Method for producing a reverse osmosis membrane and a reverse osmosis membrane produced thereby

Abstract

The present application 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 casting solution, coating the casting solution on a reinforcing material 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 through a slot coating method to form a functional layer; and obtaining the reverse osmosis membrane after post-treatment and heat treatment, wherein no heat treatment is performed before the post-treatment. The reverse osmosis membrane prepared by the method of the present application not only has a high water flux, but also has a removal rate of sodium chloride in the range of 70% to 90%, in addition, the removal rate of magnesium sulfate is above 96% and the removal rate of calcium chloride is above 80%. Therefore, both the trace elements beneficial to the human body are well retained and the desalination capacity of the influent with high salt content is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reverse osmosis membranes, in particular to a preparation method of a reverse osmosis membrane and a reverse osmosis membrane prepared therefrom. BACKGROUND

[0002] Water health has become a key issue for drinking water, and reverse osmosis filtration technology has long dominated the market due to its good filtration effect. Reverse osmosis membranes have high separation efficiency, simple separation process, low energy consumption, and green environmental protection, and have been widely used in seawater desalination, wastewater treatment, and drinking water purification. Generally, the reverse osmosis membrane used for drinking water purification treatment has a sodium chloride removal rate of more than 90%, but it removes some trace elements beneficial to the human body while removing harmful substances. Some studies have also mentioned that the reverse osmosis water is too pure and has a poor taste when directly consumed.

[0003] The Ministry of Education issued the "JY / T0593-2019 Technical Requirements and Equipment Specifications for Membrane Treatment of Drinking Water in Primary and Secondary Schools" in 2019, which clearly states that the purification of drinking water should use ultrafiltration or nanofiltration filtration methods. Only in areas with high risk of raw water pollution can reverse osmosis methods be used. However, the current market mainly uses reverse osmosis technology for drinking water purification. Of course, some technologies also use nanofiltration technology, and the nanofiltration membrane has relatively low filtration precision, although it can retain a large amount of trace elements, but China is vast in territory, and there is a large difference in water quality between the north and south, such as some cities in Shandong where the conductivity of tap water is as high as 1100 us / cm, and there is a certain seasonal variation. If only nanofiltration filtration technology is used, the conductivity of the produced water is too high, and the purification effect is poor.

[0004] Reverse osmosis membranes with a sodium chloride removal rate of 70%-90% can effectively remove harmful substances and retain trace elements beneficial to the human body. Currently, there is less research on reverse osmosis membranes with moderate desalination, and the more advanced technology is to mix nanofiltration membranes and reverse osmosis membranes to control the desalination rate. Some manufacturers also adjust the desalination rate of the entire machine by adjusting the recovery rate, but both technologies undoubtedly improve the membrane element winding technology and the entire machine technology, and do not solve the fundamental problem from the source.

[0005] The mainstream technology for reverse osmosis membrane production is interfacial polymerization, and the coating mode of the aqueous solution containing amine compounds and the oil phase solution containing acyl chloride monomers is basically immersion coating. The biggest problem is that the concentration of monomers in the solution fluctuates greatly, and the stability of the reverse osmosis membrane is relatively poor. In particular, the reverse osmosis membrane with moderate desalination requires higher stability of the concentration of acyl chloride monomers in the oil phase solution. Even a slight change in the concentration of acyl chloride monomers will cause fatal changes in the performance of the reverse osmosis membrane. Therefore, the preparation of the reverse osmosis membrane with moderate desalination by using the traditional immersion coating process has higher requirements for the process and is more difficult.

[0006] In addition, in most reverse osmosis membrane production processes, the polymer support layer is directly placed into an oven for setting after being immersed in the aqueous solution and interfacially polymerized in the oil phase solution. The reverse osmosis membrane prepared by this process generally has a high removal rate of sodium chloride, and it is difficult to obtain a reverse osmosis membrane with moderate desalination. SUMMARY

[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 application is to provide a preparation method of a reverse osmosis membrane and a reverse osmosis membrane with a sodium chloride removal rate in the range of 70%-90% prepared by the method.

[0009] Solution to the Problem

[0010] The inventors of the present application have found through in-depth research that the use of slit coating technology can solve the problem of large fluctuation in the concentration of monomers (i.e. amine compounds and acyl chloride compounds) in the aqueous solution and the oil phase solution, which cannot stably form a film or even cannot form a film. The flatness and uniformity of the functional layer (also known as the desalination layer) of the reverse osmosis membrane can be accurately controlled. By performing post-treatment (including cleaning) before heat treatment after interfacial polymerization, a functional layer with a loose structure can be obtained, thereby obtaining a reverse osmosis membrane with moderate desalination rate (i.e. sodium chloride removal rate in the range of 70%-90%) and improving the water permeability of the reverse osmosis membrane.

