Reverse osmosis membrane preparation method and reverse osmosis membrane prepared thereby

Abstract

A reverse osmosis membrane preparation method and a reverse osmosis membrane prepared thereby. The method comprises the following steps: preparing a polymer solution as a casting solution, and coating a reinforcing material with the casting solution to form a polymer support layer; contacting the 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 to form a desalination layer, wherein when the polymer support layer is in contact with the oil phase solution, N slit coating heads are arranged respectively in a transverse direction so as to form N coating areas respectively, and starting from the second coating area, a coating flow in each coating area gradually increases relative to a coating flow in the previous coating area; and performing post-treatment to obtain a reverse osmosis membrane. The reverse osmosis membrane prepared by means of the method has gradually changed water flux and gradually changed desalination rate, thereby effectively reducing the flux decline of a membrane element in an operation process and improving the anti-pollution performance.

Description

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

[0001] Citation of Related Applications

[0002] This disclosure claims priority to invention patent application number 202310872966.3, filed in China on July 17, 2023, entitled “Method for preparing reverse osmosis membrane and reverse osmosis membrane prepared thereby”, and the entire contents of that patent application are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the technical field of reverse osmosis membranes, and in particular to a method for preparing a reverse osmosis membrane with gradually changing properties (including gradually changing water flux and gradually changing salt rejection rate) and the reverse osmosis membrane prepared thereby. Background Art

[0004] Reverse osmosis membranes, with their high separation efficiency, simple separation process, low energy consumption, and environmental friendliness, have been widely used in seawater desalination, wastewater treatment, drinking water purification, brackish water desalination, industrial ultrapure water, petrochemicals, pharmaceuticals, and printing and dyeing. Despite significant progress in the past two decades, practical applications still face numerous challenges, particularly membrane fouling.

[0005] In reverse osmosis membrane production, the effective width is generally around 1000mm. The entire membrane sheet is designed to achieve uniformity in macroscopic morphology, permeability, and salt rejection. The more uniform the membrane's performance, the more stable the performance of the membrane elements rolled from it. Therefore, controlling the stability of reverse osmosis membrane production is particularly important under existing membrane manufacturing processes. However, during membrane element operation, due to water permeation and material concentration, the concentration of the brine varies across different regions of the membrane element. It is generally higher near the center tube or the brine outlet, while the concentration at the inlet is relatively lower. Consequently, fouling and scaling often occur near the center tube and the brine outlet, suggesting that overall membrane uniformity is suboptimal in actual operation. This is particularly true for reverse osmosis membranes with high water flux, as the larger pores in the membrane increase the risk of fouling. Commonly used methods to improve the anti-fouling performance of membrane elements include reducing the membrane page length, 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 degradation of membrane elements.

[0006] Summary of the Invention

[0007] Problems to be solved by the invention

[0008] In view of the above-mentioned defects in the prior art, the purpose of the present disclosure 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.

[0009] Solutions for solving problems

[0010] Through in-depth research, the inventors of the present disclosure discovered that by adopting the slit coating technology and adjusting the coating process parameters, a desalination layer with gradient properties can be formed, 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.

[0011] The present disclosure provides a method for preparing a reverse osmosis membrane, the method comprising the following steps:

[0012] preparing a polymer solution as a casting solution, and coating the casting solution on the reinforcing material to form a polymer support layer;

[0013] The polymer support layer is contacted with an aqueous solution containing an amine compound and an oily solution containing an acyl chloride compound by a slot coating method to form a desalting layer, wherein when contacting with the oily solution, N slot coating heads are respectively arranged in a transverse direction to form N coating areas, 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;

[0014] After post-treatment, a reverse osmosis membrane is obtained.

[0015] According to the preparation method disclosed herein, the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0016] According to the preparation method disclosed herein, the amine compound is one or a combination of two selected from 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.

[0017] According to the preparation method disclosed herein, 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.

[0018] According to the preparation method disclosed herein, 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-dicarbonyl chloride, 1,3,5-cyclohexane trimesoyl chloride, biphenyl trimesoyl chloride, 5-oxocarbonyl chloride-isophthaloyl chloride, biphenyl tetracarbonyl chloride, 2,6-naphthalene dicarbonyl chloride, glutaryl chloride, and benzene disulfonyl chloride; preferably, the concentration of the acyl chloride compound is 0.20-0.40 wt% based on the weight of the oil phase solution.

