A method for separating oil-containing wastewater to enhance the anti-fouling performance of membranes

Abstract

This invention utilizes a membrane separation unit comprising an oil-water separation membrane to separate oily wastewater. The membrane separation unit includes a first metal mesh, a hollow oil-water separation chamber open at both ends, an oil-water separation membrane, and a second metal mesh. One end of the oil-water separation chamber is connected to the first metal mesh, and the other end is connected to one side of the oil-water separation membrane. The other side of the oil-water separation membrane is connected to the second metal mesh. The first and second metal meshes are arranged in parallel and are respectively connected to two electrodes of a pulsed power supply to generate an external pulsed electric field. This oil-water separation method, based on dead-end filtration or cross-flow filtration using an oil-water separation membrane, effectively prevents oil droplets from accumulating, clogging, and adhering to the separation membrane during the separation process through the combined effects of dielectric electrophoresis, electrophoresis, and bubble-mediated separation within the membrane separation unit. It exhibits excellent membrane fouling inhibition capabilities, thereby improving the oil-water separation effect of oily wastewater.

Description

Technical Field

[0001] This invention relates to the field of oily wastewater treatment technology, and in particular to a method for separating oily wastewater that enhances the antifouling properties of membranes. Background Technology

[0002] With social development and accelerated industrialization, water pollution caused by oily wastewater generated in industry and daily life is becoming increasingly serious, threatening the global ecological environment and human health. Traditional oil-water pollution treatment technologies such as gravity sedimentation, centrifugation, coagulation, electrochemistry, skimming, flotation, salinization, and biodegradation, while effectively addressing oil-water pollution issues, suffer from drawbacks such as low separation efficiency, high cost, and the potential for secondary pollution. Therefore, there is an urgent need to find green and efficient separation methods to meet practical needs.

[0003] In nature, many organisms exhibit excellent surface wettability, such as lotus leaves and fish scales. Inspired by these natural surfaces, interface materials with special wettability have attracted widespread attention. Due to the selective wettability of biomimetic wettable materials towards water and oil, they have garnered significant interest in the field of oil-water separation. Membranes with special wettable surfaces (such as superhydrophobic / superoleophilic membranes, superhydrophilic / underwater superoleophobic membranes, Janus membranes, etc.) are being applied in oil-water separation due to their advantages of energy saving, high efficiency, reusability, and high safety.

[0004] While membrane technology offers numerous advantages in oil-water separation, its poor antifouling ability still poses a challenge, leading to decreased separation performance. Currently, extensive research has been conducted to improve membrane antifouling performance, including methods such as membrane surface modification, bubble-mediated antifouling, the use of hydrogel membranes, and intelligent antifouling techniques. However, over time, the membrane itself will eventually become fouled during oil-water separation. Therefore, developing a universal method to inhibit membrane fouling in oil-water separation is beneficial for improving membrane separation performance, extending membrane operating time, and is of significant importance for environmental protection. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a method for separating oily wastewater that enhances the antifouling performance of membranes.

[0006] This invention proposes a method for separating oily wastewater with enhanced membrane antifouling performance. The method uses a membrane separation unit containing an oil-water separation membrane to separate oily wastewater. The membrane separation unit includes a first metal mesh, a hollow oil-water separation chamber open at both ends, an oil-water separation membrane, and a second metal mesh. One end of the oil-water separation chamber is connected to the first metal mesh, and the other end is connected to one side of the oil-water separation membrane. The other side of the oil-water separation membrane is connected to the second metal mesh. The first and second metal meshes are arranged in parallel and are respectively connected to two electrodes of a pulse power supply to generate an external pulsed electric field. The pore size of the first metal mesh is 60–100 mesh, and the pore size of the second metal mesh is 200–300 mesh.

[0007] The method for separating oily wastewater with enhanced membrane antifouling performance includes the following steps: turning on the pulse power supply, allowing the oily wastewater to enter the oil-water separation chamber through the first metal mesh, separating the oil and water using the oil-water separation membrane under the action of the applied pulse electric field, and then discharging the filtrate through the second metal mesh.

