A polyamide reverse osmosis membrane for high-salt wastewater treatment and preparation method thereof

Abstract

The present invention relates to the technical field of reverse osmosis membranes, and specifically to a polyamide reverse osmosis membrane for high-salt wastewater treatment and a preparation method thereof. The present invention solves the problem that the polyamide reverse osmosis membrane cannot take into account both the desalination rate and the water flux. The polyamide reverse osmosis membrane in the present invention comprises a polyester non-woven fabric layer, a polysulfone porous layer, a transition layer and a polyamide layer. The present invention prepares a polysulfone porous layer, and adds a modified pore-forming agent to increase the water flux of the reverse osmosis membrane; the hydrophilicity of the reverse osmosis membrane is increased by preparing a transition layer and adding a hydrophilic additive when preparing the polyamide layer; the flux attenuation rate of the polyamide reverse osmosis membrane is reduced by preparing a polyamide layer; and the desalination rate of the reverse osmosis membrane is increased by introducing a composite ion complexing agent and graphene quantum dots into the polyamide layer.

Description

Technical Field

[0001] The invention relates to the technical field of reverse osmosis membranes, in particular to a polyamide reverse osmosis membrane for high-salt wastewater treatment and a preparation method thereof. Background Art

[0002] Due to the rising global demand for fresh water and the shortage of drinking water, a method to supplement fresh water resources is urgently needed to solve this problem. Using reverse osmosis membranes to desalinate seawater to supplement domestic water and treat high-salt wastewater to supplement industrial water has become one of the important means of fresh water resource development and resource utilization.

[0003] Today's reverse osmosis membranes mainly include asymmetric cellulose acetate membranes prepared by phase inversion and aromatic polyamide membranes prepared by interfacial polymerization. Compared with cellulose acetate membranes, polyamide reverse osmosis membranes have better mechanical stability, chemical stability and thermal stability. Since the interfacial polymerization reaction has self-inhibition and strong process controllability, polyamide reverse osmosis membranes with high desalination rates can be prepared by this method. Therefore, aromatic polyamide reverse osmosis membranes have become one of the most widely used reverse osmosis membrane materials.

[0004] In the preparation process of aromatic polyamide reverse osmosis membrane, m-phenylenediamine and trimesoyl chloride are generally used for interfacial polycondensation reaction to form a polyamide desalination layer. The water flux and desalination rate of aromatic polyamide reverse osmosis membrane are its core performance parameters, and there is a problem of one increasing while the other decreasing. Therefore, how to increase the water flux while maintaining the desalination rate has always been a difficult problem in the preparation of reverse osmosis membrane.

[0005] Therefore, a polyamide reverse osmosis membrane for high-salinity wastewater treatment and a preparation method thereof are proposed. Summary of the invention

[0006] The purpose of the present invention is to design a polyamide reverse osmosis membrane for high-salt wastewater treatment and a preparation method thereof. The polyamide reverse osmosis membrane in the present invention comprises a polyester non-woven fabric layer, a polysulfone porous layer, a transition layer and a polyamide layer. The present invention improves the water flux of the polyamide reverse osmosis membrane by synthesizing a modified pore-forming agent and controlling the content of polysulfone and the modified pore-forming agent and the parameters for preparing the polysulfone porous layer; improves the hydrophilicity of the polyamide reverse osmosis membrane by controlling the content of nano-silicon dioxide, glutaraldehyde and tannic acid and the parameters for preparing the transition layer; reduces the flux attenuation rate of the polyamide reverse osmosis membrane by controlling the content of m-phenylenediamine, a catalytic aid and trimesoyl chloride and the parameters for preparing the polyamide layer; improves the hydrophilicity of the polyamide reverse osmosis membrane by synthesizing a hydrophilic aid and controlling the content of the hydrophilic aid; improves the desalination rate of the polyamide reverse osmosis membrane by synthesizing a composite ion complexing agent and controlling the content of the composite ion complexing agent and graphene quantum dots and the parameters for preparing the reverse osmosis membrane.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] In one aspect, the present invention provides a polyamide reverse osmosis membrane for high-salt wastewater treatment, wherein the polyamide reverse osmosis membrane comprises a polyester non-woven fabric layer, a polysulfone porous layer, a transition layer and a polyamide layer;

[0009] The thickness of the polyester nonwoven fabric layer is 15 μm;

[0010] The polysulfone porous layer comprises polysulfone, a modified pore-forming agent and polyoxyethylene ether;

[0011] The transition layer comprises polyvinyl alcohol, nano silicon dioxide, glutaraldehyde and tannic acid;

[0012] The polyamide layer comprises meta-phenylenediamine, a catalytic auxiliary, a hydrophilic auxiliary, trimesoyl chloride, a composite ion complexing agent and graphene quantum dots.

[0013] Preferably, the mass concentration percentage of the polysulfone in the polysulfone porous layer is 14%-16%, the mass concentration percentage of the modified pore-forming agent is 3%-5%, and the mass concentration percentage of the polyoxyethylene ether is 1.5%.

