Process for the preparation of biodiesel by catalytic oxidation of polyethylene and biodiesel

Abstract

The application provides a method for preparing biodiesel by catalytic oxidation of polyethylene and the biodiesel, and belongs to the technical field of waste plastic resource utilization and catalytic conversion. The method comprises the following steps: adding a supported cobalt-based acidic molecular sieve catalyst and waste polyolefin plastic into a reactor, introducing oxygen and pressurizing, and performing selective oxidation under heating and stirring to generate long-chain aliphatic monocarboxylic acid with a carbon chain length of C13-C20; performing esterification reaction of the long-chain aliphatic monocarboxylic acid with alcohol, so that the long-chain aliphatic monocarboxylic acid is converted into corresponding long-chain fatty acid ester; and after post-treatment, the biodiesel is obtained; wherein the material of the waste polyolefin plastic is polyethylene, or a blend of polyethylene and polypropylene.

Description

Technical Field

[0001] This application belongs to the field of waste plastic resource utilization and catalytic conversion, and in particular relates to a method for catalytic oxidation of polyethylene to prepare biodiesel and biodiesel. Background Technology

[0002] Existing technologies for the resource recovery of waste polyethylene (PE) mainly include pyrolysis, hydrocracking, and oxidative conversion. Pyrolysis typically breaks down the PE backbone at high temperatures (400-700℃) to obtain liquid hydrocarbons or waxy products. However, this process generally requires high reaction temperatures, and the products are complex, often requiring fractionation to separate alkanes, olefins, aromatics, and different carbon groups. Hydrorefining or isomerization is then necessary to obtain a final product that meets fuel requirements. While hydrocracking technology improves the quality of liquid fuels to some extent, it usually relies on high-pressure (2MPa-7MPa) hydrogen, precious metals, or sulfurization catalysts, resulting in high equipment and hydrogen source costs and stringent process safety requirements.

[0003] In contrast, oxidation-based conversion technologies can reduce the difficulty of carbon-carbon (CC) bond breaking by introducing oxygen-containing functional groups into the PE molecular chain, and convert PE into oxygen-containing chemicals such as carboxylic acids.

[0004] However, existing PE oxidation systems still suffer from problems such as insufficient oxidative activity, harsh reaction conditions, and difficulty in controlling product distribution. The resulting carboxylic acid products often contain short-chain dicarboxylic acids, over-oxidized products, and components with a wide carbon number distribution, making it difficult to obtain long-chain monocarboxylic acid products suitable for biodiesel production. In addition, some oxidation reaction systems require precious metal catalysts such as ruthenium (Ru) and platinum (Pt), or require long reaction times, which limits practical applications. Summary of the Invention

[0005] In view of the above, this application provides a method for preparing biodiesel by catalytic oxidation of polyethylene and biodiesel, in order to at least partially solve the above-mentioned technical problems. The technical solution provided by this application is as follows.

[0006] As the first aspect of this application, a method for catalytically oxidizing polyethylene to prepare biodiesel is provided, comprising: adding a supported cobalt-based acidic molecular sieve catalyst and waste polyolefin plastic into a reactor, introducing oxygen and pressurizing, and selectively oxidizing under heating and stirring to generate C13-C20 long-chain aliphatic monocarboxylic acids; esterifying the long-chain aliphatic monocarboxylic acids with alcohols to convert the long-chain aliphatic monocarboxylic acids into corresponding long-chain fatty acid esters, and obtaining biodiesel after post-treatment; wherein the waste polyolefin plastic is made of polyethylene, or is a blend of polyethylene and polypropylene.

[0007] As a second aspect of this application, a biodiesel is provided, which is prepared by the above-described method for preparing biodiesel by catalytic oxidation of polyethylene.

[0008] Based on the above technical solution, the method for preparing biodiesel by catalytic polyethylene oxidation provided in this application and the biodiesel itself have at least one of the following beneficial effects:

[0009] (1) This application uses a supported cobalt-based acidic molecular sieve as a catalyst. Utilizing the catalytic synergy between the cobalt active species in the catalyst and the acidic sites in the acidic molecular sieve, waste polyolefin plastics undergo selective oxidative chain scission under oxygen, pressure, and heating conditions to generate C13-C20 long-chain aliphatic monocarboxylic acids. These long-chain aliphatic monocarboxylic acids can then be esterified and post-treated to obtain biodiesel. The method for catalytically oxidizing polyethylene to prepare biodiesel in this application does not rely on precious metal catalysts. It can efficiently catalyze the oxidation of polyethylene under mild reaction conditions to prepare components suitable for esterification into biodiesel. This forms a directional fuel conversion from waste polyolefin plastics to long-chain aliphatic monocarboxylic acids and biodiesel, realizing the high-value utilization of waste polyolefin plastics and providing a new technical path for the high-value resource utilization of waste polyolefin plastics.

[0010] (2) In this application, the method provided by this application improves the reaction mildness, product orientation and fuel compatibility of the waste olefin plastic resource utilization process, and solves the problems of harsh reaction conditions, strong dependence on hydrogen or precious metals, complex product composition, cumbersome post-processing process and insufficient controllability of target fuel components in the existing polyethylene plastic resource utilization process, providing a new route for the recycling of waste polyolefin plastics and the preparation of biodiesel. Attached Figure Description

[0011] Figure 1 A schematic diagram illustrating the pathway for the catalytic oxidation of polyethylene to produce biodiesel according to this application;

[0012] Figure 2 The images shown are characterization diagrams of the supported cobalt-based acidic molecular sieve catalyst in Example 1 of this application, where a is a scanning electron microscope (SEM) image of the supported cobalt-based acidic molecular sieve catalyst, b is a high-resolution transmission electron microscope (HRTEM) image of the supported cobalt-based acidic molecular sieve catalyst, c is the elemental distribution diagram and high-angle annular dark-field imaging (HAADF) image of b, and d is the lattice spacing diagram of the supported cobalt-based acidic molecular sieve catalyst.

[0013] Figure 3 This is a diagram showing the specific surface area and average pore size distribution of supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios in this application.

[0014] Figure 4The above are X-ray photoelectron spectroscopy (XPS) spectra of the supported cobalt-based acidic molecular sieve catalysts in Examples 1, 5-7 of this application.

[0015] Figure 5 The images show X-ray diffraction (XRD) patterns of different supported cobalt-based acidic molecular sieve catalysts in this application. In particular, a is the XRD pattern of different supported cobalt-based acidic molecular sieve catalysts in Examples 1-4, and b is the XRD pattern of different supported cobalt-based acidic molecular sieve catalysts in Examples 1 and 5-7.

[0016] Figure 6 The images show the infrared spectral analysis results of the catalysts used in Examples 1 and 5-7 of this application.

[0017] Figure 7 This is a compositional distribution diagram of biodiesel in Application Example 1 of this application;

[0018] Figure 8 This is a graph showing the solid conversion rate and carbon yield of the resulting carboxylic acid products of supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios in the catalysis of polyethylene.

[0019] Figure 9 This is a graph showing the solid conversion rate and carbon yield of the resulting carboxylic acid products of supported cobalt-based acidic molecular sieve catalysts with different Si / Co mass ratios in the catalysis of polyethylene.

