Flaky molecular sieve packaged metal catalyst for catalytically converting waste polyolefin into aromatic hydrocarbon as well as preparation method and application of flaky molecular sieve packaged metal catalyst

Abstract

The invention belongs to the technical field of plastic chemical recovery, and discloses a flaky molecular sieve packaged metal catalyst for catalytically converting waste polyolefin into aromatic hydrocarbon as well as a preparation method and application of the flaky molecular sieve packaged metal catalyst. The catalyst is synthesized from a topological template silicon source, a framework coordination aluminum source, a pore channel self-assembly template agent, a solvent, a crystal face oriented growth control agent and a metal salt multi-toothed ring lock stabilizer through controllable sol hydrolysis, gelation, high-temperature crystallization and heat treatment processes. The catalyst has rich outer surface acid density and a high-dispersion confinement metal active center, and the waste polyolefin conversion rate and the aromatic hydrocarbon selectivity are remarkably improved. The conversion rate of waste polyolefin reaches 90% or above, the yield of aromatic hydrocarbon reaches 40 wt.% or above, and the performance index reaches the international leading level of current field research and engineering application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plastic chemical recycling, and particularly relates to a sheet-shaped molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefin into aromatic hydrocarbon and a preparation method and application thereof. BACKGROUND

[0002] The global cumulative plastic production has exceeded 11 billion tons (1950-2023), and the annual production capacity is continuously increasing. In 2023, the global annual production reached 400 million tons, with a compound annual growth rate of 4%. However, the effective recycling rate of current plastic waste is less than 10%. The incineration process causes about 1 billion tons of greenhouse gas emissions equivalent to carbon dioxide per year, significantly increasing the load of the global climate system. Polyolefin materials account for more than 50% of waste plastics, and their stable molecular structure makes them difficult to naturally degrade through environmental action.

[0003] The chemical recycling technology of waste polyolefin mainly includes four basic paths: thermal cracking method, thermal cracking-catalytic upgrading method, catalytic hydrogenolysis method, and catalytic cracking method. The core defect of the above paths is that the products are low-value C1-C 30 alkane / olefin mixtures, and the economic value of the products is difficult to offset the comprehensive cost of waste plastic classification and pretreatment, high-temperature reaction energy consumption, and product separation, resulting in continuous pressure on technical economy. In comparison, the directed catalytic conversion of polyolefin into high-value aromatic compounds not only realizes high-order cyclic utilization of carbon resources, but also reduces the net CO2 emissions of waste plastics throughout the life cycle. However, existing waste plastic aromatization technologies face the core obstacles of high-temperature thermodynamic constraints and catalyst deactivation paths. The production of aromatic hydrocarbons by traditional process routes requires maintaining a high-temperature environment above 500℃, and the energy consumption load occupies a dominant position in the whole process. Patent CN120248924A discloses a waste plastic conversion catalyst and a preparation method thereof. This patent uses a molecular sieve loaded with double active metal components to achieve an aromatic hydrocarbon yield of <15%. Patent CN120136657A discloses a method for preparing light aromatic hydrocarbons from waste polyolefin plastics by catalytic pyrolysis, which uses ZSM-5@SBA-15 to achieve an aromatic hydrocarbon yield of about 30%. The mainstream catalyst for the aromatization route of chemical recycling of waste plastics is metal / metal oxide-acidic molecular sieve, which is easy to induce catalyst metal / metal oxide aggregation and strong dehydrogenation activity of proton acid centers, triggering the generation and irreversible deposition of precursors of carbon deposition in an abnormal state, causing explosive carbon deposition coverage of active sites and a sharp decline in single-pass aromatic hydrocarbon yield. The double bottleneck forms a closed loop chain of high energy consumption-fast deactivation-short life, which forms a fundamental technical barrier to large-scale application.

