A waste plastic recovery catalyst system and a preparation method and application thereof

Abstract

The application provides a waste plastic recovery catalyst system and a preparation method and application thereof. The catalyst comprises diatomite with surface deposition site modification, a Pt active component loaded by gas phase atomic deposition and a Cu and Si regulator, and a NaY molecular sieve in a gradient series connection; wherein the loadings of Pt, Cu and Si elements are 0.02-0.1%, 0.4-3% and 0.1-0.5% respectively. The Pt dehydrogenation active component of the catalyst is highly dispersed and stable on the diatomite carrier with special pretreatment, the agglomeration effect of the active metal at high temperature is weakened, and the thermal stability is improved. The dehydrogenation part and the cracking part of the catalyst are coupled in series, the gradient dehydrogenation activation and catalytic cracking of hydrocarbon molecules are realized, the carbon deposition of the metal component in the cracking process is slowed down, and the prepared catalyst shows good activity and stability in the waste plastic cracking test process.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic recycling, specifically relating to a waste plastic recycling catalyst system, its preparation method, and its application. Background Technology

[0002] Global plastic waste has exceeded 4.9 billion tons, but less than 9% of it is recyclable and reusable. The vast majority of it is discarded or disposed of as waste, which is costly to recycle and slow to decompose, resulting in serious environmental pollution problems.

[0003] Currently, waste plastics are treated through landfill, incineration, and resource utilization. Resource recycling of plastics is the future trend in waste plastic treatment. Chemical recycling of plastics involves breaking down large plastic molecules into smaller molecule products, such as polymer monomers, pyrolysis oil, and pyrolysis gas, which can then be used as chemical raw materials. Compared to thermal pyrolysis, catalytic pyrolysis of waste plastics under high temperature and catalytic conditions can further improve the oil yield and quality of the products.

[0004] CN202210444102.7 discloses a method for preparing cycloalkane aviation fuel by hydrodeoxygenation of aromatic oxygen-containing waste plastics, using a supported metal-metal oxide catalyst in the presence of a solvent to catalyze the direct preparation of cycloalkane aviation fuel by hydrodeoxygenation of aromatic oxygen-containing waste plastics; CN202110847013.2 discloses a method for directly preparing aviation gasoline and aviation kerosene from polyolefin waste plastics, using high-molecular-weight polyolefin waste plastics as raw materials and employing a bifunctional catalyst composed of noble metals and inorganic solid acids to achieve the coupling of hydrogenation degradation and isomerization reaction of high-molecular-weight polyolefin plastics in one step. The method has continuously enabled the production of high-value oil products from polyolefin plastics; CN202110011768.9 discloses a molecular sieve catalyst for waste plastic pyrolysis and its preparation method and waste plastic pyrolysis method, which uses calcined kaolin, water glass, directing agent and alkaline solution to prepare modified molecular sieve composite material; Constructing bifunctional catalysts is beneficial to improve the pyrolysis activity of waste plastics, but most supported bifunctional catalysts are usually prepared by traditional impregnation method, which has the characteristics of high active component dosage, poor dispersibility, easy agglomeration of active components at high temperature, low atom utilization rate, and easy carbon deposition and coverage of active components, making it difficult to apply in actual industrial applications.

[0005] Therefore, in order to address the above difficulties, developing a catalyst that combines high activity and stability is the key to achieving effective resource utilization of waste plastics. Summary of the Invention

[0006] One of the objectives of this invention is to provide a catalyst system with both high activity and stability that can be applied to the field of waste plastic resource utilization, thereby achieving effective resource utilization of waste plastics.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A catalyst system for recycling waste plastics, the catalyst comprising diatomaceous earth modified with surface deposition sites, Pt active component supported by vapor-phase atomic deposition and Cu and Si regulators, and NaY molecular sieves in series; wherein the loading amounts of Pt, Cu and Si elements are 0.02-0.1%, 0.4-3%, and 0.1-0.5%, respectively, based on the mass of diatomaceous earth.

[0009] This catalyst has the following advantages: the Pt dehydrogenation active component achieves high dispersion and stability on a specially pretreated diatomaceous earth support; the Pt nanoparticles have a particle size concentrated around 1 nm; and the deposition of Cu and Si further stabilizes the Pt nanoparticles, weakening the agglomeration effect of the active metal at high temperatures and further improving the thermal stability of the catalyst. The dehydrogenation and pyrolysis sections of the catalyst are coupled in series. The dehydrogenation section achieves pre-dehydrogenation activation of plastic macromolecules, converting saturated hydrocarbons into olefin macromolecules with higher acid catalytic activity. The olefin macromolecules further undergo carbocation pyrolysis under the action of molecular sieves to generate small molecule hydrocarbons, achieving a synergistic effect of hydrocarbon molecule pre-dehydrogenation and catalytic pyrolysis, and mitigating carbon deposition of the metal active component during the pyrolysis process. The prepared catalyst exhibits good activity and stability during waste plastic pyrolysis testing.