[0011] The present application provides a preparation method of a reverse osmosis membrane, which comprises the following steps:

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

[0013] Contacting the polymer support layer with an aqueous solution containing amine compounds and an oil phase solution containing acyl chloride compounds by slit coating to form a functional layer;

[0014] After post-treatment and heat treatment, a reverse osmosis membrane is obtained, wherein no heat treatment is performed before the post-treatment.

[0015] The preparation method according to the present application, wherein the polymer is at least one selected from the group consisting of bisphenol A type polysulfone, polyarylsulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0016] The preparation method according to the present application, wherein the amine compound is one or a combination of two selected from the group consisting of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, N,N-dimethyl-m-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 solution.

[0017] The preparation method according to the present application, wherein the aqueous solution further comprises a component for reducing surface tension, and the concentration of the component for reducing surface tension is 0.01 to 0.5 wt% based on the weight of the aqueous solution.

[0018] The preparation method according to the present application, wherein the component for reducing surface tension is a silane coupling agent having at least one amino group, preferably, the silane coupling agent having at least one amino group is at least one selected from the group consisting of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane.

[0019] The preparation method according to the present application, wherein the acid chloride compound is at least one selected from the group consisting of terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, diphenyl dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, succinyl chloride, butane tricarboxylic acid dichloride, trimesoyl chloride, cyclobutane-1,2-dicarboxylic acid dichloride, 1,3,5-cyclohexane tricarboxylic acid dichloride, diphenyl tricarboxylic acid dichloride, 5-oxalyl chloride-isophthaloyl chloride, biphenyl tetracarboxylic acid dichloride, 2,6-naphthalene dicarboxylic acid dichloride, glutaryl chloride, and benzene disulfonyl chloride, preferably, the concentration of the acid chloride compound is 0.05 to 0.30 wt% based on the weight of the oil solution.

[0020] The preparation method according to the present application, wherein the gap in the slot coating method is 0.1 to 1 mm, and the coating amount is 10 to 100 ml / min.

[0021] The preparation method according to the present application, wherein the post-treatment comprises cleaning with a cleaning agent, preferably, the cleaning agent is at least one selected from the group consisting of water, toluene, xylene, mesitylene, acetone, cyclohexane, n-hexane, petroleum ether, Isopar-G, Isopar-L, and n-heptane.

[0022] The application also provides a reverse osmosis membrane prepared by the preparation method, and the removal rate of sodium chloride is 70-90%.

[0023] According to the reverse osmosis membrane, the removal rate of magnesium sulfate is above 96%, and the removal rate of calcium chloride is above 80%.

[0024] Effects of the application

[0025] The functional layer of the reverse osmosis membrane prepared by the method has high flatness and uniformity and has a loose structure. The reverse osmosis membrane prepared by the method not only has a high water flux, up to 50 GFD, but also has a removal rate of sodium chloride in the range of 70%-90%, which not only better retains the trace elements beneficial to the human body, but also maintains good desalination capacity for the water with high salt content. In addition, the reverse osmosis membrane prepared by the method has a removal rate of magnesium sulfate above 96% and a removal rate of calcium chloride above 80%. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A scanning electron microscope picture of the surface of the desalination layer of the reverse osmosis membrane prepared for Example 1 of the application;

[0027] Figure 2 A scanning electron microscope picture of the cross section of the desalination layer of the reverse osmosis membrane prepared for Example 1 of the application. DETAILED DESCRIPTION

[0028] The application relates to a preparation method of a reverse osmosis membrane, which comprises the following steps:

[0029] 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;

[0030] The polymer support layer is contacted with an aqueous solution containing an amine compound and an oil phase solution containing an acyl chloride compound by a slit coating method to form a functional layer;

[0031] The reverse osmosis membrane is obtained after post-treatment and heat treatment, and no heat treatment is performed before the post-treatment.

[0032] The technical concept of the preparation method of the present application is to solve the problem of large fluctuation of monomer (i.e. amine compound and acyl chloride compound) concentration in aqueous phase solution and oil phase solution, which cannot form stable film or even cannot form film, by adopting slit coating technology, so as to accurately control the flatness and uniformity of the functional layer (also known as desalination layer) of the reverse osmosis membrane; by performing post-treatment (including cleaning) and then heat treatment after interfacial polymerization reaction, the functional layer with loose structure is obtained, thus obtaining the reverse osmosis membrane with moderate desalination rate (i.e. the removal rate of sodium chloride is in the range of 70%-90%) and improving the water permeability of the reverse osmosis membrane.