[0014] Preferably, the mass concentration percentage of the polyvinyl alcohol in the transition layer is 4%, the mass concentration percentage of the nano-silicon dioxide is 0.04%-0.06%; the mass concentration percentage of the glutaraldehyde is 0.5%-0.8%, and the mass concentration percentage of the tannic acid is 1%-3%.

[0015] Preferably, the mass concentration percentage of the m-phenylenediamine in the polyamide layer is 2.6-3.0%; the mass concentration percentage of the catalytic aid is 0.3%-0.5%; the mass concentration percentage of the hydrophilic aid is 0.1%-0.3%; the mass concentration percentage of the trimesoyl chloride is 0.2%-0.3%; the mass concentration percentage of the composite ion complexing agent is 0.08%-0.1%; and the mass concentration percentage of the graphene quantum dots is 0.01%-0.05%.

[0016] Preferably, the mass concentration percentage refers to the proportion of each substance in the layer.

[0017] Another aspect of the present invention provides a method for preparing a polyamide reverse osmosis membrane for high-salt wastewater treatment, the preparation method comprising the following steps:

[0018] S1. Heat and stir the polysulfone, modified pore-forming agent and polyoxyethylene ether at 80°C-100°C for 5h-8h, and form a uniform casting solution after being fully mixed; evenly apply the casting solution on the polyester non-woven fabric layer, and then immerse it in deionized water to undergo phase inversion to obtain a polysulfone porous layer, wherein the temperature of the deionized water is 30°C; repeatedly wash the polysulfone porous layer with deionized water to remove residual impurities;

[0019] S2: adding polyvinyl alcohol, concentrated hydrochloric acid, nano-silicon dioxide, glutaraldehyde and tannic acid into deionized water, and mixing them evenly to obtain a mixed solution; placing the polysulfone porous layer into the mixed solution and immersing it for 40 min-60 min, then taking out the polysulfone porous layer, placing it in an oven at a temperature of 120° C.-150° C. for a cross-linking reaction for 60 min, and forming a transition layer on the polysulfone porous layer;

[0020] S3: dissolving m-phenylenediamine, a catalyst aid and a hydrophilic aid in deionized water to prepare an aqueous phase solution, and dissolving trimesoyl chloride, a complex ion complexing agent and graphene quantum dots in n-hexane to prepare an oil phase solution;

[0021] S4: contacting the transition layer with the aqueous phase solution for 50s-70s, removing excess aqueous phase on the surface, and then contacting with the oil phase solution for 20s-40s, removing excess solvent on the surface, forming a polyamide layer on the transition layer, and obtaining a reverse osmosis membrane precursor;

[0022] S5: drying the reverse osmosis membrane precursor in an oven at 80° C.-120° C. for 15 min-25 min, and then soaking it in deionized water for 20 h to obtain the polyamide reverse osmosis membrane.

[0023] Preferably, the preparation method of the modified pore-forming agent in S1 is: 8-10 parts of polyvinyl pyrrolidone and 6 parts of methacrylic acid are placed in a reactor, 3 parts of azobisisobutyronitrile are added, and polymerization reaction is carried out at 75° C.-90° C. for 8 hours. After the reaction, the modified pore-forming agent is obtained by precipitation, filtration and drying.

[0024] Preferably, the preparation method of the catalyst aid in S3 is: mixing camphorsulfonic acid and triethylamine in a mass fraction ratio to form the catalyst aid; the mass fraction ratio of the camphorsulfonic acid to the triethylamine is 1-3:1.

[0025] Preferably, the preparation method of the hydrophilic additive in S3 is: dissolving 5-7 parts of nanocellulose and 2-4 parts of sodium dodecylbenzene sulfonate in 10 parts of toluene solution, then adding 5 parts of azobisisobutyronitrile and reacting at 68°C-88°C for 8h, washing and drying to obtain the hydrophilic additive.

[0026] Preferably, the preparation method of the composite ion complexing agent in S3 is: sequentially adding a complexing agent with a mass concentration of 13%-16% and an ion mixture with a mass concentration of 10% into deionized water, and stirring for 3 hours to obtain the composite ion complexing agent.

[0027] Preferably, the complexing agent is one of disodium ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid and sodium tripolyphosphate; the ion mixture is Fe 2+ , Cu 2+ 、Co 2+ , Mn 2+ , Cl - and NO3 - mixture.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention improves the water flux of the polyamide reverse osmosis membrane by synthesizing a modified pore-forming agent and controlling the content of polysulfone and the modified pore-forming agent as well as the parameters for preparing the polysulfone porous layer. The modified pore-forming agent can increase the porosity of the polysulfone porous layer, and will be extracted by the solvent during the phase inversion process, thereby leaving more pores in the membrane. The higher porosity is conducive to the rapid passage of water, reducing the resistance of water passing through the membrane, thereby increasing the flux of the membrane, and finally the water flux of the reverse osmosis membrane is 54.3LMH; the polysulfone porous layer, as an important component of the reverse osmosis membrane, provides a solid mechanical support for the transition layer and the polyamide layer, and acts as a pre-filtration layer to preliminarily filter larger particles of impurities and some macromolecular organic matter.

