Resource recycling treatment method for waste plastics

Abstract

The invention discloses a waste plastic resource recycling treatment method which comprises the following steps: (1) crushing waste plastic into small particles, placing the small particles in a conductive material filling container, and enabling the waste plastic particles to be fully and uniformly contacted with the surface of the conductive material filling container; and (2) connecting the two ends of the conductive material filling container with a power supply electrode, and applying pulse current to the conductive material filling container in the reaction cavity under the protection of inert atmosphere, so that the waste plastics are heated and thermally cracked, and a combustible gas product is obtained. According to the resource recycling treatment method for the waste plastics, rapid cracking of the waste plastics can be achieved, and high-value combustible gas is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of resource utilization of waste plastics, and in particular to a resource recovery and treatment method for waste plastics. Background Art

[0002] Plastics are polymer compounds that are polymerized by addition polymerization or condensation polymerization using monomers as raw materials. Plastics play a key role in various fields such as construction, medical treatment, electronics, automobiles, and packaging. Waste plastics are a resource with great potential. Its calorific value is 41-47MJ / Kg, which is much greater than coal (25-35MJ / Kg) and wood (17-19MJ / Kg), and is approximately equal to crude oil (42-47MJ / Kg). Among the main means of resource utilization of waste plastics, pyrolysis technology is a relatively environmentally friendly, economically feasible technology with prospects for large-scale disposal.

[0003] Pyrolysis technology refers to a method of heating under oxygen-free or oxygen-controlled conditions to decompose waste plastic polymers into small molecular products and coke mainly composed of hydrocarbons. Traditional pyrolysis technology can convert waste plastics into products such as pyrolysis oil and pyrolysis gas, and can also obtain light olefins in a targeted manner through the use of catalysts. However, traditional pyrolysis devices exhibit poor heat transfer and large thermal inertia, and it is difficult to control the time of temperature distribution. Therefore, it is difficult to accurately control the thermal reaction path through parameter optimization in traditional heating, resulting in poor selectivity for high-value products, which leads to complex composition of direct pyrolysis products of waste plastics, wide molecular weight distribution, low added value, and limited application. The conventional catalytic pyrolysis of plastics produces mostly oil phase products, which can reach 70%. However, the high acidity, low calorific value and high viscosity make the pyrolysis oil unsuitable for use (reference: JU PARK H, YIMJ-H, JEON JK, et al. Pyrolysis of polypropylene over mesoporous MCM-48material [J]. Journal of Physics and Chemistry of Solids, 2008, 69(5-6):1125-1128). In the conventional catalytic pyrolysis of waste plastics, the catalyst needs to be pre-treated in a complicated manner, and a lot of time is required for preheating and catalytic pyrolysis reaction (>2 hours) (reference: Chinese patent document with publication number CN118308124A). At the same time, traditional plastic catalytic pyrolysis is also prone to produce coke accumulation (>25%), which blocks the pore structure of the catalyst and causes catalyst deactivation (Reference: Barbarias I, Artetxe M, Lopez G, et al. Influence of the conditions for reforming HDPE pyrolysisvolatiles on the catalyst deactivation by coke [J]. Fuel Processing Technology, 2018, 171, 100-109).

[0004] At present, there is an urgent need for a technology that can recycle waste plastics into high-value products with low energy consumption. Summary of the invention

[0005] The invention provides a resource recovery and processing method for waste plastics, which can realize rapid cracking of waste plastics and obtain high-value combustible gas.

[0006] The technical solution of the present invention is as follows: A method for recycling waste plastics comprises the following steps: (1) After crushing the waste plastic into small particles, place them in a container filled with conductive material so that the waste plastic particles are in full and uniform contact with the surface of the container filled with conductive material; (2) The two ends of the conductive material loading container are connected to power supply electrodes, and a pulse current is applied to the conductive material loading container in a reaction chamber under the protection of an inert atmosphere to heat up the waste plastic and thermally decompose it to obtain a combustible gas product.

