Method for preparing reverse osmosis membrane and reverse osmosis membrane prepared thereby

Abstract

The present invention relates to a method for preparing a reverse osmosis membrane and a reverse osmosis membrane prepared thereby. The method comprises the following steps: preparing a polymer solution as a membrane casting solution, and coating a reinforcing material with the membrane casting solution to form a polymer supporting layer; a desalination layer is formed by contacting a polymer support layer with an aqueous phase solution containing an amine compound and an oil phase solution containing an acyl chloride compound in a slit coating manner, in which N slit coating heads are respectively provided in the lateral direction during contact with the oil phase solution so as to respectively form N coating regions, and from the second coating region, N is a positive integer greater than or equal to 1, and N is a negative integer greater than or equal to 2. The coating flow of each coating area is gradually increased relative to the coating flow of the previous coating area; and performing post-treatment to obtain the reverse osmosis membrane. The reverse osmosis membrane prepared by the method provided by the invention has gradual change performance (including gradual change of water flux and gradual change of desalination rate), effectively reduces the flux attenuation of the membrane element in the operation process, and improves the anti-pollution performance.

Description

Technical Field

[0001] The invention relates to the technical field of reverse osmosis membranes, and in particular to a method for preparing a reverse osmosis membrane with gradually changing performance (including gradually changing water flux and gradually changing desalination rate) and the reverse osmosis membrane prepared thereby. Background Art

[0002] Reverse osmosis membranes have the characteristics of high separation efficiency, simple separation process, low energy consumption and environmental protection, and have been widely used in seawater desalination, wastewater treatment, drinking water purification, brackish water desalination, industrial ultrapure water, petrochemicals, pharmaceuticals and printing and dyeing. Although it has made great progress in the past two decades, it still faces many challenges in its actual application, among which membrane pollution is particularly prominent.

[0003] In the production of reverse osmosis membranes, the effective width is basically about 1000mm. The entire reverse osmosis membrane pursues the uniformity of macroscopic morphology, permeability, desalination rate and other properties. The more uniform the performance of the reverse osmosis membrane, the more stable the performance of the membrane element rolled with it. Therefore, under the existing membrane making process, it is particularly important to control the production stability of the reverse osmosis membrane. However, during the use of the membrane element, due to the penetration of water and the concentration of materials, the concentration of concentrated water in different areas of the membrane element is not consistent. Generally, the concentration near the central tube or the concentrated water outlet is higher, while the concentration at the water inlet is relatively low. Therefore, there is often fouling and scaling near the central tube and the concentrated water outlet. It can be considered that the overall uniformity of the membrane page is not the best choice in the actual application process. Especially for reverse osmosis membranes with high water flux, due to the large micropores of the membrane, the risk of fouling of the membrane element is aggravated. Commonly used methods to improve the anti-fouling performance of membrane elements include reducing the length of membrane pages, increasing the solution flow rate and the width of the concentrate flow channel. Although these methods have a certain effect on improving the anti-fouling performance of membrane elements, they cannot fundamentally solve the problem of performance attenuation of membrane elements. Summary of the invention

[0004] Problem that the invention aims to solve

[0005] In view of the above-mentioned defects in the prior art, an object of the present invention is to provide a method for preparing a reverse osmosis membrane with improved anti-fouling performance and a reverse osmosis membrane prepared by the method.

[0006] Solutions for solving problems

[0007] The inventors of the present invention have discovered through in-depth research that a desalination layer with gradient properties can be formed by adopting slit coating technology and adjusting coating process parameters, thereby preparing a reverse osmosis membrane with gradient properties including gradient water flux and gradient desalination rate, effectively reducing the flux attenuation of the membrane element during operation and improving the anti-pollution performance.

