A method for degrading polyolefins using a zsm-5 zeolite molecular sieve

Abstract

The present application relates to a kind of methods for degrading polyolefin using ZSM-5 zeolite molecular sieve.The steps of the present application are to add the polyolefin to be degraded, the ZSM-5 zeolite molecular sieve after precalcination and water into a reaction kettle for degradation reaction.The pyrolysis efficiency of polyolefin can reach more than 90%, and the product is mainly C4 below alcohol and hydrocarbon.Compared with the prior art, the present application uses ZSM-5 zeolite as catalyst, without noble metal loading, low cost;Without high reaction temperature, low energy consumption, environment-friendly;Simple process, stable performance, strong controllability, fast and efficient and low cost, has broad development space for solving waste polyolefin materials, easy to realize large-scale production and thus promote the recycling of plastics.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, and in particular relates to a method for degrading polyolefins using ZSM-5 zeolite molecular sieves. Background Technology

[0002] Plastics are widely used in human production and daily life due to their advantages such as low cost, light weight, good stability, and ease of processing. However, plastic products are not easily degradable, and improper use and indiscriminate dumping of waste plastics pose a significant threat to the ecological environment. Globally, the annual production of waste plastics reaches nearly 300 million tons, accounting for approximately 70-85% of annual plastic production. Of this, only 9% is recycled, and about 12% is incinerated. This is far from meeting the enormous demand for waste plastic disposal, with approximately 79% of waste plastics still not properly disposed of. Statistics show that about half of plastic products are polyolefins, including linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP). Because of their low cost, light weight, and ease of processing, plastic products have been widely used in various industries, especially in agriculture, industry, and the military.

[0003] However, most polyolefin products are single-use, generating substantial solid waste and causing serious environmental pollution. Against this backdrop, the effective recycling and reuse of waste polyolefin plastics has become a pressing global concern. Plastics are synthetic polymers primarily derived from petroleum resources. Due to their abundance of hydrogen and carbon, plastics can be considered a potential alternative for fuel production to alleviate the energy crisis. Mechanical recycling is currently the main process for reusing plastic waste. However, due to limited applications of the recycled products, millions of tons of plastic are still dumped in landfills every day. Therefore, mechanical recycling has high requirements for the quality of waste plastics, limited applicability, and involves complex and costly pre-treatment processes. In recent years, researchers have focused on exploring more rational methods for utilizing waste plastics, mainly including raw material recycling and chemical recycling methods. Among chemical recycling methods, catalytic pyrolysis is considered a promising method for plastic waste re-evaluation, as it can convert polymers into basic chemicals that can be used as raw materials. Pyrolysis is a method for treating waste plastics. It involves placing the waste plastics in an oxygen-deficient or oxygen-free environment (inert atmosphere or vacuum) and subjecting them to high temperatures (300–900°C) to break down the polymer molecular chains. By controlling the reaction conditions, the plastics are converted into small-molecule products, primarily hydrocarbons (including chain hydrocarbons, cyclic hydrocarbons, and aromatic hydrocarbons). Pyrolysis not only solves the problem of waste plastic pollution but also yields value-added products, offering significant environmental and economic benefits. Compared to traditional landfill and incineration methods, pyrolysis can significantly reduce greenhouse gas emissions, decrease landfill leachate generation, and enable rapid commercialization of pyrolysis products. Compared to simple thermal decomposition, catalytic pyrolysis can significantly control the composition and distribution of products, has low energy consumption, fast reaction speed, and strong selectivity for valuable chemical substances. The presence of a catalyst significantly reduces the temperature and time of the pyrolysis reaction while increasing the conversion rate of various polymers. Therefore, adding a catalyst during pyrolysis can lower the required pyrolysis temperature, reduce reactor volume, decrease energy consumption and operating costs, enrich the target product, reduce the viscosity of the pyrolysis oil, thereby increasing product value. Furthermore, it can accelerate the breaking of long-chain molecules, promote the lightweighting of products, and optimize the molecular weight distribution of products. However, current research on the catalytic pyrolysis of waste plastics still faces problems such as low degradation efficiency, technical and economic constraints, and excessively high reaction temperatures. To date, due to relatively low yields, long processing times, high temperatures and energy demands, and the inability to adjust product distribution according to different applications, existing methods still cannot meet practical implementation requirements.

