An iron-based rare earth catalyst and a preparation method for catalytic cracking of waste plastics

Abstract

The present invention relates to an iron-based rare earth catalyst, in particular to an iron-based rare earth catalyst and a preparation method for catalytic cracking of waste plastics. First, Fe(NO3)3, Co(NO3)2 and M(NO3) are weighed separately. y After adding citric acid, deionized water was added to Fe(NO3)3, Co(NO3)2 and M(NO3) y The catalyst of the present invention is dissolved in water to form a solution, citric acid is added after ultrasonication of the solution, the mixed solution is heated at 55-65 degrees Celsius for 2-4 hours, cooled to room temperature to obtain a gel, and the obtained gel is kept warm in an atmosphere furnace under nitrogen protection to obtain FeCoMO catalyst powder. 1. The catalyst of the present invention has high activity. The catalysts involved in the present invention can remain active for a long time after preparation and do not need to be activated before use. 2. The preparation method is simple and has low energy consumption. The catalyst synthesized by the present invention can achieve a maximum hydrogen production of 68.25 mmoles per gram of plastic using only microwave technology. The overall process is significantly simple. 3. No oily by-products are produced during plastic cracking. The catalyst of the present invention reduces oil production to 0, while the hydrogen production is greatly increased and close to the theoretical value. 4. The prepared catalyst is used for catalytic cracking of a variety of plastics. The final hydrogen production of the catalytic cracking of plastics by the present invention can exceed 62 mmoles per gram of plastic, and the hydrogen conversion rate exceeds 85%.

Description

Technical Field

[0001] The present invention relates to an iron-based rare earth catalyst, in particular to an iron-based rare earth catalyst and a preparation method thereof for catalytic cracking of waste plastics. Background Art

[0002] Plastic products are ubiquitous in our daily lives. Their low cost, corrosion resistance, flexibility, durability, and light weight have led to their widespread use. This, in turn, contributes to the generation of plastic waste. Plastic recycling is a sustainable way to reduce pollution, but the requirement for plastic separation and purification increases operating costs. Secondary processing can recover energy from plastic incineration. However, significant carbon dioxide emissions exacerbate global warming. Furthermore, the majority of plastics still end up in landfills (for example, 23.4% of collected plastics in Europe in 2020). Therefore, how to effectively recycle waste plastics has become a critical issue today.

[0003] As a clean secondary energy carrier, hydrogen has an energy density of up to 142.82 kilojoules per kilogram. It can be converted into electricity and heat with high conversion efficiency and has good application prospects. Therefore, converting waste plastics into hydrogen is a research hotspot today. Because the molecular formulas of olefin polymers are similar, polyethylene is used as an example to calculate its theoretical hydrogen production value. Theoretically, the maximum hydrogen production value produced by polyethylene cracking is 71.4 millimoles per gram of polyethylene, but even if efficient cracking is achieved, it is far from the theoretical value. For example, the literature (nature catalysis, 2020.3: p902–912.DOI: 10.1038 / s41929-020-00518-5) introduces a process for producing hydrogen and carbon nanotubes by microwave-assisted catalytic cracking of polyethylene. The hydrogen production obtained by this process reaches 55.6 millimoles per gram of polyethylene. In the literature (Applied Catalysis B:Environmental 327 (2023) 122451, Dol: 10.1016 / j.apcatb.2023.122451), the iron-aluminum catalyst was doped with cobalt, which increased the hydrogen yield to 61.39 mmol per gram of polyethylene; and in the literature (Journal ofEnvironmental Chemical Engineering 11 (2023) 109710. Dol: 10.1016 / j.jece.2023.109710), FeAlOx@C was used as a catalyst to increase the hydrogen yield to 64.5 mmol per gram of plastic. Even though the hydrogen yield is already very high, it is still far from the ideal value. The main reason is that the oil in the product occupies the hydrogen element, thereby affecting the hydrogen yield. As mentioned in the literature (Sci Rep, 2023 Jun 3;13(1):9057.Doi:10.1038 / s41598-023-36254-6) used a Socony-Mobil ZSM-5 zeolite catalyst to pyrolyze waste plastics, but the hydrogen production was only 18.51 mmol per gram of plastic. The raw materials in the literature produced a large amount of liquid oil and solid products, and each component produced was low and impure. Currently, microwave cracking mainly uses iron-based catalysts because the temperature can rise rapidly under microwave irradiation, and cracking reactions occur at the contact point between the catalyst and the raw material, which can simultaneously achieve the effects of microwave absorption, heating, and catalytic dehydrogenation. However, there are still problems such as low hydrogen conversion efficiency and the flow of hydrogen elements into gaseous and oily hydrocarbons, resulting in impure synthesized hydrogen. Therefore, the preparation of a catalyst with high dehydrogenation efficiency and strong hydrogen selectivity should be the focus of attention at this stage. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an iron-based rare earth catalyst and a preparation method for catalytic cracking of waste plastics, the purpose of which is to solve the problems of low hydrogen production and loss of hydrogen into oil by using iron-based rare earth catalysts.