[0030] 2. The present invention improves the hydrophilicity of the polyamide reverse osmosis membrane by controlling the content of nano silicon dioxide, glutaraldehyde and tannic acid and the parameters of preparing the transition layer. Nano silicon dioxide itself has a certain hydrophilicity, and the hydroxyl groups on its surface can form hydrogen bonds with water molecules, thereby increasing the hydrophilicity of the transition layer, which makes it easier for water molecules to adsorb and diffuse on the membrane surface, reduces the resistance when water passes through the membrane, further improves the water flux of the membrane, and also reduces the pollution tendency of the membrane to a certain extent, making the membrane easier to clean and restore performance; the transition layer can significantly improve the surface wettability of the membrane, and its hydrophilicity enables the membrane surface to be better wetted by water, reduces the contact angle between water and the membrane, and connects the polysulfone porous layer and the polyamide layer, so that the interlayer bonding is tighter. The final contact angle of the reverse osmosis membrane with water is 36.7°.

[0031] 3. The present invention reduces the flux attenuation rate of the polyamide reverse osmosis membrane by controlling the content of m-phenylenediamine, catalytic aid and trimesoyl chloride and the parameters for preparing the polyamide layer. The catalytic aid can slow down the polycondensation reaction of m-phenylenediamine and trimesoyl chloride, making the reaction process more controllable, and helping to form a polyamide layer with a more uniform structure and more stable performance, reducing the generation of defects, and improving the integrity and compactness of the polyamide layer; the polyamide layer itself has good chemical stability and can resist a certain degree of acid-base corrosion and oxidation. Under different water quality conditions, such as in the treatment of industrial wastewater with strong acidity or alkalinity, the polyamide layer can maintain the stability of structure and performance and extend the service life of the reverse osmosis membrane. The final water flux of the reverse osmosis membrane is 78.6LMH, and the flux attenuation rate is 7.02%.

[0032] 4. The present invention improves the hydrophilicity of the polyamide reverse osmosis membrane by synthesizing a hydrophilic additive and controlling the content of the hydrophilic additive. Hydrophilic groups such as hydroxyl and carboxyl in the hydrophilic additive can increase the hydrophilicity of the surface of the polyamide layer, making it easier for water to spread and wet on the membrane surface, allowing water molecules to pass quickly, thereby increasing the water flux of the polyamide reverse osmosis membrane, and the interaction between the hydrophilic additive and the polyamide layer can enhance the force between the polyamide molecular chains and improve the chemical stability of the polyamide layer. The contact angle between the final reverse osmosis membrane and water is 24.4°.

[0033] 5. The present invention improves the desalination rate of polyamide reverse osmosis membrane by synthesizing a composite ion complexing agent and controlling the content of the composite ion complexing agent and graphene quantum dots as well as the parameter conditions for preparing the reverse osmosis membrane. The composite ion complexing agent can combine with groups such as amino or carboxyl groups in the polyamide layer to fill defective sites and reduce the possibility of salt ions passing through these channels, thereby improving the desalination rate; graphene quantum dots can form a physical barrier network in the polyamide layer, increasing the degree of tortuosity of the diffusion path of salt ions in the membrane. Salt ions need to constantly collide and turn in this complex structure, increasing the probability of being intercepted by interacting with the polyamide layer, thereby improving the desalination rate. The final desalination rate of the polyamide reverse osmosis membrane is 99.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the structure of the polyamide reverse osmosis membrane designed for the present invention.

[0035] Figure 2 It is a graph of the desalination rate of Example 63 of the present invention and Comparative Examples 10-12.

[0036] In the figure: 1. polyester non-woven fabric layer; 2. polysulfone porous layer; 3. transition layer; 4. polyamide layer. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention provides a polyamide reverse osmosis membrane for high-salt wastewater treatment and a preparation method thereof. Figure 1 As shown, the polyamide reverse osmosis membrane is composed of a polyester non-woven fabric layer 1, a polysulfone porous layer 2, a transition layer 3 and a polyamide layer 4. Figure 1 to Figure 2 , the technical solution is as follows:

[0039] The substance information involved in the present invention is as follows:

[0040] Polysulfone: CAS No.: 25135-51-7; Graphene quantum dots: Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.

[0041] Example 1

[0042] Preparation of modified pore-forming agent:

[0043] 8 parts of polyvinyl pyrrolidone and 6 parts of methacrylic acid are placed in a reactor, 3 parts of azobisisobutyronitrile are added, and polymerization reaction is carried out at 75° C. for 8 hours. After the reaction, the modified pore-forming agent is obtained by precipitation, filtration and drying.

