Method for synergistically recovering waste polyolefin plastics by photo-thermal

Abstract

This invention provides a method for the photothermal synergistic recycling of waste polyolefin plastics. The method is carried out under photothermal conditions. The ultraviolet portion of sunlight can effectively reduce the inertia of polyolefin plastics, while the visible and infrared portions can be effectively absorbed by Ru-TiO2 and converted into heat energy. This achieves efficient photothermal synergistic catalytic degradation of polyolefin plastics into waxy fuels and methane products under sunlight irradiation, realizing the resource utilization process of solid waste.

Description

Technical Field

[0001] This invention relates to the field of photothermal synergistic catalyst technology, specifically a method for photothermal synergistic recycling of waste polyolefin plastics. Background Technology

[0002] Polyolefin plastics, primarily referring to low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP), are indispensable and ubiquitous synthetic polymers in our modern lives. Abundant and inexpensive raw materials enable polyolefin plastics to be used in single-use and short-term applications, such as in packaging, transportation, medical, and industrial equipment. Approximately hundreds of millions of tons of polyolefin plastics are produced annually, but the majority of these are not recyclable (only 5% for LDPE, 10% for HDPE, and less than 1% for PP). Due to the extremely inert C-C and CH bonds in polyolefin plastics, the usual recycling method is primarily through pyrolysis to other raw materials. However, the high operating temperatures (>500°C) can lead to enormous energy input and dissipation, making polyolefin plastic recycling costly. Although advanced hydrogenolysis technology can reduce the reaction temperature to around 300°C, it typically requires tens of H2 pressures and generally uses non-renewable energy sources for heating.

[0003] While green and sustainable photocatalysis is a low-energy alternative utilizing renewable solar energy, its catalytic efficiency still falls short of practical requirements due to the chemical inertness of polyolefins and the relatively weak light absorption capacity of current photocatalysts. Furthermore, since photocatalytic reactions typically occur in aqueous solutions, the hydrophobic nature of polyolefins leads to poor contact between the polyolefin plastic and the catalyst, and the products in the aqueous solution require further separation.

[0004] Emerging photothermal synergistic catalysis has shown great potential in various reactions, such as Fischer-Tropsch synthesis, CO2 conversion, NH3 synthesis, and pollutant degradation. It can effectively collect sunlight through full-spectrum absorption, even low-energy infrared photons, thus enabling rapid heating and localized high temperatures of the catalyst. Compared to thermocatalysis or photocatalysis, photothermal catalysis is generally considered to significantly increase reaction rates due to the combined contributions of photochemistry and thermochemistry. Compared to traditional thermocatalysis, the high-energy photons in photothermal catalysis can promote the activation of inert polyolefin chains, generating active free radicals and fragments. Compared to traditional photocatalysis, the localized heat in photothermal catalysis can enhance the mobility and reaction kinetics of polyolefin chains. Furthermore, since the surface energy of thermoplastics generally decreases with increasing temperature, the localized heat in photothermal catalysis can also promote effective contact between polyolefins and the catalyst, improving reaction efficiency. These significant advantages prompt us to explore the performance and possibilities of photothermal systems for the recycling of polyolefin plastic waste. Summary of the Invention

[0005] In order to achieve efficient degradation of polyolefin plastics using renewable energy, the present invention aims to provide a method for the photothermal co-processing of waste polyolefin plastics.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for photothermal synergistic recycling of waste polyolefin plastics, wherein the method involves a reaction under photothermal conditions in a system containing a Ru-TiO2 catalyst, hydrogen, and polyolefin plastics.

[0008] According to an embodiment of the present invention, the method can obtain waxy fuel (mainly composed of C20-C50 alkanes) and methane.

[0009] According to an embodiment of the present invention, the polyolefin plastic and the Ru-TiO2 photothermal catalyst are uniformly mixed by grinding.

[0010] According to an embodiment of the present invention, the mass ratio of the polyolefin plastic to the Ru-TiO2 photothermal catalyst is (2-8):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1.

