A method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis

Abstract

This invention belongs to the field of waste plastic treatment technology, specifically relating to a method for producing light aromatics from waste polyolefin plastics through catalytic pyrolysis. This invention utilizes an ultra-dilute liquid-phase coating method to coat a microporous molecular sieve ZSM-5 within an ordered mesoporous layer SBA-15, creating a coated catalyst ZSM-5@SBA-15 with an encapsulation thickness of 60–185 nm. This coated catalyst possesses an ordered mesoporous encapsulation layer, which can pre-decompose and enrich the volatiles from plastic pyrolysis during the reaction, thereby improving the mass transfer rate, promoting the formation of light aromatics, and inhibiting the formation of large-chain hydrocarbons during catalytic pyrolysis, achieving efficient production of light aromatics from waste polyolefin plastics through catalytic pyrolysis. Compared to traditional ZSM-5, when the encapsulation thickness of ZSM-5@SBA-15 is 90 nm, the yield of light aromatics is 31.02 wt.%, an increase of 49.14%, while simultaneously reducing heavy-chain hydrocarbon byproducts by 42.17%.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic treatment technology, specifically relating to a method for producing light aromatics by catalytic pyrolysis of waste polyolefin plastics. Background Technology

[0002] Plastics are indispensable to the global economy, widely used in industries such as electronics, transportation, construction, packaging, and healthcare. Of all types of plastics, polyolefins (including polyethylene and polypropylene) account for more than 50% of global polymer production. Over 75% of plastics are discarded after a single use, and due to their short-term nature, most are not recycled. Statistics show that approximately 381 million tons of plastic waste were generated in 2015, and this figure is projected to double by 2034. The generation and improper disposal of large amounts of plastic waste pose a serious threat to the environment, including water and soil quality and biological health. Traditional methods of plastic waste disposal involve incineration to recover energy, but this leads to greenhouse gas emissions and the generation of harmful pollutants. It is noteworthy that plastics, as an important carbon resource, can be directly converted into high-value-added chemicals using catalytic technology, which is of great significance for the rational use of resources and environmental protection.

[0003] Catalytic pyrolysis using microporous zeolites such as ZSM-5 as catalysts is an effective method for upgrading plastic waste into high-value-added chemicals (such as aromatics). Among these high-value-added compounds, light aromatics (BTEX) such as benzene, toluene, ethylbenzene, and xylene are highly favored due to their key roles in the production of pharmaceuticals, cosmetics, pesticides, and as gasoline octane enhancers. Notably, compared to fossil-based BTEX, BTEX from plastic waste has a smaller environmental impact, reducing greenhouse gas emissions by approximately 12%. However, existing catalytic pyrolysis methods for waste polyolefin plastics still suffer from poor BTEX selectivity and limited heavy chain hydrocarbon (C4H4H4) selectivity. 10+ The high proportion of chain hydrocarbons and severe catalyst deactivation due to carbon buildup present technical bottlenecks. Therefore, there is an urgent need to develop a method for the efficient production of light aromatics from the catalytic pyrolysis of waste polyolefin plastics. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention synthesizes a coated composite molecular sieve catalyst ZSM-5@SBA-15 in an acidic medium via an ultra-dilute liquid phase coating method, and uses it for the catalytic pyrolysis of polypropylene (PP) to produce light aromatics. This catalyst can utilize the coating layer to pre-crack heavy volatiles and enrich chain hydrocarbon intermediates, thereby greatly increasing the yield of light aromatics during the catalytic pyrolysis of waste polyolefin plastics.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for producing light aromatics by catalytic pyrolysis of waste polyolefin plastics. Specifically, the method involves first coating a microporous molecular sieve ZSM-5 in an ordered mesoporous layer SBA-15 using an ultra-dilute liquid phase coating method to prepare a coated catalyst ZSM-5@SBA-15, which is then added to waste polyolefin plastics and subjected to catalytic pyrolysis at high temperature to obtain light aromatics.