[0044] Preparation of catalyst additives:

[0045] Camphorsulfonic acid and triethylamine are mixed according to a mass fraction ratio to form the catalyst promoter; the mass fraction ratio of the camphorsulfonic acid to the triethylamine is 1:1.

[0046] Preparation of hydrophilic additives:

[0047] 5 parts of nanocellulose and 2 parts of sodium dodecylbenzene sulfonate were dissolved in 10 parts of toluene solution, and then 5 parts of azobisisobutyronitrile were added to react at 68° C. for 8 hours, and the hydrophilic additive was obtained after washing and drying.

[0048] Preparation of composite ion complexing agent:

[0049] A complexing agent with a mass concentration of 13% and an ion mixture with a mass concentration of 10% were added to deionized water in sequence, and the composite ion complexing agent was obtained after stirring for 3 hours; the complexing agent was disodium ethylenediaminetetraacetate; the ion mixture was Fe 2+ , Cu 2+ 、Co 2+ , Mn 2+ , Cl - and NO3- mixture.

[0050] Preparation of polyamide reverse osmosis membrane:

[0051] S1. Heat and stir polysulfone, modified pore-forming agent and polyoxyethylene ether at 80° C. for 5 h, and form a uniform casting solution after being fully mixed; evenly apply the casting solution on the polyester non-woven fabric layer, and then immerse it in deionized water to undergo phase inversion to obtain a polysulfone porous layer, wherein the temperature of the deionized water is 30° C.; repeatedly wash the polysulfone porous layer with deionized water to remove residual impurities;

[0052] S2: adding polyvinyl alcohol, concentrated hydrochloric acid, nano-silicon dioxide, glutaraldehyde and tannic acid into deionized water, and mixing them evenly to obtain a mixed solution; placing the polysulfone porous layer into the mixed solution and immersing it for 40 minutes, then taking out the polysulfone porous layer, placing it in an oven at a temperature of 120° C. for a cross-linking reaction for 60 minutes, and forming a transition layer on the polysulfone porous layer;

[0053] S3: dissolving m-phenylenediamine, a catalyst aid and a hydrophilic aid in deionized water to prepare an aqueous phase solution, and dissolving trimesoyl chloride, a complex ion complexing agent and graphene quantum dots in n-hexane to prepare an oil phase solution;

[0054] S4: contacting the transition layer with the aqueous phase solution for 50 seconds, removing excess aqueous phase on the surface, and then contacting with the oil phase solution for 20 seconds to remove excess solvent on the surface, forming a polyamide layer on the transition layer to obtain a reverse osmosis membrane precursor;

[0055] S5: drying the reverse osmosis membrane precursor in an oven at 80° C. for 15 min, and then soaking it in deionized water for 20 h to obtain the polyamide reverse osmosis membrane.

[0056] Example 2-15

[0057] Referring to the parameter conditions of the preparation method in Example 1, the specific differences are shown in Table 1.

[0058] Table 1 Parameters and conditions of Examples 1-15

[0059]

[0060] Comparative Example 1 The parameters and conditions of the preparation method in Example 1 are referred to, except that no modified pore-forming agent is added.

[0061] Comparative Example 2 The parameters and conditions of the preparation method in Example 1 are referred to, except that only polyvinyl pyrrolidone is added without modification.

[0062] Example 16 Water flux test

[0063] The operating pressure was 14 bar, the flow rate was 3 LPM, and Examples 1-15 and Comparative Examples 1-2 were pre-pressed with deionized water at 25°C for 6 hours to stabilize the membrane performance. The operating pressure was adjusted to 10 bar, and the water flux of Examples 1-15 and Comparative Examples 1-2 was measured. The results are shown in Table 2.

[0064] Table 2 Water flux test of Examples 1-15 and Comparative Examples 1-2

[0065]

[0066] It can be found from Table 2 that in Comparative Example 1, no modified pore-forming agent is added, and the water flux of the reverse osmosis membrane is low, only 38.6LMH. In the polysulfone porous layer, polysulfone itself is a highly hydrophobic material, and its hydrophilicity may not be effectively improved without the addition of a modified pore-forming agent. During the reverse osmosis process, the affinity of water molecules to the membrane surface is low, and it is not easy to adsorb and diffuse on the membrane surface, thereby limiting the water flux; in Comparative Example 2, only polyvinyl pyrrolidone is added without modification. At this time, although the water flux of the reverse osmosis membrane is higher than that of Comparative Example 1, it is still lower than that of other embodiments, because the polyvinyl pyrrolidone is not modified, the performance of the pore-forming agent is unstable, which may cause uneven pore sizes in the polysulfone porous layer, thereby affecting the water flux of the reverse osmosis membrane. In Examples 4-8, the conditions for synthesizing the modified pore-forming agent are changed to improve the performance of the modified pore-forming agent, thereby improving the water flux of the reverse osmosis membrane. The water flux of Example 7 is 49.6LMH, because the modified pore-forming agent can increase the porosity of the polysulfone porous layer, and will be extracted by the solvent during the phase inversion process, thereby leaving more pores in the membrane. The higher porosity is conducive to the rapid passage of water, reducing the resistance of water passing through the membrane, and thus improving the flux of the membrane; in Examples 1-3 and Examples 9-15, the parameter conditions for controlling the synthesis of the polysulfone porous layer are changed. The water flux of Example 13 is the highest, which is 54.3LMH, because the polysulfone porous layer, as an important component of the reverse osmosis membrane, provides a solid mechanical support for the transition layer and the polyamide layer, and acts as a pre-filtration layer to perform preliminary filtration of larger particle impurities and some macromolecular organic matter.

