Multifunctional multipurpose separation membrane, polyamide layer separation membrane with defect-free compact layer and preparation method of polyamide layer separation membrane

Abstract

The invention discloses a multifunctional separation membrane and a preparation method thereof, and relates to the technical field of membrane separation materials and preparation thereof. The method comprises the steps that firstly, a prepared amine monomer solution is placed in a container, one face of a hydrophobic membrane is bent, the bottom face of the hydrophobic membrane slowly floats on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane; then, starting from the edge of the top surface of the hydrophobic membrane, dropwise adding an acyl chloride monomer solution by adopting a rubber head dropper; and finally, under the condition of normal temperature, carrying out reverse polymerization reaction on the acyl chloride monomer and the amine monomer on the bottom surface of the hydrophobic membrane, taking out, washing with water, and drying in a drying oven to obtain the hydrophobic membrane. The multifunctional membrane disclosed by the invention can be simultaneously applied to the fields of reverse osmosis, nanofiltration, pervaporation, membrane distillation and the like, the wetting resistance is improved by about 1-2 orders of magnitude, the treatment of low-surface-energy high-salinity wastewater can be greatly expanded, the steam flux and efficiency of membrane distillation can be improved, and the service life of membrane distillation can be greatly prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials and preparation thereof, and in particular to a multifunctional and multi-purpose separation membrane and a preparation method thereof. Background Art

[0002] The production and life of human society cannot be separated from the separation of substances. The separation energy consumption of chemical products accounts for 30% of the world's total energy consumption, and 70% of it is consumed by separation. In addition, with the growth of population, rapid development of industrialization and frequent extreme weather, the shortage of fresh water resources has become an urgent problem to be solved. In recent years, membrane separation technology has developed rapidly. Different types of membranes have been developed for different separation systems, such as reverse osmosis membranes, membrane distillation membranes, nanofiltration membranes, gas separation membranes, and permeation vaporization membranes.

[0003] For example, the prior art CN 108654407 A discloses a method and device for preparing a composite nanofiltration membrane, comprising the following steps:

[0004] Step 1: Select a hydrophobic support as the base membrane of the nanofiltration membrane; Step 2: Use a reverse interfacial polymerization method to place the selected base membrane in an oil phase monomer for infiltration; Step 3: Place the thoroughly infiltrated base membrane in an aqueous phase monomer for reaction; Step 4: Heat the reacted base membrane to finally prepare a composite nanofiltration membrane. This prior art uses a reverse interfacial polymerization method or an additive-assisted interfacial polymerization method to generate a polyamide active separation layer less than 50 nm on a hydrophobic PTFE / PVA nanofiber base membrane, and finally prepares a PTFE / PVA composite nanofiltration membrane.

[0005] CN114797504B discloses a method for preparing a sulfonated polyamide / hydrophobic polymer full heat exchange composite membrane, which comprises: covering a hydrophobic polymer membrane on the surface of a certain concentration of a polyamine aqueous solution, and injecting a certain concentration of a polyacyl chloride organic solution above the polymer membrane. The polyacyl chloride organic solution fully infiltrates the polymer membrane and diffuses to the other side of the polymer membrane, contacts with the polyamine aqueous solution and forms an immiscible interface layer, and the polyamine and the polyacyl chloride undergo interfacial polycondensation at the interface layer to generate a dense thin layer of aromatic cross-linked polyamide, thereby obtaining a polyamide-hydrophobic polymer composite membrane, which is applied to the field of heat exchange technology.

[0006] The membranes prepared in the above-mentioned prior art are all applied to specific fields and are difficult to be applied to different fields. The reason is that: the process technology in the prior art is difficult to prepare a membrane with a multifunctional layer. For example, in the preparation method of a sulfonated polyamide / hydrophobic polymer full heat exchange composite membrane disclosed in CN114797504B, a lower layer reaction container, an upper layer reaction container and a fixing clamp are used to fix the polyethylene porous membrane. Although the reverse polymerization method is adopted, bubbles will be generated during the addition of acyl chloride, and the bubbles are difficult to be discharged under the action of the reaction container, which will inevitably form bubbles with a certain amount at the interface, which will cause a large number of defects to be formed during film formation, resulting in low pressure of water passing through the membrane; in addition, most of the functional layers formed after hydrophilic modification are very dense, which seriously affects the transmission flux of water and leads to a decrease in separation performance. Therefore, the process of preparing the membrane is particularly critical for regulating the microscopic appearance of the membrane of the multifunctional layer and then regulating its separation performance. If the membrane process is improved so that the prepared membrane is suitable for different fields, the single technical problem of the application of the membrane in this field can be solved.