[0007] Pulse heating technology is a technology that uses the Joule heat generated when a pulse current flows through a highly conductive material for heat treatment. It has the advantages of no need for catalysts, rapid heating, precise temperature control, and high heating temperature. In addition, pulse heating technology has high heating efficiency and can accurately control the heating time, with lower energy consumption than traditional heating methods. The method of the present invention recovers high-value combustible gas products from waste plastics while consuming low energy. High-value combustible gases have high industrial value, such as hydrogen, methane, ethylene, and propylene.

[0008] Preferably, the waste plastics include at least one of polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET).

[0009] Waste plastics include but are not limited to polypropylene, polyethylene, polystyrene, polyethylene terephthalate, etc.

[0010] Preferably, the combustible gas includes at least one of hydrogen, carbon monoxide, methane, ethane, ethylene, propane, propylene, butane and butene.

[0011] Combustible gases include but are not limited to hydrogen, carbon monoxide and C1-C4 short-chain hydrocarbon gases such as methane, ethane, ethylene, propane, propylene, butane and butene.

[0012] The conductive material is a material with high conductivity, fast heat transfer, uniform heating and high temperature resistance.

[0013] Preferably, the conductive material filling container includes a carbon plate, carbon felt, graphite paper, a graphite boat, or a graphite tube.

[0014] Further preferably, the conductive material filling container is graphite paper. Graphite paper has better heating efficiency than other materials, that is, under low current and short pulse time, the heating rate of graphite paper is faster, the heating temperature is higher, and the control of reaction temperature and time is more precise.

[0015] The reaction chamber is made of materials such as quartz, Hastelloy, and S304 stainless steel.

[0016] Preferably, the reaction chamber is equipped with a water cooling device, which is used to cool the rapid temperature rise of the reaction chamber to ensure the safety of the reaction process.

[0017] Preferably, the inert atmosphere includes nitrogen, helium, or argon; and the purge flow rate of the inert atmosphere is not less than 0.05 L / min.

[0018] Preferably, the pulse current is 40-450A; the pulse time is not less than 1s; the number of pulses is not less than 1, and the pulse interval is 3-7s.

[0019] Further preferably, the pulse current is 40-450A; the pulse time is 1-10s; the number of pulses is 1-20 times, and the pulse interval is 3-7s.

[0020] The pulse time is 1-10s, the number of pulses is 1-20 times, and the pulse interval is 3-7s, which means: power-on is 1-10s, the number of power-on is 1-20 times, and the interval between two adjacent power-on times is 3-7s.

[0021] More preferably, the pulse current is 60-450A; the pulse time is 1-5s; the number of pulses is 1-20 times, and the pulse interval is 3-7s.

[0022] Preferably, in step (2), the heating rate is 40-1000° C. / s.

[0023] Preferably, in step (2), the thermal cracking temperature is controlled to be no less than 400°C.

[0024] Furthermore, in step (2), the thermal cracking temperature is controlled to be 400-1500°C.

[0025] Furthermore, in step (2), the thermal cracking temperature is controlled to be 800-1500°C.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) No need for catalyst: The method of the present invention can achieve a conversion rate similar to that of traditional catalytic pyrolysis of waste plastics without the need for additional catalyst, thus saving costs.

[0027] (2) High adjustability and simple operation: The method of the present invention does not require complicated pre-treatment of the raw materials. If one wants to adjust the product distribution by adding a catalyst later, the waste plastic can be directly mixed with the catalyst and the same reaction device can be used.

[0028] (3) Low energy consumption: The heating method used in the method of the present invention is pulse heating, that is, the Joule heat generated when a pulse current flows through a highly conductive material is used for heating. This method has the advantages of fast heating rate and high heating efficiency. The pulse time and number of pulses can be precisely controlled. There is no need for long-term high-temperature heating, and the energy consumption is low.