[0010] In one embodiment of the present invention, the diatomaceous earth modified by surface deposition sites is diatomaceous earth modified by surface hydroxylation.

[0011] Another objective of this invention is to provide a method for preparing a waste plastic recycling catalyst system.

[0012] A method for preparing a waste plastic recycling catalyst system, the method comprising the following steps:

[0013] S1: Surface-modify diatomaceous earth with a hydroxylating agent to obtain a suspension of modified diatomaceous earth;

[0014] S2: Filter, wash, and dry the suspension to obtain the modified diatomaceous earth carrier;

[0015] S3: Atomic deposition of Pt, Cu, and Si elements and ligand removal are performed on the modified diatomaceous earth support to obtain SiCu@Pt / diatomaceous earth, which serves as the dehydrogenation part of the catalyst;

[0016] S4: SiCu@Pt / diatomite and NaY molecular sieve powders are pressed into tablets and filled separately to form a composite catalyst with a two-layer cascade structure, with NaY molecular sieve as the pyrolysis part.

[0017] In one embodiment of the present invention, the hydroxylating agent in S1 is an oxidizing hydroxylating agent, preferably an aqueous solution of an alkanolamine, a weakly basic salt, or a peroxide agent; preferably, the alkanolamine comprises a C2-C4 primary amine, preferably one or more of ethanolamine, diethanolamine, isopropanolamine, and propanolamine; preferably, the weakly basic salt comprises one or more of carbonic acid, phosphoric acid, and alkali metal salts of C1-C7 organic acids, preferably one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium phosphate, sodium formate, sodium acetate, sodium citrate, sodium tartrate, and sodium salicylate. Or a variety; preferably, the peroxidizing agent comprises one or more of alkyl peroxides, peroxide salts, and peroxidizing acids, more preferably one or more of hydrogen peroxide, cumene peroxide, tert-butyl hydrogen peroxide, sodium peroxide, and peracetic acid; preferably, the mass fractions of the alkanolamine, the weakly basic salt, and the peroxidizing agent are 1-4%, 1-4%, and 1-5%, respectively, and more preferably, the content fractions are 1-2%, 1-2%, and 1-2%, respectively, based on the total mass of the oxidizing hydroxylating agent; preferably, the pH value of the aqueous solution is 8-11, more preferably 8-10.

[0018] In this invention, the synergistic effect of alkanolamine, weakly basic salt, and peroxide reagent can reduce the deposition sites of impurities on the diatomaceous earth surface and increase the density and uniformity of isolated hydroxyl sites. The uniform distribution of isolated silanol sites is a prerequisite for achieving high dispersion of loaded active metals. Infrared characterization shows that the hydroxyl peak is concentrated at 3740 cm⁻¹. -1 With 3745cm -1 This provides excellent anchoring for the subsequent highly dispersed vapor deposition of the active components. The aforementioned synergistic effect can further enhance the material's performance based on the basic scheme of this invention. The synergistic effect of the above scheme can further enhance the material's performance based on the basic scheme of this invention; the above scheme is a preferred embodiment.

[0019] In one embodiment of the present invention, the mass ratio of diatomaceous earth to solution in S1 is 1:2-10, preferably 1:6-8.

[0020] In one embodiment of the present invention, the treatment in S1 is hydrothermal treatment; preferably, the temperature of the hydrothermal treatment is 60-90°C, more preferably 80-90°C; and the time is 1-10h, more preferably 5-8h.

[0021] In one embodiment of the present invention, the hydroxyl density on the surface of the diatomaceous earth in S1 is 0.35-0.55 mmol / g.

[0022] In one embodiment of the present invention, the drying temperature in S2 is 150-200°C, preferably 160-180°C, and the drying time is 4-8 hours, preferably 6-8 hours.

[0023] In one embodiment of the present invention, the precursors of Pt, Cu, and Si elements atomically deposited in S3 are organometallic precursors of the corresponding elements, preferably trimethylmethylcyclopentadiene platinum (TMPt(MeCp)), bis[1-(dimethylamino)-2-propanol]copper (Cu(dmap)2), and octamethylcyclotetrasiloxane (D4), respectively; preferably, the deposition cycle of the trimethylmethylcyclopentadiene platinum precursor in S3 is 1-10 times, preferably 1-5 times; the deposition cycle of the bis[1-(dimethylamino)-2-propanol]copper precursor is 1-20 times, preferably 5-15 times; and the deposition cycle of the octamethylcyclotetrasiloxane precursor is 1-10 times, preferably 1-5 times.

