A 0.1μm ultra-precision filtration material, its preparation method and application

Abstract

A 0.1μm ultra-precision filtration material, its preparation method and application relate to the technical field of filtration materials, and solve the problems of insufficient precision and high maintenance cost in existing oil filtration technologies. Wood cellulose is bleached after alkali treatment, and then nano-cellulose fibers are obtained by high-pressure homogenization or enzymatic hydrolysis, and dispersed in water for ultrasonic treatment to obtain the main slurry; the surface of mesoporous SiO2 is modified with a silane coupling agent; short-cut aramid fibers, surface-modified mesoporous SiO2 and nano-silver are added to the main slurry, and stirred and ultrasonically mixed uniformly; the coarse fiber slurry is vacuum filtered to obtain the support layer; the slurry is vacuum filtered to obtain the intermediate layer; the main slurry is vacuum filtered to obtain the surface layer, and the three layers are laminated together, and pre-freezing, freeze-drying and chemical cross-linking are carried out in sequence; heat-pressed and wrinkled, and then helically wound; a polypyrrole coating is electrostatically sprayed on the surface, and then a fluorosilane oil-repellent coating is vapor deposited. The invention can be applied to the filtration of lubricating oil and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of filter materials, and particularly relates to a 0.1μm ultra-precision filter material, a preparation method thereof, and an application thereof. Background Art

[0002] Lubricating oil undertakes multiple functions such as lubrication, cooling, and sealing in mechanical equipment. However, during its service process, it will inevitably be invaded by pollutants such as particulate matter, moisture, and oxidation products, and these pollutants will trigger a chain destruction effect. When hard particles suspended in the oil enter the friction pair with the lubricating oil, if their size exceeds the oil film thickness, they will penetrate the lubricating film and directly contact the metal surface, causing abrasive wear. For example, particles larger than 5μm will scratch the gear tooth surface like a micro grinding wheel, while particles of 1 - 5μm will cause contact fatigue in rolling bearings, forming microscopic cracks invisible to the naked eye.

[0003] Research data shows that by improving the filtration accuracy of the hydraulic system from 5μm to 1μm, the wear rate of the pump valve assembly can be reduced by 70%, and the maintenance cycle can be extended from 2000h to 8000h. For a filtration system that fails to meet the standard, its hidden costs are not only reflected in the equipment maintenance costs, but more importantly, through chemical degradation processes such as catalytic oxidation and additive failure, the entire batch of lubricating oil will be scrapped in advance, forming a vicious cycle of "pollution - degradation - re - pollution". This battle at the micro scale essentially determines the reliability and economic boundaries of modern industrial equipment.

[0004] The strict requirements for filtration accuracy stem from the trend of precision in modern mechanical systems. Taking high - speed precision bearings as an example, the thickness of their elastohydrodynamic lubricating film has dropped to the order of 0.1 - 0.3μm, which means that filtration technology must break through the micron - level threshold and achieve effective interception of 0.1μm - level particles.

[0005] Existing lubricating oil filtration materials generally use traditional filter papers (glass fiber or polyester fiber) or mechanical filtration systems (such as vacuum oil filters). The working principle of the mechanical filtration system relies on pressure difference to drive the oil through the filter media, and the pore distribution of the filter media itself determines the upper limit of filtration accuracy. Due to the uneven pore distribution of traditional filter media fibers and the lack of gradient design in the multi - layer composite structure, the penetration rate of small particles is high. Its filtration accuracy is usually 1 - 5μm, and the interception rate for 0.1μm - level particles is insufficient. In addition, when the vacuum oil filter processes high - viscosity lubricating oil (such as ISO VG320 gear oil), it needs to be heated to above 60℃ to reduce the viscosity, but heating will cause the oil to oxidize more quickly and the additives to decompose.

