EMT / TS-1 mixed crystal molecular sieve, preparation method thereof and application thereof in polyethylene waste hydrocracking

Abstract

The application provides an EMT / TS-1 mixed crystal molecular sieve, a preparation method thereof and application thereof in polyethylene waste hydrogenation cracking, and belongs to the technical field of catalysts. The preparation method of the EMT / TS-1 mixed crystal molecular sieve is as follows: an aluminum source is added into a first alkali hydroxide solution, and a phosphate, a first template agent and a first silicon source are subjected to aging treatment and first crystallization treatment to obtain an EMT microcrystal emulsion; a titanium source and a second template agent are uniformly stirred, and then water and an alcohol solvent are added to obtain a first solution; a second alkali hydroxide, water and an organic ligand are uniformly mixed, and a hydrolysis reaction occurs; after the reaction is completed, a platinum source is added to obtain a second solution; the above solutions are uniformly stirred, and then a second silicon source is added to perform second crystallization treatment and calcination treatment to obtain the EMT / TS-1 mixed crystal molecular sieve. The EMT / TS-1 mixed crystal molecular sieve catalyst can completely convert a certain proportion of low-density polyethylene in a short time.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically to an EMT / TS-1 mixed-crystal molecular sieve, its preparation method, and its application in the hydrocracking of polyethylene waste. Background Technology

[0002] Plastics, with their excellent versatility, are widely used in industrial production and the manufacture of daily necessities. However, the persistent pollution they cause to the natural environment severely undermines their social benefits. Because synthetic plastics generally resist natural degradation, approximately 79% of waste plastics, once landfilled or improperly disposed of, will remain in the environment for decades to centuries. Therefore, a dual technological approach is urgently needed: on the one hand, resource utilization through physical recycling (such as PET bottle recycling systems); on the other hand, using chemical methods such as pyrolysis and catalytic cracking to convert long-chain polymers into liquid fuels (such as diesel components) or syngas (H2 / CO mixtures).

[0003] Thermochemical recycling of catalysts (such as zeolites) offers a promising alternative for treating contaminated plastic waste. This approach not only lowers the reaction temperature required for polymer decomposition but also allows for precise control of product distribution, increasing the yield of high-value products. Zeolites, due to their microporous structure, restrict macromolecular motion, creating a confinement effect that stabilizes carbocation transition states and modulates the selectivity of hydrocarbon reactions (such as β-fracture). This acidic catalytic mechanism can achieve the deconstruction of long-chain polymers under relatively mild conditions. However, the microporous structure also limits the diffusion efficiency of larger molecules, leading to reduced utilization of Brønsted acid sites. Traditional polyolefin hydrocracking employs bifunctional metal + acid (zeolite) catalysts. Rorrer, J. E et al. supported metallic Ru on Brønsted acidic zeolites with FAU and β-topology (ACS Catal. 2022, 12, 13969−13979.). Ru nanoparticles showed high activity for the cleavage of C-C bonds in PE and PP, exhibiting high liquid yields and inhibiting methane formation. Hou et al. studied the catalytic oxidation and recycling of polyethylene plastic into high-value dicarboxylic acids using TS-1 under mild conditions (Chemical Engineering Journal, 2025, 504: 158868.). The structure of TS-1 exhibits high efficiency at low temperatures, can minimize or prevent coking, and is compatible with the reaction process. However, this oxidation and recycling method requires a long reaction time (about 12 hours). Summary of the Invention

[0004] To address the above problems, this invention provides an EMT / TS-1 mixed-crystal molecular sieve, its preparation method, and its application in the hydrocracking of polyethylene waste. This invention constructs an EMT / TS-1 mixed-crystal molecular sieve catalyst through an in-situ synthesis strategy. The high silica-to-alumina ratio of EMT imparts strong Brønsted acid centers, significantly improving the C / C bond breaking efficiency. The Pt nanoparticles encapsulated in the TS-1 titanium silicate molecular sieve achieve stable anchoring of highly dispersed metal sites through microporous confinement. Its oleophilic surface can rapidly capture pyrolysis intermediates and complete deep hydrogenation, thereby inhibiting excessive pyrolysis and the generation of gaseous products. The synergistic effect of both achieves dynamic coupling of the pyrolysis-hydrogenation process.