[0024] The metal-organic precursor of this invention more readily forms a uniform Si-O-Pt monomer structure on the isolated hydroxyl sites of the modified diatomaceous earth support, and further forms Pt nanoclusters with a particle size distribution concentrated at around 1 nm, greatly improving the atomic utilization rate of noble metal atoms and giving it the characteristic of high dehydrogenation activity at a lower noble metal loading. Further deposition of Cu(dmap)2 and D4 precursors can passivate the unsaturated coordinating atoms of the Pt nanoclusters, slowing down the occurrence of deep dehydrogenation side reactions while enhancing the interaction between the Pt active component and the support, mitigating the Pt aggregation effect at high temperatures, thereby improving catalyst stability. The catalyst modified by atomic deposition is SiCu@Pt / diatomaceous earth. The metal-organic precursor of the above scheme can be further optimized based on the basic scheme of this invention, and the above scheme is a preferred scheme. The above SiCu@Pt / diatomaceous earth is an atomic catalyst system of Pt, Cu, and Si elements loaded on a diatomaceous earth support.

[0025] In one embodiment of the invention, an oxidant is added in S3 to pulse-remove the ligand; preferably, the oxidant is oxygen and / or ozone, more preferably ozone; preferably, the pulse duration of the oxidant is 20-60 s.

[0026] In one embodiment of the present invention, S4 is filled in two layers along the airflow direction, with the upper layer being SiCu@Pt / diatomite and the lower layer being NaY molecular sieve.

[0027] Based on the carbocation cracking mechanism of hydrocarbons, olefin molecules are more easily cracked than alkanes. Large hydrocarbon molecules first undergo dehydrogenation activation on Si@PtCu / diatomite, and the resulting olefin components are further cracked into smaller oil molecules in the lower NaY molecular sieve. By designing this cascaded structure of the composite catalyst, the sequential synergy between dehydrogenation centers and cracking centers can be achieved, effectively mitigating the coverage of dehydrogenation active sites by catalyst coking and improving the catalyst's coking stability. The two-stage loading of the above scheme can further enhance the material's performance based on the basic scheme of this invention; the above scheme is a preferred embodiment.

[0028] In one embodiment of the present invention, the mass ratio of SiCu@Pt / diatomite and NaY molecular sieve in S4 is 1:(1-6), preferably 1:(2-5).

[0029] In one embodiment of the present invention, the NaY molecular sieve support in S4 is a molecular sieve with SiO2 / Al2O3 ratio of 4.8-5.4.

[0030] In one embodiment of the present invention, S4 preferably involves tableting followed by sieving to obtain 20-30 mesh particles. In this invention, the particle size can be adjusted as needed.

[0031] Another object of the present invention is to provide an application of a waste plastic recycling catalyst system.

[0032] The use of a waste plastic recycling catalyst system, wherein the catalyst system is the catalyst system described above, or the catalyst system prepared by the above preparation method, and the catalyst system is used for waste plastic recycling, preferably for PE and PP waste plastic recycling.

[0033] Another object of the present invention is to provide a method for recycling waste plastics.

[0034] A method for recycling waste plastics, wherein the method employs the catalyst system described above, or the catalyst system prepared by the above preparation method, and wherein the method uses the waste plastic recycling catalyst system to catalytically pyrolyze the waste plastics.

[0035] In one embodiment of the present invention, the mass ratio of the catalyst system to waste plastic in the method is 1:(10-35), preferably 1:(10-20).

[0036] In one embodiment of the present invention, the reaction temperature of thermal cracking and catalytic cracking in the method is 350-500°C.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) By treating diatomite with hydroxylation reagent, the deposition sites of impurities on the surface of diatomite are effectively reduced and the density of isolated hydroxyl sites is increased, which has a very good anchoring effect on the highly dispersed vapor deposition of Pt active components.

[0039] (2) Loading Pt active components onto surface-modified diatomaceous earth can easily form Pt nanoclusters with a uniform particle size of about 1 nm, which greatly improves the atomic utilization rate of noble metal atoms and further deposits and passivates the unsaturated coordination sites on the Pt clusters, thus weakening the aggregation effect of Pt at high temperature.

[0040] (3) It can achieve the synergistic effect of pre-activation of dehydrogenation part and catalytic cracking of cracking part, effectively reduce the coverage of dehydrogenation active sites by catalyst carbon deposit, and improve the carbon deposit stability of catalyst. Attached Figure Description

[0041] Figure 1 The image shows a TEM image of diatomite prepared in Example 1. The black dots in the image are Pt nanoparticles loaded on the diatomite. The particle size in this image is concentrated at about 1 nm.