[0007] The coated catalyst prepared in this invention has an ordered mesoporous coating layer, which can locally enrich the volatiles of waste polyolefin plastics during the reaction and improve the mass transfer rate. Through the synergistic effect of these two factors, it promotes the formation of light aromatics and inhibits the formation of large molecular hydrocarbons during the catalytic pyrolysis of waste polyolefin plastics, thus achieving efficient production of light aromatics from the catalytic pyrolysis of waste polyolefin plastics. Compared with the traditional ZSM-5, the coated catalyst ZSM-5@SBA-15 with a coating thickness of 90 nm achieves the highest yield of light aromatics at 31.02 wt.%, an increase of 49.14%, while reducing the production of heavy chain hydrocarbon byproducts by 42.17%.

[0008] Preferably, the mass ratio of the coated catalyst ZSM-5@SBA-15 to waste polyolefin plastic is 1-2:2-3.

[0009] Preferably, the pyrolysis is carried out at 550-700°C with nitrogen as the carrier gas, and the flow rate of the carrier gas is 80-130 mL / min.

[0010] Preferably, the waste polyolefin plastic is polypropylene.

[0011] Preferably, the preparation of the coated catalyst ZSM-5@SBA-15 includes the following steps:

[0012] S1. Dissolve tetrapropylammonium hydroxide, tetraethyl orthosilicate and NaAlO2 in water, and after hydrothermal crystallization, wash until neutral, and then dry and calcinate to obtain Na-type ZSM-5 molecular sieve.

[0013] S2. The Na-type ZSM-5 molecular sieve was subjected to ammonium exchange with NH4Cl solution, dried and then calcined to obtain the H-type ZSM-5 molecular sieve.

[0014] S3. Dissolve P123 and MgSO4 in HCl solution, then add H-type ZSM-5 molecular sieve and TEOS, mix well, and place the resulting suspension at 90-120℃ for 20-30h. After the reaction, wash until neutral, and then dry and calcine to obtain the coated catalyst ZSM-5@SBA-15.

[0015] More preferably, in the encapsulated catalyst ZSM-5@SBA-15, the encapsulation thickness of ZSM-5 is 60-185 nm.

[0016] This invention utilizes an ultra-dilute liquid-phase coating method to coat microporous molecular sieve ZSM-5 within an ordered mesoporous layer SBA-15, creating coated catalysts ZSM-5@SBA-15 with varying encapsulation thicknesses. These catalysts are then applied to the catalytic pyrolysis of waste polyolefin plastics to produce light aromatics. The process provides cooperative acidic centers and a complex pore structure, which is beneficial for obtaining high-content light aromatic products. Furthermore, by adjusting the encapsulation thickness of the coated catalyst, an optimal encapsulation thickness of 90 nm was achieved for the best light aromatic yield.

[0017] More preferably, the hydrothermal crystallization temperature in S1 is 160-180°C, and the crystallization time is 2-4 days.

[0018] More preferably, the calcination temperature in S1, S2, and S3 is 500-600℃, and the time is 5-7h.

[0019] More preferably, the concentration of the NH4Cl solution in S2 is 1.0-2.0M, the ammonium exchange temperature is 70-90℃, and the time is 3-5h.

[0020] More preferably, the concentration of the HCl solution in S3 is 1-3M, and the concentration of P123 in the HCl solution is 0.45-0.7g / 200-400mL.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention discloses a method for producing light aromatics from waste polyolefin plastics via catalytic pyrolysis. First, a microporous molecular sieve ZSM-5 is coated onto an ordered mesoporous layer SBA-15 using an ultra-dilute liquid-phase coating method to prepare coated catalysts ZSM-5@SBA-15 with different encapsulation thicknesses. These catalysts are then applied to the catalytic pyrolysis of waste polyolefin plastics to produce light aromatics. The coated catalyst ZSM-5@SBA-15 provided by this invention has an ordered mesoporous coating layer, which can locally enrich the volatiles of waste polyolefin plastics during the reaction and simultaneously improve the mass transfer rate. Through the synergistic effect of these two factors, the generation of light aromatics is promoted, and the generation of large molecular weight hydrocarbons is inhibited during the catalytic pyrolysis of waste polyolefin plastics, thereby significantly improving the yield of light aromatics. Attached Figure Description

[0023] Figure 1 Transmission electron microscopy (TEM) images of the coated composite catalyst ZSM-5@SBA-15 with different encapsulation thicknesses. (a) ZSM-5@SBA-15 (0.5), (b) ZSM-5@SBA-15 (1), (c) ZSM-5@SBA-15 (2), and (d) ZSM-5@SBA-15 (3).

