Methods and systems for recycling fluororubber waste

Abstract

This invention provides a method and system for recycling fluororubber waste, belonging to the field of rubber recycling. The method includes a pre-cooling step, cooling the fluororubber waste; a low-temperature cryogenic crushing step, using a liquid refrigerant to perform a secondary cooling and freezing of the pre-cooled fluororubber waste, and then cryogenically crushing the secondary-cooled fluororubber waste, with the gas from the vaporization of the liquid refrigerant provided to the pre-cooling step for recovering cold energy; a washing step, washing the fluororubber waste during the cryogenic crushing process to remove additive powders; and a magnetic separation step, using a high-gradient magnetic field to remove ferromagnetic particles generated during the cryogenic crushing process from the washed fluororubber waste, obtaining recovered fluororubber particles. Through the processing scheme of this application, the recovered product particles are uniform in size and have few impurities, meeting the quality requirements for fluororubber reuse.

Description

Technical Field

[0001] This invention relates to the field of rubber recycling, specifically to a method and system for recycling fluorinated rubber waste. Background Technology

[0002] Fluororubber is a synthetic polymer elastomer containing fluorine atoms on the carbon atoms of its main chain or side chains. The introduction of fluorine atoms endows fluororubber with excellent heat resistance, oxidation resistance, oil resistance, corrosion resistance, and atmospheric aging resistance, making it irreplaceable in aerospace, semiconductor, automotive, chemical, light industry, metallurgy, machinery, oil extraction, shipbuilding, and environmental protection sectors. For example, the highest-volume and most widely used types are binary copolymer elastomers of vinylidene fluoride and hexafluoropropylene, or ternary copolymer elastomers with the addition of tetrafluoroethylene, collectively known as Class 26 fluororubbers, as well as perfluoroether rubbers used in high-cleanliness, plasma-resistant environments.

[0003] Currently, the global demand for fluororubber is approximately 200,000 tons per year, and is growing at a rate of 5% annually. The unique properties of fluoroelastomers make them an important member of the polymer material family. However, the production of fluororubber products generates a large amount of waste. The high cost and expensive raw materials in fluororubber product manufacturing force manufacturers to reprocess and reuse the waste generated during production to maximize economic benefits. The main sources of recycled raw materials are waste from extrusion production (flash) and other production waste. Reusing them in the process cycle not only helps protect the environment but also significantly saves raw material resources. Therefore, how to recycle fluororubber, especially perfluoroether rubber used in high-cleanliness applications, has become a major challenge. Summary of the Invention

[0004] Therefore, in order to overcome the shortcomings of the prior art, the present invention provides a method and system for recycling fluororubber waste with uniform particle size, few impurities in the recycled product, and meeting the quality requirements for fluororubber recycling.

[0005] To achieve the above objectives, the present invention provides a method for recycling fluororubber waste, comprising: a pre-cooling step, wherein the fluororubber waste is cooled; a low-temperature cryogenic pulverization step, wherein the pre-cooled fluororubber waste is subjected to secondary cooling and freezing using a liquid refrigerant, and the fluororubber waste after secondary cooling and freezing is cryogenically pulverized, wherein the gas generated by the vaporization of the liquid refrigerant is provided to the pre-cooling step for recovery of cold energy; a washing step, wherein the fluororubber waste is washed to remove additive powder released during the cryogenic pulverization process; and a magnetic separation step, wherein a high-gradient magnetic field is used to remove ferromagnetic particles generated during the cryogenic pulverization process from the washed fluororubber waste, thereby obtaining recovered fluororubber particles.

[0006] In one embodiment, the cooling energy in the cryogenic pulverization step comes from the evaporation of the cryogenic medium, and the evaporation rate of the cryogenic medium is controlled by adjusting the flow rate of the liquid refrigerant and the residence time of the liquid refrigerant in the grinding device.

[0007] In one embodiment, in the low-temperature cryogenic pulverization step, the time for secondary cooling and freezing of the pre-cooled fluorinated rubber waste using liquid refrigerant is 5 to 25 minutes.

[0008] In one embodiment, in the low-temperature cryogenic pulverization step, the brittle temperature range of the cryogenic pulverization of the fluororubber waste after secondary cooling and freezing is -45 to -70°C.

[0009] In one embodiment, during the washing step, the mesh size of the ground fluorinated rubber waste ranges from 10 to 100 mesh.

[0010] In one embodiment, during the magnetic separation step, the magnetic induction intensity within a range of 100 mm from the magnet surface is not less than 1200 GS.