[0042] Figure 2 This is a TEM image of the diatomaceous earth prepared in Comparative Example 1. The black blocks in the image represent Pt metal loaded on the diatomaceous earth. Figure 1 It has poorer dispersibility compared to Pt. Detailed Implementation

[0043] The following specific embodiments further illustrate the technical solution and effects of the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0044] Unless otherwise specified, the raw materials used in the examples or comparative examples are all available from commercially available sources.

[0045] The main raw materials used in the process are shown in the table below:

[0046] name purity factory ethanolamine 99％ Inokai Isopropanolamine 94％ Inokai Butylamine 99％ Aladdin Sodium carbonate 99.8％ Inokai Potassium carbonate 99％ Aladdin Sodium acetate 99％ Inokai hydrogen peroxide <![CDATA[31%,H2O]]> Inokai Sodium peroxide 93％ Inokai tert-butyl hydroperoxide <![CDATA[70%,H2O]]> Inokai Diatomaceous earth 545 / Inokai <![CDATA[SiO2]]> / Aladdin NaY molecular sieve <![CDATA[SiO2 / Al2O3=5.2]]> Nankai Catalyst Plant HY molecular sieve / Nankai Catalyst Plant ZSM-5 molecular sieve / Nankai Catalyst Plant

[0047] The experimental preparation and characterization equipment are listed in the table below:

[0048]

[0049] The following describes the related methods used or that may be used in the embodiments or comparative examples of the present invention:

[0050] Example 1

[0051] Preparation of catalyst A:

[0052] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 120g of hydroxylation solution (ethanolamine 1wt%, sodium carbonate 1wt%, hydrogen peroxide 1wt%, pH=9), and subjected to hydrothermal treatment by stirring in a constant temperature water bath at 80℃ for 6h. The resulting suspension was rapidly cooled to room temperature and then filtered, washed multiple times with deionized water until the filtrate was neutral. It was then dried in an oven at 180℃ for 6h to obtain a diatomaceous earth carrier with surface hydroxyl modification (hydroxyl density 0.42mmol / g). 2g of the surface hydroxyl modified diatomaceous earth was weighed and subjected to metal loading via atomic deposition. Under the following deposition conditions (pulse time of 20 s for metal precursor, nitrogen purging time of 120 s; pulse time of 60 s for ozone, nitrogen purging time of 120 s; deposition chamber temperature of 200℃; vacuum of 15 kPa; nitrogen purging rate of 200 mL / min), the deposition cycles for trimethylmethylcyclopentadiene platinum, bis[1-(dimethylamino)-2-propanol]copper, and octamethylcyclotetrasiloxane were 1, 2, and 1, respectively, corresponding to Pt, Cu, and Si metal element loadings of 0.02 wt%, 0.4 wt%, and 0.1 wt%, respectively, based on diatomaceous earth mass. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 5.2) were pressed into tablets and sieved into 20-30 mesh particles under a pressure of 10 MPaG. 2g of the pressed modified diatomaceous earth and 4g of NaY molecular sieve powder were taken and loaded into two layers along the airflow direction, labeled as catalyst A.

[0053] The TEM image of diatomite after Pt metal was loaded into catalyst A is shown below. Figure 1 It can be seen that the loaded noble metal particles are concentrated in a size of about 1 nm, and have uniform high dispersion.

[0054] Example 2

[0055] Preparation of catalyst B:

[0056] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 160g of hydroxylation solution (isopropanolamine 1.5wt%, sodium formate 2wt%, tert-butyl hydroperoxide 2wt%, pH=10), and stirred in a constant temperature water bath at 90℃ for 8h for hydrothermal treatment. The resulting suspension was rapidly cooled to room temperature and filtered, then washed several times with deionized water until the filtrate was neutral. The filtrate was then dried in an oven at 160℃ for 8h to obtain a hydroxyl-modified diatomaceous earth carrier (hydroxyl density 0.47mmol / g). 2g of the hydroxyl-modified diatomaceous earth was then subjected to atomic deposition to obtain gold... Under the following deposition conditions (pulse time of metal precursor is 20s, nitrogen purging time is 120s; pulse time of ozone is 60s, nitrogen purging time is 120s; deposition chamber temperature is 200℃, vacuum degree is 15kpa, and nitrogen purging rate during deposition is 200mL / min), the deposition cycles of trimethylmethylcyclopentadiene platinum, bis[1-(dimethylamino)-2-propanol]copper, and octamethylcyclotetrasiloxane were 5, 15, and 5, respectively, corresponding to Pt, Cu, and Si metal element loadings of 0.1wt%, 3wt%, and 0.5wt%, respectively, based on diatomaceous earth mass. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 4.8) were pressed into tablets and sieved into 20-30 mesh particles under a pressure of 10 MPaG. 2g of the pressed modified diatomaceous earth and 10g of NaY molecular sieve powder were taken and loaded into two layers along the airflow direction, labeled as catalyst B.

