A catalyst for waste plastic processing conversion and a preparation method thereof

Abstract

This invention discloses a catalyst for the processing and conversion of waste plastics and its preparation method. The preparation method includes the following steps: (1) adding a molecular sieve to a mixed solution containing a Group VIII metal compound and a Group VIB metal compound, separating and drying the sieve after impregnation to obtain a pretreated molecular sieve; (2) preparing a silica-alumina composite sol; (3) introducing the pretreated molecular sieve obtained in step (1) into the silica-alumina composite sol obtained in step (2) to prepare a catalytic precursor; (4) introducing the catalytic precursor obtained in step (3) into an active metal, followed by molding, drying, and calcination to obtain the catalyst. A catalyst for the processing and conversion of waste plastics obtained using the above preparation method is also provided. The catalyst possesses both hydrogenation and cracking functions, and has advantages such as high activity, good selectivity, and simple preparation method. When used for waste plastic processing, the conversion of waste plastics can be completed in only one step.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment technology, and more specifically relates to a catalyst for the processing and conversion of waste plastics and its preparation method. Background Technology

[0002] Plastics, due to their excellent durability, corrosion resistance, plasticity, and stability, are widely used in all aspects of society. Their production and consumption have become important indicators for assessing industrial development levels and people's quality of life. With the increasingly widespread use of plastic products, the subsequent disposal of waste plastics has become a key factor restricting its further development. Waste plastics already account for 10% of urban solid waste in my country, and one of the most effective ways to reduce plastic pollution is to increase the recycling rate of waste plastics and enhance their resource utilization value.

[0003] Comprehensive utilization of waste plastics not only contributes to environmental pollution control and comprehensive management, but also alleviates my country's resource shortage and addresses the bottleneck of oil supply falling short of demand. It is of great significance for achieving dual-carbon goals and addressing global climate change.

[0004] Currently, the main methods for managing plastic waste both domestically and internationally include landfilling, incineration, melt recycling, and pyrolysis conversion. Compared to traditional recycling methods, pyrolysis is a relatively environmentally friendly, economically feasible process with the potential for large-scale application. Pyrolysis mainly includes four methods: pyrolysis, catalytic pyrolysis, pyrolysis-catalytic modification, and catalytic pyrolysis-catalytic modification. Pyrolysis involves high reaction temperatures and long reaction times, resulting in low yields and quality of the liquid oil product. Catalytic pyrolysis catalysts are prone to deactivation and difficult to separate; therefore, current research mainly focuses on pyrolysis-catalytic modification and catalytic pyrolysis-catalytic modification. Both methods require at least two processes working together; waste plastics need to be first pyrolyzed to generate pyrolysis oil, which is then modified to obtain the target product. However, problems such as poor finished oil quality, numerous byproducts, high energy consumption during processing, and high catalyst usage still need to be addressed.

[0005] CN202110847013.2 discloses a method for directly preparing aviation gasoline and aviation kerosene from waste polyolefin plastics. This method uses high-molecular-weight waste polyolefin plastics as raw materials and employs a bifunctional catalyst composed of a precious metal and an inorganic solid acid. This couples the hydrogenation degradation and isomerization reaction of high-molecular-weight polyolefin plastics, achieving a one-step continuous process for producing high-value petroleum products from polyolefin plastics. The method features mild reaction conditions, a simple catalyst preparation process, high activity, selectivity, and good stability, making it suitable for industrial production. However, the precious metal catalyst is expensive, resulting in poor economic viability.

[0006] CN201510122785.4 discloses a method for producing high-quality gasoline and diesel from chlorinated plastic oil. The method involves injecting the chlorinated plastic oil into a high-temperature dechlorination tower containing activated alumina for high-temperature dechlorination. The dechlorinated plastic oil is then subjected to catalytic distillation and hydrorefining to obtain high-quality gasoline and diesel. This method can utilize existing equipment, offers high operational flexibility, and can meet diverse product requirements. However, it requires different process couplings, resulting in a complex process and poor economic efficiency. Summary of the Invention

[0007] The main objective of this invention is to provide a catalyst for the processing and conversion of waste plastics and its preparation method. The catalyst has both hydrogenation and cracking functions. When used for waste plastic processing, the conversion of waste plastics can be completed in only one step, which solves the problem of the cumbersome two-step operation in the existing process. At the same time, the provided catalyst has the advantages of high activity, good selectivity and simple preparation method.