[0033] In the preparation method of the present application, 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 PET non-woven fabric, PP non-woven fabric. There is no special limitation to the coating method, and flow casting, dip coating, blade coating, slit coating and the like can be used, and more preferably, slit coating can be used, so that a support layer with more uniform thickness and micropore can be obtained.

[0034] After the casting solution is coated on the reinforcing material, it is then immersed in a coagulation bath to coagulate the casting solution to form a polymer support layer. In the preparation method of the present application, preferably, the coagulation bath is a water bath, and the coagulation bath temperature is 8-20℃.

[0035] In the preparation method of the present application, the polymer support layer is contacted with the aqueous phase solution containing amine compound and the oil phase solution containing acyl chloride compound by slit coating to form a functional layer. By adopting slit coating, the monomer concentration in the aqueous phase and the oil phase can be controlled, so that a stable functional layer is formed. If the traditional dip coating process is used, the monomer concentration in the aqueous phase and the oil phase will fluctuate greatly, the stability of the functional layer (desalination layer) is poor, and especially for the preparation of moderate desalination reverse osmosis membrane, the film cannot be formed.

[0036] In the preparation method of the present application, preferably, under the condition of matching the coating flow and the coating gap (i.e. the gap between the lip and the back roller in the slit coating equipment) of the slit coating, the concentration of the acyl chloride compound is 0.05-0.30wt% based on the weight of the oil phase solution. When the concentration is in this range, the reverse osmosis membrane with moderate desalination (i.e. the removal rate of sodium chloride is in the range of 70-90%) can be obtained. If the concentration is lower than 0.05wt%, the film formability is poor, and the removal rate of sodium chloride of the prepared reverse osmosis membrane is lower than 70%; if the concentration is higher than 0.30wt%, the removal rate of sodium chloride of the obtained reverse osmosis membrane is higher than 90wt%.

[0037] In the preparation method of the present application, the reverse osmosis membrane is obtained after post-treatment and heat treatment, wherein no heat treatment is performed before the post-treatment. By performing the post-treatment (including cleaning) before the heat treatment after the interfacial polymerization reaction, a functional layer with loose structure can be obtained, thereby obtaining a reverse osmosis membrane with moderate desalination rate (i.e. the removal rate of sodium chloride is in the range of 70%-90%) and improving the water permeability of the reverse osmosis membrane, thereby increasing the water flux.

[0038] In the preparation method of the present application, the polymer is at least one selected from bisphenol A polysulfone, polyarylsulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, and polyvinyl chloride.

[0039] In the preparation method of the present application, the amine compound is one or a combination of two selected from m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, N,N-dimethyl-m-phenylenediamine, 1,4-cyclohexanediamine, N,N-dimethylcyclohexanediamine, diaminobenzenesulfonic acid, diaminobenzoic acid, melamine, and ethylenediamine, preferably, the concentration of the amine compound is 2-8 wt% based on the weight of the aqueous solution; more preferably, when a combination of two selected from the above-listed amine compounds is used, the mass ratio of the two amine compounds is 1:1.

[0040] In the preparation method of the present application, the aqueous solution further comprises a component for reducing surface tension, and the concentration of the component for reducing surface tension is 0.01-0.5 wt% based on the weight of the aqueous solution. When the concentration is lower than 0.01 wt%, the defoaming effect is poor due to the insufficient amount of the component for reducing surface tension; when the concentration is higher than 0.5 wt%, the performance of the reverse osmosis membrane is affected due to the excessive amount of the component for reducing surface tension.

[0041] In the preparation method of the present application, the component for reducing surface tension is a silane coupling agent with at least one amino group, which functions to accelerate the interfacial polymerization reaction and eliminate the micro-bubbles generated after the aqueous solution passes through the feed pump. Preferably, the silane coupling agent with at least one amino group is at least one selected from γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane.

[0042] In the preparation method of the present application, preferably, the aqueous solution further comprises an alkali metal hydroxide as an aqueous phase acid-binding agent, which can be, for example, sodium hydroxide.

[0043] In the preparation method of the present application, preferably, dimethylformamide is further contained in the aqueous solution to further improve the water flux of the reverse osmosis membrane. Preferably, the concentration of dimethylformamide is 5-20 wt% based on the weight of the aqueous solution. When the concentration is less than 5 wt%, the flux of the obtained reverse osmosis membrane is low; when the concentration is higher than 20 wt%, the membrane-forming property of the reverse osmosis membrane is poor and the desalination rate is low.

[0044] In the preparation method of the present application, the acyl chloride compound is at least one selected from terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, diphenyl dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, succinyl chloride, glutaryl chloride, trimesoyl chloride, cyclobutane-1, 2-dicarboxylic acid dichloride, 1, 3, 5-cyclohexane tricarboxylic acid chloride, biphenyl tricarboxylic acid chloride, 5-oxalyl chloride-isophthaloyl chloride, biphenyl tetracarboxylic acid chloride, 2, 6-naphthalene dicarboxylic acid dichloride, pentanetricarboxylic acid chloride, and benzenedisulfonyl chloride.

