A catalytic process for polyolefin waste

Abstract

The application relates to a method for efficient utilization of solid waste, in particular to a catalytic method for polyolefin waste. The application provides a preparation method of a catalyst for catalyzing polyolefin waste, which comprises the following steps: 1) mixing an acid molecular sieve and an active metal precursor, and roasting to obtain a catalyst precursor; and 2) reducing the catalyst precursor by a reducing agent to obtain the catalyst. In the application, the acid molecular sieve is used as a carrier, solid ion exchange is carried out through high-temperature roasting, the active metal component is solidified in the molecular sieve channel structure, the reduced catalyst has rich acid sites, defect sites and high-dispersed active metals, and in combination with the shape selection and confinement of the molecular sieve structure, efficient conversion of the polyolefin waste into naphtha can be realized.

Description

Technical Field

[0001] This application relates to a method for the efficient utilization of solid waste, specifically a catalytic method for polyolefin waste. Background Technology

[0002] The widespread use of plastics has led to severe environmental pollution and resource waste. Current physical recycling methods reduce the quality of plastics, while chemical conversion has become an effective means of plastic recycling. High-temperature pyrolysis (400-600℃) can degrade plastics into small-molecule products, but the selectivity for gasoline and diesel components is low, and it produces large amounts of C1-C4 gases and carbon deposits. Catalytic hydrogenolysis can effectively degrade plastics. Pt / SrTiO3 can convert polyethylene into 42-97% wax and lubricating oil; mesoporous Pt / SiO2, under conditions of 250℃ and 24h, has achieved the conversion of high-density polyethylene into diesel; simultaneously, Pt coupled with catalytic hydrogenolysis and aromatization has achieved the conversion of polyethylene into long-chain aromatics under hydrogen-free conditions. Catalytic hydrogenolysis generally requires high temperatures and long times. Catalytic cracking, by adjusting the acidity of the support and the hydrogenation metal catalyst, can achieve the effective conversion of plastics into gasoline and diesel, but currently used supported catalysts have problems such as high reaction temperatures, long reaction times, and wide product distribution, and the use of products as fuel still causes CO2 emissions. Summary of the Invention

[0003] The inventors of this application have discovered through research and analysis that: by efficiently converting polyethylene into naphtha via hydrocracking, and then producing ethylene monomers through steam cracking, a recycling and closed-loop utilization system for polyethylene can be constructed.

[0004] This application addresses the technical problem of poor chemical conversion efficiency of polyolefin waste in existing technologies. To achieve the technical effect of directional conversion of polyolefin waste into naphtha, a method and catalyst for the catalytic conversion of polyolefin waste are designed. Using acidic molecular sieves as a carrier, solid ion exchange is carried out through high-temperature calcination to immobilize active metal components in the pore structure of the molecular sieve. The reduced catalyst has abundant acidic sites, defect sites, and highly dispersed active metals. Combined with the shape-selective and confinement effects of the molecular sieve structure, the efficient conversion of polyolefin waste into naphtha can be achieved.

[0005] The purpose of this application is to provide a catalytic method for polyolefin waste, which solves the problems of high reaction temperature, long reaction time and wide product distribution in the prior art.

[0006] To achieve the above and other related objectives, the first aspect of this application provides a method for preparing a catalyst for catalyzing polyolefin waste, comprising the following steps:

[0007] 1) Acidic molecular sieves and active metal precursors are mixed and calcined to obtain catalyst precursors;

[0008] 2) The catalyst precursor is reduced by a reducing agent to obtain the catalyst.

[0009] In any embodiment of this application, the polyolefin of the polyolefin waste catalyst is selected from polyethylene and / or polypropylene.

[0010] In any embodiment of this application, in step 1), the acidic molecule is selected from one or more of ZSM-5, Beta, and HY molecular sieves.

[0011] In any embodiment of this application, in step 1), the active body precursor is selected from one or more combinations of platinum chloride, ruthenium chloride, nickel chloride, palladium chloride, cobalt chloride, platinum carbonate, ruthenium carbonate, nickel carbonate, palladium carbonate, and cobalt carbonate.

[0012] In any embodiment of this application, in step 1), the mixing method is selected from ball milling.

[0013] In any embodiment of this application, in step 1), the mixing time is 12 to 24 hours.

[0014] In any embodiment of this application, in step 1), the calcination temperature is 500–700°C.

[0015] In any embodiment of this application, in step 1), the calcination time is 3 to 5 hours.

[0016] In any embodiment of this application, in step 1), the mass fraction of the active metal precursor is 0.5 to 10% (w / w) based on the total mass of the catalyst.

[0017] In any embodiment of this application, in step 1), the mass fraction of the acidic molecular sieve is 90-99.5% (w / w) based on the total mass of the catalyst.