[0004] Therefore, the present application aims at the problems of high activation energy of cracking system, low cracking reaction efficiency, coking deactivation caused by the microporous structure and long diffusion path of the molecular sieve catalyst and high temperature aggregation of metal / metal oxide active species in the existing catalytic degradation process of waste polyolefin to produce aromatic hydrocarbons, and develops a sheet-shaped molecular sieve encapsulated metal catalyst for efficient catalytic conversion of waste polyolefin to aromatic hydrocarbons. The thickness of the b-axis of the molecular sieve catalyst is precisely controlled by a crystal face directional growth control agent, the acid density of the outer surface of the catalyst is enhanced, and the cracking efficiency of the waste polyolefin is strengthened. At the same time, a metal salt multi-dentate ring lock stabilizer is used to protect the metal source from aggregation during the synthesis of the molecular sieve catalyst, so that the metal active center is embedded in the molecular sieve framework during the synthesis process, and the aggregation and deactivation of the metal / metal oxide active species under the high-temperature catalytic system are effectively suppressed. SUMMARY

[0005] The present application aims at the problems of low cracking reaction efficiency and easy deactivation of the catalytic system in the process of producing aromatic hydrocarbons from waste polyolefin, and provides a preparation method of a sheet-shaped molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefin to aromatic hydrocarbons. The thickness of the b-axis of the molecular sieve is precisely controlled by a crystal face directional growth control agent, and a sheet-shaped molecular sieve encapsulated metal catalyst with strong stability and high activity is developed, which shortens the diffusion path of the process products and slows down the coking deactivation in the molecular sieve channel. The specific technical scheme is as follows:

[0006] A preparation method of a sheet-shaped molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefin to aromatic hydrocarbons, comprising the following steps:

[0007] The topological template silicon source, the framework coordination aluminum source, the channel self-assembled template agent and the solvent are mixed and hydrolyzed in a reactor to obtain a hydrolysis liquid; then a crystal face directional growth control agent and a metal salt multi-dentate ring lock stabilizer are dissolved into the hydrolysis liquid to form a gel, and the obtained gel is subjected to high-temperature induced crystallization, solvent washing and vacuum drying to remove the microporous self-assembled template agent, and then is subjected to heat treatment to remove the microporous self-assembled template agent, so as to obtain a sheet-shaped catalyst M@Zeolite with metal and proton acid dual catalytic active sites.

[0008] In the technical scheme of the present application: the topological template silicon source is an organic silicon source and / or an inorganic silicon source and / or a biomass silicon source; the framework coordination aluminum source is an organic aluminum source or an inorganic aluminum source; the channel self-assembled template agent is one or two of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylphosphonium cation and polyethylene glycol; and the solvent is one of water, dilute hydrochloric acid and dilute nitric acid, and the concentration of the dilute hydrochloric acid and the dilute nitric acid is 1-5wt%.

[0009] Further, the organic aluminum source is one of isopropyl alcohol aluminum, sec-butyl alcohol aluminum and acetylacetone aluminum; and the inorganic aluminum source is one of aluminum sulfate octadecahydrate, aluminum nitrate nonahydrate and pseudo-boehmite.

[0010] The organic silicon source is one or two of methyl orthosilicate, tetraethyl orthosilicate, phenyltrimethoxysilane, 3-aminopropyltrimethoxysilane, mercaptopropyltrimethoxysilane and hexadecyltrimethoxysilane; the inorganic silicon source is one of silica sol and white carbon black; and the biomass silicon source is one of de-impurity rice husk ash and straw ash.

[0011] In the technical scheme of the present application, the molar ratio of the topological template silicon source to the skeleton coordination aluminum source is 25:1-200:1; the molar ratio of the topological template silicon source to the channel self-assembly template agent is 2.5:1-20:1; and the molar ratio of the topological template silicon source to the solvent is 0.01:1-0.1:1.

[0012] In the technical scheme of the present application, the temperature of the hydrolysis is 50-150 DEG C, and the time is 2-24 h; preferably, the temperature of the hydrolysis is 80-100 DEG C, and the time is 10-14 h.

[0013] In the technical scheme of the present application, the crystal face directional growth control agent is one of urea, ammonium fluoride and tetramethyl guanidine; the molar ratio of the topological template silicon source to the crystal face directional growth control agent is 0.2:1-5:1; preferably, the molar ratio of the topological template silicon source to the crystal face directional growth control agent is 1:1-2:1.

[0014] In the technical scheme of the present application, the metal salt multi-dentate ring lock stabilizer is one or two of (ethylenediamine) palladium chloride, bis(ethylenediamine) palladium chloride, bis-polychloride di(2-methallyl) palladium, benzyl bis(triphenylphosphine) palladium chloride, ethylenediamine platinum chloride, bis(ethylenediamine) platinum chloride, tris(ethylenediamine) rhodium nitrate, tris(ethylenediamine) nickel chloride hydrate, tris(ethylenediamine) cobalt chloride and ethylenediamine tetraacetic acid ferric ammonium; the molar ratio of the topological template silicon source to the metal salt multi-dentate ring lock stabilizer is 450:1-1800:1; preferably, the molar ratio of the topological template silicon source to the metal salt multi-dentate ring lock stabilizer is 800:1-1200:1.

