A method for modifying an active oxygen-based polyamide composite membrane

Abstract

The application belongs to the technical field of polyamide composite membranes, and particularly relates to a modification method of a water treatment polyamide composite membrane. The method modifies the polyamide composite membrane by using active oxygen species generated by the reaction of complex metal ions and a peroxide aqueous solution, thereby improving the modification effect of the modification solution on the polyamide membrane. The method can improve the hydrophilicity of the membrane surface, regulate the pore size and structure of the polyamide separation layer of the membrane, break the mutual restriction of the water flux and desalination rate of the polyamide membrane, and simultaneously improve the water flux and desalination rate. The modification method can be carried out at room temperature, can modify the existing reverse osmosis membrane assembly, and can also be implanted into the existing reverse osmosis membrane production line to modify and improve the membrane sheet, and the prepared high-flux and high-salt rejection rate reverse osmosis membrane can be applied to the fields of seawater or brackish water desalination, power plant water desalination, household water purification, sewage reuse, industrial wastewater treatment and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of reverse osmosis water treatment, and particularly relates to a modification method for improving water flux and desalination rate of an amide composite reverse osmosis membrane. BACKGROUND

[0002] Sustainable utilization of water resources is an eternal theme for promoting social and economic development and environmental protection. Developing seawater desalination, water resource recycling and unconventional water utilization technologies is of great significance for alleviating the shortage of freshwater resources in China, improving water environmental quality and restoring the ecological function of water systems. Membrane separation has attracted worldwide attention because of its high efficiency, low energy consumption, small footprint, simple operation and environmental friendliness, and has become an important supporting technology for sustainable development in China. Reverse osmosis separation process is phase change-free, has good salt and pollutant interception performance, and is easy to control, and has been widely used in the fields of seawater and brackish water desalination, drinking water deep treatment, sewage reuse water utilization, landfill leachate and industrial wastewater treatment.

[0003] Increasing the water flux of reverse osmosis membranes can reduce their desalination energy consumption, reduce the number of membrane components used, and thus save water treatment investment and operating costs. Polyamide composite membranes are the most widely used and technically mature reverse osmosis membrane materials. However, the water flux and desalination rate of current polyamide membranes are in a trade-off relationship, i.e. increasing the water flux often reduces the desalination rate, and vice versa. The main methods for simultaneously improving the water flux and desalination rate of reverse osmosis membranes at present are embedding carbon nanotubes and water channel protein materials in the separation layer, and introducing water fast transfer channels in the membrane. However, these membrane preparation methods are complex, have high costs, are difficult to scale up, are still in the laboratory research stage or pilot verification stage, and the stability and durability of the membranes are unknown. Therefore, if the polyamide composite membranes can be directly modified to significantly improve the water flux and desalination rate, it will be of great significance for the development of reverse osmosis membrane water treatment technology. SUMMARY

[0004] One of the purposes of the present application is to provide a modification method for polyamide composite membranes based on active oxygen. The present application regulates the pore size and structure of the polyamide separation layer of the membrane through active oxygen, enhances the hydrophilicity and electronegativity, and realizes the simultaneous improvement of the water flux and desalination rate of the membrane. The modification method is simple to operate and easy to combine with existing polyamide composite membrane production lines to realize large-scale production.

[0005] To achieve the above purpose, the following technical solution is adopted in the present application: a modification method for polyamide composite membranes based on active oxygen, comprising the following steps:

[0006] S1. At room temperature, complexed metal ions are added to water containing 1-100 mmol / L of peroxide oxidant, wherein the molar ratio of the peroxide oxidant to the metal ions in the complexed metal ions is (0.1-50):1, and reactive oxygen species are generated to obtain a modified aqueous solution.

[0007] S2. Immerse the polyamide composite film in the modified aqueous solution, modify for 0.2-4 hours, then remove it and wash away the residual modified solution with water.