[0024] Figure 2 A schematic diagram of the experimental process apparatus for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis.

[0025] Figure 2 In the middle: 1-Nitrogen cylinder, 2-Gas mixing flow device, 3-Quartz tube, 4-Timer, 5-Vertical tubular heater, 6-Hanging basket, 7-Collection bottle, 8-Gas washing bottle, 9-Gas washing bottle filled with pure water, 10, 11-Gas washing bottle filled with cotton, 12-Aluminum foil gas bag.

[0026] Figure 3 The figures show the aromatics yield, light aromatics (BTEX) yield, and heavy aromatics (C) yield of waste polyolefin plastic catalytic pyrolysis when the encapsulation thickness of the ZSM-5@SBA-15 catalyst is 60 nm. 9+ Aromatic hydrocarbon yield, heavy chain hydrocarbon (C 10+ Yields of chain hydrocarbons and yields of benzene, toluene, ethylbenzene and xylene.

[0027] Figure 4 The figures show the aromatics yield, light aromatics (BTEX) yield, and heavy aromatics (C) yield of waste polyolefin plastic catalytic pyrolysis when the encapsulation thickness of the ZSM-5@SBA-15 catalyst is 90 nm. 9+ Aromatic hydrocarbon yield, heavy chain hydrocarbon (C 10+ Yields of chain hydrocarbons and yields of benzene, toluene, ethylbenzene and xylene.

[0028] Figure 5 The figures show the aromatics yield, light aromatics (BTEX) yield, and heavy aromatics (C) yield of waste polyolefin plastic catalytic pyrolysis when the encapsulation thickness of the ZSM-5@SBA-15 catalyst is 130 nm. 9+ Aromatic hydrocarbon yield, heavy chain hydrocarbon (C 10+ Yields of chain hydrocarbons and yields of benzene, toluene, ethylbenzene and xylene.

[0029] Figure 6 The figures show the aromatics yield, light aromatics (BTEX) yield, and heavy aromatics (C) yield of waste polyolefin plastic catalytic pyrolysis when the encapsulation thickness of the ZSM-5@SBA-15 catalyst is 185 nm. 9+ Aromatic hydrocarbon yield, heavy chain hydrocarbon (C 10+ Yields of chain hydrocarbons and yields of benzene, toluene, ethylbenzene and xylene.

[0030] Figure 7 The figures show the aromatic yields, light aromatics (BTEX) yield, and heavy aromatics (C) yield of waste polyolefin plastics catalytic pyrolysis when the catalyst is a traditional microporous molecular sieve ZSM-5. 9+ Aromatic hydrocarbon yield, heavy chain hydrocarbon (C 10+ Yields of chain hydrocarbons and yields of benzene, toluene, ethylbenzene and xylene.

[0031] Figure 8 The coating composite catalyst ZSM-5@SBA-15 prepared in Examples 1-4 and Comparative Example 1 and the conventional molecular sieve catalyst ZSM-5 were used to catalyze the pyrolysis of waste polyolefin plastics, increasing the yield of light aromatic hydrocarbons (BTEX) and heavy chain hydrocarbons (C) by pyrolysis. 10+ (Alternating chain hydrocarbon) yield. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0034] The following examples and comparative examples synthesize ZSM-5 and the coated catalyst ZSM-5@SBA-15 using the hydrothermal method and the ultradilute liquid phase coating method, respectively. The specific processes are as follows:

[0035] (1) Weigh 26g H2O and 15.65g TPAOH (tetrapropylammonium hydroxide) and add them to 100mL of polytetrafluoroethylene liner. Stir for 10min to dissolve completely.

[0036] (2) Weigh 8.68g of TEOS (tetraethyl orthosilicate) and add it to the solution in step (1), and stir continuously at 600rpm for 6h.

[0037] (3) Weigh 0.0344 g of NaAlO2 and add it to the solution in step (2), stir for 30 min, and then transfer it to a stainless steel hydrothermal reactor and crystallize it at 170 °C for 3 days.

