Polyethylene degradation ethylene catalyst, and preparation method and application thereof

Abstract

The application discloses a catalyst for catalyzing polyethylene degradation to prepare ethylene and a preparation method thereof. x In y WO3 / CeO2 catalyst. The application highly disperses active metals in the carrier through simple impregnation, calcination and reduction steps, and the catalyst has the ability of dehydrogenation of noble metals and breaking of carbon-carbon bonds of WO3, realizes efficient conversion of polyethylene into ethylene at a lower temperature, and has a wide application prospect compared with other polyethylene ethylene systems.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a polyethylene degradation ethylene catalyst, and belongs to the technical field of waste plastic treatment. BACKGROUND

[0002] Chemical recycling of plastic waste is a process of generating oil, gas and other intermediate chemicals through a series of chemical reactions. Chemical recycling of waste plastics is a very promising way. Studies have shown that the potential energy obtained by recycling global waste plastics is equivalent to the value of 3.5 billion barrels of oil, and the recycled carbon resources can reduce 30% of carbon emissions. Therefore, the conversion of waste polyolefins into high-value products is of great significance to solve global climate and energy problems.

[0003] Pyrolysis of polyolefins randomly breaks the carbon chain, the product is complex, and the required reaction temperature is high. In 2018, Laura used plasma technology to recycle 22-25% of ethylene from high-density polyethylene (HDPE) waste plastics, which was 55 times higher than the ethylene obtained from HDPE waste by traditional pyrolysis method (Green Chemistry, 2018, 20(8): 1813-1823). In 2002, Mastral studied the temperature and residence time of HDPE conversion to ethylene in a fluidized bed reactor, and found that the highest ethylene yield of 41.9% was obtained at 780°C and a residence time of 1.34 s (Journal of Analytical and Applied Pyrolysis, 2002, 63(2002): 1-15). In 2014, Kannan et al. used flash pyrolysis technology to depolymerize low-density polyethylene (LDPE) into monomer ethylene at 950-1000°C, and the ethylene selectivity reached 48% (Energy & Fuels, 2014, 28(5): 3363-3366). The use of catalysts can reduce the reaction temperature of polyethylene pyrolysis to ethylene. In 2012, Donaj used TiCl4 / MgCl2 catalyst to degrade polyethylene and polypropylene mixed plastics at 500°C, and obtained 22.3% ethylene and 22.1% propylene. The addition of TiCl4 / MgCl2 catalyst significantly improves the yield of gaseous olefins, especially propylene, which is higher than the olefin yield obtained by pyrolysis alone (Chemical Engineering Journal, 2012, 207(2): 27-34). Because the Gibbs free energy of polyolefin depolymerization to monomer is high, chemical depolymerization of polyolefin tends to generate by-products with low Gibbs free energy, so only a small amount of monomer selectivity is achieved.

[0004] Obviously, polyolefin plastic depolymerization requires harsh conditions such as high temperature and high pressure to achieve and the product selectivity is uncontrollable, and the use of catalysts to crack polyolefin plastics has great advantages in reducing reaction temperature and improving product selectivity, so the development of a heterogeneous catalyst system with higher application prospect to realize the efficient and selective recovery of polyolefin plastics is the key scientific problem to be solved in this field. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a catalyst for catalyzing polyethylene degradation to prepare ethylene, which takes cerium oxide as a carrier, takes metal palladium, indium and tungsten oxide as active metals, and the highly dispersed active metals on the carrier play a key role in the process of catalytic conversion of polyethylene, which can catalyze the conversion of polyethylene to ethylene at a lower temperature.

[0006] To solve the above technical problems, the implementation process of the present application is as follows:

[0007] A polyethylene degradation to ethylene catalyst, the catalyst composition is: Pd x In y WO3 / CeO2, wherein CeO2 is a carrier, and the mass of WO3 is 1-40% of the mass of cerium oxide; preferably, the mass of WO3 is 1-20% of the mass of cerium oxide; more preferably, the mass of WO3 is 1-10% of the mass of cerium oxide; Pd x In y The loading amount is 0.2-20 wt%, x and y are positive integers or decimals, and the molar ratio of Pd and In is 1-50:1-50; preferably, the molar ratio of Pd and In is 1-20:1-20; more preferably, the molar ratio of Pd and In is 1-10:1-10, and most preferably, the molar ratio of Pd and In is 1:3.

