A loose nanofiltration membrane and its preparation method and application

Abstract

The invention relates to the technical field of dye separation, and discloses a loose nanofiltration membrane, a preparation method and an application thereof. The loose nanofiltration membrane is prepared by a one-step interfacial polymerization method on the surface of a porous support membrane from a polyacyl chloride organic solution and an amine monomer aqueous phase solution. The loose nanofiltration membrane has a retention rate of more than 95% for dyes such as methyl blue and Congo red. At the same time, the loose nanofiltration membrane has a high water permeability and excellent dye / inorganic salt separation selectivity, and is expected to have broad application prospects in the fields of dye production purification and dye wastewater desalination.

Description

Technical Field

[0001] The invention relates to the technical field of dye separation, and in particular to a loose nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] The sources of dye wastewater can be mainly divided into two aspects. The first aspect is that in the process of dye production and manufacturing, in addition to its own raw materials, chemical reactions will bring a lot of intermediate products; the second aspect is in the textile processing process. The textile process mainly includes four major processes, namely: spinning, weaving, printing and dyeing, and finishing. In this process, a large amount of printing and dyeing wastewater will be generated. According to statistics, about 2.37 billion tons of textile wastewater are generated each year, but its recycling rate is less than 10%. Toxic, complex and non-biodegradable waste components pose a serious threat to aquatic life and human health. Traditional chemical oxidation, absorption, coagulation and other technologies usually have low separation efficiency, waste of resources, and may even cause secondary pollution due to the addition of new chemicals during the treatment process. In order to better solve this serious problem, it strongly requires transformation and upgrading to efficiently recover and recycle valuable materials (i.e. dyes and salts) in addition to pollutants. Compared with these traditional technologies, nanofiltration membrane separation technology is a better choice and has been proven to be a practical and competitive alternative for textile printing and dyeing industrial wastewater treatment. Generally speaking, when treating textile printing and dyeing wastewater, different types of nanofiltration membranes can be used to achieve different treatment purposes.

[0003] Most of the traditional commercial nanofiltration membranes are polypiperazineamide nanofiltration composite membranes prepared by interfacial polymerization technology. Due to their small spatial structure and short molecular chain length between cross-linking points, the separation layer formed is relatively dense, usually with a high retention rate for divalent salts, and the permeation flux is also low, which cannot achieve efficient separation of dyes / inorganic salts. In order to reduce the density of the nanofiltration composite membrane, the researchers first thought of regulating the aqueous phase monomers. It is generally believed that the use of new monomers with relatively few functional groups, relatively low reaction activity or containing cavity structures, as well as the use of additives to adjust the relatively slow diffusion rate between interfaces, the addition of nanoparticles to the aqueous phase, and the adjustment of the pore size and porosity of the nanofiltration membrane can effectively reduce the density of the network structure of the separation layer of the nanofiltration membrane. However, whether using monomers with low reaction activity or containing cavity structures, generally a higher concentration is required to form a relatively complete separation layer; the use of additives to adjust the diffusion rate between interfaces and the addition of nanoparticles to the aqueous phase to adjust the pore size of the nanofiltration membrane are not only complex in process, but also require high preparation conditions, which is not conducive to industrial production, and the cost of use is also an issue that needs to be considered. Summary of the invention

[0004] The present invention relates to a loose nanofiltration membrane and a preparation method and application thereof. From the perspective of molecular structure, a water phase monomer with a specific structure is selected to construct the loose nanofiltration membrane through an interfacial polymerization method. The polyamide separation layer of the loose nanofiltration membrane has high permeability to inorganic salts and can also maintain a high retention rate (>95%) for a variety of dyes with different molecular weights, thereby improving the dye / salt separation efficiency. The loose nanofiltration membrane has excellent dye / inorganic salt separation selectivity.

[0005] The technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a method for preparing a loose nanofiltration membrane, comprising the following steps:

[0007] S1: pre-treating the porous support membrane;

[0008] S2: soaking the pretreated porous support membrane in an aqueous solution of an amine monomer having a concentration of 0.01-0.1 w / v% for 1-2 min, taking it out and blowing off the aqueous solution to obtain a support membrane adsorbed with an amine monomer; the amine monomer is one or more of 2-aminobenzoic acid hydrazide, 3-aminobenzoic acid hydrazide, and 4-aminobenzoic acid hydrazide;

[0009] S3: pouring a polyacid chloride organic phase solution with a concentration of 0.01-0.1 w / v% on the surface of the support membrane adsorbed with the amine monomer to carry out an interfacial polymerization reaction, taking it out and drying it at room temperature to obtain a loose nanofiltration membrane.

