A process for the production of liquid oil by melt blending and depolymerization of LDPE with beta molecular sieve
By using the melt blending method of LDPE and β molecular sieve, the problems of high depolymerization temperature, high energy consumption and low liquid oil yield of LDPE in the existing technology have been solved, realizing efficient and low-cost resource recycling of LDPE.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UNIV OF JINAN
- Filing Date
- 2026-06-10
- Publication Date
- 2026-07-24
AI Technical Summary
Existing LDPE depolymerization technologies suffer from problems such as high temperature, high energy consumption, low liquid oil yield, cumbersome catalyst preparation, and uneven mixing, resulting in low depolymerization efficiency.
The LDPE and β molecular sieve melt blending method is adopted. The LDPE and β molecular sieve melt blend material is formed by extrusion molding in a specific temperature range through a twin-screw extruder. The material is then subjected to thermocatalytic depolymerization under relatively mild conditions to generate high-purity liquid oil.
This method enables efficient depolymerization of LDPE with low energy consumption to produce high-purity liquid oil, simplifies the catalyst preparation process, improves depolymerization efficiency and liquid oil yield, and reduces costs.
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Figure CN122445378A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of plastic depolymerization and resource recycling technology, specifically relating to a method for producing liquid oil by melt blending and depolymerization of LDPE and β molecular sieve. Background Technology
[0002] LDPE, due to its excellent properties such as lightweight, corrosion resistance, and ease of processing, is widely used in packaging, agriculture, industry, and other fields, with a huge global annual output. However, LDPE is characterized by its strong chemical stability and extremely slow natural depolymerization rate. Its waste accumulates in the environment over time, forming a large amount of white pollution, which not only disrupts the ecological balance but also threatens human health and agricultural production safety. Statistics show that over 90% of global waste plastics enter the natural environment without effective pretreatment, with LDPE being one of the main sources of pollution.
[0003] Currently, the main methods for treating LDPE include landfill, incineration, mechanical recycling, and chemical depolymerization. Landfill disposal occupies a large amount of land resources and easily causes soil and groundwater pollution; incineration releases toxic and harmful gases, polluting the atmosphere and wasting energy; mechanical recycling has drawbacks such as low recycling efficiency, decreased performance of recycled products, and difficulty in handling complex waste plastics, limiting its application. Chemical depolymerization, as a promising technology for the resource recovery and utilization of LDPE, can convert it into valuable chemicals or fuels, achieving "turning waste into treasure." Among them, thermal cracking technology is a more studied chemical depolymerization method, but traditional thermal cracking processes have significant shortcomings: high reaction temperatures (usually exceeding 380℃), huge energy consumption; low yield of liquid oil products (only about 18%), wide product distribution, mostly a mixture of gaseous hydrocarbons and solid residues, making separation and purification difficult; and the reaction process easily produces carbon deposits, leading to equipment blockage and wear. Therefore, catalytic depolymerization has become a current research hotspot in this field.
[0004] Upare et al. used amorphous alumina silica (ASA) solid acid catalysts, and at 300 °C, the activation energy for catalytic depolymerization of LDPE was reduced to 97.3 kJ / mol compared to direct thermal decomposition (activation energy of 117.2 kJ / mol) (Upare, DP, Lee, CW, Lee, DK et al. Effect of acidity of solid acid catalysts during non-oxidative thermal decomposition of LDPE. Carbon Lett. 35, 277–285 (2025).). However, the solid acid catalysts exhibit low catalytic activity and require higher reaction temperatures.
[0005] Wang et al. used a hierarchical Pt@Hie-TS-1 catalyst, physically mixed with β-zeolite, to convert LDPE into liquid alkanes, achieving a liquid alkanes yield of 94.0% and a C5-C7 low-carbon alkanes yield of 84.8% (Wang S, Wang W, Chu M, et al. Ultra-Narrow Alkane Product Distribution in Polyethylene WasteHydrocracking by Zeolite Micro-Mesopore Diffusion Optimization. Angew ChemInt Ed Engl. 2024;63(49):e202409288.). However, the synthesis of Pt@Hie-TS-1 as a porous molecular sieve is difficult, involving cumbersome steps and high costs, which is not conducive to large-scale industrial application.