[0008] A polyethylene degradation to ethylene catalyst Pd x In y WO3 / CeO2, the preparation method comprises the following steps:

[0009] (1) loading a soluble palladium salt to a cerium oxide carrier;

[0010] (2) loading a soluble indium salt and a tungsten salt to the carrier obtained in step (1);

[0011] (3) calcining the product obtained in step (2) at 250-600°C in an air atmosphere;

[0012] (4) reducing the product obtained in step (3) at 400-800°C in a 5-50 vol% H2 / Ar hydrogen-argon mixed gas to obtain a ternary Pd x Iny WO3 / CeO2catalyst.

[0013] Preferably, in step (1), the soluble palladium salt is selected from palladium acetylacetonate, ammonium tetrachloropalladate, palladium acetate, palladium nitrate, palladium sulfate, dichlorodiammine palladium or palladium tetraammine nitrate, and the carrier is selected from cerium oxide, aluminum oxide, zeolite or silicon oxide.

[0014] Preferably, in step (2), the soluble indium salt is selected from indium nitrate, indium chloride, indium iodide, indium fluoride, indium sulfate, indium acetate or indium phosphate, and the soluble tungsten salt is selected from ammonium metatungstate, ammonium paratungstate, phosphotungstic acid or tungsten pentachloride.

[0015] Preferably, in steps (1) and (2), the palladium loading is 0.1-10 wt%, the indium loading is 0.1-10 wt%, and the mass of WO3 is 1-10% of the mass of cerium oxide.

[0016] Preferably, in steps (1) and (2), the molar ratio of palladium to indium is 1-10:1-10, and the expression of the catalyst is Pd x In y WO3 / CeO 2， For example, Pd1In9WO3 / CeO2, Pd9In1WO3 / CeO2, Pd1In3WO3 / CeO2, Pd3In1WO3 / CeO2, etc.

[0017] Preferably, in step (3), the parameters for calcining the sample are as follows: the temperature rising rate is 0.8-20°C / min, the calcination temperature is 250-600°C, and the holding time is 1-6 h.

[0018] Preferably, in step (4), the parameters for the reduction process are as follows: the temperature rising rate is 1-20°C / min, the reducing gas is a mixture of 5-10 vol% hydrogen and argon, the gas flow rate is 10-200 sccm, the reduction temperature is 400-800°C, and the holding time is 1-6 h.

[0019] To solve the above technical problems, the second object of the present application is to provide a scheme for catalytically converting polyethylene to ethylene.

[0020] The catalytic conversion reaction of polyethylene plastic is carried out in a batch high-temperature high-pressure reaction kettle, and the specific steps and conditions are as follows:

[0021] (1) A catalyst and polyethylene are added to the reaction kettle, the polyethylene is selected from one or more of low-density polyethylene, linear low-density polyethylene and high-density polyethylene, and nitrogen is introduced for protection;

[0022] (2) The temperature is raised to 200-350°C for sufficient reaction;

[0023] (3) Collecting the gas product and using a gas chromatograph to quantitatively analyze the gas product, the polyethylene conversion rate being 25-58%, and the ethylene selectivity being 0-81%.

[0024] By the above scheme, the catalyst for preparing polyethylene degradation to ethylene prepared by the application has Pd, In and WO3 as active metals, and cerium oxide as a carrier, and the active metals are highly dispersed on the carrier; the catalyst realizes carbon chain dehydrogenation through palladium-indium cooperation, and realizes carbon-carbon bond breaking through WO3, and can convert polyethylene into ethylene with high selectivity under low temperature and solvent-free conditions.