[0007] This shows that the prior art needs to be further improved. Summary of the invention

[0008] One of the purposes of the present invention is to provide a method for preparing a multifunctional membrane. The multifunctional membrane prepared by the method can be simultaneously applied to the fields of reverse osmosis, nanofiltration, osmotic vaporization and membrane distillation. Especially in the field of membrane distillation, the anti-wetting performance is improved by about 1 to 2 orders of magnitude, which can greatly expand the treatment of low surface energy, high salt and high organic solvent wastewater. At the same time, the dense layer has little effect on the permeation flux of the membrane, which can greatly increase and improve the vapor flux and efficiency of membrane distillation.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing a multifunctional membrane, wherein the multifunctional membrane is a membrane that can be simultaneously used in the fields of reverse osmosis, nanofiltration, pervaporation or membrane distillation;

[0011] The preparation method comprises:

[0012] Step 1, respectively preparing an amine monomer solution with a mass fraction of 0.1% to 5% and an acyl chloride monomer solution with a mass fraction of 0.01% to 0.5%;

[0013] Step 2: placing the prepared amine monomer solution in a container, bending one side of the hydrophobic membrane and allowing its bottom to slowly float on the surface of the amine monomer solution, wherein the floating environment provides an open environment system for the hydrophobic membrane; placing the acyl chloride monomer solution in a rubber-tipped dropper;

[0014] Step 3: Starting from the edge of the top surface of the hydrophobic membrane, add the acyl chloride monomer solution dropwise using a rubber-tipped dropper;

[0015] The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the acyl chloride monomer; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0016] Step 4: Under normal temperature conditions, the acyl chloride monomer and the amine monomer on the bottom surface of the hydrophobic membrane undergo reverse polymerization for 18 to 180 minutes, and then the membrane is taken out, washed with water, and placed in an oven for drying to obtain a multifunctional membrane.

[0017] In the above-mentioned method for preparing a multifunctional membrane, the acyl chloride monomer solution is a n-hexane solution of trimesoyl chloride or 2,6-naphthalene dicarboxylic acid chloride.

[0018] In the above-mentioned method for preparing a multifunctional membrane, the amine monomer solution is m-phenylenediamine, polyethyleneimine, piperazine or dopamine.

[0019] In the above-mentioned method for preparing a multifunctional membrane, the amine monomer solution is m-phenylenediamine.

[0020] In the above-mentioned method for preparing a multifunctional membrane, the hydrophobic membrane is a PVDF flat membrane, a hollow fiber membrane, a PTFE flat membrane, a hydrophobic PE membrane or a hydrophobic PP membrane.

[0021] In the above-mentioned method for preparing a multifunctional membrane, the hydrophobic membrane is a PTFE flat membrane.

[0022] In the above-mentioned method for preparing a multifunctional membrane, the average molecular weight of the polyethyleneimine is 400-200,000.

[0023] An additive is added to the amine monomer solution, wherein the additive is a mixed solution of triethylamine and camphorsulfonic acid.

[0024] The object of the present invention is to provide a multifunctional membrane prepared by the above-mentioned preparation method.

[0025] A multifunctional membrane is prepared by the above-mentioned preparation method. The multifunctional membrane has the properties of acid and alkali resistance, high temperature resistance and organic solvent resistance. The multifunctional membrane has a hydrophilic-hydrophobic Janus composite structure.

[0026] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0027] The present invention provides a method for preparing a multifunctional membrane. The hydrophobic membrane is directly floated on an amine monomer solution by utilizing its own properties, and then combined with a subsequent dropping method, a multifunctional membrane suitable for reverse osmosis, nanofiltration, pervaporation or membrane distillation can be prepared.

[0028] The multifunctional membrane prepared by the invention has one and only one side deformed to form a hydrophilic and hydrophobic Janus composite structure.

[0029] In the preparation method of the present invention, the reaction time is 18 to 170 minutes, which is far beyond the reaction time of 15 minutes in the prior art. As the reaction time is prolonged, the multifunctional membrane can react to form dense sponge-like sealing agents with semi-enclosed finger-like pores, which results in its multifunctional uses.