[0029] (4) High-value combustible gas accounts for a large proportion: High-value combustible gas products have a high calorific value, and the proportion of combustible gas components in the gas products is high.

[0030] (5) Directional control of gas composition: The method of the present invention can obtain high-value combustible gas rich in hydrogen or short-chain hydrocarbons by adjusting the current size and the number of pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of a method for preparing high-value combustible gas products by pyrolyzing waste plastics using pulse heating.

[0032] Figure 2 It is a schematic diagram of the structure of the pulse heating experimental device used in the present invention.

[0033] Figure 3 is a gas composition diagram obtained in Examples 1-7.

[0034] Figure 4 Graph showing the gas conversion rates obtained in Examples 1-7. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0036] The process of the method for preparing high-value gas products by pyrolyzing waste plastics by pulse heating is as follows: Figure 1 shown.

[0037] The device structure used in the following embodiments is as follows Figure 2 As shown, the waste plastic 5 is crushed and placed in a carbon material filling container 4, the two ends of the carbon material filling container 4 are connected to the two poles of a power supply 6 and placed in a reaction chamber 3, the reaction chamber 3 is evacuated by a vacuum pump 10, and an inert atmosphere is passed from a gas cylinder 1 through a flow meter 2 into the reaction chamber 3, and the generated high-value gas products are collected by a gas bag 7. The reaction chamber 3 is equipped with a water cooling device 8, and the temperature on the carbon material filling container 4 is measured by an infrared thermometer 9.

[0038] Example 1 In this embodiment, a graphite boat with a length of 10 cm and a width of 1.5 cm is used as a carbon material filling container, 0.087 g of polypropylene (PP) is loaded, and carbon felt of the same size is cut to cover the graphite boat. The graphite boat is placed in a stainless steel reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen, and the nitrogen flow rate is 0.1 L / min. The two ends of the graphite boat are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 400 A, the pulse time is 1 s, the interval between each pulse is 5 s, and the number of pulses is 3 times. The reaction temperature was measured by an infrared thermometer to reach 1000°C. During the reaction, the gas was collected by an air bag and the gas components were quantitatively analyzed by a gas chromatograph. The results showed that the CH4 yield in the collected gas was 10.29 mg, the C2H4 yield was 17.69 mg, the C2H6 yield was 0.97 mg, the C3H6 yield was 7.54 mg, the C3H8 yield was 0.20 mg, the C4H8 yield was 3.63 mg, and the C4H 10 The output is 0.08mg, H2 output is 3.60mg, and CO output is 18.74mg. According to statistics, the high-value gas yield is 72.48wt%, of which the combustible gas component accounts for 98.90%, and the calorific value is 50.39MJ / Kg.

[0039] Example 2 In this embodiment, a carbon plate with a length of 10 cm and a width of 1.5 cm is used as a carbon material filling container, 0.116 g of polypropylene (PP) is loaded, and carbon felt of the same size is cut to cover the carbon plate. The carbon plate is placed in a Hastelloy reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen, with a nitrogen flow rate of 0.05 L / min. The two ends of the carbon plate are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 450 A, the pulse time is 2 s, and the number of pulses is 1. The reaction temperature was measured by an infrared thermometer to reach 1000°C. During the reaction, gas was collected by an air bag and the gas components were quantitatively analyzed by a gas chromatograph. The results showed that the CH4 yield in the collected gas was 15.10 mg, the C2H2 yield was 8.92 mg, the C2H4 yield was 12.97 mg, the C2H6 yield was 1.01 mg, the C3H6 yield was 6.02 mg, the C3H8 yield was 0.52 mg, the C4H8 yield was 2.87 mg, and the C4H 10 The output is 0.08mg, H2 output is 7.66mg, and CO output is 11.86mg. According to statistics, the high-value gas yield is 58.19wt%, of which the combustible gas component accounts for 94.99%, and the calorific value is 53.35MJ / Kg.