[0045] In the preparation method of the present application, in the slot coating method of the aqueous solution and the oil phase solution, the coating gap is 0.1-1 mm and the coating amount is 10-100 ml / min. Preferably, the process parameters of the slot coating are as follows: the coating speed is 15-30 m / min; and the length of the reaction zone (i.e. the region between the coating of the oil phase solution to the cleaning zone) is 0.1-2 m.

[0046] In the preparation method of the present application, after the functional layer is formed by the interfacial polymerization reaction, the reverse osmosis membrane is obtained after post-treatment and heat treatment, wherein no heat treatment is performed before the post-treatment. By first performing the post-treatment (including cleaning) and then performing the heat treatment, the functional layer with loose structure can be obtained, thereby obtaining the reverse osmosis membrane with moderate desalination rate (i.e. the removal rate of sodium chloride is in the range of 70%-90%) and improving the water permeability of the reverse osmosis membrane.

[0047] If the heat treatment is performed first after the interfacial polymerization reaction, such as directly entering the oven for heating to shape, the desalination layer (functional layer) of the obtained reverse osmosis membrane is dense, the removal rate of sodium chloride of the reverse osmosis membrane prepared by this process is greater than 90%, and it is difficult to obtain the reverse osmosis membrane with moderate desalination rate (i.e. the removal rate of sodium chloride is in the range of 70%-90%).

[0048] In the preparation method of the present application, preferably, the post-treatment includes cleaning with a cleaning agent, and preferably, the cleaning agent is at least one selected from water, toluene, xylene, mesitylene, cyclohexane, n-hexane, Isopar-G, Isopar-L, and n-heptane. When water is used as the cleaning agent, the unreacted acyl chloride compound can be hydrolyzed.

[0049] In the preparation method of the present application, preferably, the post-treatment further includes moisturizing treatment using an aqueous solution containing glycerol with a concentration of 5 wt%.

[0050] The heat treatment temperature is not particularly limited, and is usually 60°C; the heat treatment time is also not particularly limited, and is usually 1-30 minutes.

[0051] As a non-limiting example, the preparation method of the reverse osmosis membrane of the present application comprises the following steps:

[0052] First step: preparation of the polymer support layer: dissolve the polymer with a concentration of 18wt% in a solvent, stir at 80°C for 8h until the polymer is completely dissolved to obtain a casting solution. Stand for 10h to degas; apply the casting solution on the non-woven fabric by slit coating, set the coating gap to 0.15mm, set the coating amount to 2500ml / min, set the speed of the coating equipment to 20m / min, and form the polymer support layer after phase inversion in a water bath (such as reverse osmosis product water) with a temperature of 8-20°C.

[0053] Second step: preparation of the reverse osmosis membrane

[0054] (1) Preparation of the aqueous phase solution: pour the amine compound with a concentration of 2-8wt%, sodium hydroxide with a concentration of 0.01wt%, the component for reducing surface tension with a concentration of 0.01-0.5wt%, and dimethylformamide with a concentration of 5-20wt% into a container containing 75-90wt% reverse osmosis product water, stir for 2h until the amine compound and the component for reducing surface tension are completely dissolved, and then pour into a storage tank for standby;

[0055] (2) Preparation of the oil phase solution: add the acyl chloride compound with a concentration of 0.05-0.30wt% into a container containing 99.95-99.70wt% cyclohexane, stir for 1h until the acyl chloride compound is completely dissolved, and then pour into a storage tank for standby;

[0056] (3) Preparation of the reverse osmosis membrane: open the slit coating equipment, set the coating gap to 0.1-1mm, set the coating amount to 10-100ml / min, and set the speed of the coating equipment to 15-30m / min. The polymer support layer prepared in the first step is sequentially subjected to aqueous phase solution coating, oil phase solution coating, interfacial polymerization, and post-treatment zone (i.e. cleaning zone), and then enters the oven, followed by pure water cleaning and glycerol moisturizing, and finally drying to obtain the reverse osmosis membrane.

[0057] The present application also relates to a reverse osmosis membrane prepared by the preparation method according to the present application, preferably, the reverse osmosis membrane sequentially comprises, from bottom to top, a non-woven fabric layer, a polymer support layer, and a functional layer (also known as a desalination layer), and the removal rate of sodium chloride of the reverse osmosis membrane is in the range of 70%-90%. Preferably, the removal rate of magnesium sulfate of the reverse osmosis membrane of the present application is greater than 96%, and the removal rate of calcium chloride is greater than 80%.