[0008] The present invention provides a method for preparing a reverse osmosis membrane, the method comprising the following steps:

[0009] Preparing a polymer solution as a casting solution, and coating the casting solution on the reinforcing material to form a polymer support layer;

[0010] The polymer support layer is contacted with an aqueous solution containing an amine compound and an oily solution containing an acyl chloride compound by slit coating to form a desalting layer, wherein when contacting with the oily solution, N slit coating heads are respectively arranged in a transverse direction to form N coating areas respectively, and starting from the second coating area, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area;

[0011] After post-treatment, a reverse osmosis membrane is obtained.

[0012] According to the preparation method of the present invention, the polymer is at least one selected from bisphenol A type polysulfone, polyaryl sulfone, polyether sulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0013] According to the preparation method of the present invention, the amine compound is selected from one or a combination of two of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, mesitylenetriamine, 1,4-cyclohexanediamine, N,N-dimethylcyclohexanediamine, diaminobenzenesulfonic acid, diaminobenzoic acid, melamine, and ethylenediamine; preferably, the concentration of the amine compound is 2 to 8 wt % based on the weight of the aqueous phase solution.

[0014] According to the preparation method of the present invention, the aqueous phase solution further comprises an aqueous phase auxiliary agent, and the concentration of the aqueous phase auxiliary agent is 5 to 20 wt % based on the weight of the aqueous phase solution.

[0015] According to the preparation method of the present invention, the acyl chloride compound is at least one selected from terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, biphenyl dichloride, cyclohexane dichloride, succinoyl chloride, succinoyl chloride, trimesoyl chloride, cyclobutane-1,2-dicarboxylic acid chloride, 1,3,5-cyclohexane trimesoyl chloride, biphenyl trimesoyl chloride, 5-oxoformyl chloride-isophthaloyl chloride, biphenyl tetracarboxylic acid chloride, 2,6-naphthalene dicarboxylic acid chloride, glutaryl chloride, and benzene disulfonyl chloride; preferably, the concentration of the acyl chloride compound is 0.20-0.40wt% based on the weight of the oil phase solution.

[0016] According to the preparation method of the present invention, the oil phase solution further comprises an oil phase auxiliary agent, and the concentration of the oil phase auxiliary agent is 5 to 15 wt % based on the weight of the oil phase solution.

[0017] According to the preparation method of the present invention, in the slit coating mode, when in contact with the oil phase solution, the coating gap is 0.1-1 mm, the coating flow rate is 100-1000 ml / min, and preferably, N is 2-10.

[0018] The present invention also provides a reverse osmosis membrane prepared according to the preparation method of the present invention, which comprises a desalination layer with gradient performance, wherein the performance includes water flux and desalination rate.

[0019] Effects of the Invention

[0020] Compared with the reverse osmosis membrane with uniform performance prepared by the traditional dip coating process, the reverse osmosis membrane prepared by the method of the present invention comprises a desalination layer with gradual performance (including gradual water flux and gradual desalination rate), and the density of the desalination layer gradually increases along the lateral direction of the membrane page. The reverse osmosis membrane provided by the present invention has gradual performance including gradual water flux and gradual desalination rate and high water flux, effectively reducing the flux attenuation of the membrane element during operation and improving the anti-pollution performance.

[0021] When the reverse osmosis membrane with gradually changing performance provided by the present invention is rolled into a 3012 membrane element, high flux and high desalination rate can be obtained. After producing 10 tons of water, the flux attenuation rate can be as low as 10.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram showing a reverse osmosis membrane prepared according to the method of the present invention. DETAILED DESCRIPTION

[0023] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0024] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0025] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0026] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0027] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0028] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0029] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 10-40°C.

[0030] The present invention relates to a method for preparing a reverse osmosis membrane, which comprises the following steps:

[0031] Preparing a polymer solution as a casting solution, and coating the casting solution on the reinforcing material to form a polymer support layer;

[0032] The polymer support layer is contacted with an aqueous solution containing an amine compound and an oily solution containing an acyl chloride compound by slit coating to form a desalting layer, wherein when contacting with the oily solution, N slit coating heads are respectively arranged in a transverse direction to form N coating areas respectively, and starting from the second coating area, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area;

[0033] After post-treatment, a reverse osmosis membrane is obtained.