[0040] Example 3 In this embodiment, a graphite paper with a length of 10 cm and a weight of 0.3836 g is used as a carbon material filling container. The graphite paper is folded into a cylindrical shape and filled with 0.0504 g of polypropylene (PP). The graphite paper is placed in a stainless steel reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen. The nitrogen flow rate is 0.1 L / min. The two ends of the graphite paper are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 40 A, the pulse time is 1 s, the interval between each pulse is 5 s, and the number of pulses is 20 times. The reaction temperature was measured by an infrared thermometer to reach 876°C; during the reaction, gas was collected with an air bag and the gas components were quantitatively analyzed with a gas chromatograph. The CH4 yield in the collected gas was 4.39mg, C2H4 yield was 7.99mg, C2H6 yield was 0.91mg, C3H6 yield was 8.82mg, C3H8 yield was 0.20mg, C4H8 yield was 3.54mg, and H2 yield was 0.43mg. According to statistics, the high-value gas yield was 53.75wt%, of which the combustible gas component accounted for 97.05%, and the calorific value was 52.97MJ / Kg.

[0041] Example 4 In this embodiment, a graphite boat with a length of 10 cm and a width of 1.5 cm is used as a carbon material filling container, 0.164 g of polypropylene (PP) is loaded, and carbon felt of the same size is cut to cover the graphite boat. The graphite boat is placed in a stainless steel reaction chamber, vacuumed and argon is introduced, and repeated 3 times to exclude oxygen. The argon flow rate is 0.05 L / min. The two ends of the graphite boat are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 200 A, the pulse time is 10 s, and the number of pulses is 1. The reaction temperature is measured by an infrared thermometer to reach 400 ° C; during the reaction, the gas is collected with an air bag, and the gas composition is quantitatively analyzed by a gas chromatograph. The results show that the CH4 yield in the collected gas is 5.70 mg, the C2H4 yield is 13.19 mg, the C2H6 yield is 1.92 mg, the C3H6 yield is 16.49 mg, the C3H8 yield is 0.65 mg, the C4H8 yield is 5.49 mg, and the C4H 10 The output is 0.12mg, H2 output is 0.64mg, and CO output is 2.18mg. According to statistics, the high-value gas yield is 28.71wt%, of which the combustible gas component accounts for 98.78%, and the calorific value is 51.93MJ / Kg.

[0042] Example 5 In this embodiment, a graphite paper with a length of 10 cm and a weight of 0.4703 g is used as a carbon material filling container. The graphite paper is folded into a cylindrical shape and filled with 0.0543 g of polyethylene (PE). The graphite paper is placed in a stainless steel reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen. The nitrogen flow rate is 0.15 L / min. The two ends of the graphite paper are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 60 A, the pulse time is 1 s, the interval between each pulse is 5 s, and the number of pulses is 20 times. The reaction temperature was measured by an infrared thermometer to reach 1000°C. During the reaction, the gas was collected by an air bag and the gas components were quantitatively analyzed by a gas chromatograph. The CH4 yield of the collected gas was 5.28mg, the C2H2 yield was 0.64mg, the C2H4 yield was 11.37mg, the C2H6 yield was 1.42mg, the C3H6 yield was 3.27mg, the C3H8 yield was 0.51mg, the C4H8 yield was 0.55mg, and the C4H 10 The output is 0.19mg and the H2 output is 0.91mg. According to statistics, the high-value gas yield is 55.74wt%, of which the combustible gas component accounts for 98.65% and the calorific value is 54.03MJ / Kg.