[0030] The present invention directly floats the hydrophobic film on the amine monomer solution. Different from the closed environment system formed by the reaction container and the fixing clip fixing method in the prior art, the present invention directly exposes the hydrophobic film to the environment, which is equivalent to forming an open environment system. The main purpose of the arrangement is to utilize the wetting properties of the hydrophobic film itself to form a solid-liquid interface on the water surface. When the acyl chloride monomer solution is dripped onto the hydrophobic film, due to the low surface energy in the organic phase, the droplets are quickly diffused around. In addition, because the hydrophobic membrane pores themselves have a large amount of air, if dripped at will, it will cause the air in the film to be unable to be discharged, so that a large amount of bubbles are formed at the interface, which leads to a large number of defects when film is formed. Therefore, the present invention is particularly in an open environment system, first dripping slowly drop by drop along the edge of the hydrophobic film, after a drop of wetting the film, dripping again along the wetting area, until the surface of the hydrophobic film is completely wetted and covered with a certain volume of acyl chloride monomers. In addition, most importantly, in an open environment system, when a large amount of hydrogen chloride by-product is produced, this gas can be discharged and consumed well, promoting the reaction to continue, thereby obtaining the multifunctional layer of the present invention.

[0031] The present invention can well control the morphological changes of the multifunctional separation membrane by regulating the reaction time and the concentration of the reaction monomers, and can form a morphology from a porous loose layer to a dense layer, and the thickness of the in-situ grown dense layer is controllable. Relevant experimental verification has found that the multifunctional membrane of the present invention can be applied to the fields of reverse osmosis, nanofiltration, pervaporation, membrane distillation, etc., especially in the field of membrane distillation, the anti-wetting performance is improved by about 1-2 orders of magnitude, and the treatment of low surface energy, high salt, and high organic solvent wastewater can be greatly expanded. At the same time, the dense layer has little effect on the permeation flux of the membrane, which can greatly improve and improve the vapor flux and efficiency of membrane distillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the accompanying drawings:

[0033] Figure 1 The original membrane (hydrophobic membrane), multifunctional membrane and cross-sectional SEM images of the present invention;

[0034] Figure 2 The SEM images of the original membrane and the multifunctional membrane after reaction for 15 min in Example 9;

[0035] Figure 3 The SEM images of the original membrane and the multifunctional membrane after reaction for 30 min in Example 10;

[0036] Figure 4 The SEM images of the original membrane and the multifunctional membrane after reaction for 90 min in Example 11;

[0037] Figure 5 This is the SEM image of the polyamide layer separation membrane with a defect-free dense layer prepared in Example 12. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0039] The technical solution of the present application is further described in detail below in conjunction with the accompanying drawings.

[0040] The raw materials described in the present invention can be purchased through commercial channels.

[0041] The hydrophobic membrane mentioned in the present invention can be a PVDF flat membrane, a hollow fiber membrane, a PTFE flat membrane, a hydrophobic PE membrane or a hydrophobic PP membrane. The present invention selects PVDF flat membrane, PTFE flat membrane and hollow fiber membrane as the main research.

[0042] Embodiment 1:

[0043] The hydrophobic membrane in this embodiment is a PTFE flat membrane.

[0044] A method for preparing a multifunctional membrane comprises the following steps:

[0045] Step 1, respectively prepare 2.5% by mass of m-phenylenediamine, 3% by mass of additive triethylamine, 4% by mass of camphorsulfonic acid solution and 0.15% by mass of trimesoyl chloride in n-hexane solution;

[0046] Step 2: Place the prepared m-phenylenediamine solution, triethylamine and camphorsulfonic acid solution in a container, bend one side of the hydrophobic membrane and make its bottom slowly float on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0047] Step 3: Starting from the edge of the top surface of the hydrophobic film, add a n-hexane solution of trimesoyl chloride dropwise using a rubber-tipped dropper;

[0048] The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of trimesoyl chloride; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0049] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and m-phenylenediamine are subjected to reverse polymerization reaction on the bottom surface of the hydrophobic membrane for 165 minutes, and the membrane is taken out, washed with water, and then placed in a 60-degree oven for drying to obtain a multifunctional membrane having a 150-400 nm dense polymer layer on the surface, such as Figure 1 shown.

