High-flux composite filter paper for emulsified oil separation as well as preparation method and application of high-flux composite filter paper

Abstract

The invention provides high-flux composite filter paper for emulsified oil separation as well as a preparation method and application thereof, and relates to the field of oil-water separation materials. The composite filter paper comprises a modified body paper layer and a nanofiber layer, wherein the nanofiber layer is arranged on the surface of one side or two sides of the modified body paper layer. The nanofiber layer is prepared from raw materials including a framework polymer, a wettability regulating agent and nano reinforced particles. The modified body paper layer is prepared from raw materials including main body fibers, auxiliary oil guide fibers and functional additives. The composite filter paper with high interception efficiency, high flux, strong pollution resistance and excellent long-term stability is obtained, can meet the urgent requirements on high-performance separation materials in the scenes of industrial oily wastewater treatment and the like, and is particularly suitable for separating oil-water systems taking water as a continuous phase, namely oil-in-water emulsion, and the like. For example, the method can be applied to industrial oily wastewater treatment, emergency treatment of offshore oil spill and other scenes.

Description

Technical Field

[0001] This invention relates to the field of oil-water separation materials, specifically to a high-throughput composite filter paper for emulsified oil separation, its preparation method, and its application. Background Technology

[0002] In industrial sectors (such as machining and petrochemicals), oily wastewater contains over 70% emulsified oil, with particle sizes mostly concentrated between 1 and 5 μm. This emulsified oil is characterized by high stability and difficulty in separation. Traditional oil-water separation technologies (such as gravity sedimentation and centrifugal separation) suffer from low efficiency and high energy consumption. Filter media (such as oil-water separation filter paper and nanofiber membranes) are commonly used in many oil-water separation scenarios due to their ease of operation and flexible application. However, traditional filter paper or single-function separation materials often face a dilemma when dealing with multiple performance requirements, including high retention rate, high throughput, long-term stability, and anti-fouling properties. The root cause lies in the failure to systematically address the following three interrelated core contradictions: First, there is an inherent contradiction between filtration precision and flux: to improve the rejection rate of tiny oil droplets, it is often necessary to reduce the pore size of the material or densify the structure, but this inevitably leads to a surge in fluid resistance and a sharp drop in flux. For example, although electrospun nanofiber membranes can achieve high-precision rejection, their self-supporting structure lacks a large-pore flow-guiding layer, and their flux is generally below 200 L / (m²). 2 ·h), which is insufficient to meet the throughput requirements of industrial processing. Conversely, support materials with high porosity have insufficient retention accuracy.

[0003] Second, there is a persistent contradiction between separation efficiency and operational stability: many modified filter media have acceptable initial separation efficiency, but when dealing with emulsions, the trapped oil droplets tend to adhere, accumulate, and irreversibly block the pores, leading to a rapid decline in throughput and a decrease in separation efficiency. The materials need to be frequently regenerated or replaced, resulting in high operating costs.

[0004] Third, the interface contradiction between composite structure and intrinsic strength: To balance multiple functions, composites are a common approach, but the interfacial bonding between functional layers with different physicochemical properties (such as hydrophilic nanofiber layers and porous support layers) often becomes a weak link. For example, the "meltblown-base paper-meltblown" structure disclosed in patent document CN104911945A has similar functions for each layer (all are interception), failing to form a relay synergy of demulsification and flow conduction, and the interfacial bonding mechanism has not been specially optimized, raising doubts about the durability of the overall structure under complex fluid impact.

[0005] In summary, existing technologies struggle to systematically and synergistically address the coexisting challenges of high retention, high throughput, strong anti-fouling properties, and high interfacial stability. Therefore, providing an oil-water separation material that can simultaneously meet these multiple requirements has become a pressing technical problem in this field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of existing oil-water separation materials in that they cannot simultaneously achieve high retention, high throughput, strong anti-fouling and high interfacial stability, thereby providing a high-throughput composite filter paper for emulsified oil separation, its preparation method and application.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a high-throughput composite filter paper for emulsified oil separation, comprising a modified base paper layer and a nanofiber layer, wherein the nanofiber layer is disposed on one or both surfaces of the modified base paper layer and is formed by hot pressing. The modified base paper layer has a thickness of 0.55~0.70 mm and a pore size of 5~25 μm; The thickness of the nanofiber layer is 8~20 μm, and the pore size is 0.5~3 μm; The raw materials for preparing the modified base paper layer, by weight, include: 40-70 parts of main fiber, 10-25 parts of auxiliary oil-conducting fiber, and 1.2-10 parts of functional additives, wherein the main fiber is selected from at least one of bamboo fiber and wood pulp fiber, and the auxiliary oil-conducting fiber is selected from at least one of polyester fiber (PET) and polypropylene fiber (PP). The raw materials for preparing the nanofiber layer, by weight, include: 60-90 parts of a backbone polymer, 10-30 parts of a wettability regulator, and 1-8 parts of nano-reinforcing particles. The backbone polymer is selected from at least one of polyhydroxyalkanoate (PHA), polylactic acid (PLA), and polycaprolactone (PCL). The wettability regulator is selected from at least one of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). The nano-reinforcing particles are oxide nanoparticles with surface modification by a silane coupling agent.

[0008] Furthermore, by weight, the raw materials for preparing the modified base paper layer include: 50-60 parts of main fiber, 15-20 parts of auxiliary oil-guiding fiber, and 2.5-6.5 parts of functional additives.

[0009] Furthermore, by weight, the raw materials for preparing the nanofiber layer include: 70-80 parts of the backbone polymer, 15-25 parts of the wettability regulator, and 5-6 parts of the nano-reinforcing particles.

