Nanoparticles prepared from rare earth hyperaccumulator plants and methods and applications thereof

Abstract

The present application belongs to the technical field of solid waste resource, and particularly relates to a kind of nanoparticles prepared by rare earth hyperaccumulator and its preparation method and application. The present application uses simple mechanical crushing and high temperature calcination technology, directly processes functional materials from rare earth enriched hyperaccumulator biomass, and the prepared material has large specific surface area and strong weak acid acidity. When the material is used for co-pyrolysis with waste plastics, it can effectively catalyze plastic cracking, and the oil yield is as high as 70%. The catalytic effect is much higher than that of commercially available molecular sieve catalyst (ZSM-5), and it has broad application potential in the field of rare earth catalysis. The preparation method of the rare earth-based mesoporous nanoparticle stacking catalyst material is simple and easy to operate, and it is economical and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology. More specifically, it relates to nanoparticles prepared from rare earth hyperaccumulating plants, their preparation method, and their applications. Background Technology

[0002] Rare earth elements and their oxides possess high catalytic activity. They can act not only as primary catalysts but also as catalyst supports or co-catalysts to enhance catalytic performance, particularly their resistance to aging and poisoning. For example, introducing rare earth elements into cracking catalysts significantly improves their activity and stability, substantially increasing the cracking conversion rate of feedstock oil and boosting gasoline and diesel yields. Chinese patent application CN105709755A discloses a biochar catalyst, an iron-carbon catalyst, and their applications. This biochar catalyst uses biochar as a support to load rare earth metal oxides and Fe3O4, significantly improving wastewater treatment efficiency. Rare earth hyperaccumulating plants refer to a class of functional plants capable of rapidly and effectively accumulating rare earth elements within an ecosystem. Cultivating rare earth hyperaccumulating plants is an emerging technology for recovering high-value rare earth metals from polluted soil. While effectively removing soil pollutants, it also allows for the recovery of high-value resources through biomass harvesting.

[0003] For the recovery of rare earth elements from rare earth hyperaccumulating plants, existing technologies generally employ hydrometallurgical techniques to extract target metals from these plants. This involves processes such as biomass ashing, leaching, separation, purification, and refining to obtain target metal products or functional materials from the biomass of hyperaccumulating plants. However, traditional biomass hydrometallurgical techniques have the following drawbacks: (1) Leaching agents such as acids and chelating agents leach out impurity metals along with rare earths simultaneously. This non-selective leaching process poses a significant challenge to subsequent rare earth purification. (2) Due to the presence of impurity metals, the leaching process requires a large amount of leaching agent, resulting in a very low concentration of rare earths in the leachate, ultimately making the subsequent rare earth purification process complex and costly. In summary, the complex processes and high economic costs of hydrometallurgical techniques hinder the industrial application of rare earth plant mining. Therefore, there is an urgent need to provide a method for directly utilizing rare earth hyperaccumulating plants to prepare products. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the defects and shortcomings of existing technologies for extracting target metals from rare earth hyperaccumulating plants, which are complicated and costly. This invention provides a method for preparing nanoparticles from rare earth hyperaccumulating plants that is simple to prepare, low in energy consumption, and low in cost. Furthermore, the obtained nanoparticles have a large specific surface area, high acidity in weak acids, and strong catalytic activity.

[0005] The purpose of this invention is to provide nanoparticles prepared from rare earth hyperaccumulating plants.

[0006] Another objective of this invention is to provide an application of nanoparticles prepared from rare earth hyperaccumulating plants.

[0007] Another objective of this invention is to provide a catalyst for the catalytic pyrolysis of plastics.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A method for preparing nanoparticles from rare earth hyperaccumulating plants specifically includes the following steps:

[0010] S1. Dry and crush the rare earth hyperaccumulating plant biomass to obtain rare earth hyperaccumulating plant powder;

[0011] S2. The rare earth hyper-enriched plant powder obtained in step S1 is calcined at 600-800℃ and then post-treated to obtain nanoparticles. The post-treatment is conventional sieving.

[0012] In step S1, the total rare earth enrichment of the dry weight of the rare earth hyperaccumulating plant biomass is greater than 1000 mg / kg.

[0013] Preferably, the total rare earth enrichment of the plant biomass dry weight is 1000-4000 mg / kg.

[0014] This invention reveals that the catalytic material obtained by directly high-temperature calcining rare earth hyperaccumulating plants using the above method not only has a large specific surface area but also strong weak acidity. When co-pyrolyzed with plastics, it significantly reduces the reaction temperature and time required for plastic pyrolysis, decreases the formation of sticky wax, promotes the generation of high-value low-carbon alkanes and olefins, effectively solves the problem of pyrolysis pipeline blockage, and improves the utilization value of waste plastic pyrolysis products. Furthermore, the preparation of this material provides an innovative method for the treatment, disposal, and resource utilization of rare earth hyperaccumulating plants harvested after phytomining practices, showing broad application prospects in the field of hyperaccumulating plant resource utilization.