[0004] Currently, commonly used catalysts in catalytic pyrolysis include molecular sieve catalysts, oxide catalysts, clay catalysts, and transition metal supported catalysts. Directly applying these types of catalysts to the catalytic cracking of plastics often results in inferior performance compared to modified catalyst materials. However, catalyst modification is complex and costly. Previously, PE pyrolysis reactions typically employed tubular fixed-bed reactions at temperatures above 350℃. Furthermore, PE pyrolysis follows only random chain scission rules, resulting in complex hydrocarbon compositions in the products (containing various hydrocarbons such as chain hydrocarbons, cyclic hydrocarbons, and aromatics) and a wide molecular weight distribution (covering dozens to hundreds of components from C5 to C60). Consequently, the selectivity for high-value-added components is poor, leading to low added value, limited applications, and insignificant enrichment of each product. Conventional thermal degradation processes often introduce reducing gases such as hydrogen and conduct the reaction under high temperature and pressure conditions, increasing the cost and risk of the pyrolysis process. Therefore, there is an urgent need to develop a safe and efficient method for degrading polyolefins and further improve the selectivity of high-value-added products. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for degrading polyolefins using ZSM-5 zeolite molecular sieves.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for degrading polyolefins using ZSM-5 zeolite molecular sieves includes the following steps: adding the polyolefin to be degraded, pre-calcined ZSM-5 zeolite molecular sieves, and water to a reaction vessel for degradation reaction.

[0008] Furthermore, the polyolefin includes one or more of polyethylene or polypropylene.

[0009] Furthermore, the pre-calcination temperature of the ZSM-5 zeolite molecular sieve is 500-600℃, preferably 520-570℃, and more preferably 550℃.

[0010] Furthermore, the pre-calcination time of the ZSM-5 zeolite molecular sieve is 3-5 hours, preferably 4 hours.

[0011] Furthermore, the molar ratio of Si / Al in the ZSM-5 zeolite molecular sieve is 25-200, preferably 25-85.

[0012] Furthermore, the mass ratio of the ZSM-5 zeolite molecular sieve to the polyolefin is 1:(5-100), preferably 1:(5-25), and more preferably 1:10.

[0013] Furthermore, the volume ratio of the water to the volume of the reactor is 1:(5-100), preferably 1:(10-50), and more preferably 1:10.

[0014] Furthermore, the degradation reaction is carried out in an air or inert gas atmosphere, preferably an inert gas, and more preferably nitrogen.

[0015] Furthermore, the pressure of the degradation reaction is 0.1-3 MPa, preferably 0.1-1 MPa, and more preferably 0.1 MPa.

[0016] Furthermore, the temperature of the degradation reaction is 180-350℃, preferably 220-320℃, and more preferably 260℃.

[0017] Furthermore, the degradation reaction time is 0.5-15 h, preferably 3-10 h, and more preferably 4 h.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The ZSM-5 zeolite molecular sieve used in the polyolefin pyrolysis process of this invention, with its appropriate pore structure, strong acidity, and stable framework, can accelerate the catalytic cracking process. During the polyolefin depolymerization process, water acts as both a solvent and a reactant, enhancing the selectivity of heavy-chain and long-chain olefins to light-chain compounds, effectively promoting the conversion of polyolefins into lower molecular weight, high-value-added products, mainly alcohols and hydrocarbons with fewer than C4 atoms. The method of this invention can rapidly and efficiently degrade polyolefins, with a degradation rate exceeding 90%.

[0020] (2) Unlike traditional high-pressure catalytic cracking processes, this invention does not require excessively high reaction temperatures or long reaction times. Furthermore, it eliminates the need for reducing gases such as hydrogen, significantly improving the safety of the degradation process and reducing energy consumption.

[0021] (3) The present invention uses ZSM-5 zeolite molecular sieve, which, compared with other catalysts, does not require precious metal loading and is low in cost; it also does not require a complex catalyst modification process and is easy to operate.

[0022] (4) The present invention degrades polyolefin plastics quickly and efficiently, and is also environmentally friendly and economical. At the same time, it does not require expensive instruments and equipment, and is easy to promote and apply in enterprises and third-party laboratories. It is easy to achieve large-scale production and thus promote the recycling of plastics. It has high scientific value and practical significance for preventing and controlling environmental pollution. It has broad development space for solving the problem of waste polyolefin materials. Attached Figure Description

[0023] Figure 1The image shows the hydrogen NMR spectrum of the liquid-phase product from Example 1.

[0024] Figure 2 The diagram shows the gas phase and liquid phase products and yield of Example 1.

