Seawater desalination reverse osmosis membrane and preparation method thereof

Abstract

The invention relates to a seawater desalination reverse osmosis membrane and a preparation method thereof, and the seawater desalination reverse osmosis membrane comprises a support layer, a polyvinyl butyral boron removal intermediate layer and a polyamide separation layer which are sequentially arranged from bottom to top, wherein the polyvinyl butyral boron removal middle layer comprises a polyvinyl butyral boron removal bottom layer close to the supporting layer and a polyvinyl butyral boron removal middle layer top layer close to the polyamide separation layer; the polyvinyl butyral boron removal middle layer is prepared from a modified polyvinyl butyral material containing a modified carbon nanotube; wherein the addition amount of the modified carbon nanotubes in the polyvinyl butyral boron-removing bottom layer is greater than that of the polyvinyl butyral boron-removing middle layer top layer. The reverse osmosis membrane has high water flux and desalination rate, the boron removal effect of the reverse osmosis membrane is greatly improved, and the membrane is good in mechanical property, excellent in durability, long in service life and suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of reverse osmosis membranes, and in particular relates to a seawater desalination reverse osmosis membrane and a preparation method thereof. Background Art

[0002] Boron is an essential trace element for humans. However, excessive intake of boron may cause reproductive problems and threaten human health. Therefore, the World Health Organization has set a limit of 2.4ppm for boron in drinking water and 0.5ppm for boron in irrigation water. The development of effective boron removal technology is crucial. Reverse osmosis membrane technology is the core means of seawater desalination, but the boron in seawater (in the form of boric acid) has a small molecular size and is easy to pass through the membrane. The boron removal rate of conventional reverse osmosis membranes is usually less than 80%. Long-term drinking of water with excessive boron content will endanger human health. Therefore, improving the boron removal rate is a key technical difficulty of seawater desalination membranes.

[0003] In the prior art, the methods for improving the deboronization rate mostly rely on adjusting the pH of the inlet water or developing a new separation layer, but there are problems such as complex operation, high cost or decreased water flux. Although the patent application with application number CN202111386270.7 improves the water flux by introducing nanoporous materials into the polyamide separation layer, and grafts hydroxypropyl acrylate-acrylamide copolymer on the surface of the polyamide separation layer to improve the deboronization effect, although it improves the deboronization effect to a certain extent without reducing the water flux, its deboronization effect is still not ideal and needs further improvement. Secondly, since the nanoporous particles and hydroxypropyl acrylate-acrylamide copolymer are grafted and connected, the nanoporous particles are easy to fall off and lose during use, affecting the durability and service life of the reverse osmosis membrane. In addition, it also requires multiple impregnation treatments, and the impregnation time needs to be controlled at the second level, requiring too high precision, which increases the difficulty of parameter control in the production process, resulting in its industrial production difficulty and low yield. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a seawater desalination reverse osmosis membrane and a preparation method thereof. The membrane not only has high water flux and desalination rate, but also greatly improves the boron removal effect of the reverse osmosis membrane. The membrane has good mechanical properties, excellent durability, long service life, and is suitable for industrial production.

[0005] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] A seawater desalination reverse osmosis membrane comprises a support layer, a polyvinyl butyral boron removal intermediate layer, and a polyamide separation layer, which are arranged in sequence from bottom to top;

[0007] Wherein, the polyvinyl butyral boron removal intermediate layer comprises a polyvinyl butyral boron removal intermediate layer bottom layer close to the support layer and a polyvinyl butyral boron removal intermediate layer top layer close to the polyamide separation layer;

[0008] The polyvinyl butyral boron removal intermediate layer is made of modified polyvinyl butyral material containing modified carbon nanotubes;

[0009] The amount of modified carbon nanotubes added in the bottom layer of the polyvinyl butyral boron removal intermediate layer is greater than that in the top layer of the polyvinyl butyral boron removal intermediate layer.

[0010] As a further technical solution, the content of modified carbon nanotubes in the top layer of the polyvinyl butyral deboronized intermediate layer is 0.1-2%;

[0011] As a further technical solution, the content of carbon nanotubes in the bottom layer of the polyvinyl butyral intermediate layer is 1-5%.

[0012] As a further technical solution, the support layer adopts a polysulfone-based membrane;

[0013] As a further technical solution, the modified carbon nanotubes are amino-treated carbon nanotubes.

[0014] As a further technical solution, the method for preparing the amino-modified carbon nanotubes comprises the following steps:

[0015] Step 1) Acidification of carbon nanotubes: Add a nitric acid-concentrated sulfuric acid mixture to the multi-walled carbon nanotubes, reflux in an 80°C oil bath under stirring for 6 hours, terminate the reaction, wash with deionized water until the pH of the washing solution is 6-7, and vacuum dry at 60°C for 12 hours to obtain carboxylated carbon nanotubes;

[0016] Step 2) Amination treatment: The carboxylated carbon nanotubes were dispersed in a solvent, and after ultrasonic dispersion, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide were added, stirred at room temperature for 2 hours, and then ethanolamine was added, reacted at 60°C for 4 hours, and washed alternately by centrifugation with N,N-dimethylformamide and deionized water until there was no free amine, and vacuum dried at 60°C for 12 hours to obtain aminated carbon nanotubes.

[0017] As a further technical solution, the top layer of the polyvinyl butyral boron removal intermediate layer is coated with a modified polyvinyl butyral-carbon nanotube composite solution;

[0018] As a further technical solution, the modified polyvinyl butyral-carbon nanotube composite solution comprises the following raw materials in parts by weight:

[0019] 100 parts of polyvinyl butyral, 8-15 parts of amino alcohol, 12-20 parts of aliphatic vicinal diol, 2-5 parts of modified carbon nanotubes, 1500-2500 parts of solvent A (preferably alcohol aqueous solution), 2-4 parts of catalyst, and 0.5-1.5 parts of cross-linking agent;

[0020] As a further technical solution, the content of modified carbon nanotubes in the modified polyvinyl butyral-carbon nanotube composite solution is 0.01-0.3 wt%;

[0021] As a further technical solution, the polyvinyl butyral bottom layer is coated with a bottom layer polyvinyl butyral coating liquid;

[0022] As a further technical solution, the bottom polyvinyl butyral coating liquid comprises the following raw materials in parts by weight:

[0023] 100 parts of polyvinyl butyral, 1-5 parts of amino alcohol, 3-15 parts of aliphatic vicinal diol, 1-5 parts of modified carbon nanotubes, 500-1000 parts of anhydrous ethanol;

[0024] As a further technical solution, in the bottom polyvinyl butyral coating liquid, the weight ratio of amino alcohol to aliphatic vicinal diol is 1:3.