[0005] The first objective of this invention is to provide a method for preparing EMT / TS-1 mixed-crystal molecular sieves, comprising the following steps:

[0006] An aluminum source, phosphate, a first template agent and a first silicon source were added to a first alkali metal hydroxide solution, stirred evenly, aged at room temperature, and then subjected to a first crystallization treatment at 100℃~120℃ to obtain an EMT microcrystalline emulsion.

[0007] After the titanium source and the second template agent are stirred evenly, water and an alcohol solvent are added to obtain the first solution;

[0008] The second alkali metal hydroxide, water, and organic ligand are mixed evenly and a hydrolysis reaction is carried out. After the reaction is completed, a platinum source is added to obtain the second solution.

[0009] After adding the second solution and EMT microcrystalline emulsion to the first solution and stirring evenly, a second silicon source is added, and a second crystallization treatment is carried out at 170℃~180℃. Then, calcination treatment is carried out in air atmosphere to obtain EMT / TS-1 mixed crystal molecular sieve.

[0010] In a preferred embodiment of the present invention, the first crystallization treatment takes 6 to 7 days.

[0011] In a preferred embodiment of the present invention, the second crystallization treatment time is 24h~28h.

[0012] In a preferred embodiment of the present invention, the mass ratio of aluminum source to phosphate is 1:0.03~0.04;

[0013] The mass ratio of aluminum source to first template agent is 1:0.5~0.6;

[0014] The mass ratio of aluminum source to primary silicon source is 1:10~15;

[0015] The mass ratio of aluminum source to first alkali metal hydroxide is 1:0.3~0.5.

[0016] In a preferred embodiment of the present invention, the mass ratio of the second silicon source to the titanium source is 40:1~5, and the mass ratio of the second silicon source to the second template agent is 4:1~2.

[0017] In a preferred embodiment of the present invention, the mass ratio of the second alkali metal hydroxide to the organic ligand is 1:1.2~1.5, and the mass ratio of the second alkali metal hydroxide to H2PtCl6 is 1:2.5~3.

[0018] In a preferred embodiment of the present invention, the organic ligand is 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, carboxysilane, or ethylenediamine.

[0019] In a preferred embodiment of the present invention, the calcination treatment is performed at 550°C to 600°C for 5.5 to 6 hours.

[0020] The second objective of this invention is to provide the EMT / TS-1 mixed-crystal molecular sieve prepared by the above-described preparation method.

[0021] A third objective of this invention is to provide the application of the aforementioned EMT / TS-1 mixed-crystal molecular sieve in the hydrocracking of polyethylene waste.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention prepares an EMT / TS-1 mixed-crystal molecular sieve and its application in catalyzing low-density polyethylene. The mixed-crystal molecular sieve, consisting of EMT zeolite and titanium silicate molecular sieve TS-1, was prepared via hydrothermal synthesis. The two different pore structures of EMT and TS-1 promote the diffusion of long-chain low-density polyethylene, converting polyethylene into liquid alkanes under mild conditions and improving reaction efficiency. It also increases the contact area between the catalyst and the polyethylene plastic. The polyethylene generates intermediates in the EMT core reaction, which then diffuse to the Pt@TS-1 shell for hydrogenation. This mixed-crystal molecular sieve improves the hydrocracking rate, exhibits pore selectivity for polyolefins, and shifts the product distribution towards short-chain liquid alkanes.

[0024] This mixed-crystal molecular sieve integrates acidic and metallic sites, reducing the diffusion difficulty of reaction intermediates. It retains the strong acidic sites of EMT molecular sieves while also preserving the confinement effect of TS-1's unique topological structure on polyethylene hydrocracking products, resulting in a more concentrated product distribution. At the same time, this spatial proximity makes the polyethylene pyrolysis-hydrogenation process smoother, reducing the time of reaction intermediates and thus reducing carbon deposition, lowering the reaction temperature, and solving the problems of high reaction temperature, wide carbon chain length distribution of products, and spatial separation of hydrogenation and pyrolysis active sites in existing polyethylene hydrocracking technologies.

[0025] The EMT / TS-1 mixed-crystal molecular sieve catalyst synthesized in this invention exhibits milder reaction conditions in polyethylene degradation; the strong Brønsted acid centers enhance the reaction rate; the lipophilic surface of TS-1 can rapidly capture pyrolysis intermediates, and the highly dispersed Pt enables rapid hydrogenation, inhibiting the formation of gaseous products, reducing carbon deposit formation, and improving catalyst lifetime.

