A ruthenium-lanthanum-tantalum composite catalyst, a preparation method thereof and application thereof in depolymerization of polyvinyl chloride

Abstract

The application provides a ruthenium-lanthanum-tantalum composite catalyst and a preparation method and application thereof in depolymerization of polyvinyl chloride, and relates to the technical field of high-value conversion and utilization of waste plastics. The preparation method of the ruthenum-lanthanum-tantalum composite catalyst comprises the following steps: mixing a lanthanum salt, a tantalum salt, ethanol and ammonia water, and obtaining a precipitate through reaction; and calcining the precipitate to obtain a La2O3-Ta2O5 carrier; and then the carrier is immersed in a RuCl3 solution, and after the immersion is completed, heat treatment is performed to obtain the ruthenium-lanthanum-tantalum composite catalyst. The ruthenium-lanthanum-tantalum composite catalyst prepared through the above method has suitable acid centers and O vacancies at the same time, is beneficial to directional adsorption and activation of PVC functional groups in the depolymerization reaction of plastics, improves the selectivity of target products, and the RuO2 active center can make Cl rearrangement, so that the Cl2 product is obtained. The catalyst has good structural stability, can resist Cl poisoning, and the catalyst will not undergo transition chlorination and poisoning and deactivation in the reaction process.

Description

Technical Field

[0001] This invention relates to the field of high-value conversion and utilization technology of waste plastics, and in particular to a ruthenium-lanthanum-tantalum composite catalyst, its preparation method, and its application in the depolymerization of polyvinyl chloride. Background Technology

[0002] Polyvinyl chloride (PVC) is a polymer material formed by the polymerization of vinyl chloride. Due to its excellent chemical resistance, durability, and processability, it is widely used as a thermoplastic polymer in building materials, medical devices, daily necessities, and the automotive industry, and has become an indispensable material in modern industry and daily life. At the same time, the amount of waste PVC generated each year is increasing daily, causing not only significant environmental pollution but also wasting resources. Therefore, transforming waste PVC into high-value products is one of the major challenges facing modern society.

[0003] Typically, PVC is produced by reacting ethylene and Cl2 as raw materials through an addition reaction to generate 1,2-dichloroethane, followed by the removal of HCl to obtain 1-chloroethylene monomer, which is then polymerized. The Cl content in a PVC molecule is 56.8 wt%, therefore, effectively utilizing the Cl resources within the PVC molecular structure is a crucial aspect of PVC recycling.

[0004] Based on the degree of preservation of the PVC molecular structure, current recycling processes are mainly divided into two categories: mechanical recycling and chemical recycling. Mechanical recycling refers to the mechanical crushing, screening, and grinding of waste PVC before reprocessing it into PVC products. However, the mechanical properties of this type of material are significantly reduced, thus limiting its application scenarios. Chemical recycling mainly includes methods such as gasification, pyrolysis, and catalytic depolymerization, which break the chemical bonds in PVC at high temperatures to obtain small-molecule gaseous, liquid, and solid products. For example, PVC undergoes a dechlorination reaction at 200-300℃ to produce small-molecule hydrocarbons, HCl, and carbonaceous solids. Further C / C bond breaking occurs between 350-500℃, generating aliphatic or aromatic hydrocarbons and coke. Currently developed catalytic depolymerization methods mainly focus on increasing the yield of small carbon-containing molecules in the products. For example, using Ni / Al2O3 and Ru / Al2O3 catalysts can hydrogenate PVC to convert it into methane, ethane, and other products. However, these technologies still inevitably generate low-value-added products such as tar and coke. Furthermore, they pay little attention to the conversion of Cl, which accounts for 56.8 wt% of PVC. Most technologies only convert it into HCl gas or form solid metal chlorides. HCl not only corrodes recycling equipment but can also cause chemical burns to workers' skin and eyes. This means that Cl, the most abundant resource in PVC, is not effectively utilized, becoming one of the difficulties in PVC recycling and conversion.