[0011] According to embodiments of the present invention, the Ru-TiO2 catalyst can be prepared using methods known in the art, or it can be obtained through commercial purchase.

[0012] According to an embodiment of the present invention, the Ru-TiO2 catalyst comprises Ru nanoparticles and titanium dioxide (e.g., anatase titanium dioxide, or commercially available P25 titanium dioxide), and the Ru nanoparticles are supported on the TiO2 surface.

[0013] According to an embodiment of the present invention, the Ru-TiO2 catalyst is prepared by the following method:

[0014] Ru nanoparticles were loaded onto the TiO2 surface using an impregnation method and a high-temperature hydrogen reduction method.

[0015] For example, the method includes the following steps:

[0016] TiO2 and RuCl3 aqueous solution were mixed and heated to prepare RuCl3-supported TiO2; subsequently, heat treatment was carried out under hydrogen atmosphere to prepare the Ru-TiO2 photothermal catalyst.

[0017] The heating process, for example, involves heating at 60–120°C for 1–5 hours.

[0018] The hydrogen atmosphere is, for example, a mixture of H2 and Ar, wherein the volume ratio of H2 to Ar is 5–15:95–85.

[0019] The heat treatment, for example, involves heating at 400–600°C for 1–5 hours.

[0020] According to an embodiment of the present invention, in the Ru-TiO2 catalyst, the mass fraction of TiO2 is 95-99% based on 100% of the weight of the Ru-TiO2 catalyst, for example, 95.0%, 96.0%, 97.0%, 98.0% or 99.0%, and the mass fraction of Ru is 1-5%, for example, 1.0%, 2.0%, 3.0%, 4.0% or 5.0%.

[0021] According to an embodiment of the present invention, the reaction temperature is 200–400°C, and the reaction time is 1–40 h. As the reaction time increases, the selectivity for methane in the gaseous products gradually increases, reaching nearly 100% at 40 h.

[0022] According to an embodiment of the present invention, the photothermal conditions are carried out under sunlight irradiation.

[0023] According to an embodiment of the present invention, the sunlight includes ultraviolet light, visible light, and near-infrared light. The sunlight can be natural sunlight or simulated sunlight (such as from a xenon lamp). The wavelength of the sunlight is 200-1200 nm.

[0024] Ultraviolet light can reduce the crystallinity of polyolefin plastics, thereby weakening their inertness. Furthermore, since ultraviolet light can also promote the generation of active free radicals and fragments in polymer chains, or directly cause the breakage of C-C bonds, thus weakening the chemical inertness of polyolefin plastics, the above method can be carried out at a relatively low hydrogen pressure. Further, the hydrogen pressure is 0.1–1.0 bar.

[0025] The reaction system also includes argon gas, for example, the reaction system is a mixed atmosphere of H2 / Ar, wherein the volume ratio of H2 to Ar is 25-35:75-65.

[0026] Furthermore, visible and near-infrared light can be effectively absorbed by Ru-TiO2 and converted into heat energy, enabling localized high temperatures to be achieved under sunlight without additional heating. This localized high temperature can further promote the photothermal synergistic catalytic degradation of polyolefin plastics by Ru-TiO2.

[0027] Furthermore, due to the synergistic promoting effect of ultraviolet light and visible / near-infrared light, this photothermal synergistic recycling method for waste polyolefin plastics can achieve a degradation rate of 97.3%, while the degradation rate of polyolefin plastics under pure heat (in the presence of Ru-TiO2 photothermal catalyst, only heating without light) is only 2.3%, and under photolysis (in the presence of Ru-TiO2 photothermal catalyst, only light without heating (the system temperature is controlled at room temperature by cooling water)) conditions, polyolefin plastics hardly degrade.

[0028] According to an embodiment of the present invention, the polyolefin plastic is selected from at least one of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ultra-high molecular weight polyethylene (UHMWPE), and LDPE plastic bags; further, the polyolefin plastic is preferably low-density polyethylene (LDPE).

[0029] According to an embodiment of the present invention, the method further includes a method for obtaining waxy fuel.

