Novel membrane preparation method for oil-water emulsion split-phase full-amount recovery

Abstract

A large amount of oil-water emulsion is generated in industrial activities such as petrochemical industry, if the oil-water emulsion is not treated and directly discharged, serious pollution can be caused to the environment, and meanwhile, if contained oil water cannot be effectively recycled, great waste of resources can be caused. The invention discloses a novel membrane for split-phase total recovery of oil-water emulsion, and magnetic nanoparticles (Fe3O4-coated CTAB NPs) are further compounded to the surface of a membrane (PVDF) by regulating and controlling the transient state of electrostatic spinning and electrostatic spraying so as to successfully construct a magnetic response PVDF layered membrane (PVDF-S-CTAB). Under the action of a magnetic field, the magnetic particles orderly protrude upwards, water drops falling to the surface of the film convert falling kinetic energy into capillary energy for storage, and the stored capillary energy is converted into upward bouncing kinetic energy after the kinetic energy is used up, so that directional recovery of the water drops is realized. The prepared PVDF-S-CTAB membrane can efficiently separate water-in-oil emulsion driven only by gravity, the separation efficiency is as high as 15.72 * 10 < 4 > L.m <-2 >. H <-1 >. Bar <-1 >, and the separation efficiency is greater than 99.9% and is 2.5 times that before a magnetic field is applied. Therefore, the magnetic response membrane is expected to provide a strategy and a new thought for recovery after oil-water two-phase efficient separation.

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 a new membrane that can perform full recovery of oil-water emulsion phase separation, and a magnetically responsive PVDF layered membrane based on droplet bouncing behavior is finally obtained through emulsion separation performance testing. Technical Background

[0002] With the increase of industrial activities, especially in the petrochemical, food processing, metal processing and other industries, a large amount of oil-water emulsions are produced. If these emulsions are discharged directly without treatment, they will cause serious pollution to the environment. At the same time, if the oil resources contained in the oil-water emulsions cannot be effectively recovered, it will also lead to a huge waste of resources. Although a variety of oil-water separation technologies have been developed, such as gravity separation, centrifugal separation, flotation separation, adsorption separation, etc., these methods often have problems such as low separation efficiency, high processing cost, and difficulty in processing emulsions. Especially for micro-emulsified oil-water mixtures, due to the extremely small particle size and stable distribution of oil droplets, traditional methods are difficult to effectively separate. Membrane separation technology is widely used in the field of oil-water separation due to its advantages such as simple operation, low energy consumption, and continuous processing. However, to achieve efficient phase separation and full recovery of oil-water emulsions, the following two key technical problems need to be solved: (1) Selection and preparation of membrane materials: It is necessary to develop new membrane materials that not only have good chemical stability and mechanical strength, but also have excellent hydrophobicity or oleophobicity, as well as high selectivity and permeability. (2) Optimization of membrane structure: The microstructure of the membrane has a direct impact on separation performance. High porosity, specific pore size distribution, and surface properties are key to improving separation efficiency and flux.

[0003] In response to the above problems, this technology proposes a new membrane preparation method, which aims to significantly improve the phase separation and full recovery efficiency of oil-water emulsions through innovative material formulations, membrane structure design and preparation processes. This method regulates the transient state of electrospinning and electrostatic spraying, and further compounds magnetic nanoparticles (Fe3O4@CTAB NPs) onto the membrane (PVDF) surface. It successfully constructs a magnetically responsive PVDF layered membrane (PVDF-S-CTAB) with low surface energy and droplet bouncing behavior for emulsion separation under magnetic field response. The prepared PVDF-S-CTAB membrane can efficiently separate oil-in-water emulsions driven only by gravity, with a separation efficiency of up to 15.72×10 4 Lm -2 h -1 bar -1 The new membrane not only efficiently separates oil-water emulsions but also fully recovers the oil and water phases while maintaining separation efficiency, significantly contributing to environmental protection and resource conservation. Summary of the Invention

[0004] The present invention addresses the problem that the oil and water phases cannot be fully recovered after the demulsification and separation of the oil-water emulsion. By constructing a magnetically responsive PVDF layered membrane (PVDF-S-CTAB), the oil / water selectivity is increased while the directional bouncing and recovery of water droplets can be effectively achieved, achieving efficient oil-water separation flux and separation efficiency, and clarifying its mechanism of action for oil-water two-phase recovery.

