Method for preparing low-carbon olefin, low-carbon olefin and application of low-carbon olefin
By using a two-stage pyrolysis method to prepare low-carbon olefins from discarded masks, the problems of limited heat transfer and difficulty in controlling secondary reactions in traditional methods have been solved, achieving efficient preparation of low-carbon olefins and improving resource utilization efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2024-10-18
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies for preparing low-carbon olefins suffer from numerous side reactions, wide product distribution, and low yields of low-carbon olefins. In particular, when using discarded masks to prepare low-carbon olefins, heat transfer is limited and secondary reactions are difficult to control.
A two-stage pyrolysis method is adopted, firstly, a first-stage pyrolysis is carried out at a lower temperature, and then a second-stage pyrolysis is carried out at a higher temperature. By utilizing an inert gas atmosphere and controlling the specific temperature and heating rate, secondary reactions are reduced and the yield of low-carbon olefins is improved.
The two-stage pyrolysis method significantly improved the yield of low-carbon olefins, realizing the efficient resource utilization of waste masks and improving the product yield and quality of low-carbon olefins.
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Figure CN121895995A_ABST
Abstract
Description
Technical Field
[0001] This application relates to a method for preparing low-carbon olefins, low-carbon olefins and their applications. Background Technology
[0002] The disposal of waste plastics has attracted widespread attention globally. Currently, the main methods for disposing of waste plastics are landfill and incineration, with limited recycling. With the dramatic increase in the use of disposable medical masks, a large number of masks have become waste. The disposal of these discarded masks not only involves environmental pollution but also resource waste.
[0003] Discarded face masks are mainly made of plastic materials such as polypropylene, which can undergo pyrolysis at high temperatures to generate various low-molecular-weight hydrocarbon compounds, including low-carbon olefins. Low-carbon olefins, such as ethylene, propylene, and butene, are important chemical raw materials with high economic value. Therefore, how to effectively dispose of discarded face masks and realize their resource utilization has become an urgent problem to be solved. Pyrolysis, which involves heating materials in an anaerobic environment to ultimately obtain gases, water, oil, and coke, is considered to have very broad development prospects and is expected to become an efficient and environmentally friendly waste treatment technology, thus contributing to sustainable development.
[0004] However, the pyrolysis process of discarded masks is complex, involving not only various chemical reactions but also mass transfer and heat transfer. Furthermore, the distribution of various products generated during pyrolysis is also affected by the pyrolysis conditions. Currently, most experimental research and industrial treatment of waste plastics focus on obtaining pyrolysis oil, striving to improve oil quality and process efficiency. In contrast, the generation of pyrolysis gas has received less attention, mostly considered only as an auxiliary fuel in the pyrolysis process. However, polyolefin pyrolysis gas has a high olefin content, thus providing another route for olefin production. The challenges include the high temperatures required for olefin production from plastics, but the low thermal conductivity of plastics limits heat transfer; the predominantly random pyrolysis mechanism of polyolefins results in a wide distribution of products; and the tendency for low-carbon olefins to undergo secondary reactions, which are difficult to control.
[0005] Therefore, given the technical problems of numerous side reactions, wide product distribution, and low yield of low-carbon olefins in the preparation of low-carbon olefins using discarded masks in the existing technology, there is an urgent need to provide a new method for preparing low-carbon olefins using discarded masks to improve the above problems. Summary of the Invention
[0006] This invention provides a method for preparing low-carbon olefins, which solves the problems of numerous side reactions, wide product distribution, and low yield of low-carbon olefins in the preparation of low-carbon olefins in the prior art.
[0007] As one aspect of the present invention, a method for preparing low-carbon olefins is disclosed, the method comprising: in an inert gas atmosphere, sequentially and continuously performing a first-stage pyrolysis and a second-stage pyrolysis on polypropylene material; wherein the temperature of the first-stage pyrolysis is 450–550°C, the heating rate is 10–20°C / s, and the holding time at 450–550°C is 30–50s; wherein the temperature of the second-stage pyrolysis is 700–900°C, the heating rate is 200–300°C / s, and the holding time at 700–900°C is 1–2s.
[0008] In a feasible specific implementation, the polypropylene material is placed in a quartz tube and subjected to a first-stage pyrolysis and a second-stage pyrolysis in sequence, wherein the inner diameter of the quartz tube is 6-8 mm.
[0009] In a feasible specific implementation, the polypropylene material is a discarded face mask.
[0010] In a feasible specific embodiment, the inert gas is selected from one or any combination of nitrogen, argon or helium.
