Reverse osmosis membrane supporting material as well as preparation method and application thereof

Abstract

The invention provides a reverse osmosis membrane supporting material as well as a preparation method and application thereof. The reverse osmosis membrane supporting material comprises a first supporting layer and a second supporting layer which are sequentially stacked, and the first supporting layer and the second supporting layer both contain sulfonic acid groups; the sulfonation degree of the first supporting layer is higher than that of the second supporting layer, and the difference between the sulfonation degree of the first supporting layer and the sulfonation degree of the second supporting layer is 0.1%-10%. According to the reverse osmosis membrane supporting material with the double-layer structure provided by the invention, the first supporting layer and the second supporting layer have different sulfonic acid group contents, so that the reverse osmosis membrane supporting material shows different hydrophilicity, and the phase conversion speed and the penetration depth of membrane liquid on a coating surface and a non-coating surface can be effectively controlled in the coating process of membrane casting liquid; and finally, the performance of the reverse osmosis membrane in the application process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation materials, and in particular to a reverse osmosis membrane supporting material, a preparation method and application thereof. Background Art

[0002] In recent years, due to the rapid development of desalination, ultrapure water production, seawater desalination and other fields, reverse osmosis membrane technology has also undergone tremendous technological innovation. Among them, the reverse osmosis membrane support material (ROSM), which is indispensable in the field of reverse osmosis membrane technology, has also been successfully developed.

[0003] However, the matching between the existing ROSM and the casting liquid has not achieved the ideal effect. The reason is that during the preparation process of ROSM, due to the dual effects of molten fiber and main fiber, the performance of the finished product is not easy to control, including the control of hydrophilicity. In the prior art, in order to meet the basic performance of ROSM, fiber materials with pores on the surface are generally selected as the base material, because the pores on its surface drive water to penetrate and then show hydrophilicity. In the preparation process of traditional ROSM, in order to achieve a good hydrophilic effect, hydrophilic additives or other dispersants with hydrophilicity are often added during the wet papermaking process, or additional hydrophilic finishing work is performed after hot pressing. The ROSM prepared as described above can often show excellent hydrophilic properties in the early stage of use, but as the application proceeds, especially after being flushed by high-pressure water flow, the residual additives in ROSM tend to diffuse into the water and seriously affect subsequent use.

[0004] At the same time, most existing ROSMs are consistent as a whole, that is, the hydrophilicity of the two surfaces is the same, which strictly restricts the hydrophilic type of the entire reverse osmosis membrane. During the coating preparation process of the entire membrane, the coating liquid often penetrates to the back due to the slow phase conversion rate. The hydrophilicity of the coated and non-coated surfaces directly affects the phase conversion rate and penetration depth of the membrane liquid during the casting process, thereby indirectly affecting the uniformity of the entire membrane, making the various parts of the reverse osmosis membrane as a whole vary greatly, resulting in poor desalination rate and flux in individual areas of the reverse osmosis membrane, and ultimately affecting its performance.

[0005] In view of this, how to provide a reverse osmosis membrane support material to effectively improve the phase conversion rate and penetration depth of the membrane liquid during the casting process, thereby optimizing the overall water flux of the final osmosis membrane, is one of the technical problems that need to be solved in this field. Summary of the invention

[0006] The main purpose of the present invention is to provide a reverse osmosis membrane support material, a preparation method and application thereof, so as to solve the problem of poor reverse osmosis membrane performance caused by the difficulty in controlling the hydrophilicity of the coated surface and the non-coated surface of the reverse osmosis membrane support material in the prior art.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a reverse osmosis membrane support material on one hand, which includes a first support layer and a second support layer stacked in sequence, and both the first support layer and the second support layer contain sulfonic acid groups; the sulfonation degree of the first support layer is higher than that of the second support layer, and the difference in sulfonation degree between the first support layer and the second support layer is 0.1% to 10%.

[0008] Furthermore, the sulfonation degree of the first supporting layer is 6% to 11%.

[0009] Furthermore, the thickness of the reverse osmosis membrane supporting material is 80 μm to 120 μm; preferably, the ratio of the thickness of the first supporting layer to the second supporting layer is (0.92 to 1.15):1.