[0067] Examples 17-28

[0068] Referring to the parameter conditions of the preparation method in Example 13, the difference lies in that the mass concentration percentages of nano-silicon dioxide, glutaraldehyde and tannic acid and the parameters for preparing the transition layer are changed. The specific differences are shown in Table 3.

[0069] Table 3 Parameters and conditions of Example 13 and Examples 17-28

[0070]

[0071] Comparative Example 3 The parameters and conditions of the preparation method in Example 13 are referred to, except that no nano-silicon dioxide is added.

[0072] Example 29 Contact angle test

[0073] Example 13, Examples 17-28 and Comparative Example 3 were soaked in pure water, rinsed with pure water and vacuum dried at room temperature for later use. The pretreated reverse osmosis membrane was laid flat on the sample stage of the contact angle analyzer with the polyamide layer facing upward. After adjusting the parameter settings of the contact angle analyzer, a small drop of pure water or salt water was dropped onto the sample. A static image of the droplet was obtained after the droplet was balanced on the membrane. The static image of the droplet was analyzed and the contact angle was calculated using drop shape analysis software. The results are shown in Table 4.

[0074] Table 4 Contact angle test of Example 13, Examples 17-28 and Comparative Example 3

[0075]

[0076] It can be found from Table 4 that in Comparative Example 3, without adding nano-silicon dioxide, the hydrophilicity of the polyamide reverse osmosis membrane is poor, and the contact angle with water is 43.9°, indicating that the addition of nano-silicon dioxide can improve the hydrophilicity of the polyamide reverse osmosis membrane, thereby increasing the water flux of the reverse osmosis membrane. In Example 13 and Examples 17-18, the mass concentration percentage of nano-silicon dioxide was introduced and changed, and the hydrophilicity of the polyamide reverse osmosis membrane was improved. The contact angle of Example 17 was 39.5°. Because nano-silicon dioxide itself has a certain hydrophilicity, the hydroxyl groups on its surface can form hydrogen bonds with water molecules, thereby increasing the hydrophilicity of the membrane surface, which makes it easier for water molecules to adsorb and diffuse on the membrane surface, reduces the resistance when water passes through the membrane, further improves the water flux of the membrane, and also reduces the pollution tendency of the membrane to a certain extent, making the membrane easier to clean and restore performance; in Examples 19-23, the mass concentration percentages of glutaraldehyde and tannic acid were changed. When the mass concentration percentage of glutaraldehyde was 0.6% and the mass concentration percentage of tannic acid was 2%, the hydrophilicity of Example 22 was the strongest, and the contact angle was 38.2°. Because the amount of glutaraldehyde used will affect the pore size and distribution of the transition layer, an appropriate amount of glutaraldehyde can optimize the structure of the transition layer, making its pore size more uniform, playing a preliminary screening role, and assisting in improving the overall reverse osmosis membrane The desalination rate of the system, tannic acid can adjust the charge properties and surface chemical environment of the transition layer, and an appropriate amount of tannic acid can enhance the retention capacity of certain charged solutes through electrostatic repulsion and other effects, but excessive tannic acid may interfere with the synergistic effect between the transition layer and other membrane layers, or change the diffusion path of the solute in the transition layer, resulting in a decrease in the retention rate; in Examples 24-28, the preparation parameters of the transition layer are controlled, and the hydrophilicity of the polyamide reverse osmosis membrane is best when the immersion treatment time is 50 minutes and the cross-linking reaction temperature is 140°C. The contact angle of Example 27 is 36.7°. This is because the appropriate temperature helps to form a transition layer with uniform structure and appropriate pore size. Inappropriate temperature may cause degradation of the polyvinyl alcohol molecular chain or other chemical reactions, reducing the stability and durability of the transition layer, and the transition layer can significantly improve the surface wettability of the membrane. Its hydrophilicity enables the membrane surface to be better wetted by water, reducing the contact angle between water and the membrane, and connecting the polysulfone porous layer and the polyamide layer, making the interlayer bonding closer.

[0077] Examples 30-41

[0078] Referring to the parameter conditions of the preparation method in Example 27, the difference is that a catalyst aid is synthesized, the contents of m-phenylenediamine, catalyst aid and trimesoyl chloride and the parameters for preparing the polyamide layer are changed. The specific differences are shown in Table 5.