[0005] In order to achieve the above object, the present invention is used for an iron-based rare earth catalyst, firstly Fe(NO3)3, Co(NO3)2 and M(NO3) are weighed respectively. y After adding citric acid, deionized water was added to Fe(NO3)3, Co(NO3)2 and M(NO3) y The mixture was dissolved in water to form a solution, citric acid was added after ultrasonic treatment, the mixture was heated at 55-65 degrees Celsius for 2-4 hours, and cooled to room temperature to obtain a gel, and the obtained gel was kept warm in an atmosphere furnace under nitrogen protection to obtain FeCoMO catalyst powder.

[0006] The Fe(NO3)3, Co(NO3)2 and M(NO3) y and citric acid according to Fe 3+ :Co 2+ :M y+ : Weigh the citric acid at a molar ratio of (9-X):1:X:10.

[0007] The M is one of La, Ce, Pr, Zr, Yb, Nd, Gd, Sm, Dy, and Er.

[0008] The X=0.5~2.

[0009] The solution was ultrasonicated for 8-12 minutes and then citric acid was added.

[0010] The process is carried out in an atmosphere furnace under nitrogen protection at 450-550 degrees Celsius for 2.5-3.5 hours.

[0011] A method for preparing an iron-based rare earth catalyst for catalytic cracking of waste plastics comprises the following steps: 1) Preparation of a rare earth iron catalyst FeCoMO: first weighing Fe(NO3)3, Co(NO3)2 and M(NO3) y After adding citric acid, deionized water was added to Fe(NO3)3, Co(NO3)2 and M(NO3) y The FeCoMO catalyst powder was obtained by dissolving the FeCoMO catalyst in the mixture, ultrasonicating the solution, and then adding citric acid. The mixture was heated at 55-65 degrees Celsius for 2-4 hours, and cooled to room temperature to obtain a gel. The obtained gel was kept warm in an atmosphere furnace under nitrogen protection to obtain FeCoMO catalyst powder.

[0012] 2) Microwave-assisted catalytic cracking of waste plastics

[0013] (1) Mixing waste plastics and FeCoMO catalyst uniformly and placing them in a reactor;

[0014] (2) After the reactor is purged with nitrogen until all air is exhausted, the microwave power is adjusted to 350-450 watts and maintained for 1-3 minutes; then the power is adjusted to 700-800 watts and maintained for 10-13 minutes until the waste plastic is completely cracked.

[0015] The above-mentioned Fe(NO3)3, Co(NO3)2 and M(NO3) y and citric acid according to Fe 3+ :Co 2+ :M y+ : citric acid molar ratio (9-X): 1:X:10 is weighed, X=0.5~2.

[0016] The above-mentioned M is one of La, Ce, Pr, Zr, Yb, Nd, Gd, Sm, Dy, and Er.

