Process for removing solid paraffin and water in polytetrafluoroethylene material

Abstract

The invention discloses a process for removing solid paraffin and water in a polytetrafluoroethylene material. Comprising the following steps: coarse crushing of waste polytetrafluoroethylene, fine crushing of waste polytetrafluoroethylene, fine crushing of waste polytetrafluoroethylene, vibratory screening of waste polytetrafluoroethylene, extraction of waste polytetrafluoroethylene with supercritical CO2, separation and purification, and secondary extraction with supercritical CO2. The supercritical CO2 extraction equipment comprises an extraction kettle and a three-stage separation kettle; according to the method disclosed by the invention, the structure of the polytetrafluoroethylene material is a nano porous structure, and the polytetrafluoroethylene material is crushed for multiple times, so that the moisture in the polytetrafluoroethylene material is removed to the maximum extent, the supercritical CO2 extraction time is shortened, and the efficiency of treating the polytetrafluoroethylene material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of waste material recycling, and particularly relates to a process for removing solid paraffin and water from a polytetrafluoroethylene material. Background Art

[0002] During its synthesis, polytetrafluoroethylene (PTFE) requires the addition of 0.5-3% solid paraffin wax to improve processing performance. The addition of solid paraffin wax can significantly reduce the low melt viscosity, making PTFE easier to mold and process. In addition, solid paraffin wax can also reduce the friction coefficient, improve wear resistance and non-stickiness, thereby extending the product's service life. However, during the production process, waste PTFE containing excessive amounts of solid paraffin wax and water is easily produced, with contents as high as 55.22% and 40% respectively. PTFE with high content of solid paraffin wax and water will greatly affect its product quality. For example, during storage, it will turn yellow due to the high paraffin content. Therefore, this type of PTFE can only be treated as waste. Currently, this type of waste PTFE is burned, which is expensive and not environmentally friendly. Summary of the Invention

[0003] In view of the above problems, the object of the present invention is to provide a process for removing solid paraffin and water from polytetrafluoroethylene materials, which can reduce waste disposal costs and reduce the emission of harmful substances.

[0004] The present invention is achieved through the following technical solutions: A process for removing solid paraffin and moisture from polytetrafluoroethylene materials comprises the following steps: coarse crushing of waste polytetrafluoroethylene, fine crushing of waste polytetrafluoroethylene, fine crushing of waste polytetrafluoroethylene, vibration screening of waste polytetrafluoroethylene, supercritical CO2 extraction of waste polytetrafluoroethylene, separation and purification, and supercritical CO2 secondary extraction; the equipment in the supercritical CO2 extraction comprises: an extraction kettle and a three-stage separation kettle.

[0005] The waste polytetrafluoroethylene is coarsely crushed by using a high-intensity crusher to crush the waste polytetrafluoroethylene into particles with a particle size of 1-30 mm, thereby exposing the moisture in the gaps.

[0006] The waste polytetrafluoroethylene is finely pulverized by extrusion using a double-roll crusher. The thickness of the material after extrusion is controlled to be 1.5 mm, and the width is controlled to be particles with a size of 0.5-20 mm. The water content of the waste polytetrafluoroethylene after crushing by a high-strength crusher is about 40%. The double-roll crusher is used to squeeze out the water of the polytetrafluoroethylene, and the water content of the polytetrafluoroethylene after extrusion can be reduced to about 30%, and the viscosity of the waste polytetrafluoroethylene is reduced. The double-roll crusher can not only squeeze out the water of the waste polytetrafluoroethylene, but also control the uniformity of the thickness of the waste polytetrafluoroethylene through the double-roll crusher, thereby greatly improving the extraction efficiency of subsequent supercritical CO2 extraction.

[0007] The finely crushed waste polytetrafluoroethylene is crushed again using a high-intensity crusher. The thickness of the crushed material is controlled to be 1.0mm and the width is controlled to be particles with a size of 0.5-10mm.