[0025] Compared with the prior art, the application has the following advantages and beneficial effects:

[0026] (1) The raw materials used in the application are all commercial products purchased directly and do not need additional treatment, the preparation method is simple and controllable, has strong stability, can be reused, and has good application prospect;

[0027] (2) The active metals of the catalyst are uniformly dispersed on the surface of the carrier, providing more effective active sites;

[0028] (3) Compared with the reported system, the system can convert polyethylene into ethylene at a lower temperature (250°C), and the selectivity is as high as 81%;

[0029] (4) The system can be applied to various polyethylene plastics, including one or more of low-density polyethylene, linear low-density polyethylene and high-density polyethylene with different molecular weights, and has a wide range of degradable plastics. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a spherical aberration electron microscope image of the Pd1In3WO3 / CeO2 catalyst;

[0031] Figure 2 is a spherical aberration electron microscope image of the Pd1In1WO3 / CeO2 catalyst;

[0032] Figure 3 is a spherical aberration electron microscope image of the Pd1In5WO3 / CeO2 catalyst;

[0033] Figure 4 is a spherical aberration electron microscope image of the Pd1In7WO3 / CeO2 catalyst;

[0034] Figure 5 is a spherical aberration electron microscope image of the Pd3In1WO3 / CeO2 catalyst;

[0035] Figure 6 is a spherical aberration electron microscope image of the Pd7In1WO3 / CeO2 catalyst;

[0036] Figure 7 Pd x In y X-ray diffraction pattern of WO3 / CeO2 catalyst;

[0037] Figure 8 Gas product of Pd1In3WO3 / CeO2 catalyst degrading polyethylene on gas chromatogram. DETAILED DESCRIPTION

[0038] The application will be apparent from the following description and accompanying drawings. It should be apparent to the skilled in the art that the described embodiments are merely a part of the application and not all the embodiments. The reagents or instruments used are not specified by the manufacturer, and are all conventional reagents available on the market.

[0039] Example 1

[0040] In this embodiment, cerium oxide is used as the carrier, and palladium acetylacetonate, indium nitrate, and ammonium metatungstate are used as the metal precursors. The mass of cerium oxide is 1000 mg, the mass of WO3 in the prepared catalyst is 10% of the mass of cerium oxide, the molar ratio of Pd and In is 1:3, the palladium loading is 0.8 wt%, and the indium loading is 2.8 wt%. The specific steps for preparing the Pd1In3WO3 / CeO2 catalyst are as follows:

[0041] (1) Weigh 28.18 mg of palladium bis(acetylacetonate) and 1000 mg of cerium oxide. Dissolve the palladium bis(acetylacetonate) in 800 μl of chloroform. Use the incipient wetness impregnation method to load the palladium precursor on the cerium oxide. Place the impregnated product in a vacuum drying oven for drying.

[0042] (2) Transfer the solid product in step (1) to a beaker and add deionized water. Weigh 106.91 mg of ammonium metatungstate and 81.40 mg of indium nitrate and transfer them to the above beaker for stirring.

[0043] (3) Use a rotary evaporator to remove the water in the solid-liquid mixture in step (2) at 60°C with a rotation speed of 125 rpm and a vacuum degree of 100 mbar.

[0044] (4) Place the product in step (3) in a muffle furnace and calcine at 300°C for 2 h.

[0045] (5) Use 5 vol% hydrogen-argon mixed gas to reduce the calcined product in step (4) at 500°C for 2 h.

[0046] The spherical aberration electron microscope image of the prepared Pd1In3WO3 / CeO2 catalyst is as follows: Figure 1As shown in FIG. 1, it can be seen that the catalyst obtained by impregnation-calcination-reduction is spherical, the ceria support has a diameter of about 25 nm, and the metal particles with a diameter of about 2 nm are uniformly distributed on the surface of the ceria support. Figure 7 Only characteristic peaks of ceria were observed in the XRD diffraction pattern, excluding the presence of bulk metal, indicating good metal dispersion.