[0010] Furthermore, in step S1, the porous support membrane is one or more of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, a polyacrylonitrile ultrafiltration membrane, and a polyvinylidene fluoride ultrafiltration membrane with a molecular weight cutoff of 100 kDa.

[0011] Furthermore, in step S1, the concentration of the amine monomer in the aqueous amine monomer solution is 0.01-0.05 w / v%, preferably 0.01-0.03 w / v%.

[0012] Furthermore, in step S1, the pretreatment is to immerse the porous support membrane in deionized water for 6 to 24 hours, and then take it out and blow the porous support membrane with an air knife at a blowing temperature of 24 to 26°C for 1 to 2 minutes.

[0013] Furthermore, in step S2, the purging temperature is 24-26°C and the purging time is 0.5-1 min.

[0014] Furthermore, the interfacial polymerization reaction time in step S3 is 1-5 min, the reaction temperature is 24-26° C., and the drying time at room temperature is 5-10 min.

[0015] Furthermore, the polyacid chloride is trimesoyl chloride.

[0016] Furthermore, the organic solvent of the polyacyl chloride organic phase solution in step S3 is n-hexane.

[0017] The second aspect of the present invention provides a loose nanofiltration membrane prepared by the method described above.

[0018] A third aspect of the present invention provides an application of a loose nanofiltration membrane for separating dyes and inorganic salts.

[0019] The present invention uses a polyamine containing two or three structures of a long chain structure, a branched chain structure, a rigid structure, and a short chain structure as an interfacial polymerization aqueous phase monomer to prepare a loose nanofiltration membrane from the perspective of molecular structure. The compactness of the polyamine layer can be effectively regulated according to the amine group reaction activity, reaction site, and density contained in the monomer structure.

[0020] The prepared loose nanofiltration membrane consists of a base membrane and a polyamide separation layer, and is prepared by a one-step interfacial polymerization method on the surface of a porous support membrane from a polyacyl chloride organic solution and an amine monomer aqueous solution; the presence of a rigid benzene ring or a side chain containing an amine reaction site in the amine monomer gives the monomer molecule a larger spatial size and a larger reaction site distance, thereby effectively increasing the free volume of the polymer generated by the interfacial polymerization reaction, which is beneficial to the formation of a loose polyamide separation layer structure, thereby promoting the transmembrane mass transfer of inorganic salt ions, increasing the permeability of inorganic salts, and further promoting their efficient separation from dyes.

[0021] The advantages and beneficial effects of the present invention are:

[0022] (1) The loose nanofiltration membrane of the present invention has a retention rate of more than 95% for dyes such as methyl blue and Congo red, and has a high water permeability. It can be used in sewage treatment fields such as dye / inorganic salt separation, dye production purification, and dye wastewater desalination.

[0023] (2) The preparation method of the present invention has simple process, low monomer concentration, mild preparation conditions, wide application range, easy to scale up and promote, and easy to realize industrial production.

[0024] (3) The present invention selects a polyamine containing two or three structures of a long-chain structure, a branched structure, a rigid structure, and a short-chain structure as an interfacial polymerization aqueous phase monomer. According to the spatial size of the monomer structure, the reaction activity of the amine group contained, the reaction site and the density, the density of the polyamine layer can be effectively regulated, which is conducive to obtaining a high-throughput, inorganic salt ion permeable dye separation membrane.