[0008] Further improvements to the modification method of polyamide composite films based on active oxygen:

[0009] Preferably, the peroxide oxidant is one or a combination of two or more of hydrogen peroxide, monopersulfate, dipersulfate, and peracetic acid.

[0010] Preferably, the monopersulfate is one or a combination of two or more of potassium monopersulfate, sodium monopersulfate, and ammonium monopersulfate.

[0011] Preferably, the dipersulfate is one or a combination of two or more of potassium dipersulfate, sodium dipersulfate, and ammonium dipersulfate.

[0012] Preferably, the cation of the complexed metal ion is Fe. 2+ Cu 2+ Co 2+ Mn 2+ Ni 2+ Ce 3+ One or more combinations of the following, with the anion being Cl. - NO3 - SO4 2- One or more combinations of the above.

[0013] Preferably, the concentration of the complexed metal ions in water is 0.1-50 mmol / L.

[0014] Preferably, the preparation method of the complexed metal ions is as follows: a complexing agent with a concentration of 0.1-50 mmol / L and metal ions with a concentration of 0.1-50 mmol / L are added sequentially to water, wherein the molar ratio of the complexing agent to the metal ions is (0.1-10):1, and the complexed metal ions are generated by the reaction.

[0015] Preferably, the complexing agent is one or a combination of two or more of the following: cyanate, thiocyanate, oxalic acid, pyruvic acid, citric acid, tartaric acid, lactic acid, ascorbic acid, ethylenediamine, glycine, pyridine, catechol, porphyrin, pyrimidine, benzothiazole, benzimidazole, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, ethanethiol, ethylenedithiol, 1-propanethiol, 1,3-propanedithiol, cysteine, and glutathione.

[0016] Preferably, the cyanate is one or a combination of two or more of sodium cyanate, potassium cyanate, and ammonium cyanate.

[0017] Preferably, the thiocyanate is one or a combination of two or more of sodium thiocyanate, potassium thiocyanate, and ammonium thiocyanate.

[0018] The advantages of this invention compared to the prior art are as follows:

[0019] 1) The modification method of the present invention includes the following steps: adding a complexing agent and metal ions to water to form a stable, water-soluble metal ion complex; then adding an oxide oxidant to react with the metal ion complex to generate reactive oxygen species (O2). 2. - , 1 Active oxygen species (such as O2) selectively oxidize the polyamide separation layer of the reverse osmosis membrane, causing hydroxylation of the aromatic ring structure of the polyamide and partial breakage of the amide bonds to generate carboxyl and amino groups. Simultaneously, the presence of nitro ligands, oxidized to amino groups, alters the reaction pathway and active species between metal ions and peroxides, reducing the free energy required for peroxide activation. This improves the modification effect of the modified solution on the polyamide membrane, enhancing the hydrophilicity and negative charge of the membrane surface. This method can control the pore size and structure of the polyamide separation layer, breaking the mutual constraint between water flux and desalination rate of the polyamide membrane, and simultaneously improving both.

[0020] 2) The membrane modification method of this invention can be carried out at room temperature without heating or ultraviolet activation of peroxides. Because the reaction rate of metal ion-catalyzed activation of peroxides is relatively fast, both metal ions and peroxides are rapidly consumed, leading to uncontrollable reactions and low membrane modification efficiency. The reaction proposed in this invention, utilizing complexed metal ions to catalyze the activation of peroxides, is more mild and controllable, with less oxidative damage to the reverse osmosis membrane, ensuring the membrane's mechanical properties and long-term operational stability. Furthermore, metal ions readily adsorb onto negatively charged membrane surfaces, reducing modification efficiency; the addition of a complexing agent effectively solves this problem.