[0018] In any embodiment of this application, in step 1), the mass ratio of the acidic molecular sieve to the active metal precursor is 9 to 199:1.

[0019] In any embodiment of this application, in step 2), the reducing agent is selected from hydrogen and / or carbon monoxide.

[0020] In any embodiment of this application, in step 2), the reduction temperature is 400–700°C.

[0021] In any embodiment of this application, in step 2), the restoration time is 2 to 5 hours.

[0022] The second aspect of this application provides the application of the aforementioned preparation method in the preparation of catalysts for catalyzing polyolefin waste.

[0023] A third aspect of this application provides a polyolefin waste catalyst, obtained by the aforementioned preparation method.

[0024] The fourth aspect of this application provides a method for the catalytic conversion of polyolefin waste, which uses the aforementioned catalyst to mix polyolefin waste with the catalyst and react in the presence of hydrogen to obtain gas-liquid-solid products, wherein the liquid product includes naphtha.

[0025] In any embodiment of this application, the polyolefin waste is selected from polyethylene and / or polypropylene.

[0026] In any embodiment of this application, the reaction temperature is 230–280°C.

[0027] In any embodiment of this application, the pressure of the reaction is 1 to 3 MPa.

[0028] In any embodiment of this application, the reaction time is 1 to 4 hours.

[0029] In any embodiment of this application, the naphtha is selected from C5 to C10 naphtha.

[0030] Compared with the prior art, the beneficial effects of this application are as follows:

[0031] 1. The catalyst of this application has abundant acidic sites, defect sites and highly dispersed active metals. Combined with the shape selectivity and confinement effect of the molecular sieve structure, it exhibits good activity and stability.

[0032] 2. The catalytic method of this application has mild reaction conditions, is simple and easy to operate, and can convert polyolefin waste into naphtha products with high selectivity. Attached Figure Description

[0033] Figure 1 This is a product distribution diagram from Example 2. Detailed Implementation

[0034] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the following description, in conjunction with embodiments, further illustrates this application. It should be understood that the embodiments described are for illustrative purposes only and are not intended to limit the scope of the application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this description.

[0035] The inventors of this application, through extensive research and exploration, discovered a method for preparing a catalyst for catalyzing polyolefin waste, and based on this, completed this application.

[0036] This application provides a method for preparing a polyolefin waste catalyst, comprising the following steps:

[0037] 1) Acidic molecular sieves and active metal precursors are mixed and calcined to obtain catalyst precursors;

[0038] 2) The catalyst precursor is reduced by a reducing agent to obtain the catalyst.

[0039] In the preparation method provided in this application, the polyolefin of the polyolefin waste catalyst is selected from polyethylene and / or polypropylene. The polyolefin used in this application is preferred because when the polyolefin is selected from other substances such as polypropylene, the catalytic products contain more branched alkanes and cycloalkanes, making it impossible to obtain the high-value naphtha product expected in this application.

[0040] Step 1) refers to mixing an acidic molecular sieve and an active metal precursor, followed by calcination to obtain the catalyst precursor. The acidic molecular sieve is selected from one or more of ZSM-5, Beta, and HY molecular sieves. Unless otherwise specified, the molecular sieve used in this application is commercially available. The active metal precursor includes one or more combinations of platinum chloride, ruthenium chloride, nickel chloride, palladium chloride, cobalt chloride, platinum carbonate, ruthenium carbonate, nickel carbonate, palladium carbonate, and cobalt carbonate. The mixing method is ball milling, which is used to improve the contact between the acidic molecular sieve and the active metal precursor, thereby ensuring thorough mixing. The mixing time is 12–24 h; specifically, it can be 12–18 h, 18–20 h, 20–24 h, etc.

[0041] In the preparation method provided in this application, in step 1), calcination is selected from conventional heating methods in the art, such as microwave heating. The calcination temperature is 500–700°C; specifically, it can be 500–550°C, 550–650°C, or 650–700°C, etc. The calcination time is 3–5 hours; specifically, it can be 3–4 hours, 4–4.5 hours, 4.5–5 hours, etc. In a specific embodiment, ball milling followed by calcination can achieve solid-state ion exchange between the acidic molecular sieve and the active metal precursor, and under heating conditions, the active metal component is migrated and ultimately immobilized in the molecular sieve pore structure.

[0042] In the preparation method provided in this application, in step 1), the mass fraction of the active metal precursor is 0.5–10% (w / w) based on the total mass of the catalyst; specifically, it can be 0.5–2% (w / w), 2–8% (w / w), or 8–10% (w / w), etc. Based on the total mass of the catalyst, the mass fraction of the acidic molecular sieve is 90–99.5% (w / w); specifically, it can be 90–92% (w / w), 92–95% (w / w), or 95–99.5% (w / w), etc. The mass ratio of acidic molecular sieve to active metal precursor is 9–199:1; specifically, it can be 9–10:1, 10–20:1, 20–30:1, 30–40:1, 40–50:1, 50–60:1, 60–70:1, 70–80:1, 80–90:1, 90–100:1, 100–150:1, or 150–199:1, etc.

