piperazine aqueous solution to obtain a piperazine mixed aqueous solution; soaking the support layer in the piperazine mixed aqueous solution to obtain a support layer with piperazine and pyrone acid molecules attached thereto; The support layer with piperazine and pyrone acid molecules attached thereto is brought into contact with a trimesoyl chloride solution for interfacial polymerization to obtain a primary nanofiltration membrane; The primary nanofiltration membrane is heat-treated and then immersed in water to obtain the nanofiltration membrane.

2. The method for preparing nanofiltration membrane based on pyrone acidic molecular additives according to claim 1, characterized in that: The pyrone acidic molecule is at least one of chelidonic acid, γ-pyrone-2-carboxylic acid, 2-pyrone-5-carboxylic acid, 4,6-dimethylcoumaric acid, 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid, 6-carboxycoumarin, 4-benzopyrone-2-carboxylic acid, coumarin-3-carboxylic acid, 6-bromocoumarin-3-carboxylic acid, 7-hydroxycoumarin-3-carboxylic acid, 6-chloro-7-methyl-4-oxo-4H-1-benzopyran-2-carboxylic acid, 7-methoxy-2-oxo-2H-1-benzopyran-4-acetic acid and 7-hydroxy-4-methyl-3-coumarin acetic acid.

3. The method for preparing nanofiltration membrane based on pyrone acidic molecular additive regulation according to claim 1, characterized in that: The mass concentration of the piperazine aqueous solution is 0.001% to 2.0%; the mass concentration of pyrone acidic molecules in the piperazine mixed aqueous solution is 0.001% to 10.0%.

4. The method for preparing nanofiltration membrane based on pyrone acidic molecular additive regulation according to claim 1, characterized in that: The supporting layer is immersed in the piperazine mixed aqueous solution for 0.01 to 24 hours.

5. The method for preparing nanofiltration membrane based on pyrone acidic molecular additive regulation according to claim 1, characterized in that: The mass concentration of the trimesoyl chloride solution is 0.001-0.1%; the solvent of the trimesoyl chloride solution is n-hexane.

6. The method for preparing nanofiltration membrane based on pyrone acidic molecular additives according to claim 1, characterized in that: The time of the interfacial polymerization is 5 to 120 seconds.

7. The method for preparing nanofiltration membrane based on pyrone acidic molecular additive regulation according to claim 1, characterized in that: The heat treatment temperature is 20-90° C., and the time is 0.01-12 h; the soaking time in water is 0.5-30 d; and the support layer is an ultrafiltration membrane or a microfiltration membrane.

8. A nanofiltration membrane prepared by the method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecular additive according to any one of claims 1 to 7.

9. Use of the nanofiltration membrane as claimed in claim 8 in sewage treatment or seawater desalination.

10. A method for increasing the permeation flux of a nanofiltration membrane, characterized in that: A method for preparing a nanofiltration membrane based on the regulation of a pyrone acidic molecular additive as described in any one of claims 1 to 7.

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