[0005] Therefore, how to disclose a catalyst that can catalyze the depolymerization of polyvinyl chloride without producing low-value-added products such as tar and coke, or HCl gas that corrodes equipment, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a ruthenium-lanthanum-tantalum composite catalyst, its preparation method, and its application in the depolymerization of polyvinyl chloride, so as to solve the problems of existing methods for depolymerizing polyvinyl chloride, which cannot effectively utilize Cl resources, the product HCl easily corrodes the recovery equipment, and easily produces low-value-added products such as tar and coke.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a ruthenium-lanthanum-tantalum composite catalyst, comprising the following steps: 1) Lanthanum salt, tantalum salt, alcohol and ammonia are mixed and reacted to obtain a precipitate. The precipitate is then calcined to obtain a La2O3-Ta2O5 support. 2) The La2O3-Ta2O5 support was impregnated in RuCl3 solution, and after impregnation, it was heat-treated to obtain the RuO2 / La2O3-Ta2O5 ruthenium lanthanum tantalum composite catalyst.

[0008] Preferably, in step 1), the total molar amount of lanthanum in the lanthanum salt and tantalum in the tantalum salt is in a molar ratio of 1:1 to 2 to the ammonia in the ammonia water. The molar ratio of lanthanum in the lanthanum salt to tantalum in the tantalum salt is 0.02~0.2:0.01~0.2.

[0009] Preferably, the concentration of ammonia in step 1) is 0.1~1.0 mol / L; The molar volume ratio of the lanthanum salt to ethanol is 0.02~0.2 mol: 1 L; The lanthanum salt includes one or more of lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate; The tantalum salt includes one or more of tantalum ethoxide, tantalum chloride, and tantalum fluoride. The alcohol includes one or more of methanol, ethanol propanol, and isopropanol.

[0010] Preferably, the reaction temperature in step 1) is 30~90℃, and the reaction time is 2~12h; The calcination temperature is 300~600℃, and the calcination time is 2~6h.

[0011] Preferably, the concentration of the RuCl3 solution in step 2) is 0.02~0.2 mol / L; The soaking time is 2 to 12 hours.

[0012] Preferably, the heat treatment temperature in step 2) is 250~500℃, and the heat treatment time is 2~6h.

[0013] The present invention also provides a ruthenium-lanthanum-tantalum composite catalyst prepared by the above preparation method, wherein the mass fraction of ruthenium in the ruthenium-lanthanum-tantalum composite catalyst is 0.5-5%.

[0014] This invention also provides an application of the above-mentioned ruthenium-lanthanum-tantalum composite catalyst in the catalytic depolymerization of polyvinyl chloride, the application method of which is as follows: Polyvinyl chloride, ruthenium-lanthanum-tantalum composite catalyst and organic solvent are mixed and reacted to produce ethylene, benzene and chlorine gas; The organic solvent is perfluoronaphthalene.

[0015] Preferably, the mass ratio of the polyvinyl chloride to the ruthenium-lanthanum-tantalum composite catalyst is 1:0.1~1; The concentration of polyvinyl chloride in the mixture of polyvinyl chloride, ruthenium lanthanum tantalum composite catalyst and organic solvent is 1~10 g / L.

[0016] Preferably, the reaction temperature is 250~350℃ and the reaction time is 1~12h; The initial gas pressure for the reaction is 0.5~2 MPa.

[0017] The present invention has at least the following beneficial effects: 1. The ruthenium-lanthanum-tantalum composite catalyst provided by this invention fully utilizes the C and Cl resources in PVC during the oxidation and depolymerization of PVC, converting them into ethylene, benzene, and Cl2 products, thus avoiding the generation of low-value-added tar and coke. The obtained ethylene and Cl2 products can be reused in the PVC synthesis process, realizing a closed-loop cycle of PVC plastic synthesis-depolymerization-resynthesis. This invention uses perfluoronaphthalene as a solvent, which has excellent O2 dissolving ability. This solvent is non-toxic, harmless, environmentally friendly, and has good stability. It does not undergo structural changes under reaction conditions, which can not only achieve efficient breaking of C-C and C-Cl bonds in PVC molecules, but also prevent small carbon-containing compounds such as ethylene and benzene from being over-oxidized into substances such as CO2.

