A support for preparing a reverse osmosis and nanofiltration membrane and a preparation method thereof

Abstract

The application relates to a support for preparing reverse osmosis and nanofiltration membranes and a preparation method, and belongs to the technical field of supports. The preparation method comprises the following steps: first, using specific fibers to prepare non-woven cloth raw paper, and then performing hot pressing and compounding with a polyolefin porous membrane to form the support. The non-woven cloth layer serves as a support material, and the polyolefin porous membrane serves as a porous material for providing interface polymerization and water channels. The method avoids the generation of organic wastewater in the manufacturing process of a conventional non-woven cloth-poly sulfone support, guarantees good mechanical properties, provides a support material which is simple to manufacture and process, and green and environment-friendly in the manufacturing process. The support of the application can be used to prepare high-performance reverse osmosis and nanofiltration membranes, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a support for reverse osmosis and nanofiltration membranes and its preparation method. Background Technology

[0002] Reverse osmosis and nanofiltration are membrane separation technologies that use pressure to separate or selectively separate solutes from a solution. This technology is widely used in seawater desalination, brackish water treatment, industrial wastewater treatment, and concentration separation. It is extensively applied in industries such as power generation, steel, petrochemicals, and printing and dyeing.

[0003] Reverse osmosis and nanofiltration membranes are the core materials of the aforementioned technologies. They are composite membranes composed of a support layer and a functional layer. During pressure operation, the support layer supports the functional layer and provides a permeate channel. Simultaneously, during membrane material preparation, the support layer provides the interfacial reaction environment for the preparation of the functional layer of the reverse osmosis and nanofiltration membranes.

[0004] The support layer typically has a two-layer structure. Conventional industrial-scale preparation processes involve dissolving polysulfone in an organic solvent to create a casting solution, which is then coated onto a nonwoven fabric using a slot extrusion or doctor blade process. The support layer is then formed after a phase inversion in a coagulation bath. The polysulfone layer of the support layer is a porous material, and its pore size distribution, porosity, and pore structure significantly influence the performance of the reverse osmosis and nanofiltration membranes after interfacial polymerization. Conventional reverse osmosis and nanofiltration support layer preparation processes place high demands on the uniformity, smoothness, and air permeability of the nonwoven fabric.

[0005] Conventional water treatment nonwoven fabrics, due to the need to coat them with polysulfone solution, require high uniformity in surface smoothness and air permeability. Differences in thickness, air permeability, and smoothness of the nonwoven fabric can affect the pore structure, pore size distribution, pinhole number, and water permeability of the polysulfone layer, thus impacting the quality of reverse osmosis and nanofiltration membranes. This invention uses a polyolefin porous membrane, already mass-produced in the battery industry, which offers higher pore size distribution and uniformity, instead of a porous polysulfone layer. Therefore, the requirements for the bottom nonwoven fabric are significantly lower than those for nonwoven fabrics in conventional support structures.

[0006] With technological advancements, techniques using polyolefin porous membranes alone to replace traditional water treatment support layers have emerged. Most of these techniques focus on hydrophilic modification of the polyolefin surface, but these methods do not address the inherent poor pressure resistance of polyolefins. Reverse osmosis and nanofiltration are pressure-driven membrane technologies, typically operating at high pressures. For example, seawater desalination membranes operate at pressures above 40 bar, while brackish water treatment membranes operate at around 15 bar. In these large-scale applications, reverse osmosis and nanofiltration membranes prepared using polyolefin porous membranes alone suffer from poor pressure resistance and short lifespan. For instance, CN113117539B and CN112892237B coat polysulfone or polyvinylidene fluoride onto a polyethylene porous membrane. This method still uses polysulfone or polyvinylidene fluoride materials and employs a phase inversion method, generating organic wastewater during production. CN114452827B specifies that the support layer is a porous polyethylene membrane with a thickness of 10-30 μm. When such a membrane material is used to roll up membrane elements, the membrane life will be reduced under high pressure. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a novel support for reverse osmosis and nanofiltration membranes, comprising a nonwoven fabric substrate and a polyolefin porous membrane thereon; wherein the nonwoven fabric and the polyolefin porous membrane are formed by melt hot pressing, and one side of the polyolefin porous membrane is the interfacial polymerization side during the preparation of water treatment membranes.

