Hydrocracking catalyst, process for its preparation and use, and process for the hydrocracking of low density polyethylene

Abstract

The application relates to the technical field of hydrocracking, in particular to a hydrocracking catalyst, a preparation method and application thereof, and a low-density polyethylene hydrocracking method. θ The strongest diffraction peak in the range of 7.5 to 25 degrees is I0, wherein I1 to I4 represent four strongest diffraction peaks in the range of 7.5 to 25 degrees, with 2theta increasing in turn, except I0, wherein 0.45 <= I1 / I0 <= 0.56, 0.53 <= I2 / I0 <= 0.71, 0.42 <= I3 / I0 <= 0.55, and 0.30 <= I4 / I0 <= 0.39; the catalyst can hydrocrack polyolefin at a lower temperature, has a high conversion rate, and the C3-C7 product yield is more than 75%.

Description

Technical Field

[0001] This invention relates to the field of hydrocracking technology, specifically to a hydrocracking catalyst, its preparation method and application, and a method for hydrocracking low-density polyethylene. Background Technology

[0002] According to data from the United Nations Environment Programme (UNEP), approximately 9.2 billion tons of plastic were produced globally between 1950 and 2017, and this figure has climbed to 11 billion tons by 2023. It is projected that global annual plastic production will increase to 736 million tons by 2040, with waste reaching 617 million tons, of which plastic leaked into the environment will increase from 81 million tons in 2020 to 119 million tons.

[0003] Traditional recycling methods, such as mechanical recycling, are not only slow, but the recycled products are also difficult to reuse for their original purpose. Incineration, while generating electricity, releases large amounts of greenhouse gases and toxic pollutants; landfilling leads to the waste of land resources and long-term pollution. Traditional pyrolysis requires high temperatures (>400℃) and produces complex products. my country has issued policies such as the "Technical Specifications for Waste Plastic Pollution Control," explicitly supporting chemical recycling technologies and providing VAT refunds to eligible enterprises.

[0004] Polyolefins (polyethylene, polypropylene, etc.) are the most widely used plastics in daily life. Due to their inert nature, they require decades to degrade naturally. Chemical catalysis can break down plastics into basic chemicals (such as ethylene and aromatics) or crude oil substitutes. To date, most catalysts used for plastic pyrolysis involve the use of precious metals. While precious metal catalysts (Pt / Al₂O₃, Ru / CeO₂, Pt / WO₃ / ZrO₂, etc.) possess excellent catalytic performance, their high cost and low catalytic efficiency have limited their widespread application. Single-atom catalysts, however, offer high atom utilization and hold promise as a novel and efficient catalyst for degrading plastic products into high-value chemical products. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low utilization rate of precious metal atoms, high cracking temperature of polyolefins, and low conversion rate in existing technologies. This invention provides a hydrocracking catalyst, its preparation method, and its application, as well as a method for hydrocracking low-density polyethylene. The hydrocracking catalyst of this invention uses a ZSM-5 molecular sieve with specific X-ray diffraction peaks to support single-atom dispersed palladium. This catalyst can hydrocrackle polyolefins (such as polyethylene, polypropylene, etc.) at lower temperatures, and has the advantages of high conversion rate and narrow carbon number distribution of products, especially with a C3-C7 product yield of over 75%.

[0006] To achieve the above objectives, a first aspect of the present invention provides a hydrocracking catalyst comprising an H-type ZSM-5 molecular sieve and a single-atom palladium supported on the H-type ZSM-5 molecular sieve.

[0007] The palladium content is 0.01wt%-0.6wt% of the H-type ZSM-5 molecular sieve;

[0008] The silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 20-100;

[0009] In the X-ray diffraction pattern of the ZSM-5 molecular sieve, the strongest diffraction peak of 2θ in the range of 7.5° to 25° is I0. I1 to I4 represent the four strongest diffraction peaks of 2θ in the range of 7.5° to 25°, excluding I0, with 0.45 ≤ I1 / I0 ≤ 0.56, 0.53 ≤ I2 / I0 ≤ 0.71, 0.42 ≤ I3 / I0 ≤ 0.55, and 0.30 ≤ I4 / I0 ≤ 0.39.