[0006] To address the problem of insufficient filtration accuracy, existing technologies mostly adopt dehydration membrane components or off-line bypass systems, which rely on complex hollow fiber membranes or chemical additives (such as the separation aid of SKF RecondOil). However, the additives may damage the original components of the lubricating oil (such as antioxidants and extreme pressure agents); moreover, the equipment is complex and requires multi-stage treatment of pre-filtration + dehydration membrane + air compressor, resulting in high maintenance costs and large space occupation. Existing parallel filters improve the filtration accuracy by stacking multiple filters to extend the service life of the equipment, but the filters need to be replaced frequently, and the replacement process requires manually closing the valves and disassembling the pipeline joints, resulting in long downtime. In addition, traditional filters need to be replaced regularly in a short period of time, which is costly. Summary of the Invention

[0007] In order to solve the problems of insufficient accuracy and high maintenance cost in existing oil filtration technologies, the present invention provides a 0.1μm ultra-fine filtration material, its preparation method and application.

[0008] The technical solution of the present invention is as follows:

[0009] A preparation method of a 0.1μm ultra-fine filtration material, comprising the following steps:

[0010] S1. Treat lignocellulose with alkali to remove lignin and hemicellulose, then bleach it, and then prepare nanofibrillated cellulose by high-pressure homogenization or enzymatic hydrolysis;

[0011] S2. Disperse the nanofibrillated cellulose in deionized water and perform ultrasonic treatment to obtain a main slurry;

[0012] S3. Modify the surface of mesoporous SiO2 with a silane coupling agent;

[0013] Add short aramid fibers with a fiber diameter within 10μm and a length of 3mm - 5mm, surface-modified mesoporous SiO2 and silver nanoparticles to the main slurry, and use mechanical stirring combined with ultrasonic assistance to uniformly mix the slurry;

[0014] S4. Vacuum filter a coarse fiber slurry with a fiber width of 50μm - 100μm and a length of 750μm - 900μm to obtain a support layer. The coarse fiber slurry comprises the following components in mass percentage: cellulose 50%, hemicellulose 42%, lignin 5%, resin 1%, pigment 1%, pectin 0.5% and ash 0.1%; vacuum filter the slurry obtained in step S3 to obtain an intermediate layer; vacuum filter the main slurry to obtain a surface layer; press the support layer, intermediate layer and surface layer together with a roller press in the wet state to obtain a multi-layer composite filter material;

[0015] S5. Perform pre-freezing, freeze-drying and chemical cross-linking treatments on the multi-layer composite filter material in sequence;

[0016] S6, performing heat pressing and folding treatment on the treated material, and then spirally winding it using an automatic winding machine;

[0017] S7. Electrostatically spray a polypyrrole coating on the surface of the material, and then prepare a fluorosilane oleophobic coating by vapor deposition to obtain a 0.1 μm ultra-fine filter material.

[0018] Preferably, the alkali treatment in step S1 is specifically performed by soaking at 80°C for 2 hours using 5-10% NaOH; and the bleaching treatment is specifically performed by soaking at 60°C for 1 hour using 3-5% H2O2 at a pH of 10-11.

[0019] Preferably, the pressure of the high-pressure homogenization method in step S1 is 50-100 MPa, and the number of cycles is 5-10 times.

[0020] Preferably, the mass fraction of the nanocellulose fibers in step S2 is 2-5 wt %;

[0021] In step S3, the mass fraction of the chopped aramid fibers is 5-10 wt %, the mass fraction of the surface-modified mesoporous SiO 2 is 3-8 wt %, and the mass fraction of the nano-silver is 0.1-0.5 wt %.

[0022] Preferably, the frequency of the ultrasonic treatment in step S2 is 20 kHz, and the ultrasonic treatment time is 30 min;

[0023] In step S3, the rotation speed of the mechanical stirring is 500-1000 rpm, and the mechanical stirring time is 1 hour; the frequency of the ultrasonic assistance is 40 kHz, and the ultrasonic assistance time is 15 minutes.

[0024] Preferably, in step S4, the filtration condition of the support layer is filtration at -0.08 MPa for 2 min, and the thickness of the support layer is 40 μm to 50 μm; the filtration condition of the intermediate layer is filtration at -0.1 MPa for 5 min, and the thickness of the intermediate layer is 10 μm to 15 μm; the filtration condition of the surface layer is filtration at -0.05 MPa for 1 min, and the thickness of the surface layer is 35 μm to 50 μm; the gram weight of the multilayer composite filter material is 16 to 20 g / cm 2 ; The pressing pressure of the roller press is 0.5~1MPa.

