A polyimide filter material, a preparation method thereof and application thereof

Abstract

The application discloses a polyimide filter material, a preparation method thereof and application of the polyimide filter material. The polyimide fiber is pretreated by using ammonia water, and the polyimide fiber is prepared into a hard filter material by using a hot-press forming method. The polyimide filter material is used as a high-temperature hard filter material under a temperature condition of 220-300 DEG C. The hard filter material has better thermal stability, the thermal decomposition temperature is 540-600 DEG C, the filter material has good mechanical properties, high porosity and good filtering effect, and the filter material with better performance is prepared, and the added value of the product is increased.

Description

Technical Field

[0001] This invention relates to a polyimide filter material and its preparation method, belonging to the field of filter materials. Background Technology

[0002] In recent years, particulate matter pollution in the air has become a major concern, posing a significant threat to human health and reducing the quality of the surrounding environment upon which we depend for survival. Particulate matter pollution primarily originates from industrial emissions. While particles larger than 10 μm in diameter do not enter the human body through the respiratory tract, particles smaller than 10 μm do. If these particles contain heavy metals, toxic compounds, or other substances, they can trigger respiratory illnesses. Therefore, improving the effectiveness of filtration methods and enhancing air quality is of paramount importance for environmental protection.

[0003] Current industrial high-temperature flue gas filtration methods require temperatures above 750℃, necessitating the use of ceramic or metal filter materials. Within the 220-300℃ temperature range, ceramic filter media suffer from difficulties in cleaning and permanent failure. While metal filter media possess good mechanical strength and processability, allowing for long-term stable use, their high investment costs currently limit their widespread application in industrial high-temperature filtration. Consequently, polymer filter materials have long dominated the market. my country's research and application of high-temperature filtration materials started relatively late, resulting in a significant gap in technology and product performance compared to some developed countries, particularly in high-temperature polymer materials. Therefore, developing a high-temperature filtration material with excellent overall performance is of paramount importance.

[0004] Dust removal methods using polymer filter media primarily employ baghouse dust collectors. Currently used filter media are flexible, prone to clogging, and suffer from shortened lifespan. Rigid filter media could effectively solve this problem. However, existing rigid filter media sintered plates have the drawback of poor high-temperature resistance, with a maximum operating temperature of 190℃. Therefore, new methods for preparing rigid filter materials are urgently needed. Polyimide fibers, due to their advantages such as high-temperature resistance, chemical stability, and large specific surface area, are highly suitable for preparing rigid filter materials. Summary of the Invention

[0005] To address the problems of existing technologies, the present invention aims to overcome the shortcomings of existing technologies and provide a polyimide filter material, its preparation method, and its application. The invention employs hot-pressing technology to prepare polyimide fibers into rigid filter materials, providing a new approach to the preparation of rigid filter materials. This method is not only simple to operate and produces less pollution, but the rigid filter material is also more heat-resistant and has higher porosity. Furthermore, it provides a good foundation for preparing filter materials with superior performance, increasing the added value of the products.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a polyimide filter material includes the following steps:

[0008] a. Pretreatment of polyimide fibers:

[0009] Place polyimide short fibers into a beaker and pretreat them with a pretreatment agent until they are completely impregnated. Seal and let stand for at least 15 minutes. After impregnation, remove the polyimide short fibers and wash them repeatedly with deionized water to obtain pretreated polyimide fibers. Then, shake and loosen the polyimide fibers, filter them using a funnel, remove the filtered polyimide fibers, and dry them in a drying oven at a temperature not lower than 60°C.

[0010] b. Preparation of polyimide filter materials:

[0011] The polyimide fibers prepared in step a are subjected to a hot pressing process, with pressure applied throughout the entire pressing process, including the following steps:

[0012] First, the polyimide fibers are stacked into a mold. Then, the mold is placed in a flat vulcanizing machine and preheated from room temperature to at least 120°C for at least 20 minutes. Then, the temperature is raised to at least 290°C and held for at least 1.5 hours for hot pressing. After hot pressing, the desired material shape is obtained. Then, the material is cooled naturally to obtain the polyimide filter material.