[0011] In a feasible specific implementation, the flow rate of the inert gas is 50-400 mL / min, and the residence time is 0.2-1.6 s.
[0012] In a feasible specific implementation, the first stage of pyrolysis is carried out in a shell heater, and the second stage of pyrolysis is carried out in a tubular furnace, with both the shell heater and the tubular furnace being fitted over the quartz tube.
[0013] In a feasible specific implementation, the polypropylene material is purged with inert gas for 5 to 10 minutes before undergoing the first and second stages of pyrolysis.
[0014] In a feasible specific implementation, the dimensions of the polypropylene material are (3-5) mm × (3-5) mm.
[0015] As another aspect of the present invention, there is a low-carbon olefin, which is a low-carbon olefin obtained according to the above method.
[0016] As another aspect of the invention, it relates to the application of the aforementioned low-carbon olefin in the fields of plastics, solvents, and pharmaceuticals.
[0017] The present invention provides a method for preparing low-carbon olefins from discarded face masks. The first stage of pyrolysis is carried out at a lower temperature, and the second stage at a higher temperature. This first stage of pyrolysis allows the raw materials to complete pyrolysis within a very short residence time, reducing secondary reactions and significantly increasing the yield of low-carbon olefins. This achieves a two-stage pyrolysis recovery of low-carbon olefins from discarded face masks. The method provided by this invention can prepare low-carbon olefins from discarded face masks without adding a catalyst, which has significant theoretical and practical implications for improving the resource utilization efficiency of discarded face masks. Attached Figure Description
[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. In the drawings:
[0019] Figure 1 A schematic diagram of the apparatus used in the method for producing low-carbon olefins provided by the present invention;
[0020] Wherein: 10 is the crushing unit, 20 is the conveying unit, 30 is the first-stage pyrolysis unit, and 40 is the second-stage pyrolysis unit. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0022] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.
[0023] Example 1:
[0024] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and the holding time at 500℃ was 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and the holding time at 800℃ was 1s; the products were obtained. The total gas yield of the products reached 78.5wt%, and the yield of low-carbon olefins was 71.5wt%. Among them, propylene and butene accounted for the highest proportions, at 27.9wt% and 30.2wt%, respectively, while ethylene accounted for 12.4wt% and butadiene accounted for 1.0wt%.
[0025] Example 2:
[0026] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 200mL / min, with a residence time of 0.4s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the product was obtained. The total gas yield of the product was 76.5 wt%, and the yield of low-carbon olefins was 67.9 wt%, of which propylene accounted for 25.3 wt%, butene for 26.8 wt%, ethylene for 14.2 wt%, and butadiene for 1.6 wt%.
[0027] Example 3:
[0028] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 50mL / min, with a residence time of 1.6s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the products were obtained. The total gas yield of the products was 73.5 wt%, and the yield of low-carbon olefins was 56.6 wt%, of which propylene accounted for 20.5 wt%, butene for 22.8 wt%, ethylene for 12.3 wt%, and butadiene for 1.0 wt%.
[0029] Example 4:
[0030] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 450℃, with a heating rate of 20℃ / s, and held at 450℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the product was obtained. The total gas yield of the product was 74.8 wt%, and the yield of low-carbon olefins was 63.3 wt%, of which propylene accounted for 23.6 wt%, butene for 25.4 wt%, ethylene for 13.4 wt%, and butadiene for 0.9 wt%.
[0031] Example 5:
[0032] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 550℃, with a heating rate of 20℃ / s, and held at 550℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the products were obtained. The total gas yield of the products was 75.6 wt%, and the yield of low-carbon olefins was 68.8 wt%, of which propylene accounted for 25.8 wt%, butene for 27.0 wt%, ethylene for 14.3 wt%, and butadiene for 1.7 wt%.
[0033] Example 6:
[0034] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 10℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the product was obtained. The total gas yield of the product was 62.9 wt%, and the yield of low-carbon olefins was 44.6 wt%, of which propylene accounted for 17.3 wt%, butene for 16.5 wt%, ethylene for 10.1 wt%, and butadiene for 0.7 wt%.
[0035] Example 7:
[0036] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 15℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the products were obtained. The total gas yield of the products was 67.3 wt%, and the yield of low-carbon olefins was 58.5 wt%, of which propylene accounted for 21.6 wt%, butene for 21.9 wt%, ethylene for 13.8 wt%, and butadiene for 1.2 wt%.
