Biomass-based rare earth catalyst based on rare earth hyperaccumulator as well as preparation method and application of biomass-based rare earth catalyst

Abstract

The invention belongs to the technical field of solid waste recycling, and particularly relates to a biomass-based rare earth catalyst based on rare earth hyperaccumulators as well as a preparation method and application of the biomass-based rare earth catalyst. According to the method, the high-performance biomass-based rare earth catalyst is prepared from the high-potassium-content rare earth-enriched hyperaccumulation plant biomass by adopting a simple washing pretreatment technology and a high-temperature roasting technology, and most soluble metal potassium is removed by adopting the washing pretreatment technology, so that the specific surface area and acidity of the final biomass-based rare earth catalyst are improved; about 70% of liquid oil products can be obtained in pyrolysis of waste plastics, about 90% of products in the oil have the carbon number distribution of 7-12, the oil can be directly used as gasoline and has excellent application potential in the field of rare earth catalysis, and the preparation method of the catalyst is simple, easy to implement, economical and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization. More specifically, it relates to a biomass-based rare earth catalyst based on rare earth hyperaccumulator plants, its preparation method and application. Background Art

[0002] As the "industrial vitamin", rare earths, with their unique electronic layer structure and catalytic activity, can undertake the function of the main catalyst in the catalytic field or act as a promoter to synergistically enhance the effect. Related applications account for 26% of the total rare earth consumption. However, environmental problems such as soil acidification, heavy metal pollution and vegetation damage caused by large-scale rare earth mining activities are becoming increasingly serious, which has promoted the green remediation technology to become a research hotspot. Among them, phytoremediation technology can effectively absorb and transport rare earths in the soil to the above-ground parts by screening hyperaccumulator plants with special enrichment ability. While realizing the ecological restoration of mining areas, it forms plant biomass resources rich in rare earth elements, providing a sustainable solution for the secondary recovery of rare earth resources.

[0003] Regarding the resource utilization of phytoremediation products, Chinese Patent CN117046464A proposed an innovative method: by mechanically crushing and high-temperature calcining naturally withered rare earth hyperaccumulator plants, a nanoparticle material with a large specific surface area and strong surface acidity was prepared. This material showed significant catalytic cracking activity during the co-pyrolysis with waste plastics, successfully realizing the transformation of plant biomass into high-value functional materials. However, this method has obvious limitations: firstly, it depends on the natural withering process of plants, which requires a growth cycle of up to several months and is difficult to meet the requirements of industrial continuous production; secondly, fresh plants have higher tissue water content and richer metal components compared with withered plants. Direct high-temperature treatment is likely to cause the collapse of the pore structure and the loss of active sites. The existing technical system has not yet broken through the process bottleneck of preparing high-performance materials from freshly picked plants.

[0004] The current technical difficulties are mainly reflected in two aspects: (1) The pyrolysis process control of fresh hyperaccumulator plants is difficult due to their physiological activity, and the traditional calcination process is difficult to effectively retain the porous structure and surface characteristics of the material; (2) The rapid volatilization of water and organic matter in plants is likely to cause structural defects in the material, reducing the specific surface area and catalytic activity. Therefore, developing an efficient resource utilization technology based on freshly picked hyperaccumulator plants has become the key breakthrough point for achieving the dual goals of rare earth-contaminated soil remediation and resource recycling. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and deficiencies of the prior art in lacking a method for preparing high-performance biochar from freshly picked hyperaccumulator plants, and to provide a preparation method of a biomass-based rare earth catalyst based on rare earth hyperaccumulator plants.

[0006] An object of the present invention is to provide a biomass-based rare earth catalyst prepared by the described preparation method.

[0007] Another object of the present invention is to provide the application of the biomass-based rare earth catalyst.

[0008] Another object of the present invention is to provide a plastic catalytic pyrolysis catalyst.