[0008] Compared with existing technologies, the advantages of this invention are: while ensuring good mechanical properties, it provides a composite support material with uniform pore size, simple manufacturing process, low cost, and environmentally friendly manufacturing process, and is also compatible with existing reverse osmosis and nanofiltration membrane manufacturing equipment that uses non-woven fabric-polysulfone as the support. High-performance water treatment membrane materials can be manufactured on this support.

[0009] The technical solution of this invention is implemented as follows:

[0010] A support for use in reverse osmosis and nanofiltration membranes includes a nonwoven fabric substrate and a polyolefin porous membrane thereon; the nonwoven fabric and the polyolefin porous membrane are formed by hot-pressing and melting, and one side of the polyolefin porous membrane is the interfacial polymerization side during the preparation of water treatment membranes.

[0011] The polyolefin porous membrane has a thickness of 9-40 μm, an average pore size of 0.02-0.08 μm, and a porosity of 30-50%. It is made of polyethylene, polypropylene, or a composite material of polyethylene and polypropylene. Preferably, the polyolefin porous membrane is made of polyethylene or polypropylene.

[0012] The nonwoven fabric backing has a thickness of 10-100 μm and a basis weight of 8-80 g / m². Preferably, the nonwoven fabric backing has a thickness of 25-70 μm and a basis weight of 20-60 g / m².

[0013] The nonwoven fabric is composed of one or more of the following: low-melting-point ES composite fiber, low-melting-point COPET / PET fiber, PE / PET fiber, polyolefin multifiber, PP fiber, and unstretched PET fiber. The ES composite fiber is a core-shell fiber composed of a surface polyethylene layer and an inner PP polypropylene core. The COPET / PET fiber is a core-shell fiber composed of a surface modified COPET fiber and an inner PET polyester core. The PE / PET fiber is a core-shell fiber composed of a surface PE layer and an inner PET polyester core. The polyolefin multifiber is a 100% hydrophilic polyolefin multifiber.

[0014] Preferably, the nonwoven fabric backing is composed of one or more of ES composite fibers, low-melting-point COPET / PET fibers, PP fibers, PET fibers, and unstretched PET fibers.

[0015] Another object of the present invention is to provide a method for preparing a support for the aforementioned novel reverse osmosis and nanofiltration membranes. This method includes the following steps:

[0016] (a) Preparation of nonwoven base paper: One or more fibers are added into a dispersion and stirring tank containing water and dispersant in proportion, and fiber pulp is prepared after dispersion treatment; then the prepared fiber pulp is pumped into a high-level box, and then conveyed to a paper machine of inclined wire or cylinder wire at a constant flow rate through a pulp distributor, and then vacuum dewatering and forming to produce wet fiber cloth.

[0017] The wet fiber cloth is pressed by rollers and dried again in an oven. It then enters a double hard roller hot press for hot rolling. The double hard rollers are all metal mirror rollers and are heated by a heat transfer oil furnace. The hot rolling process causes the fibers to melt and bond together, thereby increasing the strength of the nonwoven fabric.

[0018] After cooling, the paper is rolled into nonwoven fabric rolls by a winding machine.

[0019] (b) Preparation of supports used in reverse osmosis and nanofiltration membranes:

[0020] The nonwoven fabric base paper roll and the polyolefin porous membrane roll prepared in step (a) are simultaneously unwound by the first unwinding device (1) and the second unwinding device, respectively. During the unwinding process, the nonwoven fabric base paper and the polyolefin porous membrane are preheated in an oven. The preheated nonwoven fabric base paper and the polyolefin porous membrane are then laminated by the same two-roller hot press laminating machine (5). The two-roller hot press laminating machine (5) consists of a metal mirror roller heated by heat transfer oil and a heat-resistant rubber elastic roller arranged in parallel for extrusion. In the process of forming, the nonwoven base paper and the polyolefin porous membrane are simultaneously stacked and extruded between a metal mirror roller and a heat-resistant rubber elastic roller. The metal mirror roller heat-presses the nonwoven side, and the heat-resistant rubber elastic roller heat-presses the polyolefin porous membrane side. The double-roller hot press laminating machine (5) can bond the nonwoven base paper and the polyolefin porous membrane together and retain the pore structure on the surface of the polyolefin porous membrane. The composite material extruded by the double-roller hot press laminating machine (5) is wound up by a winding machine (6) to obtain the support for water treatment membrane of a specific thickness.