[0019] According to the preparation method disclosed herein, 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.

[0020] According to the preparation method disclosed herein, in the slit coating method, 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.

[0021] The present disclosure also provides a reverse osmosis membrane prepared according to the preparation method described in the present disclosure, which comprises a desalination layer with gradient performance, wherein the performance includes water flux and desalination rate.

[0022] Effects of the Invention

[0023] Compared to reverse osmosis membranes with uniform properties produced using traditional dip-coating processes, the reverse osmosis membranes produced using the method disclosed herein include a desalination layer with gradually varying properties (including gradually varying water flux and gradually varying salt rejection), the density of which gradually increases along the transverse direction of the membrane sheet. The reverse osmosis membranes provided by the present disclosure have gradually varying properties, including gradually varying water flux and gradually varying salt rejection, and high water flux, effectively reducing flux attenuation during membrane operation and improving anti-fouling performance.

[0024] When the performance-gradient reverse osmosis membrane provided by the present disclosure 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

[0025] FIG1 shows a schematic diagram of a reverse osmosis membrane prepared according to the method of the present disclosure. DETAILED DESCRIPTION

[0026] Various exemplary embodiments, features, and aspects of the present disclosure are described in detail below. The word "exemplary" is used herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or preferred over other embodiments.

[0027] In addition, numerous specific details are provided in the following detailed description to better illustrate the present disclosure. Those skilled in the art will appreciate that the present disclosure can be practiced without certain specific details. In other instances, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present disclosure.

[0028] Unless otherwise stated, the units used in this specification are international standard units, and the numerical values ​​and numerical ranges appearing in this disclosure should be understood to include the inevitable systematic errors in industrial production.

[0029] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0030] In this specification, 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 be present in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0031] 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.

[0032] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 10-40°C.

[0033] The present disclosure relates to a method for preparing a reverse osmosis membrane, which comprises the following steps:

[0034] preparing a polymer solution as a casting solution, and coating the casting solution on the reinforcing material to form a polymer support layer;

[0035] The polymer support layer is contacted with an aqueous solution containing an amine compound and an oily solution containing an acyl chloride compound by a slot coating method to form a desalting layer, wherein when contacting with the oily solution, N slot coating heads are respectively arranged in a transverse direction to form N coating areas, 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;

[0036] After post-treatment, a reverse osmosis membrane is obtained.

[0037] The technical concept of the preparation method disclosed herein is to adopt a slit coating technology and adjust the coating process parameters to form a desalination layer with gradient performance. The density of the desalination layer 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 rejection rate, effectively reducing the flux attenuation of the membrane element during operation and improving the anti-pollution performance.

[0038] In the preparation method disclosed herein, a polymer solution is prepared as a casting solution, and the casting solution is coated onto 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. The coating method is not particularly limited and can include casting, dip coating, blade coating, slit coating, etc. Slit coating is more preferred, as it can produce a support layer with more uniform thickness and micropores.

[0039] After the casting solution is coated on the reinforcing material, it is then immersed in a coagulation bath to allow the casting solution to coagulate to form a polymer support layer. In the preparation method disclosed herein, preferably, the coagulation bath is a water bath with a coagulation bath temperature of 8-20°C.

[0040] In the preparation method disclosed herein, a polymer support layer is brought into contact 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 in contact with the oily solution, N slit coating heads are arranged in the transverse direction to form N coating areas, respectively. 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.

[0041] In the preparation method disclosed herein, 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 backing roller in the slit coating equipment) 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.

[0042] When in contact with the oil phase solution, N slit coating heads are respectively arranged in the transverse direction to form N coating areas. 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 onwards, the coating flow rate of each coating area increases relative to the coating flow rate of the previous coating area. Considering 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.

[0043] The incremental increase in 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.

[0044] In the preparation method disclosed herein, the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0045] In the preparation method disclosed herein, 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 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.

[0046] In the preparation method disclosed herein, 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 dimethylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, ethylene glycol monomethyl ether, methanol, ethanol, propanol, n-butanol, ethylene glycol, ethylamine, ethylenediamine, n-butylamine, ethanolamine, isopropyl alcohol, glycerol, and sorbitol.