[0021] 3) The modification method of this invention is based on the selective oxidation reaction between the polyamide active layer of the reverse osmosis membrane and active oxygen. This modification method is, in principle, applicable to improving the water flux and desalination rate of various polyamide composite membranes. Compared with the unmodified membrane, the modified membrane prepared by the method of this invention, under the same operating conditions, can increase the water flux to 150-300% of the unmodified membrane, improve the desalination rate of sodium chloride by 0.4-1.5%, and correspondingly improve the retention of small molecule organic pollutants.

[0022] 4) The modification method of the present invention is simple to operate, uses few types of reagents, and is inexpensive. It only requires one step of modification and has great potential for large-scale production of polyamide composite reverse osmosis. Attached Figure Description

[0023] Figure 1 A comparison diagram of the contact angles of the modified membranes 1-5 prepared in Examples 1-3 and Examples 1-5. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described. Obviously, the embodiments in the specification are only some embodiments of the present invention, and not all embodiments. The present invention is not limited to the following implementation methods, that is, it does not mean that the present invention must rely on the following detailed methods to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0025] Example 1

[0026] This embodiment provides a method for modifying polyamide composite films based on active oxygen, specifically including the following steps:

[0027] S1. At room temperature, add the complexing agent EDTA-2Na to water until the concentration is 2 mmol / L, then add CuSO4 containing metal ions until the concentration is 2 mmol / L. The complexing agent and metal ions react to generate complexed metal ions.

[0028] S2. Add potassium persulfate and potassium persulfate to the water to make the concentration of potassium persulfate and potassium persulfate in the solution both 5 mmol / L. The oxidizing agents react with the complexed metal ions to generate active oxygen species and form a modified solution.

[0029] S3. Immerse the SW30 polyamide composite membrane manufactured by DuPont / Dow Filmtech in the modification solution. After modification for 1 hour, remove the membrane and wash away the residual modification solution with water to obtain modified membrane 1.

[0030] The untreated membrane was used as control membrane 1, and the performance of control membrane 1 and modified membrane 1 was tested. The test conditions were: operating pressure 14 bar, flow rate 3 LPM. Both modified membrane 1 and control membrane 1 were pre-pressurized with ultrapure water at 25°C for 6 hours to stabilize their performance. The operating pressure was then adjusted to 10 bar, and the water flux of both membranes was measured. A 3000 mg / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 hour of filtration. The salt rejection rate of the membranes was also tested.

[0031] Example 2

[0032] This embodiment provides a method for modifying polyamide composite films based on active oxygen, specifically including the following steps:

[0033] S1. At room temperature, add oxalic acid, a complexing agent, to water until the concentration is 2 mmol / L, then add CuSO4, a salt containing metal ions, until the concentration is 5 mmol / L. The complexing agent and the metal ions react to generate complexed metal ions.

[0034] S2. Add the oxide oxidant hydrogen peroxide to the water above until the concentration of hydrogen peroxide in the solution is 10 mmol / L. The oxide oxidant reacts with the complexed metal ions to generate active oxygen species, forming a modified solution.

[0035] S3. Immerse the SW30 polyamide composite membrane manufactured by DuPont / Dow Filmtech in the modification solution. After modification for 2 hours, remove the membrane and wash away the residual modification solution with water to obtain modified membrane 2.

[0036] The untreated membrane was used as control membrane 2. The performance of control membrane 2 and modified membrane 2 was tested. Test conditions were: operating pressure 14 bar, flow rate 3 LPM. Both modified membrane 2 and control membrane 2 were pre-pressurized with ultrapure water at 25°C for 6 hours to stabilize membrane performance. The operating pressure was then adjusted to 10 bar, and the water flux of both membranes was measured. A 3000 mg / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 hour of filtration. The salt rejection rate of the membranes was tested.

[0037] Example 3

[0038] This embodiment provides a method for modifying polyamide composite films based on active oxygen, specifically including the following steps:

[0039] S1. At room temperature, add complexing agents oxalic acid and EDTA-2Na to water until the concentration of oxalic acid and EDTA-2Na in the water is 1 mmol / L. Then add CoSO4 containing metal ions until the concentration of CoSO4 in the water is 5 mmol / L. The complexing agent and metal ions react to generate complexed metal ions.