[0020] Figure 10 The graphs show the carbon yield of carbon dioxide when different supported cobalt-based acidic molecular sieve catalysts catalyze polyethylene, where a is the carbon yield of carbon dioxide at different Si / Al mass ratios and b is the carbon yield of carbon dioxide at different Si / Co mass ratios.

[0021] Figure 11 The graph shows the ignition and low-temperature flow performance test results of biodiesel in Application Example 1 of this application.

[0022] Figure 12 This is a radar image showing the performance of the supported cobalt-based acidic molecular sieve catalyst in Example 1 of this application for the oxidation and recycling of different waste polyolefin plastics;

[0023] Figure 13 This is a graph showing the distribution of solid conversion rates of carboxylic acid products obtained by supporting metal-based acidic molecular sieve catalysts of different metals in this application when catalyzing polyethylene. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0025] In this application, C3-C9 are short chains, C10-C12 are medium-length chains, C13-C20 are long chains, and chains longer than C20 are ultra-long chains.

[0026] In realizing the concept of this application, it was discovered that the carboxylic acid products obtained from existing polyethylene oxidation systems are mainly dicarboxylic acids, making it difficult to selectively prepare high-value-added long-chain aliphatic monocarboxylic acid products that can be used as feedstocks for renewable biodiesel. This is because current polyethylene oxidation systems suffer from problems such as excessive oxidation intensity, harsh reaction conditions, and difficulty in controlling product distribution. Furthermore, dicarboxylic acid molecules contain two carboxyl groups, exhibiting high polarity and acidity, resulting in strong hydrophilicity, poor compatibility with hydrocarbon fuels, and a tendency to cause high fuel acid values. Therefore, pure dicarboxylic acids are not suitable for direct use as components in diesel fuels.

[0027] Based on this, this application proposes a method for the catalytic oxidation of polyethylene to produce biodiesel. Unlike the traditional route that first pyrolyzes polyethylene into a complex hydrocarbon mixture before hydrorefining, fractionation, or hydrocracking to produce fuel, this method selectively introduces carboxyl functional groups to directly convert the polyethylene carbon chain into a long-chain aliphatic monocarboxylic acid intermediate suitable for esterification reactions to produce biodiesel components. This forms a fuel-oriented conversion process route of "polyethylene-long-chain aliphatic monocarboxylic acid product-biodiesel". This route features lower reaction temperature, weak hydrogen dependence, clear product targets, and relatively simple post-processing, providing a new technological path for the high-value resource utilization of waste polyethylene.

[0028] Figure 1 This is a schematic diagram illustrating the pathway for the catalytic oxidation of polyethylene to produce biodiesel according to this application.

[0029] like Figure 1 As shown, the method for preparing biodiesel by catalytic oxidation of polyethylene in this application includes: adding a supported cobalt-based acidic molecular sieve catalyst and waste polyolefin plastic into a reactor, introducing oxygen and pressurizing, and selectively oxidizing under heating and stirring to generate C13-C20 long-chain aliphatic monocarboxylic acids; esterifying the long-chain aliphatic monocarboxylic acids with alcohols to convert the long-chain aliphatic monocarboxylic acids into the corresponding long-chain fatty acid esters, and obtaining biodiesel after post-processing.

[0030] In this application, a supported cobalt-based acidic molecular sieve is used as a catalyst and placed in a reactor with waste polyolefin plastics. Oxygen is introduced and pressurized. During heating and stirring, the waste polyolefin plastics melt and form an effective contact interface with the supported cobalt-based acidic molecular sieve catalyst. Through the synergistic effect of the cobalt active species in the supported cobalt-based acidic molecular sieve catalyst and the acid sites in the acidic molecular sieve, polyolefin chain segment activation, carbon-carbon bond breaking, and selective oxidative chain scission are achieved, converting the waste polyolefin plastics into carboxylic acid products mainly composed of C13-C20 long-chain aliphatic monocarboxylic acids. These products are then further esterified with alcohols, and after post-processing, the corresponding long-chain fatty acid ester biodiesel components are obtained. The method provided in this application not only has excellent catalytic oxidation resource recovery and recycling effects on waste polyolefin plastics made of pure polyethylene, but also has good catalytic oxidation resource recovery and recycling effects on mixed plastics formed by polyethylene / polypropylene blends (i.e., polyethylene / polypropylene blends). In the mixed plastics formed by polyethylene / polypropylene blends, the presence of polyethylene can promote the synergistic oxidative conversion of polypropylene in the mixed plastics. More importantly, the catalytic system of this application is anhydrous and contains no external solvent, thus avoiding the presence of an aqueous phase and hydroxyl groups (OH). - The involvement of related species reduces the likelihood of further continuous oxidation and / or deep oxidation of carboxylic acids to generate dicarboxylic acid products, allowing the reaction to mainly remain at the stage of long-chain aliphatic monocarboxylic acids, thereby improving the selectivity of the target product.

[0031] In some embodiments, the supported cobalt-based acidic molecular sieve catalyst of this application includes an acidic molecular sieve and a cobalt active species supported on the acidic molecular sieve, wherein the cobalt active species exists in the form of cobalt single atoms and / or cobalt oxide nanoclusters, wherein the acidic molecular sieve is selected from any one of HY-type molecular sieve, Y-type molecular sieve, β-molecular sieve, and ZSM-5 molecular sieve.

[0032] The acidic molecular sieves selected in this application possess tunable acid sites and a regular microporous framework structure, which can provide abundant loading sites for cobalt active species. Among them, HY-type molecular sieves are preferred due to their larger pore structure, suitable acidity, and good long-chain hydrocarbon adsorption capacity in molecular sieve systems.

[0033] Cobalt active species are loaded onto the surface or within the pores of acidic molecular sieves in the form of cobalt single atoms and / or nanoscale cobalt oxide clusters, forming synergistic catalytic centers with the acid sites of the acidic molecular sieves. In the selective oxidation of polyethylene to C13-C20 long-chain aliphatic monocarboxylic acids, cobalt single atoms and / or cobalt oxide nanoclusters promote the adsorption and activation of oxygen molecules, while the acid sites in the acidic molecular sieve promote the adsorption and polarization of polyolefin segments, and simultaneously effectively disperse the cobalt active species. Thus, the selective oxidative conversion of polyolefins is achieved through the combined effect of these two processes.

[0034] In some embodiments, the supported cobalt-based acidic molecular sieve catalyst of this application is obtained through the following steps A1-A2.

[0035] Step A1: Mix the cobalt salt solution and the acidic molecular sieve, let them stand, and then dry them under vacuum to obtain the cobalt salt impregnated acidic molecular sieve precursor.

[0036] Step A2: After pulverizing the cobalt salt-impregnated acidic molecular sieve precursor, calcination is performed to obtain a supported cobalt-based acidic molecular sieve catalyst.

[0037] In this application, a supported cobalt-based acidic molecular sieve catalyst can be obtained by mixing, drying, pulverizing, and calcining a cobalt salt solution and an acidic molecular sieve. The preparation method is relatively simple, controllable, and can be mass-produced.

[0038] Furthermore, in the acidic molecular sieve of step A1, the Si / Al mass ratio is 3:1-100:1, for example, it can be 3:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or any value within this range, preferably 5:1-80:1, more preferably 5:1.