[0057] Example 3

[0058] Preparation of catalyst C:

[0059] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 120g of hydroxylation solution (1.5wt% butylamine, 2wt% potassium carbonate, 2wt% sodium peroxide, pH=9), and stirred in a constant temperature water bath at 90℃ for 5h for hydrothermal treatment. The resulting suspension was rapidly cooled to room temperature and filtered, then washed several times with deionized water until the filtrate was neutral. The filtrate was then dried in an oven at 180℃ for 8h to obtain a hydroxyl-modified diatomaceous earth carrier (hydroxyl density 0.45mmol / g). 2g of the hydroxyl-modified diatomaceous earth was then subjected to metal loading via atomic deposition. Under the following deposition conditions (pulse time of 20 s for metal precursor, nitrogen purging time of 120 s; pulse time of 60 s for oxygen, nitrogen purging time of 120 s; deposition chamber temperature of 200℃; vacuum of 15 kPa; nitrogen purging rate of 200 mL / min), the deposition cycles of trimethylmethylcyclopentadiene platinum, bis[1-(dimethylamino)-2-propanol]copper, and octamethylcyclotetrasiloxane were 3, 10, and 3, respectively, corresponding to Pt, Cu, and Si metal element loadings of 0.06 wt%, 2 wt%, and 0.3 wt%, respectively, based on diatomaceous earth mass. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 5.4) were pressed into tablets and sieved into 20-30 mesh particles under a pressure of 10 MPaG. 2g of the pressed modified diatomaceous earth and 8g of NaY molecular sieve powder were taken and loaded into two layers along the airflow direction, labeled as catalyst C.

[0060] Example 4

[0061] Evaluation of the plastic pyrolysis performance of the catalyst:

[0062] The catalyst performance was evaluated using a self-built small-scale test setup (a small-scale series reactor, with a 200 mL pyrolysis reactor and a 10 mL catalytic cracking fixed-bed reactor). 60 g of mixed waste plastic granules (PE:PP mass ratio 3:1, PE molecular weight 80000 g / mol, PP molecular weight 150000 g / mol) were weighed and loaded into the pyrolysis reactor. The experiment was conducted under a nitrogen atmosphere at a flow rate of 50 mL / min and a pyrolysis temperature of 500℃. The vapor generated by pyrolysis passed through the catalytic cracking section and was condensed to obtain an oil product. After the experiment, the oil product was collected, weighed, and its composition was analyzed by chromatography.

[0063] The waste plastics used were commercially available plastic pellets. The carbon number distribution of the products was determined by gas chromatography using an Agilent Technologies GC7890. The test conditions were as follows:

[0064] The chromatographic column type was ZB-5HT; carrier gas: N2 (30 mL / min), H2 (30 mL / min), air (300 mL / min); detector FID (300℃), injector (300℃), injection volume 3.5 μL; the temperature program mode was used, holding at 50℃ for 10 min, then increasing to 200℃ at a rate of 2℃ / min and holding for 1 min, and then increasing to 350℃ at a rate of 5℃ / min and holding for 5 min.

[0065] Table 1 Yields of cracked oil products using different catalysts

[0066]

[0067] The data above shows that catalysts A, B, and C have good oil yields and light component yields; the yield of light components increases with increasing temperature.

[0068] Example 5

[0069] Catalyst stability assessment:

[0070] The stability of the catalyst was evaluated through multiple consecutive pyrolysis experiments. 150g of waste PE plastic and 10g of catalyst B were used, with a mass ratio of waste plastic to catalyst B of 20:1. The evaluation was conducted using a combination of thermal pyrolysis and catalytic pyrolysis. The experiments were carried out in a nitrogen atmosphere at a flow rate of 50 mL / min, a pyrolysis temperature of 500℃, and a catalytic pyrolysis temperature of 500℃. Multiple consecutive pyrolysis trials were performed, and the results are shown in Table 3.