[0015] In the technical scheme of the present application, the temperature of the high-temperature induced crystallization is 100-200 DEG C, the crystallization time is 12-72 h; the temperature of the vacuum drying and solvent removal is 50-100 DEG C, and the time is 1-10 h; the temperature of the heat treatment is 400-700 DEG C, and the time is 5-12 h.

[0016] A sheet-shaped molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefins into aromatic hydrocarbons is prepared by the above method.

[0017] The application discloses a catalyst and a preparation method thereof.

[0018] The beneficial effects of the application are embodied in:

[0019] (1) The catalyst M@Zeolite created by the application has a b-axis oriented sheet structure, and the crystal face orientation characteristics expose a large number of catalytic cracking acid centers, thereby strengthening the reaction efficiency of waste plastics cracking into small-molecule organic matter; the short b-axis structure greatly shortens the diffusion path of aromatic hydrocarbon products, and slows down the coking deactivation phenomenon in the molecular sieve channel.

[0020] (2) The application creatively uses a metal salt multi-dentate ring lock stabilizer as a metal active site precursor in the synthesis process, and the metal catalytic active site is limited and encapsulated inside the molecular sieve skeleton, thereby effectively avoiding the high-temperature metal sintering phenomenon.

[0021] (3) The sheet catalyst M@Zeolite created by the application recycles waste polyolefin into green aromatic hydrocarbon, and the conversion rate of waste polyolefin reaches more than 90%, and the aromatic hydrocarbon yield reaches more than 40 wt.%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a transmission electron microscope image of the catalyst 0.5% Pd@Zeolite-1 of the application;

[0023] Figure 2 It is a picture of the catalyst sample of 0.5% Pd@Zeolite-1 before reaction (left), used 0.5% Pd@Zeolite-1 after reaction (middle) and a commercial catalyst 0.5% Pd / HZSM-5 after reaction;

[0024] Figure 3 It is a long-term stability result picture of the catalyst 0.5% Pd@Zeolite-1 of the application in catalytic conversion of waste polyolefin into aromatic hydrocarbon. DETAILED DESCRIPTION

[0025] The application is further described below through implementation cases, but the protection scope of the application is not limited to this:

[0026] The silica sol used in the examples and comparative examples is purchased from Shijiazhuang Shuanglian Chemical Co., Ltd.

[0027] Example 1

[0028] Tetraethyl orthosilicate, pseudoboehmite, tetrapropylammonium hydroxide, and water were mixed in a molar ratio of 50:1:5:1500 and hydrolyzed at 90°C for 12 hours to obtain a hydrolyzate. Subsequently, ammonium fluoride and bis(ethylenediamine)palladium chloride were dissolved in the hydrolyzate in a molar ratio of 1:1 tetraethyl orthosilicate: ammonium fluoride and 880:1 tetraethyl orthosilicate: bis(ethylenediamine)palladium chloride, respectively, to induce a gelation reaction. The specific addition amounts were as follows: 156 g tetraethyl orthosilicate (0.59 mol), 0.78 g pseudoboehmite (0.0118 mol), 48 g 25% tetrapropylammonium hydroxide aqueous solution (0.059 mol), 320 g water (17.78 mol), 22 g ammonium fluoride (0.59 mol), and 0.2 g bis(ethylenediamine)palladium chloride (0.00067 mol). It was then transferred to a 150°C constant temperature crystallization reactor for 72 hours. After the reaction, the sample was washed with water and vacuum dried at 100°C for 1 hour, and then placed in a 550°C heat treatment device for calcination for 5 hours. The final synthesized catalyst was named 0.5% Pd@Zeolite-1.

[0029] The transmission electron microscopy results are shown in the attached figure. Figure 1 As shown in Figure 2, 0.5% Pd@Zeolite-1 has a typical b-axis oriented flake morphology with a b-axis thickness of <100 nm. The external surface acid density is 0.87 μmol / m 2 The acid density of the catalyst's external surface is quantitatively calculated through 2,6-di-tert-butylpyridine infrared testing and nitrogen adsorption-desorption testing. 2,6-di-tert-butylpyridine is used to determine the amount of external surface acid, and nitrogen adsorption-desorption testing is used to determine the external surface area. External surface acid density = external surface acid amount / external surface area.

