Recovery method of waste water treatment membrane

Abstract

The invention relates to a recovery method of a waste water treatment membrane, which comprises the following steps: a) recovering polysulfone, polyacrylonitrile or polyvinylidene fluoride layers of the waste water treatment membrane in a solvent dissolving manner to respectively obtain a membrane casting solution and undissolved polyester; b) recovering the undissolved polyester in a manner of catalyzing ethylene glycol alcoholysis by an oxygen-enriched defect molybdenum magnesium oxide nanosheet, preparing regenerated polyester from the obtained polymeric monomer in a polycondensation manner, and then preparing a new substrate film in a spinning manner; c) sequentially carrying out solution coating, non-solvent phase conversion, curing and cleaning on the new substrate membrane and the membrane casting solution to obtain a micro-filtration membrane or an ultra-filtration membrane; and d) sequentially carrying out monomer impregnation, interfacial polymerization, washing and curing on the microfiltration membrane or the ultrafiltration membrane to obtain the nanofiltration membrane or the reverse osmosis membrane. The recycling method provided by the invention can be used for efficiently recycling polymer water treatment membranes for microfiltration, ultrafiltration, nanofiltration, reverse osmosis and the like, and has the advantages of wide application range, capability of realizing closed-loop recycling, greenness, sustainability and the like.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment membranes, and more specifically to a method for recovering waste water treatment membranes. Background Art

[0002] Membrane technology is an important development direction of water treatment technology in the future. It has been widely used and rapidly growing in the world in recent years. Water treatment membrane technology uses artificially synthesized membrane materials to remove pollutants in water by physical interception, thereby achieving water purification. The pollutants removed by membrane technology mainly include inorganic ions, organic matter and microorganisms. These pollutants are trapped on the membrane surface or deposited in the membrane pores, forming inorganic pollution, organic pollution and biological pollution, which eventually causes the membrane pore size to become smaller or the membrane to become clogged. After the clogged membrane components are replaced, most of them are discarded in the environment, causing environmental pollution problems such as microplastics and the release of small molecular organic matter.

[0003] Membrane materials are the core of this technology. The main components of polymer membranes are high molecular materials such as polyethylene terephthalate (PET), polysulfone (PSF), and polyacrylonitrile (PAN). At present, most of the research on the recycling of waste membrane materials focuses on physical recycling (flushing, oxidation), which requires the use of a large amount of chemical reagents. However, when the membrane is severely contaminated or damaged, the purpose of recycling cannot be achieved, and the problem of waste treatment and disposal cannot be fundamentally solved. Taking the membrane upgrading cycle process as an example, this process is based on the "cleaning-healing-repreparation" strategy. The contamination layer on the surface of the ultrafiltration membrane is oxidized and removed by using sodium hypochlorite-oxalic acid solution, and the cleaned membrane is further used for interfacial polymerization to prepare nanofiltration membrane materials. Although it is beneficial to upgrade the nanofiltration performance of the circulating membrane, the complex operation process, the large amount of chemical reagents used, and the serious accumulation of membrane pollutants after multiple cycles have hindered the practical application of the upgrading cycle strategy to a certain extent. Therefore, in order to achieve efficient resource recovery of waste membranes, it is necessary to try to develop new methods for recycling waste membranes.

[0004] The recycling process of discarded membranes is highly complex due to the complex composition of the waste membrane components and surface membrane pollutants. On the one hand, the membrane is composed of a variety of polymers such as PET, PA, PSF, etc. The PA content is very low and can be ignored for recycling. However, it is crucial to achieve high selectivity and high purity recycling of polymers such as PET and PSF. On the other hand, there are complex pollutants on the membrane surface, such as inorganic salts, extracellular polymers and humic acid. It is also very important to achieve effective separation of membrane surface pollutants and membrane components during the recycling process. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for recycling waste water treatment membranes, which adopts a graded recovery method of solvent dissolution-catalytic depolymerization to solve the problems existing in the current physical recovery process of water treatment membranes, such as the large-scale use of chemical reagents, serious membrane pollution or membrane damage that cannot be recycled.