[0025] As a further technical solution, the concentration of the modified carbon nanotubes in the bottom polyvinyl butyral coating liquid is 0.5%.

[0026] As a further technical solution, the aliphatic vicinal diol includes one or more of 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 1,2-hexanediol, tartaric acid, glyceraldehyde, inositol, and polyethylene glycol;

[0027] As a further technical solution, the amino alcohol includes one or more of ethanolamine and 2-amino-1,2-propylene glycol;

[0028] As a further technical solution, the solvent is prepared by mixing an organic solvent and water in a volume ratio of 1:(0.1-10) (preferably ethanol:water volume ratio = 1:0.3-3);

[0029] As a further technical solution, the organic solvent A includes one or more of methanol, propylene glycol, ethylene glycol, isopropanol, acetone, tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, and polyethylene glycol;

[0030] As a further technical solution, the catalyst is one or more of p-toluenesulfonic acid, camphorsulfonic acid, benzenesulfonic acid, oxalic acid, etc.;

[0031] As a further technical solution, the cross-linking agent is one or more of glutaraldehyde, hexamethylene diisocyanate, paraformaldehyde, epichlorohydrin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, toluene diisocyanate, and isophorone diisocyanate.

[0032] As a further technical solution, the polyvinyl butyral is purified polyvinyl butyral;

[0033] As a further technical solution, the method for purifying polyvinyl butyral comprises the following steps: adding ethanol to polyvinyl butyral, refluxing at 80° C. for 1 hour, filtering while hot to remove insoluble matter, cooling the filtrate and pouring it into deionized water to precipitate the polyvinyl butyral, filtering and vacuum drying after suction to obtain purified polyvinyl butyral for later use;

[0034] As a further technical solution, the amino alcohol is a dehydrated amino alcohol;

[0035] As a further technical solution, the aliphatic vicinal diol is a dehydrated amino alcohol.

[0036] As a further technical solution, the method for preparing the modified polyvinyl butyral-carbon nanotube composite solution comprises the following steps:

[0037] Step A, adding part of solvent A to the amino alcohol and the aliphatic vicinal diol respectively to prepare an amino alcohol solution with a mass concentration of 25-35% (preferably 30%) and an aliphatic vicinal diol solution with a mass concentration of 35-45% (preferably 40%);

[0038] Step B: Modification of polyvinyl butyral with amino alcohol and aliphatic vicinal diol:

[0039] Add part of solvent A to polyvinyl butyral, stir at 80 degrees Celsius until completely dissolved, and cool to 60 degrees Celsius to obtain a polyvinyl butyral solution, which is set aside;

[0040] The amino alcohol solution and the aliphatic vicinal diol solution were sequentially added to the polyvinyl butyral solution, and after stirring evenly, a catalyst was added, and the temperature was raised to 85° C., and the mixture was refluxed under stirring for 7 hours. The pH was adjusted to 7.0 with a 5 wt % sodium carbonate solution to terminate the reaction, thereby obtaining a modified polyvinyl butyral solution.

[0041] Step C, modification of polyvinyl butyral with carbon nanotubes: adding modified carbon nanotubes to the modified polyvinyl butyral solution, and sequentially performing high-speed shearing and ultrasonic dispersion to obtain a modified polyvinyl butyral-carbon nanotube mixed solution;

[0042] A crosslinking agent was added to the modified polyvinyl butyral-carbon nanotube mixed solution, and the mixture was stirred and reacted at 50° C. for 1 hour to form a lightly crosslinked network. The mixture was allowed to stand for degassing for 30 minutes to obtain a modified polyvinyl butyral-carbon nanotube composite solution.

[0043] As a further technical solution, the method for preparing the bottom polyvinyl butyral coating liquid comprises the following steps:

[0044] First, amino alcohol and aliphatic vicinal diol are dissolved in part of anhydrous ethanol to prepare a 5-10 wt% amino alcohol solution and a 5-10 wt% aliphatic vicinal diol solution respectively;

[0045] Then, polyvinyl butyral was dissolved in anhydrous ethanol, and the modified carbon nanotubes were added and stirred evenly, and then the amino alcohol solution and the aliphatic vicinal diol solution were added and stirred for 1 hour to prepare the bottom polyvinyl butyral coating liquid.

[0046] A method for preparing a seawater desalination reverse osmosis membrane comprises the following steps:

[0047] Step 1: Pretreatment of the support layer: Rinse the support layer with deionized water and ethanol three times in sequence. After drying, treat the surface of the support layer with oxygen plasma to improve the adhesion between the support layer and the intermediate layer.

[0048] Step 2, polyvinyl butyral bottom layer coating: Use a doctor blade coating method to evenly coat the bottom polyvinyl butyral coating liquid on the surface of the support layer to a thickness of 7-9 μm (preferably 8 μm). After coating, dry at room temperature for 2 hours, and then dry in an oven at 40-60° C. (preferably 50° C.) for 5-7 hours (preferably 6 hours) to obtain the polyvinyl butyral boron removal bottom layer;

[0049] Step 3, coating the polyvinyl butyral top layer: After the polyvinyl butyral bottom layer is dried, the modified polyvinyl butyral-carbon nanotube composite solution is immediately coated on the surface of the polyvinyl butyral bottom layer to a thickness of 2-5 μm. After the coating is completed, the mixture is left at room temperature for 0.5-1 hour, and then dried at 30-50° C. for 2-4 hours to obtain the polyvinyl butyral boron-removing intermediate layer top layer;

[0050] Step 4, post-treatment: After the top layer of the polyvinyl butyral boron removal intermediate layer is dried, the film is annealed at 50-80°C for 1-2 hours to eliminate the stress in the film, thereby obtaining a gradient polyvinyl butyral boron removal intermediate layer;

[0051] Step 5: Immerse the membrane coated with the polyvinyl butyral boron removal intermediate layer in the aqueous solution for 1 minute, take it out and blow dry the excess liquid; then immerse it in the oil phase solution for 20 seconds to form a polyamide separation layer, take it out and dry it naturally in the air for 1 minute, then heat treat it in an oven at 55-65°C (preferably 60°C) for 4-6 minutes (preferably 5 minutes), and then rinse it with clean water to obtain a seawater desalination reverse osmosis membrane.