[0047] Preferably, the concentration of the aqueous phase auxiliary agent is 5 to 20 wt % based on the weight of the aqueous phase solution. When the concentration is lower than 5 wt %, the flux of the resulting reverse osmosis membrane is low; when the concentration is higher than 20 wt %, the film forming property of the reverse osmosis membrane is poor and the desalination rate is low.

[0048] In the preparation method disclosed herein, 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.

[0049] In the preparation method disclosed herein, 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-cyclohexanetricarboxylic acid chloride, biphenyltrichloride, 5-oxocarbonyl chloride-isophthaloyl chloride, biphenyltetracarboxylic 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 to 0.40 wt% based on the weight of the oil phase solution.

[0050] In the preparation method disclosed herein, the oil phase solution further comprises an oil phase auxiliary agent, the function of which is 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 cross-linking is further increased. Preferably, the oil phase auxiliary agent is at least one selected from acetone, toluene, xylene, trimethylbenzene, trimethyl phosphate, and triphenyl phosphate.

[0051] Preferably, the concentration of the oil phase auxiliary agent is 5 to 15 wt % based on the weight of the oil phase solution.

[0052] Preferably, in the preparation method disclosed herein, in the slit coating method 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.

[0053] 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.

[0054] Afterwards, 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.

[0055] In the preparation method disclosed herein, preferably, the post-treatment further comprises moisturizing treatment with an aqueous solution containing 5 wt% glycerol, followed by drying to produce a high-flux reverse osmosis membrane with gradient performance.

[0056] As shown in FIG1 , the reverse osmosis membrane prepared by the method disclosed herein has continuous regions 1, 2, ..., N along the transverse direction, and the salt rejection rate of the reverse osmosis membrane increases along the transverse direction.

[0057] As a non-limiting example, the method for preparing the reverse osmosis membrane of the present disclosure includes the following steps:

[0058] Step 1: Prepare the polymer support layer: Dissolve the polymer in a solvent at a concentration of 18 wt% and stir at 80°C for 8 hours until the polymer is completely dissolved to obtain a casting solution. Allow to stand for 10 hours to degas. Apply the casting solution evenly to the nonwoven fabric using a slot-coating device with a coating gap set to 0.15 mm, a coating flow rate set to 2500 ml / min, and a coating speed set to 20 m / min. The solution is then placed in a water bath at 8-20°C (e.g., reverse osmosis water) for phase inversion to form the polymer support layer.

[0059] Step 2: Prepare reverse osmosis membrane

[0060] (1) Preparation of aqueous solution: Pour 2-8 wt% of an amine compound, 0.05 wt% of sodium hydroxide, and 5-20 wt% of an aqueous phase auxiliary agent into a container containing 75-90 wt% of reverse osmosis water, stir for 2 h until the amine compound and the aqueous phase auxiliary agent are completely dissolved, and then pour into a storage tank for standby use;

[0061] (2) Preparation of oil phase solution: Add 0.20-0.40 wt% of acyl chloride compound and 5-15 wt% of oil phase auxiliary agent to a container containing 84.6-94.8 wt% of cyclohexane, stir for 1 h until the acyl chloride compound is completely dissolved, and then pour into a storage tank for later use;

[0062] (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, and set the coating flow rate of the oil phase solution to 100-1000ml / min. 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 zone. After completion, it enters the oven, is then washed with pure water and moisturized with glycerin, and finally dried to produce a reverse osmosis membrane.

[0063] The present disclosure also relates to a reverse osmosis membrane prepared by the preparation method according to the present disclosure, comprising a desalination layer having graded properties, including water flux and salt rejection. Preferably, the reverse osmosis membrane comprises, from bottom to top, a non-woven fabric layer, a polymer support layer, and a desalination layer.

[0064] Example

[0065] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0066] Comparative Example 1

[0067] Step 1: Preparation of the polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18 wt%. Stir at 80°C for 8 hours until the polymer is completely dissolved, and allow to stand for 10 hours to degas. The casting solution is then coated onto a PET non-woven fabric using a slot-coating device with a coating gap of 0.15 mm, a coating flow rate of 2500 ml / min, and a coating speed of 20 m / min. The polysulfone support layer is formed after phase inversion in a coagulation bath (reverse osmosis product water) at 8°C.