[0008] I. This invention provides a method for preparing a catalyst for the processing and conversion of waste plastics, the preparation method comprising the following steps:

[0009] (1) Molecular sieves are added to a mixed solution containing Group VIII metal compounds and Group VIB metal compounds. After impregnation, the solid phase obtained by separation is dried to obtain pretreated molecular sieves.

[0010] (2) After mixing the aluminum compound solution and the dispersant, add the silica sol aqueous solution and hydrolyze to obtain a silica-alumina composite sol;

[0011] (3) Introduce the pretreated molecular sieve obtained in step (1) into the silica-alumina composite sol obtained in step (2), react at 40℃~80℃, and obtain the catalytic precursor after aging and drying;

[0012] (4) The catalyst is obtained by mixing the catalyst precursor obtained in step (3), the group VIII metal compound, the group VIB metal compound, sulfur powder, hydrocarbons, adhesive solvent and extrusion aid, and then molding, drying and calcining.

[0013] Furthermore, according to a specific embodiment of the present invention, the compound containing Group VIB metal in step (1) is an inorganic salt containing metal Mo and / or W. Specifically, the metal compound containing Group VIB can be selected from one or more of ammonium molybdate, ammonium tungstate, molybdenum oxide, and tungsten oxide.

[0014] Furthermore, according to a specific embodiment of the present invention, the compound containing Group VIII metal in step (1) is an inorganic salt containing metal Ni and / or Co. Specifically, the compound containing Group VIII metal may be selected from one or more of nickel nitrate, basic nickel carbonate, nickel citrate, cobalt nitrate, basic cobalt carbonate, and cobalt citrate.

[0015] Furthermore, according to a specific embodiment of the present invention, the molecular sieve in step (1) is a molecular sieve with acidic centers, such as at least one of Y molecular sieve, ZSM-5 molecular sieve, β molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve, preferably a modified molecular sieve, specifically one or more of HY, REY, USY, REHY, REUSY, and HZSM-5 molecular sieve.

[0016] Furthermore, according to a specific embodiment of the present invention, the drying conditions in step (1) are as follows: the drying temperature is 40-120°C, and the drying time is 2-8 hours. Vacuum drying is preferred, with a vacuum degree of -0.03 to -0.1 MPa.

[0017] Furthermore, according to a specific embodiment of the present invention, the aluminum-containing compound in step (2) can be an organic aluminum-containing compound and / or an inorganic aluminum-containing compound; wherein, the organic aluminum-containing compound can be selected from one or more of alkylaluminum and alkoxyaluminum; further, the alkylaluminum can be at least one of trimethylaluminum, triethylaluminum, tripropylaluminum, and triisobutylaluminum, and the alkoxyaluminum has 3 to 20 carbon atoms, specifically selected from at least one of triethanolaluminum, tripropoxidealuminum, triisopropoxidealuminum, and tri-n-butoxyaluminum. When using an organic aluminum-containing compound, it is preferable to mix the organic aluminum-containing compound with ethanol to obtain an aluminum sol prepreg, and the weight ratio of the organic aluminum-containing compound to ethanol is 5:1 to 1:10. The inorganic aluminum-containing compound can be selected from one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, and sodium aluminate.

[0018] Furthermore, according to a specific embodiment of the present invention, the dispersant in step (2) is a polycarboxylate ammonium salt, or one or more polycarboxylate ether compounds. The polycarboxylate ammonium salt can be at least one of polyacrylate ammonium salt and polylactic acid ammonium salt, preferably polyacrylate ammonium salt; the polycarboxylate ether compound can be at least one of methyl allyl polyoxyethylene ether and isopentenyl polyoxyethylene ether. The dispersant accounts for 1 wt% to 20 wt% of the silica-alumina sol.