[0021] Step (a) The solid content of the fiber pulp is 0.5-2 wt‰.

[0022] In step (a), the papermaking, roller pressing, drying cylinder dewatering, hot rolling, and winding are carried out simultaneously, with a running line speed of 10-80 m / min.

[0023] In step (a), the oven temperature is 100-130℃, and the drying time of the fiber cloth in the oven is 20-40 seconds.

[0024] In step (a), the hot pressing temperature of the double hard roller hot press is 20-70℃ below the melting point of the main fiber, and the roller linear pressure is 30-70kg / cm.

[0025] In step (b), unwinding, drying, hot pressing and winding are carried out simultaneously, with a linear speed of 10-60 m / min.

[0026] In step (b), the oven temperature is 0-30°C above the melting point of the polyolefin porous membrane.

[0027] In step (b), the temperature of the metal mirror roller in the double-roll hot press laminating machine is 0-30°C above the melting point of the polyolefin porous film. The upper and lower rollers are arranged in an upper and lower roller configuration, and the linear pressure of the upper and lower rollers is 30-70 kg / cm.

[0028] This invention proposes a support for reverse osmosis and nanofiltration membranes and its preparation method, which has the following advantages:

[0029] 1) The support of the present invention has good surface pore size uniformity, and the reverse osmosis and nanofiltration membranes obtained by using the support of the present invention are uniform and have a low defect rate.

[0030] 2) Interfacial polymerization can be carried out directly on the support of the present invention, eliminating the casting step, reducing energy consumption, and reducing the generation of organic wastewater.

[0031] 3) Compared with reverse osmosis and nanofiltration membranes that use polyolefin porous membranes as supports alone, reverse osmosis and nanofiltration membranes prepared using the support of the present invention have better pressure resistance and longer lifespan. Attached Figure Description

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, these drawings are intended only to conceptually illustrate the structure and process and are not necessarily drawn to scale. Figure 1 This is a schematic flowchart of step b of the present invention, which describes a support used in reverse osmosis and nanofiltration membranes.

[0033] First unwinding device (1), second unwinding device (2), first drying oven (3), second drying oven (4), double-roll hot press laminating machine (5), winding machine (6).

[0034] Figure 2 This is a SEM image of the nonwoven fabric side of the support used in a reverse osmosis and nanofiltration membrane according to the present invention.

[0035] Figure 3 This is a SEM image of the porous polyolefin membrane side of a reverse osmosis and nanofiltration membrane used in this invention. Detailed Implementation

[0036] To further illustrate the technical solution of the present invention, the following examples are provided for specific explanation, but the present invention is not limited to the following embodiments.

[0037] Example 1: A support for reverse osmosis and nanofiltration membranes and its preparation method are as follows:

[0038] a) Preparation of nonwoven base paper:

[0039] 1. Add the fiber and water according to the following ratio to a dispersion mixing tank to prepare fiber slurry. The ES composite fiber has a fineness of 1.5 dtex, a length of 5 mm, and accounts for 10% of the total. The ES composite fiber has a fineness of 1.0 dtex.

[0040] The length is 2mm, accounting for 30%; the polypropylene fiber fineness is 0.9dtex, the length is 5mm, and the proportion is 60%.

[0041] Add a dispersant and water until the fiber solids content is 0.5‰, then stir to obtain fiber slurry.

[0042] 2. The above slurry is pumped into the slurry machine at a constant flow rate from the high-level tank, flows through the inclined wire mesh forming machine, and then is vacuum dewatered and formed to obtain a wet fiber web.

[0043] 3. The wet fiber web is pressed by idler rollers and dried again in a drying cylinder. The temperature of the drying cylinder is 120℃ and the drying time is 20s. This causes the surface layer of the ES fibers in the wet fiber web to melt and the cross points between the fibers to bond together, thus initially generating adhesive strength.

[0044] 4. Then, the steel rolls are passed through a double hard roller hot press, where the surface temperature of the steel rolls is 145℃ and the pressure between the rollers is 45kg / cm.