[0010] Furthermore, the first supporting layer and the second supporting layer independently include main fibers and bonding fibers, and the main fibers carry sulfonic acid groups; preferably, the main fibers and bonding fibers have diameters independently of each other of 3 μm to 20 μm and lengths independently of each other of 2 mm to 15 mm.

[0011] Furthermore, in the first supporting layer and the second supporting layer, the weight ratio of the main fiber to the bonding fiber is independently (60-65): (35-40); preferably, the main fiber is selected from polyester fiber; and the bonding fiber is selected from one or more of polyester fiber and polyolefin fiber.

[0012] Furthermore, the first supporting layer has a first outer surface away from the second supporting layer, and the second supporting layer has a second outer surface away from the first supporting layer; the water contact angle of the first outer surface is smaller than the water contact angle of the second outer surface, and the difference between the first outer surface and the water contact angle of the second outer surface is 5.0° to 55.0°.

[0013] Another aspect of the present invention provides a method for preparing the above-mentioned reverse osmosis membrane supporting material, comprising the following steps: S1, using a first sulfuric acid solution to perform a first modification on a first fiber to obtain a first main fiber, the first main fiber carrying a sulfonic acid group; using a second sulfuric acid solution to perform a second modification on a second fiber to obtain a second main fiber; S2, preparing the first main fiber and the first bonding fiber into a first slurry, and papering the first slurry onto a mesh to obtain a first supporting layer; S3, preparing the second main fiber and the second bonding fiber into a second slurry, and papering the second slurry onto a mesh to obtain a second supporting layer; S4, after compounding and hot pressing the first supporting layer and the second supporting layer, a reverse osmosis membrane supporting material is obtained; the concentrations of the first sulfuric acid solution and the second sulfuric acid solution are each independently 1 g / L to 12 g / L.

[0014] Furthermore, the concentration of the first sulfuric acid solution is higher than that of the second sulfuric acid solution, and the concentration difference between the first sulfuric acid solution and the second sulfuric acid solution is 3 g / L to 11 g / L.

[0015] Furthermore, the reaction temperatures of the first modification and the second modification are independently 80°C to 150°C, and the reaction times are independently 0.5h to 30h; preferably, the reaction temperature of the first modification is higher than the reaction temperature of the second modification, and the difference between the reaction temperature of the first modification and the second modification is 10°C to 50°C.

[0016] Furthermore, the concentration of the first slurry and the second slurry is independently 0.05‰ to 0.5‰.

[0017] Furthermore, the temperatures of the upper and lower rolls of the hot pressing are independently 150°C to 240°C.

[0018] Another aspect of the present invention provides an application of the above reverse osmosis membrane supporting material as a casting liquid support in the field of reverse osmosis membrane technology.

[0019] By applying the technical solution of the present invention, a reverse osmosis membrane support material with a double-layer structure is provided, in which the first support layer and the second support layer have different contents of sulfonic acid groups, and thus exhibit different hydrophilicities, thereby being able to effectively control the phase conversion rate and penetration depth of the membrane liquid on the coated surface and the non-coated surface during the coating process of the casting liquid, and ultimately improve the performance of the reverse osmosis membrane during the application process. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0021] As described in the background technology, the reverse osmosis membrane support material in the prior art has the problem of poor performance of the reverse osmosis membrane due to the difficulty in controlling the hydrophilicity of the coated surface and the non-coated surface. In order to solve the above technical problems, the present invention provides a reverse osmosis membrane support material on one hand, which includes a first support layer and a second support layer stacked in sequence, and the first support layer and the second support layer both contain sulfonic acid groups; the sulfonation degree of the first support layer is higher than the sulfonation degree of the second support layer, and the difference between the sulfonation degree of the first support layer and the second support layer is 0.1% to 10%.

[0022] The reverse osmosis membrane support material with a double-layer structure provided by the present invention exhibits high hydrophilicity because both of the double-layer structures contain certain sulfonic acid groups. More importantly, the sulfonic acid group contents in the first support layer and the second support layer are different, and thus exhibit different hydrophilicities, thereby being able to effectively control the phase conversion speed and penetration depth of the membrane liquid on the coated surface and the non-coated surface during the coating process of the casting liquid, and ultimately significantly improve the performance of the reverse osmosis membrane during the application process.

