A method for preparing a surface-biased hollow fiber membrane based on coordination

Abstract

The application discloses a preparation method of a surface segregation hollow fiber membrane based on coordination. The method comprises the following steps: uniformly mixing a polymer, a pore-forming agent, a modifier and an organic solvent through heating and stirring, standing and defoaming to form a casting solution, spinning by using the obtained casting solution, and introducing the casting solution into a coagulation bath to be solidified and formed into the hollow fiber membrane. The method can improve the permeation flux, separation performance and anti-pollution performance of the hollow fiber membrane, and is simple in process and easy to be enlarged and prepared.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing a surface segregation hollow fiber membrane based on coordination. Background Technology

[0002] With the development of industrial production, the increasing amount of oily wastewater and oil spills has caused serious water pollution, threatening the human ecological environment. Traditional oil removal technologies, namely gravity sedimentation, flotation, coagulation, adsorption, biological treatment, and advanced oxidation processes, suffer from problems such as low efficiency, high cost, complex processes, and secondary pollution. In contrast, membrane technology is considered the most effective method due to its advantages such as low energy cost, high efficiency, simple operation, and environmental friendliness. In recent years, membrane separation technology has continued to develop and improve, making it a very promising oil-water separation method. However, in practical applications, some pollutants in oily wastewater adhere to the membrane surface, causing serious membrane fouling, leading to decreased membrane flux, reduced separation efficiency, and shortened membrane lifespan.

[0003] Existing methods for modifying antifouling membrane materials mainly include surface coating, surface grafting, and surface segregation. Compared with post-modification methods such as surface grafting and surface coating, surface segregation has two significant advantages: First, surface segregation is an in-situ antifouling membrane preparation method, where membrane preparation and modification occur simultaneously. Driven by thermodynamics and kinetics, it can create a uniform hydrophilic molecular brush on the membrane surface, avoiding the drawbacks of post-modification methods such as complex operation and pore blockage. Second, surface segregation occurs at all interfaces between the polymer-rich and polymer-poor phases during phase transformation, providing modification not only to the membrane surface but also to the inner walls of the membrane pores. Therefore, membrane materials prepared by surface segregation can effectively combat both trapped pollutants and small-sized pollutants that enter the membrane pores. However, the disadvantage of surface segregation lies in the difficulty of controlling its degree of control. This is reflected in the enrichment of the segregating agent during membrane preparation and the stability of the segregating agent during membrane use. Simply increasing the hydrophilic / hydrophobic segment ratio of the segregating agent will lead to an excessively fast surface segregation rate, exceeding the thermodynamic equilibrium point at the coagulation bath-casting solution interface. This causes the segregating agent to leak into the coagulation bath, resulting in a decrease in the surface coverage of the hydrophilic polymer on the membrane surface (i.e., over-segregation). Conversely, if the hydrophilic / hydrophobic segment ratio of the segregating agent is too low, the surface segregation rate will be too low, making it difficult to accumulate on the membrane surface before the bulk polymer solidifies, and ultimately most of it will be embedded in the membrane bulk (i.e., under-segregation). Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing surface segregation hollow fiber membranes based on coordination to solve problems such as severe membrane fouling and low membrane flux in the treatment of oily wastewater.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A surface segregation hollow fiber membrane based on coordination interaction is prepared by the following steps:

[0007] (1) After heating and stirring the polymer, pore-forming agent, modifier and organic solvent to mix them evenly, let them stand to remove bubbles and form a casting solution;

[0008] (2) Using a non-solvent-induced phase separation method, under constant temperature conditions, the casting liquid and core liquid obtained in step (1) are spun through a hollow fiber spinning machine and then sent to a coagulation bath to solidify and form the hollow fiber membrane.

[0009] Further, the polymer mentioned in step (1) is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyethersulfone, polysulfone, polyvinyl chloride, and polypropylene.

[0010] Further, the pore-forming agent mentioned in step (1) is polyvinylpyrrolidone (K30), which has a molecular weight of 58,000.

[0011] Further, the modifier mentioned in step (1) is 1,2,4,5-cyclohexanetetracarboxylic acid.