[0008] Preferably, in the membrane separation unit, the first metal mesh and the second metal mesh are arranged in parallel, one above the other.

[0009] Preferably, in the membrane separation unit, the first metal mesh and the second metal mesh are made of titanium, copper, or stainless steel.

[0010] Preferably, the thickness of the oil-water separation chamber is 150–400 μm.

[0011] Preferably, the separation method for separating oily wastewater using the membrane separation unit containing the oil-water separation membrane is dead-end filtration or cross-flow filtration.

[0012] In this invention, the connection method between the first metal mesh, the second metal mesh and the positive and negative terminals of the pulse power supply is related to the charge status of the oil droplets in the oily wastewater. If the oil droplets are negatively charged, the first metal mesh is connected to the positive terminal and the second metal mesh is connected to the negative terminal; if the oil droplets are uncharged or positively charged, the first metal mesh is connected to the negative terminal and the second metal mesh is connected to the positive terminal.

[0013] The present invention also discloses a membrane separation unit, comprising a first metal mesh, a hollow oil-water separation chamber with openings at both ends, an oil-water separation membrane, and a second metal mesh; one end of the oil-water separation chamber is connected to the first metal mesh, and the other end is connected to one side of the oil-water separation membrane, the other side of the oil-water separation membrane is connected to the second metal mesh, the first metal mesh and the second metal mesh are arranged in parallel and are respectively connected to two electrodes of a pulse power supply for generating an external pulse electric field; the aperture of the first metal mesh is 60-100 mesh, and the aperture of the second metal mesh is 200-300 mesh.

[0014] Preferably, in the membrane separation unit, the first metal mesh and the second metal mesh are arranged in parallel, one above the other.

[0015] Preferably, the thickness of the oil-water separation chamber is 150–400 μm.

[0016] This invention does not limit the type of oil-water separation membrane; any known oil-water separation membrane may be used. Preferably, the oil-water separation membrane is a Janus oil-water separation membrane.

[0017] In this invention, the separation process can be driven by gravity, or by vacuum or other types of external pressure.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention also provides a method for separating oily wastewater and a membrane separation unit to enhance the antifouling performance of membranes. The method involves passing oily wastewater through a first metal mesh into an oil-water separation chamber. Under the action of an external pulsed electric field, oil and water are separated using an oil-water separation membrane. The filtrate is then discharged through a second metal mesh. The non-uniform pulsed electric field formed between the first and second metal meshes with specific pore sizes utilizes a pulsed power supply to apply dielectric force and electrophoresis to the oil droplets. Furthermore, the cleaning effect of bubbles generated by water electrolysis by electrodes prevents the accumulation, clogging, and adhesion of oil droplets on the membrane surface during the oil-water separation process. This separation method couples oil-water membrane filtration with a pulsed electric field, exhibiting excellent membrane fouling suppression capabilities, thereby improving membrane separation performance and extending membrane lifespan. Attached Figure Description

[0020] Figure 1 This is a SEM image of the hydrophilic surface of the Janus oil-water separation membrane prepared in Example 1.

[0021] Figure 2 This is a cross-sectional SEM image of the Janus oil-water separation membrane prepared in Example 1.

[0022] Figure 3 The graph shows the permeation flux and separation efficiency of the Janus membrane prepared in Example 1 when using dead-end filtration to separate O / W emulsions using conventional oil-water separation methods.

[0023] Figure 4 This is a schematic diagram of the membrane separation unit used in this invention.

[0024] Figure 5 This is an exploded view of the membrane separation unit used in this invention.

[0025] Figure 6 The permeation flux and separation efficiency of O / W emulsion separation using the oil-water separation method in Example 1 are given.

[0026] Figure 7 The curve shows the change in filtrate mass per unit area over time when using the oil-water separation method in Example 1. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail through specific embodiments.

[0028] Example 1

[0029] Preparation of Janus oil-water separation membrane:

[0030] S1. PVDF-HFP is added to the first solvent and stirred at 25°C for 12 hours until completely dissolved to obtain precursor solution A. After electrospinning, the precursor solution A is dried at 40°C to obtain a hydrophobic nanofiber membrane. The mass ratio of PVDF-HFP to the first solvent is 1:4, and the first solvent is composed of tetrahydrofuran and N,N-dimethylamide in a mass ratio of 1:1.

