Method for preparing silicon dioxide microspheres by utilizing decommissioned composite insulator silicone rubber through pyrolysis method

Abstract

The invention belongs to the technical field of power equipment resource recycling, and particularly relates to a method for preparing silicon dioxide microspheres by using retired composite insulator silicone rubber through a pyrolysis method. The method provided by the invention comprises the following steps: soaking retired composite insulator silicone rubber in liquid nitrogen, and grinding at low temperature to obtain low-temperature ground silicone rubber; carrying out pyrolysis on the silicone rubber subjected to low-temperature grinding to obtain a silicon dioxide microsphere precursor in a rheological environment; the preparation method comprises the following steps: carrying out three-stage cooling and collision growth on a silicon dioxide microsphere precursor in a rheological environment, and re-sintering an obtained product to obtain the silicon dioxide microspheres, the particle size of the silicon dioxide microspheres is 800 nm to 3 microns. The method provided by the invention not only can realize resource reutilization of the decommissioned composite insulator silicone rubber, but also can obtain the high-performance (high sphericity and high purity) silicon dioxide microspheres, and provides a simple and convenient method for preparing the high-performance silicon dioxide microspheres.

Description

Technical Field

[0002] This invention belongs to the field of power equipment resource recycling technology, specifically relating to a method for preparing silica microspheres using decommissioned composite insulator silicone rubber via pyrolysis. Background Technology

[0003] In ultra-high voltage power transmission systems, composite insulators are widely used in AC and DC lines of all levels due to their excellent performance. However, due to the influence of manufacturing process, material properties and aging factors, composite insulators that have been in operation for more than 20 years should be gradually phased out to prevent safety accidents.

[0004] Currently, existing methods for recycling and reusing the silicone rubber outer sheath of decommissioned composite insulators mainly include physical crushing, chemical depolymerization, microbial degradation, and high-temperature sintering. While these methods achieve resource recycling to a certain extent, the products recovered through these methods (silicone rubber powder, organic DMC, fumed silica, and mullite) have low economic value. Furthermore, these methods also suffer from problems such as unsafe recycling practices, environmental unfriendliness, high energy consumption, and long processing times, making it difficult to effectively guarantee the safe, green, and high-value recycling of composite outer insulation materials.

[0005] Currently, there are many methods for preparing silica microspheres. However, traditional methods cannot be applied to the specific object of waste silicone rubber. Moreover, high-sphericity and high-purity silica microspheres are expensive and require stringent preparation conditions. Furthermore, there are no reports on methods for preparing high-performance silica microspheres using decommissioned composite insulator silicone rubber. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing silica microspheres using decommissioned composite insulator silicone rubber via pyrolysis. The method provided by this invention not only enables the resource reuse of decommissioned composite insulator silicone rubber, but also yields high-performance (high sphericity, high purity) silica microspheres, providing a simple and convenient method for preparing high-performance silica microspheres.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing silica microspheres using decommissioned composite insulator silicone rubber via pyrolysis, comprising the following steps: The silicone rubber of the decommissioned composite insulator was treated by immersion in liquid nitrogen and then subjected to low-temperature grinding to obtain low-temperature ground silicone rubber. Low-temperature grinding of silicone rubber was followed by pyrolysis to obtain silica microsphere precursors under rheological conditions. The silica microsphere precursor under rheological conditions was subjected to three-stage cooling and collision growth, and the resulting product was re-fired to obtain the silica microspheres. The pyrolysis includes a first-stage pyrolysis and a second-stage pyrolysis performed sequentially; the first-stage pyrolysis and the second-stage pyrolysis are carried out in different reaction regions; the second-stage pyrolysis is carried out in an oxygen atmosphere; the particle size of the silica microspheres is 800 nm to 3 μm.

[0008] Preferably, the temperature of the first stage of pyrolysis is 370-400℃, and the holding time is 30 min; the temperature of the second stage of pyrolysis is 480-650℃, and the holding time is 30 min.

[0009] Preferably, the heating rate from room temperature to the temperature of the first stage pyrolysis is 20°C / min; the heating rate from the temperature of the first stage pyrolysis to the temperature of the second stage pyrolysis is 20°C / min.

[0010] Preferably, the first stage of pyrolysis is carried out in a first reaction chamber; the second stage of pyrolysis is carried out in a second reaction chamber connected in series with the first reaction chamber.

[0011] Preferably, the first stage of pyrolysis is carried out under a protective atmosphere.