[0052] As a further technical solution, the power of the oxygen plasma treatment is 100-200W and the treatment time is 5-10 minutes;

[0053] As a further technical solution, in the aqueous phase solution, the concentration of m-phenylenediamine is 3.5 wt %, the concentration of sodium lauryl sulfate is 0.03 wt %, and the concentration of sodium hydroxide is 0.4 wt %;

[0054] As a further technical solution, the concentration of trimesoyl chloride in the oil phase solution is 0.35 wt %.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. The present invention utilizes amino carbon nanotubes, amino alcohols and aliphatic vicinal diols to modify PVB and use it as an intermediate layer. The principle of amino (-NH2), hydroxyl (-OH) and boric acid forming a stable complex is utilized to enhance the boron retention of the reverse osmosis membrane. This not only improves the water flux and desalination rate of the reverse osmosis membrane, but also greatly improves the boron removal effect of the reverse osmosis membrane, achieving a water flux ≥29LMH, a desalination rate ≥99.5%, and a boron removal rate ≥95%, meeting the core indicators of seawater desalination.

[0057] 2. The present invention selects PVB as the middle layer and utilizes layered laying technology to design the bottom and top layers of the middle layer differently. The bottom layer focuses more on playing a bridging role with the support layer. Therefore, it increases the content of modified carbon nanotubes, eliminates the compounding of carbon nanotubes and modified polyvinyl butyral (modified PVB) as well as the crosslinking agent and catalyst, and adopts a rapid blending process, which not only retains the polar groups in the bottom layer to the greatest extent, enhances the adhesion between the middle layer and the support layer, but also improves the processing efficiency; while the top layer focuses more on taking on the boron removal function. Therefore, it improves the dispersion effect of carbon nanotubes and modified polyvinyl butyral (modified PVB) through compounding and fine dispersion technology, avoids the blockage of the permeation channel, and utilizes crosslinking technology to improve the structural stability of the middle layer. In addition, it also reduces the content of carbon nanotubes, improves the smoothness of the surface of the top layer of the middle layer, promotes the formation of a uniform polyamide separation layer, and avoids the problem caused by the uneven polyamide separation layer due to excessive carbon nanotube content in the top layer of the middle layer.

[0058] 3. This invention modifies carbon nanotubes by amino modification, forming hydrogen bonds (-NH2···HO-) with the hydroxyl groups (-OH) in the PVB molecular chain. This strengthens the van der Waals forces between polar groups, significantly reducing the aggregation tendency of CNTs. Furthermore, it improves the interfacial adhesion of the reverse osmosis membrane and enhances its anti-fouling properties. Furthermore, compared to traditional grafting techniques, this method can prevent the shedding of carbon nanotubes, thereby improving the durability and service life of the reverse osmosis membrane.

[0059] 4. The present invention utilizes a layered coating process to complete the coating of the intermediate layer. The process is mature and easy to scale up for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 These are infrared scanning spectra of PVB, carbon nanotubes, amino-modified carbon nanotubes, modified PVB, and amino-modified carbon nanotubes PVB. DETAILED DESCRIPTION

[0061] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0062] In the present invention,

[0063] Multi-walled carbon nanotubes (diameter 10-20 nm, length 1-5 μm, purity ≥95%) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0064] Polyvinyl butyral (acetalization degree 70-85%, free hydroxyl content 20-25%, molecular weight 50,000-100,000) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0065] Polysulfone-based membrane (thickness 100-120 μm, average pore size 0.2-0.3 μm, porosity 70-75%), provided by Rixin Hengli;

[0066] Ethanolamine, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0067] 1,2-Propanediol, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0068] p-Toluenesulfonic acid, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0069] In the present invention, unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0070] Example 1

[0071] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps:

[0072] 1. Reagent pretreatment:

[0073] 1) Purification of polyvinyl butyral (purpose: to remove residual impurities and ensure uniform modification reaction): 100 g of polyvinyl butyral (acetalization degree 70-85%, free hydroxyl content 20-25%, molecular weight 50,000-100,000) was added to 1000 mL of anhydrous ethanol, refluxed at 80° C. for 1 h, and filtered while hot to remove insoluble matter. The filtrate was cooled and poured into 2000 mL of deionized water to precipitate the polyvinyl butyral. After filtration, the purified polyvinyl butyral was vacuum dried at 60° C. for 12 h to obtain the purified polyvinyl butyral for later use.

[0074] 2) Ethanolamine: Remove water by vacuum distillation (80-85°C / 20kPa) to obtain dehydrated ethanolamine;

[0075] 3) 1,2-propylene glycol: Dehydrate with molecular sieve for 24 hours to obtain dehydrated 1,2-propylene glycol;

[0076] 4) Modification of carbon nanotubes to prepare amino-modified carbon nanotubes, comprising the following steps:

[0077] Step a, acidification treatment: Take 2g of multi-walled carbon nanotubes (diameter 10-20nm, length 1-5μm, purity ≥95%), add 100mL of concentrated nitric acid-concentrated sulfuric acid mixture (concentrated nitric acid, concentrated sulfuric acid volume ratio 1:3), reflux in an 80℃ oil bath for 6h, during which magnetic stirring is performed at 300rpm. After the reaction is completed, centrifuge and wash with deionized water at 8000rpm (each 10min) until the pH value of the supernatant reaches 6-7, and then vacuum dry at 60℃ for 12h to obtain carboxylated carbon nanotubes.