[0010] Furthermore, the thickness of the modified base paper layer is 0.60~0.65 mm, and the pore size is 8~15 μm, preferably 8~12 μm.

[0011] Furthermore, the thickness of the nanofiber layer is 10~15 μm, and the pore size is 1.0~2.0 μm, preferably 1.0~1.8 μm.

[0012] Furthermore, the basis weight of the modified base paper layer is 170~200 g / m³. 2 Preferably, it is 175~190 g / m 2 .

[0013] Furthermore, the length of the auxiliary oil-guiding fiber is 2-6 mm, preferably 3-5 mm, and more preferably 3-4 mm.

[0014] Furthermore, the functional additives include the following raw materials in parts by weight: 0.5-3 parts wet strength agent, 0.5-5 parts dispersant, and 0.2-2 parts environmentally friendly waterproofing agent.

[0015] Furthermore, the functional additives include the following raw materials in parts by weight: 1-2 parts wet strength agent, 1-3 parts dispersant, and 0.5-1.5 parts environmentally friendly waterproofing agent.

[0016] Furthermore, the wet strength agent is polyamide epichlorohydrin resin (PPE); the dispersant is sodium carboxymethyl cellulose (CMC-Na); and the environmentally friendly waterproofing agent is waterborne polyurethane (WPU).

[0017] Furthermore, the nano-reinforcing particles are selected from at least one of silane-modified silica (SiO2) nanoparticles and silane-modified titanium dioxide (TiO2) nanoparticles.

[0018] Furthermore, the particle size of the nano-reinforcing particles is 10~50 nm, preferably 20~40 nm, and more preferably 25~30 nm.

[0019] Furthermore, the preparation method of the nano-reinforced particles includes the following steps: dispersing oxide nanoparticles (such as SiO2) in anhydrous ethanol, adding a silane coupling agent (such as KH550), refluxing and stirring at 60~80 °C for 4~6 h, centrifuging, washing, and drying to obtain the nano-reinforced particles.

[0020] Furthermore, the ratio of oxide nanoparticles, anhydrous ethanol, and silane coupling agent is 10 g: 200 mL: 2 g.

[0021] Furthermore, the mixture was refluxed and stirred at 70 °C for 5 h.

[0022] Secondly, the present invention provides a method for preparing the high-throughput composite filter paper for emulsified oil separation, comprising the following steps: (1) Mix the main fiber and auxiliary oil-conducting fiber in proportion and then pulp them. Add functional additives to the pulp and then form it into paper. After dehydration and drying, the modified base paper layer is obtained. (2) The skeleton polymer, wettability regulator and nano-reinforcing particles are mixed in proportion and then a solvent is added. The mixture is mixed evenly to obtain a spinning solution. Electrospinning is performed using the spinning solution to obtain the nanofiber layer. (3) The nanofiber layer is covered on one or both sides of the modified base paper layer, hot-pressed and cooled to obtain the high-throughput composite filter paper for emulsified oil separation.

[0023] Further, in step (1), the pulping concentration is 1.5%~3.0%, preferably 1.8%~2.5%, more preferably 1.8%~2.2%; the main fiber pulping degree is 30~60 °SR, preferably 35~50 °SR; the auxiliary oil-conducting fiber pulping degree is 15~30 °SR, preferably 18~25 °SR.

[0024] Further, in step (1), the diluted wet strength agent, dispersant and environmentally friendly waterproofing agent are added to the slurry in sequence. Each time a functional additive is added, the mixture is stirred at 400-600 rpm for 20-40 min, preferably at 500 rpm for 30 min. The concentration of the slurry after adding the functional additive is 1.5%-2.5%, preferably 1.8%-2.2%, and more preferably 1.9%-2.1%.

[0025] Further, in step (1), the drying conditions are: drying at 100~110 ℃ for 1.5~3 h, preferably drying at 105 ℃ for 2 h.

[0026] Further, in step (1), the main fibers are pretreated before pulping: the main fibers are soaked in deionized water at 50~70 ℃ for 1~3 h, stirred at 200~400 rpm during soaking, filtered, and dried at 70~90 ℃ for 3~5 h. Preferably, the main fibers are soaked in deionized water at 60 ℃ for 2 h, stirred at 300 rpm during soaking, filtered, and dried at 80 ℃ for 4 h.

[0027] Further, in step (2), the solvent is a mixture of a polar organic solvent and water, and the volume ratio of the polar organic solvent to water is 3~4:1~2.

[0028] Furthermore, the polar organic solvent is selected from at least one of N,N-dimethylformamide (DMF) and dichloromethane.

[0029] Further, in step (2), the mixing conditions are: stirring at 50~70 ℃ and 600~1000 rpm for 1~3 h, preferably at 60 ℃ and 800 rpm for 2 h.

[0030] Furthermore, in step (2), the mass concentration of the spinning solution is 6%~12%, preferably 7%~10%.

[0031] Further, in step (2), the electrospinning conditions are as follows: spinning voltage 15~25 kV, preferably 16~22 kV; receiving distance 12~25 cm, preferably 12~20 cm; spinning speed 0.3~1.0 mL / h, preferably 0.4~0.8 mL / h; ambient temperature 20~30 ℃, preferably 23~27 ℃, more preferably 25 ℃; relative humidity 30%~60%, preferably 40%~50%, more preferably 45%.

[0032] Further, in step (3), the hot-pressing composite conditions are: hot-pressing temperature 70~100 ℃, preferably 75~90 ℃; pressure 0.2~0.6 MPa, preferably 0.2~0.5 MPa; hot-pressing time 20~90 s, preferably 20~60 s.