[0012] Preferably, the low-temperature grinding relies on the frequency vibration of steel balls, the grinding balls are steel balls with a diameter of 3cm, the grinding tube has a volume of 50ml, and the raw materials and steel balls being ground do not exceed half the volume of the grinding tube; the grinding time is 1min, and the frequency is 60Hz.

[0013] Preferably, the particle size range of the silicone rubber after low-temperature grinding is 50~1000μm.

[0014] Preferably, the three-stage cooling consists of a first-stage cooling, a second-stage cooling, and a third-stage cooling performed sequentially. The first stage of cooling involves reducing the temperature of the second stage pyrolysis to 400°C. The second stage of cooling involves reducing the temperature from 400℃ to 250-300℃; The third stage of cooling involves reducing the temperature from 250-300℃ to room temperature.

[0015] Preferably, the cooling rate of the first stage of cooling is 20°C / min; the cooling rate of the second stage of cooling is 10°C / min; and the cooling rate of the third stage of cooling is 5°C / min.

[0016] Preferably, the reheating temperature is 800°C and the time is 2 hours.

[0017] This invention, by pyrolyzing silicone rubber and dividing the reaction zone, prevents the influence of other pyrolysis components on the nucleation and growth process during pyrolysis. In the second reaction chamber, only the pyrolysis products of silicone rubber react with oxygen to generate silica. By adjusting the temperature and controlling the oxygen concentration in the second reaction chamber, the nucleation rate of silica can be quantitatively regulated, thus laying the foundation for the formation of silica with high sphericity. After pyrolysis, this invention adopts a three-stage cooling process to control the collision-sintering characteristic time between silica particles, thereby achieving the preparation of silica microspheres with high sphericity.

[0018] Furthermore, the improved purity of the silica microspheres provided by this invention is due to the following reasons: First, the raw material used is solid silicone rubber. The PDMS material inside the silicone rubber is separated from the silicone rubber itself through solid-phase pyrolysis, thereby avoiding the introduction of impurities.

[0019] Secondly, by using multi-layer separation and stepped temperature control, the formation of precursors and the formation of particles are separated to avoid mutual interference and the entry of impurities.

[0020] Third, the temperature selection range is relatively low. The selected pyrolysis temperature does not reach the metal ion vaporization temperature in the waste silicone rubber, thus preventing the metal ion vaporization in the waste silicone rubber while ensuring the formation and pelletization of precursors.

[0021] Fourth, the synthesis is carried out in an oxygen atmosphere to ensure complete conversion. Therefore, the purity of the silica microspheres prepared by this invention is significantly improved. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The graphs show the pyrolysis curves of silicone rubber before and after low-temperature grinding. Figure 2 The images show the morphology of the final silica microspheres from Example 1 and Comparative Example 1. Detailed Implementation

[0024] This invention provides a method for preparing silica microspheres using decommissioned composite insulator silicone rubber via pyrolysis, comprising the following steps: The silicone rubber of the decommissioned composite insulator was treated by immersion in liquid nitrogen and then subjected to low-temperature grinding to obtain low-temperature ground silicone rubber. Low-temperature grinding of silicone rubber was followed by pyrolysis to obtain silica microsphere precursors under rheological conditions. The silica microsphere precursor under rheological conditions was subjected to three-stage cooling and collision growth, and the resulting product was re-fired to obtain the silica microspheres. The pyrolysis includes a first-stage pyrolysis and a second-stage pyrolysis performed sequentially; the first-stage pyrolysis and the second-stage pyrolysis are carried out in different reaction regions; the second-stage pyrolysis is carried out in an oxygen atmosphere; the particle size of the silica microspheres is 800 nm to 3 μm.

[0025] This invention involves treating decommissioned composite insulator silicone rubber with liquid nitrogen and then performing low-temperature grinding to obtain low-temperature ground silicone rubber.

[0026] In one embodiment of the present invention, the low-temperature grinding is preferably performed in a low-temperature grinding apparatus; the conditions for the low-temperature grinding preferably include: the low-temperature grinding relies on the frequency vibration of steel balls, the grinding balls are steel balls with a diameter of 3 cm, the volume of the grinding tube is 50 ml, and the raw material and steel balls being ground do not exceed half the volume of the grinding tube; the grinding time is 1 min, the frequency is 60 Hz; the number of low-temperature grinding cycles is ≥3; in one embodiment of the present invention, the particle size of the silicone rubber after low-temperature grinding is preferably 50~1000 μm.

[0027] After obtaining the low-temperature ground silicone rubber, the present invention pyrolyzes the low-temperature ground silicone rubber to obtain silica microsphere precursors under rheological conditions.