[0006] Therefore, how to significantly improve the catalytic depolymerization efficiency without compromising the mechanical and other properties of polyethylene has become a pressing technical challenge in this field. Summary of the Invention
[0007] To address the shortcomings of existing technologies, such as high depolymerization temperature of LDPE, high energy consumption, low liquid oil yield, cumbersome catalyst preparation, uneven mixing with LDPE molten fluid, and low depolymerization efficiency, this invention provides a method for producing liquid oil through melt blending and depolymerization of LDPE and β-molecular sieve. It also provides a blending system for this method, enabling efficient depolymerization of LDPE under milder conditions, directionally generating high-purity liquid oil products, reducing energy consumption and costs, and promoting the resource recycling of LDPE.
[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve includes the following steps: A mixture of LDPE and β-zeolite is fed into a twin-screw extruder and extruded under three-stage heating. The mixture passes through a first heating zone, a second heating zone, and a third heating zone in sequence. The temperature of the first heating zone is 115~125℃, the temperature of the second heating zone is 155~165℃, and the temperature of the third heating zone is 175~185℃, forming a melt blend of LDPE and β-zeolite. Thermocatalytic depolymerization of LDPE yields a liquid oil product.
[0009] The silicon-to-aluminum ratio of the β-molecular sieve is 25-45; preferably, the silicon-to-aluminum ratio of the β-molecular sieve is 25-30. If it is not within this range, the depolymerization conversion rate of LDPE will be reduced.
[0010] The screw speed of the twin-screw extruder is 30~50 r / min, the global residence time is 5~15 min, and the residence time in each heating zone is the same. If it is not within this range, it will affect the uniformity of melt blending.
[0011] The mass ratio of the β-molecular sieve to LDPE is 0.02~0.1, preferably 0.1; The reaction temperature for the thermocatalytic depolymerization is 240~260℃, the reaction pressure is 0.5~2MPa, and the reaction time is 1~3h.
[0012] Preferably, the melt blend material is melt-blended in a twin-screw extruder, cooled by an air-cooled cooler, and then obtained by a cutting and granulating machine.
[0013] Preferably, the reaction temperature for the thermocatalytic depolymerization is 250°C, the reaction pressure is 1 MPa, and the reaction time is 2 h.
[0014] The method of producing liquid oil by melt blending and depolymerization of LDPE and β molecular sieve is used for the depolymerization of LDFE plastic.
[0015] The beneficial effects of this invention are: 1. The preparation method of the present invention has milder reaction conditions, avoiding the problems of high temperature and high pressure and long depolymerization time in the previous LDPE depolymerization process.
[0016] 2. The melt blending extrusion molding process adopted in this invention is simple. The melt blending process requires no additives; simply mix LDPE and β-zeolite and feed them into a twin-screw extruder, then extrude them at a temperature range of 115~185℃ to form a melt blend of LDPE and β-zeolite. The proportion of β-zeolite in the blend can be adjusted by regulating the mass ratio of β-zeolite to LDPE. This invention enriches the catalytic depolymerization methods for LDPE and is of great significance for the resource recovery and utilization of LDPE. Attached Figure Description
[0017] Figure 1 The mechanical properties of the LDPE and β-zeolite melt blends prepared in Examples 1-3 are shown in the diagram. Figure 2 The graphs show the catalytic depolymerization performance of the LDPE and β-zeolite melt blends prepared in Examples 1-3 and Comparative Examples 1-3. Figure 3 The graph shows the catalytic depolymerization performance of LDPE and different molecular sieve melt blends prepared in Examples 3 and Comparative Examples 3-5. Figure 4The graph shows the catalytic depolymerization performance of the LDPE and β-zeolite melt blends prepared in Examples 3, 6, and 4 under different melt blending conditions. Detailed Implementation
[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. These embodiments are only used to illustrate the present invention and do not constitute any limitation on the scope of the present invention.