[0030] According to an embodiment of the present invention, the method for obtaining the waxy fuel is as follows: solid / liquid products are extracted using cyclohexane, and the solvent is removed by rotary evaporation at 40-80°C.

[0031] According to an embodiment of the present invention, the method further includes a method for obtaining methane.

[0032] According to an embodiment of the present invention, the method for obtaining methane is as follows: directly expelling it using a gas bag or sampling needle.

[0033] The beneficial effects of this invention are:

[0034] This invention provides a method for the photothermal synergistic recycling of waste polyolefin plastics. The method is carried out under photothermal conditions. The ultraviolet portion of sunlight can effectively reduce the inertia of polyolefin plastics, while the visible and infrared portions can be effectively absorbed by Ru-TiO2 and converted into heat energy. This achieves efficient photothermal synergistic catalytic degradation of polyolefin plastics into waxy fuels and methane products under sunlight irradiation without additional heating, realizing the resource utilization process of solid waste.

[0035] Specifically, the photothermal synergistic recycling method for waste polyolefin plastics used in this invention enables polyolefins to be fully degraded under relatively low temperature (200-400℃) and pressure operating conditions of 0.1-1.0 bar. The polymer decomposition occurs on the surface of the solid catalyst, producing waxy fuel and methane. Due to its high methanation capacity, nearly 100% selective methane can be obtained from the gaseous products.

[0036] Compared to traditional titanium dioxide catalysts, Ru-TiO2 catalysts can fully utilize the entire solar energy spectrum, exhibiting high catalytic efficiency and low energy consumption, making them widely applicable in waste plastic recycling. Ru-TiO2 catalysts achieve absorption of the entire solar spectrum, improving solar energy utilization efficiency. With low metal content, Ru-TiO2 catalysts are cost-effective, operate under reaction conditions of approximately 200–400℃, are easy to operate, save energy, and do not generate excess harmful substances during production, making them environmentally friendly and conducive to industrial-scale production.

[0037] The method of this invention can achieve a significantly improved degradation rate compared to conventional thermocatalysis and photocatalysis. Attached Figure Description

[0038] Figure 1 The UV-Vis diffuse reflectance spectra (a) and X-ray diffraction patterns (b) of the TiO2 catalyst and Ru / TiO2 photothermal catalyst prepared in Example 1 are shown.

[0039] Figure 2 The degradation rate (a) and molecular weight distribution (b) of low-density polyethylene under Ru-TiO2 photothermal catalysis, pure thermal catalysis, and photolysis catalysis in Example 1 are shown.

[0040] Figure 3 The degradation rate-reaction time curve of low-density polyethylene by Ru-TiO2 photothermal catalysis in Example 2 is shown.

[0041] Figure 4 The gaseous and solid products of Ru-TiO2 photothermal catalytic degradation of low-density polyethylene are shown in Example 2.

[0042] Figure 5 This illustrates the effect of ultraviolet light on low-density polyethylene without a catalyst in Example 3.

[0043] Figure 6 This illustrates the effects of different light bands in the photothermal catalytic degradation of low-density polyethylene by Ru-TiO2 in Example 4.

[0044] Figure 7 The effects of photothermal and pure thermal reactions without a catalyst on low-density polyethylene are shown in Example 5. Detailed Implementation

[0045] The method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0046] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0047] The simulated sunlight used in the following examples was obtained by irradiation with a xenon lamp (BeijingPerfect-light Co., Ltd., PLS-SXE300) with a wavelength of 200-1200nm and a power of 150W-300W. Furthermore, the temperature of the reaction system was controlled by adjusting the current of the xenon lamp.

[0048] Preparation Example 1

[0049] The impregnation method and the high-temperature hydrogen reduction method were employed.