[0006] The present invention provides a method for recovering a waste water treatment membrane, comprising the following steps:

[0007] a) recovering the polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by dissolving it with a solvent to obtain a casting solution and undissolved polyester, respectively;

[0008] b) recovering the undissolved polyester by alcoholysis of ethylene glycol catalyzed by oxygen-defective molybdenum-magnesium oxide nanosheets, regenerating the obtained polymerized monomers by polycondensation, and then preparing a new base film by spinning;

[0009] c) subjecting the new base membrane and the casting solution obtained in step a) to solution coating, non-solvent phase conversion, solidification and cleaning in sequence to obtain a microfiltration membrane or an ultrafiltration membrane;

[0010] d) The microfiltration membrane or ultrafiltration membrane obtained in step c) is sequentially subjected to monomer impregnation, interfacial polymerization, washing and curing to obtain a nanofiltration membrane or a reverse osmosis membrane.

[0011] Preferably, the solvent in step a) is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0012] Preferably, the mass ratio of the solvent to the waste water treatment membrane in step a) is (0.8-4):1.

[0013] Preferably, the calcination temperature of the oxygen-defective molybdenum magnesium oxide nanosheets in step b) is 200°C to 500°C.

[0014] Preferably, the amount of the oxygen-defective molybdenum-magnesium oxide nanosheets used in step b) is 0.05wt% to 4wt% of the mass of the waste water treatment membrane.

[0015] Preferably, the mass ratio of ethylene glycol to waste water treatment membrane in step b) is (1-8):1.

[0016] Preferably, the alcoholysis temperature in step b) is 140° C. to 240° C., and the time is 5 min to 360 min.

[0017] Preferably, the concentration of the casting solution in step c) is 10 wt % to 30 wt %.

[0018] Preferably, during the interfacial polymerization in step d), the aqueous phase monomer is m-phenylenediamine; and the concentration of m-phenylenediamine is 1 wt % to 11 wt %.

[0019] Preferably, during the interfacial polymerization in step d), the organic phase monomer is trimesoyl chloride; and the concentration of the trimesoyl chloride is 0.05 wt % to 1.5 wt %.

[0020] The invention provides a method for recovering a waste water treatment membrane, comprising the following steps: a) recovering a polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by solvent dissolution to obtain a casting liquid and undissolved polyester respectively; b) recovering the undissolved polyester by catalyzing ethylene glycol alcoholysis with oxygen-rich defective molybdenum magnesium oxide nanosheets, regenerating polyester by polycondensation of the obtained polymerization monomer, and then preparing a new base membrane by spinning; c) subjecting the new base membrane and the casting liquid obtained in step a) to solution coating, non-solvent phase conversion, solidification and washing in sequence to obtain a microfiltration membrane or an ultrafiltration membrane; d) subjecting the microfiltration membrane or the ultrafiltration membrane obtained in step c) to monomer impregnation, interfacial polymerization, washing and solidification in sequence to obtain a nanofiltration membrane or a reverse osmosis membrane. Compared with the prior art, the present invention provides a dissolution-depolymerization cascade recovery method for waste water treatment membrane materials. It adopts specific process steps, including solvent extraction, depolymerization and repolymerization, non-solvent induced phase separation, interfacial polymerization, etc., to achieve overall good interaction, and can efficiently recover polymer water treatment membranes such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis. It solves the problems existing in the current physical recovery process of water treatment membranes, such as the large-scale use of chemical reagents, serious membrane pollution or membrane damage that cannot be recovered, and can prepare nanofiltration membranes or reverse osmosis membranes with excellent performance, which have the advantages of wide application range, closed-loop recovery, green sustainability, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for recovering a waste water treatment membrane provided by the present invention;

[0022] Figure 2 This is a transmission electron microscope image of defect-rich molybdenum magnesium oxide nanosheets in an embodiment of the present invention;

[0023] Figure 3 is the nuclear magnetic resonance result of BHET in the embodiment of the present invention;

[0024] Figure 4 Detailed illustration of a discarded reverse osmosis membrane (a) and a recovered reverse osmosis membrane (b) in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0026] The present invention provides a method for recovering a waste water treatment membrane, comprising the following steps:

[0027] a) recovering the polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by dissolving it with a solvent to obtain a casting solution and undissolved polyester, respectively;

[0028] b) recovering the undissolved polyester by alcoholysis of ethylene glycol catalyzed by oxygen-defective molybdenum-magnesium oxide nanosheets, regenerating the obtained polymerized monomers by polycondensation, and then preparing a new base film by spinning;

[0029] c) subjecting the new base membrane and the casting solution obtained in step a) to solution coating, non-solvent phase conversion, solidification and cleaning in sequence to obtain a microfiltration membrane or an ultrafiltration membrane;

[0030] d) The microfiltration membrane or ultrafiltration membrane obtained in step c) is sequentially subjected to monomer impregnation, interfacial polymerization, washing and curing to obtain a nanofiltration membrane or a reverse osmosis membrane.

