Novel diamine monomer prepared high-flux nanofiltration membrane and method thereof

Abstract

The method comprises the following steps: immersing a pretreated nanofiltration base membrane into an aqueous phase solution to fully adsorb trans-2, 5-dimethylpiperazine, removing the surface solution by using a rubber roller, and then immersing the nanofiltration base membrane into an organic phase solution to carry out interfacial polymerization reaction, so that the trans-2, 5-dimethylpiperazine adsorbed on the surface of the nanofiltration base membrane is fully adsorbed on the surface of the nanofiltration base membrane; the preparation method comprises the following steps: taking trans-2, 5-dimethylpiperazine as a water-phase monomer, fully contacting the trans-2, 5-dimethylpiperazine with 1, 3, 5-benzoyl chloride in an organic-phase solution, carrying out polymerization reaction at a two-phase interface to form a separation layer, and then drying and curing to improve the compactness and the stability, thereby obtaining the nanofiltration membrane. The diffusion rate of an organic phase to a water phase is reduced by two methyl groups at ortho-positions of two amino groups through a steric effect, so that a relatively thin separation layer is formed, and the pure water flux of the nanofiltration membrane is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane materials, and in particular to a method for preparing a high-flux nanofiltration membrane using a novel diamine monomer. Background Art

[0002] Nanofiltration membrane is a kind of pressure-driven membrane in membrane separation technology. The pore size of nanofiltration membrane is between that of ultrafiltration membrane and reverse osmosis membrane, about 1nm-10nm, and the molecular weight cutoff is within the range of 200Da-1000Da. Nanofiltration membrane mainly relies on size screening effect and Donan effect to intercept inorganic salt ions in water. So far, in order to improve the filtration performance of nanofiltration membrane, people have made many attempts to adjust the physical and chemical properties of the nanofiltration membrane surface, such as pore size, surface charge, wettability and roughness.

[0003] However, due to the rapid diffusion of oil phase reactants into the water phase and the rapid progress of interfacial polymerization reactions, the separation layer formed is often thick, making it difficult to improve its permeation flux. Summary of the invention

[0004] The object of the present invention is to provide a novel diamine monomer for preparing a high-flux nanofiltration membrane and a method thereof, so as to solve the problem that the nanofiltration membrane in the prior art cannot be dissolved and has both high permeation flux and high retention rate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a high-flux nanofiltration membrane using a novel diamine monomer, comprising the following steps:

[0007] pre-treating the nanofiltration base membrane to obtain a pre-treated nanofiltration base membrane;

[0008] After mixing trans-2,5-dimethylpiperazine and deionized water, an aqueous phase solution is obtained;

[0009] After 1,3,5-benzenetricarboxylic acid chloride and n-hexane, an organic phase solution is obtained;

[0010] Immersing the pretreated nanofiltration base membrane in the aqueous solution, taking out the immersed nanofiltration base membrane, removing the surface solution of the nanofiltration base membrane with a rubber roller, and then immersing it in the organic solution to perform an interfacial polymerization reaction, thereby obtaining a base membrane after the interfacial polymerization reaction;

[0011] The base film after the interfacial polymerization reaction is dried and cured in sequence to obtain a nanofiltration membrane.

[0012] According to the preparation method provided by the present invention, the material of the nanofiltration base membrane is one or any combination of two or more of polyethersulfone, polyacrylonitrile and polyvinylidene fluoride.

[0013] According to the preparation method provided by the present invention, the membrane retention molecular weight of the nanofiltration base membrane is 50KDa-150KDa.

[0014] According to the preparation method provided by the present invention, the pretreatment of the nanofiltration base membrane comprises:

[0015] The nanofiltration base membrane was immersed in deionized water at 20°-30°C for 48h-72h, and the deionized water was replaced every 12h.

[0016] According to the preparation method provided by the present invention, the concentration of trans-2,5-dimethylpiperazine in the aqueous solution is 0.05wt%-1.00wt%.

[0017] According to the preparation method provided by the present invention, the concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution is 0.025wt%-0.25wt%.

[0018] According to the preparation method provided by the present invention, the immersion time of the pretreated nanofiltration base membrane into the aqueous solution is 2 min-7 min, and the time of the interfacial polymerization reaction is 20 s-120 s.

[0019] According to the preparation method provided by the present invention, the base film after the interfacial polymerization reaction is dried and cured in sequence, the curing time is 0.5min-2.5min, and the curing temperature is 20°C-80°C.

[0020] The present invention also provides a nanofiltration membrane prepared by the above preparation method.