[0009] The above objects of the present invention are achieved by the following technical solutions:

[0010] The present invention protects a preparation method of a biomass-based rare earth catalyst based on rare earth hyperaccumulator plants, comprising the following steps:

[0011] S1. Drying and crushing rare earth hyperaccumulator plant biomass to obtain rare earth hyperaccumulator plant powder;

[0012] S2. Subjecting the rare earth hyperaccumulator plant powder obtained in step S1 to water washing pretreatment with water, filtering, taking the solid matter, drying and pulverizing to obtain a brownish powder;

[0013] S3. Calcining the brownish powder of step S2 at 500-1000 °C and performing post-treatment to obtain the biomass-based rare earth catalyst;

[0014] Wherein, in step S1, the total rare earth enrichment amount of the rare earth hyperaccumulator plant biomass is ≥1000 mg / kg, and the potassium content is ≥3000 mg / kg;

[0015] The temperature of the water washing pretreatment is 40-60 °C.

[0016] The inventor team found that high-performance biochar could not be prepared by the traditional calcination method for freshly picked rare earth hyperaccumulator plants with high potassium content. It was creatively discovered that after removing most of the potassium in the rare earth hyperaccumulator plants by the method of water washing pretreatment of the rare earth hyperaccumulator plants, and then calcining at high temperature, the obtained biomass-based rare earth catalyst had a greatly increased specific surface area. When the obtained biomass-based rare earth catalyst was mixed with polypropylene plastic for catalytic pyrolysis, polypropylene could be completely cracked into liquid oil, wax and gas products, and the content of the oil product was about 70%, improving the practical application value of the waste plastic pyrolysis products.

[0017] Furthermore, in step S1, the rare earth hyperaccumulator plant biomass is freshly picked rare earth hyperaccumulator plants.

[0018] Furthermore, in step S1, the total rare earth enrichment amount of the rare earth hyperaccumulator plant biomass is ≥2000 mg / kg, and the potassium content is ≥3000 mg / kg.

[0019] Further, in step S1, the calcium content of the rare earth hyperaccumulator plant biomass is ≥ 2000 mg / kg, the sodium content is ≥ 190 mg / kg, and the magnesium content is ≥ 400 mg / kg.

[0020] Further, in step S1, the total rare earth enrichment amount of the rare earth hyperaccumulator plant biomass is 2000 - 4000 mg / kg, the potassium content is 3000 - 5000 mg / kg, the calcium content is 2000 - 3000 mg / kg, the sodium content is 190 - 300 mg / kg, and the magnesium content is 400 - 2000 mg / kg.

[0021] Further, in step S1, the rare earth hyperaccumulator plants are freshly picked.

[0022] Preferably, the time for the water washing pretreatment is 2 h.

[0023] Preferably, during the water washing pretreatment, the mixing ratio of the rare earth hyperaccumulator plant powder to water is 3 g : (10 - 100) mL, preferably 3 g : 100 mL.

[0024] Further, in step S1, the rare earth hyperaccumulator plants are at least one of Dicranopteris dichotoma, Phytolacca americana, Blechnum orientale, Stenoloma chusanum, and Pronephrium simplex.

[0025] Further, the water washing pretreatment process is carried out using a magnetic stirrer, and the stirring speed is 600 - 1000 rpm. Preferably, the stirring speed is 800 rpm.

[0026] Preferably, the time for the roasting is 1 - 3 h, more preferably 2 h.

[0027] Further, the heating rate for the roasting is 5 - 15 °C / min, preferably 10 °C / min.

[0028] Further, the atmosphere for the roasting is air.

[0029] Further, in step S1, the particle size after crushing should be < 1 mm; preferably, the particle size after crushing is 0.05 - 0.2 mm.

[0030] Further, the post-treatment includes cooling, grinding, and sieving.

[0031] Specifically, the sieving is carried out using a 100 - mesh sieve to obtain a catalyst with uniform size.

[0032] The present invention also protects the biomass-based rare earth catalyst prepared by the preparation method.

[0033] Further, the particle size of the biomass-based rare earth catalyst is 5 - 10 nm.

[0034] Furthermore, the specific surface area of the biomass-based rare earth catalyst is greater than 200m 2 / g.

[0035] Furthermore, the total rare earth element content in the biomass-based rare earth catalyst is ≥3 wt%.

[0036] Furthermore, the potassium content in the biomass-based rare earth catalyst is less than 2 wt%.

[0037] The present invention also protects the use of the biomass-based rare earth catalyst in the catalytic pyrolysis of plastics.