[0019] Furthermore, according to a specific embodiment of the present invention, the silica content in the silica sol aqueous solution in step (2) is 1wt% to 50wt%, preferably 5wt% to 35wt%; the sodium oxide content is less than 0.1wt%, preferably less than 0.05wt%; the silica sol can be prepared in-house or according to methods disclosed in the prior art, or it can be a commercially available product. The silica sol can be prepared by hydrolysis of a silicon source, and the silicon source can be selected from one or more of water glass, sodium silicate, and tetraethylsilane aqueous solution.

[0020] Furthermore, according to a specific embodiment of the present invention, the aging time in step (3) is 2 to 12 hours.

[0021] Furthermore, according to a specific embodiment of the present invention, the supercritical drying pressure in step (3) is 1 to 15 MPa, the drying temperature is 20 to 100°C, the drying medium is carbon dioxide, and the flow rate of the drying medium is 40 liters / hour to 500 liters / hour.

[0022] Furthermore, according to a specific embodiment of the present invention, the hydrocarbons in step (4) are hydrocarbons with a dry point of less than 400°C, preferably one or more of petroleum hydrocarbons and carboxylic acid esters. More specifically, the petroleum hydrocarbons can be one or more of naphtha, white oil, gasoline, kerosene, diesel, lubricating oil base oil, deasphalted oil, straight-run distillate oil, and vacuum distillate oil. The carboxylic acid esters are one or more of sesame oil, safflower oil, corn oil, cottonseed oil, peanut oil, rapeseed oil, soybean oil, walnut oil, coconut oil, olive oil, and sunflower oil. The amount of hydrocarbons used is 1-10% of the catalyst weight, and the amount of sulfur powder used is 100%-150% of the theoretical sulfur required for hydrogenation active metals, preferably 100%-120%.

[0023] Furthermore, according to a specific embodiment of the present invention, the extrusion aid and the adhesive solvent in step (4) are well known to those skilled in the art, and the specific types and amounts of substances used can be determined according to existing knowledge in the art. More preferably, the extrusion aid can be one or more of guar gum powder, starch, methylcellulose, polyvinyl alcohol, and polyethylene glycol, and its amount is 1.0wt% to 5.0wt% of the catalyst weight. The adhesive solvent is one or more of nitric acid, oxalic acid, and phosphoric acid, and its amount is 1.0wt% to 10.0wt% of the catalyst weight.

[0024] Furthermore, according to a specific embodiment of the present invention, the compound containing Group VIB metal in step (4) is an inorganic salt containing metal Mo and / or W. Specifically, the compound containing Group VIB metal can be selected from one or more of ammonium molybdate, ammonium tungstate, molybdenum oxide, and tungsten oxide.

[0025] Furthermore, according to a specific embodiment of the present invention, the compound containing Group VIII metal in step (4) is an inorganic salt containing metal Ni and / or Co. Specifically, the compound containing Group VIII metal may be selected from one or more of nickel nitrate, basic nickel carbonate, nickel citrate, cobalt nitrate, basic cobalt carbonate, and cobalt citrate.

[0026] Furthermore, according to a specific embodiment of the present invention, the drying temperature in step (4) is 50–180°C, preferably 80–150°C, and the drying time is 1–24 h, preferably 3–12 h. The calcination temperature is 400°C–770°C, preferably 450°C–650°C; the calcination time is 1–12 h, preferably 3–8 h. The calcination is carried out under a nitrogen or hydrogen atmosphere.

[0027] A second aspect of the present invention provides a catalyst for the processing and conversion of waste plastics, the catalyst being prepared by the method described above.

[0028] Furthermore, according to a specific embodiment of the present invention, the catalyst for processing and converting waste plastics includes a support and an active metal supported on the support. The support is a silica-alumina compound containing a pretreated molecular sieve, and the pretreated molecular sieve is a molecular sieve loaded with an active metal. The active metal is a Group VIII metal or a Group VIB metal. The active metal exists in the form of a sulfide.

[0029] Furthermore, according to a specific embodiment of the present invention, in the catalyst used for waste plastic processing and conversion, the content of pretreated molecular sieve in the silicon-aluminum compound is 1.5wt% to 50wt%, preferably 3 to 20wt%.

[0030] Furthermore, according to a specific embodiment of the present invention, in the catalyst used for the processing and conversion of waste plastics, the mass ratio of silicon oxide to aluminum oxide in the silicon-aluminum compound is 50-95:50-5, preferably 60-90:40-10.