[0010] A second aspect of the present invention provides a method for preparing the hydrocracking catalyst of the present invention, the method comprising:

[0011] The solution containing tetraaminopalladium nitrate was impregnated with ammonium-type ZSM-5 molecular sieve, dried, and calcined.

[0012] A third aspect of the present invention provides the application of the hydrocracking catalyst described herein in the hydrocracking of polyolefins.

[0013] A fourth aspect of the present invention provides a method for hydrocracking low-density polyethylene, the method comprising: hydrocracking low-density polyethylene in the presence of the hydrocracking catalyst and hydrogen as described in the present invention.

[0014] Through the above technical solution, the hydrocracking catalyst of the present invention uses ZSM-5 molecular sieve with specific X-ray diffraction peaks to support single-atom dispersed palladium, which has high palladium atom utilization rate. Compared with the existing technology that usually hydrocracking at 280-550℃, this catalyst can hydrocracking polyolefins (such as polyethylene, polypropylene, etc.) at a lower temperature (220-240℃), and has the advantages of high conversion rate, narrow carbon number distribution of products, and high gas product yield, especially C3-C7 product yield of more than 75%. Attached Figure Description

[0015] Figure 1 These are X-ray diffraction (XRD) images of the catalysts prepared in Examples 1-4 and Comparative Example 1;

[0016] Figure 2These are CO diffuse reflectance infrared Fourier transform (CO-DRIFT) spectra of the catalysts prepared in Examples 1-4;

[0017] Figure 3 This is a scanning electron microscope (SEM) image of the molecular sieve particles from Example 1;

[0018] Figure 4 This is an X-ray diffraction (XRD) image of ZSM-5 molecular sieve particles, as shown in Comparative Example 2.

[0019] Figure 5 The image shows the X-ray diffraction (XRD) image of the ZSM-5 molecular sieve particles prepared in Comparative Example 3.

[0020] Figure 6 This is an X-ray diffraction (XRD) image of the ZSM-5 molecular sieve particles prepared in Example 5;

[0021] Figure 7 This is an X-ray diffraction (XRD) image of the ZSM-5 molecular sieve particles prepared in Example 6. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] In the context of this invention specification, including the following embodiments, the structure of ZSM-5 molecular sieve was characterized using a Bruker AXS GmbH D8 Advance instrument to obtain X-ray powder diffraction patterns. Cu-Ka radiation (λ = 0.15406 nm) was used, with an operating current of 100 mA, a voltage of 40 kV, a scanning range of 2θ = 5-40°, and a scanning rate of 5° / min.

[0024] In the context of this specification, including the following embodiments, the CO-DRIFTS test was performed by heating in a Harrick DRIFTS in-situ cell and using an IS50 spectrometer equipped with an MCT / A detector, with 32 / 100 scans and a resolution of 4 cm⁻¹. -1 .

[0025] In the context of this specification, including the following embodiments, the silicon-aluminum molar ratio refers to the molar ratio of silicon dioxide to aluminum oxide.

[0026] The first aspect of the present invention provides a hydrocracking catalyst comprising an H-type ZSM-5 molecular sieve and a single-atom palladium supported on the H-type ZSM-5 molecular sieve;

[0027] The palladium content is 0.01wt%-0.6wt% of the H-type ZSM-5 molecular sieve;

[0028] The silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 20-100;

[0029] In the X-ray diffraction pattern of the ZSM-5 molecular sieve, 2 θ The strongest diffraction peak in the range of 7.5° to 25° is I0, where I1 to I4 represent the four strongest diffraction peaks in the range of 7.5° to 25°, excluding I0, with 2θ increasing sequentially. Specifically, 0.45 ≤ I1 / I0 ≤ 0.56, 0.53 ≤ I2 / I0 ≤ 0.71, 0.42 ≤ I3 / I0 ≤ 0.55, and 0.30 ≤ I4 / I0 ≤ 0.39. The hydrocracking catalyst of this invention uses ZSM-5 molecular sieves with specific X-ray diffraction peaks to support single-atom dispersed palladium. This catalyst, using trace amounts of palladium, can hydrocrackle polyolefins (such as polyethylene and polypropylene) at relatively low temperatures, exhibiting advantages such as high conversion rate and narrow carbon number distribution of products, especially with C3-C7 product yields exceeding 75%.

