A filter medium for heterogeneous separation and preparation method thereof

Abstract

The present application relates to the technical field of filtration separation, and in particular to a filter medium for heterogeneous separation and a preparation method thereof, wherein the filter medium comprises a fiber composite structure formed by nanometer-level interception fibers, micrometer-level fibers and cross-linked fibers; the weight proportion of the nanometer-level interception fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micrometer-level fibers in the fiber composite structure increase in sequence; the melting points of the nanometer-level interception fibers and the micrometer-level fibers are both higher than those of the cross-linked fibers; the method comprises: mixing the nanometer-level interception fibers, the micrometer-level fibers and the cross-linked fibers according to a preset weight ratio, subjecting the fibers to fiber dissociation treatment, and mixing them uniformly to obtain a fiber suspension; subjecting the fiber suspension to wet sheet forming treatment, and dehydrating and drying to obtain an initial filter medium; subjecting the initial filter medium to surface high-temperature instantaneous plasticization treatment and surface functional modification treatment to obtain a filter medium for heterogeneous separation; the present application effectively improves the medium interception accuracy and the utilization rate of effective components.

Description

Technical Field

[0001] The present application relates to the technical field of filtration separation, and in particular to a filtration medium for heterogeneous separation and a preparation method thereof. Background Art

[0002] The basis of heterogeneous separation is that there are physical property differences between dispersed substances. Mechanical force can be used to separate heterogeneous mixtures such as solid-liquid, liquid-liquid, gas-liquid or gas-solid. It is an indispensable technical link in the fields of solid-liquid separation, gas-solid separation and water treatment in industrial production. The separation methods include filtration, precipitation and centrifugal separation. In the separation process, the filter medium is the core component that determines the separation effect. It needs to withstand complex chemical working conditions and extremely high working pressure. The filter medium is required to have high mechanical strength, filtration retention accuracy and separation efficiency. The existing filter media used for heterogeneous separation generally use various forms of filter cloth, such as high retention accuracy filter cloth. However, during the filtration process, the filter cloth needs to be continuously fed and form a filter cake before effective filtration can be achieved. The average effective component loss rate is more than 30%, the filtration effect is poor, and a large amount of material particles are lost; in addition, the filtration retention accuracy of the existing filter medium can only reach 3-5 microns, which cannot reach nanometer-level accuracy, and cannot achieve nanometer-level high-precision separation in industrial applications of heterogeneous separation. Summary of the invention

[0003] In view of the above problems in the prior art, the present application provides a filter medium for heterogeneous separation and a preparation method thereof. The specific technical solution is as follows:

[0004] In one aspect, the present application provides a filtration medium for heterogeneous separation, comprising a fiber composite structure formed of nano-scale retention fibers, micron-scale fibers, and cross-linked fibers;

[0005] In the fiber composite structure, the weight proportion of the nanoscale retained fibers, the weight proportion of the cross-linked fibers, and the weight proportion of the micron-scale fibers increase successively; the melting points of the nanoscale retained fibers and the micron-scale fibers are both higher than those of the cross-linked fibers.

[0006] Specifically, the filter medium includes a retention surface layer and a flow guide surface layer, the retention surface layer and the flow guide surface layer are cross-linked, and the cross-linked fibers form a hot-melt cross-linking point structure in the filter medium;

[0007] The mass proportion of the nanoscale retention fibers in the retention surface layer is higher than the mass proportion of the micron-scale fibers and the mass proportion of the cross-linked fibers, and the mass proportion of the micron-scale fibers in the guide surface layer is higher than the mass proportion of the nanoscale retention fibers.

[0008] On the other hand, the present application provides a method for preparing a filter medium for heterogeneous separation, which is applied to the filter medium for heterogeneous separation as described above, and the method comprises the following steps:

[0009] S21: mixing the nano-scale retained fibers, the micron-scale fibers and the cross-linked fibers according to a preset weight ratio to form an initial suspension, wherein the weight ratio of the nano-scale retained fibers, the weight ratio of the cross-linked fibers and the weight ratio of the micron-scale fibers increase in sequence;

[0010] S22: performing fiber dissociation treatment on the initial suspension, mixing evenly, and obtaining a fiber suspension;

[0011] S23: performing a wet sheet forming process on the fiber suspension, and dehydrating and drying the fiber suspension to obtain an initial filter medium;

[0012] S24: performing a surface high-temperature instantaneous plasticization treatment and a surface functional modification treatment on the initial filter medium to obtain the filter medium for heterogeneous separation.

[0013] Specifically, the preset weight ratio is 1:(5-50):(2-48).

[0014] Specifically, the wet sheet forming process of the fiber suspension in S23 includes:

[0015] S231: performing gravity dehydration and sedimentation treatment on the fiber suspension to obtain an initial fiber layered medium;

[0016] S232: The initial fiber layer medium is subjected to a suction filtration and dehydration treatment to obtain a fiber layer medium to be heat-set and dried.

[0017] S233: performing moisture squeezing and heat setting drying on the fiber layered medium to obtain the initial filter medium.

[0018] Specifically, before S21, the method further includes:

[0019] S11: opening the island-in-sea type micron-sized fiber filaments in an alkaline solution to obtain the island-in-sea fiber filaments;

[0020] S12: Cutting the island fiber filaments into short fibers to obtain the micron-sized fibers.

