Oil-water emulsion separation system for improving anti-pollution performance of membrane through cooperation of bubbles and magnetic particles

Abstract

The invention discloses an oil-water emulsion separation system for cooperatively improving the anti-pollution performance of a membrane through bubbles and magnetic particles, and belongs to the technical fields of water treatment, membrane technologies and oil-water separation. The method comprises the following steps: firstly, preparing ferroferric oxide nanoparticles (Fe3O4 NPs) by virtue of a coprecipitation method, and then, carrying out modification treatment on the Fe3O4 NPs by virtue of tetraethoxysilane (TEOS) and dodecyl trimethoxy silane (KH1231), so as to prepare magnetic nanoparticles (Fe3O4-KH1231 NPs) for separating the oil-water emulsion. Grafting magnetic nanoparticles (Fe3O4 / sodium citrate) for preparing the magnetic film by using sodium citrate; pVDF and Fe3O4 / sodium citrate are blended to serve as a membrane casting solution, a magnetic membrane is prepared through electrostatic spinning, and a gas disc is selected to serve as a bubble generation device. By testing the magnetic particles collected under different gas flows, the influence of different magnetic particle addition amounts and particle sizes on the emulsion demulsification effect is tested; experiments for determining flux loss rates of emulsion treated by the system under different gas flows prove that the oil-water emulsion separation system for cooperatively improving the anti-pollution performance of the membrane based on the bubbles and the magnetic particles inhibits aggregation of the magnetic particles and emulsion droplets on the surface of the membrane, migration of retentate is realized, and the flux is maintained at a stable level within continuous 30 minutes.

Description

Technical Field

[0001] The present invention belongs to the fields of water treatment, membrane technology and oil-water separation technology, and specifically relates to the design of a magnetic particle-magnetic membrane coupling system for bubble-assisted emulsion expulsion, as well as testing the effects of magnetic particle size and addition amount on demulsification efficiency and the stability of membrane separation flux. Ultimately, an oil-water emulsion separation system is obtained in which bubbles and magnetic particles synergistically improve the membrane's anti-pollution performance. Background Art

[0002] Traditional emulsion treatment technologies include chemical, electrical, mechanical, and microwave demulsification. However, these technologies present challenges such as the formation of fine secondary droplets during coalescence, the inability to completely remove droplets due to their small size, the high hardware size and installation cost on offshore platforms, the loss of light oil fractions in the crude oil, and the high requirements for chemical demulsifiers. Furthermore, while demulsification is achieved, the oil and water remain in the same system, failing to separate them, and their adverse environmental impacts persist. Membrane technology, which integrates demulsification and oil-water separation, has become a key research area in emulsion filtration. However, as membranes separate emulsions, the dispersed phase accumulates on the membrane surface, clogging the membrane pores and reducing the separation flux. This necessitates frequent membrane cleaning, significantly hindering membrane separation. Researchers have proposed coupling magnetic particles with magnetic membranes to separate water-in-oil emulsions. This approach leverages the electrostatic repulsion between the membrane surface and the Pickering emulsion to separate the water-in-oil emulsion. The innovation of this strategy lies in that, on the one hand, after the Pickering emulsion is formed, the particle size of the Pickering emulsion is larger than the emulsion particle size, and the membrane's separation of the emulsion is transformed into separation of the Pickering emulsion, thereby improving the membrane's separation efficiency. On the other hand, it can inhibit the deposition of the dispersed phase on the membrane surface, thereby improving the membrane's anti-fouling properties. However, as the filtration proceeds, the magnetic particles, which cannot be recovered within the system, inevitably accumulate on the membrane surface, clogging the membrane pores and hindering the membrane separation process.