[0018] 2. The La2O3-Ta2O5 support in the ruthenium-lanthanum-tantalum composite catalyst provided by this invention has suitable acid centers and O vacancies, which is beneficial for the directional adsorption and activation of PVC functional groups in the depolymerization reaction of plastics, thereby improving the selectivity of the target product. The RuO2 active center can cause Cl rearrangement, resulting in high selectivity for Cl2 products. The catalyst has good structural stability and is resistant to Cl poisoning. The catalyst will not undergo over-chlorination or poisoning deactivation during the reaction. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the ruthenium-lanthanum-tantalum composite catalyst prepared in Example 1. Detailed Implementation

[0020] This invention provides a method for preparing a ruthenium-lanthanum-tantalum composite catalyst, comprising the following steps: 1) Lanthanum salt, tantalum salt, alcohol and ammonia are mixed and reacted to obtain a precipitate. The precipitate is then calcined to obtain a La2O3-Ta2O5 support. 2) The La2O3-Ta2O5 support was impregnated in RuCl3 solution, and after impregnation, it was heat-treated to obtain the RuO2 / La2O3-Ta2O5 ruthenium lanthanum tantalum composite catalyst.

[0021] In this invention, the preferred mixing method in step 1) is to first mix the lanthanum salt, tantalum salt and ethanol evenly and then add ammonia water for precipitation.

[0022] In this invention, the total molar ratio of lanthanum in the lanthanum salt and tantalum in the tantalum salt to ammonia in the ammonia water in step 1) is 1:1~2, preferably 1:1.2~1.8, more preferably 1:1.4~1.6, and even more preferably 1:1.5.

[0023] In this invention, the molar ratio of lanthanum in the lanthanum salt to tantalum in the tantalum salt is 0.02~0.2:0.01~0.2, preferably 0.05~0.18:0.03~0.15, more preferably 0.07~0.15:0.05~0.12, and even more preferably 0.10~0.12:0.07~0.10.

[0024] In this invention, the concentration of ammonia in step 1) is 0.1~1.0 mol / L, preferably 0.2~0.8 mol / L, more preferably 0.4~0.6 mol / L, and even more preferably 0.5 mol / L.

[0025] In this invention, the molar volume ratio of the lanthanum salt to ethanol is 0.02~0.2 mol:1L, preferably 0.05~0.18 mol:1L, more preferably 0.07~0.15 mol:1L, and even more preferably 0.10~0.12 mol:1L.

[0026] In this invention, the lanthanum salt includes one or more of lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate.

[0027] In this invention, the tantalum salt includes one or more of tantalum ethoxide, tantalum chloride, and tantalum fluoride.

[0028] In this invention, the alcohol includes one or more of methanol, ethanol propanol, and isopropanol.

[0029] In this invention, the reaction temperature in step 1) is 30~90℃, preferably 40~80℃, more preferably 50~70℃, and even more preferably 55~60℃; the reaction time is 2~12h, preferably 4~10h, and even more preferably 6~8h.

[0030] In this invention, the calcination temperature is 300~600℃, preferably 350~550℃, more preferably 400~500℃, and even more preferably 450℃; the calcination time is 2~6h, preferably 2.5~5.5h, more preferably 3~5h, and even more preferably 3.5~4.5h.

[0031] In this invention, the concentration of the RuCl3 solution in step 2) is 0.02~0.2 mol / L, preferably 0.05~0.18 mol / L, more preferably 0.07~0.15 mol / L, and even more preferably 0.10~0.12 mol / L.

[0032] In this invention, the soaking time is 2 to 12 hours, preferably 4 to 10 hours, and more preferably 6 to 8 hours.