[0021] Specifically, the material of the nano-scale interception fiber is cellulose microfiber, the material of the micron-scale fiber includes one or more of polyester and nylon, and the material of the cross-linked fiber includes one or more of polyester and nylon.

[0022] Specifically, the fiber length of the nano-scale interception fiber is greater than or equal to 100 μm, the fiber length of the micron-scale fiber is 1-3 mm, and the fiber length of the cross-linked fiber is 1-5 mm.

[0023] Specifically, the average diameter of the nanoscale interception fibers is 10-100 nm, the average diameter of the microscale fibers is less than or equal to 2.5 μm, and the average diameter of the cross-linked fibers is 10-25 μm.

[0024] Specifically, the gram weight of the filter medium is greater than or equal to 50 g / m 2 The filtration retention accuracy of the filter medium is 10-100nm.

[0025] In another aspect, the present application provides a filtration device, comprising the filtration medium for heterogeneous separation as described above.

[0026] In another aspect, the present application provides a use of the filter medium for heterogeneous separation as described above.

[0027] Based on the above technical solution, this application has the following beneficial effects:

[0028] 1. The present invention forms a fiber composite structure composed of nano-scale interception fibers, micron-scale fibers and cross-linked fibers in the filter medium, and controls the weight proportion of the nano-scale interception fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micron-scale fibers to increase in sequence, so that the heterogeneous phase separation filter medium can achieve nano-scale filtration accuracy, and provide up to 0.1-1 MPa / cm based on the micron-scale fibers and cross-linked fibers. 2 The above working pressure bearing capacity; in addition, the melting points of nano-scale retention fibers and micron-scale fibers are higher than those of cross-linked fibers, which is beneficial to the melt plasticization treatment in the preparation process to further improve the support strength and cross-linking strength of the filter medium, ensure the cross-linking force of the fiber units in the filter medium in the liquid phase application environment, and avoid separation and disintegration between fibers.

[0029] 2. The present application mixes a suspension of nano-scale interception fibers, micron-scale fibers and cross-linked fibers in a preset weight ratio, and performs fiber dissociation treatment to form a single fiber, which is then formed by a wet sheeting method to form a fiber composite structure. The filter medium is obtained after surface treatment. No chemical additives need to be added in each preparation link of the entire process chain, and the process water can be recycled repeatedly. The preparation method is environmentally friendly and pollution-free. In addition, through surface high-temperature instantaneous plasticization treatment and surface functional modification treatment, the cross-linked fibers can form a dense hot-melt cross-linking point structure in the filter medium. The filter medium obtained can not only achieve nano-scale interception accuracy, but also withstand 0.1-1MPa / cm 2 More work pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments or prior art descriptions. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 It is a schematic flow chart of a method for preparing a filter medium for heterogeneous separation provided in an embodiment of the present application;

[0032] Figure 2-Figure 4 is a TEM image of a filter medium for heterogeneous separation provided in an embodiment of the present application;

[0033] Figure 5 It is a process flow chart of a method for preparing a filter medium for heterogeneous separation provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0035] For the following defined terms, these definitions shall apply unless a different definition is given in the claims or elsewhere in this specification. All numerical values, whether or not explicitly indicated, are defined herein as modified by the term "about". The term "about" generally refers to a numerical range that a person of ordinary skill in the art considers to be equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A numerical range indicated by a lower value and a higher value is defined to include all numerical values ​​included in the numerical range and all subranges included in the numerical range.

[0036] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0037] Before further describing the embodiments of the present application in detail, the nouns and terms involved in the embodiments of the present application are explained. The nouns and terms involved in the embodiments of the present application are subject to the following interpretations.

[0038] Heterogeneous: refers to the existence of different phase interfaces within the system, and the properties of the materials on both sides of the interface are significantly different, with different physical properties. The system composed of dispersed phase and continuous phase with different physical properties is called a heterogeneous system or heterogeneous mixture. According to the state of the continuous phase, heterogeneous systems are divided into two categories: gaseous heterogeneous systems, such as dusty gas, misty gas, etc.; liquid heterogeneous systems, such as suspensions, emulsions and foam liquids.

[0039] It is understandable that the higher the filtration interception accuracy, the lower the filtration flux. Existing woven filter cloths are usually formed by alternating warp and weft weaving to form a fabric structure, in which almost all the warp and weft interlacing points are shielding areas that cannot achieve filtration at all. The denser the fabric density, the higher the filtration interception accuracy, but the more warp and weft interlacing points, the smaller the effective filtration area and the lower the filtration separation efficiency. Whether from the physical limitations of the weaving unit itself in the fabric or the requirements for the effective filtration area, the existing woven filter cloths cannot achieve nano-level fine filtration.

[0040] The following introduces the filter medium for heterogeneous separation provided in an embodiment of the present application, including a fiber composite structure formed by nano-scale retention fibers, micron-scale fibers and cross-linked fibers; the weight proportion of the nano-scale retention fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micron-scale fibers in the fiber composite structure increase successively; the melting points of the nano-scale retention fibers and the micron-scale fibers are both higher than those of the cross-linked fibers.