[0058] Embodiments

[0059] The application will be further described in detail in connection with specific examples, but the technical solutions of the application are by no means limited to the following examples. It should be noted that the reagents, raw materials and equipment used in the examples are all commercially available conventional products unless otherwise specified.

[0060] Example 1

[0061] First step: preparation of polysulfone support layer: dissolve polysulfone in dimethylformamide to prepare casting solution with a concentration of 18wt%, stir at 80℃ for 8h until polysulfone is completely dissolved, stand for 10h to degas. Apply the casting solution to PET non-woven fabric through a slot coating device, set the coating gap to 0.15mm, set the coating amount to 2500ml / min, set the speed of the coating device to 20m / min, and form the polysulfone support layer after phase inversion in a coagulation bath, i.e. reverse osmosis water, at a temperature of 8℃.

[0062] Second step: preparation of reverse osmosis membrane

[0063] (1) Prepare an aqueous phase solution with the following composition: m-phenylenediamine with a concentration of 6wt%, 0.01wt% sodium hydroxide, 0.1wt% γ-aminopropyltriethoxysilane and 15wt% dimethylformamide and the balance water, stir for 2h until the m-phenylenediamine and γ-aminopropyltriethoxysilane are completely dissolved, then pour into a storage tank for standby;

[0064] (2) Prepare an oil phase solution with the following composition: 0.25wt% trimesoyl chloride and the balance cyclohexane, stir for 1h until the trimesoyl chloride is completely dissolved, then pour into a storage tank for standby;

[0065] (3) Preparation of reverse osmosis membrane: open the slot coating device, set the coating gap to 0.15mm, set the coating amount to 25ml / min, set the speed of the coating device to 20m / min. The polysulfone support layer prepared in the first step is sequentially coated with the aqueous phase solution, the oil phase solution, and the interfacial polymerization reaction zone, then washed with trimethylbenzene, after completion, enter the oven with a temperature setting of 60℃, then washed with pure water and moisturized with glycerol, and finally dried at a temperature of 80℃ to obtain the reverse osmosis membrane.

[0066] Example 2

[0067] First step: prepare the polysulfone support layer in the same way as the first step of Example 1.

[0068] Second step: preparation of reverse osmosis membrane

[0069] (1) Prepare an aqueous phase solution with the following composition: 6wt% o- phenylenediamine, 0.01wt% sodium hydroxide, 0.1wt% gamma-aminopropyltriethoxysilane, 15wt% dimethylformamide and the balance water, stir for 2h until o- phenylenediamine and gamma-aminopropyltriethoxysilane are completely dissolved, pour into a storage tank for standby;

[0070] (2) Prepare an oil phase solution with the following composition: 0.25wt% m- phenylene tricarbonyl chloride and the balance cyclohexane, stir for 1h until m- phenylene tricarbonyl chloride is completely dissolved, pour into a storage tank for standby;

[0071] (3) Preparation of reverse osmosis membrane: open the slot coating equipment, set the coating gap to 0.15mm, set the coating amount to 25ml / min, set the speed of the coating equipment to 20m / min. The polysulfone support layer prepared in the first step is sequentially coated with the aqueous phase solution, the oil phase solution, the interfacial polymerization reaction zone, then washed with water, after completion, enter the oven with a temperature setting of 60℃, then pass through pure water cleaning and glycerol moisturizing, and finally dry at a temperature of 80℃ to obtain the reverse osmosis membrane.

[0072] Example 3

[0073] First step: Preparation of polyether sulfone support layer: Dissolve polyether sulfone in dimethylamide to prepare a casting solution with a concentration of 18wt%, stir at 80℃ for 8h until the polyether sulfone is completely dissolved, and stand for 10h to degas. The casting solution is coated on the PP non-woven fabric through the slot coating equipment, the coating gap is set to 0.15mm, the coating amount is set to 2500ml / min, and the speed of the coating equipment is set to 20m / min. After phase inversion in reverse osmosis product water at a temperature of 8℃, a polyether sulfone support layer is formed.