[0038] Furthermore, the temperature of the catalytic pyrolysis is 350-450° C., and the time is 0.3-1 h.

[0039] Furthermore, the catalytic pyrolysis is carried out under a protective gas atmosphere.

[0040] Furthermore, the rate of the protective gas is 0.05-0.3 mL / min, preferably 0.1 mL / min.

[0041] Furthermore, the protective gas is selected from any one of nitrogen, argon, neon and helium.

[0042] Furthermore, during the catalytic pyrolysis, the mass ratio of the biomass-based rare earth catalyst to the plastic is 1:(5-10), preferably 1:5.

[0043] Furthermore, the catalyst is used as a plastic catalytic pyrolysis catalyst to crack polypropylene plastic into hydrocarbons with a carbon number of 7 to 12.

[0044] Specifically, when the biomass-based rare earth catalyst is mixed with polypropylene plastic for catalytic pyrolysis, the polypropylene can be completely cracked into liquid oil, wax and gas products at 400°C within 30 minutes, and the mass proportion of the liquid oil is greater than 65%.

[0045] Furthermore, in the liquid oil, the mass proportion of hydrocarbons with a carbon number of 7 to 12 is greater than 89%.

[0046] The present invention also protects a plastic catalytic pyrolysis catalyst containing the biomass-based rare earth catalyst.

[0047] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a simple water washing pretreatment technology and a high-temperature calcination technology to prepare a high-performance biomass-based rare earth catalyst from the biomass of hyperaccumulating plants enriched with rare earths with a high potassium content. The water washing pretreatment technology removes most of the soluble metal potassium, thereby improving the specific surface area and acidity of the final biomass-based rare earth catalyst. When pyrolyzing with waste plastics, nearly 70% of liquid oil products can be obtained. About 90% of the product carbon numbers in the oil are distributed between 7 and 12, which can be directly used as gasoline. It has excellent application potential in the field of rare earth catalysis, and the preparation method of this catalyst is simple, easy to implement, economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the biomass-based rare earth catalyst prepared by the present invention based on rare earth hyperaccumulating plants.

[0049] Figure 2 It is a nitrogen adsorption and desorption curve graph of the catalysts obtained in Example 1 of the present invention and Comparative Example 1.

[0050] Figure 3 It is a mass percentage content graph of gas, liquid, wax and unreacted polypropylene obtained by mixing and pyrolyzing the catalysts obtained in Examples 1-2 and Comparative Examples 1-2 of the present invention with polypropylene plastics.

[0051] Figure 4 It is a carbon number distribution graph of the liquid products obtained by mixing and pyrolyzing the catalysts obtained in Examples 1-2 and Comparative Examples 1-2 of the present invention with polypropylene plastics. DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not impose any form of limitation on the present invention. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0053] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0054] Example 1 A biomass-based rare earth catalyst based on the rare earth hyperaccumulating plant Dicranopteris dichotoma D1

[0055] The rare earth hyperaccumulating plant Dicranopteris dichotoma D1 is fresh Dicranopteris dichotoma growing naturally around rare earth mining areas. The total rare earth content in the D1 sample is 2452 mg / kg, and the potassium content is 4659 mg / kg. The preparation method of the catalyst (the preparation process is as Figure 1 shown) and its application in plastic catalytic cracking specifically include the following steps:

[0056] S1. Put the harvested rare earth hyperaccumulator plant Dicranopteris dichotoma D1 into an oven for drying at 60 °C for 48 h, and then mechanically crush it using a shear crusher to obtain uniformly sized powder with a particle size usually of 0.05 - 0.2 mm;

[0057] S2. Take the powder obtained in step S1, mix it evenly with deionized water at 50 °C according to the solid - liquid ratio of 3 g:100 mL, place it on a magnetic stirrer, and stir - wash it for 2 h under the constant - temperature condition of 50 °C. The rotation speed of the magnetic stirrer is 800 rpm. After the washing, perform vacuum filtration, take the solid matter, dry it, grind it, and sieve it to obtain brownish - brown powder;