[0041] In this way, by forming a fiber composite structure including three fiber units and controlling the weight ratio of the three fiber components, the inhomogeneous phase separation filter medium can achieve nano-level filtration accuracy and provide up to 0.1-1 MPa / cm based on micron-level fibers and cross-linked fibers. 2 The above working pressure bearing capacity; in addition, the melting points of nano-scale retention fibers and micron-scale fibers are higher than those of cross-linked fibers, which is beneficial to the melt plasticization treatment in the preparation process, so that the cross-linked fibers can form a cross-linked reinforcement structure, so as to further improve the support strength and cross-linking strength of the filter medium, ensure the cross-linking force of the fiber units in the filter medium in the liquid phase application environment, and avoid separation and disintegration between fibers.

[0042] Among them, the micron-sized fiber is obtained by opening the micron-sized fiber filaments of the island-in-sea type in an alkaline solution; the filter medium is obtained by sequentially subjecting the suspension of nano-sized interception fiber, micron-sized fiber and cross-linked fiber to fiber dissociation, wet forming, heat setting and surface high-temperature instantaneous plasticization. The wet forming can be specifically wet sheet forming. Specifically, the wet sheet forming process first uses gravity dehydration and sedimentation to form the initial fiber layer, and then assists in vacuum filtration of residual water to complete the final forming.

[0043] Specifically, the fiber composite structure is composed of nano-scale interception fibers, micron-scale fibers and cross-linked fibers cross-linked with each other. The filter medium of the present application is cross-linked and combined by a non-woven method to combine nano-scale interception fibers, micron-scale fibers and cross-linked fibers, and combines fiber units with different functions to achieve overall performance enhancement of the medium.

[0044] Specifically, in the filter medium, the micron-sized fibers form a medium skeleton structure, and the medium skeleton structure has a skeleton hydrophobic channel, which plays a role of skeleton support. The skeleton bridge formed by the micron-sized fibers can not only increase the strength of the filter medium, but also increase the diversion channel, play the role of bridging and diversion, and improve the separation efficiency; the nano-sized retention fibers are cross-linked in the filter medium to form retention pores to improve the filtration retention accuracy of the filter medium; the cross-linked fibers are fusible fibers, and the cross-linked fibers form a hot-melt cross-linking point structure in the filter medium to enhance the cross-linking strength between different layers and different fiber units in the medium, and the tolerable working pressure of the medium is improved through the fiber cross-linking between the micron-sized fibers, nano-sized retention fibers and cross-linked fibers, and the hot-melt cross-linking point structure.

[0045] Specifically, the filter medium includes a retention surface layer and a guide surface layer, the retention surface layer and the guide surface layer are cross-linked, the retention surface layer and the guide surface layer are cross-linked by nano-scale retention fibers, micron-scale fibers and cross-linked fibers, and are cross-linked by hot-melt cross-linking point structures.

[0046] Specifically, the mass proportion of nano-scale interception fibers in the interception surface layer is higher than the mass proportion of micron-scale fibers and the mass proportion of cross-linked fibers, and they mainly play a filtering and interception role; the mass proportion of micron-scale fibers in the diversion surface layer is higher than the mass proportion of nano-scale interception fibers, so as to support and form a skeleton hydrophobic channel. During heterogeneous separation, the suspended matter first contacts the interception surface layer composed mainly of nano-scale interception fibers to form a primary particle material interception, achieving nano-scale interception accuracy. The separated liquid passes through the nano-scale interception fibers of the interception surface layer and enters the skeleton hydrophobic channel of the diversion surface layer to form a rapid diversion, thereby completing the overall separation process.

[0047] In some embodiments, the material of the nano-scale intercepting fibers is cellulose microfibers (microfibrillated cellulose). The nano-scale intercepting fibers used in the filter medium are made based on all-biobased materials, are non-toxic, environmentally friendly, can be suspended in water solvents, and can be 3D-cellulose microfibers. In addition, the nano-scale intercepting fibers have functional OH groups and high available surface areas, and can withstand extreme pH values, temperatures, salts, solvents and other environments. Specifically, the cellulose microfibers used in the nano-scale intercepting fibers can be microfibrillated cellulose (Micro fibrillated Cellulose, MFC), which is a degradable nano-scale intercepting cellulose functional material, which is a highly swollen colloidal cellulose, non-toxic and harmless.

[0048] In some embodiments, the material of the micron-sized fiber includes one or more of polyester and nylon. The micron-sized fiber is a sea-island fiber obtained by an alkali fiber opening process, which plays a basic skeleton role in the medium and forms a "bridging" effect to collaboratively achieve high interception accuracy and high separation efficiency of the filter medium.

[0049] In some embodiments, the material of the cross-linked fiber includes one or more of polyester and nylon. The cross-linked fiber is a fusible fiber, which can be a fully fusible type or a skin-core type. Through heat setting and surface high-temperature instantaneous plasticization treatment, dense hot-melt cross-linking points are formed between different fiber units, thereby improving the mechanical strength of the filter medium and making the breaking strength of the filter medium reach more than 30N / cm. Specifically, the melting point temperature of the cross-linked fiber can be 150-180°C.