[0050] The multifunctional membrane prepared in this example was tested, and the test results are shown in Table 1.

[0051] Table 1. Multifunctional membrane test results

[0052]

[0053]

[0054] Embodiment 2:

[0055] The difference from Example 1 is that:

[0056] In step 1, a 0.1% m-phenylenediamine solution and a 0.01% trimesoyl chloride n-hexane solution were prepared respectively. The experimental results are shown in Table 2.

[0057] Table 2. Multifunctional membrane test results

[0058] project Test medium Example 2 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 45% RO test 2000ppm sodium chloride Retention rate greater than 35% Pervaporation Ethanol: Water (8:2) Separation factor greater than 35 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.2%

[0059] Embodiment 3:

[0060] The difference from Example 1 is that:

[0061] In step 1, a 5% by mass m-phenylenediamine solution and a 0.5% by mass trimesoyl chloride n-hexane solution were prepared respectively. The experimental results are shown in Table 3.

[0062] Table 3. Multifunctional membrane test results

[0063] project Test medium Example 3 Acid resistance test hydrochloric acid Tolerance pH less than 3 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 80% RO test 2000ppm sodium chloride Retention rate greater than 75% Pervaporation Ethanol: Water (8:2) Separation factor greater than 25 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.6%

[0064] Embodiment 4:

[0065] The hydrophobic membrane in this embodiment is a PTFE flat membrane.

[0066] A method for preparing a multifunctional membrane comprises the following steps:

[0067] Step 1, respectively prepare a 3% by mass fraction of polyethyleneimine and a 0.25% by mass fraction of trimesoyl chloride in n-hexane solution;

[0068] Step 2: Place the prepared polyethyleneimine in a container, bend one side of the hydrophobic membrane and make its bottom slowly float on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0069] Step 3: Starting from the edge of the top surface of the hydrophobic film, add a n-hexane solution of trimesoyl chloride dropwise using a rubber-tipped dropper;

[0070] The dripping process is as follows: dripping one drop at a time along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dripping again along the wetted area, dripping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of 2,6-naphthalene dicarbonyl chloride; during the dripping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0071] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and polyethyleneimine were subjected to reverse polymerization reaction for 165 minutes on the bottom surface of the hydrophobic membrane, and the membrane was taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane. The experimental results are shown in Table 4.

[0072] Table 4. Multifunctional membrane test results

[0073] project Test medium Example 4 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 55% RO test 2000ppm sodium chloride Retention rate greater than 25% Pervaporation Ethanol: Water (8:2) Separation factor greater than 35 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99%

[0074] Embodiment 5:

[0075] The hydrophobic membrane in this embodiment is a PTFE flat membrane.

[0076] A method for preparing a multifunctional membrane comprises the following steps:

[0077] Step 1, respectively prepare n-hexane solutions of 3% piperazine and 0.25% trimesoyl chloride by mass fraction;

[0078] Step 2: Place the prepared piperazine in a container, bend one side of the hydrophobic membrane and make its bottom slowly float on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0079] Step 3: Starting from the edge of the top surface of the hydrophobic film, add a n-hexane solution of trimesoyl chloride dropwise using a rubber-tipped dropper;

[0080] The dripping process is as follows: dripping one drop at a time along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dripping again along the wetted area, dripping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of 2,6-naphthalene dicarbonyl chloride; during the dripping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0081] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and piperazine are subjected to reverse polymerization reaction for 165 minutes on the bottom surface of the hydrophobic membrane, and the membrane is taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane. The experimental results are shown in Table 5.

[0082] Table 5. Multifunctional membrane test results

[0083] project Test medium Example 5 Acid resistance test hydrochloric acid Tolerance pH less than 4 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 45% RO test 2000ppm sodium chloride Retention rate greater than 30% Pervaporation Ethanol: Water (8:2) Separation factor greater than 20 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99%

[0084] Embodiment 6:

[0085] The hydrophobic membrane in this embodiment is a PTFE flat membrane.