[0015] Preferably, in step S1, the rare earth hyperaccumulating plant is at least one of the following: *Dictamnus dasycarpus*, *Phytolacca americana*, *Dryopteris crescentis*, *Dryopteris unifolia*, and *Dryopteris unifolia*.

[0016] Further, in step S1, the particle size after crushing should be <1mm; preferably, the particle size after crushing is 0.05 to 0.2mm.

[0017] Furthermore, in step S2, the roasting time is 1 to 3 hours; preferably, the roasting time is 2 hours.

[0018] Preferably, in step S2, the roasting atmosphere is air.

[0019] In addition, this application also protects the nanoparticles prepared by the method; preferably, the nanoparticles have a particle size of 5 to 10 nm.

[0020] In addition, this application also provides the application of the nanoparticles in plastic catalytic pyrolysis catalysts.

[0021] Specifically, the nanoparticles serve as a catalyst for the catalytic pyrolysis of plastics, breaking down polypropylene plastics into hydrocarbons containing 4 to 16 carbon atoms, such as gasoline or diesel.

[0022] Furthermore, a plastic catalytic pyrolysis catalyst contains the nanoparticles described in this application.

[0023] The present invention has the following beneficial effects:

[0024] 1. This invention utilizes a simple high-temperature calcination method to transform rare earth hyperaccumulating plants into catalysts that can accelerate the pyrolysis of plastics, providing a new method for the resource utilization of rare earth hyperaccumulating plants.

[0025] 2. The process of preparing catalysts directly from rare earth hyper-enriched plant biomass is simple and easy to implement, with low energy consumption and wide availability of raw materials, enabling large-scale application.

[0026] 3. The material prepared by this invention can significantly reduce the reaction temperature and reaction time in the catalytic pyrolysis of waste plastics, reduce the generation of sticky wax, and promote the production of high-value gasoline and diesel, and its effect is better than that of commercially available ZSM-5 molecular sieve catalysts. Attached Figure Description

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of the nanoparticle catalytic material prepared in Example 1.

[0028] Figure 2 The image shows the elemental distribution of the nanoparticle catalytic material prepared in Example 1. C, O, Al, Si, La, and Ce represent carbon, oxygen, aluminum, silicon, rare earth lanthanum, and cerium, respectively.

[0029] Figure 3 Thermogravimetric analysis results are shown in the graphs of the nanoparticle catalytic materials prepared in Examples 1, Comparative Examples 1 and 2, and the commercially available molecular sieve catalyst (ZSM-5) mixed with waste plastic (polypropylene, 100 mesh).

[0030] Figure 4 The distribution diagram of the catalytic pyrolysis products after uniformly mixing the nanoparticle catalytic materials prepared in Examples 1, Comparative Examples 1 and 2, and the commercially available molecular sieve catalyst (ZSM-5) with waste plastic (polypropylene, 100 mesh) is shown. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0032] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0033] Example 1: Preparation of rare earth-based nanoparticle catalytic materials using rare earth-enriched dung beetle.

[0034] The rare-earth-based nanoparticle catalytic material prepared using rare-earth super-enriched dung beetle specifically includes the following steps:

[0035] S1. The rare earth content of the plant *Dictamnus dasycarpus* (4.00 mg / g) is dried and then mechanically crushed using a shear crusher to obtain uniform powder with a particle size of 0.05–0.2 mm.

[0036] S2. Take the powder obtained in step S1, spread it evenly in a crucible, and place it in a muffle furnace to be calcined at 600℃ for 2 hours. The heating rate of the muffle furnace is 10℃ / min.

[0037] S3. Once the temperature drops below 100℃, remove the crucible and sieve the high-temperature calcined product (100 mesh) to obtain rare earth-based nanoparticle catalytic materials.

[0038] The microstructure of the prepared material was observed using scanning electron microscopy, and the results are as follows: Figure 1 As shown, the material is clearly visible as an irregular shape formed by countless nanoparticles stacked together. Figure 1 The top left corner shows the appearance of the material in this application, which is apricot-colored.

[0039] The prepared material was subjected to elemental distribution analysis, and the results are as follows: Figure 2 As shown, the material contains rare earth elements lanthanum and cerium, as well as carbon, oxygen, aluminum, and silicon.