[0068] Step 2: Preparation of reverse osmosis membrane

[0069] (1) Preparation of aqueous solution: 7 wt% m-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 15 wt% dimethylpyrrolidone (as aqueous phase auxiliary agent) were poured into a container containing 79.95 wt% reverse osmosis water, stirred for 2 h until the amine monomer and aqueous phase auxiliary agent were completely dissolved, and then poured into a storage tank for later use;

[0070] (2) Preparation of oil phase solution: 0.4 wt% of trimesoyl chloride (as an acyl chloride monomer) and 15 wt% of toluene (as an oil phase auxiliary agent) were added to a container containing 84.8 wt% of cyclohexane, stirred for 1 h until the acyl chloride monomer was completely dissolved, and then poured into a storage tank for later use;

[0071] (3) Preparation of Reverse Osmosis Membrane: The slit coating apparatus was opened, 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 the aqueous phase coating, the oil phase coating, and the reaction zone for reaction. After completion, it was placed in an oven, rinsed with pure water, moisturized with glycerin, and then dried to produce reverse osmosis membrane C1.

[0072] Example 1

[0073] 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.

[0074] Example 2

[0075] 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.

[0076] Example 3

[0077] Example 3 was carried out in the same manner as Comparative Example 1, except that there were four 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 produce a reverse osmosis membrane E3.

[0078] Example 4

[0079] 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.

[0080] Example 5

[0081] Step 1: Preparation of the polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18 wt%. Stir at 80°C for 8 hours until the polymer is completely dissolved. Allow to stand for 10 hours to degas. The casting solution is then coated onto a PET nonwoven fabric using a slot-coating device with a coating gap of 0.15 mm, a coating flow rate of 2500 ml / min, and a coating speed of 20 m / min. The polysulfone support layer is formed after phase inversion in a coagulation bath (reverse osmosis product water) at 10°C.

[0082] Step 2: Preparation of reverse osmosis membrane

[0083] (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 later use;

[0084] (2) Preparation of oil phase solution: Add 0.2 wt% biphenyltetracarbonyl chloride (as acyl chloride monomer) and 15 wt% acetone (as oil phase auxiliary agent) into a container containing 84.8 wt% cyclohexane, stir for 1 h until the acyl chloride monomer is completely dissolved, and then pour into a storage tank for later use;

[0085] (3) Preparation of Reverse Osmosis Membrane: The slit coating apparatus was opened, 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 oil phase solution in the first coating zone was 900 ml / min, the flow rate in the second coating zone was 905 ml / min, the flow rate in the third coating zone was 910 ml / min, the flow rate in the fourth coating zone was 915 ml / min, and the flow rate in the fifth coating zone was 920 ml / min. The main machine 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 reaction. After completion, the polymer support layer was placed in an oven, rinsed with pure water, moisturized with glycerin, and then dried to produce reverse osmosis membrane E5.

[0086] Example 6

[0087] Step 1: Preparation of the polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18 wt%. Stir at 80°C for 8 hours until the polymer is completely dissolved. Allow to stand for 10 hours to degas. The casting solution is then coated onto a PET nonwoven fabric using a slot-coating device with a coating gap of 0.15 mm, a coating flow rate of 2500 ml / min, and a coating speed of 20 m / min. The polysulfone support layer is formed after phase inversion in a coagulation bath (reverse osmosis product water) at 20°C.

[0088] Step 2: Preparation of reverse osmosis membrane

[0089] (1) Preparation of aqueous solution: 2 wt% m-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 5 wt% dimethylformamide (as aqueous phase auxiliary agent) were poured into a container containing 92.95 wt% reverse osmosis water, stirred for 2 h until the amine monomer and auxiliary agent were completely dissolved, and then poured into a storage tank for later use;

[0090] (2) Preparation of oil phase solution: 0.3 wt% of biphenyltetracarbonyl chloride (as acyl chloride monomer) and 15 wt% of xylene (as oil phase auxiliary agent) were added to a container containing 84.7 wt% of cyclohexane, stirred for 1 h until the acyl chloride monomer was completely dissolved, and then poured into a storage tank for later use;

[0091] (3) Preparation of Reverse Osmosis Membrane: The slit coating apparatus was opened, the coating gap was set to 0.2 mm, the coating flow rate of the aqueous solution was set to 1000 ml / min, the flow rate of the oil phase solution in the first coating zone was 350 ml / min, the flow rate in the second coating zone was 355 ml / min, the flow rate in the third coating zone was 360 ml / min, the flow rate in the fourth coating zone was 365 ml / min, and the flow rate in the fifth coating zone was 370 ml / min. The main machine speed was set to 15 m / min. The polymer support layer prepared in the first step was sequentially subjected to aqueous coating, oil coating, and reaction zones for reaction. After completion, the polymer support layer was placed in an oven, rinsed with pure water, moisturized with glycerin, and then dried to produce reverse osmosis membrane E6.