[0013] Preferably, in step a, the polyimide fiber is selected with a length of 30-50 mm and a diameter of 8-10 μm.

[0014] Preferably, in step a, the pretreatment agent is an alkaline solution with a concentration of 10. -4 -10 -6 Sodium hydroxide aqueous solution with a concentration of 10 mol / L -4 -10 -6 A mol / L aqueous solution of potassium hydroxide or an ammonia solution with a concentration of 0.898-0.907 mol / L.

[0015] Preferably, in step a, the sealing and standing time is controlled to be 15-150 minutes during the impregnation pretreatment, and the pretreatment agent completely impregnates the polyimide fiber.

[0016] Preferably, in step a, drying involves placing the polyimide fibers in a drying oven at 60-80°C for 6-8 hours.

[0017] Preferably, in step a, when the polyimide fiber is subjected to oscillation loosening treatment, the polyimide fiber is placed in an oscillator containing deionized water for oscillation loosening treatment.

[0018] Preferably, in step b, the hot pressing forming step is as follows:

[0019] (1) Take the dried polyimide fibers, stack them in the mold, and put them into the flat vulcanizing machine;

[0020] (2) Hold pressure with a load of 1-7MPa, and apply pressure throughout the hot pressing process;

[0021] (3) Heat the material from room temperature to 120-150℃ and keep it at that temperature for 20-40 minutes, then heat it to 290-310℃ and keep it at that temperature for 1.5-2 hours, and then heat it to form a polyimide filter material.

[0022] A polyimide filter material is prepared using the preparation method of the polyimide filter material described in this invention.

[0023] Preferably, the polyimide filter material of the present invention is a rigid, cylindrical material with a diameter of not less than 14 cm, a thickness of not less than 2 mm, and a porosity of not less than 65.37%. More preferably, its porosity is 65.37-79.07%.

[0024] Preferably, the maximum stress of the polyimide filter material of the present invention is not less than 0.052 MPa. More preferably, the maximum stress is 0.052-0.617 MPa.

[0025] An application of the polyimide filter material described in this invention, wherein the polyimide filter material is used as a high-temperature rigid filter material at a temperature of 220-300°C.

[0026] This invention first pre-treats the polyimide fibers by immersing them in ammonia water, sealing and allowing them to stand for a period of time, then washing them clean with deionized water to obtain pre-treated polyimide fibers. The pre-treated polyimide fibers are then vibrated to loosen them, poured into a Buchner funnel for natural sedimentation, and after filtering out most of the deionized water, they are removed and dried in a drying oven. Finally, a hot-pressing method is used to obtain the polyimide filter material. This invention uses hot-pressing technology to produce rigid filter materials from polyimide fibers, which possess good mechanical properties, high porosity, excellent heat resistance, and good filtration effect. It can be used to produce high-value-added products with special functions.

[0027] This invention relates to a polyimide filter material, prepared using the method described herein. Existing technologies sinter polymer powders into rigid filter materials, which exhibit poor thermal stability and cannot be used in environments with high temperature requirements. The polyimide rigid filter material prepared by this invention is suitable for a temperature range of 220-300℃. While bag filters offer relatively high temperature resistance, their soft nature makes them prone to clogging and deformation during use, leading to secondary dust and fogging and a shortened lifespan. The rigid polyimide filter material prepared by this invention is rigid, effectively avoiding the problems associated with flexible filter materials. Furthermore, this invention provides a new approach to preparing rigid filter materials, laying the foundation for the subsequent development of filter materials with higher added value.