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

[0006] (1) Preparation of hydrophobically modified ferroferric oxide particles (CFe3O4@CTAB NPs) by coprecipitation

[0007] Weigh 0.20-0.50g of CTAB into a beaker and add 10-50mL of deionized water, stirring to dissolve. Then, weigh 2.13-3.15g of FeCl3·6H2O and 1.10-2.50g of FeCl2·4H2O and add them to the solution, stirring until completely dissolved. Then, add concentrated ammonia dropwise until the pH reaches 12-19. Incubate under nitrogen for 20-60 minutes. Wash the mixture several times with anhydrous ethanol, remove the precipitate, and dry it in an oven at 60°C for 7-15 hours. Grind the dried precipitate, Fe3O4@CTABNPs, and store in a desiccator until ready for use.

[0008] (2) Preparation of magnetically responsive layered membranes by electrospinning and blending

[0009] The first step is to prepare the nanofiber substrate. The fully dried PVDF powder is dissolved in DMF at a concentration of 14-18wt% and stirred at 50°C for 8-12h to prepare the spinning solution. Then, the spinning solution is loaded into a syringe and pumped at a fixed rate of 1.5-3.5mL / h. The syringe is periodically scanned in the horizontal direction with a width of 80-120mm. A voltage of 13-20kV is applied to the needle tip to provide a certain electric field strength. The generated fibers are collected by aluminum foil, which is tightly attached to a grounded metal shaft with a rotation speed of 140-210rpm. The distance from the needle tip to the shaft surface is 20-25cm. The relative humidity is 75±3% and the temperature is 25±2°C. The electrospinning process is maintained for 6-8 hours and then used directly as the substrate for the next step without any treatment. Dilute solutions containing different Fe304@CTAB NPs contents (3, 5, 7 and 9 wt%) and 3 wt% PVDF powder were prepared respectively, and the upper spinning solution was prepared by thorough stirring and dissolution. The upper spinning solution was loaded onto the same electrospinning machine with a solution feed rate of 0.2-0.5 mL / h, and a voltage of 20-25 kV was applied to the needle tip to atomize the solution. The relative humidity was controlled at 75±3% and the temperature was maintained at 25±2°C. The ordinary electrospun fiber membrane prepared in the previous step was placed close to a grounded metal rotating shaft and used as a collector. The distance from the needle tip to the surface of the substrate membrane was fixed at 30-35 cm. The entire spinning process was carried out for 8-10 hours without interruption.

[0010] (3) Characterization of oil-water separation performance of magnetically responsive layered membranes with different hydrophobic magnetic particle contents (3, 5, 7, and 9 wt%) under different magnetic fields

[0011] Step 1:

[0012] First, 0.1 g of surfactant and 2 mL of deionized water were mixed. Then, 98 mL of oil was added and the mixture was sonicated for 30 minutes to produce a highly emulsified water-in-oil emulsion. The resulting water-in-oil emulsion remained stable for at least 12 hours.

[0013] Step 2:

[0014] Oil-water separation performance tests were conducted using a laboratory-built dead-end filtration device. First, the membrane material was placed between two transparent glass containers and secured with clamps. The prepared water-in-oil emulsion was then quickly poured into the glass tube, maintaining a height of 10 cm. The membrane was then subjected to its own gravity and an applied magnetic field, allowing the entire oil-water separation experiment to proceed.

[0015] The permeation flux of oil-water separation is calculated by recording the volume, time, effective membrane area and pressure of the liquid column on the membrane for the emulsion to completely permeate through the membrane. The calculation formula is as follows:

[0016]

[0017] Where J is the permeation flux (L·m -2 ·h -1 bar -1 ), V is the volume of the emulsion that permeates the membrane (L), and A is the effective area of ​​the membrane (m 2 ), Δ t is the filtration time (h), Δ p is the pressure of the liquid column on the membrane (bar).

[0018] The oil-water separation efficiency is calculated by measuring the water content (ppm) in the filtrate after separation of the oil-in-water emulsion using a WS-3000 micro-moisture meter and comparing it with the water content of the original oil-in-water emulsion. The calculation formula is as follows:

[0019]

[0020] Wherein, η0 is the separation efficiency (%), C0 and Cp are the water content (ppm) in the oil before and after emulsion filtration, respectively.