[0040] Example 2: Preparation of rare earth-based nanoparticle catalytic materials using rare earth hyperenrichment of American pokeweed.

[0041] The rare-earth-based nanoparticle catalytic material prepared using rare-earth hyperenriched American pokeweed specifically includes the following steps:

[0042] S1. Dry the American pokeweed plant with high rare earth content (1.04 mg / g rare earth content), and then mechanically crush it using a shear crusher to obtain uniform powder with a particle size of 0.05-0.2 mm.

[0043] S2. Take the powder obtained in step S1, spread it evenly in a crucible, and place it in a muffle furnace to be calcined at 600℃ for 2 hours. The heating rate of the muffle furnace is 10℃ / min.

[0044] S3. Once the temperature drops below 100℃, remove the crucible and sieve the high-temperature calcined product (100 mesh) to obtain rare earth-based nanoparticle catalytic materials.

[0045] Example 3: Preparation of rare earth-based nanoparticle catalytic materials using rare earth-enriched *Dryopteris crassirhizoma*.

[0046] The rare-earth-based nanoparticle catalytic material prepared using rare-earth hyperenriched American pokeweed specifically includes the following steps:

[0047] S1. Dry the rare earth content of the plant *Acer buergerianum* (2.22 mg / g) and then mechanically crush it using a shear crusher to obtain uniform powder with a particle size of 0.05–0.2 mm.

[0048] S2. Take the powder obtained in step S1, spread it evenly in a crucible, and place it in a muffle furnace to be calcined at 600℃ for 2 hours. The heating rate of the muffle furnace is 10℃ / min.

[0049] S3. Once the temperature drops below 100℃, remove the crucible and sieve the high-temperature calcined product (100 mesh) to obtain rare earth-based nanoparticle catalytic materials.

[0050] Comparative Example 1: Rare Earth-Based Nanoparticle Catalytic Materials Prepared from Dictamnus dasycarpus with Low Rare Earth Content

[0051] The preparation method is the same as in Example 1, except that the rare earth content of the high rare earth plant (4.00 mg / kg) is replaced with the low rare earth content plant (0.449 mg / g).

[0052] Comparative Example 2: Nanoparticle Catalytic Materials Prepared from Wheat Straw

[0053] The preparation method is the same as in Example 1, except that the rare earth content of the Miscanthus plant (3996 mg / kg) was replaced with wheat straw (5.45 mg / kg).

[0054] Experimental Example 1: Rare Earth Metal Content in Different Catalysts

[0055] The rare earth content (dry weight) of the plant raw materials described in Example 1, Comparative Example 1, and Comparative Example 2, and the rare earth content of the three materials obtained after calcination, are shown in Table 1. As shown in the table, the catalytic material obtained after calcination of the high rare earth content *Dictamnus dasycarpus* biomass (4.00 mg / g rare earth content) has a rare earth content of 55.1 mg / g, which is nearly 14 times higher. The contents of lanthanum, cerium, and neodymium increased by an order of magnitude. Since rare earth elements lanthanum and cerium have strong catalytic effects, this material can be called a catalytic material. The material obtained from calcining low rare earth content *Dictamnus dasycarpus* biomass has a relatively low rare earth content of only 12.2 mg / g. The material prepared from wheat straw biomass can be considered approximately free of rare earth elements, as its rare earth content is 47.10 mg / kg.

[0056] Table 1. Rare Earth Content of Plant Biomass and Processed Materials

[0057]

[0058] Example 2: Simultaneous thermal infrared analysis of co-pyrolysis of different catalysts with polypropylene plastic

[0059] Researchers typically use catalysts to catalyze the pyrolysis of plastics to produce the target product, leading to a series of studies on catalysts to promote plastic pyrolysis. Commonly used catalysts include ZSM-5 zeolite molecular sieves and rare-earth modified Y-type zeolite catalysts such as REY. However, these catalysts are expensive, and there is an urgent need to find low-cost catalysts to reduce the economic cost of plastic recycling.

[0060] Materials with different rare earth contents obtained from Examples 1, Comparative Examples 1 and 2, along with a commercially available molecular sieve catalyst (ZSM-5) and polypropylene (PP, 100 mesh), were uniformly mixed in a ball mill at a mass ratio of 1:9 (1800 r / min, 3 min). The mixture was then subjected to thermogravimetric analysis (Thermogravimetry, TG209F1 libra) under a nitrogen atmosphere, with the temperature increased from 30°C to 900°C at a rate of 10°C / min. The differences in weight changes with temperature and time were used to highlight the differences in catalytic pyrolysis of polypropylene mixed with different materials. The experimental results of weight changes with temperature are shown below. Figure 4 As shown.