[0011] In one embodiment, a pre-cleaning treatment step is included before the pre-cooling step, in which the fluorinated rubber waste is washed with a surfactant.

[0012] A recycling system for fluororubber waste includes: a precooling unit for cooling the fluororubber waste; a low-temperature cryogenic pulverization unit for further cooling and pulverizing the precooled fluororubber waste using a liquid refrigerant, wherein the gas from the vaporization of the liquid refrigerant is provided to the precooling step to recover the cooling capacity; a washing unit for washing the fluororubber waste to remove additive powder released during the cryogenic pulverization process; and a magnetic separation unit for removing ferromagnetic particles generated during the cryogenic pulverization process from the washed fluororubber waste using a high-gradient magnetic field to obtain recovered fluororubber particles.

[0013] In one embodiment, a pre-cleaning treatment unit is provided before the pre-cooling unit for washing the fluorinated rubber waste with a surfactant.

[0014] Compared with existing technologies, the advantages of this invention are as follows: Utilizing the cold brittleness of rubber materials under low-temperature conditions for pulverization not only yields finer particles but also preserves the material's properties. Furthermore, by employing the differences in surface properties (hydrophobicity) and density between fluororubber powder and additive powder in an aqueous phase for cleaning fluororubber waste, impurities in the recycled product are reduced. The use of a high-gradient magnetic field to separate ferromagnetic particles from the fluororubber powder resulting from equipment wear during processing further reduces impurities in the recycled product, ensuring that the recovered fluororubber particles meet the requirements of the production process and realizing the reuse of fluororubber. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of a method for recycling fluorinated rubber waste in an embodiment of the present invention;

[0017] Figure 2 This is a simplified structural diagram of a fluorinated rubber waste recycling system in an embodiment of the present invention. Detailed Implementation

[0018] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0019] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0021] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0022] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0023] like Figure 1 As shown in the figure, this application provides a method for recycling fluororubber waste, including the following steps:

[0024] The S101 pre-cooling step cools the fluororubber waste. Direct cooling can be used to lower the temperature of the fluororubber waste from room temperature. In this embodiment, the low-temperature gas generated by the vaporization of the liquid refrigerant in the S102 low-temperature cryogenic pulverization step can be used to cool the fluororubber waste, thus fully utilizing the cooling capacity. The pre-cooling step lowers the material from room temperature to a low temperature, causing the fluororubber waste to change from "soft" to "hard" and gradually exhibit "warm brittleness." The low temperature range of the pre-cooling step from room temperature to low temperature can be 0 to -20°C.

[0025] In the S102 cryogenic pulverization step, a liquid refrigerant is used to perform a secondary cooling and freezing of the pre-cooled fluororubber waste. The fluororubber waste, after secondary cooling and freezing, is then pulverized. The gas produced by the vaporization of the liquid refrigerant is used to recover the cooling energy from the pre-cooling step. The liquid refrigerant can be any of liquid nitrogen, LNG, or liquid carbon dioxide. The fluororubber waste can be fed continuously or intermittently. The fluororubber waste after secondary cooling and freezing must exhibit its "warm brittleness," and the secondary cooling and freezing temperature must be lower than the brittle temperature (or glass transition temperature) of the fluororubber waste. For example, the glass transition temperature (Tg) of binary fluororubber (FKM) is approximately -20℃, while the low-temperature resistance of ternary FKM is worse than that of binary FKM. The glass transition temperature of perfluoroether rubber (FFKM) is around -29℃. DuPont's ternary perfluoroelastomer rubber products include brands such as Kalrez 1018, 1021, 1051, 1058, 3018, 3049, 3065, and 4079, with a brittle temperature of -39°C. Therefore, the cold brittle temperature can be below -40°C. In one embodiment, since fluororubber still retains some plasticity below its brittle temperature of -45°C, the cold brittle temperature range for cryogenic pulverization of the secondary-cooled fluororubber waste in the cryogenic pulverization step is -45°C to -70°C.

[0026] A cryogenic pulverizer or an immersion cryogenic pulverizer can be used to cryogenically pulverize fluororubber waste after secondary cooling and freezing. The liquid refrigerant absorbs the heat generated during the pulverization process and the heat generated by the crushing device, and vaporizes into gas. Refrigerant needs to be replenished in a timely manner during the cryogenic pulverization step. The cryogenic pulverizer or immersion cryogenic pulverizer can pulverize the fluororubber waste by grinding, or other crushing methods can be used. Taking the grinding process as an example, although the fluororubber waste is immersed in refrigerant for grinding, considering the poor thermal conductivity of rubber, in one embodiment, it is preferable to maintain a sufficient residence time to allow the fluororubber to reach below its cold brittleness temperature.