[0030] The prepared catalyst was applied to the process of preparing aromatic hydrocarbons from waste high-density polyethylene (HDPE). The specific process is as follows: 2g of catalyst 0.5% Pd@Zeolite-1 was mixed with 10g of HDPE and placed in a reactor at a temperature of 375°C. 20% oxygen was continuously introduced into the reactor at a flow rate of 50mL / min. The liquid product was collected by condensing a zero-degree ice-water mixture at the outlet. The gas was collected through an aluminum foil gas collection bag. After 2 hours of reaction, the product was collected for analysis. The HDPE conversion rate and aromatic hydrocarbon yield were 99% and 50.14wt.%, respectively. After the reaction, the catalyst still maintained the same color as the fresh catalyst, and no obvious coking and deactivation occurred (see Appendix). Figure 2 middle).

[0031] Example 2

[0032] The other conditions in the catalyst preparation process in Example 2 were the same as those in Example 1, except for the following conditions:

[0033] 1. The silicon source was changed from tetraethyl orthosilicate to methyl orthosilicate, phenyltrimethoxysilane, etc. The changes in the type of silicon source are shown in Table 1. The molar ratio of the two silicon sources was 1:1.

[0034] 2. The molar ratio of silicon / aluminum source was changed from 50:1 to 25:1, 100:1, and 200:1, respectively (see Table 1).

[0035] 3. The solvent was changed from water to 1 wt% dilute nitric acid. The molar ratio of the silicon source to the solvent was 0.1:1.

[0036] 4. The hydrolysis temperature was changed from 90°C to 150°C, and the hydrolysis time was changed from 12 h to 2 h.

[0037] 5. The vacuum drying temperature was changed from 100°C to 50°C, and the vacuum drying time was changed from 1 h to 10 h.

[0038] 6. The heat treatment time was changed from 5 h to 12 h.

[0039] The prepared catalysts were used in the preparation of aromatic hydrocarbons from waste high-density polyethylene (HDPE) under the same reaction conditions as in Example 1. The HDPE conversion and aromatic hydrocarbon yield performance results are shown in Table 1. The HDPE conversion was maintained in the range of 92.69-99.58%, and the aromatic hydrocarbon yield was 40.37-53.69 wt.%. The HDPE conversion and aromatic hydrocarbon yield of the catalysts with low silicon / aluminum source ratios were significantly higher than those of the catalysts with high silicon / aluminum source ratios.

[0040] Table 1 Comparison of the performance of catalysts with different silicon sources and silicon / aluminum source ratios in the degradation of high-density polyethylene

[0041]

[0042]

[0043] Example 3

[0044] In Example 3, the catalyst was prepared under the same conditions as in Example 1, except for the following conditions:

[0045] 1. The aluminum source was changed from pseudoboehmite to aluminum isopropoxide, aluminum sec-butoxide, etc. The changes in the type of aluminum source are shown in Table 1.

[0046] 2. The molar ratio of silicon / aluminum source was changed from 50:1 to 25:1, 100:1, and 200:1, respectively (see Table 2).

[0047] 3. The solvent was changed from water to 5 wt% dilute hydrochloric acid. The molar ratio of the silicon source to the solvent was 0.01:1.

[0048] 4. The hydrolysis temperature was changed from 90°C to 50°C, and the hydrolysis time was changed from 12 h to 24 h.

[0049] The prepared catalysts were used in the degradation of waste high density polyethylene (HDPE) to aromatics under the same reaction conditions as in Example 1. The HDPE conversion and aromatics yield performance results are shown in Table 2. The HDPE conversion was maintained in the range of 93.32-99.52%, and the aromatics yield was 40.85-52.34 wt.%. The catalysts prepared with different types of framework coordination aluminum sources had similar catalytic reaction performance, reflecting the universal applicability of the preparation method for different aluminum sources.

[0050] Table 2 Comparison table of performance of catalysts with different aluminum sources and silicon / aluminum source ratios in the degradation of high density polyethylene

[0051]

[0052] Example 4

[0053] In Example 4, the catalyst preparation process was the same as in Example 1, except for the following conditions:

[0054] 1. The channel self-assembly template agent was changed from tetrapropylammonium hydroxide to tetrapropylammonium bromide, tetrabutylphosphonium cation, and a tetrapropylammonium hydroxide-polyethylene glycol mixture, respectively. The molar ratio between the two template agents was 1:1 (see Table 3 for details);

[0055] 2. The molar ratio of silicon source / template agent was changed from 10:1 to 2.5:1 and 20:1, respectively (see Table 3 for details).