[0003] In response to the above problems, the present invention discloses an oil-water emulsion separation system that uses bubbles and magnetic particles to synergistically improve the anti-pollution performance of the membrane. The invention uses the adhesion between bubbles and magnetic particles after demulsification to migrate the magnetic particles and retained matter (emulsion) away from the membrane surface under the action of gravity, thereby achieving separation of retained matter and improving the anti-pollution performance of the membrane. Bubbles are used to achieve rapid and uniform mixing of magnetic particles with the emulsion to form a Pickering emulsion, and because the hydrophobic particles have strong adhesion to the bubbles, the bubbles can quickly and stably capture the magnetic particles on the membrane surface. Under the action of buoyancy, the bubbles adhere to the magnetic particles and migrate to the liquid surface, solving the problem of clogging of magnetic particles on the membrane surface. Secondly, the bubbles can flush the membrane surface, which also plays a role in cleaning the membrane surface. Summary of the Invention

[0004] The purpose of the present invention is to address the problems of incomplete Pickering emulsion formation, magnetic particle clogging of membrane pores, and dispersed phase contamination of the membrane surface during long-term separation of oil-water emulsions in existing magnetic particle-magnetic membrane systems. By constructing an oil-water emulsion separation system in which bubbles and magnetic particles synergistically improve the membrane's anti-pollution performance, the retained matter (emulsion and magnetic particles) migrates away from the membrane surface, avoiding magnetic particles clogging the membrane pores and emulsion contamination of the membrane surface, thereby achieving stable membrane flux in long-term emulsion separation.

[0005] The present invention specifically achieves its purpose through the following technical solutions:

[0006] (1) Preparation of magnetic nanoparticles by coprecipitation

[0007] First, FeCl2·4H2O and FeCl3·6H2O were dissolved in 125-150 mL of pure water and stirred under nitrogen until completely dissolved. Subsequently, aqueous ammonia was added dropwise to the solution until the pH reached 9-12. The solution was stirred vigorously at 80°C for 20-50 minutes to produce Fe3O4 nanoparticles (Fe3O4 NPs). The mixture was washed several times with deionized water and stored for later use. Next, the Fe3O4 NPs were dispersed in 40 mL of deionized water and sonicated for 20 minutes to form a Fe3O4 NPs suspension. 50-150 mL of anhydrous ethanol, 1-2 mL of aqueous ammonia, and 15-20 mL of the Fe3O4 NPs suspension were mixed and sonicated for 15 minutes. Subsequently, the mixture was stirred vigorously under nitrogen. When the temperature dropped to 30°C, 0.1-1 mL of TEOS was added and reacted for 40-50 minutes. After the reaction is complete, 0.2-1.0 mL of KH-1231 is added dropwise and the reaction continues for 5 hours. Finally, the resulting Fe3O4-KH1231 NPs are collected with a magnet, washed with ethanol, and dried in a vacuum oven for 24 hours. The magnetic particles prepared by this method have a particle size of approximately 10 nm.

[0008] Magnetic particles of 20 nm, 50 nm, 100 nm, and 200 nm (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) were dispersed in 40 mL of deionized water and sonicated for 20 minutes to form a Fe3O4 NPs suspension. 50-150 mL of anhydrous ethanol, 1-2 mL of aqueous ammonia, and 15-20 mL of the Fe3O4 NPs suspension were mixed and sonicated for 15 minutes. Subsequently, the mixture was stirred vigorously under nitrogen. When the temperature dropped to 30°C, 0.1-1 mL of TEOS was added and allowed to react for 40-50 minutes. After the reaction was complete, 0.2-1 mL of KH-1231 was added dropwise and the reaction continued for 5 hours. Finally, the resulting Fe3O4-KH1231 NPs were collected using a magnet, rinsed with ethanol, and dried in a vacuum oven for 24 hours.

[0009] Preferably, FeCl2·4H2O and FeCl3·6H2O are dissolved in 150 mL of pure water, the pH is adjusted to 10 with ammonia, and the stirring time is 50 minutes. The Fe3O4 NPs suspension is mixed with 150 mL of anhydrous ethanol, 1.25 mL of ammonia, and 18 mL of the Fe3O4 NPs suspension, and 0.2 mL of TEOS is added to react for 45 minutes. After the reaction is complete, 0.15 mL of KH-1231 is added dropwise and the reaction is continued for 5 hours.

[0010] (2) Preparation of magnetic film by electrospinning and blending

[0011] The first step is to prepare magnetic nanoparticles within the membrane. 4.5-9.5 g of the Fe₃O₄NPs prepared in (1) were placed in 60 mL of ultrapure water and sonicated for 20 min. Subsequently, 6.5-7.5 g of sodium citrate was added to the solution and stirred vigorously at 60-80°C for 4-6 h. The solution was then recovered and cleaned using a magnet and dried at room temperature for 24 h.