[0050] In some embodiments, the weight ratio of nano-scale interception fibers, micron-scale fibers, and cross-linked fibers in the filter medium satisfies 1:(5-50):(2-48), preferably, the weight ratio satisfies 1:(9-17):(3-10). By controlling the weight ratio of the three functional fibers within the above range, the micron-scale fibers and cross-linked fibers can form an effective support and cross-linking structure, while the nano-scale interception fibers form dense filtration pores and an appropriate effective filtration area, forming a rich and cross-linked entangled three-dimensional network structure in the medium, balancing the interception accuracy, pressure bearing strength, and breaking strength requirements, and achieving excellent strength, interception accuracy, and filtration efficiency. The filtration accuracy of the filter medium can reach 10-100nm, and can withstand a working pressure of 0.1-1MPa / cm 2 above.

[0051] In some embodiments, the average diameter of the nano-scale intercepted fibers is 10-100 nm, preferably, the average diameter of the nano-scale intercepted fibers is 10-70 nm; the average diameter of the micron-scale fibers is less than or equal to 2.5 μm, preferably, the average diameter of the micron-scale fibers is greater than or equal to 1.5 and less than or equal to 2.5 μm, and the average diameter of the cross-linked fibers is 10-25 μm, preferably, the average diameter of the cross-linked fibers is 13-21 μm. Specifically, before the micron-scale fibers are opened, their fineness is 0.05-1D. In this way, the radial dimensions of the three different functional fiber units are controlled to the above range respectively to form a fiber width gradation, so as to form nano-scale dense pores with high interception accuracy while ensuring the support strength; and, by controlling the radial dimensions of the nano-scale interception fibers to the above range, it can be ensured that the medium interception accuracy reaches below 100nm, and preferably reaches below 70nm. If the size is too high, it is not conducive to improving the interception accuracy, and if the size is too small, it is not conducive to the dispersion and molding of the preparation process; controlling the average diameter of the micron-level fibers to the above range can balance the support strength and interception accuracy requirements. If the size is too high, it is easy to cause the interception accuracy to decrease, and if the size is too low, it is not conducive to improving the medium strength; controlling the single fiber size of the cross-linked fibers to the above range can form a hot-melt cross-linking point structure of appropriate size. If the size is too large, it is easy to cause the hot-melt cross-linking point structure to be too large, reducing the effective filtration area, and if the size is too small, it is easy to cause the hot-melt cross-linking point structure to be too small and not dense enough, reducing the cross-linking strength.

[0052] In some embodiments, the fiber length of the nano-scale interception fiber is greater than or equal to 100 μm, preferably, the fiber length of the nano-scale interception fiber is greater than or equal to 110 μm; the fiber length of the micron-scale fiber is 1-3 mm, preferably, the fiber length of the micron-scale fiber is 1.5-2 mm; the fiber length of the cross-linked fiber is 1-5 mm, preferably, the fiber length of the cross-linked fiber is 2-4 mm. In this way, by adjusting the fiber lengths of the three different functional fibers to the above ranges, while forming the width gradation, the fiber length gradation is formed to form a rich and cross-linked entangled network structure, ensuring the medium strength and interception accuracy. In addition, the fiber length of the nano-scale interception fiber unit is controlled within the above range so that it is evenly distributed in the filter medium and cross-linked with each other to form dense and uniform interception pores. If it is too short, it is not conducive to improving the cross-linking strength, and if it is too long, it is easy to cause the nano-scale interception fiber to agglomerate, increase the difficulty of dispersion, and reduce the porosity; if the fiber length of the micron-scale fiber is controlled within the above range, a continuous skeleton structure and a stretched and connected hydrophobic channel can be formed, and an appropriate bridge structure can be formed to improve the medium strength and filtration efficiency. If it is too short, it is easy to increase the skeleton gap and reduce the cross-linking strength. If it is too long, it is easy to increase the difficulty of dispersion, the fiber agglomeration is unevenly dispersed, and there are weak points of the bridge, thereby reducing the overall strength; controlling the fiber length of the cross-linked fiber to the above range can increase the hot-melt cross-linking points and ensure the cross-linking strength. If the length of the cross-linked fiber is too long, under the same addition amount and fineness, the hot-melt cross-linking points formed are too few and unevenly distributed, resulting in a decrease in strength, and the cross-linked fiber itself is easy to curl and overlap in the radial direction; if the length of the cross-linked fiber is too short, the cross-linking gap is increased and the effective hot-melt cross-linking point content is reduced.

[0053] In some embodiments, the grammage of the filter medium is greater than or equal to 50 g / m 2 Preferably, the weight is greater than or equal to 120 g / m 2 And less than or equal to 300g / m 2 In this way, by achieving the above-mentioned gram weight value, the medium strength can be improved, which is beneficial to the industrial application of heterogeneous separation; the filtration retention accuracy of the filter medium can reach 10-100nm, preferably, the filtration retention accuracy is 10nm-70nm; the breaking strength of the filter medium is greater than or equal to 30N / cm.

[0054] Specifically, the surface of the filter medium has hydrophilic groups, which can improve the filtering and separation efficiency. The hydrophilic groups on the surface are obtained by performing surface functional modification treatment on the initially formed filter medium.

[0055] The above three fibers with different functions are combined in a certain mass ratio to form a filter medium for heterogeneous separation. The filter retention accuracy can reach 10-100nm, and the breaking strength of the filter medium reaches more than 30N / cm. It can be used in industrial application scenarios in the field of heterogeneous separation technology, and can achieve ultra-fine retention of high-concentration solid-liquid ratio, reduce the loss of effective ingredients, and achieve nano-level filtration retention accuracy. It can then be used in high-purity separation applications of ultra-fine nano powder particles in the fields of new energy materials, rare earths, etc., such as nano-SiO2 filtration with an average particle size of 50-100 nanometers. At the same time, through the formation of the retention surface layer, support skeleton and cross-linking structure points by different functional fibers, the filter medium can withstand 0.1-1MPa / cm 2 The working pressure can be above 150℃ and it can be used for a long time under the temperature condition of 150℃ to ensure the application performance of the medium in the working environment.