[0033] In this invention, the heat treatment temperature in step 2) is 250~500℃, preferably 300~450℃, more preferably 350~400℃; the heat treatment time is 2~6h, preferably 3~5h, more preferably 3.5~4.5h, and more preferably 4h.

[0034] The present invention also provides a ruthenium-lanthanum-tantalum composite catalyst prepared by the above preparation method, wherein the mass fraction of ruthenium in the ruthenium-lanthanum-tantalum composite catalyst is 0.5-5%, preferably 1.0-4.5%, more preferably 1.5-4.0%, more preferably 2-3.5%, and even more preferably 2.5-3.0%.

[0035] This invention also provides an application of the above-mentioned ruthenium-lanthanum-tantalum composite catalyst in the catalytic depolymerization of polyvinyl chloride, the application method of which is as follows: Polyvinyl chloride, ruthenium-lanthanum-tantalum composite catalyst and organic solvent are mixed and reacted to produce ethylene, benzene and chlorine gas; The organic solvent is perfluoronaphthalene.

[0036] In this invention, the mass ratio of the polyvinyl chloride to the ruthenium-lanthanum-tantalum composite catalyst is 1:0.1~1, preferably 1:0.2~0.8, more preferably 1:0.4~0.6, and even more preferably 1:0.5.

[0037] In this invention, the concentration of polyvinyl chloride in the mixture of polyvinyl chloride, ruthenium lanthanum tantalum composite catalyst and organic solvent is 1~10 g / L, preferably 2~8 g / L, more preferably 4~6 g / L, and even more preferably 5 g / L.

[0038] In this invention, the reaction temperature is 250~350℃, preferably 270~330℃, more preferably 290~310℃, and even more preferably 300℃; the reaction time is 1~12h, preferably 2~10h, more preferably 4~8h, and even more preferably 5~6h.

[0039] In this invention, the reaction atmosphere is preferably an air atmosphere or a mixed atmosphere of oxygen and an inert gas, and the volume fraction of oxygen is preferably 1-30%, more preferably 5-18%, and even more preferably 10-15%.

[0040] In this invention, the inert gas includes one or more of helium, argon, neon, and nitrogen.

[0041] In this invention ， The initial gas pressure for the reaction is 0.5~2 MPa.

[0042] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0043] Example 1

[0044] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 40℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.03 mol / L, 0.3 mol / L, and 0.4 mol / L, respectively. After precipitation for 4 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 120℃ for 6 h, and then calcined at 400℃ for 2 h to obtain the La2O3-Ta2O5 support.

[0045] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 4 h, the precipitate was separated by filtration, the precipitate was dried at 120 °C for 6 h, and then calcined at 300 °C for 3 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 1 wt%.

[0046] (3) Place 0.2g of waste PVC plastic, 0.06g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 10%) at a pressure of 0.5MPa into the reactor at room temperature, stir the reaction at a rate of 500r / min at 300℃ for 4h, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0047] X-ray diffraction experiments were performed on the ruthenium-lanthanum-tantalum composite catalyst prepared in this embodiment. The XRD pattern is shown below. Figure 1 As shown in the figure, the diffraction angle (2θ) is 23.0°. o 28.5 o 36.9 o The peaks at 23.5° are diffraction peaks of the hexagonal crystal system Ta₂O₅ (003), (200), and (203) planes. o 24.5 o 26.6 o 30.0 o 36.7 o The peaks at this location are the diffraction peaks of the triclinic crystal system Ta₂O₅ (011), (103), (105), (0012), and (0011) planes, at 30.0. o The peaks at 46.1 and 55.4 are the (101), (102), and (112) diffraction peaks of the hexagonal La2O3 crystal plane, indicating that the Ta2O5-La2O3 provided by this invention has a composite crystal structure, while the RuO2 content is low and highly dispersed in the catalyst, appearing only at 28.0. o and 35.1 o It has relatively weak and broad diffraction peaks.