[0071] Table 3. Evaluation of Continuous Cracking Catalyst in Small-Scale Tests

[0072] Number of consecutive cleavages Oil yield (%) ≤C12 yield (wt%) 1 86.3 37.3 2 86.2 36.7 3 86.0 36.5 4 85.9 36.2 5 85.1 35.9 6 84.1 34.2

[0073] Under the test conditions, the yield of pyrolysis oil from waste plastic obtained by the composite catalyst after five consecutive pyrolysis cycles was still over 87%, and the yield of components with less than C12 carbons was greater than 33%. A single gram of catalyst could process 75g of waste PE plastic, demonstrating high pyrolysis stability.

[0074] Comparative Example 1

[0075] Preparation of catalyst D (without surface hydroxyl modification):

[0076] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 120g of water and stirred in a constant temperature water bath at 80℃ for 6h for hydrothermal treatment. The resulting suspension was rapidly cooled to room temperature and filtered, then washed several times with deionized water until the filtrate was neutral. The filtrate was then dried in an oven at 180℃ for 6h to obtain an unmodified diatomaceous earth carrier (hydroxyl density 0.31mmol / g). 2g of the treated diatomaceous earth was weighed and metal-loaded onto it using atomic deposition. The deposition conditions were as follows (pulse time of the metal precursor was 20s). Nitrogen purging time was 120 s; ozone pulse time was 60 s, and nitrogen purging time was 120 s. Under the conditions of a deposition chamber temperature of 200℃, a vacuum of 15 kPa, and a nitrogen purging rate of 200 mL / min, the deposition cycles for trimethylmethylcyclopentadiene platinum, di[1-(dimethylamino)-2-propanol]copper, and octamethylcyclotetrasiloxane were 1, 2, and 1, respectively, corresponding to Pt, Cu, and Si metal element loadings of 0.01 wt%, 0.25 wt%, and 0.08 wt%, respectively, based on diatomaceous earth mass. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 5.2) were pressed into tablets and sieved into 20-30 mesh particles under a pressure of 10 MPaG. 2g of the pressed modified diatomaceous earth and 4g of NaY molecular sieve powder were taken and loaded into two layers along the airflow direction, labeled as catalyst D.

[0077] The TEM image of diatomite after Pt metal was loaded into catalyst D is shown below. Figure 2 As shown, the noble metal particles loaded on the unmodified diatomaceous earth have a large particle size and poor dispersion.

[0078] Comparative Example 2

[0079] Preparation of E catalyst (Pt deposition only):

[0080] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 120g of hydroxylation solution (ethanolamine 1wt%, sodium carbonate 1wt%, hydrogen peroxide 1wt%, pH=9), and stirred in a constant temperature water bath at 80℃ for 6h for hydrothermal treatment. The suspension after treatment was rapidly cooled to room temperature and filtered, and washed several times with deionized water until the filtrate was neutral. It was then dried in an oven at 180℃ for 8h to obtain the diatomaceous earth carrier with surface hydroxyl modification (hydroxyl density 0.42mmol / g). The surface hydroxyl content was then measured... 2g of modified diatomaceous earth was loaded with metal using atomic deposition. Under the following deposition conditions (pulse time of 20s for the metal precursor, nitrogen purging time of 120s; pulse time of 60s for oxygen, nitrogen purging time of 120s; deposition chamber temperature of 200℃; vacuum of 15kPa; nitrogen purging rate of 200mL / min), the trimethylmethylcyclopentadiene platinum deposition cycle was 1, corresponding to a Pt metal loading of 0.02wt%, based on the mass of diatomaceous earth. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 5.2) were pressed into tablets at 10MPaG and sieved to obtain 20-30 mesh particles. 2g of the pressed modified diatomaceous earth and 4g of NaY molecular sieve powder were then packed in two layers along the gas flow direction, labeled as catalyst E.

[0081] Comparative Example 3

[0082] Preparation of F catalysts (with different elemental contents):

[0083] 20g of diatomaceous earth (hydroxyl density 0.31mmol / g) was dissolved in 120g of hydroxylation solution (ethanolamine 1.5wt%, potassium carbonate 1wt%, hydrogen peroxide 1wt%, pH=9), and stirred in a constant temperature water bath at 80℃ for 6h for hydrothermal treatment. The resulting suspension was rapidly cooled to room temperature and filtered, then washed several times with deionized water until the filtrate was neutral. The filtrate was then dried in an oven at 180℃ for 6h to obtain a diatomaceous earth carrier with surface hydroxyl modification (hydroxyl density 0.42mmol / g). 2g of the surface hydroxyl modified diatomaceous earth was then subjected to metal loading via atomic deposition. Under the following deposition conditions (pulse time of 20 s for metal precursor, nitrogen purging time of 120 s; pulse time of 60 s for ozone, nitrogen purging time of 120 s; deposition chamber temperature of 200 ℃; vacuum of 15 kPa; nitrogen purging rate of 200 mL / min), the deposition cycles of trimethylmethylcyclopentadiene platinum, bis[1-(dimethylamino)-2-propanol]copper, and octamethylcyclotetrasiloxane were 12, 22, and 14, respectively, corresponding to Pt, Cu, and Si metal element loadings of 0.2 wt%, 4 wt%, and 1 wt%, respectively, based on diatomaceous earth mass. Modified diatomaceous earth powder and NaY molecular sieve powder (SiO2 / Al2O3 = 5.2) were pressed into tablets and sieved into 20-30 mesh particles under a pressure of 10 MPaG. 2g of the pressed modified diatomaceous earth and 4g of NaY molecular sieve powder were taken and loaded into two layers along the airflow direction, labeled as catalyst F.