[0026] The EMT / TS-1 mixed-crystal molecular sieve catalyst prepared by this invention can completely convert a certain proportion of low-density polyethylene (LDPE) in a short time of 1 hour. Attached Figure Description

[0027] Figure 1 The X-ray diffraction pattern of EMT / TS-1 mixed-crystal molecular sieve.

[0028] Figure 2 The X-ray diffraction pattern of the product prepared in Comparative Example 1.

[0029] Figure 3 This is a scanning electron microscope image of the EMT / TS-1 mixed-crystal molecular sieve.

[0030] Figure 4 Distribution diagram of polyethylene products from hydrogenation pyrolysis using EMT / TS-1 mixed-crystal molecular sieve. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] A method for preparing EMT / TS-1 mixed-crystal molecular sieve includes the following steps:

[0033] An aluminum source, phosphate, a first template agent and a first silicon source were added to a first alkali metal hydroxide solution, stirred evenly, aged at room temperature, and then subjected to a first crystallization treatment at 100℃~120℃ to obtain an EMT microcrystalline emulsion.

[0034] After the titanium source and the second template agent are stirred evenly, water and an alcohol solvent are added to obtain the first solution;

[0035] The second alkali metal hydroxide, water, and organic ligand are mixed evenly and a hydrolysis reaction is carried out. After the reaction is completed, a platinum source is added to obtain the second solution.

[0036] After adding the second solution and EMT microcrystalline emulsion to the first solution and stirring evenly, a second silicon source is added, and a second crystallization treatment is carried out at 170℃~180℃. Then, calcination treatment is carried out in air atmosphere to obtain EMT / TS-1 mixed crystal molecular sieve.

[0037] In this invention, the first alkali metal hydroxide is sodium hydroxide, the aluminum source is sodium aluminate, the phosphate is sodium phosphate or sodium hypophosphite, the first template agent is 18-crown ether-6, the first silicon source is silica sol, the silica sol used in this invention is a commercially available raw material, the silica sol is industrial grade silica sol with a mass fraction of 40%, the titanium source is tetrabutyl titanate, the second template agent is tetrapropylammonium hydroxide, the second alkali metal hydroxide is sodium hydroxide, the second silicon source is tetraethyl orthosilicate (TEOS), and the organic ligand is 3-mercaptopropyltrimethoxysilane.

[0038] The specific roles of each raw material in the preparation process are explained below: The first alkali metal hydroxide (sodium hydroxide) provides an alkaline environment for the entire reaction process; sodium phosphate reduces the time for EMT seed crystal formation; tetrabutyl titanate serves as the titanium source for TS-1; tetrapropylammonium hydroxide acts as a template agent and provides an alkaline environment; isopropanol reduces the polarity of the sol during the reaction process and prevents agglomeration; the second alkali metal hydroxide (sodium hydroxide) provides an alkaline environment for the hydrolysis of 3-mercaptopropyltrimethoxysilane and promotes its hydrolysis rate; 3-mercaptopropyltrimethoxysilane generates a silane intermediate to graft Pt species onto the organosilicon chain; H2PtCl6 introduces metallic Pt; and tetraethyl orthosilicate serves as the silicon source for TS-1.

[0039] Example 1

[0040] Step 1: Microcrystalline emulsion synthesis of EMT

[0041] Take 0.3g of sodium hydroxide (NaOH), dissolve it in 3.7g of water, then add 1g of sodium aluminate (NaAlO2) as the Al source for EMT seed crystals, and stir for 20min to dissolve; add 0.03g of sodium phosphate, and stir for 20min to dissolve; add 0.55g of template agent 18-crown ether-6, and continue stirring to mix all substances evenly; add 10g of silica sol (25wt%) under rapid stirring, using the silica sol as the silicon source for EMT seed crystals, and continue stirring for 2h; age the mixture at room temperature for 24h; transfer the aged sol to a 25ml crystallization vessel, and crystallize at 100℃ for 6 days; wash five times with deionized water to obtain 2.5g of precipitate, then disperse it in 45ml of deionized water for later use;

[0042] Step 2: Synthesis of EMT / Pt@TS-1

[0043] Step 2.1: Dissolve 2.64 g of tetrabutyl titanate and 56.72 g of 25% tetrapropylammonium hydroxide aqueous solution by stirring in an ice-water bath for 1 h; under stirring conditions in a 70 ℃ water bath, first open-air evaporation for 30 min, then add 30 g of H2O, then continue stirring to dissolve for 2.5 h, then add 48 g of isopropanol, stir for 1 h, and this is the first solution;

[0044] Step 2.2: 0.10 g NaOH, 2.0 g water and 0.12 g 3-mercaptopropyltrimethoxysilane were stirred and hydrolyzed for 20 min. Then 6.16 ml of 100 mM H2PtCl6 aqueous solution was added dropwise and stirred for another 20 min to obtain the second solution.