[0008] The waste polytetrafluoroethylene vibration screening is to dehydrate the finely crushed waste polytetrafluoroethylene using a vibration screening machine, with a vibration time of 30 minutes and a vibration frequency of 500-1000 times / min. After the vibration screening, the moisture content in the waste polytetrafluoroethylene is controlled at 10-15%. After the fine crushing, most of the moisture in the gaps of the waste polytetrafluoroethylene has been exposed. At this time, vibration screening is used to perform liquid-solid separation to prevent the material from agglomerating and affecting the extraction efficiency.

[0009] The extraction process parameters of the extraction kettle and the three-stage separation kettle in the supercritical CO2 extraction of waste polytetrafluoroethylene are as follows: extraction pressure 25-45MPa, extraction temperature 60-80°C, extraction flow rate 50-120L / h, extraction time 3-6h; first-stage separation pressure 10-12MPa, separation temperature 50-60°C; second-stage separation pressure 6-8MPa, separation temperature 40-50°C; third-stage separation pressure 4-5MPa, separation temperature 30-40°C; fill the three-stage separation kettle with absorbent cotton, because liquid carbon dioxide has a great influence on the quality of the separation kettle. Paraffin also has a certain solubility, so it is necessary to adopt a three-stage separation. By reducing the pressure and temperature, the paraffin is analyzed multiple times to reduce the paraffin content in the waste polytetrafluoroethylene. At the same time, absorbent cotton is added for adsorption to reduce the separated paraffin from being carried to the intermediate storage tank; a layer of 400-mesh steel wire mesh is placed on the screen of the material barrel of the extraction kettle. At this time, because the solid paraffin is extracted in the extraction kettle, the temperature is low and the particle size of the solid paraffin is large. If the screen is in the state of conventional extraction, the extracted solid paraffin will easily clog the inner wall of the material barrel.

[0010] The separation and purification is to take out the solid paraffin and water obtained by extraction in the separation kettle, and the material is taken out every 10-30 minutes after the cyclic extraction to prevent the extracted water from being brought into the extraction material by the CO2 during the circulation.

[0011] The supercritical CO2 secondary extraction is to extract the polytetrafluoroethylene material obtained from the first extraction again. The extraction process conditions remain unchanged, and the CO2 needs to be replaced with new CO2 before continuing the extraction. The extraction time is 1-3 hours. By replacing the new carbon dioxide, the influence of the solid paraffin dissolved in the liquid carbon dioxide in the intermediate storage tank on the polytetrafluoroethylene paraffin content of the second extraction waste is avoided. The polytetrafluoroethylene content of the waste is lower after the second extraction.

[0012] Beneficial effects of the present invention: The present invention utilizes the nanoporous structure of polytetrafluoroethylene material and crushes the polytetrafluoroethylene material multiple times to maximize the removal of moisture therein, shorten the supercritical CO2 extraction time, and improve the efficiency of treating the polytetrafluoroethylene material. DETAILED DESCRIPTION

[0013] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0014] In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. It should be noted that the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also includes elements that are inherent to such process, method, article or device. Example 1