[0050] 500 mg of TiO2 powder (Degussa P25) and 4110 μL of RuCl3 (Aladdin) aqueous solution (5 mg / mL) were added to a glass beaker containing 20 mL of deionized water under vigorous stirring. The resulting suspension was heated at 60 °C for 2 h and then dried at 120 °C. The dried sample was then heated to 500 °C in a tube furnace at a heating rate of 5 °C / min, and then held at 500 °C under a H2 / Ar (10 / 90 v / v) atmosphere for 2 h. Finally, the resulting product was cooled to room temperature under a nitrogen atmosphere to prepare the Ru-TiO2 photothermal catalyst. The mass fraction of TiO2 was 98.0% and the mass fraction of Ru was 2.0% (based on 100% Ru-TiO2 catalyst weight). The X-ray diffraction pattern and UV-Vis diffuse reflectance spectrum of the prepared Ru-TiO2 photothermal catalyst are shown below. Figure 1 a and Figure 1 As shown in b in the figure.

[0051] Example 1

[0052] LDPE and the Ru-TiO2 photothermal catalyst prepared in Example 1 were added to an atmospheric pressure reactor at a mass ratio of 4:1. A 1 bar H2 / Ar mixed gas (v / v = 30 / 70) was then introduced. Photothermal catalysis (contained under simulated sunlight for 20 h, which could heat the system to 300°C), pure thermal catalysis (contained in darkness for 20 h, while the system was heated to 300°C by an external heat source), and photocatalysis (contained under simulated sunlight for 20 h, while the system was controlled at 25°C by cooling water) were then performed to obtain the corresponding degradation rates. Figure 2 a) and molecular weight arrangement ( Figure 2(b) The significantly improved degradation rate and significantly reduced molecular weight distribution towards smaller molecules achieved by photothermal catalysis compared to pure thermal catalysis or photolysis indicate that the photothermal synergistic recycling method for waste polyolefin plastics is an efficient recycling method.

[0053] Example 2

[0054] LDPE and the Ru-TiO2 photothermal catalyst prepared in Example 1 were added to an atmospheric pressure reactor at a mass ratio of 4:1. Then, a 1 bar H2 / Ar mixed gas (v / v = 30 / 70) was introduced, and the system was irradiated under simulated sunlight for 1–40 h. This simulated sunlight could heat the system to 300 °C. The degradation rates at different reaction times were obtained. Figure 3 ) and gaseous products ( Figure 4 (a) As the reaction time increases, the degradation rate gradually increases. The Ru-TiO2 photothermal catalyst, with its excellent methanation ability, is exposed to the gaseous products, methanating the low-carbon hydrocarbon products to obtain highly selective methane. The waxy products from the 20-hour photothermal reaction exhibit a C1... 27 The distribution centered on ( Figure 4 (b) in the middle.

[0055] Example 3

[0056] LDPE was added to an atmospheric pressure reactor, followed by the introduction of a 1 bar H2 / Ar mixture (v / v = 30 / 70). Then, pure thermal + photocatalytic oxidation (continuously in darkness for 5 hours while the system was heated to 300°C using an external heat source) and pure thermal + UV photocatalytic oxidation (continuously under simulated sunlight UV light for 5 hours while the system was heated to 300°C using an external heat source) were performed in the absence of a catalyst. The infrared spectra were then measured. Figure 5 a) and molecular weight arrangement ( Figure 5 (b) in the middle.

[0057] As shown in the figure, ultraviolet light can activate inert polymer chains. Specifically, ultraviolet light can reduce the crystallinity of low-density polyethylene (LDPE), thereby weakening its inertness. Furthermore, ultraviolet light can promote the generation of active free radicals and fragments in polymer chains, or directly cause the breakage of C-C bonds.

[0058] Example 4

[0059] LDPE and the Ru-TiO2 photothermal catalyst prepared in Example 1 were added to an atmospheric pressure reactor at a mass ratio of 4:1. Then, a 1 bar H2 / Ar mixed gas (v / v = 30 / 70) was introduced. The reactor was then irradiated with different solar light bands (ultraviolet-visible, visible, and near-infrared) and heated to 300°C by an external heat source for 20 hours to obtain the corresponding degradation rate. Figure 6(a) It was found that the addition of ultraviolet light can significantly promote the degradation rate. In conjunction with Example 3, the possible reaction pathway of the preparation method of the present invention is as follows: the inert polymer chains are first activated by ultraviolet light to produce activated polymer chains, and then the Ru-TiO2 photothermal catalyst generates local high temperatures under visible / infrared light irradiation, further achieving efficient photothermal synergistic catalytic degradation of polyolefin LDPE (…). Figure 6 (b) in the middle.