[0012] Further, the organic solvent in step (1) is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0013] Furthermore, based on a total mass percentage of 100%, the casting solution obtained in step (1) contains 10%~20% polymer, 5%~10% pore-forming agent, 0.1%~1% modifier, and 70%~85% organic solvent.

[0014] Furthermore, the core fluid mentioned in step (2) is deionized water.

[0015] Further, the coagulation bath in step (2) is an aqueous solution containing ferric chloride, wherein the concentration of ferric chloride is 0.01~0.1wt%.

[0016] Furthermore, in step (2), the temperature of the coagulation bath and the core liquid is 20~30 ℃, and the temperature of the casting liquid is 30~40 ℃.

[0017] The hollow fiber membrane obtained by this invention can be applied to oil-water separation.

[0018] 1,2,4,5-Cyclohexanetetracarboxylic acid is an organic acid with four hydroxyl groups in its molecular structure, enabling it to form stable complexes with metal ions such as iron, calcium, and magnesium. This invention utilizes this polyphenolic coordination between 1,2,4,5-cyclohexanetetracarboxylic acid and iron ions. By adjusting the concentration of the ferric chloride aqueous solution coagulation bath, a stable complex can be formed, thus resolving potential over- and under-segregation phenomena during segregation. This allows the segregating agent to effectively coat the membrane surface, achieving excellent membrane surface modification.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] The preparation steps of the surface segregation hollow fiber membrane of this invention are simple, easy to control, and have low equipment requirements. Furthermore, it exhibits high rejection rate, high circulation stability, and high emulsified oil flux. Testing has shown that its water flux can reach a maximum of 602 L / m³. -2 h -1 bar -1 The emulsified oil penetration flux can reach up to 368 L / m³. -2 h -1 bar -1 The separation performance is over 99.5%. After more than three cycles of testing and long-term testing, the rejection rate of the separation membrane remains stable, and the permeation flux of emulsified oil remains at a high level of 329 L / m³. -2 h -1 bar -1 .

[0021] This invention applies reactive surface segregation technology to the preparation of hollow fiber membranes. It eliminates the need for complex synthesis processes, utilizes readily available raw materials, and facilitates large-scale and industrial production on existing hollow fiber membrane production equipment. It is expected to update existing high-performance hollow fiber membrane production processes.

[0022] In summary, considering both separation performance and preparation process, the hollow fiber membrane of this invention has great application potential. Attached Figure Description

[0023] Figure 1 Scanning electron microscope (SEM) images of a cross section (a) and a portion (b) of the hollow fiber membrane prepared in Example 1.

[0024] Figure 2 This is a comparison chart of the pure water flux of hollow fiber membranes prepared in the examples and comparative examples.

[0025] Figure 3 The graph shows a comparison of the permeation flux of hollow fiber membranes prepared in the examples and comparative examples. Detailed Implementation

[0026] A surface segregation hollow fiber membrane based on coordination interaction is prepared by the following steps:

[0027] (1) Add the polymer, pore-forming agent, modifier and organic solvent into the reaction vessel, heat and stir to mix evenly, and then let stand to degas and form a casting solution;

[0028] (2) Keep the temperature of the coagulation bath and the core liquid at 20~30 ℃ and the temperature of the casting liquid at 30~40 ℃. Using the non-solvent induced phase separation method, the casting liquid and the core liquid obtained in step (1) are spun through a hollow fiber spinning machine and sent into the coagulation bath to solidify and form a hollow fiber membrane.

[0029] (3) Soak the hollow fiber membrane obtained in step (2) in deionized water for 12 hours (replace the deionized water once at 1 hour, 3 hours and 12 hours respectively) to remove the residual organic solvent on the membrane surface and obtain the finished product.

[0030] The casting solution, by weight percentage (summing 100%), contains 10%–20% polymer, 5%–10% pore-forming agent, 0.1%–1% modifier, and 70%–85% organic solvent. The polymer is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyethersulfone, polysulfone, polyvinyl chloride, and polypropylene. The pore-forming agent is polyvinylpyrrolidone (K30), with a molecular weight of approximately 58,000. The modifier is 1,2,4,5-cyclohexanetetracarboxylic acid. The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0031] The core fluid is deionized water. The coagulation bath is an aqueous solution containing ferric chloride, wherein the concentration of ferric chloride is 0.01~0.1wt%.