[0033] The design of this hot-pressing temperature range is based on the following: for the selected backbone polymers (PLA, PHA, PCL), this temperature effectively promotes the movement of their polymer chain segments, thereby achieving a strong bond through interfacial diffusion and physical entanglement in close contact with the modified base paper fibers. Simultaneously, the upper limit of this temperature is far below the melting point of polymers such as PLA, and combined with a short hot-pressing time, it ensures that the porous structure of the nanofiber layer is not damaged. Furthermore, this temperature also facilitates the relaxation of the wettability regulator (PVA / PVP) molecular chains, promoting their interaction with the nano-reinforcing particles and the modified base paper fibers, further enhancing interfacial stability and functional durability.

[0034] Thirdly, the present invention provides the application of the high-throughput composite filter paper for emulsified oil separation, or the high-throughput composite filter paper for emulsified oil separation obtained by the preparation method, in industrial oily wastewater treatment or marine oil spill emergency response.

[0035] The high-flux composite filter paper for emulsified oil separation provided by this invention comprises a modified base paper layer and a nanofiber layer, with the nanofiber layer disposed on one or both surfaces of the modified base paper layer. The nanofiber layer is prepared from raw materials including a backbone polymer (polyhydroxyalkanoate, polylactic acid, polycaprolactone), a wetting modifier (polyvinyl alcohol, polyvinylpyrrolidone), and nano-reinforcing particles. The modified base paper layer is prepared from raw materials including main fibers, auxiliary oil-guiding fibers, and functional additives. The modified base paper layer provides mechanical support, ensures overall strength, and forms large-pore flow channels, while the nanofiber layer, with its smaller pore size, is responsible for providing the demulsification interface and fine filtration function.

[0036] By synergistically integrating a "skeleton polymer, wettability regulator, and nano-reinforcing particles" at the molecular and microscopic scales, a stable hydrophilic / underwater oleophobic gradient interface is constructed within the composite filter paper. Through the gradient design and functional relay of a "nanofiber functional layer and modified base paper support layer" at the macroscopic structural level, a separation mechanism of "surface contact demulsification" and "deep oleophilic conduction" is achieved. A hot-pressing composite process ensures a robust yet non-clogging interfacial bond between the multi-layered structures. This invention yields a composite filter paper with high retention efficiency, high throughput, strong anti-fouling properties, and excellent long-term stability, meeting the urgent need for high-performance separation materials in industrial oily wastewater treatment and other similar scenarios.

[0037] Composition and function of modified base paper layer: The main fibers are the basis for forming the modified base paper layer.

[0038] The auxiliary oil-guiding fibers have low surface energy and oleophilic properties. Their core function is to provide a low-interfacial-energy migration path for oil droplets that have passed through the nanofiber layer and begun to coalesce during filtration, guiding the droplets rapidly away from the main filtration zone along the fiber direction, thereby significantly alleviating deep clogging and maintaining high throughput. Simultaneously, their high modulus enhances the wet strength of the modified base paper.

[0039] Composition and function of nanofiber layers: The role of the backbone polymer is to form the fiber network backbone and provide wet strength. Its inherent hydrophobicity creates a thermodynamic difference with the subsequent components, which is the basis for constructing gradient structures.

[0040] The role of wettability regulators is to provide strong hydrophilic groups. During electrospinning and post-treatment, due to their difference in compatibility with the backbone polymer, they tend to migrate to the fiber surface, thereby forming a gradient distribution of "hydrophobic core-hydrophilic shell" in the fiber cross section. This is the key to achieving a stable underwater superoleophobic interface.

[0041] The role of nano-reinforcing particles: First, they serve as physical cross-linking points to enhance the mechanical strength of fiber membranes; second, their surface functional groups can "anchor" the molecular chains of wettability regulators through chemical action, preventing their loss during long-term use or in humid and hot environments, thus ensuring functional durability.

[0042] The inventiveness of this invention lies mainly in the following three interconnected and indispensable synergistic levels, which together constitute the core means to resolve the technical contradictions in the field of emulsified oil separation: I. Synergy between Molecular and Microstructure: Constructing a Durable and Stable Hydrophilic-Oleophobic Gradient Interface This invention does not simply blend hydrophilic materials (such as PVA) with hydrophobic materials (such as PLA). Instead, it actively constructs a heterogeneous gradient microstructure within nanofibers through the specific compatibility of "backbone polymer, wetting modifier, and nano-reinforcing particles." Specifically, the inherent thermodynamic incompatibility between the wetting modifier (such as PVA) and the backbone polymer (such as PLA) drives the hydrophilic segments to migrate to the fiber surface during electrospinning and post-treatment. Simultaneously, the nano-reinforcing particle component (such as SiO2 nanoparticles modified with silane coupling agent) "anchors" the molecular chains of the wetting modifier, locking this migration trend. This results in a stable and durable "hydrophobic core-hydrophilic shell" gradient heterostructure on a single nanofiber. This design lays the foundation for high and persistent retention rates.

[0043] II. Functional Synergy of Macrostructure: Achieving a Relay Mechanism Between "Demulsification" and "Flow Guidance" This invention breaks through the limitations of traditional composite filter materials where each layer has a single or similar function. It creatively proposes a gradient pore size and wettability relay design between a "nanofiber functional layer" and a "modified base paper support layer." The nanofiber layer, with its fine pore size and the aforementioned gradient interface, primarily performs the functions of "contact demulsification" and "fine interception," acting as a "precision demulsification screen" responsible for intercepting and coalescing emulsifying oil droplets. Meanwhile, the modified base paper layer, by introducing oleophilic auxiliary oil-guiding fibers (such as PET), primarily performs the functions of "macroscopic flow guidance" and "oil phase transport," acting as a "high-speed flow channel" responsible for capturing and rapidly transporting the coalesced oil droplets. Under pressure, the oil droplets, demulsified and initially coalesced by the nanofiber layer, enter the macroporous flow channel of the modified base paper layer. They are then captured by the surface of the auxiliary oil-guiding fibers and guided to rapidly migrate away along the fiber direction, thus transforming the potentially clogging "oil droplets" into an easily discharged "oil flow." This functional zoning and relay design based on wettability differences—"fine surface demulsification - deep oleophilic flow guidance"—is the core of achieving both high retention rate and high throughput, while significantly reducing throughput decay (anti-fouling, delaying channel blockage).