[0012] In the second step, the magnetic nanoparticles prepared in the first step are blended with PVDF and then electrospun to produce a magnetic membrane. PVDF powder and the magnetic nanoparticles prepared in the first step are mixed in a DMF solution and stirred thoroughly at room temperature for 8-12 hours to prepare a spinning solution. The spinning solution is then loaded into a syringe and pumped at a constant rate of 0.15-0.20 mL / h, and the spinning machine is started. After spinning, the electrospun membrane is removed and dried in a vacuum drying oven at 25°C for 24 hours to allow any residual DMF solvent to evaporate.

[0013] Preferably, the electrospinning parameters are: 15 wt% of the charged nanoparticles, 12% of the PVDF concentration, a horizontal syringe width of 80 mm, and a voltage of 14 kV. The receiving drum speed is 500 rpm, and the distance from the needle tip to the collector is approximately 10 cm. The relative humidity and temperature during the electrospinning process are 45°C and 25°C, respectively, and the electrospinning process is maintained for 7 hours.

[0014] (3) Selection of flotation equipment and determination of the gas collection rate of electromagnetic particles

[0015] The flotation technology used is the induced flotation method.

[0016] After adding the electromagnetic particles prepared in (1) into the oil-in-water emulsion, the induced flotation method was performed. An air disc was used to generate bubbles, and a magnet was placed at the liquid surface. The mass of the magnetic particles collected by the magnetic particles was measured after 30 minutes. The magnetic particles collected by the magnet under mechanical stirring were used as a control group.

[0017] Preferably, the induced flotation method uses a circular gas disk with uniform aeration; the gas generation rate is 280 mL / min.

[0018] (4) Testing the separation flux of the air flotation-magnetic particle-magnetic membrane coupling system for oil-water separation

[0019] Oil-in-water emulsions were prepared using n-hexane and deionized water in different volume ratios. The magnetic membrane prepared in (2) was further fixed to the bottom of an oil-water separation device, and the magnetic particles prepared in (1) were added to the device and bubbles were generated using a gas disc. Controllable separation tests and performance evaluations of the oil-in-water emulsions were conducted under different magnetic particle dosages, particle sizes, and gas flow rates.

[0020] The specific steps of the coupled system separation experiment are as follows:

[0021] Step 1: Deionized water and oil were mixed in a volume ratio of 2:98, blended under strong magnetic stirring at 1000 rpm for more than 4 hours and ultrasonicated for 30 minutes to prepare a stable water-in-oil emulsion.

[0022] Step 2: The magnetic particle dosage, particle size, and gas flow rate were adjusted. The water-in-oil emulsion prepared in Step 1 was then poured into the separation device for separation. The entire emulsion separation process was performed by a peristaltic pump. The emulsion was separated continuously for 30 minutes without cleaning the membrane surface. The separation flux of the water-in-oil emulsion was measured every 5 minutes. These steps were repeated to investigate the flux changes during the membrane separation process under different gas flow rates and evaluate the anti-fouling performance of the system.

[0023] Preferably, in step 1, n-hexane is selected as the oil. When preparing an oil-water emulsion containing a surfactant, Span 80 is selected to prepare an oil-in-water emulsion.

[0024] Preferably, in step 2, the magnetic particles are added in an amount of 0.5-2.5 wt % and have a particle size of 10 hm. The gas flow rate is regulated by a gas flow meter, corresponding to gas flow rates of 40 mL / min, 120 mL / min, 200 mL / min, and 280 mL / min. The peristaltic pump tubing is type 17, and the rotation speed is 70 rpm.

[0025] Compared with existing emulsion processing technologies, the magnetic particle-magnetic film coupling based on bubble-assisted emulsion expulsion proposed in the present invention has the following advantages:

[0026] (1) The present invention effectively avoids the problem of limiting the application of membrane technology, such as the deposition of dispersed phase and magnetic particles on the membrane surface, by coupling air flotation, magnetic particles and magnetic membrane. It is an effective strategy in the field of oil-water separation.