[0056] The prepared catalysts were used in the degradation of waste high density polyethylene (HDPE) to aromatics under the same reaction conditions as in Example 1. The HDPE conversion and aromatics yield performance results are shown in Table 3. The HDPE conversion was maintained in the range of 91.84-99.55%, and the aromatics yield was 40.61-51.39 wt.%. The HDPE conversion of the catalyst 0.5% Pd@Zeolite-18-22 prepared with different channel self-assembly template agents and ratios was all higher than 90%.

[0057] Table 3 Comparison table of performance of catalysts with different template agents and silicon source / template agent ratios in the degradation of high density polyethylene

[0058]

[0059] Example 5

[0060] In Example 5, the catalyst preparation process was the same as in Example 1, except for the following conditions:

[0061] 1. The crystal face directional growth control agent was changed from ammonium fluoride to urea and tetramethyl guanidine, respectively (see Table 4 for details);

[0062] 2. The molar ratio of silicon source / control agent was changed from 1:1 to 0.2:1 and 5:1, respectively (see Table 4 for details).

[0063] The prepared catalysts were used in the degradation of waste high-density polyethylene (HDPE) to produce aromatic hydrocarbons under the same reaction conditions as in Example 1. The performance results for HDPE conversion and aromatic hydrocarbon yield are shown in Table 4. The HDPE conversion was maintained in the range of 91.75-99.85%, and the aromatic hydrocarbon yield was 41.58-53.71 wt.%. The b-axis thickness of the catalysts prepared using urea, tetramethylguanidine, and ammonium fluoride as the crystal face growth control agent was in the range of 80-180 nm. As the amount of crystal face growth control agent increased, the b-axis thickness gradually decreased, and the corresponding HDPE conversion and aromatic hydrocarbon yield increased. The short b-axis catalysts exhibited a significant effect on the degradation of waste polyethylene.

[0064] Table 4 Comparison of the performance of catalysts for the degradation of high-density polyethylene with different control agents and silicon source / control agent ratios

[0065]

[0066] Example 6

[0067] In Example 6, the catalyst was prepared under the same conditions as in Example 1, except for the following conditions:

[0068] 1. The polydentate ring-locked stabilizer for metal salts was changed from bis(ethylenediamine)palladium chloride to (ethylenediamine)palladium chloride, bis(2-methallyl)palladium dichloride, and ethylenediamine platinum chloride, respectively. The molar ratio of the two stabilizers was 1:4 when both were present (see Table 5 for details).

[0069] 2. The molar ratio of silicon source / stabilizer was changed from 880:1 to 450:1, 600:1, and 1800:1, respectively (see Table 5 for details).

[0070] The prepared catalysts were used in the degradation of waste high-density polyethylene (HDPE) to produce aromatic hydrocarbons under the same reaction conditions as in Example 1. The performance results for HDPE conversion and aromatic hydrocarbon yield are shown in Table 5. The HDPE conversion was maintained in the range of 98.52-99.82%, and the aromatic hydrocarbon yield was 50.02-54.36 wt.%. The use of metal salt polydentate ring-locked stabilizers encapsulated the metal units in the zeolite framework, preventing the aggregation of noble metals at high temperatures, and the catalysts maintained high catalytic reaction performance at high temperatures.

[0071] Table 5 Comparison of the performance of catalysts for the degradation of high-density polyethylene with different stabilizers and silicon source / stabilizer ratios

[0072]

[0073] Example 7

[0074] To optimize the crystallization process and heat treatment process during catalyst preparation, a series of catalysts were prepared based on Example 1 by changing the crystallization temperature (from 150°C to 100°C and 200°C), the time from 72 h to 12 h, and the heat treatment temperature (from 550°C to 400°C, 600°C, and 700°C, respectively). The HDPE conversion and aromatics yield performance are shown in Table 6. Other catalyst preparation raw materials and conditions were the same as in Example 1. The reaction conditions for the catalytic degradation of waste high-density polyethylene to produce aromatics were the same as in Example 1.