[0048] Example 2

[0049] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 60℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.08 mol / L, 0.16 mol / L, and 0.36 mol / L, respectively. After precipitation for 6 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 100℃ for 5 h, and then calcined at 500℃ for 2.5 h to obtain the La2O3-Ta2O5 support.

[0050] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 7 h, the precipitate was separated by filtration, the precipitate was dried at 100 °C for 5 h, and then calcined at 350 °C for 4 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 2 wt%.

[0051] (3) Place 0.4g of waste PVC plastic, 0.24g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 5%) at a pressure of 1MPa into the reactor at room temperature, stir at 500r / min for 6h at 260℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0052] Example 3

[0053] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 70℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.12 mol / L, 0.06 mol / L, and 0.32 mol / L, respectively. After precipitation for 8 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 110℃ for 4 h, and then calcined at 450℃ for 3.5 h to obtain the La2O3-Ta2O5 support.

[0054] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 3 h, the precipitate was separated by filtration, the precipitate was dried at 110 °C for 4 h, and then calcined at 250 °C for 3.5 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 0.5 wt%.

[0055] (3) Place 0.6g of waste PVC plastic, 0.12g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 15%) with a pressure of 1.5MPa into the reactor at room temperature, stir the reaction at a rate of 500r / min for 8h at 280℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0056] Example 4

[0057] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 50°C to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.18 mol / L, 0.04 mol / L, and 0.35 mol / L, respectively. After precipitation for 5 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 120°C for 8 h, and then calcined at 600°C for 4 h to obtain the La2O3-Ta2O5 support.

[0058] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 6 h, the precipitate was separated by filtration, the precipitate was dried at 120 °C for 8 h, and then calcined at 400 °C for 2.5 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 1.5 wt%.

[0059] (3) Place 0.1g of waste PVC plastic, 0.04g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (8% by volume of O2) at a pressure of 2MPa into the reactor at room temperature, stir at 500r / min for 5h at 320℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0060] Example 5

[0061] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 80℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.15 mol / L, 0.3 mol / L, and 0.9 mol / L, respectively. After precipitation for 12 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 140℃ for 10 h, and then calcined at 550℃ for 2 h to obtain the La2O3-Ta2O5 support.

[0062] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 9 h, the precipitate was separated by filtration, the precipitate was dried at 140 °C for 10 h, and then calcined at 450 °C for 2 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 2.5 wt%.

[0063] (3) Place 0.3g of waste PVC plastic, 0.24g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 12%) with a pressure of 0.8MPa into the reactor at room temperature, stir the reaction at a rate of 500r / min at 350℃ for 7h, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0064] Example 6

[0065] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 90℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.02 mol / L, 0.02 mol / L, and 0.05 mol / L, respectively. After precipitation for 10 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 150℃ for 12 h, and then calcined at 350℃ for 6 h to obtain the La2O3-Ta2O5 support.

[0066] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 11 h, the precipitate was separated by filtration, the precipitate was dried at 150 °C for 12 h, and then calcined at 500 °C for 5 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 4 wt%.

[0067] (3) Place 1g of waste PVC plastic, 1g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 20%) with a pressure of 1.2MPa into the reactor at room temperature, stir the reaction at a rate of 500r / min for 2h at 250℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0068] Example 7

[0069] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 75°C to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.16 mol / L, 0.18 mol / L, and 0.5 mol / L, respectively. After precipitation for 9 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 105°C for 2 h, and then calcined at 300°C for 5.5 h to obtain the La2O3-Ta2O5 support.

[0070] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 12 h, the precipitate was separated by filtration, the precipitate was dried at 105 °C for 2 h, and then calcined at 400 °C for 5.5 h to obtain the ruthenium-lanthanum-tantalum composite catalyst, wherein the Ru content was 5 wt%.