[0028] In one embodiment of the present invention, the deheating preferably includes a first-stage pyrolysis and a second-stage pyrolysis performed sequentially; the temperature of the first-stage pyrolysis is preferably 370-400℃, specifically 370℃, 380℃, 390℃ or 400℃; the holding time is preferably 30 min; and the heating rate from room temperature to the temperature of the first-stage pyrolysis is preferably 20℃ / min.

[0029] In one embodiment of the present invention, the temperature of the second stage pyrolysis is preferably 480-650℃, specifically 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 550℃, 580℃, 600℃ or 650℃, and the holding time is preferably 30min; the heating rate from the temperature of the first stage pyrolysis to the temperature of the second stage pyrolysis can be 20℃ / min.

[0030] In one embodiment of the present invention, the first stage of pyrolysis is carried out in a first reaction chamber; the second stage of pyrolysis can be carried out in a second reaction chamber connected in series with the first reaction chamber. In another embodiment of the present invention, the second stage of pyrolysis is carried out under a protective atmosphere; the protective atmosphere can be nitrogen.

[0031] After obtaining the silica microsphere precursor, the present invention performs three-stage cooling and collision growth on the silica microsphere precursor under a rheological environment, and then re-fires the resulting product to obtain the silica microspheres.

[0032] In one embodiment of the present invention, the three-stage cooling consists of a first-stage cooling, a second-stage cooling, and a third-stage cooling performed sequentially.

[0033] In one embodiment of the present invention, the first stage of cooling is to reduce the temperature of the second stage of pyrolysis to 400°C; the second stage of cooling is to reduce the temperature of the second stage of pyrolysis to 250-300°C; and the third stage of cooling is to reduce the temperature of the second stage of pyrolysis to room temperature.

[0034] In one embodiment of the present invention, the cooling rate of the first stage cooling is preferably 20°C / min; the cooling rate of the second stage cooling is preferably 10°C / min; and the cooling rate of the third stage cooling is preferably 5°C / min.

[0035] In one embodiment of the present invention, the cooling can be carried out in a stepped trapping device, which is connected to the second reaction chamber; the stepped trapping device includes three layers of filters, which are arranged sequentially in the direction of airflow as a first layer, a second layer, and a third layer of filters. The pore size of the first layer of filters can be 1000 mesh; the pore size of the second layer of filters can be 1500 mesh; and the pore size of the third layer of filters can be 2000 mesh.

[0036] In one embodiment of the present invention, the reheating temperature can be 800°C and the time can be 2 hours.

[0037] The silica microspheres prepared by the method described above have a purity of ≥99.5%.

[0038] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1 After cleaning and drying the decommissioned composite insulator silicone rubber, it was placed in a grinding jar. Liquid nitrogen was placed in a foam box, and the grinding jar containing the decommissioned composite insulator silicone rubber was completely immersed in the liquid nitrogen until it no longer boiled. The silicone rubber after low-temperature immersion was placed in a low-temperature grinding instrument for 5 low-temperature grinding cycles (grinding conditions: the grinding ball is a steel ball with a diameter of 3 cm, the grinding tube volume is 50 ml, the frequency is 60 Hz, and the duration is 50 s), to obtain low-temperature ground silicone rubber with a particle size of micron level (average particle size of 500 μm).

[0040] The low-temperature ground silicone rubber was subjected to a first-stage pyrolysis (temperature 400℃, holding time 30min, heating rate 20℃ / min) and a second-stage pyrolysis (temperature 500℃, holding time 30min, heating rate 20℃ / min) in the first reaction chamber. The silica precursor was subjected to a series of cooling processes in a stepped trapping device, including a first stage of cooling (temperature reduced from 500°C to 400°C at a rate of 20°C / min), a second stage of cooling (temperature reduced from 400°C to 300°C at a rate of 10°C / min), and a third stage of cooling (temperature reduced from 300°C to room temperature). The resulting product was then recalcined at 800°C for 2 hours to obtain the silica microspheres.

[0041] The sphericity of the silica microspheres prepared in Example 1 was also tested using the method GB / T 32661-2016, demonstrating that the method provided by this invention can prepare silica microspheres with high sphericity.

[0042] The present invention also tested the pyrolysis properties of the silicone rubber before and after low-temperature grinding in Example 1. The heating rate was 20 K / min, and the temperature range was room temperature to 800 °C. The TG curve test results are as follows: Figure 1 As shown, the remaining mass of the sample after low-temperature liquid nitrogen grinding at 500℃ was 57.8%, while the remaining mass of the unground sample was 64.3%. The overall pyrolysis curve of the silicone rubber particles after low-temperature grinding shifted to the left, which means that silica can be collected at a lower temperature in the actual silicone rubber recycling process.