[0028] Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages:

[0029] 1. This invention uses polyimide fiber as raw material, which makes the resulting rigid filter material have excellent thermal stability;

[0030] 2. This invention uses hot pressing technology to process polyimide fibers, which can produce rigid filter materials with high porosity;

[0031] 3. This invention utilizes ammonia water to pretreat polyimide fibers and employs a hot-pressing method to prepare rigid filter materials from the polyimide fibers. This invention yields rigid filter materials with better thermal stability, a thermal decomposition temperature of 540-600℃, good mechanical properties, high porosity, and good filtration effect. Furthermore, it provides a good foundation for preparing filter materials with superior performance, increasing the added value of the products. Attached Figure Description

[0032] Figure 1 This is a physical image of the polyimide filter material prepared in Example 1 of the present invention.

[0033] Figure 2 The graph shows the thermal properties of the polyimide filter material prepared in Example 3 of this invention.

[0034] Figure 3 This is a filtration efficiency diagram of the polyimide filter material prepared in Example 3 of the present invention. Detailed Implementation

[0035] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are described in detail below:

[0036] Example 1:

[0037] In this embodiment, a method for preparing a polyimide filter material includes the following steps:

[0038] a. Pretreatment of polyimide fibers:

[0039] First, weigh 40g of polyimide fiber using an electronic balance. The fiber is 30mm long and 8μm in diameter. Place it in a beaker and pour in an appropriate amount of 10 -6 The polyimide fiber was completely impregnated with a sodium hydroxide aqueous solution of mol / L, then sealed with a sealing film and left to stand for 15 minutes. After the impregnation time was up, the polyimide fiber was removed and squeezed. The squeezed sodium hydroxide aqueous solution was poured into a waste liquid bucket. The impregnated fiber was then washed with deionized water in a beaker. After washing, the polyimide fiber was squeezed. This process was repeated to wash and squeeze dry with deionized water. The fiber was then placed in a petri dish for further processing.

[0040] Then, the pretreated polyimide fibers were placed in a shaker containing deionized water and shaken to loosen them. They were then poured into a larger beaker, shaken well, and poured into a Büchner funnel to allow them to settle naturally. After most of the deionized water was filtered out, the fibers were taken out together with the filter paper and polyimide fibers and placed in a drying oven at 60°C for 8 hours to dry.

[0041] b. Preparation of polyimide filter materials:

[0042] After the polyimide fibers impregnated with ammonia for 15 minutes were decomposed and dried, the polyimide fibers were stacked together in a mold. The mold was made of mold steel with a circular hole with a diameter of 14 cm and a thickness of 4 mm. The mold was then placed in a flat vulcanizing machine and heat-treated at a pressure of 1 MPa. The temperature was raised from room temperature to 120°C and held for 40 minutes, then raised to 310°C and held for 1.5 hours. After natural cooling, the sample was taken out to obtain polyimide filter material PI-1. The sample was a round block with a diameter of 14 cm and a thickness of more than 4 mm.

[0043] Experimental test analysis:

[0044] Figure 1 The image shows a physical picture of the polyimide filter material PI-1 prepared in Example 1 of this invention. It can be seen that the filter material prepared by the method of this example can stand upright naturally and has a uniform surface, belonging to the category of rigid filter materials. Table 1-1 shows the porosity and maximum stress value of the polyimide filter material prepared in Example 1 of this invention. It can be concluded that the porosity of the polyimide filter material PI-1 prepared in Example 1 of this invention is 79.07%, and the maximum stress of PI-1 is 0.052 MPa.

[0045] Example 2:

[0046] This embodiment is basically the same as the previous examples, except that:

[0047] In this embodiment, a method for preparing a polyimide filter material includes the following steps:

[0048] a. Pretreatment of polyimide fibers:

[0049] First, weigh 35g of polyimide fiber using an electronic balance. The fiber is 50mm long and 10μm in diameter. Place it in a beaker and pour in an appropriate amount of 10 -6 The polyimide fiber was completely impregnated with a mol / L potassium hydroxide aqueous solution, then sealed with a sealing film and left to stand for 60 minutes. After the impregnation time was up, the polyimide fiber was removed and squeezed. The squeezed potassium hydroxide aqueous solution was poured into a waste liquid bucket. The impregnated fiber was then washed with deionized water in a beaker. After washing, the polyimide fiber was squeezed. This process was repeated to wash and squeeze dry with deionized water. The fiber was then placed in a petri dish for further processing.