[0086] A method for preparing a multifunctional membrane comprises the following steps:

[0087] Step 1, respectively prepare 3% by mass of dopamine and 0.25% by mass of trimesoyl chloride in n-hexane solution;

[0088] Step 2: Place the prepared dopamine in a container, bend one side of the hydrophobic membrane and let its bottom slowly float on the surface of the amine monomer solution, the floating environment provides an open environment system for the hydrophobic membrane; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0089] Step 3: Starting from the edge of the top surface of the hydrophobic film, add a n-hexane solution of trimesoyl chloride dropwise using a rubber-tipped dropper;

[0090] The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of trimesoyl chloride; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0091] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and dopamine were subjected to reverse polymerization reaction on the bottom surface of the hydrophobic membrane for 165 minutes, and the membrane was taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane. The experimental results are shown in Table 6.

[0092] Table 6. Multifunctional membrane test results

[0093] project Test medium Example 6 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 75% RO test 2000ppm sodium chloride Retention rate greater than 55% Pervaporation Ethanol: Water (8:2) Separation factor greater than 30 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.5%

[0094] Embodiment 7:

[0095] The difference from Example 1 is that the hydrophobic membrane in this example is a PVDF flat membrane. The experimental results are shown in Table 7.

[0096] Table 7. Multifunctional membrane test results

[0097] project Test medium Example 7 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 70% RO test 2000ppm sodium chloride Retention rate greater than 60% Pervaporation Ethanol: Water (8:2) Separation factor greater than 28 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.3%

[0098] Embodiment 8:

[0099] The difference from Example 1 is that the hydrophobic membrane in this example is a hollow fiber membrane. The experimental results are shown in Table 8.

[0100] Table 8. Multifunctional membrane test results

[0101] project Test medium Example 8 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 68% RO test 2000ppm sodium chloride Retention rate greater than 57% Pervaporation Ethanol: Water (8:2) Separation factor greater than 25 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.5%

[0102] Embodiment 9:

[0103] The difference from Example 1 is that:

[0104] In step 4, under room temperature conditions, the n-hexane solution of trimesoyl chloride and m-phenylenediamine reacted with each other on the bottom surface of the hydrophobic membrane for 15 minutes. The SEM image of the multifunctional membrane after 15 minutes of reaction is shown in FIG. Figure 2 shown.

[0105] Embodiment 10:

[0106] The difference from Example 1 is that:

[0107] In step 4, at room temperature, a n-hexane solution of trimesoyl chloride and m-phenylenediamine reacted with each other on the bottom surface of the hydrophobic membrane for 30 minutes. The SEM image of the multifunctional membrane after the reaction for 30 minutes is shown in FIG. Figure 3 shown.

[0108] Embodiment 11:

[0109] The difference from Example 1 is that:

[0110] In step 4, under normal temperature conditions, a n-hexane solution of trimesoyl chloride and m-phenylenediamine reacted with each other on the bottom surface of the hydrophobic membrane for 90 minutes. The SEM image of the multifunctional membrane after 90 minutes of reaction is shown in FIG. Figure 4 shown.

[0111] Embodiment 12:

[0112] The hydrophobic membrane in this embodiment is a PTFE flat membrane.

[0113] A method for preparing a polyamide layer separation membrane without a defective dense layer comprises the following steps:

[0114] Step 1, respectively prepare 3% by mass of m-phenylenediamine containing 0.2-8% of anionic and cationic resins, 2% by mass of triethylamine as an additive, 4% by mass of camphorsulfonic acid solution and 0.15% by mass of trimesoyl chloride in n-hexane solution;

[0115] Step 2: Place the prepared m-phenylenediamine solution, triethylamine and camphorsulfonic acid solution in a container, bend one side of the hydrophobic membrane and make its bottom slowly float on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0116] Step 3: Starting from the edge of the top surface of the hydrophobic film, use a rubber-tipped dropper to drop a n-hexane solution of trimesoyl chloride;

[0117] The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of trimesoyl chloride; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0118] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and m-phenylenediamine are subjected to reverse polymerization reaction on the bottom surface of the hydrophobic membrane for 30 minutes. The membrane is taken out, washed with water, and then placed in a 60-degree oven for drying.

[0119] Step 5. Carry out secondary interfacial polymerization at room temperature. Clamp the dried membrane with a membrane frame, pour the m-phenylenediamine solution with resin into the membrane pool for a period of time, then pour out the amine solution in the membrane so that there is no visible water, and then pour in the n-hexane solution of trimesoyl chloride to make it react. Take it out, wash it with water, and then place it in a 60-degree oven for drying.