[0023] In particular, the present invention achieves precise control of the hydrophilicity difference between the first and second supporting layers by strictly controlling the difference in the degree of sulfonation between the first supporting layer and the second supporting layer, and finally optimizes the water flux of the reverse osmosis membrane supporting material as a whole, so that it is within a most suitable range. The water flux of the reverse osmosis membrane supporting material as a whole provided by the present invention can be more effectively adapted to different water qualities, flow rates and corresponding equipment only after the above optimization, and will not reduce the water treatment efficiency due to being too small, nor will it cause the surface pressure of the reverse osmosis membrane itself to be too large, reduce the service life and reduce the quality of the treated water due to being too large.

[0024] At the same time, the reverse osmosis membrane support material provided by the present invention does not include other chemical additives for improving the hydrophilicity of the support material, such as dispersants, etc. Therefore, during the application process, especially after being flushed by high-pressure water flow, the reverse osmosis membrane support material will not be affected by the redispersion of residual chemical additives in the reverse osmosis membrane support material, thereby affecting subsequent use.

[0025] In several preferred embodiments, the difference in sulfonation degree between the first support layer and the second support layer is preferably 2.0% to 6.5%, so that the overall water flux range of the reverse osmosis membrane support material formed by the two layers is more suitable and has a wider application.

[0026] Furthermore, the sulfonation degree of the first support layer is 6% to 11%. At this time, the coating surface of the reverse osmosis membrane support material shows higher hydrophilicity, which is more conducive to the phase transformation of the casting liquid and the composite with the support material.

[0027] In several preferred embodiments, the thickness of the reverse osmosis membrane support material is 80 μm to 120 μm; preferably, the ratio of the thickness of the first support layer to the thickness of the second support layer is (0.92 to 1.15): 1. The inventors have optimized the overall thickness of the reverse osmosis membrane support material through a large number of experiments to obtain the above range, and found that within this range, the reverse osmosis membrane support material can more effectively take into account both hydrophilicity and mechanical properties, especially when the thickness relationship of the two layers is set as above, so as to obtain a reverse osmosis membrane support material with better water flux and mechanical properties.

[0028] In order to obtain a support material with better film-forming properties, more complete and higher tensile strength, a low-melting-point adhesive fiber must be added thereto to ensure the normal winding of the obtained membrane support material in the wet process and provide strong support for the subsequent reverse osmosis membrane, that is, preferably, the first support layer and the second support layer each independently include a main fiber and an adhesive fiber, and the main fiber carries a sulfonic acid group. In several more preferred embodiments, in order to improve mechanical properties such as tensile strength and further improve the service life of the obtained reverse osmosis membrane support material, the diameter of the main fiber and the adhesive fiber are each independently 3μm to 20μm, and the length is each independently 2mm to 15mm.

[0029] Furthermore, in the first support layer and the second support layer, the weight ratio of the main fiber to the bonding fiber is independently (60-65): (35-40). The inventors compared and screened the weight ratio of the main fiber to the bonding fiber in each layer through a large number of experiments to obtain the above range, and found that each support layer obtained within this dosage relationship range and the corresponding material as a whole have a better and complete morphology, and can perform better in mechanical properties tests. In several preferred embodiments, the main fiber is selected from polyester fiber; the bonding fiber is selected from one or more of polyester fiber and polyolefin fiber. Theoretically, both the main fiber and the bonding fiber can be selected from the types commonly used in the field, but the inventors have selected the above specific types through a large number of experiments, especially when the two types are the same, the compatibility is higher, and the obtained reverse osmosis membrane support material can also show higher comprehensive performance.

[0030] In several preferred embodiments, the first supporting layer has a first outer surface away from the second supporting layer, the second supporting layer has a second outer surface away from the first supporting layer, the water contact angle of the first outer surface is less than the water contact angle of the second outer surface, and the difference between the water contact angle of the first outer surface and the second outer surface is 5.0° to 55.0°. The inventors have further optimized the difference relationship of the water contact angles of the corresponding outer surfaces of the two-layer structure based on the difference in the content of sulfonic acid groups in the first supporting layer and the second supporting layer through a large number of experiments, and found in actual applications that when the water contact angles of the two outer surfaces have the above-mentioned difference relationship, the water flux of the obtained reverse osmosis membrane support material can be further optimized.