[0030] According to a preferred embodiment of the present invention, the silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 20-35, which is beneficial to further improve the polyolefin conversion rate and the yield of C3-C7 products.

[0031] According to a preferred embodiment of the present invention, 2θ of I0 is 7.91° ± 0.02°.

[0032] According to a preferred embodiment of the present invention, 2θ of I1 is 8.77° ± 0.03°.

[0033] According to a preferred embodiment of the present invention, 2θ of I2 is 22.70° ± 0.02° or 23.10° ± 0.02°.

[0034] According to a preferred embodiment of the present invention, 2θ of I3 is 22.90° ± 0.02° or 23.28° ± 0.02°.

[0035] According to a preferred embodiment of the present invention, 2θ of I4 is 23.52° ± 0.02° or 23.93° ± 0.02°.

[0036] According to a preferred embodiment of the present invention, 2θ = 7.91° ± 0.02° for I0; 2θ = 8.77° ± 0.03° for I1; 2θ = 23.10° ± 0.02° for I2; 2θ = 23.28° ± 0.02° for I3; and 2θ = 23.93° ± 0.02° for I4.

[0037] According to a preferred embodiment of the present invention, the palladium content is 0.02wt%-0.5wt% of the H-type ZSM-5 molecular sieve. Although Pd clusters gradually appear starting from a palladium loading of 0.2wt%, and single-atom dispersed palladium and Pd clusters coexist, trace amounts of palladium can still further improve the hydrocracking conversion rate of polyolefins and increase the C3-C7 yield when the palladium content is within 0.5wt% of the H-type ZSM-5 molecular sieve.

[0038] In this invention, there is no particular limitation on the preparation method of the ZSM-5 molecular sieve; as long as it possesses the aforementioned characteristics, the objective of this invention can be achieved. According to one embodiment of this invention, a method for preparing the ZSM-5 molecular sieve is provided, the method comprising:

[0039] The silicon-aluminum molar ratio of ZSM-5 molecular sieve is 20-100, the aluminum source is counted in molar amounts of aluminum atoms, the molar ratio of aluminum source to tetraalkylammonium hydroxide is 1:0.5-8, and the molar ratio of aluminum source to water is 1:100-1000. The aluminum source, silicon source, tetraalkylammonium hydroxide (e.g., tetrapropylammonium hydroxide) and water are mixed, crystallized, separated, washed, dried and calcined.

[0040] In this invention, the range of selectable crystallization conditions is relatively wide. According to a preferred embodiment of this invention, the crystallization conditions include: a crystallization temperature of 150-200℃ and a crystallization time of 2-5 days. In this embodiment of the invention, a crystallization reaction at 180℃ for 3 days is used as an example.

[0041] The present invention does not have any particular limitation on the drying conditions, as long as the water is removed. In the embodiments of the present invention, drying at 100°C for 12 hours is used as an example.

[0042] In this invention, the range of selectable calcination conditions is relatively wide. According to a preferred embodiment of this invention, the calcination conditions include: a calcination temperature of 500-600℃ and a calcination time of 3-10h. In this embodiment of the invention, air calcination at 600℃ for 5h is used as an example.

[0043] A second aspect of the present invention provides a method for preparing the hydrocracking catalyst of the present invention, the method comprising:

[0044] A solution containing tetraaminopalladium nitrate is impregnated with an ammonium-type ZSM-5 molecular sieve, dried, and calcined. This invention utilizes the impregnation, drying, and calcination of tetraaminopalladium nitrate with an ammonium-type ZSM-5 molecular sieve to prepare a palladium single-atom dispersed hydrocracking catalyst.

[0045] In this invention, there are no particular limitations on the drying conditions, as long as the water is removed. According to a preferred embodiment of the invention, the drying conditions include: a drying temperature of 60-100°C and a drying time of 4-8 hours.

[0046] In this invention, the range of selectable calcination conditions is relatively wide. According to a preferred embodiment of this invention, the calcination conditions include: a calcination temperature of 400-550℃ and a calcination time of 3-6h.