[0039] Furthermore, in the cobalt salt impregnated acidic molecular sieve precursor in step A1, the Si / Co mass ratio is 10:1-100:1, for example, it can be 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or any value within this range, preferably 20:1, within which the loading of cobalt will not lead to peroxidation.

[0040] In this application, by adjusting the Si / Al mass ratio in the acidic molecular sieve and the Si / Co mass ratio in the cobalt salt-impregnated acidic molecular sieve precursor, the density of acid sites and the cobalt loading in the acidic molecular sieve are controlled, thereby improving the conversion efficiency of polyolefins to long-chain aliphatic monocarboxylic acids and reducing the generation of excessive oxidation products such as short-chain aliphatic dicarboxylic acids and carbon dioxide (CO2).

[0041] Further, in step A1, the cobalt salt is dissolved in water and subjected to ultrasonic treatment to obtain a cobalt salt solution. The ultrasonic treatment time is 1 min to 15 min, for example, 1 min, 5 min, 8 min, 10 min, 15 min, or any value within this range, with a preferred range of 5 min to 10 min. The water can be deionized water or ultrapure water. The cobalt salt can be cobalt nitrate hexahydrate (Co(NO3)2·6H2O).

[0042] Furthermore, the mixing process of the cobalt salt solution and the acidic molecular sieve can be carried out at room temperature using stirring to ensure a more uniform mixture. The stirring time at room temperature is 1-4 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or any value within this range. In some other embodiments, ultrasonic mixing of the cobalt salt solution and the acidic molecular sieve can also be achieved.

[0043] Furthermore, the settling time after mixing is 6h-24h, for example, 6h, 8h, 10h, 15h, 20h, 24h, or any value within this range. This settling process further promotes sufficient contact between the cobalt salt solution and the acidic molecular sieve, achieving adsorption equilibrium.

[0044] Furthermore, during the vacuum drying process, the temperature is 60℃-150℃, for example, 60℃, 80℃, 100℃, 120℃, 150℃, or any value within this range; the drying time is 3h-18h, for example, 3h, 5h, 8h, 10h, 15h, 18h, or any value within this range. Vacuum drying effectively removes residual moisture from the pores of the acidic molecular sieve, preventing cobalt salt agglomeration.

[0045] In this application, cobalt salt is dissolved in water, and ultrasonic treatment is used to dissolve and uniformly disperse the cobalt salt in the water, forming a homogeneous cobalt salt solution. The cobalt salt solution is mixed with an acidic molecular sieve, allowed to stand, and then dried under vacuum to obtain a cobalt salt-impregnated acidic molecular sieve precursor. Through these operations, the cobalt salt is uniformly dispersed on the surface and within the pores of the acidic molecular sieve, laying the foundation for the subsequent formation of cobalt active species uniformly dispersed on the surface and within the pores of the acidic molecular sieve.

[0046] Further, in step A2, the cobalt salt-impregnated acidic molecular sieve precursor obtained in step A1 is ground into a uniform powder, placed in a reactor (such as a muffle furnace), and calcined in air. After cooling to room temperature, a supported cobalt-based acidic molecular sieve catalyst is obtained. Through the above operations, a supported cobalt-based acidic molecular sieve catalyst with large pores, suitable acidity, and excellent adsorption capacity for long-chain aliphatic monocarboxylic acids can be prepared. The calcination temperature is 300℃-700℃, for example, it can be 300℃, 400℃, 500℃, 600℃, 700℃, or any value within this range, preferably 500℃; the calcination time is 1h-6h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, or any value within this range, preferably 2h; the calcination heating rate is 1℃ / min-5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or any value within this range, more preferably 2℃ / min.

[0047] In this application, by calcining the powdered cobalt salt-impregnated acidic molecular sieve precursor, the cobalt salt can be converted into cobalt active species, which are then dispersed on the surface and pore framework of the acidic molecular sieve. By controlling the heating rate, temperature, and time of calcination, the violent escape of moisture and gas from the pores of the acidic molecular sieve can be suppressed, and the aggregation of cobalt active species and dealumination of the acidic molecular sieve can be avoided. This ensures that the supported cobalt-based acidic molecular sieve catalyst has sufficient cobalt active species and acid sites during the catalytic oxidation of polyethylene, and maintains the stability of the acid sites in the supported cobalt-based acidic molecular sieve catalyst.

[0048] For example, taking cobalt salt as cobalt nitrate hexahydrate and HY-type molecular sieve as an example, the method for preparing a supported cobalt-based HY molecular sieve catalyst includes: dissolving 0.01g-0.5g of Co(NO3)2·6H2O in 0.10mL-2.00mL of deionized water, and then sonicating for 1min-15min to form a homogeneous cobalt salt solution. Subsequently, adding 0.1g-10.00g of HY-type molecular sieve to the cobalt salt solution, stirring at room temperature for 1h-4h, allowing the cobalt salt solution to fully impregnate and disperse on the surface and within the pores of the HY-type molecular sieve, and then allowing the resulting mixture to stand at room temperature for 6h-24h. After standing, drying the mixture under vacuum at 60℃-150℃ for 3h-18h to obtain a dried cobalt salt-impregnated HY precursor. After the dried cobalt salt impregnated HY precursor is thoroughly ground into a uniform powder, it is placed in a muffle furnace and calcined in air atmosphere. After cooling to room temperature, the cobalt-supported HY molecular sieve catalyst is obtained, denoted as HY-Co. The calcination temperature is 300℃-700℃, the calcination time is 1h-6h, and the calcination heating rate is 1℃ / min-5℃ / min.

[0049] Furthermore, the mass ratio of waste polyolefin plastic to supported cobalt-based acidic molecular sieve catalyst is 1-100:1, for example, it can be 1:1, 5:1, 10:1, 15:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or any value within this range. The preferred mass ratio of waste polyolefin plastic to supported cobalt-based acidic molecular sieve catalyst is 10:1, for example, 200mg of polyethylene is added to 20mg of supported cobalt-based acidic molecular sieve catalyst.

[0050] Furthermore, in the catalytic selective oxidation of polyethylene to produce C13-C20 long-chain aliphatic monocarboxylic acids, the oxygen pressure is 0.5 MPa-2.0 MPa, for example, 0.5 MPa, 1 MPa, 1.2 MPa, 1.5 MPa, 1.7 MPa, 2.0 MPa, or any value within this range. At this oxygen pressure, sufficient oxidation driving force can be provided, ensuring that the cobalt active species in the supported cobalt-based acidic molecular sieve catalyst effectively activate molecular oxygen. The activated molecular oxygen ( 1 O2 attacks the carbon-hydrogen bonds, removing hydrogen from the polyethylene chain and converting it into a carbon radical. The carbon radical is then oxidized by oxygen (O2) to become an aliphatic hydroperoxide. This aliphatic hydroperoxide undergoes intramolecular hydrogen atom transfer (HAT) to form a carboxylic acid. Furthermore, the oxygen pressure is preferably 1.0 MPa.