[0025] Preferably, the pre-freezing in step S4 is: freezing at -40°C; the freeze-drying is: under a vacuum degree of 10-50 Pa, raising the temperature by 5°C every 2 hours from -40°C until the temperature reaches 25°C; the chemical cross-linking is: steam cross-linking with a 5% glutaraldehyde solution for 2 hours or immersion cross-linking in epichlorohydrin with a pH of 9 at 50°C for 4 hours.

[0026] Preferably, the hot pressing wrinkling treatment in step S6 is specifically as follows: heating the mold to 80-100° C. and shaping at a pressure of 0.2 MPa for 10 minutes; the tension of the spiral winding is controlled at 5-10 N, and the winding angle is 30°-45°.

[0027] The present invention also provides a 0.1 μm ultra-fine filter material, which is prepared by the above preparation method.

[0028] The present invention also provides an application of the 0.1 μm ultra-fine filter material in lubricating oil filtration.

[0029] Compared with the prior art, the present invention has the following specific beneficial effects:

[0030] This invention overcomes the performance bottleneck of traditional lubricating oil filtration technology through an innovative low-temperature molding process and structural design. During the material preparation process, the temperature is strictly controlled below 150°C throughout, preventing carbonization and degradation of the cellulose material at high temperatures. Furthermore, through the directional temperature gradient control during the freeze-drying stage, a vertically connected, multi-level pore structure is induced. This biomimetic through-pore design enables the filter material to achieve a filtration accuracy of 0.1μm, meeting the dual requirements of high precision and high throughput.

[0031] To address the problem of lubricating oil dehydration, the present invention constructs a solid-liquid collaborative filtration mechanism. The dense fiber network on the surface can efficiently intercept solid particulate pollutants ≥0.1μm. The intermediate functional layer achieves targeted water adsorption through chemically modified mesoporous materials. A single-stage filter element can directly reduce the water content of the oil from 1500ppm to below 100ppm, successfully replacing the traditional process of pre-filtration, coalescence, and separation triple filter element system in series. The filter surface is modified with fluorosilane to form a superoleophobic interface, which can effectively block micropore blockage caused by oil molecule penetration, overcoming the pain point of traditional filter materials that are easily ineffective due to oil infiltration, and allowing the moisture adsorption layer to maintain long-term activity in the oil environment.

[0032] This invention boasts remarkable adaptability across a wide range of operating conditions. For high-viscosity lubricants like ISO VG460, it eliminates the need for the heating and viscosity reduction treatment of traditional vacuum oil filters and maintains a stable flow rate of ≥5L / min at room temperature, preventing oil oxidation and additive decomposition caused by high temperatures. The optimized spiral winding structure and homogeneous pore distribution within the filter material, combined with its oleophobic and hydrophilic dual-functional interface design, increase the system's service life by more than five times under complex operating conditions, significantly reducing equipment maintenance frequency and overall operating costs.

[0033] This invention not only solves the inherent contradiction between filtration accuracy and flux, but also provides a new solution for the reliability and energy efficiency upgrade of industrial lubrication systems through multi-dimensional collaborative innovation of materials, structures and processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the micrograph of the multi-layer composite filter material described in Example 1;

[0035] Figure 2 It is the micrograph of the composite filter material after hot pressing and wrinkling treatment described in Example 1;

[0036] Figure 3 It is the schematic diagram of the filtration test system described in Effect Example 1. Specific Embodiments

[0037] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0038] Example 1.

[0039] In this example, a superfine filtration material is prepared, and the specific operation process is as follows:

[0040] S1. Immerse lignocellulose in 8% NaOH at 80°C for 2 h to remove lignin and hemicellulose, then bleach it by immersing in 4% H2O2 with pH 10 - 11 at 60°C for 1 h, and then prepare nanofibrillated cellulose fibers CNF by circulating 8 times under the condition of 80 MPa using high-pressure homogenization method;

[0041] S2. Weigh 36.7 g of nanofibrillated cellulose fibers CNF and disperse them in deionized water, and ultrasonically treat them at 20 kHz for 30 min to obtain the main slurry;