[0021] The invention provides a novel diamine monomer for preparing a high-flux nanofiltration membrane and a method thereof. The pretreated nanofiltration base membrane, an aqueous phase solution containing trans-2,5-dimethylpiperazine, and an organic phase solution containing 1,3,5-benzenetricarboxylic acid chloride are respectively prepared. The pretreated nanofiltration base membrane is immersed in the aqueous phase solution so that the nanofiltration base membrane fully adsorbs trans-2,5-dimethylpiperazine. The immersed base membrane is then taken out and the surface solution is removed with a rubber roller to make the subsequent interfacial polymerization reaction more uniform. The base membrane is then immersed in the organic phase solution for interfacial polymerization reaction, so that the trans-2,5-dimethylpiperazine adsorbed on the surface of the nanofiltration base membrane is fully in contact with the 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution and the two phases are in contact with each other. A polymerization reaction occurs at the interface to form a separation layer on the nanofiltration base membrane, which is then dried and solidified to further cross-link the formed separation layer, thereby improving its compactness and stability. The obtained nanofiltration membrane has both high permeability flux and high retention rate. In addition, the present invention uses trans-2,5-dimethylpiperazine as an aqueous phase monomer to prepare the nanofiltration membrane. The amino group of trans-2,5-dimethylpiperazine has strong reactivity, and the ortho-methyl group thereof can produce a steric hindrance effect to slow down the diffusion of the oil phase into the aqueous phase, while reducing the reaction rate, thereby forming a lower separation layer, thereby improving the water flux of the prepared nanofiltration membrane while ensuring its retention effect on pollutants, thereby achieving high permeability flux and retention rate of the nanofiltration membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are 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.

[0023] Figure 1 Shown is a flow chart of a method for preparing a high-flux nanofiltration membrane using a new diamine monomer provided in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0025] like Figure 1 As shown, the present invention provides a method for preparing a high-flux nanofiltration membrane using a novel diamine monomer, comprising the following steps:

[0026] S1, pre-treating the nanofiltration base membrane to obtain a pre-treated nanofiltration base membrane;

[0027] S2, mixing trans-2,5-dimethylpiperazine and deionized water to obtain an aqueous solution;

[0028] S3, 1,3,5-benzenetricarboxylic acid chloride and n-hexane are added to obtain an organic phase solution;

[0029] S4, immersing the pretreated nanofiltration base membrane into an aqueous solution, taking out the immersed nanofiltration base membrane, removing the surface solution of the nanofiltration base membrane with a rubber roller, and then immersing it into an organic solution to perform an interfacial polymerization reaction to obtain a base membrane after the interfacial polymerization reaction;

[0030] S5. The base film after the interfacial polymerization reaction is dried and cured in sequence to obtain a nanofiltration membrane.

[0031] There is no order of precedence among step S1, step S2 and step S3;

[0032] In the present invention, unless otherwise specified, the raw materials used are conventional commercial products in the art.

[0033] In the present invention, the material of the nanofiltration base membrane can be one or any combination of two or more of polyethersulfone, polyacrylonitrile and polyvinylidene fluoride.

[0034] In the present invention, the membrane cut-off molecular weight of the nanofiltration base membrane may be 50 KDa-150 KDa, for example, 100 KDa.

[0035] In the present invention, the pretreatment may include: immersing the nanofiltration base membrane in deionized water at 20-30° C. for 48 h to 72 h, and replacing the deionized water every 12 h.

[0036] The invention mixes trans-2,5-dimethylpiperazine and deionized water to obtain an aqueous phase solution.

[0037] In the present invention, the concentration of trans-2,5-dimethylpiperazine in the aqueous solution can be 0.05wt%-1.00wt%, for example, 0.10-0.50wt%. The present invention controls the concentration of trans-2,5-dimethylpiperazine in the aqueous solution within the above range so that the adsorption amount of trans-2,5-dimethylpiperazine by the nanofiltration base membrane is at the optimal reaction amount. At this concentration, the separation layer can be sufficiently cross-linked and not too thick, so that the membrane maintains a high permeation flux and retention rate.

[0038] In the present invention, the concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution can be 0.025wt%-0.25wt%, for example, 0.05wt%-0.2wt%. The present invention controls the concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution within the above range to ensure that the interfacial polymerization reaction is at an optimal reaction level. At this concentration, the separation layer can have a sufficient degree of crosslinking and not be too thick, so that the membrane maintains a high permeation flux and retention rate.

[0039] In the present invention, there is no particular order in which the nanofiltration base membrane, aqueous solution and organic solution pretreated by the above technical solution are prepared.

[0040] After obtaining the pretreated nanofiltration base membrane, aqueous solution and organic solution, the present invention immerses the pretreated nanofiltration base membrane into the aqueous solution, then takes out the immersed base membrane, removes the surface solution with a rubber roller, and then immerses it into the organic solution for interfacial polymerization reaction to obtain the base membrane after interfacial polymerization reaction.