[0032] The specific parameters of the spinning process are: winding speed of 10~30 m / min, spinning pump flow rate of 5~30 mL / min, and core liquid flow rate of 10~50 mL / min.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, comparative examples and specific embodiments. The specific embodiments described are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0034] Example 1

[0035] (1) 80 g of polyvinylidene fluoride (FR904, industrial grade), 30 g of polyvinylpyrrolidone (average molecular weight 58000), 2.5 g of 1,2,4,5-cyclohexanetetracarboxylic acid and 387.5 g of N,N-dimethylacetamide were added to the reactor of a hollow fiber spinning machine and mechanically stirred at 60 °C for 6 h. Then, the mixture was allowed to stand at 60 °C for 12 h to remove bubbles and obtain the casting solution.

[0036] (2) Under nitrogen pressure of 0.15 MPa, the obtained casting solution and deionized water as core liquid are spun together using a hollow fiber spinning machine, and then introduced into a coagulation bath of ferric chloride aqueous solution to solidify and form a hollow fiber membrane. The membrane is then soaked in deionized water for 12 hours (the deionized water is replaced once at 1 hour, 3 hours and 12 hours respectively) to obtain a shaped hollow fiber membrane.

[0037] The concentration of ferric chloride in the ferric chloride aqueous solution was 0.05 wt%. During spinning in the hollow fiber spinning machine, the temperatures of the casting solution and spinning pump were 35 ℃, the spinneret was kept at a constant temperature of 60 ℃, and the core solution and coagulation bath temperatures were 25 ℃. The inner and outer diameters of the spinneret were 0.7 mm and 1.4 mm, respectively; the distance between the spinneret and the surface of the water coagulation bath was 5 cm; the spinning speed was 12 m / min; the spinning pump flow rate was 10 mL / min; and the core solution flow rate was 15 mL / min.

[0038] Example 2

[0039] Replace the 2.5 g 1,2,4,5-cyclohexanetetracarboxylic acid and 387.5 g N,N-dimethylacetamide used in step (1) with 0.5 g 1,2,4,5-cyclohexanetetracarboxylic acid and 389.5 g N,N-dimethylacetamide, and perform the other operations as in Example 1.

[0040] Example 3

[0041] Replace the 2.5 g 1,2,4,5-cyclohexanetetracarboxylic acid and 387.5 g N,N-dimethylacetamide used in step (1) with 5 g 1,2,4,5-cyclohexanetetracarboxylic acid and 385 g N,N-dimethylacetamide, and perform the other operations as in Example 1.

[0042] Example 4

[0043] The concentration of ferric chloride in the coagulation bath of the ferric chloride aqueous solution used in step (2) was changed from 0.05 wt% to 0.03 wt%, and other operations were the same as in Example 1.

[0044] Example 5

[0045] The concentration of ferric chloride in the coagulation bath of the ferric chloride aqueous solution used in step (2) was changed from 0.05 wt% to 0.07 wt%, and other operations were the same as in Example 1.

[0046] Example 6

[0047] The concentration of ferric chloride in the coagulation bath of the ferric chloride aqueous solution used in step (2) was changed from 0.05 wt% to 0.1 wt%, and other operations were the same as in Example 1.

[0048] Comparative Example 1

[0049] (1) Add 80 g of polyvinylidene fluoride (FR904, industrial purity), 30 g of polyvinylpyrrolidone (average molecular weight 58000) and 390 g of N,N-dimethylacetamide to the reactor of the hollow fiber spinning machine, mechanically stir at 60 °C for 6 h, and then let stand at 60 °C for 12 h to remove bubbles to obtain the casting solution.

[0050] (2) Under nitrogen pressure of 0.15 MPa, the obtained casting liquid and deionized water as core liquid are spun together using a hollow fiber spinning machine, and then introduced into a water coagulation bath to solidify and form. The mixture is then soaked in deionized water for 12 hours (the deionized water is replaced once at 1 hour, 3 hours and 12 hours respectively) to obtain the formed hollow fiber membrane.