[0075] Table 6 Comparison of the performance of high-density polyethylene degradation by catalysts prepared at different crystallization temperatures and heat treatment temperatures

[0076]

[0077] Example 8

[0078] The catalyst described in Example 1 was used to catalyze the degradation of various polyolefins and their mixtures to produce aromatic hydrocarbons. The process conditions were as follows: HDPE:0.5% Pd@Zeolite-1 = 5:1, in a 20% oxygen atmosphere, and at a catalytic reaction temperature of 375°C. Specifically, 2g of the 0.5% Pd@Zeolite-1 catalyst was mixed with 10g of HDPE and placed in a reactor at 375°C. 20% oxygen was continuously introduced into the reactor at a flow rate of 50 mL / min, and the liquid and gaseous products were collected. The catalytic performance of 0.5% Pd@Zeolite-1 on low-density polyethylene, high-density polyethylene, mixed polyethylene, and mixed polyolefins is shown in Table 7. The conversion of waste polyolefins exceeded 98.5%, and the aromatic hydrocarbon yield remained above 45 wt.%, demonstrating the universal applicability of the 0.5% Pd@Zeolite-1 catalyst for the degradation of various polyolefins and mixed polyolefins.

[0079] Table 7 Comparison of the catalytic degradation performance of different types of polyolefins and their mixtures by 0.5% Pd@Zeolite-1

[0080]

[0081] Example 9

[0082] The 0.5% Pd@Zeolite-1 in Example 1 was used to optimize the reaction process conditions, mainly including the waste polyolefin / catalyst, reaction temperature, and reaction atmosphere. The experimental design results and the corresponding HDPE conversion rate and aromatics yield are shown in Table 8. Temperature is the main factor affecting the HDPE conversion rate. By adjusting the polyolefin / catalyst ratio, reaction temperature, and reaction atmosphere, the HDPE conversion rate can be maintained above 90%. With the increase of oxygen content, the aromatics yield gradually increases. This is because the hydrogen in the reaction system is consumed during the aromatization process, and the hydrogen content in the system is reduced, which inhibits the olefin hydrogenation and isomerization reactions. The olefins are further dehydrogenated, cyclized, and aromatized to produce aromatic products, ultimately increasing the process aromatics yield.

[0083] Table 8 Comparison of catalytic degradation performance of polyolefins under different polyolefins / catalysts, reaction temperatures and reaction atmospheres

[0084]

[0085]

[0086] Example 10

[0087] The catalyst 0.5% Pd@Zeolite-1 was subjected to a cyclic stability test under the same reaction conditions. The HDPE conversion rate and aromatics yield results are shown in the attached figure. Figure 3 In the five tests, the HDPE conversion rate of the catalyst was maintained above 97%, and the aromatics selectivity was around 50%. No obvious performance degradation was observed, indicating that the catalyst has excellent long-term stability.

[0088] Comparative Example 1

[0089] Commercially available HZSM-5, HY, and Hβ molecular sieves were used to prepare comparative catalysts 0.5% Pd / HZSM-5, 0.5% Pd / HY, and 0.5% Pd / Hβ by impregnation, and applied to the process of catalytic degradation of waste polyolefins to produce aromatic hydrocarbons. The prepared catalysts were used in the process of producing aromatic hydrocarbons from waste high-density polyethylene (HDPE) under the same reaction conditions as in Example 1. The external surface acid density, HDPE conversion rate, and aromatic hydrocarbon yield are shown in Comparative Table 1. The results showed that the external surface acid density of the 0.5% Pd / HZSM-5, 0.5% Pd / HY, and 0.5% Pd / Hβ catalysts was much smaller than the external surface acid density of the catalyst of the present invention, which was 0.87 μmol / m 2 This indicates that the external surface acid density determines the catalytic efficiency of the production of aromatics from waste polyolefins. The HDPE conversion rates of the three catalysts were significantly lower than those of the catalyst of the present invention, and the aromatics yields were all less than 25%. After the reaction, the catalysts all showed obvious coking and deactivation. The actual image of the 0.5% Pd / HZSM-5 catalyst after the reaction is shown in the attached figure. Figure 2 (right) shown.