[0045] 5. After being hot-pressed, the nonwoven fabric is cooled by cooling rollers and air cooling to lower its temperature, and then wound up to obtain the nonwoven base paper. The resulting nonwoven base paper has a basis weight of 35 g / m².

[0046] 6. The above papermaking to hot pressing process is a continuous process with a running linear speed of 30m / min.

[0047] b) Preparation of supports for reverse osmosis and nanofiltration membranes

[0048] 1. The nonwoven fabric base paper roll prepared in step a) and the polyolefin porous membrane roll are simultaneously unwound through a double unwinding device;

[0049] In section 2.1, the polyolefin porous membrane used is a polyethylene porous membrane with a thickness of 20 μm, a basis weight of 11 g / m², and a porosity of 40%.

[0050] 3. After the non-woven fabric base paper is unwound, it is preheated in an oven at 130℃ for 2 minutes.

[0051] 4. After unwinding, the polyolefin porous membrane is preheated in an oven at 110°C. Then, it is stacked with the preheated nonwoven fabric base paper from step 3 and hot-pressed together using a double-roller hot press. The double-roller hot press consists of a metal mirror roller heated by heat-conducting oil and a heat-resistant rubber elastic roller. The metal mirror roller hot-presses the nonwoven fabric side, and the heat-resistant rubber elastic roller hot-presses the polyolefin porous membrane side. The surface temperature of the metal mirror roller is 140°C, and the roller linear pressure is 30 kg / cm.

[0052] 5. After the composite support is wound up by the winding device, the support used to make the composite water treatment membrane of a specific thickness is obtained, with a basis weight of 40g / ㎡ and a thickness of 60um.

[0053] Example 2: A support for reverse osmosis and nanofiltration membranes and its preparation method are as follows:

[0054] a) Preparation of nonwoven base paper:

[0055] 1. Add the following proportions of fiber and water to a dispersion mixing tank to prepare a fiber slurry: ES composite fiber with a fineness of 1.5 dtex and a length of 3 mm accounts for 30%; COPET / PET composite fiber with a fineness of 12 dtex and a length of 4 mm accounts for 40%; and PET fiber with a fineness of 0.8 dtex and a length of 3 mm accounts for 30%. Add a dispersant and water until the fiber solids content reaches 0.5‰. Stir to obtain the fiber slurry.

[0056] 2. The above slurry is pumped into the slurry machine at a constant flow rate from the high-level tank, flows through the inclined wire mesh forming machine, and then is vacuum dewatered and formed to obtain a wet fiber web.

[0057] 3. The wet fiber web is pressed by rollers and dried again in a drying cylinder. The temperature of the drying cylinder is 120℃ and the drying time is 20s. This causes the surface layer of COPET / PET fibers in the wet fiber web to melt, and the intersections between the fibers to bond together, thus initially generating adhesive strength.

[0058] 4. Then, the steel rolls are passed through a double hard roller hot press, where the surface temperature of the steel rolls is 145℃ and the pressure between the rollers is 45kg / cm.

[0059] 5. After being hot-pressed, the nonwoven fabric is cooled by cooling rollers and air cooling to lower its temperature, and then wound up to obtain the nonwoven base paper. The resulting nonwoven base paper has a basis weight of 35 g / m².

[0060] 6. The above papermaking to hot pressing process is a continuous process with a running linear speed of 30m / min.

[0061] b) Preparation of supports for reverse osmosis and nanofiltration membranes

[0062] 1. The nonwoven fabric base paper roll prepared in step a) and the polyolefin porous membrane roll are simultaneously unwound through a double unwinding device;

[0063] In section 2.1, the polyolefin porous membrane used is a polyethylene porous membrane with a thickness of 16 μm, a basis weight of 9 g / m², and a porosity of 40%.

[0064] 3. After the non-woven fabric base paper is unwound, it is preheated in an oven at 125℃ for 2 minutes.