[0079] Table 5 Parameter conditions of Example 27 and Examples 30-41

[0080]

[0081] Comparative Example 4 The parameters and conditions of the preparation method in Example 27 are referred to, except that no catalyst aid is added.

[0082] Comparative Example 5 The parameters and conditions of the preparation method in Example 27 are referred to, except that the catalyst auxiliary agent contains only camphorsulfonic acid.

[0083] Comparative Example 6 The parameters and conditions of the preparation method in Example 27 are referred to, except that the catalyst auxiliary agent contains only triethylamine.

[0084] Example 42 Flux decay rate test

[0085] The operating pressure was 14 bar and the flow rate was 3 LPM. Deionized water was used to pre-press Example 27, Examples 30-41 and Comparative Examples 4-6 at 25°C for 6 h to stabilize the membrane performance. The operating pressure was adjusted to 10 bar, and the water flux of Example 27, Examples 30-41 and Comparative Examples 4-6 was measured. The flux attenuation rate was recorded after running for 100 h. The results are shown in Table 6.

[0086] Table 6 Flux attenuation rate test of Example 27, Examples 30-41 and Comparative Examples 4-6

[0087]

[0088] It can be found from Table 6 that in Comparative Example 4, no catalytic promoter was added, the water flux of the polyamide reverse osmosis membrane decreased, and the flux attenuation rate increased, indicating that in the absence of a catalytic promoter, the hydrophilicity of the polyamide layer may be poor, and the resistance of water molecules passing through the membrane increases, thereby reducing the water flux of the membrane; in Comparative Examples 5-6, only one catalyst was added. At this time, although the water flux of the polyamide reverse osmosis membrane was improved compared with Comparative Example 4, it was still lower than that of the embodiment, and the flux attenuation rate was also high, indicating that only one catalyst could not meet the requirements of the polyamide reverse osmosis membrane, and two catalysts were needed to work together to promote the decrease in the flux attenuation rate of the polyamide reverse osmosis membrane. In Example 27 and Examples 30-37, the mass concentration percentages of m-phenylenediamine, catalyst aid and trimesoyl chloride were changed. The water flux of the polyamide reverse osmosis membrane was the highest when the mass concentration percentages of m-phenylenediamine, catalyst aid and trimesoyl chloride were 2.8%, 0.4% and 0.25%, respectively, and the flux attenuation rate was the smallest. At this time, the water flux of Example 36 was 75.9LMH, and the flux attenuation rate was 8.15%, indicating that an appropriate increase in the amount of m-phenylenediamine can improve the hydrophilicity of the polyamide layer to a certain extent, while optimizing the crosslinking degree and pore size distribution. Water molecules can pass through the membrane more easily, thereby increasing the water flux. However, if the dosage is too much, the membrane structure will be too loose or defective, which may reduce the water flux or desalination rate. The dosage of trimesoyl chloride must also be appropriate. Too little may fail to form a complete and dense polyamide layer, while too much may make the membrane too dense and hinder the passage of water. Catalytic additives can slow down the condensation reaction of m-phenylenediamine and trimesoyl chloride, making the reaction process more controllable, helping to form a polyamide layer with a more uniform structure and more stable performance, reducing the occurrence of defects and improving the integrity and density of the polyamide layer. In Examples 38-41, the conditions for synthesizing the polyamide layer are controlled. At this time, Example 40 has the highest water flux and the lowest flux attenuation rate, which are 78.6LMH and 7.02%, respectively. This is because adjustment to appropriate synthesis parameters is beneficial to the stability of the polyamide layer, thereby increasing the water flux of the polyamide reverse osmosis membrane and reducing the flux attenuation rate. In addition, the polyamide layer itself has good chemical stability and can resist a certain degree of acid and alkali corrosion and oxidation. Under different water quality conditions, such as in the treatment of industrial wastewater with strong acidity or alkalinity, the polyamide layer can maintain the stability of structure and performance and extend the service life of the reverse osmosis membrane.

[0089] Examples 43-50

[0090] Referring to the parameter conditions of the preparation method in Example 40, the difference is that the parameter conditions for preparing the hydrophilic additive are changed. The specific differences are shown in Table 7.

[0091] Table 7 Parameters and conditions of Example 40 and Examples 43-50

[0092]

[0093] Comparative Example 7 The parameters and conditions of the preparation method in Example 40 are referred to, except that no hydrophilic auxiliary agent is added.

[0094] Comparative Example 8 The parameters and conditions of the preparation method in Example 40 are referred to, except that the hydrophilic additive is only nanocellulose.

[0095] Comparative Example 9 The parameters and conditions of the preparation method in Example 40 are referred to, except that the hydrophilic auxiliary agent is only sodium dodecylbenzene sulfonate.