[0021] Compared with existing emulsion processing technologies, the new membrane proposed in the present invention, which can fully recover oil-water emulsions by phase separation, has the following advantages: the present invention targets extremely small particle size and highly stable emulsions. By adjusting the membrane morphology and membrane pore structure, the present invention utilizes stimulus-responsiveness to convert the falling kinetic energy of water droplets falling onto the surface of the PVDF-S-CTAB membrane into capillary energy storage. After the kinetic energy is exhausted, the stored capillary energy is converted into upward kinetic energy, thereby generating bouncing behavior to achieve directional recovery of water droplets. This provides a powerful strategy for ultra-efficient separation of oil-in-water emulsions with low energy consumption, and also provides an innovative idea for the phase separation recovery of oil and water resources after separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Characterization of the oil-water separation performance of different magnetically responsive layered membranes under different magnetic fields. (a1-b1) Diagrams of the separation process of various water-in-oil emulsions at 0T and 0.3T magnetic field strengths; permeation flux and separation efficiency of different types of water-in-oil emulsions treated by different magnetically responsive layered membranes at 0T (a2) and 0.3T (b2), respectively.

[0023] Figure 2 Permeation flux and separation efficiency of different oils using PVDF, PVDF-S-PVDF, 3 wt% PVDF-S-CTAB, 5 wt% PVDF-S-CTAB, 7 wt% PVDF-S-CTAB, and 9 wt% PVDF-S-CTAB membranes at 0 T and 0.3 T, respectively. (a) n-hexane; (b) petroleum ether; (c) 1,2-dichloroethane; (d) dodecane.

[0024] Figure 3 Short-term cyclic permeation flux of PVDF, PVDF-S-PVDF, 3 wt% PVDF-S-CTAB, 5 wt% PVDF-S-CTAB, 7 wt% PVDF-S-CTAB and 9 wt% PVDF-S-CTAB membranes treating n-hexane-water solution at magnetic field strengths of 0 T (a) and 0.3 T (b).

[0025] Figure 4 Water recovery efficiency of PVDF, PVDF-S-PVDF, 3wt% PVDF-S-CTAB, 5wt% PVDF-S-CTAB, 7wt% PVDF-S-CTAB, and 9wt% PVDF-S-CTAB membranes for treating oil-water mixtures with oil-water ratios of 1:1 (a), 2:1 (b), and 3:1 (c), respectively DETAILED DESCRIPTION

[0026] 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.

[0027] Example 1

[0028] like Figure 1 As shown, first, n-hexane-water, petroleum ether-water, 1,2-dichloroethane-water, and dodecane-water emulsions were prepared according to the viscosity and density of the oil, and then separated. The magnetically responsive dynamic membranes 3wt% PVDF-S-CTAB, 5wt% PVDF-S-CTAB, 7wt% PVDF-S-CTAB, 9wt% PVDF-S-CTAB and their control membranes PVDF and PVDF-S-PVDF membranes were respectively loaded into the membrane slot of the oil-water separation device at a magnetic field strength of 0T and 0.3T to conduct oil-water separation experiments ( Figure 1 (a1)(b1)). As shown in the digital photos, the feed emulsion is milky white and opaque, with a large number of water droplets dispersed in the oil. However, after membrane separation, the filtrate becomes clear and transparent without water droplets. The corresponding oil-water separation flux and separation efficiency are shown in Figure 2. Figure 1 As shown in (a2)(b2), compared with PVDF membrane and PVDF-S-PVDF membrane, PVDF-S-CTAB membrane shows higher separation flux and separation efficiency. In particular, 7wt% PVDF-S-CTAB membrane shows excellent performance in treating various oil-in-water emulsions. When a magnetic field of 0.3T is applied, the permeation flux and separation efficiency of PVDF-S-CTAB membrane are improved, and it has good magnetic responsiveness, such as Figure 1 (b2).

[0029] Example 2

[0030] Depend on Figure 2As shown in (a), when the magnetic field gradient is 0T and 0.3T, the PVDF-S-CTAB membrane shows good magnetic responsiveness and the permeation flux is significantly improved. In particular, the dodecane permeation flux of the 7wt% PVDF-S-CTAB membrane has achieved a flux increase of up to 2.5 times. Similarly, n-hexane water emulsion, petroleum ether water emulsion and 1,2-dichloroethane water emulsion all showed a significant increase in permeation flux after the magnetic field gradient increased. Among them, 1,2-dichloroethane water emulsion has a higher permeation flux than other oil products, but its separation efficiency is lower than that of other oil products (above 99%), only 95.99%. However, after the magnetic field gradient changes, its separation efficiency still shows a significant improvement. Therefore, the PVDF-S-CTAB membrane has excellent magnetic response characteristics.