[0043] Example 6 In this embodiment, a graphite paper with a length of 10 cm and a weight of 0.5443 g is used as a carbon material filling container. The graphite paper is folded into a cylindrical shape and filled with 0.0469 g of polyethylene terephthalate (PET). The graphite paper is placed in a stainless steel reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen. The nitrogen flow rate is 0.15 L / min. The two ends of the graphite paper are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 120 A, the pulse time is 1 s, the interval between each pulse is 5 s, and the number of pulses is 20 times. The reaction temperature was measured by an infrared thermometer to reach 1300°C; during the reaction, gas was collected with a gas bag, and the gas components were quantitatively analyzed by a gas chromatograph. The CH4 yield in the collected gas was 0.96mg, C2H2 yield was 0.85mg, C2H4 yield was 0.36mg, C2H6 yield was 0.02mg, C3H6 yield was 0.05mg, C4H8 yield was 0.01mg, H2 yield was 1.51mg, and CO yield was 21.26mg. According to statistics, the high-value gas yield was 53.57wt%, of which the combustible gas component accounted for 97.07%, and the calorific value was 80.01MJ / Kg.

[0044] Example 7 In this embodiment, a graphite paper with a length of 10 cm and a weight of 0.5340 g is used as a carbon material filling container. The graphite paper is folded into a cylindrical shape and filled with 0.06 g of polystyrene (PS). The graphite paper is placed in a stainless steel reaction chamber, evacuated and nitrogen is introduced, and repeated 3 times to exclude oxygen. The nitrogen flow rate is 0.15 L / min. The two ends of the graphite paper are connected to a power supply through electrodes, and the voltage is set to 40 V, the pulse current is 130 A, the pulse time is 1 s, the interval between each pulse is 5 s, and the number of pulses is 20 times. The reaction temperature was measured by an infrared thermometer to reach 1350°C; during the reaction, gas was collected with a gas bag, and the gas components were quantitatively analyzed by a gas chromatograph. The CH4 production in the collected gas was 1.35mg, C2H2 production was 1.15mg, C2H4 production was 0.95mg, C2H6 production was 0.04mg, C3H6 production was 0.07mg, C4H8 production was 0.01mg, H2 production was 3.75mg, and CO production was 3.34mg. According to statistics, the high-value gas yield was 17.18wt%, of which the combustible gas component accounted for 96.46%, and the calorific value was 92.45MJ / Kg.

[0045] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recycling waste plastics, characterized in that: The following steps are involved: (1) After crushing the waste plastic into small particles, place them in a container filled with conductive material so that the waste plastic particles are in full and uniform contact with the surface of the container filled with conductive material; (2) The two ends of the conductive material loading container are connected to power supply electrodes, and a pulse current is applied to the conductive material loading container in a reaction chamber under the protection of an inert atmosphere to heat up the waste plastic and thermally decompose it to obtain a combustible gas product.

2. The method for recycling waste plastics according to claim 1, characterized in that: The waste plastics include at least one of polypropylene, polyethylene, polystyrene and polyethylene terephthalate.

3. The method for recycling waste plastics according to claim 1, characterized in that: The combustible gas includes at least one of hydrogen, carbon monoxide, methane, ethane, ethylene, propane, propylene, butane and butene.

4. The method for recycling waste plastics according to claim 1, characterized in that: Conductive material filling containers include carbon plates, carbon felt, graphite paper, graphite boats, and graphite tubes.

5. The method for recycling waste plastics according to claim 1, characterized in that: The pulse current is 40-450A; the pulse time is not less than 1s; the pulse number is not less than 1 time, and the pulse interval is 3-7s.

6. The method for recycling waste plastics according to claim 5, characterized in that: The pulse current is 40-450A; the pulse time is 1-10s; the pulse number is 1-20 times, and the pulse interval is 3-7s.

7. The method for recycling waste plastics according to claim 5, characterized in that: The pulse current is 60-450A; the pulse time is 1-5s; the pulse number is 1-20 times, and the pulse interval is 3-7s.

8. The method for recycling waste plastics according to claim 1, characterized in that: In step (2), the heating rate is 40-1000°C / s.

9. The method for recycling waste plastics according to claim 1, characterized in that: In step (2), the thermal cracking temperature is controlled to be 400-1500°C.

10. The method for recycling waste plastics according to claim 1, characterized in that: In step (2), the thermal cracking temperature is controlled to be 800-1500°C.

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