[0044] III. Interfacial Synergy of Materials and Processes: Achieving a Unified Combination of High Strength and High Porosity To address the challenge of balancing interlayer bonding strength and porosity in composite filter materials, this invention abandons conventional adhesive bonding processes and employs temperature- and pressure-controlled hot-pressing composite technology. The selection of a specific temperature window is based on fully activating the mobility of all selectable polymer chain segments while remaining well below their melting points. Short-duration hot pressing within this window effectively activates the chain segment movement of each polymer component to promote interfacial diffusion and physical entanglement, while strictly preventing the melting and collapse of the nanofiber layer, achieving a strong yet pore-free interfacial bond. This process achieves a high-strength, integrated, and robust interlayer bond without introducing third-party blockages, ensuring the overall structural durability of the composite filter paper under high-pressure, high-shear filtration environments and fundamentally solving the problem of easy layer peeling.

[0045] The technical solution of this invention has the following advantages: 1. High efficiency and high throughput: With an emulsified oil rejection rate >96%, the pure water throughput exceeds 400 L / (m³). 2 The low flux decay rate breaks the deadlock of traditional technologies where "retention and flux" and "efficiency and stability" are difficult to achieve simultaneously.

[0046] 2. Excellent stability: The hot pressing process is used to composite each layer, which enhances the interlayer bonding force and interface stability without destroying the pore structure, while achieving physical bonding between layers. Combined with the anchoring effect of nano-reinforcing particles, the functional and structural stability of the material is ensured during long-term use.

[0047] 3. Green and sustainable: The main material of the filter paper is made of biodegradable polymer and natural plant fiber (main fiber). The process is environmentally friendly and meets the green requirements of low energy consumption preparation, degradable materials and low pollutant emissions throughout the entire life cycle under the "dual carbon" policy.

[0048] 4. Wide range of applications: It is suitable for various types of oils and complex working conditions, especially for separating oil-water systems with water as the continuous phase, i.e., oil-in-water emulsions. It exhibits excellent and stable high rejection rate and high throughput for oil-in-water emulsions composed of different types of oils, and has wide applicability. It can be applied to industrial oily wastewater treatment, emergency response to marine oil spills, and other scenarios. Detailed Implementation

[0049] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0050] Table 1. Sources of raw materials

[0051] KH550 modified SiO2 nanoparticles were prepared as follows: 10 g of SiO2 nanoparticles were dispersed in 200 mL of anhydrous ethanol and sonicated for 30 min. 2 g of KH550 was added, and the mixture was refluxed and stirred at 70 ℃ for 5 h. After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, and dried in a vacuum drying oven at 60 ℃ for 12 h to obtain KH550 modified SiO2 nanoparticles.

[0052] The preparation method of KH550 modified TiO2 nanoparticles is the same as that of KH550 modified SiO2 nanoparticles, except that SiO2 is replaced with an equal mass of TiO2 nanoparticles.

[0053] Instruments and preparation sources: Paper machine: RK-2A-KWT, PTI GmbH, Austria; Electrospinning equipment: JDF05, Nayi Instrument Technology Co., Ltd.; Hot pressing equipment: BD-8820-A-3, Baoding Precision Instruments Co., Ltd.

[0054] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All raw materials or instruments used are commercially available conventional products, including but not limited to those used in the embodiments of this application.

[0055] Example 1 This embodiment provides a high-throughput composite filter paper for emulsified oil separation, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0056] The raw materials for preparation are as follows: Modified base paper layer: bamboo fiber, polyester fiber (4 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 55:18:1.5:2:1.

[0057] Nanofiber layer: polylactic acid, polyvinyl alcohol and KH550 modified SiO2 nanoparticles (particle size 30 nm) in a mass ratio of 70:25:5.

[0058] The preparation steps are as follows: (1) Preparation of modified base paper layer: Bamboo fiber was soaked in deionized water at 60 ℃ for 2 h, stirred at 300 rpm to remove surface impurities, filtered, and dried at 80 ℃ for 4 h. The treated bamboo fiber and polyester fiber were mixed in a certain proportion, and deionized water was added to make a pulp with a pulping concentration of 2.0%, a pulping degree of 45 °SR for bamboo fiber and a pulping degree of 22 °SR for polyester fiber. Diluted polyamide epichlorohydrin resin, sodium carboxymethyl cellulose, and waterborne polyurethane were added to the slurry sequentially. For each functional additive added, the mixture was stirred at 500 rpm for 30 min. The slurry concentration after adding the functional additives was 2.0%. The pulp was formed on a paper machine, dehydrated by suction, and dried at 105 °C for 2 h to obtain a modified base paper layer (basis weight 185 g / m²). 2 (Thickness 0.62 mm, pore size 10 μm). (2) Preparation of nanofiber layer: Polylactic acid, polyvinyl alcohol and KH550 modified SiO2 nanoparticles were mixed in a certain proportion and then added to a DMF / water mixed solvent (DMF:water = 7:3, v / v). The mixture was stirred at 60 ℃ and 800 rpm for 2 h to obtain a spinning solution with a mass concentration of 9%. Electrospinning was performed using a spinning solution in an electrospinning apparatus. The spinning voltage was 20 kV, the receiving distance was 18 cm, the spinning speed was 0.6 mL / h, the ambient temperature was 25 ℃, and the relative humidity was 45%, resulting in a nanofiber layer (12 μm thick, 1.5 μm pore size). (3) Preparation of composite filter paper: A layer of nanofibers was coated on each side of the modified base paper layer, and the paper was placed in a hot press for lamination. The hot pressing temperature was 85 ℃, the pressure was 0.4 MPa, and the hot pressing time was 45 s. After cooling, the composite filter paper was obtained.