[0034] The technical concept of the preparation method of the present invention is to adopt a slit coating technology and adjust the coating process parameters to form a desalination layer with gradient performance, the density of which gradually increases along the lateral direction of the membrane page, thereby preparing a reverse osmosis membrane with gradient performance including gradient water flux and gradient desalination rate, effectively reducing the flux attenuation of the membrane element during operation and improving the anti-pollution performance.

[0035] In the preparation method of the present invention, a polymer solution is prepared as a casting solution, and the casting solution is coated on a reinforcing material to form a polymer support layer. Preferably, the reinforcing material is a PET non-woven fabric or a PP non-woven fabric. There is no particular limitation on the coating method, and a casting method, a dip coating method, a blade coating method, a slit coating method, etc. can be used. Slit coating is more preferred, and a support layer with more uniform thickness and micropores can be obtained.

[0036] After the casting solution is coated on the reinforcing material, it is then immersed in a coagulation bath, so that the casting solution is coagulated to form a polymer support layer. In the preparation method of the present invention, preferably, the coagulation bath is a water bath, and the coagulation bath temperature is 8-20°C.

[0037] In the preparation method of the present invention, the polymer support layer is contacted with an aqueous solution containing amine compounds and an oily solution containing acyl chloride compounds by slit coating to form a desalting layer, wherein when contacting with the oily solution, N slit coating heads are respectively arranged in the lateral direction to form N coating areas respectively, and starting from the second coating area, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area.

[0038] In the preparation method of the present invention, preferably, in the slit coating method, when in contact with the oil phase solution, the coating gap (i.e., the gap between the lip and the back roller in the slit coating device) is set to 0.1-1 mm, and the coating flow rate is set to 100-1000 ml / min. Preferably, the process parameters of the slit coating are as follows: the main machine speed is 15-30 m / min.

[0039] When in contact with the oil phase solution, N slit coating heads are respectively arranged in the lateral direction to form N coating areas respectively. The number of slit coating heads can be set according to the required performance to form a corresponding number of coating areas. From the second coating area, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area. From the perspective of the processing difficulty and manufacturing cost of the slit coating head, preferably, 2 to 10 slit coating heads are arranged to form 2 to 10 coating areas accordingly, and more preferably, 2 to 5 slit coating heads are arranged to form 2 to 5 coating areas accordingly.

[0040] The incremental increase of the coating flow rate can be set according to the required performance. Preferably, the coating flow rate of each coating area increases by 1 to 10 ml / min relative to the coating flow rate of the previous coating area. More preferably, the incremental increase is 1 to 5 ml / min.

[0041] In the preparation method of the present invention, the polymer is at least one selected from bisphenol A type polysulfone, polyaryl sulfone, polyether sulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0042] In the preparation method of the present invention, the amine compound is selected from one or a combination of two of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, iso-phenylenediamine, 1,4-cyclohexanediamine, N,N-dimethylcyclohexanediamine, diaminobenzenesulfonic acid, diaminobenzoic acid, melamine, and ethylenediamine; preferably, the concentration of the amine compound is 2 to 8 wt % based on the weight of the aqueous phase solution; more preferably, when a combination of two of the amine compounds listed above is used, the mass ratio of the two amine compounds is 1:1.

[0043] In the preparation method of the present invention, the aqueous phase solution further comprises an aqueous phase auxiliary agent, which functions to increase the water flux of the reverse osmosis membrane. Preferably, the aqueous phase auxiliary agent is at least one selected from dimethyl pyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, ethylene glycol monomethyl ether, methanol, ethanol, propanol, n-butanol, ethylene glycol, ethylamine, ethylenediamine, n-butylamine, ethanolamine, isopropanol, glycerol, and sorbitol.