[0078] Step b, amination treatment: 1 g of carboxylated carbon nanotubes was dispersed in 100 mL of N,N-dimethylformamide, and sodium dodecylbenzenesulfonate was added as a dispersant to a concentration of 1 wt %, and ultrasonic dispersion was performed at a power of 300 W for 30 min. 0.6 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and 0.4 g of N-hydroxysuccinimide (NHS) were added, and the mixture was stirred at room temperature for 2 h. Subsequently, 2 mL of ethanolamine was added, and the mixture was reacted at 60° C. for 4 h. The mixture was washed alternately by centrifugation with N,N-dimethylformamide and deionized water until free amine was removed, and vacuum dried at 60° C. for 12 h to obtain aminated carbon nanotubes. The grafting rate of the aminated carbon nanotubes described in this embodiment was 8%. If the grafting rate was too low, the stress could not be transmitted, and if the grafting rate was too high, the movement of the PVB chain segments might be restricted.

[0079] In step b, ultrasonic dispersion: power 300-500W, time 30-60min;

[0080] 2. Preparation of coating liquid for modified polyvinyl butyral boron removal intermediate layer:

[0081] 1) The top layer of the modified polyvinyl butyral boron removal intermediate layer adopts a modified polyvinyl butyral / carbon nanotube composite solution. The preparation of the modified polyvinyl butyral / carbon nanotube composite solution includes the following steps:

[0082] Step A: 8 g of dehydrated ethanolamine and 12 g of dehydrated 1,2-propylene glycol were added to each of the two solutions (ethanol to water volume ratio 7:3) to prepare a 30% ethanolamine solution and a 40% 1,2-propylene glycol solution;

[0083] Step B, modification of polyvinyl butyral: 100g of purified polyvinyl butyral was added to 1500mL of ethanol aqueous solution (ethanol and water volume ratio of 7:3), and magnetically stirred at 500rpm at 80°C for 2h until completely dissolved, and then cooled to 60°C to obtain a polyvinyl butyral solution for standby use; then, the amino alcohol solution and the aliphatic vicinal diol solution were added to the polyvinyl butyral solution in sequence, stirred for 30min until uniform, and then 2g of p-toluenesulfonic acid was added. The temperature was raised to 85°C, and the reaction was refluxed at a stirring speed of 300rpm for 7h. The pH was adjusted to 7.0 with 5wt% sodium carbonate solution, and the reaction was terminated to obtain a modified polyvinyl butyral solution.

[0084] Step D, blending modification of carbon nanotubes and polyvinyl butyral: Take 199.8 g of the modified polyvinyl butyral solution obtained in step C, add 0.2 g of amino carbon nanotubes thereto, first high-speed shear treatment at a speed of 15,000 rpm for 10 minutes, and then disperse with pulsed ultrasound at a power of 200 W (working 3 seconds / pausing 1 second) for 45 minutes to obtain a modified polyvinyl butyral-carbon nanotube mixed solution (wherein the concentration of the modified carbon nanotubes is 0.1 wt%).

[0085] In this step, the amino groups (-NH2) on the surface of the amination carbon nanotubes can form hydrogen bonds (-NH2···HO-) with the hydroxyl groups (-OH) in the PVB molecular chain. At the same time, the van der Waals force between the polar groups is enhanced, which significantly reduces the agglomeration tendency of the carbon nanotubes.

[0086] 2) The bottom layer of the polyvinyl butyral boron removal intermediate layer adopts the bottom coating liquid;

[0087] The preparation of the bottom coating liquid comprises the following steps:

[0088] Dissolve 1g of dehydrated ethanolamine in 10mL of anhydrous ethanol to prepare a 10% ethanolamine solution; dissolve 3g of dehydrated 1,2-propylene glycol in 30mL of anhydrous ethanol to prepare a 10% 1,2-propylene glycol solution;

[0089] Dissolve 10 g of PVB (purified PVB) in 100 ml of anhydrous ethanol, add 0.5 g of amino-modified CNTs, stir evenly, then add the amino alcohol solution and the aliphatic vicinal diol solution, and continue stirring for 1 hour to prepare the bottom coating solution;

[0090] The concentration of modified CNTs in the obtained bottom coating liquid was 0.5 wt %.

[0091] 3. The preparation of seawater desalination reverse osmosis membrane includes the following steps:

[0092] Step 1: Pretreatment of the support layer

[0093] First, a commercial polysulfone-based membrane (thickness 100-120 μm, average pore size 0.2-0.3 μm, porosity 70-75%) was selected as the support layer, rinsed with deionized water and ethanol three times in sequence, and dried in vacuum at 60° C. for 2 h.

[0094] Then, the surface of the polysulfone base membrane was treated with oxygen plasma at a treatment power of 150W for 8 minutes to improve the adhesion between the support layer and the intermediate layer;

[0095] Step 2: coating of the polyvinyl butyral boron-removing intermediate layer: using a doctor blade coating method;

[0096] Step 2-1, coating of the bottom layer of the polyvinyl butyral deboronizing intermediate layer:

[0097] The distance between the scraper and the support layer was set to 30 μm, and the coating speed was 2 mm / s. The modified polyvinyl butyral-carbon nanotube composite solution was evenly coated on the surface of the support layer to a thickness of about 8 μm. The coated support layer was then placed at room temperature for 2 hours and then placed in an oven and dried at 50°C for 6 hours to form a polyvinyl butyral boron-removing intermediate layer bottom layer.