[0043] Comparative Example 1 Low-temperature liquid nitrogen grinding is not performed.

[0044] The silicone rubber was subjected to a first-stage pyrolysis (temperature 450℃, holding time 30min, heating rate 20℃ / min) and a second-stage pyrolysis (temperature 540℃, holding time 30min, heating rate 20℃ / min) in the first reaction chamber. The silica precursor was subjected to a series of cooling processes in a stepped trapping device, including a first stage of cooling (temperature reduced from 540°C to 450°C and held at that temperature for 0 min, with a cooling rate of 20°C / min), a second stage of cooling (temperature reduced from 450°C to 300°C, with a cooling rate of 10°C / min), and a third stage of cooling (temperature reduced from 300°C to 25°C). The resulting product was then recalcined at 800°C for 2 h to obtain silica microspheres.

[0045] The purity of the silica microspheres prepared in Example 1 was tested using the method JC / T753-2022. The result showed a purity of 99.82%, proving that the method provided by this invention can produce high-purity silica microspheres.

[0046] The purity of the silica microspheres obtained in Example 1 and Comparative Example 1 was tested, and the test results are shown in Tables 1-2.

[0047] Table 1. Purity test results of Comparative Example 1

[0048] Table 2 Purity test results of Example 1

[0049] Note: The ignition residue is the silicon dioxide after reheating.

[0050] The present invention also tested the silica microspheres obtained in Example 1 and Comparative Example 1, and the test results are shown in [Figure 1]. Figure 2 ,from Figure 2 It can be seen that there is no significant difference between the products collected by pyrolysis before and after grinding, but the former was prepared at a temperature of 500℃ and the latter at 540℃, a decrease of 40℃.

[0051] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing silica microspheres using decommissioned composite insulator silicone rubber via pyrolysis, comprising the following steps: The silicone rubber of the decommissioned composite insulator was treated by immersion in liquid nitrogen and then subjected to low-temperature grinding to obtain low-temperature ground silicone rubber. Low-temperature grinding of silicone rubber was followed by pyrolysis to obtain silica microsphere precursors under rheological conditions. The silica microsphere precursor under rheological conditions was subjected to three-stage cooling and collision growth, and the resulting product was re-fired to obtain the silica microspheres. The pyrolysis includes a first-stage pyrolysis and a second-stage pyrolysis performed sequentially; the first-stage pyrolysis and the second-stage pyrolysis are carried out in different reaction regions; the second-stage pyrolysis is carried out in an oxygen atmosphere; the particle size of the silica microspheres is 800 nm to 3 μm.

2. The method as described in claim 1, characterized in that, The temperature of the first stage of pyrolysis is 370-400℃, and the holding time is 30 min; the temperature of the second stage of pyrolysis is 480-650℃, and the holding time is 30 min.

3. The method as described in claim 2, characterized in that, The heating rate from room temperature to the temperature of the first stage of pyrolysis is 20℃ / min; the heating rate from the temperature of the first stage of pyrolysis to the temperature of the second stage of pyrolysis is 20℃ / min.

4. The method as described in claim 1, characterized in that, The first stage of pyrolysis is carried out in the first reaction chamber; the second stage of pyrolysis is carried out in the second reaction chamber connected in series with the first reaction chamber.

5. The method as described in claim 1, characterized in that, The first stage of pyrolysis is carried out under a protective atmosphere.

6. The method as described in claim 1, characterized in that, The low-temperature grinding relies on the frequency vibration of steel balls. The grinding balls are steel balls with a diameter of 3cm. The volume of the grinding tube is 50ml. The raw materials and steel balls being ground do not exceed half the volume of the grinding tube. The grinding time is 1min and the frequency is 60Hz.

7. The method as described in claim 6, characterized in that, The particle size range of the silicone rubber after low-temperature grinding is 50~1000μm.

8. The method as described in claim 1, characterized in that, The three-stage cooling system consists of a first-stage cooling, a second-stage cooling, and a third-stage cooling performed sequentially. The first stage of cooling involves reducing the temperature of the second stage pyrolysis to 400°C. The second stage of cooling involves reducing the temperature from 400℃ to 250-300℃; The third stage of cooling involves reducing the temperature from 250-300℃ to room temperature.

9. The method as described in claim 8, characterized in that, The cooling rate of the first stage of cooling is 20℃ / min; the cooling rate of the second stage of cooling is 10℃ / min; and the cooling rate of the third stage of cooling is 5℃ / min.

10. The method as described in claim 1, characterized in that, The reheating temperature was 800℃ and the time was 2 hours.

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