[0047] In this invention, there is no particular limitation on the preparation method of the ZSM-5 molecular sieve; as long as it possesses the aforementioned characteristics, the purpose of this invention can be achieved. According to one embodiment of the invention, the preparation method of the ammonium-type ZSM-5 molecular sieve includes: mixing and stirring Na-type ZSM-5 molecular sieve with a 0.5-2 mol / L ammonium chloride solution at 60-100°C for 4-8 hours, filtering, washing with deionized water for ammonium exchange, repeating the ammonium exchange 2-4 times, and then drying at 60-80°C for 6-12 hours.

[0048] A third aspect of the present invention provides the application of the hydrocracking catalyst described herein in the hydrocracking of polyolefins.

[0049] A fourth aspect of the present invention provides a method for hydrocracking low-density polyethylene, the method comprising: hydrocracking low-density polyethylene in the presence of the hydrocracking catalyst and hydrogen as described in the present invention.

[0050] According to a preferred embodiment of the present invention, the hydrogen donor is selected from one or more of hydrogen, methane, ethane, propane, butane, pentane, ethylene, propylene, butene, pentene, and diene.

[0051] According to a preferred embodiment of the present invention, the mass ratio of the catalyst to low-density polyethylene is 1:5-10.

[0052] According to a preferred embodiment of the present invention, the hydrocracking conditions include: a temperature of 220°C-280°C, a hydrogen supply agent pressure of 0.5-3 MPa, and a time of 1-6 hours.

[0053] According to a preferred embodiment of the present invention, the density of the low-density polyethylene is 0.91-0.93 g / cm³. 3 .

[0054] According to a preferred embodiment of the present invention, the low-density polyethylene has a melt index of 18-35 g / 10 min and a weight-average molecular weight of 40,000-100,000 g / mol.

[0055] The present invention will be described in detail below through embodiments.

[0056] In the following examples, the gaseous products in the product distribution were determined by gas chromatography, and the liquid products were determined by GCMS after adding parabens as an internal standard.

[0057] In this invention, the formulas for calculating the conversion rate of low-density polyethylene and the selectivity of gaseous and liquid phase products are as follows:

[0058] Low-density polyethylene conversion rate (%) = [1 - (S - Residual solids after reaction / S - Total solids before reaction)] × 100%

[0059] Gaseous product yield (%) = [Stotal solids before reaction - Sresidual solids after reaction] × 100%

[0060] Liquid product yield (%) = Low-density polyethylene conversion rate (%) - Gas product yield (%)

[0061] In the following embodiments, the high-resolution field emission transmission electron microscope was tested using a JEM-F200 instrument manufactured by Nippon Electronics Co., Ltd.

[0062] Example 1

[0063] 0.77 g sodium aluminate, 11.4 g TPAOH aqueous solution (TPAOH content 25 wt%), and 30 g deionized water were mixed evenly. Then, 20 g TEOS was slowly added dropwise, and the mixture was stirred for 4 hours. The mixture was then sealed and heated to 180 °C and kept at that temperature for 3 days. The mixture was then filtered and washed with deionized water. The solid product was dried at 100 °C for 12 hours and then calcined in air at 600 °C for 5 hours to obtain Na-type ZSM-5 molecular sieve with a silica-to-alumina ratio of 25. Scanning electron microscopy (SEM) images of the molecular sieve particles are shown below. Figure 3 As shown;

[0064] (2) Na-type ZSM-5 molecular sieve was mixed and stirred with 2 mol / L ammonium chloride solution at 80℃ for 8 h, filtered, washed with deionized water, ammonium exchange was repeated twice, dried at 80℃ for 12 h, and impregnated with an aqueous solution of tetraaminopalladium nitrate with a palladium loading of 0.05 wt%, dried at 80℃, and calcined at 400℃ in air atmosphere for 3 h to obtain the catalyst.

[0065] The XRD pattern of the catalyst is shown below. Figure 1As shown in the table below, compared with Comparative Example 1, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading. The values ​​of I0, I1, I2, I3, and I4, and their ratios, are shown in the table below:

[0066]

[0067] Example 2

[0068] The method of Example 1 is the same, except that in step (2), the palladium loading is 0.01 wt%; the other conditions are the same as in Example 1.