[0098] Step 2-2, coating the top layer of the polyvinyl butyral deboronizing intermediate layer:

[0099] After the polyvinyl butyral boron removal intermediate layer bottom layer is dried, the polyvinyl butyral intermediate layer top layer is immediately coated, and the distance between the scraper and the polyvinyl butyral intermediate layer bottom layer is adjusted to 30 μm, and the coating speed is 3 mm / s, so that the modified polyvinyl butyral-carbon nanotube composite solution is evenly coated on the surface of the polyvinyl butyral intermediate layer bottom layer to a thickness of about 3 μm; then, it is placed at room temperature for 1 hour and then dried at 40° C. for 3 hours to form the polyvinyl butyral intermediate layer top layer;

[0100] Step 2-3, post-treatment: After the top layer of the polyvinyl butyral deboronating intermediate layer is dried, it is placed at 60°C for 1.5 hours for annealing to eliminate the stress in the membrane and improve the performance of the membrane;

[0101] Step 3: Preparation of polyamide active separation layer:

[0102] 1) Preparation of an aqueous solution: preparing an aqueous solution having a concentration of 3.5 wt % of m-phenylenediamine, 0.03 wt % of sodium lauryl sulfate, and 0.4 wt % of sodium hydroxide;

[0103] 2) Preparation of an oil phase solution: dissolving trimesoyl chloride in n-hexane to prepare an oil phase solution having a trimesoyl chloride concentration of 0.35 wt %;

[0104] 3) Immerse the polysulfone support base membrane in the aqueous solution for 1 minute, remove it, roll the support membrane surface with a roller to squeeze out the liquid, and blow dry the excess liquid; then immerse the support membrane in the oil solution for 20 seconds, and remove it; after the composite membrane is naturally dried in air for 1 minute, heat-treated in a 60°C oven for 5 minutes, and then rinsed with clean water to obtain a seawater desalination reverse osmosis membrane.

[0105] Example 2

[0106] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as Example 1, except that: 1) in step b, the amount of ethanolamine used is 2.5 mL, and the grafting rate of the obtained amino-modified carbon nanotubes is 12%; and 2) the concentration of the carbon nanotubes in the modified polyvinyl butyral-carbon nanotube composite solution is 0.3 wt%.

[0107] Example 3

[0108] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as Example 1, except that: 1) the raw materials used for the top layer of the modified polyvinyl butyral intermediate layer, i.e., in step A, are 6 g of dehydrated ethanolamine and 15 g of dehydrated 1,2-propylene glycol; and 2) the concentration of carbon nanotubes in the modified polyvinyl butyral-carbon nanotube composite solution is 0.05 wt%.

[0109] Example 4

[0110] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as in Example 1, except that: 1) in step b, the amount of ethanolamine used is 1.5 mL, and the grafting rate of the obtained amino-modified carbon nanotubes is 5%; 2) the annealing temperature is 80° C. and the time is 1 hour;

[0111] Example 5

[0112] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as in Example 1, except that, when coating the polyvinyl butyral boron removal intermediate layer, i.e., in step 2, ethylene glycol is used as the aliphatic vicinal diol; when coating the bottom layer of the polyvinyl butyral intermediate layer, the coating speed is 3 mm / s; when coating the top layer of the polyvinyl butyral intermediate layer, the coating speed is 2 mm / s.

[0113] Comparative Example 1

[0114] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as Example 1, except that no amino-treated carbon nanotubes are added to the polyvinyl butyral middle layer, and therefore, the polyvinyl butyral middle layer does not distinguish between a bottom layer and a top layer.

[0115] Comparative Example 2

[0116] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as in Example 1, except that:

[0117] The polyvinyl butyral intermediate layer does not distinguish between a bottom layer and a top layer. The polyvinyl butyral intermediate layer is obtained by coating a modified polyvinyl butyral-carbon nanotube composite solution with a carbon nanotube concentration of 0.3 wt %. The thickness is 10 μm. After coating, the solution is placed at room temperature for 2 hours, dried at 45° C. for 4 hours, and then annealed at 60° C. for 1.5 hours to obtain the polyvinyl butyral intermediate layer.

[0118] Comparative Example 3

[0119] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as Example 1, except that unmodified carbon nanotubes are added to the modified polyvinyl butyral-carbon nanotube composite solution and the bottom coating solution.

[0120] Comparative Example 4

[0121] A seawater desalination reverse osmosis membrane, and a preparation method thereof, comprising the following steps: the same as Example 1, except that only ethanolamine is added to the modified polyvinyl butyral, and 1,2-propylene glycol is not added;

[0122] In the preparation of the primer coating liquid, only ethanolamine was added, and 1,2-propylene glycol was not added.

[0123] Comparative Example 5

[0124] A seawater desalination reverse osmosis membrane and a preparation method thereof, comprising the following steps:

[0125] Step 1: Preparation of each solution:

[0126] Preparation of a polysulfone-based membrane: Dissolve polysulfone particles at a ratio of 18 wt% in a solvent with the balance being N,N-dimethylformamide, and stir at 60°C for 5 hours. After filtration, place the mixture in a -0.1 MPa atmosphere, degas at 60°C, and cool to 25°C to obtain a casting solution. The resulting casting solution is coated onto a polyester non-woven fabric using an automatic scraper, then immersed in a 10°C pure water bath to solidify the film. The porous polysulfone-based membrane is then washed with water to obtain the resulting film.

[0127] Polyamine monomer solution: 35 g of m-phenylenediamine, 40 g of triethylamine, 60 g of camphorsulfonic acid, and 10 g of sodium lauryl sulfate were dissolved in 855 g of pure water, and 30 mg of carboxylated nanographene oxide was added to prepare a polyamine monomer solution;

[0128] Acyl chloride monomer solution: 2 g of trimesoyl chloride was dissolved in 998 g of Isopar G solvent to prepare an acyl chloride monomer solution;

[0129] Diethanolamine solution: prepare a diethanolamine solution according to 3 wt% of diethanolamine, 2 wt% of triethylamine, 4 wt% of camphorsulfonic acid, and the balance being pure water.

[0130] Carboxyl activator solution: Weigh 5 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 3.5 g of N-hydroxysuccinimide (NHS) and dissolve them in 995 ml of room temperature pure water. Add hydrochloric acid dropwise to adjust the pH of the solution to 5-6 to obtain a carboxyl activator solution.