[0071] (3) Place 0.8g of waste PVC plastic, 0.4g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 1%) at a pressure of 1.6MPa into the reactor at room temperature, stir at a rate of 500r / min for 10h at 340℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0072] Example 8

[0073] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 65℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.2 mol / L, 0.02 mol / L, and 0.3 mol / L, respectively. After precipitation for 7 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 115℃ for 7 h, and then calcined at 400℃ for 5 h to obtain the La2O3-Ta2O5 support.

[0074] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 10 h, the precipitate was separated by filtration, the precipitate was dried at 115 °C for 7 h, and then calcined at 350 °C for 6 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 4.5 wt%.

[0075] (3) Place 0.9g of waste PVC plastic, 0.63g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 12%) with a pressure of 0.1MPa into the reactor at room temperature, stir the reaction at a rate of 500r / min at 310℃ for 12h, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0076] Example 9

[0077] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 55℃ to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.06 mol / L, 0.01 mol / L, and 0.12 mol / L, respectively. After precipitation for 2 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 135℃ for 11 h, and then calcined at 450℃ for 2.5 h to obtain the La2O3-Ta2O5 support.

[0078] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 11 h, the precipitate was separated by filtration, the precipitate was dried at 135 °C for 11 h, and then calcined at 300 °C for 3.5 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 3.5 wt%.

[0079] (3) Place 0.4g of waste PVC plastic, 0.4g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 6%) with a pressure of 1.7MPa into the reactor at room temperature, stir at 500r / min for 3h at 330℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0080] Example 10

[0081] (1) Lanthanum nitrate and tantalum ethoxide were dissolved in ethanol, and ammonia water with a concentration of 14 mol / L was added to a constant temperature water bath at 50°C to precipitate the mixture. The concentrations of lanthanum nitrate, tantalum ethoxide, and NH3 in the mixture were 0.1 mol / L, 0.15 mol / L, and 0.45 mol / L, respectively. After precipitation for 3 h, the reaction system was filtered to separate the precipitate. The precipitate was washed three times with distilled water, dried at 145°C for 9 h, and then calcined at 500°C for 4 h to obtain the La2O3-Ta2O5 support.

[0082] (2) The La2O3-Ta2O5 support prepared in step (1) was immersed in a RuCl3 solution with a concentration of 0.1 mol / L for 8 h, the precipitate was separated by filtration, the precipitate was dried at 145 °C for 9 h, and then calcined at 450 °C for 4 h to obtain a ruthenium-lanthanum-tantalum composite catalyst with a Ru content of 3 wt%.

[0083] (3) Place 0.5g of waste PVC plastic, 0.45g of the ruthenium-lanthanum-tantalum composite catalyst prepared in step (2) and 100mL of perfluoronaphthalene in a 300mL sealed high-pressure reactor; introduce O2 / N2 mixed gas (O2 volume fraction of 18%) with a pressure of 0.3MPa into the reactor at room temperature, stir at 500r / min for 9h at 290℃, collect the gaseous products as ethylene and Cl2, and filter the liquid products to obtain benzene.

[0084] Comparative Example 1

[0085] (1) Lanthanum nitrate was dissolved in ethanol, and precipitated by adding 14 mol / L ammonia water in a constant temperature water bath at 40°C. The concentration of lanthanum nitrate in the mixture was 0.03 mol / L and the concentration of NH3 was 0.4 mol / L. After reacting for 4 h, the product was filtered with filter paper, washed three times with distilled water, dried at 120°C for 6 h, and then calcined at 400°C for 2 h to obtain La2O3 support; (2) The La2O3 support prepared in step (1) was impregnated in a RuCl3 solution with a concentration of 0.1 mol / L for 4 h. After impregnation, it was dried at 120 °C for 6 h and calcined at 300 °C for 3 h to obtain RuO2 / La2O3 catalyst, wherein the Ru content was 1 wt%.

[0086] (3) Disperse 0.2 g of PVC and 0.06 g of RuO2 / La2O3 catalyst in 100 mL of perfluoronaphthalene, then place them in a 300 mL high-pressure reactor, introduce a 0.5 MPa O2 / N2 mixture (O2 volume fraction of 10%) into it, heat to 300 °C, and react for 4 h. After the reaction is complete, collect the gaseous products and filter the liquid to obtain the liquid product.