[0031] Furthermore, according to a specific embodiment of the present invention, in the catalyst used for waste plastic processing and conversion, the molecular sieve is a molecular sieve with acidic centers, such as at least one of Y molecular sieve, ZSM-5 molecular sieve, β molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve, preferably a modified molecular sieve, specifically one or more of HY, REY, USY, REHY, REUSY, and HZSM-5 molecular sieve.

[0032] Furthermore, according to a specific embodiment of the present invention, in the catalyst used for waste plastic processing and conversion, the content of active metal as oxide is 10-40 wt% based on the weight of the catalyst, and the active metal includes active metal supported on molecular sieve and active metal supported on carrier.

[0033] Furthermore, according to a specific embodiment of the present invention, the pore volume of the catalyst used for waste plastic processing and conversion is 0.3–3.0 cm³. 3 / g.

[0034] Furthermore, according to a specific embodiment of the present invention, the catalyst for processing and converting waste plastics includes two levels of channels, wherein the pore size of the first level channel is 1-8 nm and the pore size of the second level channel is 20-200 nm; further still, the pores of the first level channel account for 5-30% of the total number of pores, and the pores of the second level channel account for 60-90% of the total number of pores.

[0035] The present invention also provides a waste plastic treatment process in which waste plastics are treated by contacting hydrogen gas in the presence of the catalyst used for waste plastic processing and conversion.

[0036] Furthermore, according to a specific embodiment of the present invention, the waste plastic is a polyolefin waste plastic.

[0037] Furthermore, according to a specific embodiment of the present invention, the processing conditions are generally as follows: reaction temperature of 320–440°C and reaction pressure of 1.0–10.0 MPa. The reaction can be carried out in a closed or flowing state, with a hydrogen flow rate of 50–500 mL / min in the flowing state.

[0038] The catalyst and its preparation method for waste plastic processing and conversion provided by this invention have the following advantages:

[0039] (1) The catalyst for processing and converting waste plastics provided by the present invention has two active centers: cracking and hydrogenation. It can hydrogenate the generated small molecules at the same time as cracking. Macroporous silica-alumina first depolymerizes the polymer of waste plastics into large molecular fragments, and then further cracks them in the molecular sieve channels to form smaller fragments. After hydrogenation, high-quality low-carbon hydrocarbons and middle distillates are obtained. The gas yield is low and the residue is small, which improves the quality of the target product.

[0040] (2) In the catalyst preparation method for waste plastic processing and conversion provided by the present invention, after the dispersant in the sol is adsorbed on the surface of the molecular sieve particles, the branches and the branches on the surface of other particles form a three-dimensional cross, which hinders the particles from approaching each other, so that the molecular sieve is uniformly dispersed in the sol and gel and is not easy to aggregate. Moreover, during drying, it is ensured that the formed silicon-aluminum composite is a network structure of silicon-aluminum aerogel that does not collapse, while the molecular sieve is interspersed in it. The molecular sieve channels are filled with active metal salts, which also prevents sol molecules from entering the molecular sieve channels. After calcination, the channels of the molecular sieve are restored, which is conducive to the entry and exit of reactants.

[0041] (3) Waste plastics are macromolecular polymers with large molecular weights and long carbon chains. They cannot directly enter the channels of conventional acidic molecular sieves, which affects the pyrolysis activity of the molecular sieve. The catalyst support of this invention is a silicon-aluminum compound containing a molecular sieve. The silicon-aluminum compound has large channels and high porosity, which is conducive to the entry of polymer molecules. The polymer decomposes into smaller molecules in the silicon-aluminum compound channels and then undergoes further pyrolysis in the molecular sieve channels. At the same time, hydrogen is added to the metal active sites to finally generate the target product. Detailed Implementation

[0042] The technical features of the present invention are further described below through embodiments, but these embodiments are not intended to limit the present invention.

[0043] Unless otherwise specified, the pore volume and pore size in this study were measured using the cryogenic liquid nitrogen physical adsorption method, and the instrument used was the ASAP2405 and 2420 physical adsorption instrument manufactured by the American company.

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] All chemical reagents used in this study are commercially available and can be purchased. The pore size of the HY molecular sieve is 2.76 nm, and the pore size of the β molecular sieve is 1.48 nm.