[0120] The polyamide layer separation membrane without defective dense layer is obtained, and the surface of the membrane has a layer of dense polymer layer with wrinkles, such as Figure 5 shown.

[0121] The polyamide layer separation membrane with no defective dense layer prepared in this example was tested, and the test results are shown in Table 9.

[0122] Table 9. Multifunctional membrane test results

[0123] project Test medium Example 1 Acid resistance test hydrochloric acid Tolerance pH less than 2 Alkali resistance test Sodium hydroxide Tolerance pH greater than 10 Nanofiltration test 2000ppm sodium sulfate Retention rate greater than 90% RO test 2000ppm sodium chloride Retention rate greater than 80% Pervaporation Ethanol: Water (8:2) Separation factor greater than 30 Membrane distillation Test 3.5% Sodium Chloride Retention rate greater than 99.5%

[0124] Comparative Example 1:

[0125] The hydrophobic membrane in this comparative example is a PTFE flat membrane.

[0126] A method for preparing a multifunctional membrane comprises the following steps:

[0127] Step 1, respectively prepare a 3% by mass solution of m-phenylenediamine and a 0.25% by mass solution of trimesoyl chloride in n-hexane;

[0128] Step 2: Place the prepared m-phenylenediamine solution in a container, bend one side of the hydrophobic membrane and allow its bottom to slowly float on the surface of the amine monomer solution, and the floating environment provides an open environment system for the hydrophobic membrane;

[0129] Step 3: Place a n-hexane solution of trimesoyl chloride in a beaker, and pour the n-hexane solution of trimesoyl chloride onto the hydrophobic membrane to completely wet the hydrophobic membrane;

[0130] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and m-phenylenediamine were subjected to reverse polymerization reaction on the bottom surface of the hydrophobic membrane for 15 minutes, and the membrane was taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane. The experimental results are shown in Table 10.

[0131] Table 10

[0132]

[0133] Comparative Example 2:

[0134] The hydrophobic membrane in this comparative example is a PTFE flat membrane.

[0135] A method for preparing a multifunctional membrane comprises the following steps:

[0136] Step 1, respectively prepare a 3% by mass solution of m-phenylenediamine and a 0.25% by mass solution of trimesoyl chloride in n-hexane;

[0137] Step 2: Place the prepared m-phenylenediamine solution in a container, use a reactor to fix the hydrophobic membrane, and make the bottom surface of the hydrophobic membrane just contact the m-phenylenediamine solution; place the n-hexane solution of trimesoyl chloride in a rubber-tipped dropper;

[0138] Step 3: Starting from the edge of the top surface of the hydrophobic film, add a n-hexane solution of trimesoyl chloride dropwise using a rubber-tipped dropper;

[0139] The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when one drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the n-hexane solution of trimesoyl chloride; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system;

[0140] Step 4: Under normal temperature conditions, a n-hexane solution of trimesoyl chloride and m-phenylenediamine were subjected to reverse polymerization reaction on the bottom surface of the hydrophobic membrane for 15 minutes, and the membrane was taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane. The experimental results are shown in Table 11.

[0141] Table 11

[0142]

[0143] Under the guidance of the above embodiments, those skilled in the art can also use other hydrophobic membranes such as hydrophobic PE membrane or hydrophobic PP membrane to prepare a multifunctional membrane.

[0144] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection claimed in the present application.

Claims

1. A method for preparing a multifunctional membrane, characterized in that: The multifunctional membrane refers to a membrane that can be simultaneously used in the fields of reverse osmosis, nanofiltration, pervaporation or membrane distillation; The preparation method comprises: Step 1, respectively preparing an amine monomer solution with a mass fraction of 0.1% to 5% and an acyl chloride monomer solution with a mass fraction of 0.01% to 0.5%; Step 2: placing the prepared amine monomer solution in a container, bending one side of the hydrophobic membrane and allowing its bottom to slowly float on the surface of the amine monomer solution, wherein the floating environment provides an open environment system for the hydrophobic membrane; placing the acyl chloride monomer solution in a rubber-tipped dropper; Step 3: Starting from the edge of the top surface of the hydrophobic membrane, add the acyl chloride monomer solution dropwise using a rubber-tipped dropper; The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when the first drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the acyl chloride monomer; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system; Step 4: Under normal temperature conditions, the acyl chloride monomer and the amine monomer on the bottom surface of the hydrophobic membrane undergo a reverse polymerization reaction for 18 to 180 minutes. The membrane is taken out, washed with water, and then placed in an oven for drying to obtain a multifunctional membrane.