[0038] (4) The suspension obtained in step (3) was washed several times with a large amount of water until it was neutral, and then dried at 80°C for 12 hours. The resulting powder was then calcined at 550°C for 6 hours to obtain Na-type ZSM-5 molecular sieve.

[0039] (5) The ZSM-5 powder obtained in step (4) was subjected to ammonium exchange at 80°C for 4 hours using NH4Cl (1.0M) solution (mixing ratio of 1g ZSM-5 / 50mL solution), and the process was repeated twice. After drying, the powder was calcined at 550°C for 6 hours to obtain H-type ZSM-5 molecular sieve.

[0040] (6) Weigh 0.58g of P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer) and add it to 300mL of 2M HCl solution, and stir until dissolved.

[0041] (7) Weigh 1.74g of MgSO4 and add it to the solution in step (6), and stir until completely dissolved.

[0042] (8) Weigh 1.5g of the molecular sieve ZSM-5 powder obtained in step (5) and add it to the solution obtained in step (7), and then sonicate for 30min.

[0043] (9) Weigh 1.5g of TEOS and add it dropwise into the solution obtained in step (8). Stir at 600rpm for 24h, and then transfer the suspension into an autoclave and react at 100℃ for 24h.

[0044] (10) The suspension obtained in step (9) was washed several times with a large amount of water until it was neutral, then dried at 80°C for 12 hours, and then the obtained powder was calcined at 550°C for 6 hours to obtain the encapsulated catalyst ZSM-5@SBA-15 with an encapsulation thickness of 90 nm.

[0045] Following the above method, by changing the amount of TEOS weighed in step (9) to 0.75g, 3g and 4.5g respectively, the encapsulated catalyst ZSM-5@SBA-15 with encapsulation thicknesses of 60nm, 130nm and 185nm can be prepared.

[0046] from Figure 1 It can be observed that the encapsulation thickness of the coated catalyst ZSM-5@SBA-15 increases with the increase of silicon source (TEOS) addition, indicating that the encapsulation thickness is controllable.

[0047] Examples and comparative examples:

[0048] The coated catalyst ZSM-5@SBA-15 was used for the catalytic pyrolysis of waste polyolefin plastics to produce light aromatics. The following experiments were conducted using polypropylene as a representative example.

[0049] 1. Catalytic pyrolysis of waste polyolefin plastics to produce light aromatics

[0050] A schematic diagram of the experimental apparatus for the catalytic pyrolysis of waste polyolefins is shown below. Figure 2 As shown, the specific process is as follows:

[0051] (1) Weigh 0.5g of catalyst and 1g of polypropylene respectively. Weigh the quartz tube 3 and the collection bottle 7 separately. Select nitrogen as the carrier gas (provided by nitrogen cylinder 1). Control the gas flow rate to 100mL / min using the gas mixing flow device 1.

[0052] (2) Place the catalyst weighed in step (1) into the quartz tube 3 and spread it evenly in the lower quartz layer. Place the polypropylene powder in the quartz basket 6 with the bottom opening and hang it in the upper inner part of the quartz tube 3 (outside the heating zone) using hooks.

[0053] (3) After heating the vertical tube furnace 5 to 600°C, nitrogen gas is introduced for 20 minutes to allow the pyrolysis device to reach a stable state.

[0054] (4) During the reaction, the quartz basket 6 is sent into the heating zone for 60 minutes to react fully and collect the product. Both the pyrolysis reaction and the catalytic reaction occur in the heating zone in the middle section of the tube furnace cavity.

[0055] (5) During the pyrolysis process, the pyrolysis temperature is set to 600℃. Waste polyolefin plastic is placed in a quartz basket. The condensable vapor is purged by the carrier gas through a collection bottle 7 containing absorbent liquid (20mL dichloromethane) and an empty collection bottle to collect liquid products at low temperature (-20℃). The tail gas passes through an empty gas washing bottle 8 (to prevent backflow), a gas washing bottle 9 containing pure water (to observe whether the gas velocity is stable by the bubbles), and two gas washing bottles 10 and 11 filled with cotton (to filter the tail gas) and is then collected by an 8L aluminum foil gas bag 12.