[0031] See also Figure 1 As shown, Figure 1A flow chart of a method for recovering a waste water treatment membrane provided by the present invention; the recovery method mainly comprises the following four steps: (1) solvent extraction: the polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste membrane material is completely recovered by a solvent dissolution method to obtain a casting solution for preparing an ultrafiltration membrane and undissolved polyester; wherein the solvents that can be used to recover the polysulfone, polyacrylonitrile or polyvinylidene fluoride include: dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide. (2) Depolymerization and repolymerization: The undissolved polyester is recovered by alcoholysis of ethylene glycol catalyzed by oxygen-defective molybdenum magnesium oxide nanosheets; this process obtains the polymer monomer of polyester, bis(hydroxyethyl) terephthalate (BHET). Under the preferred reaction conditions, the polyester is completely converted, and the BHET yield is 90% to 94%; the membrane pollutants and oligomers produced by depolymerization are separated and removed during the crystallization and recrystallization of BHET, and the purity of BHET is >99%; the recovered BHET is re-prepared into regenerated polyester by polycondensation, and then a new base membrane is prepared by spinning. (3) Non-solvent induced phase separation: The base membrane obtained in step (2) and the polysulfone casting solution obtained in step (1) are used to prepare a microfiltration membrane or an ultrafiltration membrane through solution coating, non-solvent induced phase conversion, curing and washing. (4) Interfacial polymerization: The microfiltration membrane or ultrafiltration membrane obtained in step (3) is used to prepare a nanofiltration membrane or a reverse osmosis membrane with excellent performance through monomer impregnation, interfacial polymerization, washing and curing. This recycling method is a dissolution-depolymerization cascade recycling method for waste water treatment membrane materials. It can efficiently recycle polymer water treatment membranes such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis. It has the advantages of a wide range of applications, closed-loop recycling, and green sustainability.

[0032] The present invention firstly recovers the polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by dissolving it with a solvent, and obtains a casting solution and undissolved polyester respectively.

[0033] The present invention has no special restrictions on the type and source of the waste water treatment membrane, and any waste water treatment membrane materials to be treated that are well known to those skilled in the art can be used.

[0034] In the present invention, the solvent, i.e., the solvent used to dissolve and recover polysulfone, polyacrylonitrile or polyvinylidene fluoride, is preferably selected from one or more of dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide, more preferably dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide, and even more preferably N,N-dimethylformamide. The present invention has no particular restrictions on the source of the solvent, and commercially available products well known to those skilled in the art can be used.

[0035] In the present invention, the mass ratio of the solvent to the waste water treatment membrane is preferably (0.8-4):1, more preferably 2:1.

[0036] In the present invention, the solvent dissolution process is preferably carried out under stirring conditions, the temperature is preferably 20° C. to 30° C., and the time is preferably 1 min to 10 min.

[0037] After obtaining the undissolved polyester, the present invention recovers the undissolved polyester by catalyzing the alcoholysis of ethylene glycol using oxygen-defective molybdenum-magnesium oxide nanosheets, and the obtained polymerized monomer is re-prepared into regenerated polyester by polycondensation, and then a new base film is prepared by spinning.

[0038] The present invention uses oxygen-defective molybdenum-magnesium oxide nanosheets as catalysts to carry out the above-mentioned depolymerization and repolymerization process; the oxygen-defective molybdenum-magnesium oxide nanosheets are prepared using a preparation method well known to those skilled in the art.

[0039] In the present invention, the calcination temperature of the oxygen-rich molybdenum-magnesium oxide nanosheets is preferably 200°C to 500°C, more preferably 400°C.

[0040] In the present invention, the amount of the oxygen-defective molybdenum-magnesium oxide nanosheets is preferably 0.05wt% to 4wt% of the mass of the waste water treatment membrane, and more preferably 0.8wt% to 4wt%.

[0041] The present invention has no particular limitation on the source of the ethylene glycol, and commercially available products known to those skilled in the art may be used.