[0061] from Figure 3It can be seen that the temperature required for pyrolysis of polypropylene plastic in Example 1 is about 300℃, which is much lower than the temperature required for pyrolysis of polypropylene by ZSM-5 molecular sieve (325℃), material of Comparative Example 1 (400℃), and material of Comparative Example 2 (400℃). That is, the catalytic material obtained in Example 1 of this application significantly reduces the initial temperature and reaction time of polypropylene plastic pyrolysis, and the reduction effect is much better than that of commercially available ZSM-5 zeolite molecular sieve, Comparative Example 1, and Comparative Example 2. The preparation cost is much lower than that of ZSM-5, and the raw material, dung beetle, is also widely available. It is easy to implement and low in cost to prepare rare earth-based mesoporous nanoparticle stacked catalytic material according to the steps of Example 1.

[0062] Experimental Example 3: Yield distribution of co-pyrolysis products of different materials and polypropylene plastic

[0063] First, using a ball mill, the three materials obtained in Example 1, Comparative Example 1, and Comparative Example 2, along with a commercially available ZSM-5 molecular sieve catalyst and polypropylene plastic, were uniformly mixed (1800 r / min, 3 min) at a mass ratio of 1:5 (material: polypropylene). Next, the mixture was pyrolyzed for 30 min in a vertical tube furnace connected to nitrogen gas at a temperature of 450°C and a nitrogen flow rate of 0.1 L / min. For each experiment, 1.2 g of the mixture was weighed into a quartz crucible, placed inside the pyrolysis tube, and the pyrolysis apparatus was installed. The vertical tube furnace was positioned above the sample, and air was purged from the furnace using a nitrogen flow rate of 0.3 L / min to ensure the experiment was conducted in an inert nitrogen atmosphere. Once the furnace reached the set temperature of 450°C, it was moved to a suitable position to ensure the sample was centered within the furnace, and pyrolysis began, timed for 30 min, with a nitrogen flow rate of 0.1 L / min. Finally, the condensable gaseous products are stored in a condenser via an ice bath device, and are in the form of liquid products such as oil or wax. The non-condensable gaseous products are collected in a gas bag for subsequent testing, and are in the form of nitrogen, hydrogen, and C1-C4 hydrocarbons. A large portion of the condensed products that adhere to the walls of the pyrolysis tube are wax.

[0064] Experimental results are as follows Figure 4 As shown in the figure, at 450℃, the oil yield of polypropylene plastic pyrolysis in Example 1 reached 70%, while the oil yield of Comparative Examples 1 and 2 was 0%, and the oil yield of ZSM-5 molecular sieve was approximately 55%. Furthermore, compared to the pyrolysis of pure polypropylene plastic, the addition of the nanoparticle stacked catalyst material obtained in Example 1 (total rare earth content ΣREE>5.5wt%) significantly reduced wax formation, and all products were converted into pale yellow liquid oil products. Commercially available ZSM-5 molecular sieve also reduced wax formation, but its effect was far less than that of the material obtained in Example 1. The co-pyrolysis effect of the plastics obtained by adding the materials from Comparative Examples 1 and 2 was comparable to that of pure plastic pyrolysis, indicating that these two materials had no significant effect on the pyrolysis of polypropylene plastic.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. Use of a rare earth hyperaccumulator plant to prepare nanoparticles for catalytic pyrolysis of plastics, characterized in that, The method for preparing nanoparticles from rare earth hyperaccumulating plants comprises the following steps: S1. drying and crushing the biomass of rare earth hyperaccumulating plants to obtain rare earth hyperaccumulating plant powder; S2. calcining the rare earth hyperaccumulating plant powder obtained in step S1 at 600-800 ℃, and post-treating to obtain nanoparticles; In step S1, the total rare earth enrichment of the rare earth hyperaccumulating plant is greater than 1000 mg / kg; In step S2, the calcination time is 1-3 h; in step S2, the calcination atmosphere is air; The nanoparticles contain lanthanum, cerium, oxygen, aluminum and silicon.

2. Use according to claim 1, characterized in that, In step S1, the rare earth hyperaccumulating plant is at least one of Dicranopteris dichotoma, Phytolacca americana, Hymenophyllum pubescens, Hymenophyllum, and Leptoleonia scolopendrium.

3. Use according to claim 1, characterized in that, In step S1, the particle size after crushing is <1 mm.

4. The use according to claim 1, characterized in that, The particle size of the nanoparticles is 5-10 nm.

5. The use according to claim 1, characterized in that, The nanoparticles are used as a plastic catalytic pyrolysis catalyst to crack polypropylene plastic into hydrocarbons containing 4-16 carbon atoms.

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