[0058] S3. Use an inductively coupled plasma optical emission spectrometer (ICP - OES) to measure the contents of potassium, calcium, sodium, and magnesium in the powder samples of S1 and S2. The results are shown in Table 1. The potassium content in the brownish - brown powder after washing is 992 mg / kg. Assuming the mass remains unchanged before and after, the removal rate of metallic potassium is 78.70%, and the removal rates of metallic calcium, sodium, and magnesium are also nearly 50%. This shows that simple washing can remove most of the alkali metals and alkaline earth metals in the biomass. Use an inductively coupled plasma mass spectrometer (ICP - MS) to measure the rare earth contents in the powder samples of S1 and S2. The results are shown in Table 1. The rare earth content after washing has increased. This is because some organic substances are lost during the washing process, resulting in an increase in the rare earth content, indicating that there is no loss of rare earth during the washing pretreatment process, ensuring that the raw materials for preparing the catalyst have more active components;

[0059] S4. Take the brownish - brown powder obtained in step S2, evenly spread it to cover half of the volume of a corundum crucible, place it in a muffle furnace. The muffle furnace first heats up from room temperature to 250 °C for roasting for 30 min and then continues to heat up to 600 °C for roasting for 2 h. The whole process maintains a heating rate of 10 °C / min;

[0060] S5. Wait for the temperature to drop to room temperature, take out the crucible, grind and sieve the high - temperature roasted product (100 - mesh), and then the biomass - based rare earth catalyst can be obtained;

[0061] S6. Perform the treatments of steps S3 to S5 on the powder obtained in S1 without washing pretreatment to obtain the biomass - based rare earth catalyst without washing pretreatment as the control material for Example 1.

[0062] Perform specific surface area and porosity test analysis on the prepared biomass - based rare earth catalyst. The results are as Figure 2 shown. Whether there is washing pretreatment greatly affects the specific surface area and pore size distribution of the material. The specific surface area of the material without washing pretreatment is only 37.86 m 2 / g, and the specific surface area of the material with washing pretreatment is as high as 207.35 m 2 / g, an increase of 4.47 times, and its pore volume also increased from 0.13 cm 3 / g to 0.31 cm 3 / g. A larger pore volume is beneficial to the adsorption and desorption of molecules during the catalytic reaction, thereby improving the activity of the catalyst. The total acidity of the two materials was tested by ammonia temperature-programmed desorption (NH3-TPD), and its content increased from 0.37 mmol / g to 0.43 mmol / g, proving that water washing can appropriately increase the acidity of the final catalyst, which is beneficial to the final catalytic cracking of plastics. The content of each element in the catalyst was tested by ICP-OES and ICP-MS, and the results are shown in Table 2. The contents of metal potassium, calcium, sodium and magnesium all decreased, while the rare earth increased slightly with little change. It can be explained that water washing pretreatment removed the inactive components and effectively retained the active component of rare earth, which is beneficial to subsequent catalytic applications.

[0063] The biomass-based rare earth catalyst prepared in this example was used for plastic pyrolysis experiments: The biomass-based rare earth catalyst and polypropylene plastic were evenly mixed at a mass ratio of 1:5 and placed in a vertical tube furnace. Pyrolysis was carried out for 30 min under a nitrogen atmosphere at 400 °C and 0.1 mL / min. The pyrolysis products included gaseous products, liquid oils or waxes and gas products collected by condensation and circulation respectively, wax products attached to the tube wall, and residual solid substances remaining in the crucible. The specific product distribution is as follows Figure 3 shown. The results show that the biomass-based rare earth catalyst obtained by water washing pretreatment and then high-temperature calcination can completely crack polypropylene plastic at 400 °C for 30 min, and nearly 70% of liquid oil products are obtained. The specific components of the compounds in the liquid products were analyzed by GC-MS, and the results are as follows Figure 4 shown. 90% of the liquid oil products have a carbon number distribution of 7-12, belonging to gasoline components, which have high practical application value. However, the catalyst prepared from rare earth hyperaccumulator plant powder without water washing pretreatment still had 48.9% of polypropylene unreacted under these conditions, proving that water washing pretreatment of rare earth hyperaccumulator plants plays an important role in the catalytic performance of the catalyst.