[0051] In the hollow fiber spinning machine, the temperature of the casting solution and spinning pump is 35 ℃, the spinneret is kept at a constant temperature of 60 ℃, and the core solution and coagulation bath temperature is 25 ℃. The inner and outer diameters of the spinneret are 0.7 mm and 1.4 mm, respectively. The distance between the spinneret and the surface of the water coagulation bath is 5 cm. The spinning speed is 12 m / min, the spinning pump flow rate is 10 mL / min, and the core solution flow rate is 15 mL / min.

[0052] Comparative Example 2

[0053] (1) 80 g of polyvinylidene fluoride (FR904, industrial grade), 30 g of polyvinylpyrrolidone (average molecular weight 58000), 2.5 g of 1,2,4,5-cyclohexanetetracarboxylic acid and 387.5 g of N,N-dimethylacetamide were added to the reactor of a hollow fiber spinning machine and mechanically stirred at 60 °C for 6 h. Then, the mixture was allowed to stand at 60 °C for 12 h to remove bubbles and obtain the casting solution.

[0054] (2) Under nitrogen pressure of 0.15 MPa, the obtained casting liquid and deionized water as core liquid are spun together using a hollow fiber spinning machine, and then introduced into an aqueous coagulation bath to solidify and form. The mixture is then soaked in deionized water for 12 hours (the deionized water is replaced once at 1 hour, 3 hours and 12 hours respectively) to obtain the formed hollow fiber membrane.

[0055] In the hollow fiber spinning machine, the temperature of the casting solution and spinning pump is 35 ℃, the spinneret is kept at a constant temperature of 60 ℃, and the core solution and coagulation bath temperature is 25 ℃. The inner and outer diameters of the spinneret are 0.7 mm and 1.4 mm, respectively. The distance between the spinneret and the surface of the water coagulation bath is 5 cm. The spinning speed is 12 m / min, the spinning pump flow rate is 10 mL / min, and the core solution flow rate is 15 mL / min.

[0056] Comparative Example 3

[0057] (1) Add 80 g of polyvinylidene fluoride (FR904, industrial grade), 30 g of polyvinylpyrrolidone (average molecular weight 58000), 2.5 g of tannic acid and 387.5 g of N,N-dimethylacetamide to the reactor of a hollow fiber spinning machine, stir mechanically at 60 °C for 6 h, and then let stand at 60 °C for 12 h to remove bubbles, and obtain casting solution.

[0058] (2) Under nitrogen pressure of 0.15 MPa, the obtained casting solution and deionized water as core liquid are spun together using a hollow fiber spinning machine, and then introduced into a coagulation bath of ferric chloride aqueous solution to solidify and form a hollow fiber membrane. The membrane is then soaked in deionized water for 12 hours (the deionized water is replaced once at 1 hour, 3 hours and 12 hours respectively) to obtain a shaped hollow fiber membrane.

[0059] The concentration of ferric chloride in the ferric chloride aqueous solution was 0.05 wt%. During spinning in the hollow fiber spinning machine, the temperatures of the casting solution and spinning pump were 35 ℃, the spinneret was kept at a constant temperature of 60 ℃, and the core solution and coagulation bath temperatures were 25 ℃. The inner and outer diameters of the spinneret were 0.7 mm and 1.4 mm, respectively; the distance between the spinneret and the surface of the water coagulation bath was 5 cm; the spinning speed was 12 m / min; the spinning pump flow rate was 10 mL / min; and the core solution flow rate was 15 mL / min.

[0060] Comparative Example 4

[0061] (1) 80 g of polyvinylidene fluoride (FR904, industrial purity), 30 g of polyvinylpyrrolidone (average molecular weight 58000), 2.5 g of phytic acid and 387.5 g of N,N-dimethylacetamide were added to the reactor of the hollow fiber spinning machine and mechanically stirred at 60°C for 6 h. Then, the mixture was allowed to stand at 60°C for 12 h to remove bubbles and obtain the casting solution.

[0062] (2) Under nitrogen pressure of 0.15 MPa, the obtained casting solution and deionized water as core liquid are spun together using a hollow fiber spinning machine, and then introduced into a coagulation bath of ferric chloride aqueous solution to solidify and form a hollow fiber membrane. The membrane is then soaked in deionized water for 12 hours (the deionized water is replaced once at 1 hour, 3 hours and 12 hours respectively) to obtain a shaped hollow fiber membrane.