[0087] Comparative Example 2

[0088] (1) Tantalum ethoxide was dissolved in ethanol, and precipitated by adding 14 mol / L ammonia water in a constant temperature water bath at 40°C. The concentration of tantalum ethoxide in the mixed system was 0.3 mol / L and the concentration of NH3 was 0.4 mol / L. After reacting for 4 h, the product was filtered with filter paper, washed three times with distilled water, dried at 120°C for 6 h, and then calcined at 400°C for 2 h to obtain Ta2O5 support.

[0089] (2) The Ta2O5 support prepared in step (1) was impregnated in a RuCl3 solution with a concentration of 0.1 mol / L for 4 h. After impregnation, it was dried at 120 °C for 6 h and calcined at 300 °C for 3 h to obtain the RuO2 / Ta2O5 catalyst, wherein the Ru content was 1 wt%.

[0090] (3) Disperse 0.2g of PVC and 0.06g of RuO2 / Ta2O5 catalyst in 100mL of perfluoronaphthalene, then place them in a 300mL high-pressure reactor, and purge them with a 0.5MPa O2 / N2 mixture (O2 volume fraction of 10%). Heat to 300℃ and react for 4h. After the reaction is complete, collect the gaseous products and filter the liquid to obtain the liquid product.

[0091] Qualitative and quantitative analyses were performed on the gaseous and liquid products obtained from the depolymerization of PVC in Examples 1-10 and Comparative Examples 1-2. The analytical methods are as follows: First, the obtained gaseous product was passed into 100 mL of a 0.5 mol / L KI solution to absorb the Cl2 in the gas. Then, the Cl2 and ethylene were quantitatively analyzed by potentiometric titration and gas chromatography, respectively.

[0092] Potentiometric titration (refer to Maximilian Moser, Cecilia Mondelli, Amol P. Amrute, Atsushi Tazawa, Detre Teschner, Manfred E. Schuster, Achim Klein-Hoffman, N ria L pez, Timm Schmidt, Javier P (Rez-Ramírez, HCl Oxidation on IrO2-Based Catalysts: From Fundamentals to Scale-Up, ACS Catalysis, 2013, 3, 2813-2822) was performed using a Mettler Toledo G20s automated point titrator in Switzerland. I2 was titrated with a 0.1 mol / L Na2S2O3 standard solution. The volume V (in mL) of the Na2S2O3 standard solution used was recorded to analyze the amount of Cl2 generated (mmol / g). , where m(PVC) is the mass (in g) of PVC added in the reaction.

[0093] Ethylene products were quantitatively analyzed using an Agilent Technologies 8890 gas chromatograph (USA) using the external standard method. The injection port temperature was 200℃, the column oven temperature was 60℃ for 5 min, then increased to 150℃ at a rate of 10℃ / min and held for 5 min. A Gas-CarbonPLOT capillary column (60 m long, 0.32 mm diameter, 1.5 μm film thickness) was used. He was the carrier gas, the column flow rate was 0.5 mL / min, and an FID detector was used at 200℃. The amount of ethylene product generated (mmol / g) was... , where n(ethylene) and m(PVC) are the amount of ethylene analyzed by gas chromatography (in mmol) and the mass of PVC added in the reaction (in g), respectively.

[0094] The liquid product after the reaction was filtered, and the benzene content was quantitatively analyzed using an Agilent Technologies 8890 gas chromatograph (USA) using the external standard method. The injection port temperature was 250℃, the column oven temperature was 100℃ for 5 min, then increased to 220℃ at a rate of 10℃ / min and held for 10 min. An HP-5 capillary column (60 m long, 0.32 mm diameter, 0.25 μm film thickness) was used, with He as the carrier gas and a column flow rate of 0.5 mL / min. An FID detector was used at 250℃. The amount of benzene product formed (mmol / g) was... Where n(benzene) and m(PVC) are the amount of ethylene analyzed by gas chromatography (in mmol) and the mass of PVC added in the reaction (in g), respectively.