[0050] Then, the pretreated polyimide fibers were placed in a shaker containing deionized water and shaken to loosen them. They were then poured into a larger beaker, shaken well, and poured into a Büchner funnel to allow them to settle naturally. After most of the deionized water was filtered out, the fibers were taken out together with the filter paper and polyimide fibers and placed in a drying oven at 70°C for 8 hours to dry.

[0051] b. Preparation of polyimide filter materials:

[0052] After the polyimide fibers impregnated with ammonia for 150 minutes were decomposed and dried, the polyimide fibers were stacked together in a mold. The mold was made of mold steel with a diameter of 14 cm and a thickness of 3 mm. The mold was then placed in a flat vulcanizing machine and heat-treated at a pressure of 7 MPa. The temperature was raised from room temperature to 140°C and held for 30 minutes, then raised to 290°C and held for 2 hours. After natural cooling, the sample was taken out to obtain polyimide filter material PI-2. The sample was a round block with a diameter of 14 cm and a thickness of more than 3 mm.

[0053] Experimental test analysis:

[0054] Table 1-1 shows the porosity and maximum stress value of the polyimide filter material prepared in Example 2 of the present invention. It can be concluded that the porosity of the polyimide filter material PI-2 prepared in Example 2 of the present invention is 65.37%, and the maximum stress of PI-2 is 0.617 MPa.

[0055] Example 3:

[0056] This embodiment is basically the same as the previous examples, except that:

[0057] In this embodiment, a method for preparing a polyimide filter material includes the following steps:

[0058] a. Pretreatment of polyimide fibers:

[0059] First, weigh 20g of polyimide fiber (38mm in length and 10μm in diameter) using an electronic balance. Place the fiber in a beaker and pour in an appropriate amount of 0.9mol / L ammonia water to completely immerse the fiber. Then, seal the beaker with a sealing film and let it stand for 60 minutes. After the immersion time is up, remove the polyimide fiber and squeeze it. Pour the squeezed ammonia water into a waste liquid container. Then, wash the immersed fiber with deionized water in a beaker. After washing, squeeze the polyimide fiber. Repeat this process of washing and squeezing with deionized water until dry. Then, place the fiber in a petri dish for further processing.

[0060] Then, the pretreated polyimide fibers were placed in a shaker containing deionized water and shaken to loosen them. They were then poured into a larger beaker, shaken well, and poured into a Büchner funnel to allow them to settle naturally. After most of the deionized water was filtered out, the fibers were taken out together with the filter paper and polyimide fibers and placed in an 80°C drying oven for 6 hours to dry.

[0061] b. Preparation of polyimide filter materials:

[0062] After the polyimide fibers impregnated with ammonia for 60 minutes were decomposed and dried, the polyimide fibers were stacked together in a mold. The mold was made of mold steel with a diameter of 14 cm and a thickness of 2 mm. The mold was then placed in a flat vulcanizing machine and heat-treated at a pressure of 1 MPa. The temperature was raised from room temperature to 150°C and held for 30 minutes, then raised to 300°C and held for 2 hours. After natural cooling, the sample was taken out to obtain polyimide filter material PI-3. The sample was a round block with a diameter of 14 cm and a thickness of more than 2 mm.

[0063] Experimental test analysis:

[0064] Table 1-1 shows the porosity and maximum stress value of the polyimide filter material prepared in Example 3 of the present invention. It can be concluded that the porosity of the polyimide filter material PI-3 prepared in Example 3 of the present invention is 77.3%, and the maximum stress of PI-3 is 0.129 MPa. Figure 2 To assess the thermal properties of the polyimide filter material prepared in Example 3 of this invention, the temperature at which the PI-3 sample loses 10% of its weight is 600℃. Figure 3 The graph shows the filtration efficiency of the polyimide filter material prepared in Example 3 of the present invention. It can be clearly seen that the average filtration efficiency of the polyimide filter material prepared in Example 3 of the present invention is 77.28%.