[0025] (4) The amine monomer used in the present invention is a molecule containing a rigid benzene ring and a highly reactive amine reaction site. The larger spatial size of the molecule and the larger reaction site distance can effectively increase the free volume of the polymer in the interfacial polymerization reaction, which is conducive to the formation of a loose polyamide separation layer structure, thereby promoting the transmembrane mass transfer of inorganic salt ions, increasing the permeability of inorganic salts, and further promoting their efficient separation from dyes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The charge characteristic curves of the loose nanofiltration membranes prepared at different 4ABH (4-aminobenzoyl hydrazide) monomer concentrations in Examples 1 to 3;

[0027] Figure 2 These are the charge characteristic curves of the loose nanofiltration membranes prepared at different TMC (trimethylenediamine chloride) monomer concentrations in Examples 4 to 6. DETAILED DESCRIPTION

[0028] In order to better understand the purpose, preparation method and function of the present invention, the following is a further detailed description of a method for preparing a loose nanofiltration membrane that can be used for dye / inorganic salt separation. The raw materials used in the following examples are all commercially available analytically pure raw materials. Example 1

[0029] A method for preparing a loose nanofiltration membrane for dye / inorganic salt separation, the steps are as follows:

[0030] S1: pre-treating the porous support membrane;

[0031] Cut out several pieces of 12 cm × 15 cm polysulfone ultrafiltration membranes, soak them in deionized water for 24 h, take them out and stick them on a polytetrafluoroethylene plate, and use an air knife to blow to remove the deionized water on the surface; the blowing temperature is 26 ° C and the blowing time is 2 min.

[0032] S2: Use an analytical balance to weigh 0.075 g of 4-aminobenzoic acid hydrazide, then use deionized water to completely dissolve the weighed 4-aminobenzoic acid hydrazide in a 100 mL beaker, then transfer to a volumetric flask and add deionized water to make up to 500 mL; obtain an aqueous solution with a concentration of 0.015 w / v% 4-aminobenzoic acid hydrazide, soak the pretreated polysulfone ultrafiltration membrane in the aqueous solution containing 0.015 w / v% 4-aminobenzoic acid hydrazide for 2 minutes, take it out and use an air knife to blow away excess aqueous solution on the surface of the base membrane, the blowing temperature is 25°C, and the blowing time is 0.5 min, to obtain a polysulfone ultrafiltration membrane adsorbed with 4-aminobenzoic acid hydrazide.

[0033] S3: Use an analytical balance to weigh 0.25 g of trimesoyl chloride, then use n-hexane to completely dissolve the weighed trimesoyl chloride in a 100 mL beaker, and then quickly transfer it to a volumetric flask and dilute it to 500 mL to obtain a n-hexane solution of trimesoyl chloride with a concentration of 0.05 w / v%; then pour the n-hexane solution of trimesoyl chloride with a concentration of 0.05 w / v% on the polysulfone ultrafiltration membrane adsorbed with 4-aminobenzoyl hydrazide to carry out an interfacial polymerization reaction, let it stand for 5 minutes, then pour out the excess solution, take it out and dry it at room temperature for 5 minutes to obtain a loose nanofiltration membrane, which is stored in deionized water. Example 2

[0034] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation method steps are the same as those in Example 1, except that the concentration of the 4-aminobenzoylhydrazide aqueous solution is 0.02 w / v%. Example 3

[0035] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation method steps are the same as those in Example 1, except that the concentration of the 4-aminobenzoylhydrazide aqueous solution is 0.03 w / v%. Example 4

[0036] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the steps of the preparation method are the same as those of Example 1, except that the concentration of the n-hexane solution of trimesoyl chloride is 0.01 w / v%. Example 5

[0037] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those in Example 1, except that the concentration of the n-hexane solution of trimesoyl chloride is 0.05 w / v%. Example 6

[0038] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the steps of the preparation method are the same as those of Example 1, except that the concentration of the n-hexane solution of trimesoyl chloride is 0.07 w / v%. Example 7

[0039] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the steps of the preparation method are the same as those of Example 6, except that the time for the interfacial polymerization reaction after pouring the n-hexane solution containing trimesoyl chloride is 3 minutes. Example 8

[0040] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the steps of the preparation method are the same as those of Example 6, except that the time for the interfacial polymerization reaction after pouring the n-hexane solution containing trimesoyl chloride is 4 minutes. Example 9

[0041] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 8, except that the aqueous phase solution used is a 2-aminobenzoyl hydrazide aqueous solution with a concentration of 0.02 w / v%. Example 10

[0042] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 8, except that the aqueous phase solution used is a 3-aminobenzoyl hydrazide aqueous solution with a concentration of 0.02 w / v%. Embodiment 11

[0043] A method for preparing a loose nanofiltration membrane for dye / salt separation, the preparation method steps are the same as those of Example 8, the only difference being that the aqueous phase solution used is a mixed aqueous solution of 0.02 w / v% 4-aminobenzoic acid hydrazide and 0.02 w / v% hydrazine.