[0027] (2) The present invention avoids the use of a large-volume, high-energy-consuming, and complex-process air flotation method by utilizing the high capture efficiency of hydrophobic magnetic particles and bubbles. Instead, it uses only the induced flotation method, which is low-cost, low-energy-consuming, small-footprint, and easy to move. It is an effective strategy that can be easily expanded to treat large-scale wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 System operation flow chart

[0029] Figure 2 (a) Transmission electron microscopy image of Fe3O4 prepared and average particle size (b) Transmission electron microscopy image of 10nm Fe3O4-KH1231NPs prepared by co-precipitation method and average particle size

[0030] Figure 3 The effect of different magnetic particle sizes and dosages on demulsification efficiency

[0031] Figure 4 The flux trend of the system processing emulsion at a gas flow rate of 360 mL / min. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below with reference to the accompanying drawings, but the scope of protection claimed in the present invention is not limited thereto.

[0033] Example 1

[0034] in accordance with Figure 1 , using the adhesion between bubbles and magnetic particles after demulsification, under the action of gravity, the magnetic particles and retained matter (emulsion) are migrated away from the membrane surface, achieving the separation of retained matter and improving the membrane's anti-fouling performance. Bubbles are used to quickly and evenly mix the magnetic particles with the emulsion to form a Pickering emulsion. Due to the strong adhesion between hydrophobic particles and bubbles, the bubbles can quickly and stably capture the magnetic particles on the membrane surface. Under the action of buoyancy, the bubbles adhere to the magnetic particles and migrate to the liquid surface, solving the problem of magnetic particle blockage on the membrane surface. Secondly, the bubbles can flush the membrane surface, which also plays a role in cleaning the membrane surface.

[0035] in accordance with Figure 2 The average size of the prepared Fe3O4-KH1231 nanoparticles is mainly distributed in 12.97±3.38nm, and the average size of Fe3O4 is 10.54±2.95nm.

[0036] Example 3

[0037] In order to explore the effect of magnetic particle size on emulsion demulsification, magnetic particles with particle sizes of 10nm, 20nm, 100nm, and 200nm were selected to demulsify the emulsion, with a dosage of 2wt%. After the emulsion and magnetic particles were evenly mixed, the magnetic particles were collected under a magnetic field, and the water content of the upper layer of the liquid was measured to calculate the demulsification efficiency. Figure 2 The results show that after 10nm magnetic particles are added to the emulsion under sufficient stirring, the demulsification efficiency is 90.23% as measured by a moisture meter, showing a significant demulsification effect. The demulsification efficiency of particles with particle sizes of 20nm, 100nm, and 200nm is 83.73%, 72.51%, and 51.36%, respectively, which is far lower than the demulsification effect of 10nm particles.

[0038] The effect of adding different amounts of magnetic particles to the emulsion on the separation effect was investigated. The addition amount of magnetic particles was 0.5wt%, 1wt%, 1.5wt%, 2wt%, and 2.5wt%. The experimental results are shown in Figure 2. Figure 3 After the magnetic particles were added to the emulsion, the emulsion was agitated by stirring to break the emulsion. As the amount of magnetic particles added increased, the separation efficiency of the emulsion increased significantly. At a dosage of 2wt%, the demulsification efficiency of the particles reached a maximum of 97.79%. However, after continuing to add magnetic particles to 2.5wt%, the demulsification efficiency of the emulsion hardly increased.

[0039] Example 4

[0040] The oil-water emulsion was prepared by using n-hexane and deionized water in a volume ratio of 98:2. The magnetic membrane prepared in (2) was fixed on the bottom of the oil-water separation device, and the magnetic particles prepared in (1) were added to the device. The amount of magnetic particles added was 2 wt%. A gas disc was used to generate bubbles with a gas flow rate of 360 mL / min. The flux of the membrane filtration emulsion within 30 minutes was measured without cleaning the membrane surface to evaluate the long-term anti-fouling performance of the system. Figure 4 As shown, the flux decay rate is 11.78%. A lower decay rate indicates less contamination on the membrane surface, which is more conducive to long-term, continuous, and stable operation. Therefore, our designed bubble-assisted emulsion expulsion magnetic particle-membrane coupling system achieves continuous and efficient separation of oil-in-water emulsions.