[0031] Another aspect of the present invention provides a method for preparing the above-mentioned reverse osmosis membrane supporting material, comprising the following steps: S1, using a first sulfuric acid solution to perform a first modification on a first fiber to obtain a first main fiber, the first main fiber carrying a sulfonic acid group; using a second sulfuric acid solution to perform a second modification on a second fiber to obtain a second main fiber; S2, preparing the first main fiber and the first bonding fiber into a first slurry, and papering the first slurry onto a mesh to obtain a first supporting layer; S3, preparing the second main fiber and the second bonding fiber into a second slurry, and papering the second slurry onto a mesh to obtain a second supporting layer; S4, after compounding and hot pressing the first supporting layer and the second supporting layer, a reverse osmosis membrane supporting material is obtained; the concentrations of the first sulfuric acid solution and the second sulfuric acid solution are each independently 1 g / L to 12 g / L.

[0032] By applying the above-mentioned preparation method provided by the present invention, a double-layer structure reverse osmosis membrane support material with different hydrophilicity is obtained by a simple method without adding any chemical additives. Specifically, in step S1, the first fiber and the second fiber are modified respectively by dilute sulfuric acid, so that the fiber and sulfuric acid undergo sulfonation reaction, and sulfonic acid groups are generated on the fiber surface, thereby giving it excellent hydrophilicity. Different from the prior art, that is, adding chemical additives for improving its dispersibility and hydrophilicity in the wet process formed by the support material, the method provided by the present invention of pre-modifying the main fiber with dilute sulfuric acid is more environmentally friendly and can also reduce the post-treatment of white water (i.e., water after papermaking on the Internet). Of course, as mentioned above, because no other chemical additives are added during the preparation process, the reverse osmosis membrane support material obtained, and even the reverse osmosis membrane obtained after the subsequent compounding with the casting liquid, will not have the seepage and diffusion of the additives in each process of application, thereby effectively ensuring its water treatment effect in various scenarios.

[0033] In particular, the preparation method provided by the present invention uses sulfuric acid for modification operation, which can more accurately control the degree of sulfonation of the main fiber compared to other reagents that can be used for sulfonation modification in the art, such as chlorosulfonic acid or oleum (i.e., sulfuric acid solution of sulfur trioxide), so that the difference between the two sides of the reverse osmosis membrane support material is more obvious. And, regarding the concentration of sulfuric acid used, the present invention clarifies that it is 1g / L to 12g / L. Compared with a higher concentration, it can effectively avoid the damage to the structure and the operational insecurity caused by the use of concentrated sulfuric acid while optimizing the comprehensive performance of the obtained support material, thereby improving the feasibility and safety of the entire operation.

[0034] In several typical embodiments, the concentration of the first sulfuric acid solution is higher than that of the second sulfuric acid solution, and the concentration difference with the second sulfuric acid solution is 3 g / L to 11 g / L. The inventors preferably set the concentration relationship between the first sulfuric acid and the second sulfuric acid used for modification to be within the above range, and thus found that the reverse osmosis membrane support material prepared under such conditions has a better coordination of the sulfonic acid group content in each layer, thereby more effectively improving its hydrophilicity.

[0035] Furthermore, the reaction temperature of the first modification and the second modification is independently 80 to 150°C, and the reaction time is independently 0.5 to 30 hours. After a large number of experiments, the inventors optimized the reaction conditions of the first modification and the second modification, and obtained the above range, so as to more effectively realize the sulfonation modification of the main fiber, optimize the hydrophilicity of each layer finally obtained, and make it show better water treatment after being compounded with the plating liquid. On the basis of the above content, it is more preferred that the reaction temperature of the first modification is higher than the reaction temperature of the second modification, and the difference with the reaction temperature of the second modification is 10°C to 50°C, so as to optimize the content of sulfonic acid groups in each supporting layer obtained subsequently, and then optimize the water flux of the reverse osmosis membrane supporting material obtained.