[0043] In the preparation method provided in this application, step 2) refers to reducing the intermediate product with a reducing agent to obtain the catalyst. The reducing agent is selected from hydrogen and / or carbon monoxide. The reduction temperature is 400–700℃; specifically, it can be 400–500℃, 500–550℃, 550–600℃, or 600–700℃, etc. The reduction time is 2–5 h; specifically, it can be 2–3 h, 3–4 h, 4–5 h, etc.

[0044] This application uses acidic molecular sieves as a carrier and performs solid ion exchange through high-temperature calcination to immobilize active metal components in the molecular sieve pore structure. The reduced catalyst has abundant acidic sites, defect sites, and highly dispersed active metals combined with the shape selection and confinement effect of the molecular sieve structure, which can achieve efficient conversion of polyolefin waste.

[0045] This application also provides the use of the aforementioned preparation method in the preparation of catalysts for catalyzing polyolefin waste.

[0046] This application also provides a polyolefin waste catalyst, obtained by the aforementioned preparation method. The catalyst of this application exhibits good activity and stability in the selective conversion of waste plastics, and can selectively break down polyolefins into naphtha products. These products can serve as precursors for ethylene and propylene, connecting subsequent polymerization stages, thereby achieving the recycling of plastics.

[0047] Another aspect of this application provides a method for the catalytic conversion of polyolefin waste, which uses the aforementioned catalyst to mix polyolefin waste with the catalyst and react in the presence of hydrogen to obtain gaseous-liquid-solid products, wherein the liquid products include naphtha, the gaseous products are small molecule gases such as methane, and the solids are a small amount of unreacted raw materials.

[0048] In the method provided in this application, the polyolefin waste is selected from polyethylene and / or polypropylene. The polyolefin in this application is preferred because when the polyolefin is selected from other substances such as polypropylene, the catalytic products contain more branched alkanes and cycloalkanes, which cannot produce the high-value naphtha products expected in this application.

[0049] In the method provided in this application, the reaction temperature is 230–280℃; specifically, it can be 230–250℃, 250–260℃, 260–270℃, or 270–280℃, etc. The reaction pressure is 1–3 MPa; specifically, it can be 1–2 MPa, 2–2.5 MPa, or 2.5–3 MPa, etc. The naphtha is selected from C5–C10 naphtha. The naphtha obtained in this application has a selectivity of ≥96%. Naphtha is a petroleum product, also known as light chemical oil. It is a light oil produced from crude oil or other raw materials and used as a chemical feedstock. It is mainly used for reforming and chemical feedstock. Naphtha can be used as a precursor for ethylene and propylene to connect subsequent polymerization stages, thereby realizing the recycling of plastics.

[0050] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0051] Example 1

[0052] 99.5% (w / w) platinum chloride and 0.5% (w / w) ZSM-5 molecular sieve were mixed, ball-milled for 12 h, and then transferred to microwave high-temperature calcination at 500 °C for 5 h. The resulting product was then reduced with H₂ at 400 °C for 5 h to obtain the catalyst. The catalyst was mixed with polyethylene and placed in a high-pressure reactor. The reaction was carried out at 230 °C and 3 MPa H₂ pressure for 4 h. The gas, liquid, and solid products were collected, and the liquid yield was calculated to be 94%. GC-MS analysis of the liquid products was performed, and the peak areas and correction factors of all liquid products were statistically analyzed. The selectivity of naphtha (C5-C10) in all liquids was calculated to be 98%.

[0053] Example 2

[0054] 90% (w / w) Beta molecular sieve and 10% (w / w) nickel carbonate were mixed, ball-milled for 24 h, and then transferred to microwave high-temperature calcination at 700 °C for 3 h. The resulting catalyst was obtained after reduction with H₂ at 700 °C for 2 h. The catalyst was mixed with polypropylene and placed in a high-pressure reactor. The reaction was carried out at 280 °C and 1 MPa H₂ pressure for 1 h. The gas-liquid-solid products were collected, and the liquid yield was calculated to be 92%. GC-MS analysis of the liquid product composition showed a naphtha (C5-C10) selectivity of 99%. The product distribution diagram is shown below. Figure 1 As shown.