[0044] Preferably, the concentration of the aqueous phase auxiliary agent is 5-20wt% based on the weight of the aqueous phase solution. When the concentration is lower than 5wt%, the flux of the obtained reverse osmosis membrane is lower; when the concentration is higher than 20wt%, the film forming property of the reverse osmosis membrane is poor and the desalination rate is lower.

[0045] In the preparation method of the present invention, preferably, the aqueous phase solution further comprises an alkali metal hydroxide as an aqueous phase acid-binding agent, and the alkali metal hydroxide may be, for example, sodium hydroxide.

[0046] In the preparation method of the present invention, the acyl chloride compound is at least one selected from terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, biphenyl dichloride, cyclohexane dichloride, succinoyl chloride, succinoyl chloride, trimesoyl chloride, cyclobutane-1,2-dicarboxylic acid chloride, 1,3,5-cyclohexane trimesoyl chloride, biphenyl trimesoyl chloride, 5-oxoformyl chloride-isophthaloyl chloride, biphenyl tetracarboxylic acid chloride, 2,6-naphthalene dicarboxylic acid chloride, glutaryl trichloride, and benzene disulfonyl chloride; preferably, based on the weight of the oil phase solution, the concentration of the acyl chloride compound is 0.20-0.40wt%.

[0047] In the preparation method of the present invention, the oil phase solution also contains an oil phase auxiliary agent, which functions to enhance the miscibility of the oil phase with water, thereby increasing the diffusion rate of the amine compound and forming a thicker interfacial reaction zone, so that the degree of crosslinking is further increased. Preferably, the oil phase auxiliary agent is at least one selected from acetone, toluene, xylene, trimethylbenzene, trimethyl phosphate, and triphenyl phosphate.

[0048] Preferably, the concentration of the oil phase auxiliary agent is 5 to 15 wt % based on the weight of the oil phase solution.

[0049] Preferably, in the preparation method of the present invention, in the slit coating mode of the aqueous solution, the coating gap is set to 0.1-1 mm, and the coating flow rate is set to 500-1500 ml / min. Preferably, the process parameters of the slit coating are as follows: the main machine speed is 15-30 m / min.

[0050] The prepared polymer support layer is sequentially subjected to aqueous solution slit coating, oil solution slit coating and reaction zone (ie, the area between the oil solution slit coating and the cleaning zone) for interfacial polymerization reaction to form a desalting layer.

[0051] After that, post-treatment is performed, which includes heat treatment, such as heating in an oven. There is no particular restriction on the heat treatment temperature, which is usually 60° C.; there is no particular restriction on the heat treatment time, which is usually 1 to 10 minutes.

[0052] In the preparation method of the present invention, preferably, the post-treatment further comprises moisturizing treatment using an aqueous solution containing 5 wt% glycerol, and drying is performed after moisturizing to obtain a high-flux reverse osmosis membrane with gradient performance.

[0053] like Figure 1 As shown, the reverse osmosis membrane prepared by the method of the present invention has continuous regions 1, 2, ..., N along the transverse direction, and the salt rejection rate of the reverse osmosis membrane increases gradually along the transverse direction.

[0054] As a non-limiting example, the method for preparing a reverse osmosis membrane of the present invention comprises the following steps:

[0055] Step 1: Prepare the polymer support layer: Dissolve the polymer with a concentration of 18wt% in the solvent, stir at 80℃ for 8h until the polymer is completely dissolved to obtain the casting solution. Let it stand for 10h to degas; apply the casting solution evenly on the non-woven fabric through a slit coating device, set the coating gap to 0.15mm, the coating flow rate to 2500ml / min, and the speed of the coating device to 20m / min, and form the polymer support layer after phase inversion in a water bath (such as reverse osmosis water) at a temperature of 8-20℃;