[0059] Example 2 This embodiment provides a high-throughput composite filter paper for emulsified oil separation, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0060] The raw materials for preparation are as follows: Modified base paper layer: softwood pulp fiber, polypropylene fiber (3 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 50:20:2:3:1.5.

[0061] Nanofiber layer: polyhydroxyalkanoate, polyvinylpyrrolidone and KH550 modified TiO2 nanoparticles (particle size 25nm) in a mass ratio of 75:20:5.

[0062] The preparation steps are as follows: (1) Preparation of modified base paper layer: The softwood pulp fiber was soaked in deionized water at 60 ℃ for 2 h, stirred at 300 rpm to remove surface impurities, filtered, and dried at 80 ℃ for 4 h. The treated softwood pulp fiber and polypropylene fiber were mixed in a certain proportion, and deionized water was added to make pulp. The pulping concentration was 1.8%, the freeness of the softwood pulp fiber was 40 °SR, and the freeness of the polypropylene fiber was 18 °SR. Diluted polyamide epichlorohydrin resin, sodium carboxymethyl cellulose, and waterborne polyurethane were added to the slurry sequentially. For each functional additive added, the mixture was stirred at 500 rpm for 30 min. The slurry concentration after adding the functional additives was 1.9%. The pulp was formed on a paper machine, dehydrated by suction, and dried at 105 ℃ for 2 h to obtain a modified base paper layer (basis weight 180 g / m²). 2 (Thickness 0.60 mm, pore size 12 μm). (2) Preparation of nanofiber layer: Polyhydroxyalkanoate, polyvinylpyrrolidone and KH550 modified TiO2 nanoparticles were mixed in a certain proportion and then added to a DMF / water mixed solvent (DMF:water = 6:4, v / v). The mixture was stirred at 60 ℃ and 800 rpm for 2 h to obtain a spinning solution with a mass concentration of 8%. Electrospinning was performed using a spinning solution in an electrospinning apparatus. The spinning voltage was 18 kV, the receiving distance was 15 cm, the spinning speed was 0.5 mL / h, the ambient temperature was 25 ℃, and the relative humidity was 45%, resulting in a nanofiber layer (10 μm thick, 1.2 μm pore size). (3) Preparation of composite filter paper: A layer of nanofibers was coated on each side of the modified base paper layer, and the paper was placed in a hot press for lamination. The hot pressing temperature was 80 ℃, the pressure was 0.3 MPa, and the hot pressing time was 30 s. After cooling, the composite filter paper was obtained.

[0063] Example 3 This embodiment provides a high-throughput composite filter paper for emulsified oil separation, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0064] The raw materials for preparation are as follows: Modified base paper layer: bamboo fiber, polyester fiber (4 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 60:15:1:1:0.5.

[0065] Nanofiber layer: polyhydroxyalkanoate, polyvinyl alcohol and KH550 modified SiO2 nanoparticles (particle size 30 nm) in a mass ratio of 80:15:5.

[0066] The preparation steps are as follows: (1) Preparation of modified base paper layer: Bamboo fiber was soaked in deionized water at 60 ℃ for 2 h, stirred at 300 rpm to remove surface impurities, filtered, and dried at 80 ℃ for 4 h. The treated bamboo fiber and polyester fiber were mixed in a certain proportion, and deionized water was added to make a pulp with a beating concentration of 2.2%, a beating degree of 50 °SR for bamboo fiber, and a beating degree of 25 °SR for polyester fiber. Diluted polyamide epichlorohydrin resin, sodium carboxymethyl cellulose, and waterborne polyurethane were added to the slurry sequentially. For each functional additive added, the mixture was stirred at 500 rpm for 30 min. The slurry concentration after adding the functional additives was 2.1%. The pulp was formed on a paper machine, dehydrated by suction, and dried at 105 °C for 2 h to obtain a modified base paper layer (basis weight 190 g / m²). 2 (Thickness 0.65 mm, pore size 8 μm); (2) Preparation of nanofiber layer: Polyhydroxyalkanoate, polyvinyl alcohol and KH550 modified SiO2 nanoparticles were mixed in a certain proportion and then added to a DMF / water mixed solvent (DMF:water = 8:2, v / v). The mixture was stirred at 60 ℃ and 800 rpm for 2 h to obtain a spinning solution with a mass concentration of 10%. Electrospinning was performed using a spinning solution in an electrospinning apparatus. The spinning voltage was 22 kV, the receiving distance was 20 cm, the spinning speed was 0.8 mL / h, the ambient temperature was 25 ℃, and the relative humidity was 45%, resulting in a nanofiber layer (thickness 15 μm, pore size 1.8 μm). (3) Preparation of composite filter paper: A layer of nanofibers was coated on each side of the modified base paper layer, and the paper was placed in a hot press for lamination. The hot pressing temperature was 90 ℃, the pressure was 0.5 MPa, and the hot pressing time was 60 s. After cooling, the composite filter paper was obtained.