[0065] 4. After unwinding, the polyolefin porous membrane is preheated in an oven at 110°C. Then, it is stacked with the preheated nonwoven fabric base paper from step 3 and hot-pressed together using a double-roller hot press. The double-roller hot press consists of a metal mirror roller heated by heat-conducting oil and a heat-resistant rubber elastic roller. The metal mirror roller hot-presses the nonwoven fabric side, and the heat-resistant rubber elastic roller hot-presses the polyolefin porous membrane side. The surface temperature of the metal mirror roller is 135°C, and the roller linear pressure is 30 kg / cm.

[0066] 5. After the composite support is wound up by the winding device, the support used to make the composite water treatment membrane of a specific thickness is obtained, with a basis weight of 42g / ㎡ and a thickness of 62um.

[0067] Example 3: A support for reverse osmosis and nanofiltration membranes and its preparation method are as follows:

[0068] a) Preparation of nonwoven base paper:

[0069] 1. Add the fiber and water in the following proportions to a dispersion mixing tank to prepare a fiber slurry: 1.2 dtex unstretched modified low-melting-point PET fiber with a length of 5 mm, accounting for 40%; 0.9 dtex PE fiber, accounting for 60%. Add dispersant and water until the fiber solids content is 0.5‰. Stir to obtain the fiber slurry.

[0070] 2. The above slurry is pumped into the slurry machine at a constant flow rate from the high-level tank, flows through the inclined wire mesh forming machine, and then is vacuum dewatered and formed to obtain a wet fiber web.

[0071] 3. The wet fiber web is pressed by rollers and dried again in a drying cylinder. The temperature of the drying cylinder is 120℃ and the drying time is 20s. This causes the surface layer of COPET / PET fibers in the wet fiber web to melt, and the intersections between the fibers to bond together, thus initially generating adhesive strength.

[0072] 4. Then, the steel rolls are passed through a double hard roller hot press, where the surface temperature of the steel rolls is 170℃ and the pressure between the rollers is 45kg / cm.

[0073] 5. After being hot-pressed, the nonwoven fabric is cooled by cooling rollers and air cooling to lower its temperature, and then wound up to obtain the nonwoven base paper. The resulting nonwoven base paper has a basis weight of 50 g / m².

[0074] 6. The above papermaking to hot pressing process is a continuous process with a running linear speed of 30m / min.

[0075] b) Preparation of supports for reverse osmosis and nanofiltration membranes

[0076] 1. The nonwoven fabric base paper roll prepared in step a) and the polyolefin porous membrane roll are simultaneously unwound through a double unwinding device;

[0077] In section 2.1, the polyolefin porous membrane used is a polypropylene porous membrane with a thickness of 40 μm, a basis weight of 20 g / m², and a porosity of 44%.

[0078] 3. After the non-woven fabric base paper is unwound, it is preheated in an oven at 150℃ for 2 minutes.

[0079] 4. After unwinding, the polyolefin porous membrane is preheated in an oven at 140°C. Then, it is stacked with the preheated nonwoven fabric base paper from step 3 and hot-pressed together using a double-roller hot press. The double-roller hot press consists of a metal mirror roller heated by heat-conducting oil and a heat-resistant rubber elastic roller. The metal mirror roller hot-presses the nonwoven fabric side, and the heat-resistant rubber elastic roller hot-presses the polyolefin porous membrane side. The surface temperature of the metal mirror roller is 160°C, and the roller linear pressure is 30 kg / cm.

[0080] 5. After the composite support is wound up by the winding device, the support used to make the composite water treatment membrane of a specific thickness is obtained, with a basis weight of 68g / ㎡ and a thickness of 110um.

[0081] Comparative Example

[0082] A commercially available 75g / m² nonwoven fabric was used as the support layer, and a 16% polysulfone DMF solution was used as the casting solution. After dissolving and degassing, the solution was uniformly coated onto the aforementioned commercially available nonwoven fabric, and then a reverse osmosis support was prepared by phase inversion. A comparative sample with a thickness of 130µm was obtained.

[0083] In the embodiments and comparative examples of this patent, the relevant technical indicators of the support used for reverse osmosis and nanofiltration membranes refer to the following standards: "areal density" is determined according to GB / T451.2-2002; "thickness" is determined according to GB / T 451.3-2002; "tensile strength" is determined according to GB / T 12914-2008, and the pore size distribution is tested using a gas-liquid method pore size analyzer.