[0056] Step 2: Prepare the reverse osmosis membrane

[0057] (1) preparing an aqueous phase solution: pouring an amine compound with a concentration of 2-8 wt%, sodium hydroxide with a concentration of 0.05 wt%, and an aqueous phase auxiliary agent with a concentration of 5-20 wt% into a container containing 75-90 wt% of reverse osmosis water, stirring for 2 h until the amine compound and the aqueous phase auxiliary agent are completely dissolved, and then pouring into a storage tank for standby use;

[0058] (2) preparing an oil phase solution: adding 0.20-0.40 wt% of an acyl chloride compound and 5-15 wt% of an oil phase additive into a container containing 84.6-94.8 wt% of cyclohexane, stirring for 1 h until the acyl chloride compound is completely dissolved, and then pouring into a storage tank for standby use;

[0059] (3) Preparation of reverse osmosis membrane: Open the slit coating equipment, set the coating gap to 0.1-1mm, set the main engine speed to 15-30m / min, set the coating flow rate of the aqueous solution to 500-1500ml / min, set the coating flow rate of the oil phase solution to 100-1000ml / min, and for each additional coating area, if the coating flow rate of the previous area is X, the coating flow rate of this area is X+5ml / min, and so on. The polymer support layer prepared in the first step is sequentially subjected to aqueous solution coating, oil phase solution coating, and interfacial polymerization reaction area, and then enters the oven, and then is washed with pure water and moisturized with glycerol, and finally dried to obtain a reverse osmosis membrane.

[0060] The present invention also relates to a reverse osmosis membrane prepared by the preparation method according to the present invention, which comprises a desalination layer with gradient performance, wherein the performance includes water flux and desalination rate. Preferably, the reverse osmosis membrane comprises, from bottom to top, a non-woven fabric layer, a polymer support layer, and a desalination layer.

[0061] Example

[0062] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0063] Comparative Example 1

[0064] Step 1: Preparation of polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18wt%, stir at 80°C for 8h until the polymer is completely dissolved, and stand for degassing for 10h. The casting solution is coated on the PET non-woven fabric through a slit coating device, the coating gap is set to 0.15mm, the coating flow rate is set to 2500ml / min, and the speed of the coating device is set to 20m / min. The polysulfone support layer is formed after phase inversion in a coagulation bath at a temperature of 8°C, i.e., reverse osmosis produced water.

[0065] Step 2: Preparation of reverse osmosis membrane

[0066] (1) Preparation of aqueous solution: Pour 7 wt % m-phenylenediamine (as amine monomer), 0.05 wt % sodium hydroxide, and 15 wt % dimethylpyrrolidone (as aqueous phase auxiliary agent) into a container containing 79.95 wt % reverse osmosis water, stir for 2 h until the amine monomer and aqueous phase auxiliary agent are completely dissolved, and then pour into a storage tank for standby use;

[0067] (2) Preparation of oil phase solution: Add 0.4 wt % of trimesoyl chloride (as acyl chloride monomer) and 15 wt % of toluene (as oil phase auxiliary agent) into a container containing 84.8 wt % of cyclohexane, stir for 1 h until the acyl chloride monomer is completely dissolved, and then pour into a storage tank for standby use;

[0068] (3) Preparation of reverse osmosis membrane: The slit coating device was turned on, the coating gap was set to 0.1 mm, the main engine speed was set to 20 m / min, the coating flow rate of the aqueous solution was set to 1000 ml / min, and the coating flow rate of the oil phase solution was set to 500 ml / min. The polymer support layer prepared in the first step was sequentially subjected to aqueous coating, oil phase coating and reaction zone for reaction, and then entered into an oven for washing with pure water and moisturizing with glycerol, and then dried to obtain a reverse osmosis membrane C1.

[0069] Example 1

[0070] Example 1 was carried out in the same manner as Comparative Example 1, except that there were two coating areas, the flow rate of the oil phase solution in the first coating area was 500 ml / min, and the flow rate in the second coating area was 505 ml / min, to prepare a reverse osmosis membrane E1.