[0017] The above-mentioned waste plastics and FeCoMO catalyst are mixed in a mass ratio of 3:5.

[0018] 1. The catalyst activity of the present invention is high. In the current research on microwave-assisted processes, the catalyst basically needs to be activated before use. For example, in the literature (Materials Today Chemistry, 2022.26: p101166. DOI: 10.1016 / j.mtchem.2022.101166.), it is necessary to mix with activated carbon and activate it at 500 degrees Celsius under nitrogen protection for 2 hours before use. In the literature (Journal of Analytical and Applied Pyrolysis, 2022.165: p105577. DOI: 10.1016 / j.jaap.2022.105577.), the catalyst needs to be activated at 800 degrees Celsius for 4 hours in an atmosphere of 10% hydrogen mixed with nitrogen before use. The catalysts involved in the present invention can remain active for a long time after preparation and do not need to be activated before use.

[0019] 2. The preparation method is simple and energy-efficient. The literature (Journal of Hazardous Materials, 2023.445: p130609. DOI: 10.1016 / j.jhazmat.2022.130609.) utilizes pyrolysis technology, which requires complex experimental setup and results in a mere 57.28 mmoles per gram of plastic. However, the catalyst synthesized in this invention achieves a maximum hydrogen yield of 68.25 mmoles per gram of plastic using only microwave technology. The overall process is significantly simpler.

[0020] 3. No oily by-products are produced during plastic pyrolysis. The literature (Materialstoday Chemistry 2022, 101166. Dol: 10.1016 / j.mtchem.2022.101166) uses FeAlO x The catalyst's final oil production reached approximately 6% by mass, severely impacting hydrogen production. For example, a study (Nature Catalysis, 2020.3: p902–912. DOI: 10.1038 / s41929-020-00518-5) using the best catalyst in the literature for catalytic cracking, Fe₃O₄, also achieved a final oil production of 3.4% by mass. While oil production significantly impacts hydrogen production, the catalyst of this invention reduces oil production to zero, significantly increasing hydrogen production to near theoretical values.

[0021] 4. Plastic cracking products produce high-hydrogen content and high-performance carbon materials. Current microwave cracking methods for plastics still yield hydrogen at a rate somewhat below the theoretical value of 71.4 mmol / g plastic. To increase hydrogen production, a study (Journal of Environmental Chemical Engineering 11 (2023) 109710. Dol: 10.1016 / j.jece.2023.109710) used FeAlOx@C as a catalyst to crack polyethylene, raising hydrogen production to 64.5 mmol / g plastic. However, the final hydrogen production was only 64.5 mmol / g plastic. However, the present invention achieves a maximum hydrogen production of 68.25 mmol / g plastic, increasing hydrogen production and producing high-performance carbon materials.

[0022] 5. The prepared catalyst is used for the catalytic cracking of various plastics. A previous study (ACS Sustainable Chem. Eng. 2023, 11, 27, 10108–10118, Dol: 10.1021 / acssuschemeng.3c02178) reported the catalytic cracking of high-density polyethylene using an Fe2O3 / Al2O3 catalyst, resulting in a final hydrogen yield of 53.43 mmol / g polyethylene and a hydrogen conversion rate of 70%. The present invention's catalytic cracking of plastics can achieve a final hydrogen yield exceeding 62 mmol / g plastic, with a hydrogen conversion rate exceeding 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the XRD pattern of the catalyst before and after the reaction of the present invention.

[0024] Figure 2 This is a morphology diagram of the catalyst before the reaction of the present invention.

[0025] Figure 3 This is a morphology diagram of the cracking product of the present invention. DETAILED DESCRIPTION

[0026] The following examples and accompanying drawings further illustrate the microwave-assisted double-layer catalytic cracking method for producing hydrogen and carbon nanotubes. Based on the examples provided herein, all other embodiments derived by persons of ordinary skill in the art without inventive effort are intended to fall within the scope of this invention. Example 1

[0027] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0028] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 into a solution. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0029] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0030] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0031] 2. Microwave-assisted catalytic cracking of waste plastics

[0032] (1) LLDPE (linear low-density polyethylene) and FeCoPrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0033] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0034] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked.