[0056] (6) After the reaction is complete, collect the waste catalyst in the quartz tube 3 and weigh the quartz tube 3 and the collection bottle 7 after drying.

[0057] Following the above process, four examples and one comparative example were set up. The types of catalysts used and their encapsulation thickness are shown in Table 1.

[0058] Table 1. Details of each embodiment and comparative example.

[0059]

[0060] 2. Detection of aromatic hydrocarbon and chain hydrocarbon content in the product and calculation of yield.

[0061] The products collected in the above embodiments and comparative examples were analyzed to determine the content of aromatic hydrocarbons. The specific process is as follows:

[0062] (1) Dissolve and dilute the collected product with dichloromethane to a final volume of 20 mL;

[0063] (2) Take 50 μL of the solution from step (1), dilute it to 0.5 mL with ethyl acetate, and then transfer it to a brown sample vial;

[0064] (3) The above-mentioned samples were tested by GC-MS (gas chromatography-mass spectrometry) to determine the content of aromatic hydrocarbons and their components.

[0065] (4) The mass of gas collected in the aluminum foil gas bag was determined using GC-FID (gas chromatography-flame ionization detector).

[0066] (5) Use TGA (Thermogravimetric Analysis) to determine the mass of carbon deposits on the spent catalyst.

[0067] (6) Determine the mass of the paraffin product based on the mass difference between the quartz tube and the collection bottle before and after the reaction.

[0068] The pretreated samples were analyzed using GC-MS (7890B-5977B, HP-5ms column) for component identification, with a scan mode of 30–500 amu. The column oven temperature program was as follows: 35 °C for 8 min, then increased to 100 °C at 5 °C / min and held for 3 min, then increased to 220 °C at 5 °C / min, and finally increased to 290 °C at 10 °C / min and held for 5 min. The compounds corresponding to each peak were identified using the NIST spectral library and relevant literature (http: / / doi.org / 10.1021 / acscatal.3c05098; ​​http: / / doi.org / 10.1016 / j.jhazmat.2023.131547). The percentage of peak area to total area was recorded as the relative abundance (area%) of the component.

[0069] Gas detection was performed using a gas chromatograph (GC9800), including an FID detector and a TCD detector. Samples were injected when the temperature was ready (60°C), with continuous injections lasting approximately 30 seconds. Simultaneously, the carrier gas exhaust was monitored during injection. The total detection time was approximately 20 minutes.

[0070] Based on the law of conservation of mass, the calculation process for the yields of aromatics and their components is as follows:

[0071]

[0072] Yield of each component (wt.%) = relative content × liquid product yield × PP mass Eq. (5)

[0073] The results of the detection of aromatic hydrocarbon content in the products of each embodiment and comparative example are shown in Table 2, where the detection results of each component of the aromatic hydrocarbon and its content are as follows: Figures 3-8 As shown, where Figure 3 The results are from Example 1. Figure 4 The results are from Example 2. Figure 5 The results are from Example 3. Figure 6 The results are from Example 4. Figure 7 This is the result of Comparative Example 1. Figure 8 The yields of light aromatic hydrocarbons (BTEX) and heavy chain hydrocarbons (C) in Examples 1-4 and Comparative Example 1 are shown. 10+(Alternating chain hydrocarbon) yield.

[0074] Table 2. Yields of aromatics, heavy chain hydrocarbons, and light aromatics in the products of each example and comparative example.

[0075] Yield, wt.% Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Total aromatic hydrocarbons 33.53 34.71 26.83 21.21 23.76 Heavy aromatics 5.77 3.69 4.37 1.90 2.96 BTEX 27.76 31.02 22.47 19.31 20.80 benzene 0.77 3.05 0.88 1.88 1.52 Toluene 6.23 13.27 7.09 7.66 7.65 Ethylbenzene 1.82 1.33 1.07 0.98 1.05 xylene 18.94 13.37 13.43 8.79 10.59 Heavy chain hydrocarbons 14.17 10.92 15.58 12.74 18.88

[0076] As can be seen from the comparison of the total aromatic hydrocarbon results in Table 2, the total aromatic hydrocarbon content of Examples 1-2 is significantly higher than that of Comparative Example 1. Furthermore, comparing Examples 3-4 with Examples 1-2, and comparing Examples 3-4 with Comparative Example 1, it was found that as the encapsulation thickness of the coated catalyst gradually increases, the aromatic hydrocarbon production of the catalytic waste polyolefin plastic first increases and then decreases, reaching its highest point at an encapsulation thickness of 90 nm (Example 2), while it is lower than that of conventional ZSM-5 at an encapsulation thickness of 185 nm (Example 4).