[0071] Example 2

[0072] Example 2 was carried out in the same manner as Comparative Example 1, except that there were three coating areas, the flow rate of the oil phase solution in the first coating area was 500 ml / min, the flow rate in the second coating area was 505 ml / min, and the flow rate in the third coating area was 510 ml / min, to produce reverse osmosis membrane E2.

[0073] Example 3

[0074] Example 3 was carried out in the same manner as Comparative Example 1, except that there were 4 coating areas, the flow rate of the oil phase solution in the first coating area was 500 ml / min, the flow rate in the second coating area was 505 ml / min, the flow rate in the third coating area was 510 ml / min, and the flow rate in the fourth coating area was 515 ml / min, to obtain reverse osmosis membrane E3.

[0075] Example 4

[0076] Example 4 was carried out in the same manner as Comparative Example 1, except that there were 5 coating areas, the flow rate of the oil phase solution in the first coating area was 500 ml / min, the flow rate in the second coating area was 505 ml / min, the flow rate in the third coating area was 510 ml / min, the flow rate in the fourth coating area was 515 ml / min, and the flow rate in the fifth coating area was 520 ml / min, to obtain reverse osmosis membrane E4.

[0077] Example 5

[0078] Step 1: Preparation of polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18wt%, and stir at 80°C for 8h until the polymer is completely dissolved. Let it stand for degassing for 10h. Coat the casting solution on the PET non-woven fabric through a slit coating device, set the coating gap to 0.15mm, the coating flow rate to 2500ml / min, and the speed of the coating device to 20m / min. After phase inversion in a coagulation bath at a temperature of 10°C, i.e., reverse osmosis produced water, a polysulfone support layer is formed.

[0079] Step 2: Preparation of reverse osmosis membrane

[0080] (1) Preparation of aqueous solution: Pour 4.95 wt% p-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 20 wt% dimethyl sulfoxide (as aqueous phase auxiliary agent) into a container containing 75 wt% reverse osmosis water, stir for 2 h until the amine monomer and aqueous phase auxiliary agent are completely dissolved, and then pour into a storage tank for standby use;

[0081] (2) Preparation of oil phase solution: Add 0.2 wt % of biphenyltetracarbonyl chloride (as acyl chloride monomer) and 15 wt % of acetone (as oil phase auxiliary agent) into a container containing 84.8 wt % of cyclohexane, stir for 1 h until the acyl chloride monomer is completely dissolved, and then pour into a storage tank for standby use;

[0082] (3) Preparation of reverse osmosis membrane: The slit coating device was turned on, the coating gap was set to 0.3 mm, the coating flow rate of the aqueous solution was set to 1500 ml / min, the flow rate of the first coating area of ​​the oil solution was 900 ml / min, the flow rate of the second coating area was 905 ml / min, the flow rate of the third coating area was 910 ml / min, the flow rate of the fourth coating area was 915 ml / min, the flow rate of the fifth coating area was 920 ml / min, and the main engine speed was set to 30 m / min. The polymer support layer prepared in the first step was sequentially subjected to aqueous coating, oil coating and reaction zone for reaction, and then entered into an oven, washed with pure water and moisturized with glycerol, and then dried to obtain a reverse osmosis membrane E5.

[0083] Example 6

[0084] Step 1: Preparation of polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18wt%, and stir at 80°C for 8h until the polymer is completely dissolved. Let it stand for degassing for 10h. Coat the casting solution on the PET non-woven fabric through a slit coating device, set the coating gap to 0.15mm, the coating flow rate to 2500ml / min, and the speed of the coating device to 20m / min. After phase inversion in a coagulation bath at a temperature of 20°C, i.e., reverse osmosis produced water, a polysulfone support layer is formed.