[0027] In the S103 washing step, the pulverized fluororubber waste is ground in a liquid refrigerant. During the low-temperature freeze-crushing process, solid additives such as silica, titanium dioxide, and carbon black powder will separate from the fluororubber, resulting in free impurities. Washing removes the released additive powders from the low-temperature freeze-crushing process. To effectively remove impurities such as additive powders, the differences in surface properties (hydrophobicity) and density between the fluororubber powder and additive powder in the aqueous phase can be used for sieving. Therefore, during the washing process, based on the differences in additive powders, the low-temperature fluororubber waste can be reheated for further impurity separation. In one embodiment, the particle size of the washed fluororubber waste can be determined, and fluororubber particles with a particle size smaller than 10 mesh can be returned to the S101 pre-cooling step.

[0028] In step S104, a high-gradient magnetic field is used to remove ferromagnetic particles generated during the freeze-crushing process from the cleaned fluororubber waste, yielding recovered fluororubber particles. The high-gradient magnetic field used has the following characteristics:

[0029] 1) The magnetic focusing medium in a high-gradient magnetic separator can be made of ferritic stainless steel with high magnetization, which has excellent corrosion resistance. The smaller the cross-sectional area of ​​the magnetic focusing medium, the higher the magnetic field gradient.

[0030] 2) The high gradient magnetic separator can remove ferromagnetic particles ranging from a few micrometers to hundreds of micrometers. The magnetic separator can generate a magnetic field of 1T and a magnetic field gradient of 100T / cm.

[0031] 3) High gradient magnetic separators consume less energy, are easy to operate, do not produce secondary pollution, have lower costs, and have high separation efficiency.

[0032] In one embodiment, a near-parallel magnetic field is created using permanent magnet materials, with a magnetic induction intensity of not less than 1200 GS within a 100mm radius of the magnet surface. A magnetic focusing device, such as a filter screen or magnetic separator composed of magnetizable materials, is placed within the space of this near-parallel magnetic field to remove ferromagnetic impurities. Using permanent magnet materials as the magnetic source to create an ultra-strong magnetic separation device, the selection of the permanent magnet material and the design of the magnetic circuit are two crucial yet mutually restrictive aspects.

[0033] The above method utilizes the cold brittleness of rubber materials under low-temperature conditions for pulverization, which not only yields finer particles but also preserves the material's properties. Furthermore, by leveraging the differences in surface properties (hydrophobicity) and density between fluororubber powder and additive powder in an aqueous phase to clean fluororubber waste, impurities in the recycled product are reduced. The use of a high-gradient magnetic field to separate ferromagnetic particles from the fluororubber powder, resulting from equipment wear during processing, further reduces impurities in the recycled product. This ensures that the recovered fluororubber particles meet the requirements of the production process, realizing the reuse of fluororubber.

[0034] In one embodiment, the cooling energy in the cryogenic pulverization step comes from the evaporation of the cryogenic medium, and the evaporation rate of the cryogenic medium is controlled by adjusting the flow rate of the liquid refrigerant and the residence time of the liquid refrigerant in the grinding device.

[0035] In one embodiment, in the low-temperature cryogenic pulverization step, the time for secondary cooling and freezing of the pre-cooled fluorinated rubber waste using liquid refrigerant is 5 to 25 minutes.

[0036] In one embodiment, during the washing step, the mesh size of the ground fluorinated rubber waste ranges from 10 to 100 mesh.

[0037] In one embodiment, the particle size and particle size distribution of the fluororubber are determined by the cold brittleness temperature of the fluororubber raw material to be ground and the characteristics of the grinding unit (such as grinding speed and tooth spacing, residence time).

[0038] In one embodiment, a pre-cleaning treatment step is included before the pre-cooling step, in which the fluorinated rubber waste is washed with a surfactant.

[0039] like Figure 2 As shown, this application provides a recycling system for fluororubber waste, including a pre-cleaning unit 01, a first drying unit 02, a pre-cooling unit 03, a low-temperature freezing and pulverizing unit 04, a washing unit 05, a second drying unit 06, a magnetic separation unit 07, and a screening and storage unit 08.

[0040] The pre-cleaning treatment unit 01 is used to wash fluororubber waste with surfactants to remove surface contaminants and impurities from the waste fluororubber. The fluororubber waste can be washed with a surfactant aqueous solution, dehydrated, and then rinsed twice with clean water. The cleaning solution enters the pre-cleaning treatment unit 01 through inlet 011 and exits through outlet 012.