[0051] Furthermore, the reaction temperature for the selective oxidation to generate C13-C20 long-chain aliphatic monocarboxylic acids is 110℃-160℃, for example, any value within this range such as 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, etc., with a preferred reaction temperature of 120℃; the reaction time is 1h-12h, for example, 1h, 2h, 4h, 6h, 8h, 9h, 10h, 12h, etc., or any value within this range. In this application, half of the polyethylene can be oxidized into long-chain aliphatic monocarboxylic acids in 1h, and complete oxidation is achieved in 3h. The obtained long-chain aliphatic monocarboxylic acids can then undergo an esterification reaction of 0.5h-3h to obtain biodiesel (such as long-chain aliphatic monocarboxylic acid methyl ester). Therefore, the preferred reaction time for the selective oxidation to generate C13-C20 long-chain aliphatic monocarboxylic acids in this application is 2h-10h, and a more preferred reaction time is 3h. Under these reaction temperatures and conditions, the degree of chain scission in polyolefins can be precisely controlled, suppressing excessive oxidation. Furthermore, the reaction is ensured to be fully completed, efficiently yielding the target product, a long-chain aliphatic monocarboxylic acid of C13-C20. In addition, this application achieves highly selective conversion of waste polyolefins into long-chain aliphatic monocarboxylic acids of C13-C20 under low-temperature conditions (110℃-120℃), reducing energy consumption and stringent requirements on reaction equipment and parameters.

[0052] Furthermore, biodiesel can be obtained by esterification of C13-C20 long-chain aliphatic monocarboxylic acids with alcohols, followed by post-treatment. The alcohols used in the esterification reaction are selected from methanol, ethanol, propanol, and butanol, with methanol being preferred. All of the aforementioned alcohols can undergo esterification with the C13-C20 long-chain aliphatic monocarboxylic acid products to generate the corresponding long-chain fatty acid ester components. The esterification reaction is carried out in the presence of an acid catalyst, preferably sulfuric acid, and more preferably 5 wt% sulfuric acid, which provides suitable acidity, balances the esterification reaction efficiency, and suppresses side reactions. The esterification reaction temperature is 60℃-80℃, for example, 60℃, 70℃, 80℃, or any value within this range, with 70℃ being preferred. The esterification reaction time is 1h-3h, for example, 1h, 2h, 3h, or any value within this range, with 2h being preferred. Furthermore, after the esterification reaction is completed, post-processing is required to obtain biodiesel. This post-processing includes extraction, washing, and purification. These operations can remove residual catalysts and acidic impurities from the biodiesel components, ensuring the purity and stability of the product.

[0053] Furthermore, waste polyolefin plastics can exist in the form of polyolefin fabrics, polyolefin films, polyolefin bottles, polyolefin powders, polyolefin gloves, etc. The waste polyolefin plastics used in this application are made of polyethylene, or are mixed plastics formed by blending polyethylene and polypropylene, wherein the polyethylene includes at least one of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). Furthermore, polyethylene plastics can exist in any form of polyethylene fabrics, polyethylene bags, polyethylene films, polyethylene bottles, polyethylene powders, and polyethylene gloves. The waste polyolefin plastics used in this application can fully melt at a temperature of 110-160℃. The method for catalytically oxidizing polyethylene to prepare biodiesel in this application has good adaptability to different types and / or forms of polyethylene, and can achieve the directional oxidative conversion of various polyolefin waste plastics, demonstrating process stability and universality.

[0054] In summary, the method for catalytic oxidation of polyethylene to prepare biodiesel in this application achieves the selective conversion of waste polyolefin plastics into C13-C20 long-chain aliphatic monocarboxylic acids and biodiesel. It improves the reaction mildness, product orientation, and fuel compatibility of the waste polyolefin plastic resource recycling process. It solves the problems of harsh reaction conditions, strong dependence on hydrogen or precious metals, complex product composition, cumbersome post-processing procedures, and insufficient controllability of target fuel components in the existing polyolefin plastic fuel utilization process. It provides different technical solutions for the recycling of waste polyolefin plastics and the preparation of biodiesel.

[0055] As a second aspect of this application, a biodiesel is provided, which is prepared by the above-described method of catalytic oxidation of polyethylene to produce biodiesel.

[0056] In this application, waste polyolefin plastics (mainly polyethylene) are selectively oxidized using the aforementioned supported cobalt-based acidic molecular sieve as a catalyst to convert the carbon chains in the polyolefins into carboxylic acid products, primarily C13-C20 long-chain aliphatic monocarboxylic acids. After esterification and post-treatment, these carboxylic acid products yield corresponding long-chain fatty acid ester biodiesel components. This application achieves the resource conversion of polyolefins (such as polyethylene) into long-chain aliphatic monocarboxylic acids into biodiesel. This conversion pathway differs from traditional pyrolysis for biodiesel production or hydrocracking for gasoline production. Instead, it introduces carboxylic acid functionality through oxidation, directly converting polyolefins into long-chain aliphatic monocarboxylic acid intermediates suitable for biodiesel preparation. The resulting biodiesel has a cetane number of 43.9 and a cold filter plugging point of 1 ± 0.1 °C, indicating good ignition performance and good flowability. After blending with diesel fuel, it can be used in vehicles, generators, and other equipment.

[0057] To further illustrate this application, the method for preparing biodiesel by catalytic polyethylene oxidation and the biodiesel provided in this application are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of this application.

[0058] 1. Preparation of supported cobalt-based acidic molecular sieve catalysts with different Si / Co mass ratios

[0059] Example 1

[0060] The preparation of supported cobalt-based acidic molecular sieve catalysts includes steps B1-B3.

[0061] Step B1: Weigh 0.23g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 1.00mL of deionized water. Sonicate the solution for 5min to ensure complete dissolution and form a homogeneous cobalt salt solution.

[0062] Step B2: Add 1.00 g of HY-type molecular sieve (Si / Al mass ratio 5:1, Si / Co mass ratio 20:1) to the cobalt salt solution obtained in Step B1, and stir at room temperature for 2 h to allow the cobalt salt solution to fully impregnate and disperse on the surface and within the pores of the HY-type molecular sieve. Then, let the resulting mixture stand overnight at room temperature. After standing, dry the resulting mixture under vacuum at 100℃ for 12 h to obtain the cobalt salt-impregnated acidic molecular sieve precursor.

[0063] Step B3: The cobalt salt-impregnated acidic molecular sieve precursor obtained in Step B2 is thoroughly ground into a uniform powder, then placed in a muffle furnace and calcined in air atmosphere at a temperature of 500℃ for 2 hours at a heating rate of 2℃ / min. After cooling to room temperature, a supported cobalt-based acidic molecular sieve catalyst, denoted as HY, is obtained. 5:1 -Co 20:1 .

[0064] Example 2

[0065] Supported cobalt-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that the amount of cobalt nitrate hexahydrate added was adjusted to achieve a Si / Co mass ratio of 10:1. The resulting supported cobalt-based acidic molecular sieve catalyst is denoted as HY. 5:1 -Co 10:1 .

[0066] Example 3

[0067] Supported cobalt-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that the amount of cobalt nitrate hexahydrate added was adjusted to achieve a Si / Co mass ratio of 50:1. The resulting supported cobalt-based acidic molecular sieve catalyst is denoted as HY. 5:1 -Co 50:1 .