[0035] Figure 1 From the XRD patterns of the catalyst before and after the reaction, it can be seen that the catalyst mainly catalyzes the reactants with Fe3O4 and PrFe2O3 as active sites. The catalyst presents dual active sites, which makes it have higher catalytic activity. It proves that the addition of rare earth Pr increases the activity of the catalyst, promotes catalytic cracking, and thus increases the production of hydrogen. Figure 2 and Figure 3The morphologies of the catalyst before the reaction and the cracking product after the reaction show that the catalyst is porous. After catalytic cracking, the product produces longer carbon nanotubes and some irregular carbon nanotubes, proving that the cracking gas is cracked to produce hydrogen and carbon materials when passing through the catalyst. Example 2

[0036] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0037] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 8.5:1:0.5:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 into a solution. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0038] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0039] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0040] 2. Microwave-assisted catalytic cracking of waste plastics

[0041] (1) LLDPE (linear low-density polyethylene) and FeCoPrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0042] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0043] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked. Example 3

[0044] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0045] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 7:1:2:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0046] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0047] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0048] 2. Microwave-assisted catalytic cracking of waste plastics

[0049] (1) LLDPE (linear low-density polyethylene) and FeCoPrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0050] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0051] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked.

[0052] Comparative Example 1

[0053] The first step of step 1 in Example 1 is: (1) Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 are mixed with citric acid according to the Fe 3+ :Co 2+ :Pr 3+ The mixture was weighed in a molar ratio of 6:1:3:10 of citric acid. Other steps were the same as in Example 1.

[0054] Comparative Example 2

[0055] The first step of step 1 in Example 1 is as follows: (1) Fe(NO3)3, Co(NO3)2, and citric acid are weighed in a molar ratio of 9:1:10, deionized water is added to dissolve the Fe(NO3)3 and Co(NO3)2, and the solution is sonicated for 10 minutes before adding the citric acid. Other aspects are the same as in Example 1.

[0056] Comparison of the results of linear low-density polyethylene cracking reaction between catalysts with different proportions of rare earth and catalysts without rare earth:

[0057] The cracking reaction results of Example 1-2 were compared with those of Comparative Example 1-2.

[0058] Table 1 Product ratios of linear low-density polyethylene from microwave-assisted catalytic cracking

[0059] serial number Solids (wt%) Water (wt%) Gas (wt%) Hydrogen production (mmol / g plastic) Theoretical hydrogen production (mmol / g plastic) Example 1 45.98 3.56 50.46 68.25 71.4285 Example 2 46.56 4.08 49.36 66.96 71.4285 Example 3 52.25 4.56 43.19 65.86 71.4285 Comparative Example 1 54.03 4.71 41.26 61.56 71.4285 Comparative Example 2 51.56 0.64 (oil) 47.80 59.68 71.4285

[0060] As shown in Table 1, Example 1, with a 10% rare earth addition, yielded a final hydrogen production of 68.25 mmoles per gram of linear low-density polyethylene. Example 2, with a 5% rare earth addition, yielded a final hydrogen production of 66.96 mmoles per gram of linear low-density polyethylene. Example 3, with a 20% rare earth addition, yielded a final hydrogen production of 65.86 mmoles per gram of linear low-density polyethylene. However, with a 30% rare earth addition, as shown in Comparative Example 1, only 61.56 mmoles per gram of linear low-density polyethylene was produced. Therefore, excessive rare earth addition can affect hydrogen production. Without the addition of rare earth, as in Comparative Example 2, the final production was only 59.68 mmoles per gram of linear low-density polyethylene, and oil was produced. This indicates that omitting the addition of rare earth also affects hydrogen production. Therefore, controlling the rare earth content to 5% to 20% can achieve high hydrogen production levels. Regardless of the amount of rare earth added, the final liquid product contains no oil, only a small amount of water.