[0042] S3. Weigh 61.7 g of mesoporous SiO2, disperse it in 100 mL of ethanol, add 1.85 g of KH-550 silane coupling agent, magnetically stir it at 60°C for 2 h, centrifuge and wash it 3 times, and then vacuum dry it at 60°C to obtain surface-modified mesoporous SiO2;

[0043] Add 83.3 g of chopped aramid fibers, the above-mentioned surface-modified mesoporous SiO2 and 3.3 g of silver nanoparticles to the main slurry, mechanically stir it at 800 rpm for 1 h and assist it with 40 kHz ultrasonic for 15 min to make the slurry uniformly mixed;

[0044] S4. Mix 50 g of cellulose, 42 g of hemicellulose, 5 g of lignin, 1 g of resin, 1 g of pigment, 0.5 g of pectin, 0.1 g of ash and 0.4 g of water to form a crude fiber slurry, and filter it under -0.08 MPa for 2 min to obtain a support layer; filter the slurry obtained in step S3 under -0.1 MPa for 5 min to obtain an intermediate layer; prepare the main slurry by the same operation in step S2, and filter it under -0.05 MPa for 1 min to obtain a surface layer; press the support layer, intermediate layer and surface layer together under 0.5 - 1 MPa with a roller press in the wet state to obtain a multi-layer composite filter material, and the schematic diagram of its microstructure is shown in Figure 1 ;

[0045] S5. Subject the multi-layer composite filter material to rapid pre-freezing at -40 °C, and then maintain a vacuum degree of 10 - 50 Pa. Starting from -40 °C, raise the temperature by 5 °C every 2 h until the temperature reaches 25 °C, and perform freeze-drying. Then, perform chemical cross-linking treatment by steam cross-linking with a 5% glutaraldehyde solution for 2 h;

[0046] S6. Pleating and spiral forming:

[0047] Heat the mold to 80 - 100 °C, shape it under a pressure of 0.2 MPa for 10 min, and perform hot pressing pleating treatment on the treated material. The schematic diagram of the microstructure of the treated material is shown in Figure 2 as shown, and then perform spiral winding with an automatic winding machine, control the tension at 5 - 10 N, and the winding angle is 30° - 45°; make a wound filter element with a diameter of 24 cm and a height of 26 cm;

[0048] S7. Electrostatically spray a polypyrrole coating with a conductivity of 10 -3 S / cm and a thickness of 0.5 - 1 μm on the surface of the filter element, and then prepare a fluorosilane oleophobic coating by vapor deposition at 150 °C for 30 min to obtain a 0.1 μm ultra-precision filter element.

[0049] Example 2.

[0050] In this example, the dosage of CNF is 20.4 g, the dosage of mesoporous SiO2 is 31.2 g, the dosage of short-cut aramid fiber is 50 g, and the dosage of nano silver is 1.04 g. The chemical cross-linking process in step S5 is: impregnate and cross-link in epichlorohydrin with pH = 9 at 50 °C for 4 h. The rest of the operations are the same as those in Example 1.

[0051] Example 3.

[0052] In this example, the dosage of CNF is 52.6 g, the dosage of mesoporous SiO2 is 98 g, the dosage of KH-550 is 2.94 g, the dosage of short-cut aramid fiber is 111.1 g, and the dosage of nano silver is 5.56 g. The rest of the operations are the same as those in Example 1.

[0053] Comparative Example 1

[0054] A commercially available glass fiber filter paper was made into a wound filter element with a diameter of 24 mm and a height of 26 mm.

[0055] Comparative Example 2

[0056] The stainless steel sintered mesh in a commercial vacuum oil filter was used as the filter element.

[0057] Effect Example 1

[0058] The filter elements in Examples 1 to 3 and Comparative Examples 1 and 2 were respectively installed in the filter, and the cleanliness of the oil before and after filtration was monitored by two sets of KZ-4 particle sensors of Tianjin Luogen Kexing Company, and a filtration test system as shown in Figure 3 was established, where the filtration system and the oil storage tank could be weighed separately.

[0059] 1 kg of silica powder with a particle size of 20 nm was prepared as the test filtration material.