[0064] Example 2 A biomass-based rare earth catalyst based on the rare earth hyperaccumulator plant Dicranopteris dichotoma D2

[0065] The rare earth hyperaccumulator plant Dicranopteris dichotoma D2 is fresh Dicranopteris dichotoma growing naturally on rare earth tailings. The total rare earth content in the D2 sample is 3805 mg / kg, and the potassium content is 3398 mg / kg. The preparation method of the catalyst and its application in plastic catalytic cracking specifically include the following steps:

[0066] S1. After harvesting, the rare earth hyperaccumulator plant Dicranopteris dichotoma D2 was placed in an oven for drying at 60 °C for 48 h, and then mechanically crushed by a shear crusher to obtain uniformly sized powder with a particle size usually of 0.05-0.2 mm;

[0067] S2. Take the powder obtained in step S1 and uniformly mix it with deionized water at 50 °C in a ratio of 3 g:100 mL. Place it on a magnetic stirrer and perform stirring and water washing at a constant temperature of 50 °C for 2 h. The rotation speed of the magnetic stirrer is 800 rpm. After the water washing is completed, perform vacuum filtration. Take the solid substance, dry it, grind it, and sieve it to obtain a brownish powder;

[0068] S3. Use ICP-OES to measure the contents of potassium, calcium, sodium, and magnesium in the powder samples of S1 and S2. The results are shown in Table 1. The potassium content in the washed powder is 1012 mg / kg. Assuming that the mass remains unchanged before and after, the removal rate of metallic potassium is 70.21%. Part of calcium and magnesium are removed, indicating that simple water washing can remove most of the alkali metals and alkaline earth metals in the biomass. Use ICP-MS to measure the rare earth contents in the powder samples of S1 and S2. The results are shown in Table 1. The rare earth content after water washing has increased. This is because part of the organic matter is lost during the water washing process, resulting in an increase in the rare earth content, indicating that there will be no loss of rare earth during the water washing pretreatment, ensuring that there are more active components in the raw materials used for preparing the catalyst;

[0069] S4. Take the brownish powder obtained in step S2 and evenly spread it over half of the volume of a corundum crucible. Place it in a muffle furnace and first heat it from room temperature to 250 °C and bake for 30 min, then continue to heat it to 600 °C and bake for 2 h. Keep the heating rate at 10 °C / min throughout the process;

[0070] S5. Wait for the temperature to drop to room temperature and take out the crucible. Grind and sieve (100 mesh) the high-temperature calcined product to obtain a biomass-based rare earth catalyst;

[0071] S6. Perform steps S3 to S5 on the powder obtained from S1 without water washing pretreatment to obtain a biomass-based rare earth catalyst without water washing pretreatment as the control material for Example 2. Use ICP-OES and ICP-MS to test the contents of various elements in the catalyst. The results are shown in Table 2. Metallic potassium, calcium, sodium, and magnesium all decrease, while rare earth increases but the change is not significant, indicating that water washing pretreatment removes the non-active components and effectively retains the rare earth, an active component, which is beneficial for subsequent catalytic applications.

[0072] Perform a plastic pyrolysis experiment on the biomass-based rare earth catalyst prepared in this example: Uniformly mix the biomass-based rare earth catalyst and polypropylene plastic in a mass ratio of 1:5 and place them in a vertical tube furnace. Pyrolyze at 400 °C under a nitrogen atmosphere of 0.1 mL / min for 30 min. The pyrolysis products include gaseous products, liquid oil or wax and gas products collected by condensation and circulation respectively, wax products attached to the tube wall, and remaining solid substances still retained in the crucible. The specific product distribution is as follows Figure 3As shown in the figure. The results show that the biomass-based rare earth catalyst obtained by water washing pretreatment and then high-temperature calcination can completely crack polypropylene plastics at 400 °C for 30 minutes, and nearly 70% of liquid oil products are obtained. The specific components of the compounds in the liquid products are analyzed by GC-MS, and the results are as Figure 4 shown. 80% of the carbon number distribution of the liquid oil products is in the range of 7-12, belonging to gasoline components, and has high practical application value. However, 75.5% of the polypropylene remains unreacted under the same catalytic conditions for the catalyst prepared from the rare earth hyperaccumulator plant powder without water washing pretreatment, proving that water washing pretreatment of rare earth hyperaccumulator plants plays an important role in the catalytic performance of the catalyst.