[0077] like Figures 3-8 As shown, by comparing the BTEX and heavy aromatic hydrocarbon yields of each example and the comparative example, it was found that when the encapsulation thickness was 90 nm, the promoting effect on light aromatic hydrocarbons in the catalytic production of aromatic hydrocarbons from waste polyolefin plastics was the most significant, and the yield of heavy aromatic hydrocarbons was lower compared to encapsulated catalysts with other encapsulation thicknesses. Furthermore, among the various components of BTEX, the yield increase was most significant for toluene and xylene, which have a larger proportion. By comparing the heavy chain hydrocarbon yields of each example and the comparative example, it can be seen that the encapsulated catalyst has a significant inhibitory effect on the surface side reactions of ZSM-5, and the heavy chain hydrocarbon yield of Example 2 was the lowest.

[0078] In summary, compared with the traditional ZSM-5, the coated catalyst prepared by the method of this invention can significantly improve the aromatic yield, especially the yield of light aromatic hydrocarbon BTEX, in the process of catalytic production of aromatic hydrocarbons from waste polyolefin plastics. Furthermore, the effect of improving the aromatic yield, especially the BTEX yield, is optimal when the encapsulation thickness of the coated catalyst is 90 nm.

[0079] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis, characterized in that, First, the microporous molecular sieve ZSM-5 is coated in the ordered mesoporous layer SBA-15 using an ultra-dilute liquid phase coating method to prepare the coated catalyst ZSM-5@SBA-15. Then, it is added to waste polyolefin plastic and catalyzed at high temperature to produce light aromatics. The mass ratio of the coated catalyst ZSM-5@SBA-15 to the waste polyolefin plastic is 1-2: 2-3; the pyrolysis is carried out at 550-700℃ with nitrogen as the carrier gas and the flow rate of the carrier gas is 80-130 mL / min; the waste polyolefin plastic is polypropylene. In the coated catalyst ZSM-5@SBA-15, the encapsulation thickness of ZSM-5 is 60-130 nm; the preparation of the coated catalyst ZSM-5@SBA-15 includes the following steps: S1. Dissolve tetrapropylammonium hydroxide, tetraethyl orthosilicate and NaAlO2 in water, and after hydrothermal crystallization, wash until neutral, and then dry and calcinate to obtain Na-type ZSM-5 molecular sieve. S2. The Na-type ZSM-5 molecular sieve was subjected to ammonium exchange with NH4Cl solution, dried and then calcined to obtain the H-type ZSM-5 molecular sieve. S3. P123 polyoxyethylene-polypropylene oxide-polyoxyethylene triblock copolymer and MgSO4 were dissolved in HCl solution, and then H-type ZSM-5 molecular sieve and TEOS were added. After mixing, the resulting suspension was placed at 90-120℃ for 20-30 h. After the reaction, it was washed until neutral, and then dried and calcined to obtain the coated catalyst ZSM-5@SBA-15.

2. The method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis according to claim 1, characterized in that, The hydrothermal crystallization temperature described in S1 is 160-180℃, and the crystallization time is 2-4 days.

3. The method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis according to claim 1, characterized in that, The roasting temperature described in S1, S2, and S3 is 500-600℃, and the time is 5-7 hours.

4. The method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis according to claim 1, characterized in that, The concentration of the NH4Cl solution in S2 is 1.0-2.0M, the ammonium exchange temperature is 70-90℃, and the time is 3-5h.

5. The method for producing light aromatics from waste polyolefin plastics by catalytic pyrolysis according to claim 1, characterized in that, The concentration of the HCl solution in S3 is 1-3M, and the concentration of P123 in the HCl solution is 0.45-0.7g / 200-400mL.

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