[0060] The test process was as follows:

[0061] White oil was injected into the oil storage bottle, and the filtration system was started. Filtration was stopped when it reached Nas3 level. At this time, the filtration system was filled with oil and the weight was in a constant state;

[0062] The oil sample in the oil storage bottle was kept at 200 mL (150 g), and 20 g of silica powder was added and stirred evenly;

[0063] The filtration system was started and the filtration time was 30 min to 1 h, and then the filtration system was stopped;

[0064] The weight of the oil storage bottle was measured and recorded;

[0065] The above process was repeated and relevant data were obtained.

[0066] The test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] According to the test results, using 0.02 μm fine particles, verified by the change in the weight of the oil in the oil storage bottle before and after filtration, the fine particles could already be captured by the filter material in the filtration system. The 0.1 μm ultra-precision filter material for lubricating oil based on cellulose reinforcement passed the test.

[0070] Effect Example 2

[0071] The filter elements in Examples 1 to 3 and Comparative Examples 1 and 2 were respectively installed in the filter, and the ISO VG460 compressor oil (initial water content 1500 ppm) was used to test the filtration performance.

[0072] At room temperature, with a flow rate of 5 L / min and continuous operation for 1000 h, the real-time pressure difference was monitored, and the results are shown in Table 2.

[0073] Table 2

[0074]

[0075] The above test results can prove that the special material and structure design of the filter material of the present invention can delay the pore blockage, and the pressure difference growth rate is much lower than that of the traditional filter element. For the ISO VG460 grade compressor oil, it is not necessary to rely on the heating and viscosity reduction treatment of the traditional vacuum oil filter, and a stable flow rate of ≥5 L / min can be maintained at room temperature, avoiding oil oxidation and additive decomposition caused by high temperature.

[0076] The water content of the oil before and after filtration was compared, and the results are shown in Table 3.

[0077] Table 3

[0078]

[0079] The above test results can prove that the traditional filter paper only intercepts particles and has poor water adsorption capacity, and vacuum heating dehydration is required. However, the water molecule adsorption capacity of the mesoporous SiO2 inside the filter material of the present invention, combined with the oleophobic-hydrophilic bifunctional interface design, can reduce the water content of the oil from 1500 ppm to ≤100 ppm.

[0080] Effect Example 3.

[0081] Case of oil purification for the coal vertical mill box in a cement plant:

[0082] Operating conditions: L-HM 68 anti-wear hydraulic oil, initial particle count pollution degree (NAS1638 grade) 12, water content 80 ppm.

[0083] Implementation effect: After treatment, the particle count pollution degree (NAS1638 grade) dropped to 7, and the water content ≤40 ppm.

[0084] The oil change cycle was extended from 3 months to 18 months, and the maintenance cost was greatly reduced.

[0085] It can be proved that the optimized helical winding structure and homogeneous pore distribution inside the filter medium of the present invention, combined with the oil-repellent and hydrophilic bifunctional interface design, significantly improve the service life of the system under complex working conditions, and greatly reduce the equipment maintenance frequency and comprehensive operation cost. The present invention not only solves the inherent contradiction between filtration accuracy and flux, but also provides a new solution for the reliability and energy efficiency upgrade of industrial lubrication systems through multi-dimensional collaborative innovation of materials, structures and processes.