[0084] Comparative Example 4

[0085] Evaluation of the plastic pyrolysis performance of the catalyst:

[0086] The catalyst performance was evaluated using a self-built small-scale test setup (a small-scale series reactor, with a 200 mL pyrolysis reactor and a 10 mL catalytic cracking fixed-bed reactor). 60 g of mixed waste plastic granules (PE:PP mass ratio 3:1, PE molecular weight 80000 g / mol, PP molecular weight 150000 g / mol) were weighed and loaded into the pyrolysis reactor. The experiment was conducted under a nitrogen atmosphere at a flow rate of 50 mL / min and a pyrolysis temperature of 500℃. The vapor generated by pyrolysis passed through the catalytic cracking section and was condensed to obtain an oil product. After the experiment, the oil product was collected, weighed, and its composition was analyzed by chromatography.

[0087] Table 2 Yields of cracked oil products using different catalysts

[0088]

[0089] A comparison of the results of catalyst A with those of catalysts D and E shows that the diatomaceous earth in the composite catalyst, after surface hydroxyl modification and atomic deposition modification, can improve the oil yield and the yield of components below C12.

[0090] Comparative Example 5

[0091] Evaluation of the cracking performance of SiO2+NaY catalyst:

[0092] Compared to Example 2, this comparative example replaced the modified diatomaceous earth in catalyst B with ordinary diatomaceous earth; all other aspects remained the same as in Example 2. The cracking performance of the NaY catalyst was tested, and the results are shown in the table below:

[0093]

[0094] Compared with catalyst B, the composite catalyst constructed in a cascade series exhibits higher yield, higher per-gram throughput, and better stability.

[0095] Comparative Example 6

[0096] Evaluation of the cracking performance of modified diatomaceous earth + ZSM-5 catalyst:

[0097] Compared to Example 2, this comparative example replaced the NaY in catalyst B with ZSM-5 molecular sieve; all other aspects remained the same as in Example 2. The cracking performance of the NaY catalyst was tested, and the results are shown in the table below:

[0098]

[0099] Compared with catalyst B, the composite catalyst using NaY has a higher yield and per-gram throughput, as well as better stability compared with ZSM-5.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A catalyst for recycling waste plastics, characterized in that, The catalyst comprises diatomaceous earth modified with surface deposition sites, Pt active components supported by vapor-phase atomic deposition and Cu and Si regulators, and NaY molecular sieves in a cascade series. The loadings of Pt, Cu, and Si elements are 0.02-0.1%, 0.4-3%, and 0.1-0.5%, respectively, based on the mass of diatomite. In this process, hydrocarbon macromolecules are first dehydrogenated and activated on Si@PtCu / diatomite, and the resulting olefin components are further cracked into small molecule oils in the lower NaY molecular sieve.

2. The catalyst according to claim 1, characterized in that, The diatomaceous earth modified by surface deposition sites is a diatomaceous earth modified by surface hydroxylation.

3. A method for preparing the waste plastic recycling catalyst according to claim 1 or 2, characterized in that, The method includes the following steps: S1: Surface-modify diatomaceous earth with a hydroxylating agent to obtain a suspension of modified diatomaceous earth; S2: Filter, wash, and dry the suspension to obtain the modified diatomaceous earth carrier; S3: Atomic deposition of Pt, Cu, and Si elements and ligand removal are performed on the modified diatomaceous earth support to obtain SiCu@Pt / diatomaceous earth, which serves as the dehydrogenation part of the catalyst; S4: SiCu@Pt / diatomite and NaY molecular sieve powders are pressed into tablets and filled separately to form a composite catalyst with a two-layer cascade structure, with NaY molecular sieve as the pyrolysis part.

4. The preparation method according to claim 3, characterized in that, The hydroxylating agent in S1 is an oxidizing hydroxylating agent; And / or, the treatment described in S1 is hydrothermal treatment.