[0031] PAN was dissolved in a second solvent to obtain precursor solution B. Precursor solution B was electrospun, and the collected product was dried at 60°C to obtain a carbon fiber precursor nanofiber membrane. The carbon fiber precursor nanofiber membrane was first heat-treated at 280°C for 2 hours in air, and then carbonized at 800°C for 2 hours in nitrogen atmosphere at a rate of 5°C / min to obtain a carbon nanofiber membrane. The carbon nanofiber membrane was cut into small pieces and added to a 2% (w / w) PVP solution. After adding bacterial cellulose, the mixture was homogenized at 12000 rpm for 10 minutes using an IKA T25 homogenizer to obtain a CNF composite dispersion. The mass ratio of PAN to the second solvent was 1:9, the second solvent was DMF, the mass ratio of the carbon nanofiber membrane to the PVP solution was 2:10000, and the mass ratio of bacterial cellulose to the carbon nanofiber membrane was 1:25.

[0032] S2. CNF is deposited onto one surface of the hydrophobic nanofiber membrane by filtration, and then heat-treated at 130°C for 1 hour. After cleaning and drying with anhydrous ethanol, CNF-hydrophobic nanofiber composite membrane is obtained.

[0033] S3. The CNF-hydrophobic nanofiber composite membrane was completely immersed in a hexane solution containing 1 wt% octadecyltrimethoxysilane. After standing at 40°C for 5 h for hydrophobication treatment, and then washed with hexane, the composite membrane was floated on the surface of the chemical bath deposition solution with the CNF side of the composite membrane in contact with the solution surface. Chemical bath deposition was performed at 95°C for 6 h to obtain a Janus oil-water separation membrane with asymmetric wettability. The chemical bath deposition solution was obtained by dissolving cobalt nitrate and urea in water, with a cobalt nitrate concentration of 0.03 M and a urea concentration of 0.15 M.

[0034] Figure 1 This is a SEM image of the hydrophilic surface of the Janus oil-water separation membrane prepared in Example 1. (From...) Figure 1 It can be seen that Co(CO3) 0.5 The outline of CNF encapsulated by OH·0.11H2O nanoneedles is clearly visible.

[0035] Figure 2 This is a cross-sectional SEM image of the Janus oil-water separator prepared in Example 1. (From...) Figure 2 It can be seen that the Janus membrane consists of CNF@Co(CO3) at the bottom. 0.5 It is composed of an OH·0.11H2O membrane and the PVDF-HFP membrane above.

[0036] Figure 3 The graph shows the permeate flux and separation efficiency of the Janus membrane prepared in Example 1, using dead-end filtration and conventional oil-water separation methods to separate an O / W emulsion (obtained by dispersing 1 ml of oil in an aqueous solution of sodium dodecyl sulfate, wherein the aqueous solution of sodium dodecyl sulfate was obtained by adding 30 mg of sodium dodecyl sulfate to 99 ml of water). The permeate flux of each emulsion, measured using the emulsion's own weight and conventional dead-end filtration, all exceeded 9000 L / m³. -2 h -1 bar -1 The separation efficiencies were all above 99.3%. Dodecane, Toluene, Liquid paraffin, and Carbon tetrachloride were used.

[0037] Dead-end filtration is used to separate oil and water in O / W emulsions. The membrane separation unit used is as follows: Figure 4As shown, the device includes a first titanium mesh 1, a hollow oil-water separation chamber 2 with openings at both the top and bottom, an oil-water separation membrane 3, and a second titanium mesh 4. The upper opening of the oil-water separation chamber 2 is connected to the first titanium mesh 1, and the lower opening is connected to the hydrophilic surface of the oil-water separation membrane 3. The hydrophobic surface of the oil-water separation membrane 3 is connected to the second titanium mesh 4. The first titanium mesh 1 and the second titanium mesh 4 are respectively connected to the positive and negative electrodes of the pulse power supply 5 to generate an external pulsed electric field. The thickness of the oil-water separation chamber 2 is 150 μm, the pore size of the first titanium mesh 1 is 80 mesh, and the pore size of the second titanium mesh 4 is 200 mesh. The first titanium mesh 1 and the second titanium mesh 4 are arranged parallel to each other. The oil-water separation membrane 3 is the Janus oil-water separation membrane prepared above.