[0069] The XRD pattern of the catalyst is shown below. Figure 1 As shown, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading, and the X-ray diffraction patterns are basically consistent with those of Example 1.

[0070] Example 3

[0071] The method of Example 1 is the same, except that in step (2), the palladium loading is 0.2 wt%; the other conditions are the same as in Example 1.

[0072] The XRD pattern of the catalyst is shown below. Figure 1 As shown, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading, and the X-ray diffraction patterns are basically consistent with those of Example 1.

[0073] Example 4

[0074] The method of Example 1 is the same, except that in step (2), the palladium loading is 0.5 wt%; the other conditions are the same as in Example 1.

[0075] The XRD pattern of the catalyst is shown below. Figure 1 As shown, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading, and the X-ray diffraction patterns are basically consistent with those of Example 1.

[0076] The CO diffuse reflectance infrared Fourier transform (CO-DRIFT) spectra of the catalysts in Examples 1-4 are shown below. Figure 2 As shown, two CO adsorption peaks are observed, at 2148 cm⁻¹. -1 2114cm -1 Among them 2148cm -1 The adsorption of CO by monodisperse PdO species, 2114 cm⁻¹ -1 (0.2wt% and 0.5wt%) are attributed to the adsorption of CO by Pd cluster species, indicating that when the catalyst is prepared according to the method described in this invention, Pd clusters gradually appear starting from a palladium loading of 0.2wt%, and single-atom dispersed palladium and Pd clusters coexist.

[0077] Example 5

[0078] (1) Mix 0.44g sodium aluminate, 11.4g TPAOH aqueous solution (TPAOH content 25wt%), and 30g deionized water evenly, then slowly add 20g TEOS dropwise, stir for 4h, seal, heat to 180℃, and crystallize for 3 days. Filter the deionized water, dry at 100℃ for 12h, and calcine in air at 600℃ for 5h to obtain Na-type ZSM-5 molecular sieve with a silica-alumina ratio of 40;

[0079] (2) Na-type ZSM-5 molecular sieve was mixed and stirred with 2 mol / L ammonium chloride solution at 80℃ for 8 h, filtered, washed with deionized water, ammonium exchange was repeated twice, dried at 80℃ for 12 h, and impregnated with an aqueous solution of tetraaminopalladium nitrate with a palladium loading of 0.05 wt%, dried at 80℃, and calcined in air at 400℃ for 3 h to obtain the catalyst;

[0080] XRD images of the catalyst are as follows Figure 6 As shown, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading. The values ​​of I0, I1, I2, I3, and I4 in the X-ray diffraction patterns and their ratios are shown in the table below.

[0081]

[0082] Example 6

[0083] 0.22 g sodium aluminate, 11.4 g TPAOH aqueous solution (TPAOH content 25 wt%), and 30 g deionized water were mixed evenly. Then, 20 g TEOS was slowly added dropwise. After stirring for 4 hours, the mixture was sealed and heated to 180℃ and kept at that temperature for 3 days. The deionized water was filtered and dried at 100℃ for 12 hours. After drying, it was calcined in air at 600℃ for 5 hours to obtain Na-type ZSM-5 molecular sieve with a silica-alumina ratio of 80.

[0084] (2) Na-type ZSM-5 molecular sieve was mixed and stirred with 2 mol / L ammonium chloride solution at 80℃ for 8 h, filtered, washed with deionized water, ammonium exchange was repeated twice, dried at 80℃ for 12 h, and impregnated with an aqueous solution of tetraaminopalladium nitrate with a palladium loading of 0.05 wt%, dried at 80℃, and calcined in air at 400℃ for 3 h to obtain the catalyst;

[0085] Catalyst XRD images as follows Figure 7 As shown, the X-ray diffraction patterns of ZSM-5 molecular sieve are consistent before and after Pd loading. The I0, I1, I2, I3, and I4 in the X-ray diffraction patterns and their ratios are shown in the table below:

[0086]

[0087] Comparative Example 1

[0088] 0.77 g sodium aluminate, 11.4 g TPAOH aqueous solution (TPAOH content 25 wt%), and 30 g deionized water were mixed evenly. Then, 20 g TEOS was slowly added dropwise. After stirring for 4 hours, the mixture was sealed and heated to 180℃ and kept at that temperature for 3 days. The deionized water was filtered, dried at 100℃ for 12 hours, and then calcined in air at 600℃ for 5 hours to obtain Na-type ZSM-5 molecular sieve with a silica-alumina ratio of 25.