[0090] Table 1 Performance of different comparative catalysts in degrading high density polyethylene

[0091]

Claims

1. A method for preparing a sheet-like molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefins into aromatic hydrocarbons, characterized in that: The following steps are involved: placing a topological template silicon source, a framework coordinated aluminum source, a pore self-assembly template agent, and a solvent in a reactor, mixing and hydrolyzing the mixture to obtain a hydrolyzate; The crystal plane directional growth controller and the metal salt multi-tooth ring lock stabilizer are then dissolved in the hydrolyzate to form a gel. The resulting gel is sequentially subjected to high-temperature induced crystallization, solvent washing, vacuum drying and desolvation, and then heat treatment to remove the microporous self-assembly template agent, thereby obtaining a sheet catalyst M@Zeolite with dual catalytic active sites of metal and protonic acid.

2. The preparation method according to claim 1, wherein: The topological template silicon source is an organic silicon source and / or an inorganic silicon source and / or a biomass silicon source; the skeleton coordinated aluminum source is an organic aluminum source or an inorganic aluminum source; the pore self-assembly template agent is one or two of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylphosphonium cation and polyethylene glycol; and the solvent is one of water, dilute hydrochloric acid and dilute nitric acid, and the concentrations of the dilute hydrochloric acid and dilute nitric acid are both 1-5wt%.

3. The preparation method according to claim 2, wherein: The organic aluminum source is one of aluminum isopropoxide, aluminum sec-butoxide and aluminum acetylacetonate; the inorganic aluminum source is one of aluminum sulfate 18hydrate, aluminum nitrate nonahydrate and pseudo-boehmite; The organic silicon source is one or two of methyl orthosilicate, tetraethyl orthosilicate, phenyltrimethoxysilane, 3-aminopropyltrimethoxysilane, mercaptopropyltrimethoxysilane and hexadecyltrimethoxysilane; the inorganic silicon source is one of silica sol and white carbon black; and the biomass silicon source is one of de-mixed rice husk ash and straw ash.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the topological template silicon source to the skeleton coordinated aluminum source is 25:1-200:1; the molar ratio of the topological template silicon source to the pore self-assembly template agent is 2.5:1-20:1; and the molar ratio of the topological template silicon source to the solvent is 0.01:1-0.1:

1.

5. The preparation method according to claim 1, characterized in that: The hydrolysis temperature is 50-150° C., and the time is 2-24 hours; preferably, the hydrolysis temperature is 80-100° C., and the time is 10-14 hours.

6. The preparation method according to claim 1, characterized in that: The crystal plane oriented growth controller is one of urea, ammonium fluoride and tetramethylguanidine; the molar ratio of the topological template silicon source to the crystal plane oriented growth controller is 0.2:1 to 5:1; preferably, the molar ratio of the topological template silicon source to the crystal plane oriented growth controller is 1:1 to 2:

1.

7. The sheet-shaped molecular sieve encapsulated metal catalyst for catalytic conversion of waste polyolefins into aromatic hydrocarbons according to claim 1, characterized in that: The metal salt multi-toothed ring lock stabilizer is one or two of (ethylenediamine) palladium chloride, bis(ethylenediamine) palladium chloride, bis(2-methallyl) palladium chloride, benzylbis(triphenylphosphine) palladium chloride, ethylenediamine platinum chloride, bis(ethylenediamine) platinum chloride, tri(ethylenediamine) rhodium nitrate, tri(ethylenediamine) nickel chloride hydrate, tri(ethylenediamine) cobalt chloride, and ethylenediaminetetraacetic acid ammonium ferric; the molar ratio of the topological template silicon source to the metal salt multi-toothed ring lock stabilizer is 450:1 to 1800:1; preferably, the molar ratio of the topological template silicon source to the metal salt multi-toothed ring lock stabilizer is 800:1 to 1200:

1.

8. The preparation method according to claim 1, characterized in that: The temperature of the high-temperature induced crystallization is 100-200°C, and the crystallization time is 12-72 hours; the temperature of the vacuum drying and desolvation is 50-100°C, and the time is 1-10 hours; the temperature of the heat treatment is 400-700°C, and the time is 5-12 hours.

9. A sheet-like molecular sieve encapsulated metal catalyst for catalytically converting waste polyolefins into aromatic hydrocarbons, characterized by: The method according to any one of claims 1 to 8 is used to prepare the present invention.

10. Use of the catalyst prepared by the method of claim 1 in catalytically converting waste polyolefins into aromatic hydrocarbons; preferably, the mass ratio of the waste polyolefins to the catalyst is 0.5:1 to 10:1, the catalytic reaction temperature is 300 to 500°C, and the catalytic reaction atmosphere is 1 to 20% oxygen by volume.

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