[0015] 1. Use a high-intensity crusher to crush the waste polytetrafluoroethylene into particles with a diameter of 1-30mm. The moisture in the crushed waste polytetrafluoroethylene is exposed; 2. Use a double-roll crusher for extrusion. The thickness of the extruded material is controlled at 1.5mm and the width is controlled at 0.5-20mm. After crushing by the double-roll crusher, the moisture content of the waste polytetrafluoroethylene is reduced to about 30%, and the viscosity is also relatively reduced; 3. Use a high-strength crusher to crush the material again. After crushing, the thickness of the material is controlled to 1.0mm and the width is controlled to particles with a size of 0.5-10mm. The moisture in the waste polytetrafluoroethylene after the second crushing is exposed; 4. Dehydrate the crushed waste polytetrafluoroethylene using a vibration screening machine with a vibration time of 30 minutes and a vibration frequency of 600 times / min. After vibration screening, the moisture content of the waste polytetrafluoroethylene is controlled at 10-15%; 5. The treated raw materials were subjected to supercritical CO2 extraction of waste polytetrafluoroethylene. First, the screen of the material barrel of the extraction kettle was placed with a layer of 400-mesh steel wire mesh. The extraction process parameters were set as follows: extraction pressure 30 MPa, extraction temperature 60°C, extraction flow rate 90 L / h, extraction time 3 h, first-stage separation pressure 10 MPa, separation temperature 50°C, second-stage separation pressure 8 MPa, separation temperature 40°C, third-stage separation pressure 5 MPa, separation temperature 30°C; 6. After 30 minutes of circulation, discharge the materials at the material outlets of separation kettle No. 1 and separation kettle No. 2. Note that after the water is extracted, the materials should be collected in time at the discharge ports of the material outlets of separation kettle No. 1 and separation kettle No. 2 to prevent the extracted water from being brought into the extracted material by the CO2 during circulation; 7. After the first extraction is completed, the pressure is released, the material is taken out, and the carbon dioxide in the intermediate storage tank is replaced. According to the above extraction process, the material that has been extracted for the first time is subjected to a second extraction. The second extraction only takes 1 hour. After the extraction is completed, the polytetrafluoroethylene solid paraffin and moisture content of the material are tested. Example 2

[0016] The difference between Example 2 and Example 1 is that the treated raw material is subjected to supercritical CO2 extraction of waste polytetrafluoroethylene, and the extraction process parameters are set as follows: extraction process parameters are: extraction pressure 35 MPa, extraction temperature 65°C, extraction flow rate 100 L / h, extraction time 3 h, first-stage separation pressure 10 MPa, separation temperature 55°C, second-stage separation pressure 8 MPa, separation temperature 45°C, third-stage separation pressure 5 MPa, separation temperature 35°C; Example 3

[0017] The difference between Example 3 and Example 1 is that the treated raw material is subjected to supercritical CO2 extraction of waste polytetrafluoroethylene, and the extraction process parameters are set as: extraction pressure 45 MPa, extraction temperature 65°C, extraction flow rate 110 L / h, extraction time 3h, first-level separation pressure 10 MPa, separation temperature 55°C, second-level separation pressure 8 MPa, separation temperature 45°C, third-level separation pressure 5 MPa, separation temperature 35°C.

[0018] Table 1 Solid paraffin content and moisture content of waste polytetrafluoroethylene raw materials

[0019] It can be seen from the table that in the solid waste polytetrafluoroethylene raw materials, the average paraffin content is 55.22%, and the average moisture content is 40.13%, indicating that the proportion of paraffin and moisture in the raw materials is relatively high, and there is extraction and recovery value.

[0020] Table 2 Waste polytetrafluoroethylene solid paraffin and moisture content after the first extraction of Example 1

[0021] Table 3 Waste polytetrafluoroethylene solid paraffin and moisture content after the second extraction of Example 1

[0022] It can be seen from Tables 2 and 3 that after the first extraction, the paraffin content of Example 1 dropped from an average of 55.22% of the raw material to 5.17%, and the average extraction rate reached 90.63%; the moisture content dropped from 40.13% to 7.40%, and the average extraction rate was 81.57%. The first extraction significantly reduced the paraffin and moisture contents.

[0023] In the second extraction, the paraffin content was further reduced to an average of 0.17%, and the extraction rate was 99.69% on average; the water content was reduced to 0.10%, and the extraction rate was 99.74% on average. After the second extraction, there was very little paraffin and water residue, and the extraction effect was significant.

[0024] Table 4 Example 2 waste polytetrafluoroethylene solid paraffin and moisture content after the first extraction

[0025] Table 5 Example 2 waste polytetrafluoroethylene solid paraffin and moisture content after the second extraction

[0026] It can be seen from Tables 4 and 5 that the paraffin content of Example 2 after extraction from the raw materials is an average of 6.39%, and the extraction rate is an average of 88.44%; the water content is an average of 8.38%, and the extraction rate is an average of 79.12%. The first extraction has a certain effect, but the extraction rate is slightly lower than that of Example 1.