[0047] Example 2

[0048] Similar to Example 1, ceria was used as the support, and palladium acetylacetonate, indium nitrate, and ammonium metatungstate were used as the metal precursors, wherein the mass of ceria was 1000 mg, and the mass of WO3 in the catalyst was 10% of the mass of ceria. The difference was that the molar ratio of Pd to In was changed to 1:1, the palladium loading was 1.7 wt%, and the indium loading was 1.9 wt%. Under the same preparation conditions as in Example 1, the spherical aberration electron microscopy of the Pd1In1WO3 / CeO2 catalyst is shown in FIG. 2. Figure 2 As shown in FIG. 2, the active metal is a particle with a diameter of about 5 nm. Figure 7 The XRD diffraction pattern of FIG. 2 did not observe the relevant peaks of palladium, indium, and tungsten oxide, indicating that no bulk metal was generated, indicating good metal dispersion.

[0049] Example 3

[0050] Similar to Example 1, ceria was used as the support, and palladium acetylacetonate, indium nitrate, and ammonium metatungstate were used as the metal precursors, wherein the mass of ceria was 1000 mg, and the mass of WO3 in the catalyst was 10% of the mass of ceria. The difference was that the molar ratio of Pd to In was changed to 1:5, the palladium loading was 0.6 wt%, and the indium loading was 3.1 wt%. Under the same preparation conditions as in Example 1, the spherical aberration electron microscopy of the Pd1In5WO3 / CeO2 catalyst is shown in FIG. 3. Figure 3 As shown in FIG. 3, the size of the ceria support is about 15 nm, and no obvious metal particles are observed, Figure 7 The XRD diffraction pattern of FIG. 3 did not observe the relevant peaks of palladium, indium, and tungsten oxide, indicating that no bulk metal was generated.

[0051] Example 4

[0052] Similar to Example 1, ceria was used as the support, and palladium acetylacetonate, indium nitrate, and ammonium metatungstate were used as the metal precursors, wherein the mass of ceria was 1000 mg, and the mass of WO3 in the catalyst was 10% of the mass of ceria. The difference was that the molar ratio of Pd to In was changed to 1:7, the palladium loading was 0.42 wt%, and the indium loading was 3.2 wt%. Under the same preparation conditions as in Example 1, the spherical aberration electron microscopy of the Pd1In7WO3 / CeO2 catalyst is shown in FIG. 4. Figure 4 As shown in FIG. 4, the size of the ceria support is about 20 nm, and a layer of active metal is dispersed on the surface of the support,Figure 7 The XRD diffraction pattern of Pd1In3WO3 / CeO2 did not observe the relevant peaks of palladium, indium and tungsten, indicating that no bulk metal was generated.

[0053] Example 5

[0054] Similar to Example 1, cerium oxide was used as the carrier, palladium acetylacetonate, indium nitrate, and ammonium metatungstate were used as metal precursors, wherein the mass of cerium oxide was 1000 mg, the mass of WO3 in the catalyst was 10% of the mass of cerium oxide, and the difference was that the molar ratio of Pd and In was 3:1, the palladium loading was 2.7 wt%, and the indium loading was 1 wt%. The spherical aberration electron microscopy of the Pd3In1WO3 / CeO2 catalyst obtained under the same preparation conditions as Example 1 is shown in FIG. 4, the size of the carrier cerium oxide is about 10 nm, and active metal particles with a diameter of about 2 nm can be observed on the surface of the cerium oxide. Figure 5 Figure 7 The XRD diffraction pattern of Pd1In3WO3 / CeO2 did not observe the relevant peaks of palladium, indium and tungsten, indicating that no bulk metal was generated.

[0055] Example 6

[0056] Similar to Example 1, cerium oxide was used as the carrier, palladium acetylacetonate, indium nitrate, and ammonium metatungstate were used as metal precursors, wherein the mass of cerium oxide was 1000 mg, the mass of WO3 in the catalyst was 10% of the mass of cerium oxide, and the difference was that the molar ratio of Pd and In was 3:1, the palladium loading was 2.7 wt%, and the indium loading was 1 wt%. The spherical aberration electron microscopy of the Pd3In1WO3 / CeO2 catalyst obtained under the same preparation conditions as Example 1 is shown in FIG. 4, the size of the carrier cerium oxide is about 10 nm, and active metal particles with a diameter of about 2 nm can be observed on the surface of the cerium oxide. Figure 6 Figure 7 The XRD diffraction pattern of Pd1In3WO3 / CeO2 did not observe the relevant peaks of palladium, indium and tungsten, indicating that no bulk metal was generated.