[0036] In order to make the fibers fully dispersed and the supporting layer more uniform after being put on the net, and thus obtain a reverse osmosis membrane supporting material with better comprehensive performance, the inventors further preferred that the concentrations of the first slurry and the second slurry be independently 0.05‰ to 0.5‰ after a large number of experiments.

[0037] And, with respect to the composite between the first support layer and the second support layer provided by the present invention, in several typical embodiments, the temperatures of the upper and lower rollers of the hot pressing are independently 150°C to 240°C, so as to obtain a reverse osmosis membrane support material with a more complete and stable structure, thereby more effectively improving its performance.

[0038] Another aspect of the present invention provides an application of the above-mentioned reverse osmosis membrane support material as a support for a casting liquid in the field of reverse osmosis membrane technology. The obtained reverse osmosis membrane support material has a double-layer structure with different sulfonic acid group contents, and also exhibits different hydrophilicity on the outer surfaces on both sides. Therefore, when used as a support material and compounded with the casting liquid of the reverse osmosis membrane, the phase conversion speed and penetration depth of the membrane liquid on the coated surface and the non-coated surface during the casting process can be accurately and effectively controlled, thereby optimizing the structure of the entire reverse osmosis membrane, improving its water flux, and ultimately improving its comprehensive water treatment effect.

[0039] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0040] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0041] Example 1

[0042] Preparation of a reverse osmosis membrane supporting material:

[0043] S1, using polyethylene terephthalate fibers with a diameter of 10 μm, a length of 7 mm, and a normal moisture regain of 0.4% as the first and second fibers, spraying 4 g / L of dilute sulfuric acid on the surface of the first fiber, then heating the fiber in an oven at 90° C. for 1 h, to obtain a first main fiber with a normal moisture regain of 0.54%; spraying 1 g / L of dilute sulfuric acid on the surface of the second fiber, then heating the fiber in an oven at 80° C. for 0.5 h, to obtain a second main fiber with a normal moisture regain of 0.45%;

[0044] S2, using polyethylene terephthalate fiber with a diameter of 10 μm and a length of 7 mm as the first bonding fiber, and water as the dilution dispersion, and preparing the obtained first main fiber and the first bonding fiber into a first slurry at a mass ratio of 65:35, diluting the obtained first slurry to a concentration of 0.05‰, and then papermaking and screen-printing, and drying to obtain a first base paper with a thickness of 134 μm, i.e., a first supporting layer;

[0045] S3, in the same manner as S2, the first main fiber is replaced with the second main fiber obtained in S1 to obtain a second base paper with a thickness of 117 μm, i.e., a second support layer;

[0046] S4, the first base paper and the second base paper are rolled into a roll by a rewinder, i.e., the third base paper, wherein the first base paper is on the top and the second base paper is on the bottom; after hot pressing treatment with the upper and lower rollers at a temperature of 200° C., a reverse osmosis membrane supporting material with a thickness of 104 μm is obtained, wherein the thickness ratio of the first supporting layer to the second supporting layer is 1.15:1.

[0047] Example 2

[0048] Preparation of a reverse osmosis membrane supporting material:

[0049] The difference between this embodiment and embodiment 1 is only that:

[0050] In step S1, the modification conditions of the first fiber are changed to: spraying 5 g / L of dilute sulfuric acid on the surface of the first fiber, and then heating the fiber in an oven at 130° C. for 1 h to obtain a first main fiber with a normal moisture regain of 0.58%;

[0051] In step S4, the temperature of the upper and lower rollers during the hot pressing treatment is 230° C., and a reverse osmosis membrane support material with a thickness of 99 μm is obtained;

[0052] The rest of the conditions are the same.

[0053] Example 3

[0054] Preparation of a reverse osmosis membrane supporting material:

[0055] The only difference between this embodiment and embodiment 1 is that in step S1, the modification condition of the first fiber is changed to: spray 12 g / L of dilute sulfuric acid on the surface of the first fiber, and then place the fiber in an oven at 130°C and heat it for 1 hour to obtain a first main fiber with a formal moisture regain of 0.81%; step S4 is consistent with embodiment 2; and the other conditions are the same.