[0025] Figure 3 The diagram shows the gas phase, liquid phase products, and yield of Example 2.

[0026] Figure 4 The diagram shows the gas phase, liquid phase products, and yield of Example 3.

[0027] Figure 5 The diagram shows the gas phase and liquid phase products and yield of Example 4.

[0028] Figure 6 The diagram shows the gas phase and liquid phase products and yield of Example 5.

[0029] Figure 7 The diagram shows the gas phase and liquid phase products and yield of Example 6.

[0030] Figure 8 The diagram shows the gas phase, liquid phase products, and yield of Example 7.

[0031] Figure 9 The diagram shows the gas phase, liquid phase products, and yield of Example 8. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0033] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available and of analytical grade.

[0034] In the following examples, ZSM-5 zeolite molecular sieve was purchased from the Catalyst Plant of Nankai University; PE was purchased from China Petroleum & Chemical Corporation (Sinopec), model DFDA7042; and PP was purchased from Sinopec, model PPB-M02.

[0035] Example 1:

[0036] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1326 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 10 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, and the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 4 hours of reaction, heating was stopped, and the gaseous product was analyzed by gas chromatography. After adjusting the back pressure valve until the pressure inside the reactor dropped to atmospheric pressure, the reactor was opened, cooled to room temperature, and the liquid was centrifuged. A certain amount of the solution was analyzed by proton nuclear magnetic resonance (NMR). The remaining polyolefin solid was weighed, and the conversion rate was measured.

[0037] Example 2:

[0038] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1305 g of PP was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 10 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, and the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 4 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0039] Example 3:

[0040] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1324 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 10 mL of water were added to the reactor. After sealing, the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. Heating was stopped after 4 hours of reaction, and then gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0041] Example 4:

[0042] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1324 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 20 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, and the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 4 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0043] Example 5:

[0044] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1317 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 10 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, and the reactor heating switch was turned on, and the degradation reaction was carried out at 180℃. After 4 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0045] Example 6:

[0046] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 200) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1324 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 20 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, and the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 4 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0047] Example 7:

[0048] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1324 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.0013 g of ZSM-5 zeolite molecular sieve catalyst and 20 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 4 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0049] Example 8:

[0050] ZSM-5 zeolite molecular sieve (Si / Al molar ratio of 25) was pretreated by calcining in a high-temperature furnace at 550℃ for 4 hours. 0.1324 g of PE was weighed and placed in a quartz-lined reactor (effective volume 100 mL). 0.013 g of ZSM-5 zeolite molecular sieve catalyst and 20 mL of water were added to the reactor. After sealing, the reactor was purged with nitrogen for 5 minutes until the final reaction pressure reached 0.1 MPa, while simultaneously checking for leaks in the reactor and gas pipelines. Then, the nitrogen was turned off, the reactor heating switch was turned on, and the degradation reaction was carried out at 260℃. After 0.5 hours of reaction, heating was stopped, and gas-phase and liquid-phase product analysis and pyrolysis rate testing were performed according to Example 1.

[0051] The present invention conducted the following tests on Examples 1-8 to demonstrate the beneficial effects of the present invention:

[0052] (1) Degradation performance test of polyolefins: The degradation performance of polyolefins is characterized by conversion rate. The conversion rate is calculated according to the formula Conversion=(M1-M2) / M1×% where M1 and M2 represent the weight of the plastic sample before and after the experiment, respectively.

[0053] (2) Gas phase product analysis: Gas products were analyzed using a gas chromatograph (GC7900) equipped with an automated unit and an FID detector. Gas components such as CO, CO2, CH4 and H2 were analyzed in the GC chromatograms after plastic pyrolysis.

[0054] (3) Liquid phase product analysis: Liquid products were obtained using a Bruker 600MHz NMR instrument. 1 Analysis was performed using 1H NMR spectroscopy, with tetramethylsilane (TMS) as the reference standard.

[0055] The degradation performance of Examples 1-8 was reflected by measuring the pyrolysis rate, and the test results are shown in Table 1.

[0056] Table 1. Pyrolysis rate of polyolefins

[0057] Example 1 2 3 4 5 6 7 8 Pyrolysis rate 93.77％ 95.02％ 56.53％ 30.67％ 21.17％ 11.63％ 8.93％ 27.80％

[0058] The gaseous and liquid phase products and yields of Examples 1-8 are shown in the graphs. Figure 2-9 The analysis results are shown in Table 2.