[0068] Example 4

[0069] Supported cobalt-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that the amount of cobalt nitrate hexahydrate added was adjusted to achieve a Si / Co mass ratio of 100:1. The resulting supported cobalt-based acidic molecular sieve catalyst is denoted as HY. 5:1 -Co 100:1 .

[0070] 2. Preparation of supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios

[0071] Example 5

[0072] The supported cobalt-based acidic molecular sieve catalyst was prepared using the same method as in Example 1, except that the Si / Al mass ratio in the HY-type molecular sieve was 30:1. The resulting supported cobalt-based acidic molecular sieve catalyst is denoted as HY. 30:1 -Co 20:1 .

[0073] Example 6

[0074] The supported cobalt-based acidic molecular sieve catalyst was prepared using the same method as in Example 1, except that the Si / Al mass ratio of the HY-type molecular sieve was 60:1. The resulting supported cobalt-based acidic molecular sieve catalyst is denoted as HY.60:1 -Co 20:1 .

[0075] Example 7

[0076] Supported cobalt-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that the Si / Al mass ratio of the HY-type molecular sieve was 80:1. The resulting supported cobalt-based acidic molecular sieve catalyst was denoted as HY. 80:1 -Co 20:1 .

[0077] 3. Preparation of supported metal-based acidic molecular sieve catalysts with different metals

[0078] Example 8

[0079] Supported transition metal-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that cobalt nitrate hexahydrate was replaced with an equal mass of manganese nitrate tetrahydrate (Mn(NO3)2·4H2O), and the metal loading was adjusted so that the Si / Mn mass ratio was 20:1. The resulting supported manganese-based acidic molecular sieve catalyst was denoted as HY. 5:1 -Mn 20:1 .

[0080] Example 9

[0081] Supported transition metal-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that cobalt nitrate hexahydrate was replaced with ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and the metal loading was adjusted to a Si / Fe mass ratio of 20:1. The resulting supported iron-based acidic molecular sieve catalyst was designated HY. 5:1 -Fe 20:1 .

[0082] Example 10

[0083] Supported transition metal-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that cobalt nitrate hexahydrate was replaced with nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and the metal loading was adjusted so that the Si / Ni mass ratio was 20:1. The resulting supported nickel-based acidic molecular sieve catalyst was designated HY. 5:1 -Ni 20:1 .

[0084] Example 11

[0085] Supported transition metal-based acidic molecular sieve catalysts were prepared using the same method as in Example 1, except that cobalt nitrate hexahydrate was replaced with copper nitrate trihydrate (Cu(NO3)2·3H2O), and the metal loading was adjusted to a Si / Cu mass ratio of 20:1. The resulting supported copper-based acidic molecular sieve catalyst was designated HY. 5:1 -Cu 20:1 .

[0086] The supported cobalt-based acidic molecular sieve catalyst prepared in Example 1 was characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and energy dispersive spectroscopy (EDS). Specific characterization results are as follows: Figure 2 As shown.

[0087] Figure 2 The images shown are characterization diagrams of the supported cobalt-based acidic molecular sieve catalyst in Example 1 of this application. In the diagram, a is a SEM image of the supported cobalt-based acidic molecular sieve catalyst, b is an HRTEM image of the supported cobalt-based acidic molecular sieve catalyst, c is an elemental distribution diagram and high-angle annular dark-field imaging (HAADF) image of b, and d is a lattice spacing diagram of the supported cobalt-based acidic molecular sieve catalyst.

[0088] like Figure 2 As shown in a, the supported cobalt-based acidic molecular sieve catalyst prepared in Example 1 retains the typical bulk or polyhedral crystal morphology of HY-type molecular sieves. Further, as... Figure 2 As shown in Figure bd, HRTEM (high-resolution transmission electron microscopy) and energy dispersive spectroscopy results show that cobalt active species are uniformly dispersed on the surface and in the pore structure of the HY-type molecular sieve, and no obvious large cobalt particles or agglomerates were observed, indicating that the cobalt active species can be stably loaded and highly dispersed on the HY-type molecular sieve framework.

[0089] The pore size and specific surface area of ​​the supported cobalt-based acidic molecular sieve catalysts prepared in Examples 1 and 5-7 were tested using a Beta-Touch (BET) surface area and porosity analyzer. Specific test results are as follows: Figure 3 As shown.

[0090] Figure 3 This is a diagram showing the specific surface area and average pore size distribution of supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios according to this application.

[0091] like Figure 3 The N2 adsorption-desorption results showed that the supported cobalt-based acidic molecular sieve catalysts prepared using HY-type molecular sieves with different Si / Al mass ratios all maintained an average pore size of around 2 nm, indicating that the differences in catalytic performance of the supported cobalt-based acidic molecular sieve catalysts were not caused by pore collapse or blockage. Furthermore, from... Figure 3It can also be seen that the specific surface area of ​​the supported cobalt-based acidic molecular sieve catalysts in Examples 1 and 5-7 is 500-700 m². 2 / g, wherein the specific surface area of ​​Examples 5-7 is slightly higher than that of Example 1. This is because different Si / Al mass ratios cause changes in the aluminum content and defect structure of the HY molecular sieve framework, thereby affecting its pore structure parameters and specific surface area.

[0092] Furthermore, the elemental valence states of the supported cobalt-based acidic molecular sieve catalysts prepared in Examples 1 and 5-7 were analyzed using X-ray photoelectron spectroscopy (XPS). Specific test results are as follows: Figure 4 As shown.

[0093] Figure 4 The above are X-ray photoelectron spectroscopy (XPS) spectra of the supported cobalt-based acidic molecular sieve catalysts in Examples 1, 5-7 of this application.

[0094] like Figure 4 As shown, XPS results indicate that HY-type molecular sieves with different Si / Al mass ratios (i.e., different acid densities) can modulate the electronic structure of cobalt active species. In HY-type molecular sieves with high acid site density... 5:1 -Co 20:1 In the catalyst, Co 2+ The presence of Co as the primary active species indicates that the acidic environment of the HY-type molecular sieve is conducive to the stability of Co. 2+ Active site.

[0095] Using X-ray diffraction (XRD) to examine HY 5:1 The crystal phases of the supported cobalt-based acidic molecular sieve catalysts prepared in Examples 1-7 (i.e., pure HY type molecular sieve) were analyzed, and the specific test results are as follows: Figure 5 As shown.

[0096] Figure 5 The images show X-ray diffraction (XRD) patterns of different supported cobalt-based acidic molecular sieve catalysts in this application. In particular, a is the XRD pattern of different supported cobalt-based acidic molecular sieve catalysts in Examples 1-4, and b is the XRD pattern of different supported cobalt-based acidic molecular sieve catalysts in Examples 1 and 5-7.

[0097] like Figure 5As shown, supported cobalt-based acidic molecular sieve catalysts with different cobalt loadings and different Si / Al mass ratios all maintain the FAU (octahedral zeolite) framework structure of HY molecular sieve. The characteristic diffraction peaks at 2θ=6.2°, 10.2° and 11.9° correspond to the (111), (220) and (311) crystal planes of the FAU structure, respectively, indicating that the cobalt active species did not destroy the main structure of the HY molecular sieve during the loading and calcination process.