[0056] On the other hand, the present application provides a method for preparing a filter medium for heterogeneous separation, which is applied to the filter medium for heterogeneous separation as described above, and the method comprises the following steps S21-S24.

[0057] S21: The nano-scale retained fibers, micron-scale fibers and cross-linked fibers are mixed in a preset weight ratio to form an initial suspension, wherein the weight proportion of the nano-scale retained fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micron-scale fibers increase in sequence.

[0058] In some embodiments, the preset weight ratio is 1:(5-50):(2-48), preferably, the preset weight ratio is 1:(9-17):(3-10). By controlling the weight ratio of the three functional fibers within the above range, the micron-sized fibers and the cross-linked fibers can form an effective support and cross-linked structure, while the nano-sized interception fibers form dense filtration pores and an appropriate effective filtration area, forming a rich and cross-linked entangled three-dimensional network structure in the medium, balancing the interception accuracy, pressure bearing strength and breaking strength requirements, and achieving excellent strength, interception accuracy and filtration efficiency. The filtration accuracy of the filter medium can reach 10-100nm, and can withstand a working pressure of 0.1-1MPa / cm 2 above.

[0059] In some embodiments, the mass concentration of the initial suspension is 0.15-0.5%, preferably, the mass concentration is 0.2-0.4%; by controlling the mass concentration of the initial suspension to the above range, it is beneficial to the uniformity of dispersion of various fibers and to keep the subsequent fiber sedimentation rate within a reasonable range, thereby ensuring effective crosslinking and stratified sedimentation between nano-scale retention fibers, micron-scale fibers and cross-linked fibers, thereby forming a medium structure with a cross-linked retention surface layer and a guide surface layer.

[0060] In some embodiments, before S21, the method further includes S11-S12:

[0061] S11: opening the island-in-sea type micron-sized fiber filaments in an alkaline solution to obtain the island-in-sea fiber filaments;

[0062] S12: Cutting the island fiber filaments into staple fibers to obtain micron-sized fibers.

[0063] Specifically, a sea-island type micron-sized fiber filament is provided, and a continuous ultrasonic alkali fiber opening process is performed on the fiber filament, wherein the mass concentration of the alkali solution is 4-10%, the fiber opening temperature is 95-98°C, the fiber opening time is 20-40min, the washing time in water after the fiber opening treatment is 30-300s, and the drying temperature is 100-120°C.

[0064] Specifically, the island-in-sea type micron-sized fiber filament has an island-in-sea ratio of (2-3):(7-8), preferably 3:7, and the fiber opening process specifically dissolves the sea portion in the fiber and leaves the island portion. In one embodiment, the island-in-sea type micron-sized fiber filament may be a polyester island-in-sea fiber filament produced by the FDY process, and the single fiber fineness may be 0.05-0.2D.

[0065] After the fiber filaments with only island fibers are formed, they are rolled and cut to form short fibers of the required fiber length, thereby obtaining micron-grade fibers used in the filter medium.

[0066] In some embodiments, the cross-linked fibers may be short fibers obtained by cutting FDY cross-linked fiber filaments, and the cross-linked fibers may be fully melt-type or sheath-core-type.

[0067] In some embodiments, the material of the nano-scale interception fiber is cellulose microfiber (microfibrillated cellulose), the material of the micron-scale fiber includes one or more of polyester and nylon, and the material of the cross-linked fiber includes one or more of polyester and nylon. Specifically, the nano-scale interception fiber used in the filter medium is made based on a fully bio-based material, is non-toxic, environmentally friendly, can be suspended in an aqueous solvent, and can be a 3D-cellulose microfiber. In addition, the nano-scale interception fiber has a functional OH group and a high available surface area, and can thus withstand extreme pH values, temperatures, salts, solvents and other environments. The cellulose microfibers used in the nano-scale interception fiber can be microfibrillated cellulose (Micro fibrillated Cellulose, MFC), which is a degradable nano-scale interception cellulose functional material, which is a highly swollen colloidal cellulose, non-toxic and harmless. Micron-scale fibers play a basic skeleton role in the medium and form a "bridging" effect to collaboratively achieve high interception accuracy and high separation efficiency of the filter medium. The cross-linked fibers form dense hot-melt cross-linking points between different fiber units, which improves the mechanical strength of the filter medium and makes the breaking strength of the filter medium reach above 30N / cm.

[0068] Specifically, the melting point temperature of the cross-linked fibers may be 150-180°C.

[0069] S22: performing fiber dissociation treatment on the initial suspension, mixing evenly, and obtaining a fiber suspension.

[0070] Specifically, nanoscale interception fibers, micron-scale fibers and cross-linked fibers are mixed in a preset weight ratio, deionized water is added to form an initial suspension, and then a fiber disintegrator is used to dissociate the fibers in the initial suspension into single fibers, which are mixed evenly to obtain a fiber suspension.