[0067] Example 4 This embodiment provides a high-throughput composite filter paper for emulsified oil separation. The raw materials and preparation steps are the same as in Example 1. The only difference is that in step (3), a nanofiber layer is composited only on one side of the modified base paper layer. The hot pressing temperature is 75 ℃, the pressure is 0.2 MPa, and the hot pressing time is 20 s.

[0068] Comparative Example 1 This comparative example provides a nanofiber membrane, and the specific preparation steps are as follows: Polylactic acid, polyvinyl alcohol and KH550 modified SiO2 nanoparticles were mixed in a mass ratio of 70:25:5 and then DMF / water mixed solvent (DMF:water = 7:3, v / v) was added. The mixture was stirred at 60 ℃ and 800 rpm for 2 h to obtain a spinning solution with a mass concentration of 9%. Electrospinning was performed using a spinning solution in an electrospinning apparatus. The spinning voltage was 20 kV, the receiving distance was 18 cm, the spinning speed was 0.6 mL / h, the ambient temperature was 25 ℃, and the relative humidity was 45%, resulting in a nanofiber membrane (thickness 25 μm, pore size 1.5 μm).

[0069] Comparative Example 2 This comparative example provides a composite filter paper, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0070] Raw materials for preparation: (KH550 modified SiO2 nanoparticles are omitted compared to Example 1) Modified base paper layer: bamboo fiber, polyester fiber (4 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 55:18:1.5:2:1.

[0071] Nanofiber layer: polylactic acid and polyvinyl alcohol in a mass ratio of 70:25.

[0072] The preparation steps are the same as in Example 1, except that in step (2), the electrospinning process parameters are adjusted to make the thickness of the nanofiber layer consistent with that in Example 1 (12 μm).

[0073] Comparative Example 3 This comparative example provides a composite filter paper, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0074] Raw materials for preparation: (Compared to Example 1, polyvinyl alcohol is omitted, and polylactic acid is used in an equal amount to replace polyvinyl alcohol as the backbone polymer) Modified base paper layer: bamboo fiber, polyester fiber (4 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 55:18:1.5:2:1.

[0075] Nanofiber layer: polylactic acid and KH550 modified SiO2 nanoparticles (particle size 30 nm) in a mass ratio of 95:5.

[0076] The preparation steps are the same as in Example 1.

[0077] Comparative Example 4 This comparative example provides a composite filter paper, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0078] Raw materials for preparation: (Compared to Example 1, polylactic acid is omitted, and an equal amount of polyvinyl alcohol is used instead of polylactic acid as the backbone polymer) Modified base paper layer: bamboo fiber, polyester fiber (4 mm in length), polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 55:18:1.5:2:1.

[0079] Nanofiber layer: polyvinyl alcohol and KH550 modified SiO2 nanoparticles (particle size 30 nm) in a mass ratio of 95:5.

[0080] The preparation steps are the same as in Example 1, except that in step (2), the solvent is changed to a mixture of deionized water and a small amount of ethanol (volume ratio 9:1); the mixing temperature is adjusted to 85 °C to ensure that PVA is completely dissolved; the relative humidity of the electrospinning environment is <40% to prevent PVA fibers from absorbing moisture and sticking together; the obtained nanofiber layer is heat-treated at 120 °C for 30 min to promote partial crystallization of PVA and improve its water insolubility.

[0081] Comparative Example 5 This comparative example provides a composite filter paper, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0082] Raw materials for preparation: (Compared to Example 1, polyester fiber is omitted and replaced with an equal amount of bamboo fiber) Modified base paper layer: bamboo fiber, polyamide epichlorohydrin resin, sodium carboxymethyl cellulose and waterborne polyurethane, in a mass ratio of 73:1.5:2:1.

[0083] Nanofiber layer: polylactic acid, polyvinyl alcohol and KH550 modified SiO2 nanoparticles (particle size 30 nm) in a mass ratio of 70:25:5.

[0084] The preparation steps are the same as in Example 1.

[0085] Comparative Example 6 This comparative example provides a composite filter paper, which consists of a modified base paper layer and nanofiber layers disposed on both sides of the modified base paper layer.

[0086] The raw materials and preparation steps are the same as in Example 1. The only difference is that in step (3), hot pressing is not used. Instead, a 3% solid content acrylic water-based adhesive is sprayed evenly and then bonded together, and cured at 80 °C for 10 min.

[0087] Experimental Example 1 This experiment aims to test the performance of the filter media in Examples 1-4 and Comparative Examples 1-6. The specific test indicators and test methods are as follows: Emulsified oil retention efficiency: Refer to GB / T 2679.13, and adjust the test conditions according to the standard: Prepare a soybean oil emulsion in water with an average particle size of 5μm (oil phase concentration of 1000 mg / L, prepared by emulsification at 10000 rpm for 5 min using an emulsifier), and use it as feed liquid for filtration test. Calculate the retention rate by measuring the oil content of the filtrate. Pure water flux: Measured at a transmembrane pressure of 127 Pa, referring to common methods in the field of membrane separation, the amount of water permeated per unit time per unit membrane area is recorded; Initial flux of emulsion: Measured at a transmembrane pressure of 127 Pa, using the same 5 μm soybean oil emulsion as the feed liquid, the initial permeation rate of the entire emulsion (i.e., the oil-water mixture) was determined. Flux decay rate: The percentage decrease in flux after continuous cyclic filtration of the same 5 μm soybean oil emulsion for 2 h, calculated according to the following formula: Flux decay rate = (initial flux - flux after 2 hours) / initial flux × 100% Interlayer peel strength: determined according to ASTM D1876; Retention rate: After the sample was accelerated aged in an 80 ℃ oven for 500 h, its emulsified oil retention rate was re-measured, and the retention rate was calculated according to the following formula: Retention efficiency = (Retention rate after aging / Initial retention rate) × 100% Flux retention rate: After the sample was accelerated to age in an 80 ℃ oven for 500 h, its pure water flux was re-measured, and the flux retention rate was calculated according to the following formula: Flux retention rate = (Pure water flux after aging / Initial pure water flux) × 100% The experimental results are shown in Table 2.