2. The method for preparing a multifunctional membrane according to claim 1, characterized in that: The acyl chloride monomer solution is a n-hexane solution of trimesoyl chloride or 2,6-naphthalene dicarboxylic acid chloride.

3. The method for preparing a multifunctional membrane according to claim 1, characterized in that: The amine monomer solution is m-phenylenediamine, polyethyleneimine, piperazine or dopamine.

4. The method for preparing a multifunctional membrane according to claim 3, characterized in that: The amine monomer solution is m-phenylenediamine.

5. The method for preparing a multifunctional membrane according to claim 1, characterized in that: The hydrophobic membrane is a PVDF flat membrane, a PTFE flat membrane, a hydrophobic hollow fiber membrane, a hydrophobic PE membrane or a hydrophobic PP membrane.

6. The method for preparing a multifunctional membrane according to claim 5, characterized in that: The hydrophobic membrane is a PTFE flat membrane; the average molecular weight of the polyethyleneimine is 400-200000.

7. The method for preparing a multifunctional membrane according to claim 1, characterized in that: In step 1, an additive is added to the amine monomer solution, wherein the additive is a mixed solution of triethylamine and camphorsulfonic acid.

8. A multifunctional membrane, characterized in that It is prepared by the preparation method described in any one of claims 1 to 7. The multifunctional membrane has acid and alkali resistance, high temperature resistance and organic solvent resistance. The multifunctional membrane has a hydrophilic-hydrophobic Janus composite structure.

9. A method for preparing a polyamide layer separation membrane having a defect-free dense layer, characterized in that: The polyamide layer separation membrane without defective dense layer refers to a membrane that can be simultaneously applied to the fields of reverse osmosis, nanofiltration, pervaporation or membrane distillation; The preparation method comprises: Step 1, respectively preparing an amine monomer solution with a mass fraction of 0.1% to 5% and an acyl chloride monomer solution with a mass fraction of 0.01% to 0.5%; Step 2: placing the prepared amine monomer solution in a container, bending one side of the hydrophobic membrane and allowing its bottom to slowly float on the surface of the amine monomer solution, wherein the floating environment provides an open environment system for the hydrophobic membrane; placing the acyl chloride monomer solution in a rubber-tipped dropper; Step 3: Starting from the edge of the top surface of the hydrophobic membrane, add the acyl chloride monomer solution dropwise using a rubber-tipped dropper; The dropping process is as follows: dropping drop by drop along the edge of the top surface of the hydrophobic membrane, and when the first drop wets the hydrophobic membrane, dropping again along the wetted area, and dropping from the outside to the inside in sequence until the surface of the hydrophobic membrane is completely wetted and covered with a certain volume of the acyl chloride monomer; during the dropping process, the hydrophobic membrane can remove the generated byproduct gas in an open environment system; Step 4: Under normal temperature conditions, the acyl chloride monomer and the amine monomer react with each other on the bottom surface of the hydrophobic membrane for 18 to 180 minutes, and then the membrane is taken out, washed with water, and placed in an oven for drying to complete an interfacial polymerization. Step 5, prepare a certain concentration of amine monomer solution with anionic and cationic resin and acyl chloride monomer solution; fix the membrane dried in step 4, and then pour the amine monomer solution with anionic and cationic resin or quaternary ammonium and sulfonated polymers on the dried membrane, react for a period of time, and then blow dry; then pour the acyl chloride monomer solution on the dried membrane, react for a period of time; finally, dry in an oven to complete the secondary interfacial polymerization, and obtain a polyamide layer separation membrane with a defect-free dense layer.

10. The method for preparing a polyamide layer separation membrane having a defect-free dense layer according to claim 9, characterized in that: The anionic and cationic resins are: polystyrene resins and functionalized acrylic resins with sulfonic acid groups or quaternary ammonium groups; quaternized and sulfonated polymers are: perfluorosulfonic acid membranes, quaternized polystyrene, sulfonated polystyrene, sulfonated polyetheretherketone, sulfonated polyarylethersulfone and quaternized chitosan membranes.

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