[0089] (2) Na-type ZSM-5 molecular sieve was mixed and stirred with 2 mol / L ammonium chloride solution at 80℃ for 8 hours, filtered, washed with deionized water, and ammonium exchange was repeated twice. After drying at 80℃ for 12 hours, it was calcined at 400℃ in air atmosphere for 3 hours to obtain H-ZSM-5 molecular sieve.

[0090] Comparative Example 2

[0091] The method of Example 1 was followed, except that the molecular sieve used was ZSM-5 (SAR=25) purchased from the Catalyst Factory of Nankai University, and its morphology was hexagonal; the other conditions were the same as in Example 1.

[0092] Catalyst XRD images as follows Figure 4 As shown in the table below, the X-ray diffraction patterns of I0, I1, I2, I3, and I4, and their ratios, are as follows:

[0093]

[0094] Comparative Example 3

[0095] The method described in Example 1 differs in that the ZSM-5 molecular sieve is prepared as follows:

[0096] A sol-gel solid was prepared by dissolving a silica solution (Ludox HS-40), deionized water, sodium hydroxide, and sodium aluminate. The specific procedure was as follows: 40g of Ludox HS-40 was slowly added dropwise to an 80°C, 2mol / L sodium hydroxide solution (18.66ml water, 0.7464g sodium hydroxide), and stirred until the solution became clear, yielding solution A. 1.2g of sodium aluminate was dissolved in the 2mol / L sodium hydroxide solution (18.66ml water, 0.7464g sodium hydroxide), and stirred until clear, yielding solution B. Solution B was slowly added dropwise to solution A, and after mixing, an aluminosilicate gel was obtained. The gel was vigorously stirred at 100°C and kept at that temperature for 2 hours. The gel was then transferred to a sealed reactor and heated to 180°C for 48 hours. It was then dried at 100°C for 12 hours, and finally calcined in air at 600°C for 6 hours to obtain a Na-type ZSM-5 molecular sieve with a silica-to-alumina ratio of 40. The remaining conditions were the same as in Example 1.

[0097] Catalyst XRD images as follows Figure 5 As shown in the table below, the X-ray diffraction patterns of I0, I1, I2, I3, and I4, and their ratios, are as follows:

[0098]

[0099] Comparative Example 4

[0100] The method is the same as in Example 1, except that H-type ZSM-5 molecular sieve is prepared first, and then Pd is loaded onto it. Specifically:

[0101] 0.77 g sodium aluminate, 11.4 g TPAOH aqueous solution (TPAOH content 25 wt%), and 30 g deionized water were mixed evenly. Then, 20 g TEOS was slowly added dropwise. After stirring for 4 hours, the mixture was sealed and heated to 180℃ and kept at that temperature for 3 days. The deionized water was filtered, dried at 100℃ for 12 hours, and then calcined in air at 600℃ for 5 hours to obtain Na-type ZSM-5 molecular sieve with a silica-alumina ratio of 25.

[0102] (2) Na-type ZSM-5 molecular sieve was mixed and stirred with 2 mol / L ammonium chloride solution at 80℃ for 8 h, filtered, washed with deionized water, ammonium exchange was repeated twice, dried at 80℃ for 12 h, and then calcined in air at 400℃ for 3 h to obtain H-type ZSM-5 molecular sieve; according to the palladium loading of 0.05 wt%, it was impregnated with an aqueous solution of tetraaminopalladium nitrate, dried at 80℃, and calcined in air at 400℃ for 3 h to obtain catalyst.

[0103] Catalyst evaluation:

[0104] 50 mg of catalyst was mixed with 0.5 g of LDPE (melt index 25 g / 10 min, weight average molecular weight = 82005 g / mol, density 0.92 g / cm³). 3 After being mixed evenly, the mixture was placed into a reaction vessel and kept at 240℃ and 1 MPa hydrogen for 4 hours. The test results are shown in Table 1.