[0074] Second step: Preparation of reverse osmosis membrane

[0075] (1) Prepare an aqueous phase solution with the following composition: 8wt% p- phenylenediamine, 0.01wt% sodium hydroxide, 0.5wt% gamma-glycidoxypropyltrimethoxysilane, 5wt% dimethylformamide and the balance water, stir for 2h until p- phenylenediamine and gamma-glycidoxypropyltrimethoxysilane are completely dissolved, pour into a storage tank for standby;

[0076] (2) Prepare an oil phase solution with the following composition: 0.05wt% biphenyl tetracarbonyl chloride and the balance cyclohexane, stir for 1h until biphenyl tetracarbonyl chloride is completely dissolved, pour into a storage tank for standby;

[0077] (3) Preparation of reverse osmosis membrane: open the slot coating equipment, set the coating gap to 1 mm, set the coating amount to 100 ml / min, and set the speed of the coating equipment to 15 m / min. The polyether sulfone support layer prepared in the first step is sequentially subjected to water phase solution coating, oil phase solution coating, interfacial polymerization reaction zone, then cleaned with n-heptane, after completion, enters the oven with a temperature setting of 60°C, then subjected to pure water cleaning and glycerol moisturizing, and finally dried at a temperature of 80°C to prepare the reverse osmosis membrane.

[0078] Example 4

[0079] First step: Preparation of polyacrylonitrile support layer: polyacrylonitrile is dissolved in dimethylformamide to prepare a casting solution with a concentration of 18 wt%, stirred at 80°C for 8 h until the polyacrylonitrile is completely dissolved, and left to stand for 10 h to degas. The casting solution is coated on the PET non-woven fabric through the slot coating equipment, the coating gap is set to 0.15 mm, the coating amount is set to 2500 ml / min, and the speed of the coating equipment is set to 20 m / min. After phase inversion in reverse osmosis product water with a temperature of 15°C, the polyacrylonitrile support layer is formed.

[0080] Second step: Preparation of reverse osmosis membrane

[0081] (1) Preparation of water phase solution with the following composition: 4 wt% of N,N-dimethyl-m-phenylenediamine, 0.01 wt% of sodium hydroxide, 0.2 wt% of γ-(methacryloyloxy)propyltrimethoxysilane, 5.8 wt% of dimethylformamide, and the balance of water, stirring for 2 h until the N,N-dimethyl-m-phenylenediamine and γ-(methacryloyloxy)propyltrimethoxysilane are completely dissolved, then pouring into a storage tank for standby;

[0082] (2) Preparation of oil phase solution with the following composition: 0.3 wt% of terephthaloyl chloride and the balance of cyclohexane, stirring for 1 h until the terephthaloyl chloride is completely dissolved, then pouring into a storage tank for standby;

[0083] (3) Preparation of reverse osmosis membrane: open the slot coating equipment, set the coating gap to 0.5 mm, set the coating amount to 10 ml / min, and set the speed of the coating equipment to 30 m / min. The polyacrylonitrile support layer prepared in the first step is sequentially subjected to water phase solution coating, oil phase solution coating, interfacial polymerization reaction zone, then cleaned with n-heptane, after completion, enters the oven with a temperature setting of 60°C, then subjected to pure water cleaning and glycerol moisturizing, and finally dried at a temperature of 80°C to prepare the reverse osmosis membrane.

[0084] Example 5

[0085] First step: preparation of polyvinylidene fluoride support layer: polyvinylidene fluoride was dissolved in dimethylformamide to prepare casting solution with concentration of 18wt%, stirred at 80℃ for 8h until polyvinylidene fluoride was completely dissolved, and left to stand for 10h to remove bubbles. The casting solution was coated on PET non-woven fabric by slit coating equipment, the coating gap was set to 0.15mm, the coating amount was set to 2500ml / min, and the speed of the coating equipment was set to 20m / min. After phase inversion in reverse osmosis produced water with temperature of 20℃, the polyvinylidene fluoride support layer was formed.

[0086] Second step: preparation of reverse osmosis membrane

[0087] (1) prepare an aqueous phase solution with the following composition: 3.45wt% of diaminobenzene sulfonic acid, 3.45wt% of m-phenylenediamine, 0.01wt% of sodium hydroxide, 0.1wt% of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane, 5.8wt% of dimethylformamide and the balance of water, stir for 2h until diaminobenzene sulfonic acid, m-phenylenediamine and N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane are completely dissolved, then pour into the storage tank for standby;

[0088] (2) prepare an oil phase solution with the following composition: 0.2wt% of isophthaloyl dichloride and the balance of cyclohexane, stir for 1h until isophthaloyl dichloride is completely dissolved, then pour into the storage tank for standby;

[0089] (3) preparation of reverse osmosis membrane: open the slit coating equipment, set the coating gap to 0.2mm, the coating amount to 20ml / min, and the speed of the coating equipment to 25m / min. The polyvinylidene fluoride support layer prepared in the first step was successively coated with the aqueous phase solution, the oil phase solution, and the interfacial polymerization reaction zone, then washed with n-hexane, after completion, entered the oven with temperature set to 60℃, then washed with pure water and moisturized with glycerol, and finally dried at a temperature of 80℃ to obtain the reverse osmosis membrane.