[0073] Comparative Example 1 A biomass-based rare earth catalyst based on the non-rare earth hyperaccumulator plant Dicranopteris dichotoma D3

[0074] The non-rare earth hyperaccumulator plant Dicranopteris dichotoma D3 is fresh Dicranopteris dichotoma growing naturally in non-rare earth mining areas. The total rare earth content in the D3 sample is 78 mg / kg, and the potassium content is 3652 mg / kg. The preparation method of the catalyst and its application in plastic catalytic cracking specifically include the following steps:

[0075] S1. After harvesting, the non-rare earth hyperaccumulator plant Dicranopteris dichotoma D3 is placed in an oven for drying at 60 °C for 48 hours, and then mechanically crushed by a shear crusher to obtain uniformly sized powder with a particle size usually of 0.05-0.2 mm;

[0076] S2. Take the powder obtained in step S1, and uniformly mix it with deionized water at a temperature of 50 °C in a ratio of 3 g:100 mL. Place it on a magnetic stirrer and stir and wash it with water at a constant temperature of 50 °C for 2 hours. The rotation speed of the magnetic stirrer is 800 rpm. After the water washing is completed, vacuum filtration is carried out. Take the solid substance, dry it, grind it, and sieve it to obtain brownish powder;

[0077] S3. Use ICP-OES to measure the contents of potassium, calcium, sodium, and magnesium in the powder samples of S1 and S2. The results are shown in Table 1. The potassium content in the washed brownish powder is 675 mg / kg. Assuming that the mass remains unchanged before and after, the removal rate of metallic potassium is 81.48%. Use ICP-MS to measure the rare earth contents in the powder samples of S1 and S2. The results are shown in Table 2. Even though the rare earth content after water washing has increased, the rare earth content used to prepare the rare earth catalyst in this example is only 150 mg / kg, which can be ignored compared with Examples 1 and 2 and can be considered as the raw material for preparing the catalyst without rare earth doping;

[0078] S4. Take the brownish powder obtained in step S2 and evenly spread it over half of the volume of the corundum crucible. Place it in a muffle furnace, first heat it from room temperature to 250 °C and calcine it for 30 minutes, and then continue to heat it to 600 °C and calcine it for 2 hours. The whole process maintains a heating rate of 10 °C / min;

[0079] S5. Wait for the temperature to drop to room temperature, take out the crucible, grind and sieve (100 mesh) the high-temperature calcination product to obtain the biomass-based catalyst.

[0080] S6. Treat the powder obtained from the anhydrous washing pretreatment S1 with the steps S3 to S5 to obtain the biomass-based catalyst without anhydrous washing pretreatment as the control material for Comparative Example 1.

[0081] The specific surface area and porosity of the prepared biomass-based rare earth catalyst were tested and analyzed. The results are as Figure 2 shown. Whether there is anhydrous washing pretreatment greatly affects the specific surface area and pore size distribution of the material. The specific surface area of the material without anhydrous washing pretreatment is only 32.94 m 2 / g, and the specific surface area of the material with water washing pretreatment is 98.49 m 2 / g, which is nearly doubled. Its pore volume also increases from 0.15 cm 3 / g to 0.23 cm 3 / g. Compared with the Dicranopteris dichotoma biomass rich in rare earth in Example 1, the improvement space of its specific surface area is small, which proves that rare earth has a certain regulatory effect on the structure of the material. A larger pore volume is beneficial to the adsorption and desorption of molecules during the catalytic reaction, thereby improving the activity of the catalyst. The total acidity of the two materials was tested by temperature-programmed desorption of ammonia (NH3-TPD). Its content increased from 0.09 mmol / g to 0.56 mmol / g, which proves that washing away a large amount of potassium can appropriately increase the acidity of the final catalyst, which is beneficial to the final catalytic cracking of plastics. The contents of various elements in the catalyst were tested by ICP-OES and ICP-MS. The results are shown in Table 2. Even after calcination, the content of rare earth is only 0.4 wt%, which is much lower than the rare earth content of the catalysts in Examples 1 and 2, and it can still be considered as a catalyst without rare earth doping.