[0019] In Examples 1-3 and Comparative Examples 1-3 and Comparative Example 6, the β molecular sieve was purchased from Tianjin Nanhua Catalyst Co., Ltd., model NKF-6-25YY, with a silicon-to-aluminum ratio of 25; in Example 4, the β molecular sieve was purchased from Tianjin Nanhua Catalyst Co., Ltd., model NKF-6-40LY, with a silicon-to-aluminum ratio of 40; in Comparative Examples 4 and 5, the ZSM-5 molecular sieve was purchased from Qingdao Yuanke Catalyst Co., Ltd., model Z5-NP-35H-45H, with a silicon-to-aluminum ratio of 35-45; the low-density polyethylene (LDPE) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., model L875016, with a melt index of 20-30 g / 10 min and a particle size of ~1000 mesh.
[0020] Example 1 (a) 50g of LDPE and 1.0g of β-molecular sieve were first physically mixed by stirring at 200r / min for 5min; then fed into a twin-screw extruder and extruded under three-stage heating. The mixture passed through the first heating zone, the second heating zone, and the third heating zone in sequence. The temperature of the first heating zone was 120℃, the temperature of the second heating zone was 160℃, and the temperature of the third heating zone was 180℃. The screw speed of the twin-screw extruder was 40r / min, the total residence time was 10min, and the residence time in each heating zone was the same. Afterward, the mixture was cooled by an air-cooled cooler and then passed through a cutting granulator to obtain a melt blend of LDPE and β-molecular sieve (the mass ratio of β-molecular sieve to LDPE was 0.02). (b) 1.1 g of the above melt blend material was added to a closed reactor and reacted at 250 °C and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0021] Example 2 (a) 50g of LDPE and 2.5g of β-molecular sieve were first physically mixed by stirring at 200r / min for 5min; then fed into a twin-screw extruder and extruded under three-stage heating. The mixture passed through the first heating zone, the second heating zone, and the third heating zone in sequence. The temperature of the first heating zone was 120℃, the temperature of the second heating zone was 160℃, and the temperature of the third heating zone was 180℃. The screw speed of the twin-screw extruder was 40r / min, the total residence time was 10min, and the residence time in each heating zone was the same. Afterward, the mixture was cooled by an air-cooled cooler and then passed through a cutting and granulating machine to form a melt blend of LDPE and β-molecular sieve (the mass ratio of β-molecular sieve to LDPE was 0.05). (b) 1.1 g of the above melt blend material was added to a closed reactor and reacted at 250 °C and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0022] Example 3 (a) 50g of LDPE and 5.0g of β-molecular sieve were first physically mixed by stirring at 200r / min for 5min; then fed into a twin-screw extruder and extruded under three-stage heating. The mixture passed through the first heating zone, the second heating zone, and the third heating zone in sequence. The temperature of the first heating zone was 120℃, the temperature of the second heating zone was 160℃, and the temperature of the third heating zone was 180℃. The screw speed of the twin-screw extruder was 40r / min, the total residence time was 10min, and the residence time in each heating zone was the same. Afterward, the mixture was cooled by an air-cooled cooler and then passed through a cutting and granulating machine to form a melt blend of LDPE and β-molecular sieve (the mass ratio of β-molecular sieve to LDPE was 0.1). (b) 1.1 g of the above melt blend material was added to a closed reactor and reacted at 250 °C and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0023] Comparative Example 1 1.078 g LDPE and 0.022 g β molecular sieve (the mass ratio of β molecular sieve to LDPE is 0.02) were physically mixed by stirring at 200 r / min for 5 min, and then put into a closed reaction vessel. The reaction was carried out at 250 °C and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0024] Comparative Example 2 1.048 g LDPE and 0.052 g β molecular sieve (the mass ratio of β molecular sieve to LDPE is 0.05) were physically mixed by stirring at 200 r / min for 5 min, and then put into a closed reaction vessel. The reaction was carried out at 250 °C and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0025] Comparative Example 3 1.0 g LDPE and 0.1 g β molecular sieve (the mass ratio of β molecular sieve to LDPE is 0.1) were physically mixed by stirring at 200 r / min for 5 min, and then put into a closed reaction vessel. The reaction was carried out at 250℃ and 1 MPa for 2 h. After cooling to room temperature, the liquid and gaseous products were collected and analyzed by gas chromatography.
[0026] Comparative Example 4 This comparative example is the same as Example 3, except that the β molecular sieve is replaced with ZSM-5 molecular sieve.
[0027] Comparative Example 5 This comparative example is the same as Comparative Example 4, except that it was not melt-blended and extruded. The LDPE content was 1.0 g and the ZSM-5 molecular sieve content was 0.1 g.