[0041] In the present invention, the time for the pretreated nanofiltration base membrane to be immersed in the aqueous solution can be 2 min-7 min, for example, 3 min-6 min. The present invention controls the time for the pretreated nanofiltration base membrane to be immersed in the aqueous solution within the above range, so that trans-2,5-dimethylpiperazine in the aqueous solution is fully adsorbed onto the surface of the pretreated nanofiltration base membrane.

[0042] In the present invention, the time of the interfacial polymerization reaction can be 20s-120s, for example, 30-100s. The present invention controls the time of the interfacial polymerization reaction within the above range to allow trans-2,5-dimethylpiperazine adsorbed on the surface of the pretreated nanofiltration base membrane and 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution to fully react.

[0043] After obtaining the base membrane after the interfacial polymerization reaction, the present invention sequentially dries and solidifies the base membrane after the interfacial polymerization reaction to obtain a nanofiltration membrane with high permeability flux and high retention rate.

[0044] In the present invention, the curing time may be 0.5 min-2.5 min, for example, 1 min-2 min. In the present invention, the curing temperature may be 20° C.-80° C. The present invention controls the curing temperature and time within the above range to make the nanofiltration membrane separation layer in the optimal cross-linking state.

[0045] The method for preparing a high-flux nanofiltration membrane using a novel diamine monomer provided by the invention has the advantages of simple operation, mild reaction conditions and suitability for large-scale production.

[0046] The embodiment of the present invention also provides a nanofiltration membrane prepared by the above preparation method.

[0047] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example 1

[0049] The steps of preparing a high-flux nanofiltration membrane with a novel diamine monomer are as follows (the following steps without temperature indication are all carried out at room temperature):

[0050] (1) A polyethersulfone (PES) nanofiltration membrane (with a molecular weight cutoff of 100 KDa) with a size of 7 cm×7 cm was pretreated by soaking it in deionized water for 48 hours. The deionized water needed to be replaced every 24 hours.

[0051] (2) 0.2 g of trans-2,5-dimethylpiperazine was mixed with 199.8 g of deionized water to prepare an aqueous solution having a trans-2,5-dimethylpiperazine concentration of 0.1 wt %.

[0052] (3) 0.31 g of 1,3,5-benzenetricarboxylic acid chloride and 199.69 g of n-hexane solvent were mixed to prepare an organic phase solution having a 1,3,5-benzenetricarboxylic acid chloride concentration of 0.155 wt %.

[0053] (4) The pretreated nanofiltration base membrane obtained in step (1) is immersed in the aqueous solution obtained in step (2) for 5 minutes, and then the immersed base membrane is taken out and the surface solution is removed with a rubber roller, and then immersed in the organic phase solution for interfacial polymerization reaction for 30 seconds to obtain a base membrane after interfacial polymerization reaction.

[0054] (5) After drying the base film obtained after the interfacial polymerization reaction in step (4), the base film was placed in a constant temperature drying oven at 50° C. for curing for 1 minute to obtain a nanofiltration membrane.

[0055] The nanofiltration membrane prepared in Example 1 was sealed in a water environment for subsequent measurements. The performance of the nanofiltration membrane prepared in Example 1 was tested with pure water and 2000ppm Na2SO4 at a pressure of 0.2Mpa. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Example 1 was 26.55L·m-2h-1bar-1, and the retention rate of the Na2SO4 aqueous solution was 96.84%.

[0056] Example 2

[0057] A nanofiltration membrane was prepared according to the method of Example 1, except that in step (2), 0.4 g of trans-2,5-dimethylpiperazine was mixed with 199.6 g of deionized water to prepare an aqueous solution having a trans-2,5-dimethylpiperazine concentration of 0.2 wt %.

[0058] The performance of the nanofiltration membrane prepared in Example 2 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Example 2 was 28.74 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 97.31%.

[0059] Example 3

[0060] The nanofiltration membrane was prepared according to the method of Example 1, except that: step (5) was to mix 0.6 g of trans-2,5-dimethylpiperazine with 199.4 g of deionized water to prepare an aqueous solution with a trans-2,5-dimethylpiperazine concentration of 0.3 wt%. The nanofiltration membrane prepared in Example 3 was tested for performance in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Example 3 was 27.56 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 95.15%.

[0061] Example 4

[0062] A nanofiltration membrane was prepared according to the method of Example 3, except that the base film obtained after the interfacial polymerization reaction in step (4) was dried and placed in a constant temperature drying oven at 25° C. for 1 minute to obtain a nanofiltration membrane.

[0063] The performance of the nanofiltration membrane prepared in Example 4 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Example 4 was 30.36 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 96.61%.