[0031] Example 3

[0032] Considering the complex oil-water system in the actual environment, membrane materials with good stability and anti-fouling properties are crucial. Figure 3 The short-term cyclic permeation flux diagrams of PVDF, PVDF-S-PVDF, 3wt% PVDF-S-CTAB, 5wt% PVDF-S-CTAB, 7wt% PVDF-S-CTAB and 9wt% PVDF-S-CTAB membranes treating n-hexane-containing water solution at 0T and 0.3T are shown in Figure 2. Figure 3 It shows that the modified PVDF-S-CTAB membrane material has excellent cyclic stability compared with PVDF and PVDF-S-PVDF membranes. In particular, the 7wt% PVDF-S-CTAB membrane still maintains ultra-high flux after 10 consecutive cycles of separation, and has certain durability and persistence. It is also surprising that when a magnetic field is applied, the PVDF-S-CTAB membrane material becomes more stable, which may be related to the dynamic mesh protrusions, which can well realize the bouncing of water droplets. Compared with PVDF and PVDF-S-PVDF membranes, the PVDF-S-CTAB membrane can respond to the magnetic field faster and show increased permeation flux and stable cyclic performance. These results show that the PVDF-S-CTAB magnetically responsive layered membrane can be effectively used in actual complex environments, and still has excellent separation performance as well as good durability and stability after multiple cycles.

[0033] Example 4

[0034] Since the magnetically responsive dynamic membrane has excellent magnetic responsiveness and can achieve a droplet bouncing effect, it can effectively recover the water phase in the oil-water separation process and realize the directional recovery of water and oil resources. The directional rebound recovery performance of PVDF-S-CTAB membrane for water resources was measured using oil-water mixtures with oil-water ratios of 1:1, 2:1 and 3:1. Figure 4The results show that compared with PVDF and PVDF-S-PVDF membranes, the PVDF-S-CTAB membrane exhibited excellent water recovery performance for oil-water mixtures with oil-water ratios of 1:1, 2:1, and 3:1. In particular, the 7wt% PVDF-S-CTAB membrane recovered up to 98.26% of water, while the PVDF membrane and PVDF-S-PVDF membrane only recovered 81.31% and 81.34% of water, respectively. Furthermore, when a magnetic field gradient of 0.3T was applied, the water recovery rate of the PVDF-S-CTAB membrane was significantly improved.

[0035] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

[0036] In summary, the present invention provides a novel membrane for phase separation and full recovery of oil-water emulsions. Oil-water separation experiments demonstrate that the PVDF-S-CTAB membrane exhibits excellent permeation flux and separation efficiency for any oil-water emulsion, particularly when a magnetic field is applied, achieving a flux increase of up to 2.5 times. Oil-water separation and recovery experiments demonstrate that the PVDF-S-CTAB membrane can achieve efficient simultaneous recovery of both oil and water phases, representing a novel and effective strategy for practical oil-water separation processes.

Claims

1. A novel membrane preparation method for phase separation and full recovery of oil-water emulsion; characterized by: The new membrane is a magnetically responsive PVDF layered membrane formed by compounding magnetic nanoparticles (NPs) onto an electrospun fiber membrane. The membrane forms an ultra-thin and highly porous microsphere mesh hydrophobic surface. Under the action of the magnetic particles in response to the magnetic field, peak-like protrusions are formed to achieve directional bouncing of water droplets, thereby improving the flux and efficiency of oil-water two-phase separation. The magnetic nanoparticles are hydrophobically modified ferrosoferric oxide particles (Fe3O4@CTAB NPs); and the electrospun fiber membrane is formed by stacking polyvinylidene fluoride (PVDF) electrospun fibers.

2. A novel membrane preparation method for phase separation and full recovery of an oil-water emulsion according to claim 1, characterized in that: The following steps are involved: S1, preparation of hydrophobically modified Fe3O4@CTAB NPs; S2, preparing a nanofiber substrate with an added content of 10-14 wt% PVDF; S3, adding the Fe3O4@CTAB NPs prepared in step S1 to the dilute solution of PVDF powder, and stirring and dissolving the mixture to obtain an upper spinning solution; S4. The spinning solution is loaded into a syringe and sprayed onto the PVDF nanofiber substrate prepared in step S2. The entire spinning process is carried out for 6-8 hours.