[0084] Table 1. Supports used in reverse osmosis and nanofiltration and comparative examples.

[0085]

[0086] As can be seen from Table 1, the samples using Examples 1-3 of this invention exhibit good mechanical properties, and their tensile strength is essentially equivalent to that of conventional supports, i.e., the comparative examples. In the comparison of pore size distribution data using the gas-liquid method, the polyolefin porous membrane, due to its uniform pore size distribution, yields a pore size distribution that is relatively narrower than that of the comparative examples.

[0087] In summary, this invention provides a support and its preparation method for reverse osmosis and nanofiltration. It utilizes a polyolefin porous membrane as a porous layer material for interfacial polymerization, which is then composited with a nonwoven fabric to obtain a support with thinner thickness, more uniform pore size distribution, and maintained mechanical properties. This method is simple, highly controllable, and meets the needs of industrial production, possessing high practical application value.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various changes and modifications can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A support for the preparation of reverse osmosis and nanofiltration membranes, characterized in that, It includes a non-woven fabric substrate and a polyolefin porous membrane thereon; the non-woven fabric and the polyolefin porous membrane are formed by hot-pressing and melting, and one side of the polyolefin porous membrane is the interfacial polymerization side during the preparation of the water treatment membrane. The polyolefin porous membrane has a thickness of 9-40 μm, an average pore size of 0.02-0.08 μm, a porosity of 30-50%, and is made of polyethylene, polypropylene, or a composite material of polyethylene and polypropylene. The nonwoven fabric is composed of one or more of the following: low-melting-point ES composite fiber, low-melting-point COPET / PET fiber, PE / PET fiber, polyolefin multifiber, PP fiber, PET fiber, and unstretched PET fiber. The method for preparing the support includes the following steps: (a) Preparation of nonwoven base paper: One or more fibers are added into a dispersion and stirring tank containing water and dispersant in proportion, and fiber pulp is prepared after dispersion treatment; then the prepared fiber pulp is pumped into a high-level box, and then conveyed to a paper machine with a constant flow rate through a pulp distributor, and then vacuum dewatered and formed to produce wet fiber cloth. The wet fiber cloth is pressed by rollers and dried again in an oven. It then enters a double hard roller hot press for hot rolling. The double hard rollers are all metal mirror rollers and are heated by a heat transfer oil furnace. The hot rolling process causes the fibers to melt and bond together, thereby increasing the strength of the nonwoven fabric. After cooling, the paper is rolled into a nonwoven fabric roll by a winding machine. (b) Preparation of supports for reverse osmosis and nanofiltration membranes: The nonwoven fabric base paper roll and the polyolefin porous membrane roll prepared in step (a) are simultaneously unwound by the first unwinding device (1) and the second unwinding device (2), respectively. The nonwoven fabric base paper and the polyolefin porous membrane unwound during the unwinding process are preheated in an oven. The preheated nonwoven fabric base paper and the polyolefin porous membrane are then laminated by the same two-roller hot press laminating machine (5). The two-roller hot press laminating machine (5) consists of a metal mirror roller heated by heat transfer oil and a heat-resistant rubber elastic roller arranged in parallel for extrusion. The nonwoven base paper and polyolefin porous membrane are synchronously stacked and extruded between a metal mirror roller and a heat-resistant rubber elastic roller. The metal mirror roller heat-presses the nonwoven side, and the heat-resistant rubber elastic roller heat-presses the polyolefin porous membrane side. The double-roller hot press composite machine (5) can bond the nonwoven base paper and polyolefin porous membrane together and retain the pore structure on the surface of the polyolefin porous membrane. The composite material extruded by the double-roller hot press composite machine (5) is wound up by a winding machine to obtain a support for water treatment membrane of a specific thickness.

2. A support for preparing reverse osmosis and nanofiltration membranes according to claim 1, characterized in that, The ES composite fiber is a core-shell fiber composed of a surface polyethylene layer and an inner PP polypropylene core. The COPET / PET fiber is a core-shell fiber composed of a surface modified COPET fiber and an inner PET polyester core. The PE / PET fiber is a core-shell fiber composed of a surface PE layer and an inner PET polyester core. The polyolefin multifiber is a 100% polyolefin multifiber with hydrophilic properties.