[0071] S23: wet-sheeting the fiber suspension, and dehydrating and drying it to obtain an initial filter medium.

[0072] In some embodiments, the wet sheeting process of the fiber suspension in S23 includes:

[0073] S231: performing gravity dehydration and sedimentation treatment on the fiber suspension to obtain an initial fiber layered medium;

[0074] S232: performing a suction filtration and dehydration treatment on the initial fiber layered medium to obtain a fiber layered medium to be heat-set and dried;

[0075] S233: The fiber layered medium is subjected to moisture extrusion and heat setting drying to obtain an initial filter medium.

[0076] Specifically, there are size and weight differences between nano-scale retention fibers, micron-scale fibers and cross-linked fibers, which result in different sedimentation rates. The sedimentation rate of nano-scale retention fibers is slower, while the sedimentation rates of micron-scale fibers and cross-linked fibers are faster. In the wet forming process, gravity dehydration and sedimentation are first used to form the initial fiber layer, that is, self-weight sedimentation and dehydration are carried out under the action of gravity without external force, and then vacuum filtration of residual water is assisted to complete the final forming. The nano-scale retention fibers and the other two types of fibers will naturally form an initial fiber layered medium with both cross-linking and obvious stratification. Microscopically, the fibers in the medium part with nano-scale retention fibers as the main component are cross-linked and entangled with each other, and the internal fibers in the medium part with micron-scale fibers and cross-linked fibers as the main components are also cross-linked and entangled with each other. At the same time, the bottom fiber part in the medium part with nano-scale retention fibers as the main component forms a cross-linked and entangled state with the surface fiber part in the medium part with micron-scale fibers and cross-linked fibers as the main components.

[0077] Specifically, the formed filter medium includes an intercepting surface layer and a guide surface layer, and the intercepting surface layer and the guide surface layer are cross-linked, and the intercepting surface layer and the guide surface layer are cross-linked by nano-scale intercepting fibers, micron-scale fibers and cross-linked fibers, and are cross-linked by hot-melt cross-linking point structures. The intercepting surface layer is mainly composed of nano-scale intercepting fibers, and the guide surface layer is mainly composed of micron-scale fibers. During heterogeneous separation, the suspended matter first contacts the intercepting surface layer to form a primary particulate material interception, achieving nano-scale interception accuracy; the separated liquid passes through the nanofibers and enters the guide channel of the guide surface layer to form rapid diversion, thereby completing the overall separation process. The skeleton bridge formed by the micron-scale fibers can not only increase the strength of the filter medium, but also increase the guide channel and improve the separation efficiency.

[0078] In some embodiments, step S233 may specifically include: squeezing moisture out of the fiber layered medium again with a felt pressing device and then drying and molding it with a heat setting device to obtain an initial filter medium, so as to ensure the shape and dimensional stability of the filter medium.

[0079] Specifically, the dehydration by filtration can be achieved by vacuum filtration, the negative pressure of the vacuum filtration can be 0.01-0.04 MPa, the heat setting temperature can be 150-180° C., and the heat setting time can be 5-30 min.

[0080] S24: performing surface high-temperature instantaneous plasticization treatment and surface functional modification treatment on the initial filter medium to obtain a filter medium for heterogeneous separation.

[0081] Specifically, the instantaneous plasticizing temperature of the surface high temperature instantaneous plasticizing treatment is 170-190°C, the surface high temperature instantaneous plasticizing treatment time is 1-5s, and the surface high temperature instantaneous plasticizing treatment pressure is 5-10MPa / cm 2 , so that the cross-linked fibers are melted and cooled to plasticize, so as to form a hot-melt cross-linking point structure in the filter medium. It is understandable that the melting points of nano-scale retention fibers and micron-scale fibers are higher than 170-190°C. In this way, the product is changed from a wet state to a dry state by heat setting, and the cross-linked fibers are melted by surface high-temperature instantaneous plasticization treatment to produce polycondensation, and the fibers are melted and shrunk into points, which adhere to each fiber layer to form hot-melt cross-linking points. It is understandable that the molten cross-linking points adhere to the nano-scale retention fibers and the micron-scale fibers, and will not form a complete blockage, and the impact on the effective filtration area of ​​the medium can be ignored.

[0082] Specifically, the surface functional modification treatment may be a jet plasma treatment for surface functional modification, so as to form hydrophilic groups on the surface of the shaped medium and improve the filtration separation efficiency.

[0083] Specifically, the fiber length of the nano-scale interception fiber is greater than or equal to 100 μm, the fiber length of the micron-scale fiber is 1-3 mm, and the fiber length of the cross-linked fiber is 1-5 mm.

[0084] Specifically, the average diameter of the nano-scale intercepted fibers is 10-100 nm, the average diameter of the micron-scale fibers is less than or equal to 2.5 μm, and the average diameter of the cross-linked fibers is 10-25 μm.

[0085] Specifically, the gram weight of the filter medium is greater than or equal to 50 g / m 2 , the filter medium can withstand 0.1-1MPa / cm 2 Above working pressure, the breaking strength reaches above 30N / cm, and the filtration retention accuracy is 10-100nm.