[0045] The second solution was slowly added dropwise to the first solution, and the mixture was stirred in a water bath at 70°C for 30 minutes.

[0046] Take 10 ml of the EMT microcrystalline emulsion prepared in step 1, slowly add it dropwise to the above solution, sonicate for 15 min, and continue stirring for 60 min. Then, slowly introduce 40 g of TEOS with a glass rod, preferably with the bottom of the glass rod flush with the page in the flask. The whole process is controlled between 30 s and 60 s. Transfer to a crystallization kettle and crystallize at 170 °C for 24 hours. Wash, dry, and calcine at 550 °C in air atmosphere for 6 h to obtain EMT / Pt@TS-1.

[0047] Example 2

[0048] Step 1: Microcrystalline emulsion synthesis of EMT

[0049] Take 0.5g of sodium hydroxide (NaOH), dissolve it in 3.7g of water, then add 1g of sodium aluminate (NaAlO2) as the Al source for EMT seed crystals, and stir for 20min to dissolve; add 0.04g of sodium phosphate, and stir for 20min to dissolve; add 0.6g of template agent 18-crown ether-6, and continue stirring to mix all substances evenly; add 15g of silica sol (25wt%) under rapid stirring, using the silica sol as the silicon source for EMT seed crystals, and continue stirring for 2h; age the mixture at room temperature for 24h; transfer the aged sol to a 25ml crystallization vessel, and crystallize at 110℃ for 7 days; wash five times with deionized water to obtain the precipitate, then take 2.5g of the precipitate and disperse it in 45ml of deionized water for later use;

[0050] Step 2: Synthesis of EMT / Pt@TS-1

[0051] Step 2.1: Dissolve 1 g of tetrabutyl titanate and 80 g of 25% tetrapropylammonium hydroxide aqueous solution by stirring in an ice-water bath for 1 h; under stirring conditions in a 70 ℃ water bath, first open-air evaporation for 30 min, then add 30 g of H2O, then continue stirring to dissolve for 2.5 h, then add 48 g of isopropanol, stir for 1 h, and use as the first solution;

[0052] Step 2.2: 0.10 g NaOH, 2.0 g water and 0.15 g 3-mercaptopropyltrimethoxysilane were stirred and hydrolyzed for 20 min. Then 7.32 ml of 100 mM H2PtCl6 aqueous solution was added dropwise and stirred for another 20 min to obtain the second solution.

[0053] The second solution was slowly added dropwise to the first solution, and the mixture was stirred in a water bath at 70°C for 30 minutes.

[0054] Take 10 ml of the EMT microcrystalline emulsion prepared in step 1, slowly add it dropwise to the above solution, sonicate for 15 min, and continue stirring for 60 min. Then, slowly introduce 40 g of TEOS using a glass rod, preferably with the bottom of the glass rod flush with the page in the flask. The whole process is controlled between 30 s and 60 s. Transfer to a crystallization vessel and crystallize at 180 °C for 28 hours. Wash, dry, and calcine at 580 °C in air atmosphere for 5.8 h to obtain EMT / Pt@TS-1.

[0055] Example 3

[0056] Step 1: Microcrystalline emulsion synthesis of EMT

[0057] Take 0.4g of sodium hydroxide (NaOH), dissolve it in 3.7g of water, then add 1g of sodium aluminate (NaAlO2) as the Al source for EMT seed crystals, and stir for 20min to dissolve; add 0.035g of sodium phosphate, and stir for 20min to dissolve; add 0.6g of template agent 18-crown ether-6, and continue stirring to mix all substances evenly; add 13g of silica sol (25wt%) under rapid stirring, using the silica sol as the silicon source for EMT seed crystals, and continue stirring for 2h; age the mixture at room temperature for 24h; transfer the aged sol to a 25ml crystallization vessel, and crystallize at 120℃ for 6.5 days; wash five times with deionized water to obtain the precipitate, then take 2.5g of the precipitate and disperse it in 45ml of deionized water for later use;