[0042] In the present invention, the mass ratio of ethylene glycol to waste water treatment membrane is preferably (1-8):1, and more preferably (3-5):1.

[0043] In the present invention, the alcoholysis temperature is preferably 140°C to 240°C, more preferably 150°C to 180°C, and even more preferably 175°C; the alcoholysis time is preferably 5min to 360min, more preferably 20min to 120min, and even more preferably 40min.

[0044] After obtaining the new base membrane, the present invention sequentially subjects the new base membrane and the casting solution obtained in step a) to solution coating, non-solvent phase conversion, solidification and washing to obtain a microfiltration membrane or an ultrafiltration membrane.

[0045] In the present invention, the concentration of the casting solution is preferably 10 wt% to 30 wt%.

[0046] The present invention has no special restrictions on the process and condition parameters of solution coating, non-solvent phase conversion, solidification and cleaning, and the process steps, conditions and parameters for preparing microfiltration membranes or ultrafiltration membranes well known to those skilled in the art can be adopted.

[0047] Finally, the present invention sequentially performs monomer impregnation, interface polymerization, washing and solidification on the obtained microfiltration membrane or ultrafiltration membrane to obtain a nanofiltration membrane or a reverse osmosis membrane.

[0048] In the present invention, during the interfacial polymerization, the aqueous phase monomer is preferably meta-phenylenediamine (MPD); the concentration of the meta-phenylenediamine is preferably 1 wt % to 11 wt %, more preferably 10%.

[0049] In the present invention, during the interfacial polymerization, the organic phase monomer is preferably trimesoyl chloride (TMC); the concentration of the trimesoyl chloride is preferably 0.05 wt % to 1.5 wt %, more preferably 1 wt %.

[0050] The present invention has no special restriction on the sources of the m-phenylenediamine and trimesoyl chloride, and commercially available products known to those skilled in the art can be used.

[0051] The present invention has no special restrictions on the process and condition parameters of the monomer impregnation, interfacial polymerization, washing and curing, and the process steps, conditions and parameters for preparing nanofiltration membranes or reverse osmosis membranes well known to those skilled in the art can be adopted.

[0052] The present invention provides a dissolution-depolymerization cascade recovery method for waste water treatment membrane materials. PSF can be specifically dissolved and recovered by green organic solvents such as N,N-dimethylformamide, while PET chemical alcoholysis recovery can directly convert the waste basement membrane into monomer molecules. The monomer molecules separate the pollutants on the membrane surface through the crystallization and recrystallization process and are used to re-prepare membrane materials. The present invention adopts the above-mentioned solvent dissolution-catalytic depolymerization waste water treatment membrane graded recovery method, which can achieve efficient and low-cost closed-loop recovery of various waste water treatment membrane materials, and prepare regenerated water treatment membranes from waste water treatment membranes. The above-mentioned method recovers polysulfone, polyacrylonitrile, polyvinylidene fluoride and bis(hydroxyethyl) terephthalate monomers from waste water treatment membranes, all of which are within the protection scope of the present invention.

[0053] The invention provides a method for recovering a waste water treatment membrane, comprising the following steps: a) recovering a polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by solvent dissolution to obtain a casting liquid and undissolved polyester respectively; b) recovering the undissolved polyester by catalyzing ethylene glycol alcoholysis with oxygen-rich defective molybdenum magnesium oxide nanosheets, regenerating polyester by polycondensation of the obtained polymerization monomer, and then preparing a new base membrane by spinning; c) subjecting the new base membrane and the casting liquid obtained in step a) to solution coating, non-solvent phase conversion, solidification and washing in sequence to obtain a microfiltration membrane or an ultrafiltration membrane; d) subjecting the microfiltration membrane or the ultrafiltration membrane obtained in step c) to monomer impregnation, interfacial polymerization, washing and solidification in sequence to obtain a nanofiltration membrane or a reverse osmosis membrane. Compared with the prior art, the present invention provides a dissolution-depolymerization cascade recovery method for waste water treatment membrane materials. It adopts specific process steps, including solvent extraction, depolymerization and repolymerization, non-solvent induced phase separation, interfacial polymerization, etc., to achieve overall good interaction, and can efficiently recover polymer water treatment membranes such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis. It solves the problems existing in the current physical recovery process of water treatment membranes, such as the large-scale use of chemical reagents, serious membrane pollution or membrane damage that cannot be recovered, and can prepare nanofiltration membranes or reverse osmosis membranes with excellent performance, which have the advantages of wide application range, closed-loop recovery, green sustainability, etc.