[0086] In some embodiments, the preparation process of the filter medium can be as follows: Figure 5 As shown, the island-type micron-sized fiber filaments are placed in a continuous ultrasonic fiber-opening device 1 for alkali fiber-opening treatment, then enter the cleaning device 2 for cleaning, then enter the drying device 3 for drying, and then enter the winding and cutting device 4 for winding and cutting into the required length; the resulting product enters the mixing and fiber dissociation device 5 to form an initial suspension with the nano-scale retained fibers and cross-linked fibers, and dissociate to obtain single fibers; then the product is passed through a gravity dehydration sedimentation device 6, a vacuum filtration device 7, a felt pressing device 8 and a heat setting device 9 to achieve wet sheet forming and dehydration and drying treatment; then the product is passed through a high-temperature surface instantaneous plasticization treatment device 10 and a jet plasma treatment device 11 to perform high-temperature instantaneous plasticization and surface functionalization treatment to obtain a filter medium for heterogeneous separation, and finally the product is wound up by a winding device to form a final product.

[0087] In summary, by mixing a suspension of nano-scale interception fibers, micron-scale fibers, and cross-linked fibers in a preset weight ratio, and performing fiber dissociation treatment to form a single fiber, a wet sheeting method is used to form a fiber composite structure, and a filter medium is obtained after surface treatment. No chemical additives need to be added in each preparation link of the entire process chain, and the process water can be recycled repeatedly. The preparation method is environmentally friendly and pollution-free. In addition, through surface high-temperature instantaneous plasticization treatment and surface functional modification treatment, the cross-linked fibers can form a dense hot-melt cross-linking point structure in the filter medium. The filter medium obtained can achieve nano-scale interception accuracy, and the filtration interception accuracy can reach 10-100nm, and can also withstand 0.1-1MPa / cm 2 The working pressure is above 150℃, and it can be used for a long time under the temperature condition of 150℃, which can adapt to the harsh working conditions. In addition, the material components in the filter medium are all environmentally friendly materials, which can be recycled and reused. There are no chemical additives in the whole process chain. The process water can be recycled and reused, which is non-toxic and pollution-free, and the product and process are environmentally friendly.

[0088] In another aspect, the present application provides a filtration device, which includes the above filtration medium for heterogeneous separation.

[0089] In another aspect, the present application provides a use of the above filter medium for heterogeneous separation.

[0090] The following describes the embodiments and comparative examples of the present application in combination with the above technical solutions.

[0091] The filter media for heterogeneous separation in the embodiment and comparative example 2 were prepared by the following method:

[0092] S1: micron-sized fiber filaments of a certain fiber fineness are subjected to a continuous ultrasonic alkali fiber opening process, wherein the fiber fineness, alkali solution mass concentration, fiber opening temperature, fiber opening time, washing time, drying temperature and sea island ratio are shown in Table 1;

[0093] The micron-sized fiber filaments may be FDY fiber filaments;

[0094] S2: rolling up the micron-sized fiber filaments after fiber opening and drying, and cutting them into short fibers to obtain micron-sized fibers, the fiber lengths of which are shown in Table 1;

[0095] S3: Cutting the core-sheath type or full-melt type FDY cross-linked fiber filaments of a certain tow fineness into staple fibers to obtain cross-linked fibers. The tow fineness, fiber length, and melting point temperature are shown in Table 1;

[0096] S4: nano-scale intercepted fibers, micron-scale fibers and cross-linked fibers are mixed in a preset mass ratio, and deionized water is added to prepare an initial suspension. The mass concentration of the initial suspension is shown in Table 1. The fibers are dissociated into single fibers using a fiber dissociator, and the fibers are mixed evenly to obtain a fiber suspension;

[0097] S5: The fiber suspension separated in step S4 is formed into wet sheets by a continuous forming device, and the water is squeezed out again by a felt pressing device, and then dried and formed by a heat setting device. The initial filter medium weight after forming, the heat setting temperature, and the vacuum filtration negative pressure during the wet sheet forming process are shown in Table 1;

[0098] S6: subjecting the initial filter medium after heat setting and drying to surface high temperature instantaneous plasticization treatment, the treatment temperature is shown in Table 1;

[0099] S7: performing jet plasma treatment on the filter medium treated in S6 to modify the surface function, and rolling it up to obtain a filter medium for heterogeneous separation.

[0100] Table 1

[0101]

[0102]

[0103] Among them, the fiber bundle fineness is 75D / 36F 25 islands means that the total fineness of the fiber bundle is 75D, which is composed of 36 filaments, each of which has 25 islands, and the fineness of each island is 75 / 36 / 25D. The fineness of other fiber bundles has similar meanings and will not be repeated.

[0104] Based on the above Table 1, Figure 2-4 It can be seen that the filter media prepared in Examples 1 to 5 form a strong bonding structure of three types of cross-linked and entangled fibers, and the working pressure, interception accuracy, breaking strength and filtration efficiency of Examples 1 to 5 are significantly improved. Figure 4 One cross-linked fiber (18.297 μm) and two micron-sized fibers (0.889 μm and 1.987 μm) are exemplarily indicated. It is understandable that the nanoscale retention fiber size is not indicated due to image resolution limitations.