3. A support for preparing reverse osmosis and nanofiltration membranes according to claim 1, characterized in that, The nonwoven fabric backing is composed of one or more of the following: low-melting-point ES composite fibers, low-melting-point COPET / PET fibers, PP fibers, PET fibers, and unstretched PET fibers.

4. A support for preparing reverse osmosis and nanofiltration membranes according to claim 1, characterized in that, The nonwoven fabric bottom layer has a thickness of 10-100um and a basis weight of 8-80g / ㎡.

5. A support for preparing reverse osmosis and nanofiltration membranes according to claim 4, characterized in that, The nonwoven fabric bottom layer has a thickness of 25-70um and a weight of 20-60g / ㎡.

6. A method for preparing a support for reverse osmosis and nanofiltration membranes according to any one of claims 1-5, characterized in that, Includes the following steps: (a) Preparation of nonwoven base paper: One or more fibers are added into a dispersion and stirring tank containing water and dispersant in proportion, and fiber pulp is prepared after dispersion treatment; then the prepared fiber pulp is pumped into a high-level box, and then conveyed to a paper machine with a constant flow rate through a pulp distributor, and then vacuum dewatered and formed to produce wet fiber cloth. The wet fiber cloth is pressed by rollers and dried again in an oven. It then enters a double hard roller hot press for hot rolling. The double hard rollers are all metal mirror rollers and are heated by a heat transfer oil furnace. The hot rolling process causes the fibers to melt and bond together, thereby increasing the strength of the nonwoven fabric. After cooling, the paper is rolled into a nonwoven fabric roll by a winding machine. (b) Preparation of supports for reverse osmosis and nanofiltration membranes: The nonwoven fabric base paper roll and the polyolefin porous membrane roll prepared in step (a) are simultaneously unwound by the first unwinding device (1) and the second unwinding device (2), respectively. The nonwoven fabric base paper and the polyolefin porous membrane unwound during the unwinding process are preheated in an oven. The preheated nonwoven fabric base paper and the polyolefin porous membrane are then laminated by the same two-roller hot press laminating machine (5). The two-roller hot press laminating machine (5) consists of a metal mirror roller heated by heat transfer oil and a heat-resistant rubber elastic roller arranged in parallel for extrusion. The nonwoven base paper and polyolefin porous membrane are synchronously stacked and extruded between a metal mirror roller and a heat-resistant rubber elastic roller. The metal mirror roller heat-presses the nonwoven side, and the heat-resistant rubber elastic roller heat-presses the polyolefin porous membrane side. The double-roller hot press composite machine (5) can bond the nonwoven base paper and polyolefin porous membrane together and retain the pore structure on the surface of the polyolefin porous membrane. The composite material extruded by the double-roller hot press composite machine (5) is wound up by a winding machine to obtain a support for water treatment membrane of a specific thickness.

7. The preparation method according to claim 6, characterized in that, In step (a), the solid content of the fiber pulp is 0.5-2wt‰; the papermaking, roller pressing, drying and dewatering, hot rolling and winding processes described in step (a) are carried out simultaneously, and the running line speed is 10-80m / min.

8. The preparation method according to claim 6, characterized in that, In step (a), the oven temperature is 100-130℃, and the drying time of the fiber cloth in the oven is 20-40 seconds; in step (a), the hot pressing temperature of the double hard roller hot press is 20-70℃ below the melting point of the main fiber, and the roller linear pressure is 30-70kg / cm.

9. The preparation method according to claim 6, characterized in that, In step (b), unwinding, drying, hot pressing and winding are carried out simultaneously, with a running line speed of 10-60 m / min; the oven temperature in step (b) is 0-30℃ above the melting point temperature of the polyolefin porous membrane.

10. The preparation method according to claim 6, characterized in that, In step (b), the temperature of the metal mirror roller in the double-roller hot press laminating machine is 0-30°C above the melting point of the polyolefin porous film. The upper and lower rollers are arranged in an upper and lower roller configuration, and the linear pressure of the upper and lower rollers is 30-70 kg / cm.

11. The application of the support for preparing reverse osmosis and nanofiltration membranes as described in any one of claims 1-5, directly used as a support for preparing reverse osmosis and nanofiltration membranes.

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