5. The preparation method according to claim 4, characterized in that, The hydroxylating agent in S1 is an aqueous solution of an alcohol amine, a weak basic salt, or a peroxide reagent; The alcohol amines described in S1 include C2-C4 primary amines; The weakly basic salts described in S1 include one or more of the following: carbonic acid, phosphoric acid, and alkali metal salts of C1-C7 organic acids; The peroxidizing agent described in S1 includes one or more of alkyl peroxides, peroxide salts, and peroxidizing acids; The mass fractions of alcohol amine, weak basic salt, and peroxidizing agent in S1 are 1-4%, 1-4%, and 1-5%, respectively, based on the total mass of oxidizing hydroxylating agents; The pH value of the aqueous solution in S1 is 8-11; The hydrothermal treatment temperature in S1 is 60-90℃; the time is 1-10h.

6. The preparation method according to claim 5, characterized in that, The alkanolamine mentioned in S1 includes one or more of ethanolamine, diethanolamine, isopropanolamine, and propanolamine; The weakly basic salt described in S1 includes one or more of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium phosphate, sodium formate, sodium acetate, sodium citrate, sodium tartrate, and sodium salicylate. The peroxidizing agent described in S1 includes one or more of hydrogen peroxide, cumene peroxide, tert-butyl hydroperoxide, sodium peroxide, and peracetic acid. The mass fractions of alcohol amine, weak basic salt, and peroxidizing agent in S1 are 1-2%, 1-2%, and 1-2%, respectively, based on the total mass of oxidizing hydroxylating agents; The pH value of the aqueous solution in S1 is 8-10; The hydrothermal treatment temperature in S1 is 80-90℃; the time is 5-8h.

7. The preparation method according to claim 3, characterized in that, The drying temperature in S2 is 150-200℃, and the drying time is 4-8 hours.

8. The preparation method according to claim 7, characterized in that, The drying temperature in S2 is 160-180℃, and the drying time is 6-8 hours.

9. The preparation method according to claim 3, characterized in that, The precursors of Pt, Cu, and Si elements in S3 atomic deposition are the corresponding metal-organic precursors. And / or, an oxidant is added to S3 to pulse-remove the ligand.

10. The preparation method according to claim 9, characterized in that, The precursors of Pt, Cu and Si elements atomically deposited in S3 are trimethylmethylcyclopentadiene platinum, di[1-(dimethylamino)-2-propanol]copper and octamethylcyclotetrasiloxane, respectively. The deposition cycles for the trimethylmethylcyclopentadiene platinum precursor in S3 were 1-10; the deposition cycles for the di[1-(dimethylamino)-2-propanol]copper precursor were 1-20. The octamethylcyclotetrasiloxane precursor deposition cycle was 1-10 times; The oxidant in S3 is oxygen and / or ozone; The pulse duration of the oxidant in S3 is 20-60 seconds.

11. The preparation method according to claim 10, characterized in that, In S3, the deposition cycles for the trimethylmethylcyclopentadiene platinum precursor were 1-5 times; the deposition cycles for the di[1-(dimethylamino)-2-propanol]copper precursor were 5-15 times; and the deposition cycles for the octamethylcyclotetrasiloxane precursor were 1-5 times. The oxidant in S3 is ozone.

12. The preparation method according to claim 3, characterized in that, S4 is filled in two layers along the airflow direction: the upper layer is SiCu@Pt / diatomite, and the lower layer is NaY molecular sieve. And / or, the mass ratio of SiCu@Pt / diatomite and NaY molecular sieve in S4 is 1:(1-6); And / or, the NaY molecular sieve support in S4 is a molecular sieve with SiO2 / Al2O3 = 4.8-5.

4.

13. The preparation method according to claim 12, characterized in that, The mass ratio of SiCu@Pt / diatomite and NaY molecular sieve in S4 is 1:(2-5).

14. Use of a waste plastic recycling catalyst, wherein the catalyst is the catalyst according to claim 1 or 2, or the catalyst prepared by any one of claims 3-13, and the catalyst is used for waste plastic recycling.

15. The use according to claim 14, characterized in that, The catalyst is used for the recycling of PE and PP waste plastics.

16. A method for recycling waste plastics, wherein the method uses the catalyst according to claim 1 or 2, or the catalyst prepared by any one of claims 3-13, characterized in that, The method uses a waste plastic recycling catalyst to catalytically pyrolyze waste plastics.

17. The method according to claim 16, characterized in that, In the method described, the mass ratio of catalyst to waste plastic is 1:(10-35); And / or, the reaction temperature for catalytic cracking in the method is 350-500℃.

18. The method according to claim 17, characterized in that, In the method described, the mass ratio of catalyst to waste plastic is 1:(10-20).

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