[0058] Step 2: Synthesis of EMT / Pt@TS-1

[0059] Step 2.1: Dissolve 5 g of tetrabutyl titanate and 40 g of 25% tetrapropylammonium hydroxide aqueous solution by stirring in an ice-water bath for 1 h; under stirring conditions in a 70 ℃ water bath, first open-air evaporation for 30 min, then add 30 g of H2O, then continue stirring to dissolve for 2.5 h, then add 48 g of isopropanol, stir for 1 h, and use as the first solution;

[0060] Step 2.2: 0.10 g NaOH, 2.0 g water and 0.13 g 3-mercaptopropyltrimethoxysilane were stirred and hydrolyzed for 20 min. Then 6.83 ml of 100 mM H2PtCl6 aqueous solution was added dropwise and stirred for another 20 min to obtain the second solution.

[0061] The second solution was slowly added dropwise to the first solution, and the mixture was stirred in a water bath at 70°C for 30 minutes.

[0062] Take 10 ml of the EMT microcrystalline emulsion prepared in step 1, slowly add it dropwise to the above solution, sonicate for 15 min, and continue stirring for 60 min. Then, slowly introduce 40 g of TEOS with a glass rod, preferably with the bottom of the glass rod flush with the page in the flask. The whole process is controlled between 30 s and 60 s. Transfer to a crystallization kettle and crystallize at 175 °C for 26 hours. Wash, dry, and calcine at 600 °C in air atmosphere for 5.5 h to obtain EMT / Pt@TS-1.

[0063] Comparative Example 1

[0064] Step 1: Synthesis of EMT / Pt@TS-1

[0065] Step 1.1: Dissolve 2.64 g of tetrabutyl titanate and 56.72 g of 25% tetrapropylammonium hydroxide aqueous solution in an ice-water bath with stirring for 1 h; under stirring conditions in a 70 ℃ water bath, first open-air evaporation for 30 min, then add 30 g of H2O, then continue stirring to dissolve for 2.5 h, then add 48 g of isopropanol, stir for 1 h, and this is the first solution;

[0066] Step 1.2: 0.10 g NaOH, 2.0 g water and 0.12 g 3-mercaptopropyltrimethoxysilane were stirred and hydrolyzed for 20 min. Then 6.16 ml of 100 mM H2PtCl6 aqueous solution was added dropwise and stirred for another 20 min to obtain the second solution.

[0067] The second solution was slowly added dropwise to the first solution, and the mixture was stirred in a water bath at 70°C for 30 minutes. 40 g of TEOS was slowly introduced with a glass rod, the bottom of which was preferably flush with the end of the glass rod in the flask. The whole process was controlled between 30 and 60 seconds. The mixture was then transferred to a crystallization vessel at 170°C and crystallized for 24 hours. The mixture was washed five times with deionized water, and the precipitate was dispersed in 45 ml of deionized water to obtain TS-1 microcrystalline emulsion.

[0068] Step 2: Microcrystalline emulsion synthesis of EMT

[0069] Take 0.3g of sodium hydroxide (NaOH), dissolve it in 3.7g of water, then add 1g of sodium aluminate (NaAlO2) as the Al source for EMT seed crystals, and stir for 20min to dissolve; add 0.03g of sodium phosphate, and stir for 20min to dissolve; add 0.55g of 18-crown ether-6 (as the template agent for EMT molecular sieves), and continue stirring to mix all substances evenly; under rapid stirring, add 10g of silica sol (25wt%), which serves as the silicon source for EMT seed crystals, and continue stirring for 2h;

[0070] Take 10 ml of the TS-1 microcrystalline emulsion prepared in step 1, slowly add it dropwise to the above solution, sonicate for 15 min, and continue stirring for 60 min. Let the mixture age at room temperature for 24 h. Transfer the aged sol to a 100 ml crystallization vessel and crystallize at 100 °C for 6 days. Wash five times with deionized water, dry, and calcine at 550 °C in air atmosphere for 6 h to obtain the control sample.

[0071] Polyethylene hydrocracking: 1g of low-density polyethylene with a melt index of 20-30g / 10min and a particle size of approximately 1000 mesh was mixed uniformly with 0.1g of EMT / Pt@TS-1 catalyst. The reaction conditions were 250℃, 1MPa H2, and 1h. After cooling of the high-pressure reactor, the gas at the top of the reactor was collected and detected. The product in the reactor was extracted with dichloromethane, and the solid and liquid products after the reaction were separated. The collected liquid and gas products were analyzed by gas chromatography.