[0028] Comparative Example 6 This comparative example is the same as Example 3, except that step (a) is as follows: 50g of LDPE and 5.0g of β molecular sieve are first physically mixed by stirring at 200r / min for 5min; then fed into a twin-screw extruder and extruded under three-stage heating. The mixture passes through the first heating zone, the second heating zone, and the third heating zone in sequence. The temperature of the first heating zone is 120℃, the temperature of the second heating zone is 160℃, and the temperature of the third heating zone is 240℃. The screw speed of the twin-screw extruder is 40r / min, the total residence time is 10min, and the residence time in each heating zone is the same. Afterward, it is cooled by an air-cooled cooler and then passed through a cutting and granulating machine to form a melt blend of LDPE and β molecular sieve.
[0029] Example 4 This embodiment is the same as Embodiment 3, except that the silicon-to-aluminum ratio of the β molecular sieve is 40.
[0030] The mechanical properties of the melt blends obtained in Examples 1-3 were compared with those of LDPE, such as... Figure 1 As shown in the figure, it can be seen that as the LDPE / β ratio gradually increases, both tensile strength and elongation at break show a certain downward trend. The above results indicate that the melt blend material maintains certain mechanical properties of LDPE.
[0031] The gas chromatographic analysis results of Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 2 As shown in the figure, it can be seen that, at the same ratio, the thermal catalytic depolymerization conversion rate of the molten comaterial and the selectivity of the liquid oil are both improved to a certain extent.
[0032] The gas chromatographic analysis results of Examples 3 and 3-5 are as follows: Figure 3 As shown in the figure, compared with Comparative Example 4, the conversion rate of Example 3 increased by 41.2% and the selectivity increased by 0.7%; while compared with Comparative Example 5, the selectivity of Comparative Example 4 increased by 13.7%, but the conversion rate decreased sharply (the conversion rate of Comparative Example 4 was 24.3% and the conversion rate of Comparative Example 5 was 69.4%). For plastic depolymerization and resource recycling, the decrease in conversion rate will undoubtedly limit the application of this method in this field.
[0033] The gas chromatographic analysis results of Example 3, Comparative Example 6, and Example 4 are as follows: Figure 4 As shown in the figure, compared with Comparative Example 6, the conversion rate of Example 3 increased by 18.7%, and the selectivity increased by 5.9%; while compared with Example 4, the conversion rate of Example 3 increased by 8.1%. The above results indicate that the most suitable three-stage heating temperature for melt blending is 120°C for the first heating zone, 160°C for the second heating zone, and 180°C for the third heating zone; the most suitable silicon-to-aluminum ratio for β-zeolite is 25.
Claims
1. A method for producing liquid oil by melt blending and depolymerization of LDPE and β molecular sieve, characterized in that, Includes the following steps: The mixture of LDPE and β molecular sieve is fed into a twin-screw extruder and extruded under three-stage heating. The mixture passes through the first heating zone, the second heating zone and the third heating zone in sequence. The temperature of the first heating zone is 115~125℃, the temperature of the second heating zone is 155~165℃ and the temperature of the third heating zone is 175~185℃, forming a melt blend of LDPE and β molecular sieve. Thermal catalytic depolymerization of LDPE yields a liquid oil product. The mass ratio of the β-molecular sieve to LDPE is 0.02~0.
1.
2. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The reaction temperature for the thermocatalytic depolymerization is 240~260℃, the reaction pressure is 0.5~2MPa, and the reaction time is 1~3h.
3. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The silica-to-alumina ratio of the β-molecular sieve is 25-45.
4. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The screw speed of the twin-screw extruder is 30~50 r / min, and the global residence time is 5~15 min.
5. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 4, characterized in that, The dwell time is the same in each heating zone.
6. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The mass ratio of the β molecular sieve to LDPE is 0.
1.
7. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The melt blend material is melt-blended in a twin-screw extruder, cooled by an air-cooled cooler, and then processed by a cutting and granulating machine.
8. The method for producing liquid oil by melt blending and depolymerization of LDPE and β-molecular sieve according to claim 1, characterized in that, The thermocatalytic depolymerization reaction temperature is 250℃, the reaction pressure is 1MPa, and the reaction time is 2h.