[0098] Furthermore, 1 mg of the supported cobalt-based acidic molecular sieve catalyst from Examples 1-4 was digested in 1 mL of sulfuric acid and 2 mL of nitric acid at 120 °C using a microwave digester, and then brought to a final volume of 10 mL. The Co content was detected using ICP-OES (inductively coupled plasma optical emission spectrometry). The Co loading of the supported cobalt-based acidic molecular sieve catalyst is shown in Table 1 below.

[0099] Table 1. ICP-OES test results of digestion leachates of supported cobalt-based acidic molecular sieves (1 mg / 10 mL) with different Si / Co mass ratios.

[0100]

[0101] Furthermore, the catalysts of Examples 1 and 5-7 were subjected to pyridine infrared spectroscopy, and the specific test results are as follows: Figure 6 As shown.

[0102] Figure 6 The images show the infrared test results of the pyridine catalysts in Examples 1 and 5-7 of this application.

[0103] like Figure 6 The pyridine infrared results show that reducing the Si / Al mass ratio in the HY-type molecular sieve can increase the acid site density.

[0104] In summary, the highly dispersed cobalt active species in the supported cobalt-based acidic molecular sieve catalyst form a synergistic catalytic interface with the acid sites in the HY type, which can promote the activation of polyethylene segments and oxygen, thereby driving the selective conversion of polyethylene to long-chain aliphatic monocarboxylic acids and providing a suitable precursor for subsequent esterification to produce biodiesel.

[0105] 4. Catalytic oxidation of polyethylene to biodiesel using supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios.

[0106] Application Example 1

[0107] The supported cobalt-based acidic molecular sieve prepared in Example 1 above was used as a catalyst for the catalytic oxidation of polyethylene to prepare biodiesel. The specific method for preparing biodiesel includes the following steps C1-C3.

[0108] Step C1: Mix polyethylene (200 mg) powder with a supported cobalt-based acidic molecular sieve catalyst (20 mg, HY) 5:1 -Co 20:1 The mixture was placed in a 30mL stainless steel high-pressure reactor after being mixed at a mass ratio of 10:1. After alternating oxygen / vacuum replacement, 1.0MPa oxygen was introduced, and the selective oxidation reaction was carried out at 120℃ and 200rpm for 3h.

[0109] Step C2: The product from the reaction in Step C1 is extracted with methanol and the supported cobalt-based acidic molecular sieve catalyst is removed by centrifugation. The resulting aliphatic carboxylic acid product is further esterified with methanol to obtain the corresponding aliphatic carboxylic acid methyl ester. The esterification reaction is carried out in a methanol solution containing 5 wt% sulfuric acid at a temperature of 70 °C for 2 h.

[0110] Step C3: The aliphatic carboxylic acid methyl ester product obtained in step C2 is extracted, washed and purified to obtain biodiesel components.

[0111] Application Example 2

[0112] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 2 was used. 5:1 -Co 10:1 ).

[0113] Application Example 3

[0114] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 3 was used. 5:1 -Co 50:1 ).

[0115] Application Example 4

[0116] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 4 was used. 5:1 -Co 100:1 ).

[0117] Application Example 5

[0118] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 5 was used. 30:1 -Co 20:1 ).

[0119] Application Example 6

[0120] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 6 was used. 60:1 -Co 20:1 ).

[0121] Application Example 7

[0122] Biodiesel was prepared using the same method as in Application Example 1, except that the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 7 was used. 80:1 -Co 20:1 ).

[0123] Comparative Application Example 1

[0124] Biodiesel was prepared using the same method as in Application Example 1, except that HY acid molecular sieve (HY...) was used. 5:1 ( ) as a catalyst.

[0125] Comparative Application Example 2

[0126] Biodiesel was prepared using the same method as in Application Example 1, except that cobalt oxide (Co3O4) was used as the catalyst.

[0127] The biodiesel components obtained in Example 1 were analyzed using gas chromatography-mass spectrometry (GC-MS), and the specific test results are as follows: Figure 7 As shown.

[0128] Figure 7 This is a compositional distribution diagram of biodiesel in Application Example 1 of this application.

[0129] like Figure 7 As shown, the supported cobalt-based acidic molecular sieve catalyst (HY) from Example 1 was used. 5:1 -Co 20:1The carboxylic acid products obtained from the selective oxidation of polyethylene under catalysis and its esterification with methanol are mainly composed of C13-C20 long-chain aliphatic monocarboxylic acids, including tridecanoic acid (C13), myristic acid (C14), pentadecanoic acid (C15), palmitic acid (C16), heptadecanoic acid (C17), stearic acid (C18), oleic acid (C18), linoleic acid (C18), nonadecanoic acid (C19), and arachidic acid (C20). Among these, C13-C20 long-chain aliphatic monocarboxylic acids account for 51.9% of the total carboxylic acid products (including monocarboxylic acids and dicarboxylic acids). Furthermore, C16-C18 long-chain aliphatic monocarboxylic acids are the main component, with a carbon yield of 50.6%. These C16 and C18 long-chain aliphatic monocarboxylic acids have carbon chain lengths matching those of diesel fractions and can be used as precursors for biodiesel production. The carbon yield represents the percentage of the molar amount of carbon in the target product relative to the initial molar amount of carbon in the raw polyethylene. For example, in 200 mg of PE (0.014 mol of carbon (C)), 0.0077 mol of carbon (C) is converted into monocarboxylic acid.

[0130] The effects of supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios on the catalytic oxidation of polyethylene to biodiesel were further investigated. Specific test results are as follows: Figure 8 As shown.

[0131] Figure 8 This diagram shows the solid conversion rate and carbon yield of the resulting carboxylic acid products when using supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios in the catalysis of polyethylene.

[0132] like Figure 8 As shown, supported cobalt-based acidic molecular sieve catalysts with different Si / Al mass ratios exhibit significant catalytic effects on polyethylene oxidation. Specifically, reducing the Si / Al mass ratio of the HY-type molecular sieve increases the acid site density, and this increase is positively correlated with polyethylene conversion and the yield of carboxylic acid products.

[0133] Under a fixed cobalt loading (i.e., a Si / Co mass ratio of 20:1), as the acid site density in the HY-type molecular sieve increases, the solid conversion rate of polyethylene increases from 36.3% (HY in Example 7). 80:1 -Co 20:1 (catalyst) to increase to complete conversion (HY in Example 1) 5:1 -Co 20:1 catalyst).

[0134] Supported cobalt-based acidic molecular sieve catalysts with higher acid site density are more conducive to the formation of C13-C20 long-chain aliphatic monocarboxylic acid products. For example... Figure 8As shown, the carbon yield of the C13-C20 long-chain aliphatic monocarboxylic acid products increased from 20.2% (HY in Example 5). 30:1 -Co 20:1 The catalyst content was increased to 51.9% (HY in Example 1). 5:1 -Co 20:1 (catalysts), of which C16-C18 long-chain aliphatic monocarboxylic acids account for 50.6%.

[0135] The above results indicate that the Si / Al mass ratio in HY-type molecular sieves is a key parameter affecting the "polyethylene-long-chain aliphatic monocarboxylic acid-biodiesel" route, and a lower Si / Al mass ratio is beneficial to promoting the selective conversion of polyethylene to long-chain aliphatic monocarboxylic acid precursors.