[0046] Example 1

[0047] 12g of HY molecular sieve powder was saturated and impregnated in a molybdenum-nickel-phosphorus solution (32wt% molybdenum oxide, 6wt% nickel oxide) for 2 hours. After draining, it was treated in a vacuum drying oven at 50℃ and -0.05MPa for 3 hours. Aluminum nitrate and ammonium polyacrylate were mixed at a ratio of 100:5 (by weight), and silica gel solution (commercially available solution containing 25wt% SiO2) was added and mixed. The alumina:silica ratio in the sol was 12:88 (by weight). Ammonia was added to adjust the pH to 7, and the reaction was carried out at 50℃ to obtain the sol. The treated molecular sieve was added to the sol, making it occupy 12% of the aerosol, and stirred evenly. Then, it was transferred to a constant temperature water bath at 50℃ and aged for 4 hours to form a silica-alumina gel. The gel was supercritically dried in a carbon dioxide system at 5MPa, 50℃, and a flow rate of 200L / h to obtain the silica-alumina composite. The composite material was mixed with a molybdenum-nickel-phosphorus solution (containing 8 wt% nickel oxide and 45 wt% molybdenum oxide), 12 g of sulfur powder, 3 ml of corn oil, 1.5 g of nitric acid, and 4 g of guar gum powder. The mixture was kneaded and extruded into strips, dried at 150 °C for 5 hours under nitrogen, and calcined at 550 °C for 3 hours to obtain the catalyst product. The composition and properties of the catalyst are shown in Table 1.

[0048] Example 2

[0049] 10g of β-molecular sieve powder was saturated and impregnated in a molybdenum-cobalt-phosphorus solution (30 wt% molybdenum oxide, 8 wt% cobalt oxide) for 3 hours. After draining, it was treated in a vacuum drying oven at 70℃ and -0.04MPa for 3 hours. Aluminum nitrate and methyl allyl polyoxyethylene ether were mixed at a ratio of 100:3 (by weight), and silica gel solution (commercially available solution containing 20 wt% SiO2) was added to make the alumina:silica ratio of 25:75 (by weight) in the sol. Ammonia was added to adjust the pH to 7.5, and the reaction was carried out at 45℃ to obtain the sol. The treated molecular sieve was added to the sol to make it occupy 10% of the aerosol, and stirred evenly. Then, it was transferred to a constant temperature water bath at 60℃ and allowed to stand for 2 hours to form a silica-alumina gel. The gel was supercritically dried in a carbon dioxide system at 6MPa, 60℃, and a flow rate of 300L / h to obtain the silica-alumina composite. The composite material was mixed with a molybdenum-nickel-phosphorus solution (containing 6 wt% nickel oxide and 48 wt% molybdenum oxide), 13 g of sulfur powder, 3 ml of olive oil, 1.5 g of nitric acid, and 4 g of guar gum powder. The mixture was kneaded and extruded into strips, dried at 150 °C for 5 hours under nitrogen, and calcined at 600 °C for 3 hours to obtain the catalyst product. The composition and properties of the catalyst are shown in Table 1.

[0050] Example 3

[0051] 20g of β-molecular sieve powder was saturated and impregnated in a molybdenum-nickel-phosphorus solution (same as in Example 1) for 2 hours. After draining, it was treated in a vacuum drying oven at 60℃ and a vacuum degree of -0.06MPa for 3 hours. Aluminum isopropoxide and ethanol were mixed in a 10:1 ratio, and 5% isopentenyl polyoxyethylene ether was added and mixed evenly. Then, it was mixed with silica gel solution (commercially available solution with a silica content of 30%), so that the alumina:silica ratio in the sol was 20:80 (m). The solution was slowly hydrolyzed at 60℃ to make the pH of the solution 7.0. The treated molecular sieve was added to the sol, so that it accounted for 20%m in the aerosol. The mixture was stirred evenly and then transferred to a constant temperature water bath at 70℃ and allowed to stand for 2 hours to form a silica-alumina gel. The gel was supercritically dried in a carbon dioxide system at 5MPa, 50℃, and a flow rate of 200L / h to obtain the silica-alumina composite. The composite was mixed with nickel nitrate solution (containing 15 wt% nickel oxide), ammonium molybdate solution (containing 20 wt% molybdenum oxide), 13 g sulfur powder, 5 ml white oil, 2.5 g nitric acid, and 3 g guar gum powder. The mixture was kneaded and extruded into strips, dried at 180 °C for 4 hours under nitrogen, and calcined at 500 °C for 5 hours to obtain the catalyst product. The composition and properties of the catalyst are shown in Table 1.