[0065] Table 1-1 Porosity and Maximum Stress of Samples

[0066]

[0067] In summary, the embodiments of this invention utilize ammonia water to pretreat polyimide fibers and employ hot pressing technology to prepare rigid filter materials from the polyimide fibers. This invention yields a rigid filter material with better thermal stability, a thermal decomposition temperature of 540-600℃, and also possesses good mechanical properties, high porosity, and excellent filtration effect. Furthermore, it provides a good foundation for preparing filter materials with superior performance, increasing the added value of the product.

[0068] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyimide filter material, characterized in that, Includes the following steps: a. Pretreatment of polyimide fibers: Place polyimide short fibers in a beaker and pretreat them with a pretreatment agent until completely impregnated. Seal and let stand for at least 15 minutes. After impregnation, remove the polyimide short fibers and wash them repeatedly with deionized water to obtain pretreated polyimide fibers. Then, shake and loosen the polyimide fibers, filter them using a funnel, and place the filtered polyimide fibers in a drying oven at a temperature not lower than 60°C. The pretreatment agent used is an alkaline solution with a concentration of 10%. -4 -10 -6 A 10 mol / L sodium hydroxide aqueous solution -4 -10 -6 A potassium hydroxide aqueous solution with a concentration of 0.898-0.907 mol / L or an ammonia solution with a concentration of 0.898-0.907 mol / L; b. Preparation of polyimide filter material: The polyimide fibers prepared in step a are subjected to a hot pressing process, with pressure applied throughout the pressing process, including the following steps: First, the polyimide fibers are stacked into a mold. Then, the mold is placed in a flat vulcanizing machine and preheated from room temperature to at least 120°C for at least 20 minutes. Then, the temperature is raised to at least 290°C and held for at least 1.5 hours for hot pressing. After hot pressing, the desired material shape is obtained. Then, the material is cooled naturally to obtain the polyimide filter material.

2. The method for preparing the polyimide filter material according to claim 1, characterized in that: In step a, the polyimide fiber selected has a length of 30-50 mm and a diameter of 8-10 μm.

3. The method for preparing the polyimide filter material according to claim 1, characterized in that: In step a, the sealing and standing time is controlled to be 15-150 min during the impregnation pretreatment, and the pretreatment agent completely impregnates the polyimide fiber.

4. The method for preparing the polyimide filter material according to claim 1, characterized in that: In step a, drying involves placing the polyimide fibers in a drying oven at 60-80°C for 6-8 hours.

5. The method for preparing the polyimide filter material according to claim 1, characterized in that: In step a, when the polyimide fiber is subjected to oscillation loosening treatment, the polyimide fiber is placed in an oscillator containing deionized water for oscillation loosening treatment.

6. The method for preparing the polyimide filter material according to claim 1, characterized in that: In step b, the hot pressing process is as follows: (1) Take the dried polyimide fibers, stack them in the mold, and put them into the flat vulcanizing machine; (2) Maintain pressure with a load of 1-7 MPa, and apply pressure throughout the hot pressing process; (3) Heat the material from room temperature to 120-150℃ and keep it at that temperature for 20-40 min, then heat it to 290-310℃ and keep it at that temperature for 1.5-2 h, and then heat it to form a polyimide filter material.

7. A polyimide filter material, characterized in that: It is prepared using the preparation method of the polyimide filter material according to claim 1.

8. The polyimide filter material according to claim 7, characterized in that: The polyimide filter material is a rigid, cylindrical material with a diameter of not less than 14 cm, a thickness of not less than 2 mm, and a porosity of not less than 65.37%.

9. An application of the polyimide filter material according to claim 7, characterized in that: Polyimide filter material is used as a high-temperature rigid filter material at temperatures of 220-300℃.

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