[0136] The effects of supported cobalt-based acidic molecular sieve catalysts with different Si / Co mass ratios on the catalytic oxidation of polyethylene to biodiesel were further investigated. Specific test results are as follows: Figure 9 As shown.

[0137] Figure 9 This diagram shows the solid conversion rate and carbon yield of the resulting carboxylic acid products when using supported cobalt-based acidic molecular sieve catalysts with different Si / Co mass ratios in the catalysis of polyethylene. Figure 10 The graphs show the carbon yield of carbon dioxide when catalyzing polyethylene using cobalt-based acidic molecular sieve catalysts with different supported types. In the graphs, a represents the carbon yield of carbon dioxide at different Si / Al mass ratios, and b represents the carbon yield of carbon dioxide at different Si / Co mass ratios.

[0138] like Figures 9-10 As shown, with increasing cobalt loading, the solid conversion rate of polyethylene and the total carbon yield of monocarboxylic and dicarboxylic acid products gradually increase. At the same Si / Al mass ratio, when the Si / Co mass ratio is 20:1 (HY in Example 1), 5:1 -Co 20:1 When the catalyst is used, polyethylene can achieve complete solid-state conversion within 3 hours. The carbon yield of dicarboxylic acid increases from 28.2% (HY in Example 4). 5:1 -Co 100:1 The catalyst content was increased to 91.1% (HY in Example 1). 5:1 -Co 20:1 Catalyst); the carbon yield of carbon dioxide increased from 4.6% (HY in Example 4). 5:1 -Co 100:1 The catalyst content was increased to 6.8% (HY in Example 1). 5:1 -Co 20:1(Catalyst). At the same Si / Co mass ratio, the carbon yield of carbon dioxide also increased as the Si / Al mass ratio increased from 80:1 to 5:1. Further increasing the cobalt loading, i.e., increasing the Si / Co mass ratio (e.g., from 20:1 to 10:1), did not further improve the solids conversion of polyethylene, but the conversion of monocarboxylic acids to dicarboxylic acids and carbon dioxide occurred, indicating that excessively high cobalt loading enhances deep oxidation (e.g., catalyst). Figure 9 , Figure 10 (As shown).

[0139] Thus, the above results indicate that supported cobalt-based molecular sieve catalysts with an appropriate Si / Co mass ratio are beneficial for the directional conversion of polyethylene to long-chain aliphatic monocarboxylic acid intermediates. Among them, Example 1, as a preferred supported cobalt-based molecular sieve catalyst, can effectively serve the fuel conversion route of "polyethylene-long-chain aliphatic monocarboxylic acid-biodiesel".

[0140] Furthermore, the biodiesel prepared according to Example 1 was tested for ignition performance and low-temperature flow properties. The test results are as follows: Figure 11 As shown in the figure. Ignition performance was primarily evaluated using cetane number. Oil samples were filtered through a 0.45 μm polytetrafluoroethylene (PTFE) membrane to remove impurities, and after settling to remove air bubbles, they were used as pretreated samples for subsequent testing. During testing, the pretreated oil was kept at a constant temperature of 20±0.25℃, and its density at 20℃ was measured. The 50% distillation temperature was obtained through distillation testing, and the cetane number was calculated. Low-temperature flow properties were evaluated using cold filter plugging point (CPP). The CPP of common palm oil biodiesel is around 10℃. During testing, the filtered oil sample was placed in a CPP testing device, and a constant vacuum was applied during cooling. The temperature at which filtration was obstructed due to wax crystal precipitation was recorded.

[0141] Figure 11 The figure shows the ignition and low-temperature flow performance test results of biodiesel in Application Example 1 of this application.

[0142] like Figure 11 As shown, the cetane number of the biodiesel in Application Example 1 of this application is 43.9, indicating that it has good ignition performance. The cold filter plugging point is 0.9℃, indicating that it still has good fluidity under near-freezing conditions, and its low-temperature performance is superior to commercial biodiesel (Hubei Maidehao Biotechnology Co., Ltd., CAS No.: 67784-80-9, active ingredient content 99%, 25kg). Therefore, the long-chain aliphatic monocarboxylic acid product obtained in this application can be esterified to form biodiesel with fuel application potential, realizing the directional conversion of polyethylene waste plastics into liquid fuels.

[0143] Furthermore, using the supported cobalt-based acidic molecular sieve from Example 1 as a catalyst, and different waste polyolefin plastics as raw materials, the effect of the catalytic system of this application on the catalytic oxidation of different waste polyolefin plastics to achieve resource utilization was investigated, as detailed in Application Examples 8-14 below.

[0144] Application Example 8

[0145] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was high-density polyethylene (HDPE) powder (Maclean, CAS: 9002-88-4, melt flow index (MFI): 12 g / 10 min).

[0146] Application Example 9

[0147] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was replaced with purchased polyethylene bags.

[0148] Application Example 10

[0149] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was replaced with purchased polyethylene film.

[0150] Application Example 11

[0151] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was replaced with purchased polyethylene gloves.

[0152] Application Example 12

[0153] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was replaced with purchased polyethylene bottles.

[0154] Application Example 13

[0155] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was replaced with purchased polyethylene fabric.

[0156] Application Example 14

[0157] Biodiesel was prepared using the same method as in Application Example 1, except that the waste polyolefin plastic was a mixed plastic formed by melt blending polyethylene (PE) and polypropylene (PP).

[0158] Figure 12 This is a radar diagram showing the oxidation and recycling performance of the supported cobalt-based acidic molecular sieve catalyst for different waste polyolefin plastics in Example 1 of this application.

[0159] like Figure 12As shown, the supported cobalt-based acidic molecular sieve catalyst of this application (Example 1) exhibits good catalytic oxidation and recycling effects on various waste plastics containing polyethylene. Although different commercial plastic products differ in molecular weight, morphology, and additive composition, and the presence of additives such as antioxidants may compete for and consume active oxygen species, leading to certain changes in product distribution, the overall carboxylic acid conversion rate and carboxylic acid yield of various commercial polyethylene plastics after oxidation treatment remain above 70%, and the products are still mainly long-chain aliphatic monocarboxylic acids.

[0160] Figure 12 The results show that the supported cobalt-based acidic molecular sieve catalyst of this application has good raw material adaptability and additive tolerance to waste polyethylene products, and can convert waste polyethylene plastics such as plastic bags, films, gloves, and bottles into biodiesel precursors such as long-chain aliphatic monocarboxylic acids. At the same time, the catalytic system of this application can also treat PE / PP mixed plastics, indicating that the supported cobalt-based acidic molecular sieve catalyst of this application has the application potential to convert mixed polyolefin waste plastics into high-value aliphatic fuel precursors.

[0161] Comparative Application Example 3

[0162] Biodiesel was prepared using the same method as in Application Example 1, except that different metal-supported metal-based acidic molecular sieve catalysts were used in Examples 8-11.

[0163] Figure 13 This is a graph showing the distribution of solid conversion rates of carboxylic acid products obtained by supporting metal-based acidic molecular sieve catalysts of different metals in this application when catalyzing polyethylene.