[0038] The oil-water separation steps are as follows: turn on the pulse power supply 5, and let the O / W emulsion pass through the first titanium mesh 1 into the oil-water separation chamber 2. Under the action of the external pulse electric field, the oil and water are separated by the oil-water separation membrane 3, and then the filtrate is discharged through the second titanium mesh 4. This separation process is driven by gravity.

[0039] Figure 6 This study examines the permeation flux and separation efficiency of O / W emulsion separation using the aforementioned oil-water separation method at different pulse width / pulse interval ratios. Figure 6 It can be seen that changing the pulse width / pulse interval ratio affects the emulsion separation flux under constant pulsed current. Maintaining a separation efficiency of 98.4%, using the above oil-water separation method, the Janus oil-water separation membrane achieved a permeation flux of 17750.3 L / m³ for a n-dodecane / water emulsion (obtained by dispersing 1 ml of n-dodecane in an aqueous solution of sodium dodecyl sulfate, which was obtained by adding 30 mg of sodium dodecyl sulfate to 99 ml of water) using a pulsed current of 20 mA and a pulse width / pulse interval of 0.4 s / 1.0 s. -2 h -1 bar -1 When the filtration efficiency is close to that of pure dead-end filtration (9912.3 L m), -2 h -1 bar -1 ) twice as much.

[0040] Figure 7 The graph shows the change in filtrate mass per unit area over time when using the above-mentioned oil-water separation method. From... Figure 7 As can be seen, stable emulsion separation can still be obtained after 5.5 hours of continuous separation under the action of pulsed electric field, indicating that the method enhances the membrane's antifouling ability.

[0041] Comparative Example 1

[0042] The only difference between the oil-water separation method in Comparative Example 1 and Example 1 is that the pore size of the first titanium mesh 1 in the oil-water separation unit used is 200 mesh. In Comparative Example 1, the Janus oil-water separation membrane achieved a permeation flux of 10012.6 L / m³ for a n-dodecane / water emulsion (obtained by dispersing 1 ml of n-dodecane in an aqueous solution of sodium dodecyl sulfate, wherein the aqueous solution of sodium dodecyl sulfate was obtained by adding 30 mg of sodium dodecyl sulfate to 99 ml of water) using a pulsed current of 20 mA and a pulse width / pulse interval of 0.4 s / 1.0 s. -2 h -1 bar -1 .

[0043] Comparative Example 2

[0044] The only difference between Comparative Example 2 and Example 1 is that the second titanium mesh 4 in the oil-water separation unit has a pore size of 80 mesh. In Comparative Example 2, the Janus oil-water separation membrane exhibited a permeation flux of 10¹⁰³ L / m³ for a n-dodecane / water emulsion (obtained by dispersing 1 ml of n-dodecane in an aqueous solution of sodium dodecyl sulfate, which was obtained by adding 30 mg of sodium dodecyl sulfate to 99 ml of water) using a pulsed current of 20 mA and a pulse width / pulse interval of 0.4 s / 1.0 s. -2 h -1 bar -1 .

[0045] Example 2

[0046] Dead-end filtration is used to separate oil and water in O / W emulsions. The membrane separation unit used is as follows: Figure 4 As shown, the device includes a first titanium mesh 1, a hollow oil-water separation chamber 2 with openings at both the top and bottom, an oil-water separation membrane 3, and a second titanium mesh 4. The upper opening of the oil-water separation chamber 2 is connected to the first titanium mesh 1, and the lower opening is connected to one side of the oil-water separation membrane 3. The other side of the oil-water separation membrane 3 is connected to the second titanium mesh 4. The first titanium mesh 1 and the second titanium mesh 4 are respectively connected to the two electrodes of the pulse power supply 5 to generate an external pulsed electric field. The thickness of the oil-water separation chamber 2 is 150 μm, the pore size of the first titanium mesh 1 is 80 mesh, and the pore size of the second titanium mesh 4 is 200 mesh. The first titanium mesh 1 and the second titanium mesh 4 are arranged parallel to each other. The oil-water separation membrane 3 is a commercially available PVDF separation membrane with a pore size of 0.45 μm and hydrophilic on both sides.