[0063] The concentration of ferric chloride in the ferric chloride aqueous solution was 0.05 wt%. During spinning in the hollow fiber spinning machine, the temperatures of the casting solution and spinning pump were 35 ℃, the spinneret was kept at a constant temperature of 60 ℃, and the core solution and coagulation bath temperatures were 25 ℃. The inner and outer diameters of the spinneret were 0.7 mm and 1.4 mm, respectively; the distance between the spinneret and the surface of the water coagulation bath was 5 cm; the spinning speed was 12 m / min; the spinning pump flow rate was 10 mL / min; and the core solution flow rate was 15 mL / min.

[0064] Using a prepared oil-water emulsion (0.1 wt% vacuum pump oil, 0.01 wt% sodium dodecyl sulfate, 99.89 wt% deionized water, mechanically stirred at 700 r / min for 24 h) as the treatment object, the pure water flux and permeate flux of the hollow fiber membranes obtained in the examples and comparative examples were detected by cross-flow filtration. Simultaneously, the rejection rate was detected using a UV spectrophotometer. The results are shown in Table 1 and... Figure 2 , 3 .

[0065] Table 1

[0066]

[0067] As can be seen from the results in Table 1, compared with the comparative example, the hollow fiber membranes prepared in the examples have improved pure water flux and permeation flux, while the rejection rate remains basically unchanged. Among them, the hollow fiber membrane prepared in Example 1 has the best overall performance.

[0068] In summary, this invention employs a one-step method to prepare and modify hollow fiber membranes. By introducing 1,2,4,5-cyclohexanetetracarboxylic acid, a hydrophilic membrane surface is constructed, resisting membrane fouling through the hydration layer effect. Furthermore, by altering the composition and concentration of the coagulation bath, a hydrophilic gel layer is formed on the membrane surface, increasing the permeate flux of the emulsified oil. Therefore, the combined use of 1,2,4,5-cyclohexanetetracarboxylic acid and a ferric chloride aqueous solution coagulation bath significantly improves both the pure water flux and the permeate flux of the membrane.

[0069] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing a surface segregation hollow fiber membrane based on coordination, characterized in that, Includes the following steps: (1) After heating and stirring the polymer, pore-forming agent, modifier and organic solvent to mix them evenly, let them stand to remove bubbles and form a casting solution; (2) Under constant temperature conditions, the casting liquid and core liquid obtained in step (1) are spun by a hollow fiber spinning machine and then sent to a coagulation bath to solidify and form the hollow fiber membrane. Based on a total mass percentage of 100%, the casting solution obtained in step (1) contains 16%~20% polymer, 5%~10% pore-forming agent, 0.1%~1% modifier, and 70%~77.9% organic solvent; wherein the modifier is 1,2,4,5-cyclohexanetetracarboxylic acid; The coagulation bath mentioned in step (2) is an aqueous solution containing ferric chloride, wherein the concentration of ferric chloride is 0.01~0.1wt%.

2. The method for preparing a surface segregation hollow fiber membrane based on coordination interaction according to claim 1, characterized in that, The polymer is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyethersulfone, polysulfone, polyvinyl chloride, and polypropylene.

3. The method for preparing a surface segregation hollow fiber membrane based on coordination interaction according to claim 1, characterized in that, The pore-forming agent is polyvinylpyrrolidone, with a molecular weight of 58,000.

4. The method for preparing a surface segregation hollow fiber membrane based on coordination interaction according to claim 1, characterized in that, The organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

5. The method for preparing a surface segregation hollow fiber membrane based on coordination interaction according to claim 1, characterized in that, The core fluid mentioned in step (2) is deionized water.

6. The method for preparing a surface segregation hollow fiber membrane based on coordination interaction according to claim 1, characterized in that, In step (2), the temperature of the coagulation bath and the core liquid is 20~30 ℃, and the temperature of the casting liquid is 30~40 ℃.

7. A surface segregation hollow fiber membrane prepared by the method described in claim 1.

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