[0072] The EMT / TS-1 mixed crystal molecular sieves prepared in Examples 1 to 3 have similar properties. The following description uses Example 1 as an example for characterization.

[0073] X-ray diffraction analysis was performed on the EMT / TS-1 mixed-crystal molecular sieve of Example 1, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that three peaks appear in the range of 5°≤2θ≤7°, which are the 100, 002 and 101 reflections of the hexagonal EMT molecular sieve, proving the synthesis of EMT molecular sieve.

[0074] The XRD pattern of the product prepared in Comparative Example 1 is shown below. Figure 2 As shown, by Figure 2 It can be seen that the final product is composed of amorphous SiO2, while the TS-1 generated in the first step may decompose for a long time in the strong alkaline environment of NaOH.

[0075] Scanning electron microscopy analysis was performed on the EMT / TS-1 mixed-crystal molecular sieve prepared in Example 1, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that TS-1 molecular sieve particles grow on plate-like EMT molecular sieves. The two different crystals exhibit a high degree of mixing, presenting a core-shell structure where the EMT molecular sieve forms the core and the TS-1 molecular sieve forms the shell, growing amorphously on the EMT surface. During the polyethylene partitioning reaction, polyethylene forms intermediates on the EMT. TS-1 has a strong ability to adsorb these intermediates, and the intermediates undergo hydrogenation on TS-1. This structure promotes the diffusion of reaction intermediates, reduces carbon deposition, improves catalyst activity, and results in more concentrated product selectivity.

[0076] Figure 4 It can be seen that the liquid products are concentrated in C5-C9 hydrocarbons, with a high liquid fuel yield of 85%. The application of EMT / TS-1 mixed crystal molecular sieve has improved the hydrocracking rate and realized the shift of polyolefin catalytic product distribution to narrow distribution of oil alkanes.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing EMT / TS-1 mixed-crystal molecular sieve, characterized in that, Includes the following steps: An aluminum source, phosphate, a first template agent, and a first silicon source are added to a first alkali metal hydroxide solution, stirred until homogeneous, aged at room temperature, and then subjected to a first crystallization treatment at 100℃~120℃ to obtain an EMT microcrystalline emulsion; the first silicon source is silica sol; the phosphate is sodium phosphate or sodium hypophosphite. After the titanium source and the second template agent are stirred evenly, water and an alcohol solvent are added to obtain the first solution; The second alkali metal hydroxide, water, and organic ligand were mixed evenly and a hydrolysis reaction was carried out. After the reaction was completed, a platinum source was added to obtain a second solution. The organic ligand was 3-mercaptopropyltrimethoxysilane. After adding the second solution and EMT microcrystalline emulsion to the first solution and stirring evenly, a second silicon source is added, and a second crystallization treatment is carried out at 170℃~180℃. Then, calcination treatment is carried out in air atmosphere to obtain a core-shell structure with EMT molecular sieve as the core and TS-1 molecular sieve as the shell, and EMT / TS-1 mixed crystal molecular sieve with TS-1 molecular sieve amorphously grown on the surface of EMT molecular sieve; the second silicon source is tetraethyl orthosilicate.

2. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The first crystallization treatment takes 6 to 7 days.

3. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The second crystallization treatment takes 24 to 28 hours.

4. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The mass ratio of aluminum source to phosphate is 1:0.03~0.04; The mass ratio of aluminum source to first template agent is 1:0.5~0.6; The mass ratio of aluminum source to primary silicon source is 1:10~15; The mass ratio of aluminum source to first alkali metal hydroxide is 1:0.3~0.

5.

5. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The mass ratio of the second silicon source to the titanium source is 40:1~5, and the mass ratio of the second silicon source to the second template agent is 4:1~2.

6. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The mass ratio of the second alkali metal hydroxide to the organic ligand is 1:1.2~1.5, and the mass ratio of the second alkali metal hydroxide to H2PtCl6 is 1:2.5~3.

7. The method for preparing an EMT / TS-1 mixed-crystal molecular sieve according to claim 1, characterized in that, The calcination treatment is carried out at 550℃~600℃ for 5.5h~6h.

8. An EMT / TS-1 mixed-crystal molecular sieve prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the EMT / TS-1 mixed-crystal molecular sieve according to claim 8 in the hydrocracking of polyethylene waste.

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