[0060] Example 5

[0061] LDPE was added to an atmospheric pressure reactor, followed by the introduction of a 1 bar H2 / Ar mixture (v / v = 30 / 70). Then, pure thermal + photocatalytic degradation (maintaining darkness for 20 hours while simultaneously heating the system to 300°C via an external heat source, i.e., pure thermal - no catalyst) and photothermal degradation (maintaining simulated sunlight for 20 hours while simultaneously heating the system to 300°C via an external heat source, i.e., photothermal - no catalyst) were performed to obtain the corresponding degradation rates. Figure 7 a) and molecular weight arrangement ( Figure 7 (b) As can be seen from the figure, the low degradation rate (<10%) and high molecular weight (>10000Da) also indicate that this photothermal synergistic recycling method for waste polyolefin plastics requires a catalyst with excellent light absorption capacity and catalytic effect.

[0062] Example 6

[0063] Different types of polyolefin plastics (LDPE, PP, HDPE, UHMWPE and LDPE plastic bags) and Ru-TiO2 photothermal catalyst were added to an atmospheric pressure reactor at a mass ratio of 4:1. Then, a 1 bar H2 / Ar mixed gas (v / v = 30 / 70) was introduced. The system was then irradiated with simulated sunlight for 20 h or 40 h (simulated sunlight can heat the system to 300 °C without the need for additional heat source, i.e., photothermal reaction), or in the dark, the system was heated to 300 °C by an external heat source and maintained for 20 h or 40 h (i.e., pure thermal reaction). The corresponding degradation rates and gaseous / solid product distributions were obtained (Table 1).

[0064] Table 1 shows the photothermal or pure thermal degradation effects of different types of polyolefin plastics in Example 6 of the present invention.

[0065]

[0066] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for waste polyolefin plastic recycling by photo-thermal synergy, the method comprising a reaction in a system containing a Ru-TiO 2 catalyst, hydrogen and polyolefin plastic under photo-thermal conditions. The reaction is carried out at a temperature of 200-400 ℃, a hydrogen pressure of 0.1-1.0 bar, and under photo-thermal conditions of solar light irradiation, wherein the solar light comprises ultraviolet light, visible light and near-infrared light. The reaction produces waxy fuel and methane, and the main component of the waxy fuel is C 20-C 50 alkanes.

2. The method of claim 1, wherein, The mass ratio of the polyolefin plastic to the Ru-TiO 2 photo-thermal catalyst is (2-8) :

1.

3. The method of claim 1, wherein, The Ru-TiO 2 catalyst comprises Ru nanoparticles and titanium dioxide, and the Ru nanoparticles are loaded on the surface of the TiO 2.

4. The method according to any one of claims 1 to 3, wherein, The Ru-TiO 2 catalyst is prepared by the following method: The Ru nanoparticles are loaded on the surface of the TiO 2 by an impregnation method and a high-temperature hydrogen reduction method.

5. The method according to any one of claims 1-3, wherein, In the Ru-TiO 2 catalyst, the mass fraction of TiO 2 is 95-99% and the mass fraction of Ru is 1-5% based on 100% of the weight of the Ru-TiO 2 catalyst.

6. The method of any one of claims 1-3, wherein, The reaction is carried out for 1-40 h.

7. The method of any one of claims 1-3, wherein, The solar light is natural sunlight or simulated sunlight.

8. The method of any one of claims 1-3, wherein, The polyolefin plastic is selected from at least one of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ultra-high molecular weight polyethylene (UHMWPE) and LDPE plastic bags.

9. The method of any one of claims 1-3, wherein, The method further comprises a method for obtaining waxy fuel, which is obtained by extracting the solid / liquid product with cyclohexane and removing the solvent by rotary evaporation at 40-80 ℃. And / or, the method further comprises a method for obtaining methane, which is directly discharged by a gas bag or a sampling needle.

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