[0056] Example 4

[0057] Preparation of a reverse osmosis membrane supporting material:

[0058] The difference between this embodiment and embodiment 1 is only that:

[0059] In step S2, the thickness of the first base paper is 108 μm;

[0060] In step S3, the thickness of the first base paper is 135 μm;

[0061] The rest of the conditions are the same.

[0062] The thickness ratio of the first supporting layer to the second supporting layer in the obtained reverse osmosis membrane supporting material is 0.8:1.

[0063] Example 5

[0064] Preparation of a reverse osmosis membrane supporting material:

[0065] The difference between this embodiment and embodiment 1 is only that:

[0066] In step S2, the thickness of the first base paper is 108 μm;

[0067] In step S3, the thickness of the first base paper is 118 μm;

[0068] The rest of the conditions are the same.

[0069] The thickness ratio of the first supporting layer to the second supporting layer in the obtained reverse osmosis membrane supporting material is 0.92:1.

[0070] Example 6

[0071] Preparation of a reverse osmosis membrane supporting material:

[0072] The difference between this embodiment and embodiment 1 is only that:

[0073] In step S2, the thickness of the first base paper is 142 μm;

[0074] In step S3, the thickness of the first base paper is 118 μm;

[0075] The rest of the conditions are the same.

[0076] The thickness ratio of the first supporting layer to the second supporting layer in the obtained reverse osmosis membrane supporting material is 1.20:1.

[0077] Example 7

[0078] Preparation of a reverse osmosis membrane supporting material:

[0079] The only difference between this embodiment and embodiment 1 is that in step S2, the weight ratio of the first main fiber to the first bonding fiber is 50:50.

[0080] The rest of the conditions are the same.

[0081] Example 8

[0082] Preparation of a reverse osmosis membrane supporting material:

[0083] The only difference between this embodiment and embodiment 1 is that in step S2, the weight ratio of the first main fiber to the first bonding fiber is 70:30.

[0084] The rest of the conditions are the same.

[0085] Example 9

[0086] Preparation of a reverse osmosis membrane supporting material:

[0087] The only difference between this embodiment and embodiment 1 is that in step S1, the modification temperature of the first fiber is 75°C, and the modification temperature of the second fiber is 70°C.

[0088] Example 10

[0089] Preparation of a reverse osmosis membrane supporting material:

[0090] The only difference between this embodiment and embodiment 1 is that in step S1, the modification temperature of the first fiber is 160°C, and the modification temperature of the second fiber is 70°C.

[0091] Embodiment 11

[0092] Preparation of a reverse osmosis membrane supporting material:

[0093] The only difference between this embodiment and embodiment 1 is that in steps S2 and S3, the concentration of the first slurry and the second slurry is 0.04‰; and in step S4, the temperature of the upper and lower rollers is 140°C.

[0094] Example 12

[0095] Preparation of a reverse osmosis membrane supporting material:

[0096] The only difference between this embodiment and embodiment 1 is that in steps S2 and S3, the concentration of the first slurry and the second slurry is 0.6‰; and in step S4, the temperature of the upper and lower rollers is 250°C.

[0097] Example 13

[0098] Preparation of a reverse osmosis membrane supporting material:

[0099] The only difference between this embodiment and embodiment 1 is that the modification of the first fiber and the second fiber is not achieved by dilute sulfuric acid, but the fibers are first formulated into a slurry and then paper-made onto a mesh to obtain base paper, and then the obtained first and second base papers are modified with reference to the method in the specific implementation manner of patent document CN108671755A (the first base paper uses 1% chlorosulfonic acid, and the second base paper uses 0.25% chlorosulfonic acid, and the neutralization and washing conditions are the same).

[0100] Comparative Example 1

[0101] Preparation of a reverse osmosis membrane supporting material:

[0102] The difference between this comparative example and Example 1 is that in step S3, the first main fiber is not replaced by the second main fiber, but the same steps are repeated with the first main fiber to obtain a support layer identical to the first support layer. That is, this comparative example is a reverse osmosis membrane support material obtained by compounding two identical first support layers.