[0096] Example 51 Hydrophilicity Test

[0097] The hydrophilicity of Example 40, Examples 43-50 and Comparative Examples 7-9 was tested by referring to the test method of Example 29. The results are shown in Table 8.

[0098] Table 8 Hydrophilicity test of Example 40, Examples 43-50 and Comparative Examples 7-9

[0099]

[0100] It can be found from Table 8 that in Comparative Example 7, when no hydrophilic additive is added, the hydrophilicity of the polyamide reverse osmosis membrane is low, which shows that the addition of a hydrophilic additive can significantly improve the hydrophilicity of the reverse osmosis membrane; in Comparative Examples 8-9, only one additive is added and it is not modified, and the hydrophilicity of the polyamide reverse osmosis membrane is also relatively weak, which shows that modifying the additive can improve the performance of the additive, thereby improving the hydrophilicity of the reverse osmosis membrane. In Examples 40-50, by changing the mass concentration percentage of the hydrophilic additive in the polyamide layer and controlling the parameter conditions for the synthesis of the hydrophilic additive, the hydrophilicity of Example 49 is the strongest, and the contact angle with water is only 24.4°, because the hydrophilic groups such as hydroxyl and carboxyl in the hydrophilic additive can increase the hydrophilicity of the surface of the polyamide layer, making it easier for water to spread and wet on the membrane surface, so that water molecules can pass quickly, thereby increasing the water flux of the polyamide reverse osmosis membrane, and the interaction between the hydrophilic additive and the polyamide layer can enhance the force between the polyamide molecular chains and improve the chemical stability of the polyamide layer.

[0101] Examples 52-64

[0102] Referring to the parameter conditions of the preparation method in Example 49, the difference is that the parameter conditions for preparing the composite ion complexing agent are changed and the contents of the composite ion complexing agent and graphene quantum dots and the parameter conditions for preparing the reverse osmosis membrane are controlled. The specific differences are shown in Table 9.

[0103] Table 9 Parameter conditions of Example 49 and Examples 52-64

[0104]

[0105] Comparative Example 10 The parameters and conditions of the preparation method in Example 49 were used with the exception that no complex ion complexing agent was added.

[0106] Comparative Example 11 The parameters and conditions of the preparation method in Example 49 are referred to, except that the ion mixture is not complexed.

[0107] Comparative Example 12 The parameters and conditions of the preparation method in Example 49 were used with the exception that no graphene quantum dots were added.

[0108] Example 65 Salt rejection test

[0109] A 3000 mg / L sodium chloride solution was prepared. Under the same operating conditions as in Example 16, the conductivity of the solution on the raw material side and the filtration side after 1 h of filtration was measured to test the salt retention rate of the membrane, i.e., the desalination rate. The results are shown in Table 10. The desalination rates of Example 63 and Comparative Examples 10-12 are shown in Table 10. Figure 2 shown.

[0110] Table 10 Desalination rate test of Example 49, Examples 52-64 and Comparative Examples 10-12

[0111]

[0112] From Table 10 and Figure 2 It can be found that in Comparative Example 10, no composite ion complexing agent is added, and the desalination rate of the polyamide reverse osmosis membrane is low, which indicates that the composite ion complexing agent promotes the desalination rate of the reverse osmosis membrane; in Comparative Example 11, the ion mixture is not complexed, and although the desalination rate of the reverse osmosis membrane increases to a certain extent, it is still lower than that of the embodiment. This is because the ion mixture is not complexed, and the ion mixture is prone to agglomeration, thereby reducing the desalination rate of the reverse osmosis membrane; in Example 12, graphene quantum dots are not added, and the desalination rate of the reverse osmosis membrane also decreases significantly, which indicates that graphene quantum dots play an important role in the desalination process of the reverse osmosis membrane. In Examples 49 and 52-58, the complex ion complexing agent plays an important role. The complex ion complexing agent can combine with groups such as amino or carboxyl in the polyamide layer to fill defective sites and reduce the possibility of salt ions passing through these channels, thereby improving the desalination rate. The desalination rate of Example 58 is 99.2%; in Examples 59-64, graphene quantum dots can form a physical barrier network in the polyamide layer, which increases the tortuosity of the diffusion path of salt ions in the membrane. The salt ions need to constantly collide and turn in this complex structure, which increases the probability of interacting with the polyamide layer and being intercepted, thereby improving the desalination rate. The heat provided by the drying process can promote the continued cross-linking reaction of the incompletely reacted functional groups in the polyamide layer, thereby improving the degree of cross-linking. Finally, the desalination rate of Example 63 is 99.8%.