3. The preparation method according to claim 2, wherein: In step S1, 0.3-0.5 g of hexadecyltrimethylammonium bromide (CTAB) is weighed and placed in a beaker, and 20-40 mL of deionized water is added and stirred to dissolve; then 2-3 g of FeCl3·6H2O and 1-2 g of FeCl2·4H2O are weighed and added to the above solution, and stirred until completely dissolved; then concentrated ammonia water is added dropwise until the pH reaches 10-12, and the mixture is reacted for 30 minutes under nitrogen protection; in step S2, fully dried PVDF powder is dissolved in N,N-dimethylformamide (DMF) at a concentration of 10-14 wt%, and stirred at 50° C. for 6-8 hours to prepare a spinning solution; then, the spinning solution is loaded into a syringe and pumped at a fixed rate of 1.5-2.0 mL / h. The syringe is periodically scanned in the horizontal direction with a width of 80-100 mm; a voltage of 13-15 kV is applied to the needle tip to provide a certain electric field strength; the generated fibers are collected by aluminum foil, which is tightly attached to a grounded metal shaft, and the rotation speed is 140 rpm; the distance from the needle tip to the shaft surface is 20 cm; the relative humidity is 75±3% and the temperature is 25±2°C; the electrospinning process is maintained for 6 hours; the steps S3 and S4 respectively prepare Fe3O4@CTAB containing different A dilute solution of NPs content (3, 5, 7 and 9 wt%) and 3 wt% PVDF powder was used as the spinning solution; the electrospinning solution feed rate was 0.2-0.5 mL / h, and a voltage of 18-20 kV was applied to the needle tip to atomize the solution; the relative humidity was controlled at 75±3%, and the temperature was maintained at 25±2°C; the ordinary electrospun fiber membrane prepared in the previous step was placed tightly on a grounded metal rotating shaft and used as a collector; the distance from the needle tip to the surface of the substrate membrane was fixed at 30 cm, and the magnetically responsive PVDF layered membrane was obtained by spinning for 8 h.

4. An application of the novel membrane according to claim 3 in full recovery of oil-water emulsion phase separation; characterized in that: According to the different properties of oil products, four different oil-in-water emulsion systems were prepared, namely n-hexane-in-water emulsion, petroleum ether-in-water emulsion, 1,2-dichloroethane-in-water emulsion and dodecane-in-water emulsion; Span 80 was used as a surfactant to stabilize the emulsion. First, 0.1g of Span 80 was mixed with 2mL of deionized water to prepare 4 parts of such aqueous solution; then 98mL of oil (n-hexane, petroleum ether, 1,2-dichloroethane and dodecane) was added respectively and the oil-water mixture was ultrasonicated for 30min to obtain a highly emulsified oil-in-water emulsion; the prepared oil-in-water emulsion can maintain a stable state for at least 12h; single gravity, short-term and long-term cyclic separation tests were carried out under the action of a magnetic field. The single gravity test was carried out using a laboratory-made dead-end filtration device. The membrane material was placed between two transparent glass containers and fixed with a clamp; the prepared oil-in-water emulsion was then quickly poured into a glass tube, and the emulsion height was always maintained at 10cm; in the short-term cyclic experiment , after 10mL of n-hexane-water emulsion was quickly poured into the dead-end device, the volume of the filtrate that permeated within 1 minute was measured; after the filtration was completed, the membrane was immediately rinsed with ethanol solution to remove pollutants on the membrane surface, and then the membrane was used to perform the next cycle of oil-water separation experiment, which was repeated 10 times; in the long-term circulation experiment, ethanol was first continuously permeated through the membrane and separated continuously for 3 minutes to test the ethanol flux of the membrane, and then the n-hexane-water emulsion was poured into the dead-end device for continuous separation of the oil-water emulsion; the filtrate volume was recorded every 5 minutes, and the filtration was continuous for 30 minutes, and then the membrane was removed for cleaning; after cleaning, ethanol was continued to be filtered for 3 minutes and the oil-water emulsion for 30 minutes, and the cycle was repeated 2.5 times.

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