[0041] The first drying unit 02 is used to dry the fluorinated rubber waste material after it has been processed by the pre-cleaning treatment unit 01.

[0042] Precooling unit 03 is used to cool fluororubber waste. Precooling unit 03 uses direct cooling to cool the fluororubber waste. Gas refrigerant enters precooling unit 03 from inlet 031 and flows out of precooling unit 03 from outlet 032. In addition to fully utilizing the recovered cold energy, precooling unit 03 is also replenished with refrigerant to ensure that the fluororubber to be ground reaches the set outlet temperature of the precooling system.

[0043] The low-temperature cryogenic pulverizing unit 04 is used to perform secondary cooling and freezing of pre-cooled fluororubber waste using liquid refrigerant, and then freeze-pulverizes the fluororubber waste after secondary cooling and freezing. The gas produced by the vaporization of the liquid refrigerant is supplied to the pre-cooling step to recover the cold energy. The liquid refrigerant is replenished by inlet 041. Waste fluororubber is fed continuously or intermittently. The gas produced by the vaporization of the liquid refrigerant is filtered and discharged through outlet 042, and then connected to pre-cooling unit 031 to recover the cold energy. If the cold energy recovered by 031 is insufficient to meet the pre-cooling requirements, it can be supplemented by liquid refrigerant.

[0044] Washing unit 05 is used to wash the additive powder released from the fluororubber waste during the freeze-crushing process. The washing solution enters washing unit 05 from inlet 051 and flows out of washing unit 05 from outlet 052.

[0045] The second drying unit 06 is used to dry the fluorinated rubber waste material after it has been processed by the washing unit 05.

[0046] Magnetic separation unit 07 is used to remove ferromagnetic particles generated during the cryogenic crushing process from the cleaned fluororubber waste using a high-gradient magnetic field, obtaining recovered fluororubber particles. The magnetic separation unit removes ferromagnetic particles, such as solid particles containing iron, chromium, and nickel, generated during low-temperature grinding. The removed ferromagnetic particles are discharged from magnetic separation unit 07 through outlet 071.

[0047] The screening and storage unit 08 is used to store fluororubber powder of different particle sizes that meet quality requirements.

[0048] In one embodiment, the cryogenic pulverizing unit 04 further includes an auxiliary adjustment unit to assist in adjusting the flow rate of the refrigerant and the residence time of the refrigerant in the grinding device, so as to control the grinding temperature and temperature gradient changes.

[0049] In all embodiments of this invention, the method for detecting ferromagnetic abrasive particles adopts the enterprise standard. The specific detection method is as follows:

[0050] 1) Weigh 2 kg of sample.

[0051] 2) Prepare a funnel, and connect a magnetic rod made of permanent magnet material placed at an angle of about 70° to the discharge port at the bottom of the funnel (the magnetic rod is about 30cm long and about 25mm in diameter; the surface magnetic field strength is about 12000GS or 1.2T).

[0052] 3) The 2kg sample was fed in about 30 minutes; the ferromagnetic particles captured by the permanent magnet rod were collected.

[0053] 4) Use a microscope to detect the number of ferromagnetic particles.

[0054] 5) Qualified product indicators: 3 particles smaller than 200 micrometers, 0 particles larger than 200 micrometers.

[0055] In each embodiment of the present invention, the content of inorganic fillers in the fluororubber is tested by thermogravimetric analysis (TGA) at 500-600℃, which measures the content of titanium dioxide or silicon dioxide in ash. The content of carbon black is detected by energy dispersive spectroscopy (EDS). Assuming that the monomer composition of the fluororubber remains unchanged during the recycling process, the change in carbon content before and after recycling is the weight loss of carbon black as a filler.

[0056] The thermogravimetric analyzer and energy dispersive spectrometer were Shimadzu's DTG-60 and EDX-8100, respectively.

[0057] Example 1

[0058] The glass transition temperature (Tg) of binary fluororubber is approximately -19.2℃. The residence time of the rubber in liquid nitrogen is set to 8 minutes, and the brittle temperature is approximately -60℃. After crushing and sieving, 60-80 mesh rubber particles are obtained. The content of ferromagnetic abrasive particles and free inorganic particles is shown in Table 1.

[0059] The amount of liquid nitrogen consumed is approximately 0.7 kg / kg of fluororubber.

[0060] Table 1. Raw materials to be processed and powder (gray) after cryogenic grinding.

[0061]

[0062] Example 2

[0063] The glass transition temperature of perfluoroether rubber (FFKM) is around -29.7℃. The residence time of the rubber in liquid nitrogen was set to 10 min, and the brittle temperature was approximately -66℃. After crushing and sieving, 60-80 mesh rubber particles were obtained. The content of ferromagnetic abrasive particles and free inorganic particles is shown in Table 2.