[0113] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyamide reverse osmosis membrane for high-salt wastewater treatment, characterized in that: The polyamide reverse osmosis membrane comprises, by mass fraction, a polyester non-woven fabric layer, a polysulfone porous layer, a transition layer and a polyamide layer; The thickness of the polyester nonwoven fabric layer is 15 μm; The polysulfone porous layer comprises polysulfone, a modified pore-forming agent and polyoxyethylene ether; The preparation method of the modified pore-forming agent is as follows: 8-10 parts of polyvinyl pyrrolidone and 6 parts of methacrylic acid are placed in a reactor, 3 parts of azobisisobutyronitrile are added, and polymerization reaction is carried out at 75° C.-90° C. for 8 hours, and after the reaction, precipitation, filtration and drying are performed to obtain the modified pore-forming agent; The transition layer comprises polyvinyl alcohol, nano silicon dioxide, glutaraldehyde and tannic acid; The polyamide layer comprises m-phenylenediamine, a catalytic aid, a hydrophilic aid, trimesoyl chloride, a composite ion complexing agent and graphene quantum dots; The preparation method of the catalyst aid is: camphorsulfonic acid and triethylamine are mixed according to a mass fraction ratio to form the catalyst aid; the mass fraction ratio of the camphorsulfonic acid to the triethylamine is 1-3:1; The preparation method of the hydrophilic additive is as follows: 5-7 parts of nanocellulose and 2-4 parts of sodium dodecylbenzene sulfonate are dissolved in 10 parts of toluene solution, and then 5 parts of azobisisobutyronitrile are added to react at 68° C.-88° C. for 8 hours, and the hydrophilic additive is obtained after washing and drying; The preparation method of the composite ion complexing agent is as follows: a complexing agent with a mass concentration of 13% to 16% and an ion mixture with a mass concentration of 10% are sequentially added into deionized water, and the composite ion complexing agent is obtained after stirring for 3 hours; the complexing agent is one of disodium ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid and sodium tripolyphosphate, and the ion mixture is Fe 2+ , Cu 2+ 、Co 2+ , Mn 2+ , Cl - and NO3 - mixture.

2. The polyamide reverse osmosis membrane for high-salt wastewater treatment according to claim 1, characterized in that: The mass concentration percentage of the polysulfone in the polysulfone porous layer is 14%-16%, the mass concentration percentage of the modified pore-forming agent is 3%-5%, and the mass concentration percentage of the polyoxyethylene ether is 1.5%.

3. The polyamide reverse osmosis membrane for high-salt wastewater treatment according to claim 1, characterized in that: The mass concentration percentage of the polyvinyl alcohol in the transition layer is 4%, the mass concentration percentage of the nano-silicon dioxide is 0.04%-0.06%; the mass concentration percentage of the glutaraldehyde is 0.5%-0.8%, and the mass concentration percentage of the tannic acid is 1%-3%.

4. The polyamide reverse osmosis membrane for high-salt wastewater treatment according to claim 1, characterized in that: The mass concentration percentage of the m-phenylenediamine in the polyamide layer is 2.6-3.0%; the mass concentration percentage of the catalytic additive is 0.3%-0.5%; the mass concentration percentage of the hydrophilic additive is 0.1%-0.3%; the mass concentration percentage of the trimesoyl chloride is 0.2%-0.3%; the mass concentration percentage of the composite ion complexing agent is 0.08%-0.1%; and the mass concentration percentage of the graphene quantum dots is 0.01%-0.05%.

5. A method for preparing a polyamide reverse osmosis membrane for high-salt wastewater treatment, characterized in that: The polyamide reverse osmosis membrane according to claim 1 is prepared, and the preparation method comprises the following steps: S1. Heat and stir the polysulfone, modified pore-forming agent and polyoxyethylene ether at 80°C-100°C for 5h-8h, and form a uniform casting solution after being fully mixed; evenly apply the casting solution on the polyester non-woven fabric layer, and then immerse it in deionized water to undergo phase inversion to obtain a polysulfone porous layer, wherein the temperature of the deionized water is 30°C; repeatedly wash the polysulfone porous layer with deionized water to remove residual impurities; S2: adding polyvinyl alcohol, concentrated hydrochloric acid, nano-silicon dioxide, glutaraldehyde and tannic acid into deionized water, and mixing them evenly to obtain a mixed solution; placing the polysulfone porous layer into the mixed solution and immersing it for 40 min-60 min, then taking out the polysulfone porous layer, placing it in an oven at a temperature of 120° C.-150° C. for a cross-linking reaction for 60 min, and forming a transition layer on the polysulfone porous layer; S3: dissolving m-phenylenediamine, a catalyst aid and a hydrophilic aid in deionized water to prepare an aqueous phase solution, and dissolving trimesoyl chloride, a complex ion complexing agent and graphene quantum dots in n-hexane to prepare an oil phase solution; S4: contacting the transition layer with the aqueous phase solution for 50s-70s, removing excess aqueous phase on the surface, and then contacting with the oil phase solution for 20s-40s, removing excess solvent on the surface, forming a polyamide layer on the transition layer, and obtaining a reverse osmosis membrane precursor; S5: drying the reverse osmosis membrane precursor in an oven at 80° C.-120° C. for 15 min-25 min, and then soaking it in deionized water for 20 h to obtain the polyamide reverse osmosis membrane.

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