[0037] Example 8:
[0038] Discarded masks were disassembled and crushed into small fragments with sides of 3mm × 3mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the products were obtained. The total gas yield of the products was 79.5 wt%, and the yield of low-carbon olefins was 71.2 wt%, of which propylene accounted for 28.2 wt%, butene for 29.0 wt%, ethylene for 12.6 wt%, and butadiene for 1.4 wt%.
[0039] Example 9:
[0040] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 8mm and another in a quartz tube with an inner diameter of 6mm. Nitrogen gas was introduced to purge the material for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater was wrapped around the front end of the quartz tube, and the tubular furnace was wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially and continuously. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. Nitrogen gas was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, with a residence time of 0.36s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and held at 800℃ for 1s; the products were obtained. The total gas yield of the products was 76.2 wt%, and the yield of low-carbon olefins was 68.4 wt%, of which propylene accounted for 25.8 wt%, butene for 26.6 wt%, ethylene for 14.1 wt%, and butadiene for 1.9 wt%.
[0041] Comparative Example 1:
[0042] Discarded masks were disassembled and shredded into small fragments with sides of 5mm × 5mm, which were used as the shredded material. The shredded material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the shredded material were fixed with quartz wool and placed in a sleeve heater. Pyrolysis was carried out in a nitrogen atmosphere. Nitrogen was passed through the sleeve heater at a flow rate of 400mL / min controlled by a mass flow meter, and the residence time was controlled to be 0.2s. The temperature of the sleeve heater was set to 500℃, the heating rate was 20℃ / s, and the temperature was held at 500℃ for 30s to obtain the product. The total gas yield of the product was 56.4wt%, and the yield of low-carbon olefins was 24.9wt%, of which propylene accounted for 10.3wt%, butene for 8.5wt%, ethylene for 5.7wt%, and butadiene for 0.4wt%.
[0043] Comparative Example 2:
[0044] The only difference from Example 1 is that: the discarded masks were disassembled and crushed into small fragments with a side length of 5mm × 5mm as the crushed material; the crushed material was placed in a quartz tube with an inner diameter of 6mm, and nitrogen was introduced to purge for 5 minutes; after fixing both ends of the quartz tube containing the crushed material with quartz wool, the sleeve heater for the first stage of pyrolysis and the tube furnace for the second stage of pyrolysis were both placed on the outside of the quartz tube, with the sleeve heater wrapped around the front end of the quartz tube and the tube furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially and continuously. The first stage of pyrolysis and the second stage of pyrolysis were both carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tube furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 2℃ / s, and the holding time at 500℃ was 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 300℃ / s, and the holding time at 800℃ was 1s. The yields of each component were as follows: total gas yield was 62.7 wt%, low-carbon olefin yield was 38.5 wt%, of which propylene yielded 16.3 wt%, butene yielded 12.6 wt%, ethylene yielded 8.1 wt%, and butadiene yielded 1.5 wt%.
[0045] Comparative Example 3:
[0046] Discarded masks were disassembled and crushed into small fragments with sides of 5mm × 5mm as the pulverized material. The pulverized material was placed in a quartz tube with an inner diameter of 6mm and purged with nitrogen for 5 minutes. The two ends of the quartz tube containing the pulverized material were fixed with quartz wool. A sleeve heater for the first stage of pyrolysis and a tubular furnace for the second stage of pyrolysis were placed on the outside of the quartz tube. The sleeve heater wrapped around the front end of the quartz tube, and the tubular furnace wrapped around the rest of the quartz tube. The first stage of pyrolysis and the second stage of pyrolysis were carried out sequentially. Both the first stage of pyrolysis and the second stage of pyrolysis were carried out in a nitrogen atmosphere. The nitrogen was controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 400mL / min, and the residence time was controlled to be 0.2s. The temperature of the shell heater was set to 500℃, with a heating rate of 20℃ / s, and held at 500℃ for 30s; the temperature of the tube furnace was set to 800℃, with a heating rate of 30℃ / s, and held at 800℃ for 1s; the product was obtained. The total gas yield of the product was 56.3wt%, and the yield of low-carbon olefins was 35.8wt%, of which propylene accounted for 16.5wt%, butene for 12.9wt%, ethylene for 5.2wt%, and butadiene for 1.2wt%.