[0085] Step 2: Preparation of reverse osmosis membrane

[0086] (1) Preparation of aqueous solution: Pour 2 wt% m-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 5 wt% dimethylformamide (as aqueous phase auxiliary agent) into a container containing 92.95 wt% reverse osmosis water, stir for 2 h until the amine monomer and auxiliary agent are completely dissolved, and then pour into a storage tank for standby use;

[0087] (2) Preparation of oil phase solution: Add 0.3 wt % of biphenyltetracarbonyl chloride (as acyl chloride monomer) and 15 wt % of xylene (as oil phase auxiliary agent) into a container containing 84.7 wt % of cyclohexane, stir for 1 h until the acyl chloride monomer is completely dissolved, and then pour into a storage tank for standby use;

[0088] (3) Preparation of reverse osmosis membrane: Open the slit coating equipment, set the coating gap to 0.2 mm, set the coating flow rate of the aqueous solution to 1000 ml / min, set the flow rate of the first coating area of ​​the oil solution to 350 ml / min, the flow rate of the second coating area to 355 ml / min, the flow rate of the third coating area to 360 ml / min, the flow rate of the fourth coating area to 365 ml / min, the flow rate of the fifth coating area to 370 ml / min, and set the main engine speed to 15 m / min. The polymer support layer prepared in the first step was sequentially subjected to aqueous coating, oil coating and reaction zone for reaction, and then entered into an oven, washed with pure water and moisturized with glycerol, and then dried to obtain a reverse osmosis membrane E6.

[0089] Example 7

[0090] Step 1: Preparation of polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18wt%, and stir at 80°C for 8h until the polymer is completely dissolved. Let it stand for degassing for 10h. Coat the casting solution on the PET non-woven fabric through a slit coating device, set the coating gap to 0.15mm, the coating flow rate to 2500ml / min, and the speed of the coating device to 20m / min. After phase inversion in a coagulation bath at a temperature of 8°C, i.e., reverse osmosis produced water, a polysulfone support layer is formed.

[0091] Step 2: Preparation of reverse osmosis membrane

[0092] (1) Preparation of aqueous phase solution: Pour 4 wt% m-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 15 wt% isopropanol (as aqueous phase auxiliary agent) into a container containing 81.95 wt% reverse osmosis water, stir for 2 h until the amine monomer and auxiliary agent are completely dissolved, and then pour into a storage tank for standby use;

[0093] (2) Preparation of oil phase solution: Add 0.25 wt % of biphenyltrichloride (as acyl chloride monomer) and 15 wt % of trimethylbenzene (as oil phase auxiliary agent) into a container containing 84.75 wt % of cyclohexane, stir for 1 h until the acyl chloride monomer is completely dissolved, and then pour into a storage tank for standby use;

[0094] (3) Preparation of reverse osmosis membrane: The slit coating device was turned on, the coating gap was set to 1 mm, the coating flow rate of the aqueous solution was set to 1500 ml / min, the flow rate of the first coating area of ​​the oil solution was 500 ml / min, the flow rate of the second coating area was 505 ml / min, the flow rate of the third coating area was 510 ml / min, the flow rate of the fourth coating area was 520 ml / min, the flow rate of the fifth coating area was 525 ml / min, and the main engine speed was set to 25 m / min. The polymer support layer prepared in the first step was sequentially subjected to aqueous coating, oil coating and reaction zone for reaction, and then entered into an oven, washed with pure water and moisturized with glycerol, and then dried to obtain a reverse osmosis membrane E7.