[0103] Comparative Example 2

[0104] Preparation of a reverse osmosis membrane supporting material:

[0105] The difference between this comparative example and Example 1 is that two identical second support layers composed of the second main fibers obtained in step S3 are compounded. That is, this comparative example is a reverse osmosis membrane support material obtained by compounding two identical second support layers.

[0106] Comparative Example 3

[0107] Preparation of a reverse osmosis membrane supporting material:

[0108] The only difference between this comparative example and Example 1 is that the first fiber and the second fiber are not modified with dilute sulfuric acid, but are directly mixed with the bonding fiber to prepare two layers of base paper, and then composited to obtain the supporting material.

[0109] That is, this comparative example is a reverse osmosis membrane support material obtained by compounding two identical support layers prepared from fibers that have not been modified in any way.

[0110] Comparative Example 4

[0111] Preparation of a reverse osmosis membrane supporting material:

[0112] The difference between this comparative example and Example 1 is that in step S1, the second fiber is not modified with dilute sulfuric acid. That is, in this comparative example, the first support layer is compounded with the support layer prepared from the fiber without any modification, thereby obtaining the reverse osmosis membrane support material.

[0113] Comparative Example 5

[0114] Preparation of a reverse osmosis membrane supporting material:

[0115] The only difference between this comparative example and Example 1 is that in step S1, the concentration of the dilute sulfuric acid used for modifying the first fiber is 14 g / L, and the concentration of the dilute sulfuric acid used for modifying the second fiber is 0.8 g / L.

[0116] Test Method

[0117] The official moisture regain of the fiber: According to the method of GB / T 6503-2008, the official moisture regain of each main fiber obtained in each embodiment and comparative example was tested respectively;

[0118] Sulfonation degree: The percentage of sulfur on the surface of the support layer is directly measured by an element analyzer to determine the sulfonation degree of the support layer. The sulfonation degrees of each support layer obtained in each embodiment and comparative example are tested respectively;

[0119] Thickness: According to the method of GB / T451.3-2002, the thickness of each layer and the entire reverse osmosis membrane support material obtained in each embodiment and comparative example was tested;

[0120] Gram weight: According to the method of GB / T451.2-2002, the gram weight of the whole reverse osmosis membrane support material obtained in each embodiment and comparative example was tested;

[0121] Longitudinal tensile strength: According to the method of GB / T 12914-2018, the longitudinal tensile strength of the entire reverse osmosis membrane support material obtained in each embodiment and comparative example was tested;

[0122] Surface roughness: A KOSAKA LAB SE8C surface roughness meter was used with a probe test force of 0.75 mN and a measurement length of 5 mm to test the surface roughness of the upper surface and the lower surface of the reverse osmosis membrane support material obtained in each embodiment and comparative example (the upper surface is defined as the outer surface of the first support layer, and the lower surface is defined as the outer surface of the second support layer);

[0123] Water contact angle: using a JY-82A fully automatic video contact angle measuring instrument, the droplet size was controlled at 2 μL, and the water contact angles of the upper surface and lower surface of the reverse osmosis membrane support material obtained in each embodiment and comparative example were tested respectively (the upper surface is defined as the outer surface of the first support layer, and the lower surface is defined as the outer surface of the second support layer);

[0124] Water flux: The water flux of the reverse osmosis membrane support material obtained in each embodiment and comparative example is tested according to the volume of water flowing through the unit area per unit time at 0.1 MPa. For the reverse osmosis membrane support material obtained in the present invention, when its water flux is 9000 L / m 2 *h~14000L / m 2 *h, it can be considered that the reverse osmosis membrane supporting material can provide sufficient water path channels for the reverse osmosis membrane to ensure sufficient water flux.

[0125] The test results are shown in Tables 1-1 and 1-2 (the first layer in the table is the first supporting layer, and the second layer is the second supporting layer).

[0126] Table 1-1

[0127]

[0128] Table 1-2

[0129]

[0130] From the above description, it can be seen that the above embodiments of the present invention achieve the preparation of reverse osmosis membrane supporting materials with excellent performance. The obtained materials not only have excellent mechanical properties, but also can provide sufficient water path channels for the reverse osmosis membrane to ensure sufficient water flux.