Claims

1. A preparation method of a 0.1μm ultra-fine filtration material, characterized in that, It includes the following steps: S1. Subject the lignocellulose to alkali treatment to remove lignin and hemicellulose, then perform bleaching treatment, and then prepare nanocellulose fibers by high-pressure homogenization method or enzymatic hydrolysis method; S2. Disperse the nanocellulose fibers in deionized water and perform ultrasonic treatment to obtain the main slurry; S3. Perform surface modification on mesoporous SiO2 with a silane coupling agent; Add short aramid fibers with a fiber diameter within 10 μm and a length of 3 mm to 5 mm, surface-modified mesoporous SiO2, and silver nanoparticles to the main slurry, and perform mechanical stirring combined with ultrasonic assistance to uniformly mix the slurry; S4. Vacuum filter the coarse fiber slurry with a fiber width of 50 μm to 100 μm and a length of 750 μm to 900 μm to obtain a support layer. The coarse fiber slurry includes the following components in mass percentage: cellulose 50%, hemicellulose 42%, lignin 5%, resin 1%, pigment 1%, pectin 0.5%, and ash 0.1%; Vacuum filter the slurry obtained in step S3 to obtain an intermediate layer; Vacuum filter the main slurry to obtain a surface layer; Press the support layer, intermediate layer, and surface layer together with a roll press in the wet state to obtain a multi-layer composite filter material; S5. Perform pre-freezing, freeze-drying, and chemical cross-linking treatment on the multi-layer composite filter material in sequence; S6. Perform hot pressing and wrinkling treatment on the treated material, and then perform spiral winding with an automatic winding machine; S7. Electrostatically spray a polypyrrole coating on the surface of the material, and then prepare a fluorosilane oil-repellent coating by chemical vapor deposition to obtain a 0.1 μm ultra-precise filter material.

2. The preparation method of the 0.1μm ultra-precision filtration material according to claim 1, characterized in that, The alkali treatment in step S1 is specifically to soak with 5-10% NaOH at 80°C for 2 h; The bleaching treatment is specifically to soak with 3-5% H2O2 with a pH of 10-11 at 60°C for 1 h.

3. The preparation method of the 0.1μm ultra-fine filtration material according to claim 1, characterized in that, The pressure of the high-pressure homogenization method in step S1 is 50-100 MPa, and the number of cycles is 5-10 times.

4. The preparation method of the 0.1μm ultra-precision filtration material according to claim 1, characterized in that, The mass fraction of the nanocellulose fibers in step S2 is 2-5 wt%; The mass fraction of the short aramid fibers in step S3 is 5-10 wt%, the mass fraction of the surface-modified mesoporous SiO2 is 3-8 wt%, and the mass fraction of the silver nanoparticles is 0.1-0.5 wt%.

5. The preparation method of the 0.1μm ultra-precision filtration material according to claim 1, characterized in that, The frequency of the ultrasonic treatment in step S2 is 20 kHz, and the ultrasonic treatment time is 30 min; The rotation speed of the mechanical stirring in step S3 is 500-1000 rpm, and the mechanical stirring time is 1 h; The frequency of the ultrasonic assistance is 40 kHz, and the ultrasonic assistance time is 15 min.

6. The preparation method of the 0.1μm ultra-fine filtration material according to claim 1, characterized in that, The suction filtration conditions of the support layer described in step S4 are suction filtration for 2 min under -0.08 MPa, and the thickness of the support layer is 40 μm to 50 μm; the suction filtration conditions of the intermediate layer are suction filtration for 5 min under -0.1 MPa, and the thickness of the intermediate layer is 10 μm to 15 μm; the suction filtration conditions of the surface layer are suction filtration for 1 min under -0.05 MPa, and the thickness of the surface layer is 35 μm to 50 μm; the grammage of the multi-layer composite filter material is 16 to 20 g / cm 2 ; the pressing pressure of the roll press is 0.5 to 1 MPa.

7. The preparation method of the 0.1μm ultra-fine filtration material according to claim 1, characterized in that, The pre-freezing in step S4 is: freeze at -40°C; The freeze-drying is: under a vacuum of 10-50 Pa, heat up 5°C every 2 h starting from -40°C until the temperature rises to 25°C; The chemical cross-linking is: perform steam cross-linking with 5% glutaraldehyde solution for 2 h or impregnate and cross-link in epichlorohydrin with a pH of 9 at 50°C for 4 h.

8. The preparation method of the 0.1μm ultra-fine filtration material according to claim 1, characterized in that, The hot pressing and wrinkling treatment in step S6 is specifically: heat the mold to 80-100°C and set the shape at a pressure of 0.2 MPa for 10 min; The tension of the spiral winding is controlled at 5-10 N, and the winding angle is 30°-45°.

9. A 0.1μm ultra-fine filtration material, characterized in that, It is prepared by using the preparation method described in any one of claims 1 to 8.

10. Application of a 0.1 μm ultra-precision filtration material as described in claim 9 in the filtration of lubricating oil.

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