[0095] The results are shown in Table 1.

[0096] Table 1. Yield results of each product in Examples 1-10 and Comparative Examples 1-2

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a ruthenium-lanthanum-tantalum composite catalyst, characterized in that, Includes the following steps: 1) Lanthanum salt, tantalum salt, alcohol and ammonia are mixed and reacted to obtain a precipitate. The precipitate is then calcined to obtain a La2O3-Ta2O5 support. The molar ratio of lanthanum in the lanthanum salt to tantalum in the tantalum salt is 0.02~0.2:0.01~0.

2. 2) The La2O3-Ta2O5 support was impregnated in RuCl3 solution, and after impregnation, it was heat-treated to obtain RuO2 / La2O3-Ta2O5 ruthenium-lanthanum-tantalum composite catalyst. The mass fraction of ruthenium in the ruthenium-lanthanum-tantalum composite catalyst was 0.5~5%.

2. The method for preparing a ruthenium-lanthanum-tantalum composite catalyst according to claim 1, characterized in that, In step 1), the total molar ratio of lanthanum in the lanthanum salt and tantalum in the tantalum salt to the molar ratio of ammonia in the ammonia water is 1:1~2.

3. The method for preparing a ruthenium-lanthanum-tantalum composite catalyst according to claim 2, characterized in that, The concentration of ammonia in step 1) is 0.1~1.0 mol / L; The molar volume ratio of the lanthanum salt to the alcohol is 0.02~0.2 mol: 1 L; The lanthanum salt includes one or more of lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate; The tantalum salt includes one or more of tantalum ethoxide, tantalum chloride, and tantalum fluoride. The alcohols include one or more of methanol, ethanol, propanol, and isopropanol.

4. The method for preparing a ruthenium-lanthanum-tantalum composite catalyst according to claim 3, characterized in that, The reaction temperature in step 1) is 30~90℃, and the reaction time is 2~12h; The calcination temperature is 300~600℃, and the calcination time is 2~6h.

5. A method for preparing a ruthenium-lanthanum-tantalum composite catalyst according to any one of claims 1 to 4, characterized in that, In step 2), the concentration of the RuCl3 solution is 0.02~0.2 mol / L; The soaking time is 2 to 12 hours.

6. The method for preparing a ruthenium-lanthanum-tantalum composite catalyst according to claim 5, characterized in that, In step 2), the heat treatment temperature is 250~500℃ and the heat treatment time is 2~6h.

7. A ruthenium-lanthanum-tantalum composite catalyst prepared by the method according to any one of claims 1 to 6.

8. The application of the ruthenium-lanthanum-tantalum composite catalyst according to claim 7 in the catalytic depolymerization of polyvinyl chloride, characterized in that, The application method is as follows: Polyvinyl chloride, ruthenium-lanthanum-tantalum composite catalyst and organic solvent are mixed and reacted to produce ethylene, benzene and chlorine gas; The organic solvent is perfluoronaphthalene.

9. The application of the ruthenium-lanthanum-tantalum composite catalyst according to claim 8 in the catalytic depolymerization of polyvinyl chloride, characterized in that, The mass ratio of the polyvinyl chloride to the ruthenium-lanthanum-tantalum composite catalyst is 1:0.1~1; The concentration of polyvinyl chloride in the mixture of polyvinyl chloride, ruthenium lanthanum tantalum composite catalyst and organic solvent is 1~10 g / L.

10. The application of the ruthenium-lanthanum-tantalum composite catalyst according to claim 8 or 9 in the catalytic depolymerization of polyvinyl chloride, characterized in that, The reaction temperature is 250~350℃, and the reaction time is 1~12h; The initial gas pressure for the reaction is 0.5~2 MPa.

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