[0052] Example 4

[0053] Aluminum isopropoxide and ethanol were mixed in a 10:1 ratio, and 5% isopentenyl polyoxyethylene ether was added and mixed thoroughly. Tetraethyl orthosilicate was then diluted with water to a SiO2 concentration of 30 g / L, resulting in an alumina:silica ratio of 30:70 (by weight) in the sol. The mixture was heated to 65°C for hydrolysis and aged at this temperature for 2 hours. A 10% acetic acid solution was added dropwise until the pH reached 6.0. The mixture was then stirred and mixed with the aluminum sol. Ammonia was added to adjust the pH to 7.0, and 15 g of Y molecular sieve powder was added. The molecular sieve pretreatment was the same as in Example 1, ensuring it comprised 15% of the aerosol. The mixture was heated to 80°C and held at this temperature for 3.5 hours to form an aluminosilicate gel. The gel was then subjected to supercritical drying in a carbon dioxide system to obtain the aluminosilicate composite. The drying conditions were the same as in Example 1.

[0054] The aerogel and tungsten-cobalt solution (25 wt% tungsten oxide, 3.5 wt% cobalt oxide), 1 g nitric acid, 11 g sulfur powder, 3 ml gasoline, and 3 g guar gum powder were mixed, kneaded, and extruded into strips. The mixture was dried at 150°C for 5 hours under nitrogen atmosphere and then calcined at 550°C for 3 hours to obtain the catalyst product. The composition and properties of the catalyst are shown in Table 1.

[0055] Comparative Example 1

[0056] Amorphous silica-alumina (pore volume 1.25 mL / g), SB powder, and Y molecular sieve were mixed evenly in a ratio of 20:75:5. This mixture was then combined with ammonium thiomolybdate solution (molybdenum oxide concentration 35 g / 100 mL), nickel nitrate solution (containing nickel oxide 16 g / 100 mL), guar gum powder, and dilute nitric acid, kneaded, and extruded into strips. The mixture was dried at 150 °C for 5 hours under nitrogen atmosphere and calcined at 500 °C for 3 hours to obtain the final catalyst. The composition and properties of the catalyst are shown in Table 1.

[0057] Comparative Example 2

[0058] The preparation of the silica-alumina sol was the same as in Example 1, except that no dispersant was added. 12g of HY molecular sieve powder was directly added to the sol, and other conditions were the same as in Example 1, to obtain the silica-alumina composite.

[0059] The composite material was mixed with a molybdenum-nickel-phosphorus solution (containing 8 wt% nickel oxide and 45 wt% molybdenum oxide), 10 g of sulfur powder, 3 ml of corn oil, 1.5 g of nitric acid, and 4 g of guar gum powder. The mixture was kneaded and extruded into strips, dried at 150 °C for 5 hours under nitrogen, and calcined at 550 °C for 3 hours to obtain the catalyst product. The composition and properties of the catalyst are shown in Table 1.

[0060] Evaluation Test

[0061] Methods for evaluating the activity of catalysts prepared in Examples 1-4 and Comparative Examples 1 and 2:

[0062] The catalyst and waste plastic (a mixture of PP and PE, PP:PE = 1:1) were loaded into a high-pressure reactor. The reactor was sealed with hydrogen at 3 MPa and heated to 350°C at a rate of 20°C / h with a hydrogen flow rate of 100 mL / min. The reactor was stirred while heating. After the temperature reached 150°C, the gas from the apparatus was collected for analysis. After reaching the reaction temperature, the reactor was kept at a constant temperature for 0.6 h before cooling began. The high-pressure reactor was then opened, and the collected liquid was analyzed. The evaluation results are shown in Table 2, and the product properties are shown in Table 3.