[0061] Example 4

[0062] 1. Preparation of rare earth iron catalyst FeCoCeO:

[0063] (1) Fe(NO3)3, Co(NO3)2, Ce(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Ce(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0064] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0065] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0066] 2. Microwave-assisted catalytic cracking of waste plastics

[0067] (1) PP (polypropylene) and FeCoCeO catalyst were mixed evenly in a mass ratio of 3:5 and placed in a reactor;

[0068] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0069] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0070] Example 5

[0071] 1. Preparation of rare earth iron catalyst FeCoZrO:

[0072] (1) Fe(NO3)3, Co(NO3)2, Zr(NO3)4 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Zr(NO3)4 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0073] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0074] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0075] 2. Microwave-assisted catalytic cracking of waste plastics

[0076] (1) LDPE (low-density polyethylene) and FeCoZrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0077] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0078] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0079] Example 6

[0080] 1. Preparation of rare earth iron catalyst FeCoYbO:

[0081] (1) Fe(NO3)3, Co(NO3)2, Yb(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Yb(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0082] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0083] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0084] 2. Microwave-assisted catalytic cracking of waste plastics

[0085] (1) HDPE (high-density polyethylene) and FeCoYbO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0086] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0087] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0088] Example 7

[0089] 1. Preparation of rare earth iron catalyst FeCoNdO:

[0090] (1) Fe(NO3)3, Co(NO3)2, Nd(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Nd(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0091] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0092] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0093] 2. Microwave-assisted catalytic cracking of waste plastics

[0094] (1) EVA-530 (ethylene-vinyl acetate copolymer containing 94% ethylene) and FeCoNdO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0095] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0096] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0097] Example 8

[0098] 1. Preparation of rare earth iron catalyst FeCoGdO:

[0099] (1) Fe(NO3)3, Co(NO3)2, Gd(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Gd(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0100] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0101] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0102] 2. Microwave-assisted catalytic cracking of waste plastics

[0103] (1) POE (ethylene and octene polymer) and FeCoGdO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0104] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0105] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0106] Example 9

[0107] 1. Preparation of rare earth iron catalyst FeCoSmO:

[0108] (1) Fe(NO3)3, Co(NO3)2, Sm(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Sm(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0109] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0110] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0111] 2. Microwave-assisted catalytic cracking of waste plastics

[0112] (1) Mix colored PP (colored polypropylene) and FeCoSmO catalyst in a mass ratio of 3:5 and place in a reactor;

[0113] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0114] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0115] Example 10

[0116] 1. Preparation of rare earth iron catalyst FeCoDyO:

[0117] (1) Fe(NO3)3, Co(NO3)2, Dy(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Dy(NO3)3 into a solution. The solution was ultrasonicated for 12 minutes and then citric acid was added.

[0118] (2) heating the mixture at 65°C for 2 hours and cooling it to room temperature to obtain a gel;

[0119] (3) The obtained gel was kept at 550 °C in an atmosphere furnace under nitrogen protection for 3.5 hours to obtain FeCoCeO catalyst powder;

[0120] 2. Microwave-assisted catalytic cracking of waste plastics

[0121] (1) Mix colored PE (colored polyethylene) and FeCoDyO catalyst in a mass ratio of 3:5 and place in a reactor;

[0122] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0123] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 350 watts and maintaining it for 1 minute; then adjusting the power to 700 watts and maintaining it for 13 minutes until the waste plastic is completely cracked.

[0124] Comparative Example 3

[0125] The first step in step 1 of Example 5 is replaced by (1) weighing Fe(NO3)3, Co(NO3)2, Cu(NO3)2 and citric acid in a molar ratio of 8:1:1:10, first adding deionized water to dissolve Fe(NO3)3, Co(NO3)2, Cu(NO3)2 into a solution, ultrasonicating the solution for 12 minutes and then adding citric acid; the rest is the same as Example 5.