[0088] Table 2 Filter Media Test Results

[0089] As shown in Table 2, the filter paper materials prepared in Examples 1-4 of the present invention have high retention efficiency and high flux, good temperature resistance and durability, low performance degradation rate over long-term use, and high interlayer bonding strength. Compared with Example 1, Example 4 omits the nanofiber layer on one side of the modified base paper layer. Compared with the double-sided symmetrical Example 1, the single-sided structure achieves a higher pure water flux, but the retention rate, antifouling properties (higher flux degradation rate) and interlayer bonding strength are all reduced, which reflects the advantages of the double-sided structure in terms of comprehensive performance.

[0090] Comparative Example 1, compared to Example 1, omits the modified base paper layer and increases the thickness of the nanofiber membrane to form a self-supporting structure. Although the retention rate is high, the extremely low throughput and poor mechanical strength make it impractical (therefore, long-term aging tests were not conducted), demonstrating the necessity of introducing a macroporous, high-strength support layer to achieve "high throughput" and "robust structure." Comparative Example 2, compared to Example 1, omits the nano-reinforcing particles. Due to the lack of "anchoring" of PVA by nanoparticles, the initial retention rate decreases, and the hydrophilic function is severely degraded after thermal aging, demonstrating the key role of nanoparticles in constructing a "durable and stable" interface and achieving excellent long-term stability. Comparative Example 3, compared to Example 1, uses an equal amount of polylactic acid to replace polyvinyl alcohol. Although high throughput is achieved, the retention efficiency decreases significantly. Due to the lack of a hydrophilic interface, it cannot effectively demulsify and retain oil droplets, and the separation function is basically ineffective, demonstrating the indispensability of wettability regulators in achieving "high retention rate." Comparative Example 4, compared to Example 1, uses an equal amount of polyvinyl alcohol to replace polylactic acid. Although a certain retention rate is still achieved, the throughput is significantly reduced. The decrease in flux and the worsening of long-term stability demonstrate that a single hydrophilic polymer (PVA) cannot form an effective "hydrophobic core-hydrophilic shell" gradient structure. Its dense structure leads to low flux, and the lack of hydrophobic skeleton support results in insufficient hygrothermal stability, which in turn proves the necessity of the skeleton polymer being compatible with the wettability regulator. In Comparative Example 5, compared to Example 1, the same amount of bamboo fiber was used to replace polyester fiber, resulting in a decrease in both retention efficiency and flux. Due to the lack of oleophilic flow channels, the flux was low and the decline was rapid, demonstrating the core contribution of auxiliary oil-conducting fibers to achieving and maintaining "high flux" and "strong anti-fouling properties". In Comparative Example 6, compared to Example 1, the adhesive process was used to replace the hot-pressing composite process, resulting in a decrease in interlayer peel strength of more than 50% compared to Example 1. Significant interlayer peeling was observed in the circulating filtration experiment. This is because the adhesive severely blocked the pores, causing a sharp drop in flux, and the direct adhesive composite method resulted in weak interfacial bonding. This demonstrates the unique advantage of the specific hot-pressing process of this invention in achieving a balance between "high-strength interfacial bonding" and "maintaining high porosity / high flux".

[0091] Experiment Example 2 This experimental example aims to verify the universality of the composite filter paper provided in Example 1 for different emulsion oil-water separation functions.

[0092] Oil-in-water emulsions of soybean oil (vegetable oil), mineral oil (hydrocarbon oil), and n-octane (representing low-viscosity light oil) with a particle size of 5 μm were prepared (oil phase concentration 1000 mg / L, prepared by emulsification at 10000 rpm for 5 min using an emulsifier). The emulsion oil rejection rate, initial flux of the emulsion, and flux decay rate were tested according to the test method of Experiment Example 1.

[0093] The test results are shown in Table 3: Table 3. Separation effect of composite filter paper on different emulsions

[0094] As shown in Table 3, the composite filter paper prepared in Example 1 of the present invention exhibits excellent and stable high rejection rate and high throughput for oil-in-water emulsions composed of different types of oils, proving that it has wide applicability.

[0095] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-throughput composite filter paper for emulsified oil separation, characterized in that, It includes a modified base paper layer and a nanofiber layer, wherein the nanofiber layer is disposed on one or both surfaces of the modified base paper layer and is formed by hot pressing. The modified base paper layer has a thickness of 0.55~0.70 mm and a pore size of 5~25 μm; The thickness of the nanofiber layer is 8~20 μm, and the pore size is 0.5~3 μm; The raw materials for preparing the modified base paper layer, by weight, include: 40-70 parts of main fiber, 10-25 parts of auxiliary oil-guiding fiber and 1.2-10 parts of functional additives, wherein the main fiber is selected from at least one of bamboo fiber and wood pulp fiber, and the auxiliary oil-guiding fiber is selected from at least one of polyester fiber and polypropylene fiber. The raw materials for preparing the nanofiber layer, by weight, include: 60-90 parts of a backbone polymer, 10-30 parts of a wettability regulator, and 1-8 parts of nano-reinforcing particles. The backbone polymer is selected from at least one of polyhydroxyalkanoate, polylactic acid, and polycaprolactone. The wettability regulator is selected from at least one of polyvinyl alcohol and polyvinylpyrrolidone. The nano-reinforcing particles are oxide nanoparticles surface-modified with a silane coupling agent.