[0055] Example 3

[0056] 98% (w / w) HY molecular sieve and 2% (w / w) ruthenium chloride were mixed, ball-milled for 18 h, and then transferred to microwave high-temperature calcination at 600 °C for 4 h. The resulting product was then reduced with H₂ at 500 °C for 3 h to obtain the catalyst. The catalyst was mixed with polyethylene and placed in a high-pressure reactor. The reaction was carried out at 250 °C and 2 MPa H₂ pressure for 2 h. The gas-liquid-solid products were collected, and the liquid yield was calculated to be 92%. GC-MS analysis of the liquid product yielded a naphtha (C5-C10) selectivity of 97%.

[0057] Example 4

[0058] 99.5% (w / w) ZSM-5 molecular sieve and 0.5% (w / w) palladium chloride were mixed, ball-milled for 20 h, and then transferred to microwave high-temperature calcination at 650 °C for 3 h. The resulting product was then reduced with H₂ at 550 °C for 2 h to obtain the catalyst. The catalyst was mixed with polypropylene and placed in a high-pressure reactor. The reaction was carried out at 260 °C and 2 MPa H₂ pressure for 3 h. The gas-liquid-solid products were collected, and the liquid yield was calculated to be 91%. GC-MS analysis of the liquid product yielded a naphtha (C5-C10) selectivity of 98%.

[0059] Example 5

[0060] A mixture of 92% (w / w) Beta molecular sieve and 8% (w / w) cobalt carbonate was ball-milled for 24 h and then microwave-calcined at 700 °C for 3 h, followed by reduction with H₂ at 600 °C for 4 h to obtain a catalyst. The catalyst was mixed with polyethylene and placed in a high-pressure reactor, reacted at 270 °C and 2 MPa H₂ pressure for 4 h, and the gas-liquid-solid products were collected. The liquid yield was calculated to be 90%. GC-MS analysis of the liquid product yielded a naphtha (C5-C10) selectivity of 97%.

[0061] Comparative Example 1

[0062] After reducing 0.3% (w / w) Pt@S-1 under a hydrogen atmosphere at 300℃ for 3 hours, it was mixed with Beta molecular sieve at a mass ratio of 1:1 and then mixed with polyethylene. The mixture was placed in a high-pressure reactor and reacted at 250℃ and H2 pressure of 3 MPa for 2 hours. The gas-liquid-solid products were collected, and the liquid yield was calculated to be 89%. The composition of the obtained liquid product was analyzed by GCMS, and the selectivity for naphtha (C5-C10) was calculated to be 96%.

[0063] In summary, the catalytic method of this application features mild reaction conditions, a simple and easy-to-operate process, and the ability to convert polyolefin waste into naphtha products with high selectivity. The catalyst of this application possesses abundant acidic sites, defect sites, and highly dispersed active metals. Combined with the shape-selective and confinement effects of the molecular sieve structure, it exhibits excellent activity and stability, as well as better product yield.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this application.

Claims

1. A method for catalytic conversion of polyolefin waste, characterized in that, The method for preparing the catalyst for catalyzing polyolefin waste includes the following steps: 1) Acidic molecular sieves and active metal precursors are mixed and calcined to obtain a catalyst precursor; the acidic molecular sieves are selected from one or more of ZSM-5, Beta, and HY molecular sieves; the active metal precursors are selected from one or more of platinum chloride, ruthenium chloride, nickel chloride, palladium chloride, cobalt chloride, platinum carbonate, ruthenium carbonate, nickel carbonate, palladium carbonate, and cobalt carbonate. 2) The catalyst precursor is reduced by a reducing agent to obtain the catalyst; the catalyst prepared by the above method is mixed with polyolefin waste and reacted in the presence of hydrogen to obtain gas-liquid-solid products, wherein the liquid product includes naphtha, and the polyolefin waste is selected from polyethylene and / or polypropylene; the reaction temperature is 230-280℃; the reaction pressure is 1-3MPa; and the reaction time is 1-4h.

2. The method as described in claim 1, characterized in that, The naphtha is selected from C5 to C10 naphtha.

3. The method as described in claim 1, characterized in that, In step 1), the mixing method is selected from ball milling; And / or, in step 1), the mixing time is 12 to 24 hours.

4. The method as described in claim 1, characterized in that, In step 1), the roasting temperature is 500–700°C; And / or, in step 1), the roasting time is 3 to 5 hours.

5. The method as described in claim 1, characterized in that, In step 1), the mass fraction of the active metal precursor is 0.5-10% (w / w), based on the total mass of the catalyst precursor. And / or, in step 1), the acidic molecular sieve has a mass fraction of 90–99.5% (w / w) based on the total mass of the catalyst precursor; And / or, in step 1), the mass ratio of the acidic molecular sieve to the active metal precursor is 9 to 199:1; And / or, in step 2), the reducing agent is selected from hydrogen and / or carbon monoxide; And / or, in step 2), the reduction temperature is 400–700°C; And / or, in step 2), the reduction time is 2 to 5 hours.

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