[0064] The amount of liquid nitrogen consumed is approximately 0.8 kg / kg of fluororubber.

[0065] Table 2. Raw materials to be processed and powder after cryogenic grinding (colorless / light yellow)

[0066]

[0067] As can be seen from Examples 1 and 2, the recycled materials obtained by freezing and grinding binary fluororubber and perfluoroether rubber, combined with the method and system provided in this application, meet the requirements for recycling.

[0068] Table 3 shows the performance changes of fluororubber prepared using recycled materials.

[0069] Table 3. Performance changes of fluororubber prepared using recycled materials

[0070] F content C content O content Tensile strength, MPa Elongation at break, % 100% raw materials 73.6 22.4 4.0 32.7 3.9 1. Recycled materials account for 15%. 73.6 22.4 4.0 31.5 3.7 2. Recycled materials account for 10%. 73.6 22.4 4.0 32.0 3.6

[0071] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for recycling fluorinated rubber waste, characterized in that, include: The pre-cooling step cools the fluororubber waste. The low-temperature cryogenic pulverization step involves using a liquid refrigerant to perform a secondary cooling and freezing of the pre-cooled fluororubber waste, followed by cryogenic pulverization of the secondary-cooled fluororubber waste. The gas produced by the vaporization of the liquid refrigerant is provided to the pre-cooling step to recover the cold energy. The cryogenic pulverization includes grinding the fluororubber waste. The washing step utilizes the differences in surface properties and density between fluororubber powder and additive powder in the aqueous phase for sieving, and removes the additive powder released from the fluororubber waste during the washing and freezing crushing process; based on the differences in additive powder, the fluororubber waste that has been frozen and crushed at low temperature is reheated, and then impurities are separated. In the magnetic separation step, a high-gradient magnetic field is used to remove ferromagnetic particles generated during the freeze-crushing process from the cleaned fluororubber waste, resulting in recovered fluororubber particles.

2. The recycling method according to claim 1, characterized in that, The cooling energy in the cryogenic pulverization step comes from the evaporation of the cryogenic medium, and the evaporation rate of the cryogenic medium is controlled by adjusting the flow rate of the liquid refrigerant and the residence time of the liquid refrigerant in the grinding device.

3. The recycling method according to claim 2, characterized in that, In the low-temperature cryogenic pulverization step, the time for secondary cooling and freezing of the pre-cooled fluorinated rubber waste using liquid refrigerant is 5~25 minutes.

4. The recycling method according to claim 1, characterized in that, In the low-temperature cryogenic pulverization step, the brittle temperature range for cryogenic pulverization of the fluororubber waste after secondary cooling and freezing is -45 to -70℃.

5. The recycling method according to claim 1, characterized in that, In the washing step, the mesh size of the ground fluorinated rubber waste ranges from 10 to 100 mesh.

6. The recycling method according to claim 1, characterized in that, In the magnetic separation step, the magnetic induction intensity within a range of 100 mm from the magnet surface is not less than 1200 GS.

7. The recycling method according to claim 1, characterized in that, It also includes a pre-cleaning treatment step set before the pre-cooling step, which uses surfactants to wash the fluorinated rubber waste.

8. A recycling system for fluorinated rubber waste, characterized in that, The recycling system is used to implement the recycling method as described in any one of claims 1-7, and includes: The precooling unit is used to cool fluororubber waste. The low-temperature cryogenic pulverizing unit is used to perform secondary cooling and freezing on the pre-cooled fluorinated rubber waste using liquid refrigerant, and to freeze and pulverize the fluorinated rubber waste after secondary cooling and freezing. The gas generated by the vaporization of the liquid refrigerant is provided to the above pre-cooling step to recover the cold energy. The washing unit is used to screen the fluororubber powder and additive powder in the aqueous phase by utilizing the differences in surface properties and density. The washing unit removes the additive powder released from the fluororubber waste during the freezing and crushing process. Based on the differences in the additive powder, the fluororubber waste that has been frozen and crushed at low temperature is reheated and then impurities are separated. A magnetic separation unit is used to remove ferromagnetic particles generated during the freeze-crushing process from the cleaned fluororubber waste using a high-gradient magnetic field, thereby obtaining recycled fluororubber particles.

9. The recycling system according to claim 8, characterized in that, It also includes a pre-cleaning treatment unit located before the pre-cooling unit, used to wash fluorinated rubber waste with surfactants.

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