[0090] Example 6

[0091] First step: preparation of polysulfone support layer: polysulfone was dissolved in dimethylformamide to prepare casting solution with concentration of 18wt%, stirred at 80℃ for 8h until polysulfone was completely dissolved, and left to stand for 10h to remove bubbles. The casting solution was coated on PET non-woven fabric by doctor blade coating equipment, and the polysulfone support layer was formed after phase inversion in reverse osmosis produced water with temperature of 8℃.

[0092] Second step: prepare the reverse osmosis membrane in the same way as the second step of Example 1.

[0093] Comparative Example 1

[0094] First step: prepare the polyethersulfone support layer in the same way as the first step of Example 3.

[0095] Second step: prepare the reverse osmosis membrane

[0096] (1) Prepare an aqueous phase solution with the following composition: 8wt% p- phenylenediamine, 0.01wt% sodium hydroxide, 0.5wt% γ-glycidoxypropyltrimethoxysilane, 5wt% dimethylformamide and the balance water, stir for 2h until the p-phenylenediamine and γ-glycidoxypropyltrimethoxysilane are completely dissolved, then pour into the storage tank for standby;

[0097] (2) Prepare an oil phase solution with the following composition: 0.05wt% biphenyl tetracarboxylic acid chloride and the balance cyclohexane, stir for 1h until the biphenyl tetracarboxylic acid chloride is completely dissolved, then pour into the storage tank for standby;

[0098] (3) Preparation of the reverse osmosis membrane: open the slot coating equipment, set the coating gap to 1mm, set the coating amount to 100ml / min, and set the speed of the coating equipment to 15m / min. After the polyethersulfone support layer prepared in the first step passes through the aqueous phase solution coating, the oil phase solution coating, and the interfacial polymerization reaction zone in turn, it enters the oven with a temperature setting of 60℃, then passes through pure water cleaning and glycerol moisturizing, and finally is dried at a temperature of 80℃ to obtain the reverse osmosis membrane.

[0099] Comparative Example 2

[0100] First step: prepare the polyethersulfone support layer in the same way as the first step of Example 3.

[0101] Second step: prepare the reverse osmosis membrane

[0102] (1) Prepare an aqueous phase solution with the following composition: 8wt% p- phenylenediamine, 0.01wt% sodium hydroxide, 0.5wt% γ-glycidoxypropyltrimethoxysilane, 5wt% dimethylformamide and the balance water, stir for 2h until the p-phenylenediamine and γ-glycidoxypropyltrimethoxysilane are completely dissolved, then pour into the storage tank for standby;

[0103] (2) Prepare an oil phase solution with the following composition: 0.05wt% biphenyl tetracarboxylic acid chloride and the balance cyclohexane, stir for 1h until the biphenyl tetracarboxylic acid chloride is completely dissolved, then pour into the storage tank for standby;

[0104] (3) Preparation of reverse osmosis membrane: the polyethersulfone support layer prepared in the first step is coated with the water phase solution and the oil phase solution in turn by way of dip coating, after the interfacial polymerization reaction zone, cleaned with Isopar-G, then enters the oven with the temperature set at 60°C, then cleaned with pure water and moisturized with glycerol, and finally dried at a temperature of 80°C to prepare the reverse osmosis membrane.

[0105] Due to the use of dip coating, the performance of the first 50 meters of the reverse osmosis membrane is stable during the preparation of the reverse osmosis membrane, but the film-forming property is poor thereafter, and the performance of the membrane fluctuates greatly.

[0106] Test of membrane performance-water flux and desalination rate

[0107] The reverse osmosis membranes prepared in Examples 1 to 6 and Comparative Example 1 are subjected to the following performance test, and the operating conditions are as follows: the pressure is 100 psi, the concentrations of sodium chloride, magnesium sulfate and calcium chloride in the aqueous solution are 500 ppm respectively, the solution temperature is 25°C, the pH value is 6.5-7, and the running time is 0.5 h. The water flux and the removal rate of the membranes to the aqueous solution containing sodium chloride, magnesium sulfate and calcium chloride respectively are shown in Table 1.

[0108] Table 1

[0109]

[0110] From the above results, in Examples 1 to 6, since the water phase solution and the oil phase solution are coated on the polymer support layer by way of slit coating and after the completion of the interfacial polymerization reaction, the post-treatment including cleaning is performed first and then the heat treatment is performed, the prepared reverse osmosis membrane not only has a high water flux, but also has a removal rate of sodium chloride in the range of 70%-90%, a removal rate of magnesium sulfate of more than 96% and a removal rate of calcium chloride of more than 80%. Therefore, not only the trace elements beneficial to the human body are well preserved, but also the desalination capacity of the feed water with high salt content is maintained.