[0131] Graft polymer solution: Dissolve 7g acrylamide (AAm) and 3g hydroxypropyl methacrylate (HPMA) in 15ml dimethylformamide and add to a four-necked flask, stir and heat to 80°C, add 10ml dimethylformamide solution containing 0.25g benzoyl peroxide (BPO) dropwise to the flask, react at 80°C for 2 hours, stop heating, and the obtained product is a white viscous substance. The obtained product is dissolved in acetic acid, and the homopolymer insoluble matter of AAm is filtered out. Acetone is slowly added to the remaining product, and the filtered insoluble matter is repeatedly washed with acetone several times. The product is dried to obtain a pure hydroxypropyl methacrylate-acrylamide (HPMA-AAm) copolymer; weigh 3g of the hydroxypropyl methacrylate-acrylamide copolymer prepared above and dissolve it in 997g of pure water at room temperature, and sodium hydroxide solution is added dropwise to adjust the pH to 8-9 to obtain a graft polymer solution;

[0132] Crosslinker solution: Dissolve 1.25 g of glutaraldehyde solution (40 wt%) in 100 g of pure water and dilute to 1000 g with water. Add sulfuric acid dropwise to adjust the pH to 2.5-3.5.

[0133] Polyvinyl alcohol solution: Weigh 35g of polyvinyl alcohol powder, 2g of hydrochloric acid solution and 8g of glutaraldehyde solution in 455g of 90℃ hot water, stir for 0.5 hours, add 500g of room temperature pure water to dilute, and set aside;

[0134] Step 2, preparation:

[0135] The prepared polysulfone-based membrane was immersed in an ethanol solution for 5 minutes, then immersed in a polyamine monomer solution for 30 seconds. After removal, the excess solution on the membrane surface was removed. The membrane was then immersed in an acyl chloride monomer solution for interfacial polymerization to form a polyamide layer for 30 seconds. The membrane was then heat-treated in a 60°C oven for 1 minute to further promote cross-linking. The membrane was then immersed in a 30°C diethanolamine solution for 2 minutes, washed with 80°C hot water for 2 minutes and 25°C cold water for 1 minute, oxidized with nitrous acid for 2 minutes, immersed in a carboxyl activator solution for 2.5 minutes to activate the carboxyl groups, and then immersed in a grafting polymer solution for 2 minutes at 25°C. After the grafting process was completed, the membrane was immersed in a crosslinker solution for 2 minutes and coated with a polyvinyl alcohol solution as a protective layer at 25°C for 10 seconds. The membrane was then dried at 65°C for 1.5 minutes to obtain the final reverse osmosis membrane.

[0136] Effect example 1:

[0137] Infrared spectroscopy was performed on the carbon nanotubes, ethanolamine and 1,2-propylene glycol modified PVB and the modified polyvinyl butyral-amino carbon nanotube composite (amino carbon nanotubes, ethanolamine and 1,2-propylene glycol modified PVB) in Example 1. The results are shown in FIG. Figure 1 ;

[0138] from Figure 1 It can be seen that ethanolamine and 1,2-propylene glycol modified PVB contain a large number of hydroxyl groups (-OH), and the amino CNTs carry amino groups (-NH2), which can easily form hydrogen bonds between them. The -OH stretching vibration peak of the modified PVB before the reaction is at 3400 cm -1 The -NH2 stretching vibration peak of amino CNTs is at 3350cm -1 There are obvious double peaks near 3200-3500cm -1 A broad and strong peak appears in the region, indicating that a large number of hydrogen bonds are formed between the two. The bending vibration peak of -NH2 may be from 1550cm -1 Displacement to 1580cm -1 At the same time, the peak intensity increases. This is because the formation of hydrogen bonds changes the chemical environment of -NH2, causing its vibration frequency to change and the absorption intensity to increase. -1The C=N stretching vibration peak appears at 1580 cm, indicating that ethanolamine and PVB undergo a covalent reaction to form a C=N double bond. -1 The C=C skeleton stretching vibration peak nearby decreased in intensity and increased in width after the reaction, indicating that there was a strong interaction between the amino-modified carbon nanotubes and the PVB modified with ethanolamine and 1,2-propylene glycol.

[0139] Effect Example 2: Performance and Durability Testing

[0140] The deboronization, desalination and water flux tests of the seawater desalination reverse osmosis membranes prepared in each embodiment and each comparative example were carried out on the first day and 90 days after operation, respectively. In addition, the mechanical strength test was also carried out. The results are shown in Table 1.

[0141] 1. Detection method of deboronization rate:

[0142] Pretreatment process: Take a piece of seawater reverse osmosis membrane. The membrane size should be able to completely cover the test pool seal ring in the reverse osmosis membrane test device. The effective membrane area is 25-40cm 2 Soak the membrane in deionized or distilled water at room temperature for 30-60 minutes.

[0143] Prepare the test solution: Prepare a 30,000-34,000 mg / L sodium chloride solution with deionized water in the water tank of the reverse osmosis membrane test device. Add boric acid to the solution to achieve a boron concentration of 5-8 mg / L, and adjust the pH of the solution to 7.5-8.5 with sodium hydroxide.

[0144] Boron Removal Rate Test: Place the soaked seawater reverse osmosis membrane into the test cell of the reverse osmosis membrane test apparatus, with the membrane separation layer facing the inlet side of the test cell. Sequentially start the reverse osmosis membrane test apparatus's raw water pump and high-pressure pump, raising the inlet pressure to 5-6 MPa. Control the flow velocity across the membrane surface at 0.85-1.00 m / s, and adjust the test fluid temperature to 24-26°C. After operating under these conditions for 30-60 minutes, perform sampling tests. Collect the test apparatus's inlet and product water three times every 10-15 minutes. Analyze the boron concentration of both the inlet and product water using an atomic emission spectrometer (ICP) or atomic absorption spectrometer. After testing, slowly adjust the shutoff valve to reduce the pressure to below 0.1 MPa. Then, shut off the high-pressure and raw water pumps.

[0145] Data processing: The arithmetic average of the boron concentrations in the multiple influent samples is taken as the final influent boron concentration, and the arithmetic average of the boron concentrations in the multiple produced water samples is taken as the final produced water boron concentration.