[0064] Example 5

[0065] A nanofiltration membrane was prepared according to the method of Example 2, except that the base film obtained after the interfacial polymerization reaction in step (4) was dried and placed in a constant temperature drying oven at 25° C. for 1 minute to obtain a nanofiltration membrane.

[0066] The performance of the nanofiltration membrane prepared in Example 5 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Example 5 was 34.11 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 98.04%.

[0067] Comparative Example 1

[0068] A nanofiltration membrane was prepared according to the method of Example 5, except that in step (2), 0.4 g of piperazine was mixed with 199.6 g of deionized water to prepare an aqueous solution with a piperazine concentration of 0.2 wt %.

[0069] The nanofiltration membrane prepared in Comparative Example 1 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Comparative Example 1 was 13.39 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 99.24%.

[0070] Comparative Example 2

[0071] A nanofiltration membrane was prepared according to the method of Example 5, except that in step (2), 0.4 g of N-aminoethylpiperazine was mixed with 199.6 g of deionized water to prepare an aqueous solution having a concentration of 0.2 wt % of N-aminoethylpiperazine.

[0072] The performance of the nanofiltration membrane prepared in Comparative Example 2 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Comparative Example 2 was 6.47 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 98.43%.

[0073] Comparative Example 3

[0074] A nanofiltration membrane was prepared according to the method of Example 5, except that in step (2), 0.4 g of 2-methylpiperazine was mixed with 199.6 g of deionized water to prepare an aqueous solution with a 2-methylpiperazine concentration of 0.2 wt %.

[0075] The performance of the nanofiltration membrane prepared in Comparative Example 3 was tested in the same manner as in Example 1. The test results showed that the pure water permeability of the nanofiltration membrane prepared in Comparative Example 2 was 50.61 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution was 49.96%.

[0076] In summary, the pure water permeability of the nanofiltration membrane prepared in Example 5 of the present invention is 34.11 L·m-2h-1bar-1, and the retention rate of Na2SO4 aqueous solution is 98.04%. The comprehensive consideration of water flux and the retention rate of Na2SO4 aqueous solution is significantly better than that of the control example.

[0077] The above are only possible implementation methods of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0078] The phrases "one embodiment", "an embodiment", etc. mentioned in the specification indicate that the embodiment described may include a specific feature, structure or characteristic, but not every embodiment may include the specific feature, structure or characteristic. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure or characteristic is described in conjunction with an embodiment, it is within the knowledge of those skilled in the art to implement such feature, structure or characteristic in conjunction with other embodiments, whether explicitly or not explicitly described.

[0079] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0080] The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A method for preparing a high-flux nanofiltration membrane using a novel diamine monomer, comprising the following steps: pre-treating the nanofiltration base membrane to obtain a pre-treated nanofiltration base membrane; After mixing trans-2,5-dimethylpiperazine and deionized water, an aqueous phase solution is obtained; After 1,3,5-benzenetricarboxylic acid chloride and n-hexane, an organic phase solution is obtained; Immersing the pretreated nanofiltration base membrane in the aqueous solution, taking out the immersed nanofiltration base membrane, removing the surface solution of the nanofiltration base membrane with a rubber roller, and then immersing it in the organic solution to perform an interfacial polymerization reaction, thereby obtaining a base membrane after the interfacial polymerization reaction; The base film after the interfacial polymerization reaction is dried and cured in sequence to obtain a nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that: The material of the nanofiltration base membrane is one or any combination of two or more of polyethersulfone, polyacrylonitrile and polyvinylidene fluoride.

3. The preparation method according to claim 1, characterized in that: The membrane cut-off molecular weight of the nanofiltration base membrane is 50 KDa-150 KDa.

4. The preparation method according to claim 1, characterized in that: The pretreatment of the nanofiltration base membrane comprises: The nanofiltration base membrane was immersed in deionized water at 20°-30°C for 48h-72h, and the deionized water was replaced every 12h.

5. The preparation method according to any one of claims 1 or 4, characterized in that: The concentration of trans-2,5-dimethylpiperazine in the aqueous phase solution is 0.05 wt % to 1.00 wt %.

6. The preparation method according to claim 1, characterized in that: The concentration of 1,3,5-benzenetricarboxylic acid chloride in the organic phase solution is 0.025 wt % to 0.25 wt %.

7. The preparation method according to claim 1, characterized in that: The immersion time of the pretreated nanofiltration base membrane in the aqueous solution is 2 min-7 min, and the time of the interfacial polymerization reaction is 20 s-120 s.

8. The preparation method according to claim 1, characterized in that: The base film after the interfacial polymerization reaction is dried and cured in sequence, wherein the curing time is 0.5 min-2.5 min and the curing temperature is 20° C.-80° C.

9. The nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

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