[0054] In order to further illustrate the present invention, the following examples are used to explain it in detail. The raw materials used in the following examples of the present invention are all commercially available; the conversion rate of polyester in the water treatment membrane and the yield of BHET are as shown in the public

[0055] Formula 1 and Formula 2:

[0056]

[0057] The sodium chloride rejection rate and water flux of the reverse osmosis membrane are shown in Formula 3 and Formula 4:

[0058]

[0059] 1. Synthesis method of defect-rich molybdenum magnesium oxide nanosheets:

[0060] First, add 50 mL of ultrapure water to a 250 mL beaker, then add 4.066 g of magnesium chloride and 0.420 g of L-asparagine and stir for 10 min; then add 1.581 g of ammonium bicarbonate to 50 mL of ultrapure water and mix well, add to the above mixed solution and continue stirring for 1 h to form a reaction system.

[0061] The reaction system was heated to 90°C and magnetically stirred for 6 hours. After the reaction was completed, water and ethanol were used for centrifugation three times, and the collected precipitates were transferred to a vacuum drying oven at 70°C for drying overnight. The collected precipitates were evenly spread on a magnetic boat, and then transferred to a muffle furnace. The calcination atmosphere was air, and the temperature was raised to 350°C at a rate of 2°C / min and kept warm for 2 hours to finally obtain defect-rich molybdenum magnesium oxide nanosheets, such as Figure 2 shown.

[0062] 2. Impact of different solvents dissolving waste water treatment membranes:

[0063] Examples 1 to 8

[0064] First, the waste reverse osmosis membrane from the desalination plant was dried (the membrane model was BW30, the main components were PET (79%) and PSF (20%)), and then immersed in one of the solvents or several mixed solvents of N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dichloromethane (DCM), tetrahydrofuran (THF), N-methylpyrrolidone (NMP), ethanol (EtOH), methanol (MeOH), and n-hexane (n-Hexane), and stirred at room temperature for 5 minutes. After the reaction was completed, the undissolved membrane was taken out and placed in a blast drying oven at 60°C for overnight drying. The dissolution rate of the waste water treatment membrane polysulfone dissolved in different solvents was weighed and calculated. The detailed data is shown in Table 1. And the undissolved membrane was used to carry out Examples 9 to 27.

[0065] Table 1 Effect of different solvents on dissolving waste water treatment membrane

[0066] Example Solvents Dissolution rate of polysulfone in waste water treatment membrane / % 1 DMF 100 2 DMSO 100 3 DCM 100 4 THF 100 5 NMP 100 6 EtOH <1 7 MeOH <1 8 n-Hexane <1

[0067] 3. Effect of Calcination Temperature of Defective Molybdenum-Magnesium Oxide on Catalytic Alcoholysis of Ethylene Glycol in Waste Water Treatment Membranes:

[0068] Examples 9 to 12

[0069] The molybdenum-magnesium precursor was placed in a muffle furnace, and different calcination temperatures (200°C, 300°C, 400°C, and 500°C) were set. After the calcination, the molybdenum-magnesium oxide was 0.8wt% of the mass of the waste water treatment membrane, and the mass ratio of ethylene glycol to the membrane was 4:1. They were added to a single-necked flask in sequence, heated to 175°C, reacted for 40 minutes, and magnetically stirred. After the reaction was completed, 400mL of ultrapure water was added and stirred vigorously to prevent the crystallization of the monomer. Then, the filtered insoluble polyester and oligomers and the filtrate were collected, and the filtrate was fixed to 1L, and an appropriate amount of solution was taken for standby use. After the reaction was completed, the product BHET was analyzed by HPLC, and the purity of the BHET product was identified as follows: Figure 3The calculated BHET yield and polyester conversion rate are shown in Table 2. The effect of calcination temperature of defect-rich molybdenum-magnesium oxide on catalytic glycolization of waste water treatment membrane is shown in Table 2, No. 9 to 12.