[0059] Table 2. Analysis of gas and liquid phase products (unit: μmol / g / h)

[0060] Example 1 2 3 4 5 6 7 8 Total gas volume 1240.96 1338.36 909.28 171.10 45.63 41.07 36.87 109.62 CO 1123.46 1216.00 828.51 151.76 32.50 28.20 27.02 91.07 <![CDATA[CH4]]> 99.20 103.60 70.26 13.05 8.00 6.88 6.75 14.00 <![CDATA[H2]]> 15.76 15.89 8.08 4.13 3.85 3.66 2.18 3.35 <![CDATA[CO2]]> 2.54 2.87 2.43 2.15 1.29 2.32 0.93 1.20 Total liquid volume 1625.60 1779.56 928.49 305.50 126.79 35.88 36.90 202.61 2-Butanol 145.29 157.09 108.38 14.88 5.03 2.11 2.32 9.11 ethanol 235.47 275.25 120.07 50.37 6.18 3.13 3.50 32.49 Isopropanol 216.47 234.90 88.91 47.39 12.26 4.50 5.69 33.83 tert-Butanol 431.57 451.70 277.59 97.42 45.78 10.84 13.16 68.77 Acetic acid 356.69 400.78 205.58 78.15 31.62 8.81 9.24 45.97 acetone 240.12 259.84 127.96 17.29 25.91 6.49 3.00 12.45

[0061] Figure 1 The distribution of liquid phase products from the pyrolysis experiment is shown. As can be seen from the figure, the main liquid phase products are alcohols between C1 and C4, which are produced by catalytic random cleavage reaction.

[0062] As shown in Tables 1 and 2, the polyolefins in Examples 1-8 all exhibited a certain degree of degradation under the catalysis of ZSM-5 zeolite molecular sieves, with the thermal degradation rates of polyethylene and polypropylene reaching over 90% (Examples 1 and 2). Compared to Example 1, Example 3, by replacing the reaction atmosphere with air, showed a certain decrease in the concentration of gas-liquid phase products and the pyrolysis rate of polyolefins, indicating that an inert gas atmosphere is more conducive to the degradation of polyolefins. Example 4, by increasing the water content of the reaction, also showed a decrease in the concentration of gas-liquid phase products and the pyrolysis rate of polyolefins, indicating that the catalyst-to-water ratio can achieve the best catalytic degradation effect within a certain range. Example 5 shows that lowering the reaction temperature also reduces the catalytic activity of ZSM-5 zeolite molecular sieves, thereby reducing the concentration of gas-liquid phase products and the pyrolysis rate of polyolefins. Example 6, using ZSM-5 zeolite with Si / Al = 200, showed a lower degradation rate than ZSM-5 zeolite with a lower silicon-to-aluminum ratio, indicating that a higher silicon-to-aluminum ratio leads to a decrease in catalytic activity. Example 7, by reducing the catalyst-to-plastic ratio to 1:100, PE could be degraded. In Example 8, the degradation rate reached 27.8% when the reaction time was only 0.5 h. The degradation rate also increased with the increase of reaction time.

[0063] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for degrading polyolefins using a ZSM-5 zeolite molecular sieve, characterized by, The method comprises the following steps: adding polyolefin to be degraded, pre-calcined ZSM-5 zeolite molecular sieve and water into a reaction kettle to carry out a degradation reaction; The polyolefin is polyethylene or polypropylene; The molar ratio of Si / Al in the ZSM-5 zeolite molecular sieve is 25-85, and the mass ratio of the ZSM-5 zeolite molecular sieve to the polyolefin is 1:(5-25); The volume ratio of the water to the volume of the reaction kettle is 1:(10-50), and the water has a dual role of solvent and reactant; The degradation reaction is carried out in an inert gas atmosphere, and the temperature of the degradation reaction is 220-320 DEG C; The thermal degradation rate of the polyolefin is greater than 90%, and the degradation product is mainly alcohol and hydrocarbon with less than C4.

2. The method for degrading polyolefin using ZSM-5 zeolite molecular sieve according to claim 1, characterized in that, The pre-calcination temperature of the ZSM-5 zeolite molecular sieve is 500-600 DEG C, and the pre-calcination time is 3-5 h.

3. The method for degrading polyolefin using ZSM-5 zeolite molecular sieve according to claim 1, characterized in that, The initial pressure of the degradation reaction is 0.1-3 MPa.

4. The method for degrading polyolefin using ZSM-5 zeolite molecular sieve according to claim 1, characterized in that, The time of the degradation reaction is 4-15 h.

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