[0126] The cracking reaction results of Examples 4-10 in which different rare earth catalysts were added were compared with the cracking reaction results of Comparative Example 3 in which a copper metal catalyst was added.

[0127] Table 2 Ratio of plastic products from microwave-assisted catalytic cracking

[0128] serial number Solids (wt%) Water (wt%) Gas (wt%) Hydrogen production (mmol / g plastic) Theoretical hydrogen production (mmol / g plastic) Example 4 51.19 3.5 45.31 63.91 71.4285 Example 5 41.28 3.96 54.76 62.86 71.4285 Example 6 45.25 3.74 51.01 62.02 71.4285 Example 7 48.15 3.59 48.26 59.85 65.4383 Example 8 45.79 2.91 51.29 62.99 71.4285 Example 9 44.51 7.89 47.60 63.38 71.4285 Example 10 47.54 5.63 46.83 63.53 71.4285 Comparative Example 3 45.16 4.56 50.28 59.36 71.4285

[0129] As shown in Table 2, different rare earth catalysts were added to carry out microwave catalytic cracking of waste plastics with different chain structures. The hydrogen production of different types of plastics by catalytic cracking ranged from 62 to 64 mmol per gram of plastic, and no oil was produced, only a small amount of water was produced. For example, when the iron-cobalt-copper catalyst without rare earth was used to carry out catalytic cracking of the plastic in Example 5, the hydrogen production ranged from 59 to 60 mmol per gram of plastic. It can be inferred that the addition of rare earth enhances the selectivity of the catalyst for hydrogen, thereby increasing the hydrogen production.

[0130] Example 11

[0131] 1. Preparation of rare earth iron catalyst FeCoLaO:

[0132] (1) Fe(NO3)3, Co(NO3)2, La(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and La(NO3)3 into a solution. The solution was ultrasonicated for 8 minutes and then citric acid was added.

[0133] (2) heating the mixture at 55°C for 4 hours and cooling it to room temperature to obtain a gel;

[0134] (3) The obtained gel was kept at 450°C in an atmosphere furnace under nitrogen protection for 2.5 hours to obtain FeCoLaO catalyst powder;

[0135] 2. Microwave-assisted catalytic cracking of waste plastics

[0136] (1) PET (polyethylene terephthalate) and FeCoLaO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0137] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0138] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 450 watts and maintaining it for 3 minutes; then adjusting the power to 800 watts and maintaining it for 10 minutes until the waste plastic is completely cracked.

[0139] Example 12

[0140] 1. Preparation of rare earth iron catalyst FeCoErO:

[0141] (1) Fe(NO3)3, Co(NO3)2, Er(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Er(NO3)3 into a solution. The solution was ultrasonicated for 8 minutes and then citric acid was added.

[0142] (2) heating the mixture at 55°C for 4 hours and cooling it to room temperature to obtain a gel;

[0143] (3) The obtained gel was kept at 450°C in an atmosphere furnace under nitrogen protection for 2.5 hours to obtain FeCoLaO catalyst powder;

[0144] 2. Microwave-assisted catalytic cracking of waste plastics

[0145] (1) PCL (polycaprolactone) and FeCoErO catalyst were mixed evenly in a mass ratio of 3:5 and placed in a reactor;

[0146] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0147] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 450 watts and maintaining it for 3 minutes; then adjusting the power to 800 watts and maintaining it for 10 minutes until the waste plastic is completely cracked.

[0148] Example 13

[0149] 1. Preparation of rare earth iron catalyst FeCoDyO:

[0150] (1) Fe(NO3)3, Co(NO3)2, Dy(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Dy(NO3)3 into a solution. The solution was ultrasonicated for 8 minutes and then citric acid was added.

[0151] (2) heating the mixture at 55°C for 4 hours and cooling it to room temperature to obtain a gel;

[0152] (3) The obtained gel was kept at 450°C in an atmosphere furnace under nitrogen protection for 2.5 hours to obtain FeCoLaO catalyst powder;

[0153] 2. Microwave-assisted catalytic cracking of waste plastics

[0154] (1) PS (polystyrene) and FeCoDyO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0155] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0156] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 450 watts and maintaining it for 3 minutes; then adjusting the power to 800 watts and maintaining it for 10 minutes until the waste plastic is completely cracked.