[0146] Rb=(1-Cp / Cf)×100%

[0147] Calculate the boron removal rate of the flat seawater reverse osmosis membrane.

[0148] Rb represents the deboronization rate,

[0149] Cp represents the final boron concentration of produced water (mg / L),

[0150] Cf represents the final influent boron concentration (mg / L).

[0151] 2. Salt rejection rate test method: in accordance with GB / T 32373-2015);

[0152] Water flux detection method: in accordance with GB / T 32373-2015);

[0153] Mechanical strength test method: tensile strength and other related tests are carried out in accordance with "Determination of tensile properties of plastics Part 1: General principles" (GB / T 1040.1-2018). The following are the specific steps:

[0154] Sample Preparation: Cut the desalination membrane into standard sizes. Specific dimensions can be determined based on the selected standard or the requirements of the testing machine fixture. Typically, the membrane is in a long strip shape. Care should be taken to avoid damaging the membrane edges during cutting, ensuring the sample surface is flat and wrinkle-free. Precondition the cut samples in a constant temperature and humidity environment for a period of time, for example, at 23±2°C and 50±5% relative humidity for 24 hours, to stabilize the membrane performance.

[0155] Install the sample: Securely secure both ends of the pre-treated sample in the tensile testing machine's fixtures, ensuring the sample is centered to avoid uneven force. Ensure the clamping force is moderate, preventing the diaphragm from being too tight and breaking, or from being too loose and causing the diaphragm to slip during the test.

[0156] Apply tension: Start the tensile testing machine and set the loading speed, typically 50 mm / min. The specific speed depends on the diaphragm material and standard requirements. The testing machine applies axial tension to the sample at a constant speed, and the sensor collects tension and displacement data in real time.

[0157] Data recording: During the test, as the tension increases, the diaphragm will gradually stretch. When the diaphragm breaks, the maximum tension value at this time is recorded.

[0158] Data analysis: Calculate the tensile strength of the membrane based on the recorded data using the formula: tensile strength = maximum tensile force / sample cross-sectional area.

[0159] Table 1

[0160]

[0161]

[0162] As can be seen from the data in Table 1, the seawater desalination reverse osmosis membranes of Examples 1-5 have a water flux ≥29LMH, a salt rejection rate ≥99.5%, a boron removal rate ≥95%, and a tensile strength ≥25MPa. After long-term operation, the attenuation of each indicator is lower than that of the comparative examples. The present invention utilizes amino-modified carbon nanotubes, amino alcohols, and aliphatic vicinal diols to modify PVB, and utilizes the principle that amino groups (-NH2), hydroxyl groups (-OH) form stable complexes with boric acid to enhance the boron retention of the reverse osmosis membrane. This not only improves the water flux and salt rejection of the reverse osmosis membrane, but also greatly improves the boron removal effect of the reverse osmosis membrane, enabling it to meet the core indicators of seawater desalination.

[0163] The above-described embodiments are only preferred embodiments of the present invention and are not exhaustive of all feasible implementations of the present invention. For those skilled in the art, any obvious modifications made thereto without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A seawater desalination reverse osmosis membrane, characterized in that: It includes a support layer, a polyvinyl butyral boron removal intermediate layer, and a polyamide separation layer arranged in sequence from bottom to top; Wherein, the polyvinyl butyral boron removal intermediate layer comprises a polyvinyl butyral boron removal intermediate layer bottom layer close to the support layer and a polyvinyl butyral boron removal intermediate layer top layer close to the polyamide separation layer; The polyvinyl butyral boron removal intermediate layer is made of modified polyvinyl butyral material containing modified carbon nanotubes; The amount of modified carbon nanotubes added in the bottom layer of the polyvinyl butyral boron removal intermediate layer is greater than that in the top layer of the polyvinyl butyral boron removal intermediate layer.

2. A seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The support layer adopts a polysulfone-based membrane; The modified carbon nanotubes are amino-treated carbon nanotubes.

3. A seawater desalination reverse osmosis membrane according to claim 2, characterized in that: The preparation method of the amino-modified carbon nanotubes comprises the following steps: Step 1) Acidification of carbon nanotubes: adding a nitric acid-concentrated sulfuric acid mixture to the multi-walled carbon nanotubes, heating under reflux under stirring conditions, washing with deionized water until the pH of the washing solution is 6-7, and vacuum drying to obtain carboxylated carbon nanotubes; Step 2) Amination treatment: The carboxylated carbon nanotubes are dispersed in a solvent, and after ultrasonic dispersion, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide are added, and stirred at room temperature for 1.5-2.5 hours. Then, ethanolamine is added, and the reaction is carried out at 55-65°C for 3-5 hours. The mixture is washed with N,N-dimethylformamide and deionized water by alternating centrifugation until there is no free amine, and vacuum dried to obtain the amination carbon nanotubes.

4. A seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The top layer of the polyvinyl butyral boron removal intermediate layer is coated with a modified polyvinyl butyral-carbon nanotube composite solution; The modified polyvinyl butyral-carbon nanotube composite solution comprises the following raw materials in parts by weight: 100 parts of polyvinyl butyral, 8-15 parts of amino alcohol, 12-20 parts of aliphatic vicinal diol, 2-5 parts of modified carbon nanotubes, 1500-2500 parts of solvent, 2-4 parts of catalyst, 0.5-1.5 parts of cross-linking agent; The content of modified carbon nanotubes in the modified polyvinyl butyral-carbon nanotube composite solution is 0.01-0.3 wt %; The polyvinyl butyral bottom layer is coated with a polyvinyl butyral bottom layer coating liquid; The bottom polyvinyl butyral coating liquid comprises the following raw materials in parts by weight: 100 parts of polyvinyl butyral, 1-5 parts of amino alcohol, 3-15 parts of aliphatic vicinal diol, 1-5 parts of modified carbon nanotubes, 500-1000 parts of anhydrous ethanol; The concentration of modified carbon nanotubes in the bottom polyvinyl butyral coating liquid is 0.5%.