[0044] Comparative Example 1

[0045] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 7, except that the aqueous phase solution used is an aqueous solution of piperazine with a concentration of 0.015 w / v%.

[0046] Comparative Example 2

[0047] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 7, except that the aqueous phase solution used is an aqueous solution of piperazine with a concentration of 0.03 w / v%.

[0048] Comparative Example 3

[0049] A method for preparing a loose nanofiltration membrane for dye / salt separation, the preparation method steps are the same as those of Example 7, the only difference is that several pieces of 12cm×15cm commercial nanofiltration membrane NF270 are cut out and stored in deionized water for 24 hours for use.

[0050] Comparative Example 4

[0051] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 7, except that the porous base membrane used is a commercial polyethersulfone ultrafiltration membrane, and the organic solvent is n-heptane.

[0052] Comparative Example 5

[0053] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 7, except that the porous base membrane used is a commercial polyacrylonitrile ultrafiltration membrane.

[0054] Comparative Example 6

[0055] A method for preparing a loose nanofiltration membrane for dye / salt separation, wherein the preparation steps are the same as those of Example 7, except that the organic solvent used is n-heptane.

[0056] The separation performance of the loose nanofiltration membranes prepared in Examples 1 to 11 and Comparative Examples 1 to 6 was tested using a membrane performance evaluation instrument. The test conditions were: room temperature; feed pressure 3.5 bar; inorganic salt concentration: 1 g / L; dye concentration: 0.1 g / L. The test results are shown in Table 1.

[0057] Table 1 Separation performance test results of loose nanofiltration membranes prepared in Examples 1 to 11 and Comparative Examples 1 to 6

[0058]

[0059] As shown in Table 1, it can be seen from the above Examples 1 to 11 and Comparative Examples 1 to 6 that the loose nanofiltration membranes prepared using 2-aminobenzoic acid hydrazide, 3-aminobenzoic acid hydrazide, 4-aminobenzoic acid hydrazide, and a mixture of 4-aminobenzoic acid hydrazide and hydrazine have lower inorganic salt retention rates than the loose nanofiltration membranes prepared using piperazine as the aqueous phase monomer and the commercial NF 270 membrane under the same dye retention capacity. In particular, the loose nanofiltration membrane prepared from 4-aminobenzoic acid hydrazide monomer in Example 7 has excellent water permeability (45.03 L·m -2 ·h -1 bar -1 ), which can achieve a high retention rate for the dye methyl blue (95.18%) and a low retention rate for two inorganic salts (NaCl: 6.79%, Na2SO4: 24.37%), thus having excellent dye / salt separation selectivity.

[0060] As shown in Table 1, the loose nanofiltration membrane (Comparative Example 1) prepared with traditional aqueous phase monomer piperazine under the same preparation process conditions has a retention rate of only 51.24% for the dye methyl blue, indicating that a complete and dense separation layer cannot be formed at a lower piperazine concentration, and selective separation of dyes / salts cannot be achieved; the loose nanofiltration membranes prepared in Comparative Examples 2 and 3 have low water flux, high retention rates for dyes and inorganic salts, and poor dye / salt separation selectivity. The loose nanofiltration membrane (Example 7) prepared using 4-aminobenzoyl hydrazide monomer forms a complete and loose separation layer structure under a lower aqueous phase concentration environment without sacrificing the retention rate for dyes, and the dye retention rate can still be maintained at more than 95%.