[0164] like Figure 13 As shown, under the same reaction conditions, HY 5:1 -Mn 20:1 The catalyst can achieve a polyethylene conversion rate of approximately 50% and exhibits some selectivity for long-chain monocarboxylic acids. Supported metal-based acidic molecular sieve catalysts made from different metals such as iron (Fe), nickel (Ni), and copper (Cu) also show certain polyethylene solids conversion rates and product selectivity when catalyzing polyethylene. However, compared to this, the HY catalyst in Example 1 of this application... 5:1 -Co 20:1 The catalyst exhibits higher polyethylene conversion and product selectivity, indicating that cobalt species possess superior catalytic performance in oxygen activation and selective oxidation of polyethylene. Therefore, cobalt is preferred as the supported metal.

[0165] In summary, the supported cobalt-based acidic molecular sieve catalyst of this application and its application in the catalytic oxidation of polyethylene to produce biodiesel, and the biodiesel production, have at least one of the following beneficial effects:

[0166] (1) This application establishes a fuel conversion route of “polyethylene-long-chain aliphatic monocarboxylic acid-biodiesel”, using long-chain aliphatic monocarboxylic acid as a key intermediate, and directly converts waste polyethylene into a precursor suitable for esterification preparation of biodiesel (i.e., long-chain aliphatic monocarboxylic acid) through low-temperature (110-120℃) selective oxidation, avoiding the problems of complex pyrolysis products of traditional waste polyolefin plastics and cumbersome subsequent fractionation and refining steps.

[0167] (2) The reaction conditions for the selective oxidation preparation of biodiesel in this application are mild and do not require high-temperature cracking and high-pressure hydrogenation (2MPa-7MPa). Polyethylene plastic can undergo oxidative conversion under the preferred conditions of 120°C and 1.0MPa oxygen. Compared with the pyrolysis route that usually requires high temperature and the hydrocracking route that depends on hydrogen, it has the advantages of low energy consumption, simple process and milder operating conditions.

[0168] (3) The supported cobalt-based acidic molecular sieve catalyst used in this application promotes the activation and oxidative chain breaking of polyethylene segments by utilizing the synergistic effect of acid sites and cobalt active sites (i.e., cobalt active species) in HY-type acidic molecular sieves. By adjusting the density of acidic sites in the molecular sieve and the dispersion state of cobalt active species, the generation rate of reactive oxygen species and the degree of polyethylene chain breaking are controlled, thus avoiding excessive oxidation process and achieving oxidation depth regulation. This allows the product to preferentially accumulate towards long-chain aliphatic monocarboxylic acids, reducing the generation of short-chain dicarboxylic acids and CO2 and other over-oxidized products.

[0169] (4) The catalytic system of this application exhibits high carboxylic acid yield and good directional selective oxidation of long-chain aliphatic monocarboxylic acid products. In Example 1, HY... 5:1 -Co 20:1 When catalyzed, the carbon yield of all carboxylic acids is 91.1%, and the carbon yield of all monocarboxylic acids is 55.3%. Among them, the carbon yield of C10-C24 is 53.7%, the carbon yield of C13-C20 long-chain aliphatic monocarboxylic acids can reach 51.9%, and the carbon yield of C16-C18 long-chain aliphatic monocarboxylic acids is 50.6%. The resulting products are suitable as feedstocks for biodiesel production.

[0170] (5) The biodiesel obtained in this application has good ignition performance and low temperature flow performance, with a cetane number of up to 43.9 and a cold filter plugging point of up to 0.9℃. It can be used as a blended fuel for biodiesel, realizing the high-value conversion of waste polyethylene plastics into liquid fuel.

[0171] (6) The catalytic system of this application is applicable to different types and forms of waste polyethylene products and PE / PP mixed plastics, and has good raw material adaptability. Under the catalytic action of the preferred supported cobalt-based acidic molecular sieve catalyst, the carboxylic acid carbon yield of various commercial polyethylene plastics can be maintained above 70%, indicating that the catalytic system of this application has a certain tolerance to the differences in the form of waste plastics and common additives, and has the potential for further scale-up application and industrialization.

[0172] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing biodiesel by catalytic oxidation of polyethylene, characterized in that, include: A supported cobalt-based acidic molecular sieve catalyst and waste polyolefin plastics are added to the reactor, oxygen is introduced and pressurized, and selective oxidation is carried out under heating and stirring to generate C13-C20 long-chain aliphatic monocarboxylic acids. The long-chain aliphatic monocarboxylic acid is esterified with an alcohol to convert the long-chain aliphatic monocarboxylic acid into the corresponding long-chain fatty acid ester. After post-processing, biodiesel is obtained. The waste polyolefin plastic is made of polyethylene, or is a blend of polyethylene and polypropylene.

2. The method according to claim 1, characterized in that, The supported cobalt-based acidic molecular sieve catalyst includes: An acidic molecular sieve and cobalt active species supported on the acidic molecular sieve, wherein the cobalt active species exist in the form of cobalt single atoms and / or cobalt oxide nanoclusters; The acidic molecular sieve is selected from any one of HY-type molecular sieve, Y-type molecular sieve, β-molecular sieve, and ZSM-5 molecular sieve.

3. The method according to claim 2, characterized in that, The supported cobalt-based acidic molecular sieve catalyst was obtained by the following method: After mixing and allowing the cobalt salt solution and acidic molecular sieve to stand, the mixture is dried under vacuum to obtain a cobalt salt-impregnated acidic molecular sieve precursor. The cobalt salt-impregnated acidic molecular sieve precursor is pulverized and then calcined to obtain the supported cobalt-based acidic molecular sieve catalyst.

4. The method according to claim 3, characterized in that: In the acidic molecular sieve, the Si / Al mass ratio is 3:1-100:1; In the cobalt salt impregnated acidic molecular sieve precursor, the Si / Co mass ratio is 10:1-100:

1.

5. The method according to claim 3, characterized in that: The settling time is 6h-24h; The vacuum drying temperature is 60℃-150℃, and the vacuum drying time is 3h-18h; The calcination temperature is 300℃-700℃, the calcination time is 1h-6h, and the calcination heating rate is 1℃ / min-5℃ / min.

6. The method according to claim 1, characterized in that: The pressure of the oxygen is 0.5 MPa-2.0 MPa; The mass ratio of the waste polyolefin plastic to the supported cobalt-based acidic molecular sieve catalyst is 1-100:1; The selective oxidation to generate C13-C20 long-chain aliphatic monocarboxylic acids is carried out at a temperature of 110℃-160℃ for a reaction time of 1h-12h.

7. The method according to claim 1, characterized in that: The alcohols are selected from any one of methanol, ethanol, propanol, and butanol; The esterification reaction was carried out in the presence of an acid catalyst; The esterification reaction is carried out at a temperature of 60℃-80℃ for 1h-3h.

8. The method according to claim 1, characterized in that: The polyethylene includes at least one of high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene.

9. A biodiesel, characterized in that, The biodiesel is prepared by the method according to any one of claims 1-8.

10. The biodiesel according to claim 9, characterized in that, The biodiesel has a cetane number of 43.9 and a cold filter plugging point of 1 ± 0.1 °C.

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