[0105] Table 1

[0106]

[0107] Example 7

[0108] The method of Example 1 was followed, except that the catalyst evaluation was carried out at a temperature of 0.5 h; the test results are shown in Table 1.

[0109] Example 8

[0110] The method of Example 1 was followed, except that the catalyst evaluation was conducted under the conditions of 240°C and 0.5 MPa hydrogen, with a 4-hour heat preservation test; the test results are shown in Table 1.

[0111] Example 9

[0112] The method of Example 1 was followed, except that the catalyst evaluation was conducted under the conditions of 240°C and 2 MPa hydrogen gas for 4 hours; the test results are shown in Table 1.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for hydrocracking low-density polyethylene, characterized in that, The method includes: hydrocracking low-density polyethylene in the presence of a hydrocracking catalyst and a hydrogen donor; The hydrocracking catalyst comprises an H-type ZSM-5 molecular sieve and a single-atom palladium supported on the H-type ZSM-5 molecular sieve; The palladium content is 0.02wt%-0.5wt% of the H-type ZSM-5 molecular sieve; The silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 20-35; In the X-ray diffraction pattern of the ZSM-5 molecular sieve, the strongest diffraction peak of 2θ in the range of 7.5° to 25° is I0, where I1 to I4 represent the four strongest diffraction peaks of 2θ in the range of 7.5° to 25°, excluding I0, with 0.45≤ I1 / I0≤ 0.56, 0.53≤ I2 / I0≤ 0.71, 0.42≤ I3 / I0≤ 0.55, and 0.30≤ I4 / I0≤ 0.

39. The preparation method of the hydrocracking catalyst includes: impregnating a solution containing tetraaminopalladium nitrate with an ammonium-type ZSM-5 molecular sieve, drying, and calcining.

2. The hydrocracking method according to claim 1, characterized in that, I0 has 2θ = 7.91° ± 0.02°; and / or I1 has 2θ = 8.77° ± 0.03°; and / or I² = 22.70° ± 0.02° or 23.10° ± 0.02°; and / or I3 has 2θ = 22.90° ± 0.02° or 23.28° ± 0.02°; and / or The 2θ of I4 is 23.52° ± 0.02° or 23.93° ± 0.02°.

3. The hydrocracking method according to claim 1 or 2, characterized in that, The 2θ of I0 is 7.91° ± 0.02°; the 2θ of I1 is 8.77° ± 0.03°; the 2θ of I2 is 23.10° ± 0.02°; the 2θ of I3 is 23.28° ± 0.02°; and the 2θ of I4 is 23.93° ± 0.02°.

4. The hydrocracking method according to claim 1 or 2, characterized in that, 0.49 ≤ I1 / I0 ≤ 0.56, 0.59 ≤ I2 / I0 ≤ 0.71, 0.48 ≤ I3 / I0 ≤ 0.55, 0.36 ≤ I4 / I0 ≤ 0.

39.

5. The hydrocracking method according to claim 1, characterized in that, Drying conditions include: a drying temperature of 60-100℃ and a drying time of 4-8 hours; and / or The calcination conditions include: calcination temperature of 400-550℃ and calcination time of 3-6h.

6. The hydrocracking method according to claim 1 or 5, characterized in that, The preparation method of the ammonium-type ZSM-5 molecular sieve includes: mixing and stirring the Na-type ZSM-5 molecular sieve with a 0.5-2 mol / L ammonium chloride solution at 60-100℃ for 4-8 hours, filtering, washing with deionized water for ammonium exchange, repeating the ammonium exchange 2-4 times, and drying at 60-80℃ for 6-12 hours.

7. The hydrocracking method according to claim 1, characterized in that, The hydrogen donor is selected from one or more of hydrogen, methane, ethane, propane, butane, pentane, ethylene, propylene, butene, and pentene; and / or The mass ratio of catalyst to low-density polyethylene is 1:5-10; and / or Hydrocracking conditions include: a temperature of 220℃-280℃, a hydrogen supply pressure of 0.5-3MPa, and a time of 1h-6h; and / or The density of the low-density polyethylene is 0.91-0.93 g / cm³. 3 ; and / or The low-density polyethylene has a melt index of 18-35 g / 10 min and a weight-average molecular weight of 40,000-100,000 g / mol.

Images