[0047] The oil-water separation steps are as follows: turn on the pulse power supply 5, and let the O / W emulsion pass through the first titanium mesh 1 into the oil-water separation chamber 2. Under the action of the external pulse electric field, the oil and water are separated by the oil-water separation membrane 3, and then the filtrate is discharged through the second titanium mesh 4. This separation process is driven by gravity.

[0048] Using a pulsed current of 20 mA and a pulse width / pulse interval of 0.4 s / 1.0 s, the permeation flux of the PVDF membrane to a dodecane / water emulsion (the emulsion was obtained by dispersing 1 ml of n-dodecane in an aqueous solution of sodium dodecyl sulfate, wherein the aqueous solution of sodium dodecyl sulfate was obtained by adding 30 mg of sodium dodecyl sulfate to 99 ml of water) was 15698.7 L m. -2 h -1 bar -1 .

[0049] In addition to the Janus oil-water separation membrane prepared in the above embodiments, other oil-water separation membranes, including self-made or commercial membranes, or those using a cross-flow mode, can also be used in this way to separate oil and water, thus extending the service life of the membrane.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for separating oil-containing wastewater to enhance the antifouling performance of a membrane, characterized by, The oil-containing wastewater is separated by using a membrane separation unit comprising an oil-water separation membrane, the membrane separation unit comprising a first metal mesh, a hollow oil-water separation chamber with open ends, an oil-water separation membrane, and a second metal mesh; one end of the oil-water separation chamber is connected with the first metal mesh, the other end is connected with one side of the oil-water separation membrane, the other side of the oil-water separation membrane is connected with the second metal mesh, the first metal mesh and the second metal mesh are arranged in parallel and are respectively connected with two electrodes of a pulse power source for generating an external pulse electric field. The pore size of the first metal mesh is 60-100 mesh, and the pore size of the second metal mesh is 200-300 mesh; the thickness of the oil-water separation chamber is 150-400 μm. The method for separating the oil-containing wastewater by enhancing the anti-pollution performance of the membrane comprises the following steps: turning on the pulse power source, making the oil-containing wastewater pass through the first metal mesh into the oil-water separation chamber, separating the oil and water by using the oil-water separation membrane under the action of the external pulse electric field, and then making the filtrate pass through the second metal mesh and be discharged.

2. The method for separating oily wastewater according to the pollution resistance of the reinforcing film according to claim 1, characterized by, In the membrane separation unit, the first metal mesh and the second metal mesh are arranged in parallel from top to bottom.

3. The method for separating oily wastewater according to the pollution resistance of the reinforcing film according to claim 1, characterized by, In the membrane separation unit, the material of the first metal mesh and the second metal mesh is titanium, copper or stainless steel.

4. The method for separating oily wastewater according to the pollution resistance of the reinforcing film according to claim 1, characterized by, The separation mode for separating the oil-containing wastewater by using the membrane separation unit comprising the oil-water separation membrane is dead-end filtration or cross-flow filtration.

5. A membrane separation unit, characterized by, The membrane separation unit comprises a first metal mesh, a hollow oil-water separation chamber with open ends, an oil-water separation membrane, and a second metal mesh; one end of the oil-water separation chamber is connected with the first metal mesh, the other end is connected with one side of the oil-water separation membrane, the other side of the oil-water separation membrane is connected with the second metal mesh, the first metal mesh and the second metal mesh are arranged in parallel and are respectively connected with two electrodes of a pulse power source for generating an external pulse electric field. The pore size of the first metal mesh is 60-100 mesh, and the pore size of the second metal mesh is 200-300 mesh; the thickness of the oil-water separation chamber is 150-400 μm.

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