[0070] Table 2 Effect of calcination temperature on catalytic glycol hydrolysis of waste water treatment membrane

[0071] Example Catalyst calcination temperature / ℃ Water treatment membrane polyester conversion rate / % BHET yield / % 9 200 100 85.9 10 300 100 86.7 11 400 100 93.4 12 500 100 92.6

[0072] 4. Effect of the dosage of defect-rich molybdenum-magnesium oxide nanosheets on the glycol hydrolysis of waste water treatment membranes:

[0073] Embodiments 13 to 17

[0074] The waste water treatment membrane, 0.08-4wt% of defect-rich molybdenum-magnesium oxide and ethylene glycol in a mass ratio of 4:1 were put into a single-necked flask, heated to 175°C, and reacted for 40 minutes. After the reaction, the product BHET was analyzed by HPLC, and the BHET yield and polyester conversion rate were calculated, as shown in Table 3, No. 13-17.

[0075] Table 3 Effect of the dosage of defect-rich molybdenum-magnesium oxide on the catalytic alcoholysis of ethylene glycol in waste water treatment membranes

[0076] Example Catalyst / wt% Water treatment membrane polyester conversion rate / % BHET yield / % 13 0.08 63.2 40.6 14 0.16 82.6 60.3 15 0.8 100 93.4 16 1.6 100 92.6 17 4 100 88.3

[0077] 5. Effect of reaction temperature on ethylene glycol alcoholysis of waste water treatment membrane catalyzed by defect-rich molybdenum-magnesium oxides:

[0078] Examples 18 to 22

[0079] The waste water treatment membrane, 0.8 wt% of defect-rich molybdenum magnesium oxide and ethylene glycol in a mass ratio of 4:1 were put into a single-necked flask, heated to 150°C-180°C, and reacted for 40 minutes. After the reaction, the product BHET was analyzed by HPLC, and the yield of BHET and the conversion rate of polyester were calculated, as shown in Table 4, No. 18-22.

[0080] Table 4 Effect of reaction temperature on ethylene glycol alcoholysis of waste water treatment membrane catalyzed by defect-rich molybdenum-magnesium oxides

[0081]

[0082]

[0083] 6. Effect of reaction time on glycol hydrolysis of waste water treatment membrane rich in defective molybdenum and magnesium oxides:

[0084] Embodiments 23 to 27

[0085] The waste water treatment membrane, 0.8wt% of defective molybdenum and magnesium oxide and ethylene glycol with a mass ratio of 4:1 were put into a single-necked flask, heated to 175°C, and reacted for 20min to 120min; after the reaction, the product BHET was analyzed by HPLC, and the yield of BHET and the conversion rate of polyester were calculated. The effect of reaction time on the BHET yield and polyester conversion rate of ethylene glycol alcoholysis of defective molybdenum and magnesium oxide waste water treatment membrane is shown in Table 5, No. 23 to 27.

[0086] Table 5 Effect of reaction time on ethylene glycol hydrolysis of waste water treatment membrane rich in defective molybdenum and magnesium oxide

[0087] Example Reaction time / min Water treatment membrane conversion rate / % BHET yield / % 23 20 56.8 38.5 24 30 96.2 80.1 25 40 100 93.4 26 80 100 90.1 27 120 100 92.6

[0088] 7. The waste reverse osmosis membrane is recycled in a closed loop to obtain a new reverse osmosis membrane through a dissolution-depolymerization cascade recovery method:

[0089] Example 28 (Complete Example)

[0090] First, take the dry waste BW30 reverse osmosis membrane (waste reverse osmosis membrane such as Figure 4 (a)), mixed with N,N-dimethylformamide (the mass ratio of membrane to N,N-dimethylformamide is 1:1), stirred at room temperature for 5 minutes and then filtered to obtain 20wt% casting liquid and contaminated membrane substrate; 0.8wt% defect-rich molybdenum magnesium oxide calcined at 400℃ was taken, and the contaminated membrane substrate was completely depolymerized at 175℃ for 40min; BHET was then purified and crystallized using 80℃ hot water to obtain high-purity BHET monomer, and then repolymerized and spun; BHET and 1wt% antimony ethylene glycol were added to a customized titanium polyester reactor, heated to 250℃ for 2 hours, then heated to 290℃ for 1 hour, and then melt-spinning, cooling and drawing and hot-rolling reinforcement were performed to produce a clean membrane substrate, the melt spinning temperature was 330℃, and the hot-rolling temperature was 260℃; the casting liquid was spread on the clean membrane substrate using a film applicator, immersed in the water phase, and a recycled ultrafiltration membrane was prepared. The recovered ultrafiltration membrane was then immersed in 10% MPD and 1% TMC solutions to prepare a recovered reverse osmosis membrane. Figure 4 (b) as shown.