Claims

1. An oil-water emulsion separation system that uses bubbles and magnetic particles to synergistically improve the anti-fouling performance of the membrane, characterized in that: The wettable magnetic particles collide with the emulsion in the emulsion to form a Pickering emulsion. The active agent on the surface of the emulsion droplets is replaced by the magnetic particles, and eventually the emulsion droplets are covered by the magnetic particles. The bubbles generated by the air disk at the bottom collide with the magnetic particles gathered on the membrane surface, and the two adhere tightly and firmly. Under the action of buoyancy, the bubbles move toward the water surface, driving the magnetic particles to migrate toward the water surface, thereby migrating the retained matter away from the membrane surface and improving the membrane's anti-fouling performance.

2. According to claim 1, an oil-water emulsion separation system with bubble-magnetic particles synergistically improving the anti-fouling performance of the membrane, the preparation method of the magnetic particles is as follows: FeCl2·4H2O and FeCl3·6H2O are dissolved in 125-150mL of pure water, and stirred under the protection of nitrogen until completely dissolved; then, ammonia water is added dropwise to the above solution until the solution pH is 9-12, and vigorously stirred at 80°C for 20-50min to obtain Fe3O4 nanoparticles (Fe3O4NPs), which are washed several times with deionized water and stored for use; then, the Fe3O4NPs are dispersed in 40mL of deionized water and ultrasonicated for 20min to form a Fe3O4NPs suspension; 50-150mL of anhydrous ethanol, 1-2mL of ammonia water and 15-20mL of The Fe3O4NPs suspension was mixed and ultrasonically treated for 15 minutes; then, it was vigorously stirred under nitrogen protection. When the temperature dropped to 30°C, 0.1-1mL LTEOS was added and reacted for 40-50 minutes. After the reaction was complete, 0.2-1.0mL KH-1231 was added dropwise and the reaction continued for 5 hours. Finally, the Fe3O4-KH1231NPs generated by the reaction were collected with a magnet, washed with ethanol, and placed in a vacuum drying oven for 24 hours. The particle size of the magnetic particles was 10-500nm, and the addition amount was 0-3wt%.

3. According to the oil-water emulsion separation system of claim 1, which uses bubbles and magnetic particles to synergistically improve the anti-pollution performance of the membrane, the preparation method of the magnetic membrane is as follows: 4.5g-9.5g of the Fe3O4 NPs prepared in step (1) is placed in 60mL of ultrapure water and ultrasonicated for 20min; then, 6.5g-7.5g of sodium citrate is added to the above solution, and after vigorously stirring at 60℃-80℃ for 4-6h, it is recovered and cleaned with a magnet and dried at room temperature for 24h; PVDF powder and the prepared magnetic nanoparticles are mixed in DMF solution, and fully stirred at room temperature for 8-12h to obtain a spinning solution; then, the spinning solution is loaded into a syringe and pumped at a fixed speed of 0.15-0.20mL / h, and the spinning machine is started; after spinning, the electrospun membrane is removed and placed in a vacuum drying oven at 25℃ for 24h to facilitate the volatilization of residual DMF solvent.

4. According to claim 1, an oil-water emulsion separation system that uses bubbles and magnetic particles to synergistically enhance the anti-fouling performance of the membrane, characterized in that: The gas flow rate is 360 mL / min, the bubble size is 2-20 μm, and the total cross-sectional area of ​​the bubble per unit volume is 200-500 m 2 / m 3 .

5. The use of the oil-water emulsion separation system for improving the anti-fouling performance of the membrane by synergistically combining air bubbles and magnetic particles according to claim 1, characterized in that: The membrane was clamped to a cross-sectional area of ​​0.84 cm 2 Deionized water and n-hexane were mixed in a volume ratio of 2:98 between circular glass tubes, blended under strong magnetic stirring at 1000 rpm for more than 4 hours and ultrasonicated for 30 minutes to prepare a stable oil-in-water emulsion, which was poured into a separation device for separation. The liquid level was maintained at 10 cm and the separation was carried out under the action of gravity. Bubbles were generated on the membrane surface using an aeration disk at a gas flow rate of 360 mL / min. The emulsion was continuously separated for 30 minutes without cleaning the membrane surface. The separation flux of the oil-in-water emulsion was measured every 5 minutes.

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