[0111] However, in Comparative Example 1, since the heat treatment is performed first and then the post-treatment including cleaning is performed after the completion of the interfacial polymerization reaction, the desalination layer of the prepared reverse osmosis membrane is dense, and therefore the removal rate of sodium chloride is higher than 90%, and the removal rate of sodium chloride in the range of 70%-90% cannot be obtained.

[0112] In Comparative Example 2, since the water phase solution and the oil phase solution are coated on the polymer support layer by way of dip coating, the performance of the first 50 meters of the reverse osmosis membrane is stable during the preparation of the reverse osmosis membrane, but the film-forming property is poor thereafter, and the performance of the membrane fluctuates greatly.

[0113] Figure 1 and Figure 2The scanning electron microscope photos of the surface and cross section of the desalination layer of the reverse osmosis membrane prepared in Example 1 of the present application are shown in Figures 1 and 2, respectively. Figure 1 It can be seen that the surface of the desalination layer of the reverse osmosis membrane has a large "blade" structure, and thus the prepared reverse osmosis membrane has a large water flux. Figure 2 It can be seen that the thickness of the desalination layer of the reverse osmosis membrane is uniform and the structure is regular.

[0114] The above-described specific embodiments further illustrate the purpose, technical solutions and advantages of the present application, and it should be understood that the above-described embodiments are only examples of the present application and are not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the principles and spirit of the present application should be included in the protection scope of the present application.

[0115] Industrial applicability

[0116] The functional layer of the reverse osmosis membrane prepared by the method of the present application has high flatness and uniformity and has a loose structure, the reverse osmosis membrane prepared by the method of the present application not only has a high water flux, which can be up to 50 GFD, but also has a removal rate of sodium chloride in the range of 70% to 90%, in addition, the removal rate of magnesium sulfate is above 96% and the removal rate of calcium chloride is above 80%, which not only better retains the trace elements beneficial to human body, but also maintains good desalination capacity for the water with high salt content.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, Includes the following steps: A polymer solution is prepared as a casting solution, which is then applied to the reinforcing material to form a polymer support layer. A functional layer is formed by contacting a polymer support layer with an aqueous solution containing an amine compound and a component for reducing surface tension, and an oil solution containing an acyl chloride compound, via a slot coating method. The concentration of the component for reducing surface tension is 0.01–0.5 wt% based on the weight of the aqueous solution. The component for reducing surface tension is a silane coupling agent having at least one amino group. This silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane. In the slot coating method, the coating gap is 0.1–1 mm, and the coating rate is 10–100 ml / min. A reverse osmosis membrane is obtained after post-treatment and heat treatment, wherein the post-treatment includes cleaning with a cleaning agent, and no heat treatment is performed before the post-treatment, and the heat treatment temperature is 60°C.

2. The preparation method according to claim 1, wherein the polymer is at least one selected from bisphenol A type polysulfone, polyarylsulfone, polyethersulfone, 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 the following: m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, mesopraninine, N,N-dimethylm-phenylenediamine, 1,4-cyclohexanediamine, N,N-dimethylcyclohexanediamine, diaminobenzenesulfonic acid, diaminobenzoic acid, melamine, and ethylenediamine.

4. The preparation method according to claim 1 or 2, wherein the concentration of the amine compound is 2-8 wt% based on the weight of the aqueous solution.

5. The preparation method according to claim 1 or 2, wherein the acyl chloride compound is selected from at least one of terephthaloyl chloride, isophthaloyl chloride, o-phthaloyl chloride, biphenyl dicarboxylate chloride, cyclohexanediol chloride, succinyl chloride, succinyl tricarboxylate chloride, pyromellitic tricarboxylate chloride, cyclobutane-1,2-dicarboxylate chloride, 1,3,5-cyclohexanetricarboxylate chloride, biphenyl tricarboxylate chloride, 5-oxoformyl chloride-isophthaloyl chloride, biphenyl tetracarboxylate chloride, 2,6-naphthalenedicarboxylate chloride, pentyltriacyl chloride, and benzene disulfonyl chloride.

6. The preparation method according to claim 1 or 2, wherein the concentration of the acyl chloride compound is 0.05 to 0.30 wt% based on the weight of the oil phase solution.

7. The preparation method according to claim 1 or 2, wherein the cleaning agent is at least one selected from water, toluene, xylene, trimethylbenzene, acetone, cyclohexane, n-hexane, petroleum ether, Isopar-G, Isopar-L, and n-heptane.

8. A reverse osmosis membrane prepared by the preparation method according to any one of claims 1-7, characterized in that, The removal rate of sodium chloride is 70-90%.

9. The reverse osmosis membrane according to claim 8, characterized in that, The removal rate of magnesium sulfate is over 96%, and the removal rate of calcium chloride is over 80%.

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