[0082] The plastic pyrolysis experiment was carried out on the biomass-based rare earth catalyst prepared in this example: The biomass-based rare earth catalyst and polypropylene plastic were uniformly mixed at a mass ratio of 1:5 and placed in a vertical tube furnace. Pyrolysis was carried out for 30 min under a nitrogen atmosphere at 400 °C and 0.1 mL / min. The pyrolysis products include gaseous products, liquid oil or wax and gas products collected by condensation and circulation respectively, wax products attached to the tube wall, and residual solid substances remaining in the crucible. The specific product distribution is as Figure 3 shown. The results show that the biomass-based catalyst obtained by water washing pretreatment and then high-temperature calcination cannot completely crack polypropylene plastic at 400 °C for 30 min. Even though 57% of the liquid product was obtained by condensation, 25% of the polypropylene was still not cracked. The specific components of the compounds in the liquid product were analyzed by GC-MS. The results are as Figure 4As shown, only 51% of the carbon number of the liquid products is distributed between 7 and 12, belonging to gasoline components, and nearly 20% of the liquid products have a carbon number greater than 21, belonging to wax components. It has a poorer catalytic cracking ability than the biomass-based rare earth catalysts prepared from Dicranopteris dichotoma rich in rare earths in Examples 1 and 2, and the products are more complex, proving that rare earth plays an important role in the catalytic cracking of plastics.

[0083] Comparative Example 2 A biomass-based rare earth catalyst based on the rare earth hyperaccumulator Dicranopteris dichotoma D4

[0084] The rare earth hyperaccumulator Dicranopteris dichotoma D4 is the withered Dicranopteris dichotoma growing naturally around the rare earth mining area. The total rare earth content in the D3 sample is 3124 mg / kg, and the potassium content is 616 mg / kg, which is much lower than the potassium content in Example 1, Example 2 and Comparative Example 1. The preparation method of the catalyst and its application in the catalytic cracking of plastics specifically include the following steps:

[0085] S1. Put the harvested Dicranopteris dichotoma D4 without rare earth hyperaccumulation into an oven for drying at 60 °C for 48 h, and then use a shear crusher for mechanical crushing to obtain uniformly sized powder, with a particle size usually of 0.05 - 0.2 mm;

[0086] S2. Take the powder obtained in step S1, and uniformly mix it with deionized water at a temperature of 50 °C in a ratio of 3 g:100 mL. Place it on a magnetic stirrer and stir and wash it for 2 h under the constant temperature condition of 50 °C. The rotation speed of the magnetic stirrer is 800 rpm. After the washing is completed, perform vacuum filtration, and take the solid substance, dry it, grind it, and sieve it to obtain a brownish powder;

[0087] S3. Use ICP-OES and ICP-MS to measure the content of each element in the powder samples of S1 and S2. The results are shown in Table 1. The potassium content in the brownish powder after washing is 675 mg / kg. Assuming that the mass remains unchanged before and after, the removal rate of metallic potassium is 36.46%.

[0088] S4. Take the brownish powder obtained in step S2 and evenly spread it over half of the volume of the corundum crucible. Place it in a muffle furnace and first heat it from room temperature to 250 °C for roasting for 30 min, and then continuously heat it to 600 °C for roasting for 2 h. Keep the heating rate at 10 °C / min throughout the process;

[0089] S5. Wait for the temperature to drop to room temperature and take out the crucible. Grind and sieve the high-temperature roasted product (100 mesh) to obtain the biomass-based catalyst;

[0090] S6. Treat the powder obtained from the water-free washing pretreatment S1 through steps S3 to S5 to obtain a water-free washing pretreated biomass-based catalyst as the control material for Comparative Example 1. Use ICP-OES and ICP-MS to test the content of each element in the catalyst. The results are shown in Table 2. The contents of metals potassium, calcium, sodium, and magnesium all decrease, while the rare earth increases slightly with little change. It can be shown that the water washing pretreatment removes the inactive components and effectively retains the rare earth, which is an active component, and is beneficial for subsequent catalytic applications.