[0040] S2. Then add peracetic acid, an oxide oxidant, to the water until the concentration of peracetic acid in the solution is 10 mmol / L. The oxide oxidant reacts with the complexed metal ions to generate active oxygen species, forming a modified solution.

[0041] S3. Immerse the BW30 polyamide composite membrane from DuPont / Dow Filmtech in the modification solution. After modification for 1 hour, remove the membrane and wash away the residual modification solution with water to obtain modified membrane 3.

[0042] The untreated membrane was used as control membrane 3. The performance of control membrane 3 and modified membrane 3 was tested. Test conditions were: operating pressure 14 bar, flow rate 3 LPM. Both modified membrane 3 and control membrane 3 were pre-pressurized with ultrapure water at 25°C for 6 hours to stabilize membrane performance. The operating pressure was then adjusted to 10 bar, and the water flux of both membranes was measured. A 3000 mg / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 hour of filtration. The salt rejection rate of the membranes was also tested.

[0043] Example 4

[0044] This embodiment provides a method for modifying polyamide composite films based on active oxygen, specifically including the following steps:

[0045] S1. At room temperature, add oxalic acid, a complexing agent, to water until the concentration of oxalic acid is 5 mmol / L. Then add CoSO4 and NiSO4, salts containing metal ions, until the concentrations of CoSO4 and NiSO4 are both 1 mmol / L. The complexing agent reacts with the metal ions to generate complexed metal ions.

[0046] S2. Add potassium persulfate, an oxide oxidant, to the water above until the concentration of potassium persulfate in the solution is 10 mmol / L. The oxide oxidant reacts with the complexed metal ions to generate active oxygen species, forming a modified solution.

[0047] S3. Immerse the BW30 polyamide composite membrane from DuPont / Dow Filmtech in the modification solution. After 5 hours of modification, remove the membrane and wash away the residual modification solution with water to obtain the modified membrane 4.

[0048] The untreated membrane was used as control membrane 4. The performance of control membrane 4 and modified membrane 4 was tested. Test conditions were: operating pressure 14 bar, flow rate 3 LPM. Both modified and control membranes were pre-pressurized with ultrapure water at 25°C for 6 hours to stabilize membrane performance. The operating pressure was then adjusted to 10 bar, and the water flux of both membranes was measured. A 3000 mg / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 hour of filtration. The salt rejection rate of the membranes was also tested.

[0049] Example 5

[0050] This embodiment provides a method for modifying polyamide composite films based on active oxygen, specifically including the following steps:

[0051] S1. At room temperature, add complexing agents oxalic acid and citric acid to water until the concentration of oxalic acid and citric acid in the water is 2 mmol / L. Then add salts containing metal ions, CuSO4 and FeSO4, until the concentration of CuSO4 and FeSO4 in the water is 1 mmol / L. The complexing agents and metal ions react to generate complexed metal ions.

[0052] S2. Add the oxidizing agents potassium persulfate and hydrogen peroxide to the water above until the concentration of potassium persulfate and hydrogen peroxide in the solution is 10 mmol / L. The oxidizing agents react with the complexed metal ions to generate active oxygen species, forming a modified solution.

[0053] S3. Immerse the RO1 polyamide composite membrane produced by Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd. in the modification solution. After modification for 1 hour, take it out and wash away the residual modification solution with water to obtain the modified membrane 5.

[0054] The untreated membrane was used as control membrane 5. The performance of control membrane 5 and modified membrane 5 was tested. Test conditions were: operating pressure 14 bar, flow rate 3 LPM. Both modified and control membranes were pre-pressurized with ultrapure water at 25°C for 6 hours to stabilize membrane performance. The operating pressure was then adjusted to 10 bar, and the water flux of both membranes was measured. A 3000 mg / L sodium chloride solution was prepared, and under the same operating conditions, the solution conductivity on both the feed side and the filter side was measured after 1 hour of filtration. The salt rejection rate of the membranes was also tested.