[0092] Example 7

[0093] Step 1: Preparation of the polymer support layer: Dissolve bisphenol A polysulfone in dimethylformamide to prepare a casting solution with a concentration of 18 wt%. Stir at 80°C for 8 hours until the polymer is completely dissolved. Allow to stand for 10 hours to degas. The casting solution is then coated onto a PET nonwoven fabric using a slot-coating device with a coating gap of 0.15 mm, a coating flow rate of 2500 ml / min, and a coating speed of 20 m / min. The polysulfone support layer is formed after phase inversion in a coagulation bath (reverse osmosis product water) at 8°C.

[0094] Step 2: Preparation of reverse osmosis membrane

[0095] (1) Preparation of aqueous solution: 4 wt% m-phenylenediamine (as amine monomer), 0.05 wt% sodium hydroxide, and 15 wt% isopropyl alcohol (as aqueous phase auxiliary agent) were poured into a container containing 81.95 wt% reverse osmosis water, stirred for 2 h until the amine monomer and auxiliary agent were completely dissolved, and then poured into a storage tank for later use;

[0096] (2) Preparation of oil phase solution: 0.25 wt% of biphenyltriacyl chloride (as acyl chloride monomer) and 15 wt% of trimethylbenzene (as oil phase auxiliary agent) were added to a container containing 84.75 wt% of cyclohexane, stirred for 1 h until the acyl chloride monomer was completely dissolved, and then poured into a storage tank for later use;

[0097] (3) Preparation of Reverse Osmosis Membrane: The slit coating apparatus was opened, 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 oil phase solution in the first coating zone was 500 ml / min, the flow rate in the second coating zone was 505 ml / min, the flow rate in the third coating zone was 510 ml / min, the flow rate in the fourth coating zone was 520 ml / min, and the flow rate in the fifth coating zone was 525 ml / min. The main machine speed was set to 25 m / min. The polymer support layer prepared in the first step was sequentially subjected to the aqueous coating, oil phase coating, and reaction zone for reaction. After completion, the polymer support layer was placed in an oven, rinsed with pure water, moisturized with glycerin, and then dried to produce reverse osmosis membrane E7.

[0098] Membrane performance - water flux and salt rejection test

[0099] The performance tests were performed on various regions of the reverse osmosis membranes 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 in accordance with the national standard GB34914-2021, the solution temperature was 25° C., the run time was 0.5 h, and the concentrated water flow rate was 1 L / min. The water flux and salt rejection of the membranes are shown in Table 1:

[0100] Table 1

[0101] The reverse osmosis membranes prepared in Comparative Example 1 and Examples 1 to 7 were rolled into 3012 membrane elements for performance testing. The membrane sheets were cut crosswise, and the water entered from the low desalination area of ​​the membrane. The specific test conditions of the membrane elements were as follows: the pressure was 100 psi, the water-effect solution was prepared in accordance with 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 elements were shown in Table 2:

[0102] Table 2

[0103] It should be noted that, although the technical solutions of the present disclosure are described with specific examples, those skilled in the art will appreciate that the present disclosure should not be limited thereto.

[0104] While various embodiments of the present disclosure have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

[0105] Industrial applicability

[0106] The reverse osmosis membrane prepared by the method of the present disclosure comprises a desalination layer with gradually varying properties (including gradually varying water flux and gradually varying salt rejection), wherein the density of the desalination layer gradually increases along the transverse direction of the membrane sheet. The reverse osmosis membrane provided by the present disclosure has gradually varying properties, including gradually varying water flux and gradually varying salt rejection, and high water flux, effectively reducing flux attenuation during membrane operation and improving anti-fouling 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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