[0105] In summary, the present application has the following beneficial effects: by forming a fiber composite structure formed by nano-scale interception fibers, micron-scale fibers and cross-linked fibers in the filter medium, and controlling the weight proportion of the nano-scale interception fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micron-scale fibers to increase in sequence, the filter medium for heterogeneous phase separation can achieve nano-scale filtration accuracy, and provide a high filtration accuracy of up to 0.1-1 MPa / cm based on the micron-scale fibers and the cross-linked fibers. 2 The above working pressure bearing capacity; in addition, the melting point of nano-scale interception fiber and micron-scale fiber is higher than that of cross-linked fiber, which is beneficial to the melt plasticization treatment in the preparation process, so as to further improve the support strength and cross-linking strength of the filter medium, ensure the cross-linking force of the fiber unit in the filter medium in the liquid phase application environment, and avoid separation and disintegration between fibers. In addition, by mixing and configuring the suspension of nano-scale interception fiber, micron-scale fiber and cross-linked fiber according to the preset weight ratio, and performing fiber dissociation treatment to form a single fiber, the wet sheeting method is used for molding to form a fiber composite structure, and the filter medium is obtained after surface treatment. No chemical additive components need to be added in each preparation link of the entire process chain, and the process water can be repeatedly recycled. The preparation method is environmentally friendly and pollution-free. In addition, through the surface high-temperature instantaneous plasticization treatment and surface functional modification treatment, the cross-linked fiber can form a dense hot-melt cross-linking point structure in the filter medium. The filter medium prepared can not only achieve nano-scale interception accuracy, but also withstand 0.1-1MPa / cm 2 More work pressure.

[0106] The above description has fully disclosed the specific implementation methods of the present application. It should be pointed out that any changes made by technicians familiar with the field to the specific implementation methods of the present application do not deviate from the scope of the claims of the present application. Accordingly, the scope of the claims of the present application is not limited to the above specific implementation methods.

Claims

1. A filter medium for heterogeneous separation, characterized in that: including a fiber composite structure formed of nano-scale trapped fibers, micron-scale fibers, and cross-linked fibers; The weight proportion of the nanoscale retained fibers, the weight proportion of the cross-linked fibers and the weight proportion of the micron-scale fibers in the fiber composite structure increase successively; the melting points of the nanoscale retained fibers and the micron-scale fibers are both higher than that of the cross-linked fibers; the average diameter of the nanoscale retained fibers is 10-100 nm.

2. The filter medium according to claim 1, characterized in that The filter medium comprises a retention surface layer and a flow guiding surface layer, the retention surface layer and the flow guiding surface layer are cross-linked, and the cross-linked fibers form a hot-melt cross-linking point structure in the filter medium; The mass proportion of the nanoscale retention fibers in the retention surface layer is higher than the mass proportion of the micron-scale fibers and the mass proportion of the cross-linked fibers, and the mass proportion of the micron-scale fibers in the guide surface layer is higher than the mass proportion of the nanoscale retention fibers.

3. A method for preparing a filter medium for heterogeneous separation, applied to the filter medium for heterogeneous separation as claimed in any one of claims 1 to 2, characterized in that: The method comprises the following steps: S21: mixing the nano-scale retained fibers, the micron-scale fibers and the cross-linked fibers according to a preset weight ratio to form an initial suspension, wherein the weight ratio of the nano-scale retained fibers, the weight ratio of the cross-linked fibers and the weight ratio of the micron-scale fibers increase in sequence; and the average diameter of the nano-scale retained fibers is 10-100 nm; S22: performing fiber dissociation treatment on the initial suspension, mixing evenly, and obtaining a fiber suspension; S23: performing a wet sheet forming process on the fiber suspension, and dehydrating and drying the fiber suspension to obtain an initial filter medium; S24: performing a surface high-temperature instantaneous plasticization treatment and a surface functional modification treatment on the initial filter medium to obtain the filter medium for heterogeneous separation.

4. The method according to claim 3, characterized in that The preset weight ratio is 1:(5-50):(2-48).

5. The method according to claim 3, characterized in that The wet sheet forming process of the fiber suspension in S23 includes: S231: performing gravity dehydration and sedimentation treatment on the fiber suspension to obtain an initial fiber layered medium; S232: performing a suction filtration and dehydration treatment on the initial fiber layered medium to obtain a fiber layered medium to be heat-set and dried; S233: performing moisture squeezing and heat setting drying on the fiber layered medium to obtain the initial filter medium.

6. The method according to claim 3, characterized in that Before S21, the method further includes: S11: opening the island-in-sea type micron-sized fiber filaments in an alkaline solution to obtain the island-in-sea fiber filaments; S12: Cutting the island fiber filaments into short fibers to obtain the micron-sized fibers.

7. The method according to any one of claims 3 to 6, characterized in that: The material of the nano-scale interception fiber is cellulose microfiber, the material of the micron-scale fiber includes one or more of polyester and nylon, and the material of the cross-linked fiber includes one or more of polyester and nylon.

8. The method according to any one of claims 3 to 6, characterized in that: The fiber length of the nano-scale interception fiber is greater than or equal to 100 μm, the fiber length of the micron-scale fiber is 1-3 mm, and the fiber length of the cross-linked fiber is 1-5 mm.

9. The method according to any one of claims 3 to 6, characterized in that The average diameter of the micron-sized fibers is less than or equal to 2.5 μm, and the average diameter of the cross-linked fibers is 10-25 μm.

10. The method according to any one of claims 3 to 6, characterized in that: The gram weight of the filter medium is greater than or equal to 50 g / m 2 The filtration retention accuracy of the filter medium is 10-100nm.

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