[0091] 8. Performance comparison between new reverse osmosis membranes obtained by closed-loop recycling of waste reverse osmosis membranes and commercial membranes:

[0092] Embodiments 29 to 30

[0093] The recovered new reverse osmosis membrane and the commercial reverse osmosis membrane were pre-pressed at 15 bar for 12 hours and then the water flux was tested. The filtration raw liquid was replaced with a 2 g / L sodium chloride solution, and the conductivity of the filtered water and the water before filtration was tested after stabilization at 15 bar for 12 hours, and the sodium chloride retention rate was calculated. The filtration method was cross-flow filtration. The water flux and sodium chloride retention rate data of the recovered new reverse osmosis membrane and the commercial reverse osmosis membrane are detailed in No. 29 to 30 in Table 6.

[0094] Table 6 Performance comparison of new reverse osmosis membranes obtained from closed-loop recycling of discarded reverse osmosis membranes

[0095] Example Membrane Type Sodium chloride retention rate / % <![CDATA[Water flux / L / (m 2 hbar)]]> 29 Reverse Osmosis Membrane Recovery 99.0 2.55 30 Commercial reverse osmosis membrane 99.4 3.00

[0096] In summary, the present invention has the following beneficial effects:

[0097] The present invention has the characteristics of high recovery rate of waste water treatment membrane polysulfone / polyacrylonitrile / polyvinylidene fluoride, easy recovery of catalyst, low cost, recyclable use, high polyester conversion rate of waste water treatment membrane, high selectivity of target product, green and pollution-free reaction process, mild reaction conditions, achieving the purpose of closed-loop recovery, and can be used for the recovery of seriously polluted or damaged membranes, and the prepared water treatment membrane has similar performance to commercial membranes.

[0098] The present invention provides a method and idea for dissolution-depolymerization of waste water treatment membrane materials. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment 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 principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

[0099] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering waste water treatment membranes, characterized in that: The following steps are involved: a) recovering the polysulfone, polyacrylonitrile or polyvinylidene fluoride layer of the waste water treatment membrane by dissolving it with a solvent to obtain a casting solution and undissolved polyester, respectively; b) recovering the undissolved polyester by alcoholysis of ethylene glycol catalyzed by oxygen-defective molybdenum-magnesium oxide nanosheets, regenerating the obtained polymerized monomers by polycondensation, and then preparing a new base film by spinning; c) subjecting the new base membrane and the casting solution obtained in step a) to solution coating, non-solvent phase conversion, solidification and cleaning in sequence to obtain a microfiltration membrane or an ultrafiltration membrane; d) The microfiltration membrane or ultrafiltration membrane obtained in step c) is sequentially subjected to monomer impregnation, interfacial polymerization, washing and curing to obtain a nanofiltration membrane or a reverse osmosis membrane.

2. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The solvent in step a) is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

3. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The mass ratio of the solvent to the waste water treatment membrane in step a) is (0.8-4):

1.

4. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The calcination temperature of the oxygen-defective molybdenum-magnesium oxide nanosheets in step b) is 200°C to 500°C.

5. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The amount of the oxygen-defective molybdenum-magnesium oxide nanosheets used in step b) is 0.05wt% to 4wt% of the mass of the waste water treatment membrane.

6. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The mass ratio of ethylene glycol to waste water treatment membrane in step b) is (1-8):

1.

7. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The alcoholysis temperature in step b) is 140° C. to 240° C., and the time is 5 min to 360 min.

8. The method for recovering waste water treatment membrane according to claim 1, characterized in that: The concentration of the casting solution in step c) is 10wt% to 30wt%.

9. The method for recovering waste water treatment membrane according to claim 1, characterized in that: During the interfacial polymerization in step d), the aqueous phase monomer is m-phenylenediamine; the concentration of m-phenylenediamine is 1 wt % to 11 wt %.

10. The method for recycling waste water treatment membrane according to claim 1, characterized in that: During the interfacial polymerization in step d), the organic phase monomer is trimesoyl chloride; the concentration of the trimesoyl chloride is 0.05 wt % to 1.5 wt %.

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