[0091] Carry out a plastic pyrolysis experiment on the biomass-based rare earth catalyst prepared in this example: Uniformly mix the biomass-based rare earth catalyst and polypropylene plastic at a mass ratio of 1:5 and place them in a vertical tube furnace. Pyrolyze for 30 min under a nitrogen atmosphere at 400 °C and 0.1 mL / min. The pyrolysis products include liquid oil or wax and gas products collected separately through condensation circulation of the gaseous products, wax products attached to the tube wall, and residual solid substances remaining in the crucible. The specific product distribution is as Figure 3 shown. Use GC-MS to analyze the specific components of the compounds in the liquid product. The results are as Figure 4 shown. The results show that the biomass-based catalysts obtained by high-temperature roasting of rare earth hyperaccumulator plant biomass with low potassium content after water washing pretreatment can completely crack polypropylene plastic within 30 min at 400 °C. However, when the catalyst obtained after water washing pretreatment is used for cracking, the content of the liquid product decreases, and the content with carbon numbers distributed from 7 to 12 also decreases, indicating that water washing pretreatment is more suitable for rare earth hyperaccumulator plants with high potassium content. That is, using freshly picked rare earth hyperaccumulator plants as raw materials, high-performance catalysts can be obtained by first performing water washing pretreatment and then high-temperature roasting.

[0092] Table 1 Element contents (mg / kg) of biomass powders with or without water washing pretreatment in examples and comparative examples

[0093]

[0094]

[0095] Table 2 Element contents (wt%) of catalysts prepared with or without water washing pretreatment in examples and comparative examples

[0096]

[0097] In summary, after most of the potassium in the rare earth hyperaccumulator plants with high potassium content is removed by the method of washing pretreatment of rare earth hyperaccumulator plants in the present invention, and then the biomass-based rare earth catalyst obtained by high-temperature roasting has a significantly increased specific surface area. When the catalyst described in the present invention is mixed with polypropylene plastic for catalytic pyrolysis, polypropylene can be completely cracked into liquid oil, wax and gas products at 400 °C for 30 minutes, and the content of the oil product is about 70%, effectively reducing the temperature and time required for plastic pyrolysis and improving the practical application value of the pyrolysis products of waste plastics. In addition, the preparation of this material innovatively provides a way for the resource utilization of fresh rare earth hyperaccumulator plants harvested after using phytoremediation technology to repair rare earth tailings, and has broad application prospects in the field of resource utilization of hyperaccumulator plants.

[0098] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a biomass-based rare earth catalyst based on rare earth hyperaccumulator plants, characterized in that, It includes the following steps: S1. Dry and crush the rare earth hyperaccumulator plant biomass to obtain rare earth hyperaccumulator plant powder; S2. Perform water washing pretreatment on the rare earth hyperaccumulator plant powder obtained in step S1, filter, take the solid matter, dry and crush it to obtain brown powder; S3. Calcinate the brown powder in step S2 at 500-1000 °C, and perform post-treatment to obtain the biomass-based rare earth catalyst; Among them, in step S1, the total rare earth enrichment amount of the rare earth hyperaccumulator plant biomass is ≥1000 mg / kg, and the potassium content is ≥3000 mg / kg; The temperature of the water washing pretreatment is 40-60 °C.

2. The preparation method according to claim 1, wherein The time of the water washing pretreatment is 1-3 h.

3. The preparation method according to claim 1, characterized in that, During the water washing pretreatment, the mixing ratio of the rare earth hyperaccumulator plant powder to water is 3 g:(10-100) mL.

4. The preparation method according to claim 1, characterized in that, The calcination time is 1-3 h.

5. The preparation method according to claim 1, characterized in that, The calcination atmosphere is air.

6. The preparation method according to claim 1, characterized in that, The rare earth hyperaccumulator plant is at least one of Dicranopteris dichotoma, Phytolacca americana, Blechnum orientale, Stenoloma chusanum, Pronephrium simplex.

7. The biomass-based rare earth catalyst prepared by the preparation method according to any one of claims 1-6.

8. The application of the biomass-based rare earth catalyst according to claim 7 in the catalytic pyrolysis of plastics.

9. The application according to claim 8, wherein As a catalyst for the catalytic pyrolysis of plastics, the catalyst pyrolyzes polypropylene plastics into hydrocarbons with 7-12 carbon atoms.

10. A plastic catalytic pyrolysis catalyst, characterized in that, Containing the biomass-based rare earth catalyst according to claim 7.

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