2. The high-throughput composite filter paper for emulsified oil separation according to claim 1, characterized in that, The raw materials for preparing the modified base paper layer, by weight, include: 50-60 parts of main fiber, 15-20 parts of auxiliary oil-guiding fiber, and 2.5-6.5 parts of functional additives; The raw materials for preparing the nanofiber layer, by weight, include: 70-80 parts of the backbone polymer, 15-25 parts of the wettability regulator, and 5-6 parts of the nano-reinforcing particles.

3. The high-throughput composite filter paper for emulsified oil separation according to claim 1, characterized in that, The modified base paper layer has a thickness of 0.60~0.65 mm and a pore size of 8~15 μm; The nanofiber layer has a thickness of 10~15 μm and a pore size of 1.0~2.0 μm.

4. The high-throughput composite filter paper for emulsified oil separation according to claim 1, characterized in that, The basis weight of the modified base paper layer is 170~200 g / m³. 2 ; The length of the auxiliary oil-guiding fiber is 2~6 mm; The functional additives include the following raw materials in parts by weight: 0.5-3 parts wet strength agent, 0.5-5 parts dispersant, and 0.2-2 parts environmentally friendly waterproofing agent.

5. The high-throughput composite filter paper for emulsified oil separation according to claim 1, characterized in that, The basis weight of the modified base paper layer is 175~190 g / m³. 2 ; The length of the auxiliary oil-guiding fiber is 3~5 mm; The functional additives include the following raw materials in parts by weight: 1-2 parts wet strength agent, 1-3 parts dispersant, and 0.5-1.5 parts environmentally friendly waterproofing agent; The wet strength agent is polyamide epichlorohydrin resin; the dispersant is sodium carboxymethyl cellulose; the environmentally friendly waterproofing agent is waterborne polyurethane. The particle size of the nano-reinforcing particles is 10~50 nm.

6. The high-throughput composite filter paper for emulsified oil separation according to claim 1, characterized in that, The particle size of the nano-reinforcing particles is 20~40 nm; The nano-reinforcing particles are selected from at least one of silica nanoparticles surface-modified with silane coupling agent and titanium dioxide nanoparticles surface-modified with silane coupling agent.

7. The method for preparing high-throughput composite filter paper for emulsified oil separation according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Mix the main fiber and auxiliary oil-conducting fiber in proportion and then pulp them. Add functional additives to the pulp and then form it into paper. After dehydration and drying, the modified base paper layer is obtained. (2) The skeleton polymer, wettability regulator and nano-reinforcing particles are mixed in proportion and then a solvent is added. The mixture is mixed evenly to obtain a spinning solution. Electrospinning is performed using the spinning solution to obtain the nanofiber layer. (3) The nanofiber layer is covered on one or both sides of the modified base paper layer, hot-pressed and cooled to obtain the high-throughput composite filter paper for emulsified oil separation.

8. The method for preparing high-throughput composite filter paper for emulsified oil separation according to claim 7, characterized in that, In step (1), Pulping concentration 1.5%~3.0%; main fiber freeness 30~60 °SR; auxiliary oil-conducting fiber freeness 15~30 °SR; In step (2), The solvent is a mixture of a polar organic solvent and water, wherein the volume ratio of the polar organic solvent to water is 3-4:1-2; the polar organic solvent is selected from at least one of N,N-dimethylformamide and dichloromethane. The mass concentration of the spinning solution is 6%~12%; The electrospinning conditions are as follows: spinning voltage 15~25 kV; receiving distance 12~25 cm; spinning speed 0.3~1.0 mL / h; ambient temperature 20~30 ℃; relative humidity 30%~60%. In step (3), The hot-pressing composite conditions are: hot-pressing temperature 70~100 ℃; pressure 0.2~0.6 MPa; hot-pressing time 20~90 s.

9. The method for preparing high-throughput composite filter paper for emulsified oil separation according to claim 7, characterized in that, In step (1), The pulping concentration is 1.8%~2.5%; the freeness of the main fiber is 35~50 °SR; the freeness of the auxiliary oil-conducting fiber is 18~25 °SR. Add the diluted wet strength agent, dispersant, and environmentally friendly waterproofing agent to the slurry in sequence. Stir at 400-600 rpm for 20-40 minutes after each addition of a functional additive. The slurry concentration after adding the functional additives is 1.5%-2.5%. The drying conditions are: drying at 100~110 ℃ for 1.5~3 h; The main fiber is pretreated before pulping: the main fiber is soaked in deionized water at 50~70 ℃ for 1~3 hours, and stirred at 200~400 rpm during the soaking process, filtered, and dried at 70~90 ℃ for 3~5 hours; In step (2), The mixing conditions are: stirring at 50~70 ℃ and 600~1000 rpm for 1~3 h; The mass concentration of the spinning solution is 7%~10%; The electrospinning conditions were as follows: spinning voltage 16~22 kV; receiving distance 12~20 cm; spinning speed 0.4~0.8 mL / h; ambient temperature 23~27 ℃; relative humidity 40%~50%. In step (3), The hot-pressing composite conditions are: hot-pressing temperature 75~90 ℃; pressure 0.2~0.5 MPa; hot-pressing time 20~60 s.

10. The high-throughput composite filter paper for emulsified oil separation according to any one of claims 1 to 6, or the high-throughput composite filter paper for emulsified oil separation obtained by the preparation method according to any one of claims 7 to 9, is used in industrial oily wastewater treatment or marine oil spill emergency response.

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