[0157] Comparative Example 4

[0158] The first step in step 1 of Example 13 is replaced by (1) weighing Fe(NO3)3, Co(NO3)2, Ni(NO3)2 and citric acid in a molar ratio of 8:1:1:10, first adding deionized water to dissolve Fe(NO3)3, Co(NO3)2, Ni(NO3)2 into a solution, ultrasonicating the solution for 8 minutes and then adding citric acid; the rest is the same as Example 13.

[0159] Comparison of cleavage reaction results:

[0160] The results of the cracking reactions of nonlinear plastics in Examples 11-13 in which different rare earth catalysts were added were compared with those in Comparative Example 4 in which nickel metal was added.

[0161] Table 3 Proportion of plastic products from microwave-assisted catalytic cracking

[0162] serial number Solids (wt%) Water (wt%) Gas (wt%) Hydrogen production (mmol / g plastic) Theoretical hydrogen production (mmol / g plastic) Example 11 40.31 5.47 54.22 19.93 20.8333 Example 12 42.95 5.26 51.78 39.03 43.8596 Example 13 56.72 5.35 37.93 31.32 38.4600 Comparative Example 4 46.59 5.24 48.17 26.35 38.4600

[0163] As shown in Table 3, microwave catalytic cracking of various plastic materials containing non-chain structures, using the addition of lanthanum as an example, revealed that, as shown in Examples 11-13, the products after microwave cracking were oil-free, contained a small amount of water, and exhibited high selectivity for hydrogen, with hydrogen conversion rates ranging from 85% to 98%. In contrast, microwave cracking of an iron-cobalt-nickel catalyst without the addition of rare earth elements yielded only 26.35 mmol per gram of plastic. This demonstrates that catalysts containing rare earth elements also exhibit high selectivity and conversion for non-chain plastic materials.

[0164] Example 14

[0165] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0166] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 into a solution. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0167] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0168] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0169] 2. Microwave-assisted catalytic cracking of waste plastics

[0170] (1) POE (ethylene and octene polymer) and FeCoPrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0171] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0172] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked.

[0173] Example 15

[0174] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0175] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 into a solution. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0176] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0177] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0178] 2. Microwave-assisted catalytic cracking of waste plastics

[0179] (1) PS (polystyrene) and FeCoPrO catalyst were mixed uniformly in a mass ratio of 3:5 and placed in a reactor;

[0180] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0181] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked.

[0182] Example 16

[0183] 1. Preparation of rare earth iron catalyst FeCoPrO:

[0184] (1) Fe(NO3)3, Co(NO3)2, Pr(NO3)3 and citric acid were weighed in a molar ratio of 8:1:1:10. Deionized water was first added to dissolve Fe(NO3)3, Co(NO3)2 and Pr(NO3)3 into a solution. The solution was ultrasonicated for 10 minutes and then citric acid was added.

[0185] (2) heating the mixture at 60 degrees Celsius for 3 hours and cooling it to room temperature to obtain a gel;

[0186] (3) The obtained gel was kept at 500 degrees Celsius in an atmosphere furnace under nitrogen protection for 3 hours to obtain FeCoPrO catalyst powder;

[0187] 2. Microwave-assisted catalytic cracking of waste plastics

[0188] (1) Mix colored PP (colored polypropylene) and FeCoPrO catalyst in a mass ratio of 3:5 and place in a reactor;

[0189] (2) After the reactor is purged with nitrogen until all the air is exhausted, the microwave cracking reaction is carried out by gradually increasing the microwave power.

[0190] The above-mentioned method of gradually increasing the microwave power to carry out the microwave cracking reaction means first adjusting the microwave power to 400 watts and maintaining it for 2 minutes; then adjusting the power to 750 watts and maintaining it for 12 minutes until the waste plastic is completely cracked.