[0061] As shown in Table 1, Example 7 has a better balance between high dye retention, high salt permeability and high water permeability than the loose nanofiltration membrane prepared with polyethersulfone, polyacrylonitrile as the base membrane or n-heptane as the organic solvent in Comparative Examples 4 to 6 under the same preparation process conditions and test conditions. This may be attributed to the more suitable affinity between the polysulfone membrane surface and the water molecules, which can provide a relatively stable and complete and uniform "phase interface" for the polymerization reaction between the amine monomer and the n-hexane solution of the acyl chloride. As shown in Table 1, compared with the comparative example, the embodiment proves that the method of the present invention improves the inorganic salt ion permeability and pure water flux while maintaining the dye retention of the loose nanofiltration membrane. This is because the long-chain molecules containing benzene rings or polyamine reaction sites have larger spatial dimensions and reaction steric hindrance than the traditional interfacial polymerization diamine monomer (such as piperazine), which can effectively increase the free volume of the polymer in the interfacial polymerization reaction, which is conducive to the formation of a loose separation layer structure and a larger pore size structure, improve the permeability of water and inorganic salts, and further promote their efficient separation from dyes.

[0062] The charge characteristics of the loose nanofiltration membranes prepared at different 4ABH (4-aminobenzoyl hydrazide) monomer concentrations in Examples 1 to 3 are as follows: Figure 1 As shown. It can be seen that with the increase of 4ABH concentration, the negative charge on the surface of the loose nanofiltration membrane decreases. This is because with the increase of 4ABH concentration, the contact opportunity between the acyl chloride group and the amine group in the reaction zone increases, so that more 4ABH monomers participate in the polymerization reaction, the amine content on the surface of the polysulfone ultrafiltration membrane increases, and at the same time, the content of the acyl chloride group hydrolyzed into the carboxyl group after the reaction decreases, thereby reducing the negative charge on the surface of the loose nanofiltration membrane.

[0063] The charge characteristics of the loose nanofiltration membranes prepared at different TMC (trimethylenediamine chloride) monomer concentrations in Examples 4 to 6 are as follows: Figure 2 As shown in the figure, as the TMC concentration gradually increases to 0.07w / v%, the negative charge on the surface of the loose nanofiltration membrane gradually increases. This is because as the TMC concentration increases, more TMC monomers participate in the polymerization reaction, and the content of acyl chloride groups on the surface of the PA membrane increases, resulting in an increase in the content of acyl chloride groups hydrolyzed into carboxyl groups after the reaction, thereby enhancing the negative charge on the surface of the loose nanofiltration membrane.

[0064] The above description is only a preferred implementation case of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a loose nanofiltration membrane, characterized in that: The following steps are involved: S1: pre-treating the porous support membrane; S2: soaking the pretreated porous support membrane in an aqueous solution of amine monomers for 1-2 min, taking it out and blowing away the aqueous solution to obtain a support membrane adsorbed with amine monomers; the amine monomers are one or more of 2-aminobenzoyl hydrazide, 3-aminobenzoyl hydrazide and 4-aminobenzoyl hydrazide; the concentration of the amine monomers in the aqueous solution of amine monomers is 0.01-0.05w / v%, and the amine monomers have rigid benzene rings and highly reactive amine reaction sites, which increase the free volume of the polymer in the interfacial polymerization reaction, form a loose polyamide separation layer structure, promote the transmembrane mass transfer of inorganic salt ions, increase the permeability of inorganic salts, and promote the efficient separation of inorganic salts and dyes; S3: pouring a polyacyl chloride organic phase solution with a concentration of 0.01-0.1 w / v% on the surface of the support membrane adsorbed with amine monomers to carry out interfacial polymerization reaction, taking it out and drying it at room temperature to obtain a loose nanofiltration membrane; the polyacyl chloride is trimesoyl chloride; the organic solvent of the polyacyl chloride organic phase solution is n-hexane; the time of the interfacial polymerization reaction is 1-5min, the reaction temperature is 24-26℃, and the drying time at room temperature is 5-10 min.

2. The preparation method according to claim 1, characterized in that: In step S1, the porous support membrane is one or more of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, a polyacrylonitrile ultrafiltration membrane, and a polyvinylidene fluoride ultrafiltration membrane with a molecular weight cutoff of 100 kDa.

3. The preparation method according to claim 1, characterized in that: In step S1, the pretreatment is to soak the porous support membrane in deionized water for 6-24 hours, and then take it out and blow the porous support membrane with an air knife at a blowing temperature of 24-26° C. for 1-2 minutes.

4. The preparation method according to claim 1, characterized in that: In step S2, the purge temperature is 24-26°C and the purge time is 0.5-1 min.

5. A loose nanofiltration membrane, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the loose nanofiltration membrane according to claim 5 for separating dyes and inorganic salts.

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