[0055] Table 1 shows the desalination rate and water flux test results of the modified membranes 1-5 prepared in comparison membranes 1-5 and examples 1-5:

[0056] Table 1 shows the performance test results of the comparison membrane 1-5 and the modified membrane 1-5.

[0057]

[0058] As can be seen from the results in Table 1, firstly, after modification, the water flux of different polyamide composite membranes significantly increased to approximately 150%-300% of that before modification, while the sodium chloride removal rate increased by 0.3%-1.5%. Overall, the modification method described in this invention is applicable to polyamide composite membranes produced by different manufacturers. Therefore, the method described in this invention has significant advantages in modifying polyamide composite membranes.

[0059] Figure 1 To compare the contact angles of membranes 1-3 and the modified membranes 1-5 prepared in Examples 1-5, the following was used: Figure 1 It can be seen that the contact angles of the modified membranes are all smaller than those of the unmodified membranes, indicating that the modified membranes have better surface hydrophilicity, which is beneficial to the transport of water molecules and increases the water flux of the membrane.

[0060] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for modifying polyamide composite films based on active oxygen, characterized in that, Includes the following steps: S1. At room temperature, complexed metal ions are added to water containing 1-100 mmol / L of peroxide oxidant, wherein the molar ratio of the peroxide oxidant to the metal ions in the complexed metal ions is (0.1-50):1, and reactive oxygen species are generated to obtain a modified aqueous solution. The peroxide oxidant is one or a combination of two or more of hydrogen peroxide, monopersulfate, dipersulfate, and peracetic acid; The cation of the complexed metal ion is Fe. 2+ Cu 2+ Co 2+ Mn 2+ Ni 2+ Ce 3+ One or more combinations of the following, with the anion being Cl. - NO3 - SO4 2- One or more combinations thereof; the preparation method of the complexed metal ions is as follows: a complexing agent with a concentration of 0.1-50 mmol / L and metal ions with a concentration of 0.1-50 mmol / L are added sequentially to water, wherein the molar ratio of the complexing agent to the metal ions is (0.1-10):1, and the reaction generates complexed metal ions; S2. Immerse the polyamide composite film containing aromatic rings in its molecular structure in the modified aqueous solution, and remove it after modification for 0.2-4 h. Wash away the residual modified solution with water.

2. The method for modifying polyamide composite films based on active oxygen according to claim 1, characterized in that, The monopersulfate is one or a combination of two or more of potassium monopersulfate, sodium monopersulfate, and ammonium monopersulfate.

3. The method for modifying polyamide composite films based on active oxygen according to claim 1, characterized in that, The persulfate is one or a combination of two or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

4. The method for modifying polyamide composite films based on active oxygen according to claim 1, characterized in that, The concentration of the complexed metal ions added to the water is 0.1-50 mmol / L.

5. The method for modifying polyamide composite films based on active oxygen according to claim 1, characterized in that, The complexing agent is one or a combination of two or more of the following: cyanate, thiocyanate, oxalic acid, pyruvic acid, citric acid, tartaric acid, lactic acid, ascorbic acid, ethylenediamine, glycine, pyridine, catechol, porphyrin, pyrimidine, benzothiazole, benzimidazole, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, ethanethiol, ethylenedithiol, 1-propanethiol, 1,3-propanedithiol, cysteine, and glutathione.

6. The method for modifying polyamide composite films based on active oxygen according to claim 5, characterized in that, The cyanate is one or a combination of two or more of sodium cyanate, potassium cyanate, and ammonium cyanate.

7. The method for modifying polyamide composite films based on active oxygen according to claim 5, characterized in that, The thiocyanate is one or a combination of two or more of sodium thiocyanate, potassium thiocyanate, and ammonium thiocyanate.

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