[0047] Based on the above embodiments and comparative examples, it can be seen that the total gas yield of the products obtained by the methods in Examples 1-9 reached 62.9wt% to 79.5wt%, and the low-carbon olefin yield reached 44.6wt% to 71.5wt%, both of which are higher than those in Comparative Examples 1-3. The methods in Examples 1-9 can be summarized as follows: Discarded masks are disassembled and crushed into small fragments with a side length of 3-5mm as the crushed material; the crushed material is placed in a quartz tube with an inner diameter of 6-8mm, and nitrogen is introduced for purging for 5 minutes; the two ends of the quartz tube containing the crushed material are fixed with quartz wool, and the first-stage pyrolysis sleeve heater and the second-stage pyrolysis tube furnace are both sleeved on the outside of the quartz tube, with the sleeve heater wrapped around the quartz tube. At the front end, a tubular furnace encloses the remaining part of the quartz tube, and sequentially performs a first-stage pyrolysis treatment and a second-stage pyrolysis treatment. Both the first-stage and second-stage pyrolysis processes are carried out under a nitrogen atmosphere. Nitrogen gas is controlled by a mass flow meter to pass through the sleeve heater and the tubular furnace at a flow rate of 50-400 mL / min, with a residence time controlled at 0.2-1.6 s. Specifically, the temperature of the sleeve heater is set to 450-550℃, with a heating rate of 10-20℃ / s, and the holding time at 450-550℃ is 30-50 s. The temperature of the tubular furnace is set to 700-900℃, with a heating rate of 200-300℃ / s, and the holding time at 700-900℃ is 1-2 s, yielding the product.
[0048] The present invention provides a method for preparing low-carbon olefins from discarded face masks, comprising a first stage of pyrolysis at a lower temperature and a second stage of pyrolysis at a higher temperature. The first stage of pyrolysis allows the raw materials to complete pyrolysis within a very short residence time, reducing secondary reactions and significantly increasing the yield of low-carbon olefins. This achieves a two-stage pyrolysis recovery of low-carbon olefins from discarded face masks. Furthermore, it has significant theoretical and practical implications for improving the resource utilization efficiency of discarded face masks.
[0049] While this specification contains numerous specific implementation details, these should not be construed as limiting the scope of any invention or the scope of the claims, but rather are primarily intended to describe features of specific embodiments of a particular invention. Certain features described in the various embodiments herein may also be implemented in combination in a single embodiment. Conversely, various features described in a single embodiment may also be implemented separately in various embodiments or in any suitable sub-combination. Furthermore, while features may function in certain combinations as described above and even initially claimed in this way, one or more features from a claimed combination may be removed from that combination in some cases, and a claimed combination may refer to a sub-combination or a variation thereof.
[0050] Thus, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired result. Furthermore, the processes depicted in the drawings are not necessarily shown in a specific order or sequence to achieve the desired result. In some implementations, multitasking and parallel processing may be advantageous.
[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0052] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.
Claims
1. A method for preparing low-carbon olefins, characterized in that, The method includes: in an inert gas atmosphere, polypropylene material undergoes sequential and continuous first-stage pyrolysis and second-stage pyrolysis; wherein, the temperature of the first-stage pyrolysis is 450-550℃, the heating rate is 10-20℃ / s, and the holding time at 450-550℃ is 30-50s; wherein, the temperature of the second-stage pyrolysis is 700-900℃, the heating rate is 200-300℃ / s, and the holding time at 700-900℃ is 1-2s.
2. The method according to claim 1, characterized in that, The polypropylene material is placed in a quartz tube and subjected to a first-stage pyrolysis and a second-stage pyrolysis in sequence. The inner diameter of the quartz tube is 6-8 mm.
3. The method according to claim 1, characterized in that, The polypropylene material mentioned is from discarded face masks.
4. The method according to claim 1, characterized in that, The inert gas is selected from nitrogen, argon, or helium, or any combination thereof.
5. The inert gas of claim 4 has a flow rate of 50-400 mL / min and a residence time of 0.2-1.6 s.
6. The method according to any one of claims 1-5, characterized in that, The first stage of pyrolysis is carried out in a shell-and-tube heater, and the second stage of pyrolysis is carried out in a tubular furnace. Both the shell-and-tube heater and the tubular furnace are fitted over the quartz tube.
7. The method according to claim 1, characterized in that, Before undergoing first-stage and second-stage pyrolysis, the polypropylene material is purged with inert gas for 5–10 minutes.
8. The method according to claim 1, characterized in that, The dimensions of the polypropylene material are (3-5) mm × (3-5) mm.
9. A low-carbon olefin, characterized in that, The low-carbon olefin is a low-carbon olefin obtained by any one of the methods described in claims 1-8.
10. The use of the low-carbon olefin of claim 9 in the fields of plastics, solvents and pharmaceuticals.