[0095] Membrane performance - water flux and salt rejection test

[0096] The performance test was carried out on each area of ​​the reverse osmosis membrane prepared in Comparative Example 1 and Examples 1 to 7. The operating conditions were as follows: the pressure was 100 psi, the water-effect solution was prepared according to the national standard GB34914-2021, the solution temperature was 25 ° C, the operation time was 0.5 h, the concentrated water flow rate was 1 L / min, and the water flux and desalination rate of the membrane were shown in Table 1:

[0097] Table 1

[0098]

[0099] The reverse osmosis membranes prepared in Comparative Example 1 and Examples 1 to 7 were respectively rolled into 3012 membrane elements for performance testing. The membrane pages were cut in a cross-cut manner, and the inlet water entered from the low desalination area end of the membrane. The specific test conditions of the membrane element were as follows: the pressure was 100 psi, the water-effect solution was prepared according to the national standard GB34914-2021, the solution temperature was 25 ° C, the recovery rate was 50%, and the flux and desalination rate of the membrane element were shown in Table 2:

[0100] Table 2

[0101]

[0102] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0103] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

[0104] Industrial Applicability

[0105] The reverse osmosis membrane prepared by the method of the present invention comprises a desalination layer with gradually changing performance (including gradually changing water flux and gradually changing salt rejection rate), and the density of the desalination layer gradually increases along the lateral direction of the membrane page. The reverse osmosis membrane provided by the present invention has gradually changing performance including gradually changing water flux and gradually changing salt rejection rate and high water flux, effectively reducing the flux attenuation of the membrane element during operation and improving the anti-pollution performance.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that: The following steps are involved: Preparing a polymer solution as a casting solution, and coating the casting solution on the reinforcing material to form a polymer support layer; The polymer support layer is contacted with an aqueous solution containing an amine compound and an oily solution containing an acyl chloride compound by slit coating to form a desalting layer, wherein when contacting with the oily solution, N slit coating heads are respectively arranged in a transverse direction to form N coating areas respectively, and starting from the second coating area, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area; After post-treatment, a reverse osmosis membrane is obtained.

2. The preparation method according to claim 1, wherein the polymer is at least one selected from bisphenol A type polysulfone, polyaryl sulfone, polyether sulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

3. The preparation method according to claim 1 or 2, wherein the amine compound is selected from one or a combination of two of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, mesitylenetriamine, 1,4-cyclohexanediamine, N,N-dimethylcyclohexanediamine, diaminobenzenesulfonic acid, diaminobenzoic acid, melamine, and ethylenediamine; preferably, the concentration of the amine compound is 2 to 8 wt % based on the weight of the aqueous phase solution.

4. The preparation method according to claim 1 or 2, wherein the aqueous phase solution further comprises an aqueous phase auxiliary agent, and the concentration of the aqueous phase auxiliary agent is 5 to 20 wt% based on the weight of the aqueous phase solution.

5. The preparation method according to claim 1 or 2, wherein the acyl chloride compound is at least one selected from terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, biphenyl dichloride, cyclohexane dichloride, succinoyl chloride, succinoyl chloride, trimesoyl chloride, cyclobutane-1,2-dicarboxylic acid chloride, 1,3,5-cyclohexane trimesoyl chloride, biphenyl trimesoyl chloride, 5-oxoformyl chloride-isophthaloyl chloride, biphenyl tetracarboxylic acid chloride, 2,6-naphthalene dicarboxylic acid chloride, glutaryl trichloride, and benzene disulfonyl chloride; preferably, the concentration of the acyl chloride compound is 0.20-0.40wt% based on the weight of the oil phase solution.

6. The preparation method according to claim 1 or 2, wherein the oil phase solution further comprises an oil phase auxiliary agent, and the concentration of the oil phase auxiliary agent is 5 to 15 wt% based on the weight of the oil phase solution. 7 . The preparation method according to claim 1 , wherein in the slit coating method, when in contact with the oil phase solution, the coating gap is 0.1 to 1 mm, the coating flow rate is 100 to 1000 ml / min, and preferably, N is 2 to 10.

8. A reverse osmosis membrane prepared by the preparation method according to any one of claims 1 to 7, characterized in that: Contains a desalination layer with graded properties.

9. The reverse osmosis membrane according to claim 8, wherein the performance includes water flux and salt rejection rate.

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