[0131] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0132] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A reverse osmosis membrane supporting material, characterized in that: The reverse osmosis membrane supporting material comprises a first supporting layer and a second supporting layer stacked in sequence, wherein the first supporting layer and the second supporting layer both contain sulfonic acid groups; The sulfonation degree of the first supporting layer is higher than that of the second supporting layer, and the difference between the sulfonation degree of the first supporting layer and the second supporting layer is 0.1% to 10%.

2. The reverse osmosis membrane supporting material according to claim 1, characterized in that: The sulfonation degree of the first supporting layer is 6% to 11%.

3. The reverse osmosis membrane supporting material according to claim 1 or 2, characterized in that: The thickness of the reverse osmosis membrane supporting material is 80 μm to 120 μm; Preferably, the thickness ratio of the first supporting layer to the second supporting layer is (0.92-1.15):

1.

4. The reverse osmosis membrane supporting material according to any one of claims 1 to 3, characterized in that: The first supporting layer and the second supporting layer each independently include a main fiber and a bonding fiber, and the main fiber carries the sulfonic acid group; Preferably, the diameter of the main fiber and the bonding fiber are each independently 3 μm to 20 μm, and the length of the main fiber and the bonding fiber are each independently 2 mm to 15 mm.

5. The reverse osmosis membrane supporting material according to claim 4, characterized in that: In the first supporting layer and the second supporting layer, the weight ratio of the main fiber to the bonding fiber is independently (60-65): (35-40); Preferably, the main fiber is selected from polyester fiber; and the bonding fiber is selected from one or more of polyester fiber and polyolefin fiber.

6. The reverse osmosis membrane supporting material according to any one of claims 1 to 5, characterized in that: The first supporting layer has a first outer surface away from the second supporting layer, and the second supporting layer has a second outer surface away from the first supporting layer; the water contact angle of the first outer surface is smaller than the water contact angle of the second outer surface, and the difference between the first outer surface and the water contact angle of the second outer surface is 5.0° to 55.0°.

7. A method for preparing a reverse osmosis membrane supporting material according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, performing a first modification on the first fiber using a first sulfuric acid solution to obtain a first main fiber, wherein the first main fiber carries the sulfonic acid group; performing a second modification on the second fiber using a second sulfuric acid solution to obtain a second main fiber; S2, preparing the first main fiber and the first bonding fiber into a first slurry, and applying the first slurry to a web to obtain the first supporting layer; S3, preparing the second main fiber and the second bonding fiber into a second slurry, and applying the second slurry to a web to obtain the second supporting layer; S4, the first supporting layer and the second supporting layer are compounded and hot-pressed to obtain the reverse osmosis membrane supporting material; The concentrations of the first sulfuric acid solution and the second sulfuric acid solution are each independently 1 g / L to 12 g / L.

8. The method for preparing a reverse osmosis membrane supporting material according to claim 7, characterized in that: The concentration of the first sulfuric acid solution is higher than that of the second sulfuric acid solution, and the difference in concentration between the first sulfuric acid solution and the second sulfuric acid solution is 3 g / L to 11 g / L.

9. The method for preparing a reverse osmosis membrane supporting material according to claim 7 or 8, characterized in that: The reaction temperature of the first modification and the second modification is independently 80°C to 150°C, and the reaction time is independently 0.5h to 30h; Preferably, the reaction temperature of the first modification is higher than the reaction temperature of the second modification, and the difference between the reaction temperature of the first modification and the reaction temperature of the second modification is 10°C to 50°C.

10. The method for preparing a reverse osmosis membrane supporting material according to any one of claims 7 to 9, characterized in that: The concentrations of the first slurry and the second slurry are independently 0.05‰ to 0.5‰.

11. The method for preparing a reverse osmosis membrane supporting material according to any one of claims 7 to 10, characterized in that: The temperatures of the upper and lower rollers of the hot pressing are independently 150°C to 240°C.

12. Use of the reverse osmosis membrane supporting material according to any one of claims 1 to 6 as a support for a membrane casting liquid in the field of reverse osmosis membrane technology.

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