[0063] Table 1. Catalyst composition and properties

[0064]

[0065] Table 2 Evaluation Results

[0066]

[0067] Table 3 Product Properties

[0068]

[0069] As shown in Tables 1 and 2, the waste plastic conversion catalyst prepared by this technology possesses large pore volume and secondary channels, which is beneficial for the adsorption and reaction of macromolecules. This results in a high conversion rate of waste plastics, a high proportion of diesel fuel in the products, and low generation of pyrolysis gas, thus improving the utilization rate of waste plastics. Table 3 shows that, because the catalyst in this technology is a bifunctional catalyst, the pyrolyzed oil is directly hydrogenated. The final product, after hydrogenation, consists of low-carbon hydrocarbons (gasoline fraction), which is a high-quality ethylene feedstock. The middle distillate has a high cetane number and good combustion performance, making it a high-quality diesel fuel fraction.

Claims

1. A method for preparing a catalyst for the processing and conversion of waste plastics, the preparation method comprising the following steps: (1) Add the molecular sieve to a mixed solution containing Group VIII metal compounds and Group VIB metal compounds. After impregnation, the solid phase obtained by separation is dried to obtain the pretreated molecular sieve. (2) After mixing the aluminum compound solution and the dispersant, add the silica sol aqueous solution and hydrolyze to obtain a silica-alumina composite sol; The dispersant is one or more of polycarboxylic acid ammonium salts and polycarboxylic acid ether compounds; (3) Introduce the pretreated molecular sieve obtained in step (1) into the silica-alumina composite sol obtained in step (2), react at 40℃~80℃, and obtain the catalytic precursor after aging and drying; (4) The catalyst is obtained by mixing the catalyst precursor obtained in step (3), one or more of the group VIII metal compound, the group VIB metal compound, sulfur powder, petroleum hydrocarbon and carboxylic acid ester, a peptizing agent and an extrusion aid, and then molding, drying and calcining. The petroleum hydrocarbon has a drying point of less than 400°C. The drying temperature is 50 to 180°C and the calcination temperature is 400°C to 770°C. The calcination is carried out in a nitrogen or hydrogen atmosphere.

2. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, In step (1), the compound containing a Group VIB metal is an inorganic salt containing the metals Mo and / or W. The Group VIB metal compound is selected from one or more of the following: ammonium molybdate, ammonium tungstate, molybdenum oxide, and tungsten oxide.

3. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, In step (1), the compound containing a Group VIII metal is an inorganic salt containing metals Ni and / or Co. The compound containing a Group VIII metal is selected from one or more of nickel nitrate, basic nickel carbonate, nickel citrate, cobalt nitrate, basic cobalt carbonate, and cobalt citrate.

4. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The molecular sieve in step (1) is at least one of Y molecular sieve, ZSM-5 molecular sieve, β molecular sieve, MOR molecular sieve, and MCM-22 molecular sieve.

5. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The drying conditions in step (1) are as follows: the drying temperature is 40-120℃ and the drying time is 2-8h.

6. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1 or 5, wherein, The drying in step (1) is done by vacuum drying, with a vacuum degree of -0.03 to -0.1 MPa.

7. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The aluminum-containing compound in step (2) is an organic aluminum-containing compound and / or an inorganic aluminum-containing compound; wherein, the organic aluminum-containing compound is selected from one or more of alkyl aluminum and alkoxy aluminum; and the inorganic aluminum-containing compound is selected from one or more of aluminum sulfate, aluminum nitrate, aluminum chloride, and sodium aluminate.

8. The method for preparing the catalyst for waste plastic processing and conversion according to claim 7, wherein, The alkylaluminum is at least one of trimethylaluminum, triethylaluminum, tripropylaluminum, and triisobutylaluminum, and the alkoxyaluminum has 3 to 20 carbon atoms and is selected from at least one of triethanolaluminum, tripropoxidealuminum, triisopropoxidealuminum, and tri-n-butoxyaluminum.

9. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The polycarboxylic acid ammonium salt is at least one of polyacrylate ammonium salt and polylactic acid ammonium salt; the polycarboxylic acid ether compound is at least one of methyl allyl polyoxyethylene ether and isopentenyl polyoxyethylene ether.

10. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1 or 9, wherein, The polycarboxylate ammonium salt is the polyacrylate ammonium salt.

11. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The silica content in the silica sol aqueous solution in step (2) is 1wt% to 50wt%.

12. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The silica content in the silica sol aqueous solution in step (2) is 5wt% to 35wt%.

13. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The aging time in step (3) is 2 to 12 hours.

14. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The supercritical drying pressure in step (3) is 1-15 MPa, the drying temperature is 20-100℃, and the drying medium is carbon dioxide.

15. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, Petroleum hydrocarbons are one or more of naphtha, white oil, gasoline, kerosene, diesel, lubricating oil base oil, deasphalted oil, straight-run distillate oil, and vacuum distillate oil; carboxylic acid esters are one or more of sesame oil, safflower oil, corn oil, cottonseed oil, peanut oil, rapeseed oil, soybean oil, walnut oil, coconut oil, olive oil, and sunflower oil.

16. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, In step (4), the compound containing a Group VIB metal is an inorganic salt containing the metals Mo and / or W. The compound containing a Group VIB metal is selected from one or more of the following: ammonium molybdate, ammonium tungstate, molybdenum oxide, and tungsten oxide.

17. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, In step (4), the compound containing a Group VIII metal is an inorganic salt containing metals Ni and / or Co. The compound containing a Group VIII metal is selected from one or more of nickel nitrate, basic nickel carbonate, nickel citrate, cobalt nitrate, basic cobalt carbonate, and cobalt citrate.

18. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1, wherein, The drying temperature in step (4) is 80-150℃ and the drying time is 1-24h; the calcination temperature is 450℃-650℃ and the calcination time is 1-12h.

19. The method for preparing the catalyst for waste plastic processing and conversion according to claim 1 or 18, wherein, The drying time in step (4) is 3 to 12 hours, and the calcination time is 3 to 8 hours.

20. A catalyst for the processing and conversion of waste plastics, wherein, The catalyst is obtained by the preparation method described in any one of claims 1-19.

21. The catalyst for processing and converting waste plastics according to claim 20, wherein, The catalyst used for the processing and conversion of waste plastics includes a support and an active metal supported on the support. The support is a silica-alumina compound containing a pretreated molecular sieve, and the pretreated molecular sieve is a molecular sieve loaded with an active metal. The active metal is a Group VIII metal or a Group VIB metal. The active metal exists in the form of a sulfide.

22. The catalyst for processing and converting waste plastics according to claim 21, wherein, In catalysts used for the processing and conversion of waste plastics, the content of pretreated molecular sieves in silicon-aluminum compounds is 1.5wt% to 50wt%.

23. The catalyst for processing and converting waste plastics according to claim 21, wherein, In catalysts used for the processing and conversion of waste plastics, the content of pretreated molecular sieves in silicon-aluminum compounds is 3–20 wt%.

24. The catalyst for processing and converting waste plastics according to claim 21, wherein, In catalysts used for the processing and conversion of waste plastics, the mass ratio of silicon oxide to aluminum oxide in the silicon-aluminum compound is 50–95:50–5.

25. The catalyst for processing and converting waste plastics according to claim 21, wherein, In catalysts used for the processing and conversion of waste plastics, the mass ratio of silicon oxide to aluminum oxide in the silicon-aluminum compound is 60–90:40–10.

26. The catalyst for processing and converting waste plastics according to claim 21, wherein, In catalysts used for processing and converting waste plastics, the carrier content is 60-90 wt% based on the catalyst weight.

27. The catalyst for processing and converting waste plastics according to claim 21, wherein, The catalyst used for processing and converting waste plastics has a pore volume of 0.3–3.0 cm³. 3 / g.

28. The catalyst for processing and converting waste plastics according to claim 21, wherein, The catalyst used for processing and converting waste plastics includes two levels of pores, wherein the pore size of the first level pores is 1-8 nm and the pore size of the second level pores is 20-200 nm; the pores of the first level pores account for 5-30% of the total, and the pores of the second level pores account for 60-90% of the total.

29. A waste plastic treatment process, wherein, in the presence of the catalyst for waste plastic processing and conversion as described in any one of claims 20-28, waste plastic is treated by contacting hydrogen.

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