[0027] The average paraffin content of the second extraction was 0.39%, and the average extraction rate was 99.02%; the average water content was 0.15%, and the average extraction rate was 99.63%. After the second extraction, the residual amount was low, and the final extraction effect was close to that of Example 1, but there was a difference in the first extraction efficiency.

[0028] Table 6 Example 3 waste polytetrafluoroethylene solid paraffin and moisture content after the first extraction

[0029] Table 7 Example 3 waste polytetrafluoroethylene solid paraffin and moisture content after the second extraction

[0030] It can be seen from Tables 6 and 7 that in the first extraction of Example 3, the paraffin content after extraction from the raw material averaged 7.63%, and the extraction rate averaged 86.19%; the water content averaged 7.77%, and the extraction rate averaged 80.64%. The first extraction efficiency was relatively lower among the three examples.

[0031] The average paraffin content of the second extraction was 0.54%, and the average extraction rate was 98.66%. The average water content was 0.24%, and the average extraction rate was 99.41%. The residual amount after the second extraction was slightly higher than that of Examples 1 and 2, but overall efficient removal was achieved.

[0032] In summary, Examples 1, 2 and 3 of the present invention can all achieve efficient removal of paraffin and water, and a large number of experiments have found that the process parameters in Example 1 are more efficient.

[0033] The protection scope of the present invention is not limited to the technical solutions disclosed in the specific implementation methods. Any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the present invention.

Claims

1. A process for removing solid paraffin and water from polytetrafluoroethylene material, characterized by: The following steps are involved: The waste polytetrafluoroethylene is coarsely crushed, finely crushed, finely crushed, vibrated and screened, extracted with supercritical CO2, separated and purified, and subjected to secondary supercritical CO2 extraction. The equipment in the supercritical CO2 extraction includes an extraction kettle and a three-stage separation kettle.

2. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The waste polytetrafluoroethylene is coarsely crushed by using a high-intensity crusher to crush the waste polytetrafluoroethylene into particles with a particle size of 1-30 mm.

3. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The waste polytetrafluoroethylene is finely crushed by adopting a double-roll crusher for extrusion, and the thickness of the extruded material is controlled to be 1.5 mm and the width is controlled to be particles with a size of 0.5-20 mm.

4. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The finely crushed waste polytetrafluoroethylene is crushed again using a high-intensity crusher. After crushing, the material thickness is controlled to be 1.0mm and the width is controlled to be particles with a size of 0.5-10mm.

5. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The waste polytetrafluoroethylene vibration screening is to dehydrate the finely crushed waste polytetrafluoroethylene using a vibration screening machine, with a vibration time of 30 minutes and a vibration frequency of 500-1000 times / min. After vibration screening, the moisture content in the waste polytetrafluoroethylene is controlled to 10-15%.

6. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The extraction process parameters of the extraction kettle and the three-stage separation kettle for supercritical CO2 extraction of waste polytetrafluoroethylene are as follows: extraction pressure 25-45MPa, extraction temperature 60-80°C, extraction flow rate 50-120L / h, extraction time 3-6h; first-stage separation pressure 10-12MPa, separation temperature 50-60°C; second-stage separation pressure 6-8MPa, separation temperature 40-50°C; third-stage separation pressure 4-5MPa, separation temperature 30-40°C; and the three-stage separation kettle is filled with absorbent cotton.

7. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The separation and purification is to take out the solid paraffin and water obtained by extraction in a separation kettle, and the material taking time is every 10-30 minutes after the cyclic extraction.

8. The process for removing solid paraffin and water from polytetrafluoroethylene material according to claim 1, characterized in that: The supercritical CO2 secondary extraction is to extract the polytetrafluoroethylene material obtained from the first extraction again, and the extraction process conditions remain unchanged, wherein the CO2 needs to be replaced with new CO2 before continuing the extraction, and the extraction time is 1-3 hours.

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