5. A seawater desalination reverse osmosis membrane according to claim 4, characterized in that: The aliphatic vicinal diol includes one or more of 1,2-propylene glycol, ethylene glycol, 1,2-butanediol, 1,2-hexanediol, tartaric acid, glyceraldehyde, inositol, and polyethylene glycol; The amino alcohol includes one or more of ethanolamine and 2-amino-1,2-propylene glycol; The solvent is prepared by mixing an organic solvent and water in a volume ratio of 1: (0.1-10); Wherein, the organic solvent A includes one or more of methanol, propylene glycol, ethylene glycol, isopropanol, acetone, tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, and polyethylene glycol; The catalyst is one or more of p-toluenesulfonic acid, camphorsulfonic acid, benzenesulfonic acid, oxalic acid, etc.; The cross-linking agent is one or more of glutaraldehyde, hexamethylene diisocyanate, paraformaldehyde, epichlorohydrin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, toluene diisocyanate, and isophorone diisocyanate.

6. A seawater desalination reverse osmosis membrane according to claim 4, characterized in that: The polyvinyl butyral is purified polyvinyl butyral; The method for purifying polyvinyl butyral comprises the following steps: adding anhydrous ethanol to polyvinyl butyral, refluxing at 75-85° C. for 0.5-1.5 hours, filtering while hot to remove insoluble matter, cooling the filtrate and pouring it into deionized water to precipitate the polyvinyl butyral, filtering and vacuum drying to obtain purified polyvinyl butyral for later use; The amino alcohol is a dehydrated amino alcohol; The aliphatic vicinal diol is an amino alcohol which has been subjected to a dehydration treatment.

7. A seawater desalination reverse osmosis membrane according to claim 4, characterized in that: The method for preparing the modified polyvinyl butyral-carbon nanotube composite solution comprises the following steps: Step A, adding part of the solvent to the amino alcohol and the aliphatic vicinal diol respectively to prepare an amino alcohol solution with a mass concentration of 25-35% and an aliphatic vicinal diol solution with a mass concentration of 35-45%; Step B: Modification of polyvinyl butyral with amino alcohol and aliphatic vicinal diol: Add part of the solvent to the polyvinyl butyral, stir at 75-85 degrees Celsius until completely dissolved, and cool to 60 degrees Celsius to obtain a polyvinyl butyral solution for later use; Sequentially add the amino alcohol solution and the aliphatic vicinal diol solution to the polyvinyl butyral solution, stir evenly, add the catalyst, heat to 80-90°C, reflux under stirring for 6-8 hours, adjust the pH to 7.0 with sodium carbonate solution, terminate the reaction, and obtain a modified polyvinyl butyral solution; Step C, modification of polyvinyl butyral with carbon nanotubes: adding modified carbon nanotubes to the modified polyvinyl butyral solution, and sequentially performing high-speed shearing and ultrasonic dispersion to obtain a modified polyvinyl butyral-carbon nanotube mixed solution; A crosslinking agent is added to the modified polyvinyl butyral-carbon nanotube mixed solution, stirred and reacted at 45-55° C. for 0.5-1.5 hours, and then allowed to stand for degassing to obtain a modified polyvinyl butyral-carbon nanotube composite solution.

8. A seawater desalination reverse osmosis membrane according to claim 4, characterized in that: The method for preparing the bottom polyvinyl butyral coating liquid comprises the following steps: First, amino alcohol and aliphatic vicinal diol are dissolved in part of anhydrous ethanol to prepare a 5-10 wt% amino alcohol solution and a 5-10 wt% aliphatic vicinal diol solution respectively; Then, polyvinyl butyral was dissolved in anhydrous ethanol, and the modified carbon nanotubes were added and stirred evenly, and then the amino alcohol solution and the aliphatic vicinal diol solution were added and stirred for 1 hour to prepare the bottom polyvinyl butyral coating liquid.

9. A method for preparing a seawater desalination reverse osmosis membrane according to claim 1, characterized in that: The steps include: Step 1: Pretreatment of the support layer: rinse the support layer with deionized water and ethanol 2-4 times in sequence, dry it, and then treat the surface of the support layer with oxygen plasma; Step 2, polyvinyl butyral bottom layer coating: Use a doctor blade coating method to evenly coat the bottom polyvinyl butyral coating liquid on the surface of the support layer to a thickness of 7-9 μm. After coating, dry at room temperature for 2 hours, and then dry in an oven at 40-60°C for 5-7 hours to obtain the polyvinyl butyral boron-removing bottom layer; Step 3, coating the polyvinyl butyral top layer: After the polyvinyl butyral bottom layer is dried, the modified polyvinyl butyral-carbon nanotube composite solution is immediately coated on the surface of the polyvinyl butyral bottom layer to a thickness of 2-5 μm. After the coating is completed, the mixture is left at room temperature for 0.5-1 hour, and then dried at 30-50° C. for 2-4 hours to obtain the polyvinyl butyral boron-removing intermediate layer top layer; Step 4, post-treatment: After the top layer of the polyvinyl butyral boron removal intermediate layer is dried, the film is annealed at 50-80°C for 1-2 hours to obtain a gradient polyvinyl butyral boron removal intermediate layer; Step 5: Immerse the membrane coated with the polyvinyl butyral boron removal intermediate layer in the aqueous solution for 1 minute, take it out and blow off the excess liquid; then immerse it in the oil solution for 20 seconds to form a polyamide separation layer, take it out and dry it naturally in the air for 1 minute, then heat treat it in an oven at 55-65°C for 4-6 minutes, and then rinse it with clean water to obtain a seawater desalination reverse osmosis membrane.

10. The method for preparing a water desalination reverse osmosis membrane according to claim 9, characterized in that: The power of oxygen plasma treatment is 100-200W, and the treatment time is 5-10 minutes; In the aqueous phase solution, the concentration of m-phenylenediamine is 3.5 wt %, the concentration of sodium lauryl sulfate is 0.03 wt %, and the concentration of sodium hydroxide is 0.4 wt %; The concentration of trimesoyl chloride in the oil phase solution was 0.35 wt %.

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