[0191] Comparison of cleavage reaction results:

[0192] The prepared FeCoPrO catalyst was used to catalytically crack different types of waste plastics. The results are shown in Table 4.

[0193] Table 4 Ratio of plastic products from microwave-assisted catalytic cracking

[0194] serial number Solids (wt%) Water (wt%) Gas (wt%) Hydrogen production (mmol / g plastic) Theoretical hydrogen production (mmol / g plastic) Example 14 46.93 3.89 49.18 67.02 71.4285 Example 15 55.28 4.59 40.13 35.76 38.4600 Example 16 43.73 4.67 51.60 66.53 71.4285

[0195] As shown in Table 4, when different types of waste plastics were catalytically cracked using rare earth praseodymium as a catalyst, the hydrogen conversion rate was between 92% and 94%, proving that this catalyst has a slightly higher selectivity for hydrogen than other rare earth catalysts. However, regardless of the type of rare earth added, the final liquid product was oil-free and had a high selectivity for hydrogen. This shows that the addition of rare earth modification improves the catalytic performance of the catalyst.

Claims

1. An iron-based rare earth catalyst, characterized in that First weigh Fe(NO3)3, Co(NO3)2 and M(NO3) separately y After adding citric acid, deionized water was added to Fe(NO3)3, Co(NO3)2 and M(NO3) y The Fe(NO3)3, Co(NO3)2 and M(NO3)3 are dissolved in water to form a solution, the solution is ultrasonicated and then citric acid is added, the mixture is heated at 55-65 degrees Celsius for 2-4 hours, cooled to room temperature to obtain a gel, and the obtained gel is kept warm in an atmosphere furnace under nitrogen protection to obtain FeCoMO catalyst powder; the Fe(NO3)3, Co(NO3)2 and M(NO3) y and citric acid according to Fe 3+ :Co 2+ :M y+ : citric acid molar ratio of (9-X): 1:X:10 is weighed; X=0.5-2; citric acid is added after the solution is ultrasonicated for 8-12 minutes; the mixture is kept at 450-550 degrees Celsius in an atmosphere furnace under nitrogen protection for 2.5-3.5 hours; and M is one of La, Ce, Pr, Zr, Yb, Nd, Gd, Sm, Dy, and Er.

2. A method for catalytic cracking of waste plastics using an iron-based rare earth catalyst, characterized in that The process includes the following steps: 1) Preparation of rare earth iron catalyst FeCoMO: First, Fe(NO3)3, Co(NO3)2 and M(NO3) are weighed separately. y After adding citric acid, deionized water was added to Fe(NO3)3, Co(NO3)2 and M(NO3) y The FeCoMO catalyst powder was obtained by dissolving the FeCoMO catalyst in the mixture, ultrasonicating the solution, adding citric acid, heating the mixture at 55-65 degrees Celsius for 2-4 hours, cooling to room temperature, and keeping the obtained gel at 450-550 degrees Celsius in an atmosphere furnace under nitrogen protection to obtain a FeCoMO catalyst powder. 2) Microwave-assisted catalytic cracking of waste plastics (1) Mixing waste plastics and FeCoMO catalyst uniformly and placing them in a reactor; (2) After the reactor is purged with nitrogen until all air is exhausted, the microwave power is adjusted to 350-450 watts and maintained for 1-3 minutes; then the power is adjusted to 700-800 watts and maintained for 10-13 minutes until the waste plastic is completely cracked; The Fe(NO3)3, Co(NO3)2 and M(NO3) y and citric acid according to Fe 3+ :Co 2+ :M y+ : citric acid molar ratio (9-X): 1:X:10 weighing, X = 0.5 ~ 2; waste plastics and FeCoMO catalyst in a mass ratio of 3:5 ratio; The M is one of La, Ce, Pr, Zr, Yb, Nd, Gd, Sm, Dy, and Er.

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