[0057] Example 7

[0058] A method for catalytically degrading polyolefin plastic to produce ethylene, comprising the following steps: adding 100 mg of low-density polyethylene and 200 mg of Pd1In3WO3 / CeO2 catalyst into a reaction kettle, and filling 4 MPa of nitrogen. The reaction time is adjusted to 12 h, and the reaction temperature is 250°C. After the reaction is completed, the gas product is collected. The gas product is quantitatively analyzed using gas chromatography. Figure 8 The peak spectrum of the gas phase produced in the catalytic conversion of polyethylene is shown in FIG. 6. As can be seen from the figure, the retention time of ethylene on the gas chromatogram is 9.3 min, and the selectivity of ethylene is as high as 81%.

[0059] ​​Example 8

[0060] Similar to Example 7, except that Pd1In1WO3 / CeO2 catalyst, Pd1In5WO3 / CeO2 catalyst, Pd1In7WO3 / CeO2 catalyst, Pd3In1WO3 / CeO2 catalyst and Pd7In1WO3 / CeO2 catalyst were used respectively to catalyze the polyethylene reaction.

[0061]

[0062] From Table 1, it can be seen that the results of catalytic conversion of polyethylene reaction under different ratios of palladium and indium, Pd1In3WO3 / CeO2 catalyst catalyzing the conversion of polyethylene has the highest polyethylene conversion rate (58%) and the highest ethylene product selectivity (81%).

[0063] Example 9

[0064] Similar to Example 1, except that alumina, silica and zeolite (SBA-15) were used respectively as the carrier, the mass of the carrier was 1000 mg, the mass of WO3 in the catalyst was 10% of the mass of cerium oxide, the molar ratio of Pd and In was 1:3, the palladium loading was 0.8 wt%, and the indium loading was 2.8 wt%. Table 2 is the results of catalytic conversion of polyethylene reaction with different carriers. When cerium oxide is used as the carrier, the polyethylene conversion rate is the highest, and the polyethylene will be converted into ethylene to the maximum extent; when alumina is used as the carrier, the polyethylene conversion rate is lower than that of the catalyst with cerium oxide as the carrier, there is a small amount of ethylene in the degradation product, and the main product is ≥C4 product; when the carrier is SiO2, the catalyst activity is the lowest; when the carrier is SBA-15, the polyethylene conversion rate is comparable to that of the catalyst with cerium oxide as the carrier, but the main product in the degradation product is ≥C4 product. The experiment proves that the basic carrier is more conducive to the depolymerization of polyethylene to generate ethylene.

[0065]

[0066] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments cannot be exhausted. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A Pd catalyst for the degradation of polyethylene to ethylene x In y The method for preparing WO3 / CeO2 is characterized by: The catalyst Pd x In y In WO3 / CeO2, CeO2 serves as the support, and the mass of WO3 is 1-40% of the mass of CeO2; Pd x In y The loading is 0.2~20 wt%, x and y are positive integers or decimals, and the molar ratio of Pd to In is 1~50:1~50; The preparation method of the above catalyst includes the following steps: (1) Loading soluble palladium salts onto a cerium oxide support; (2) Soluble indium salt and tungsten salt are loaded onto the support obtained in step (1), Pd x In y The loading is 0.2~20 wt%, x and y are positive integers or decimals, and the molar ratio of Pd to In is 1~50:1~50; (3) The product obtained in step (2) is calcined in air at 250~600℃; (4) The product obtained in step (3) is reduced in a 5~50 vol% H2 / Ar hydrogen-argon mixture at 400~800℃ to obtain ternary Pd. x In y WO3 / CeO2 catalyst.

2. The preparation method according to claim 1, characterized in that: The mass of WO3 is 1-20% of the mass of CeO2, and the molar ratio of Pd to In is 1-20:1-20.

3. The preparation method according to claim 2, characterized in that: The mass of WO3 is 1-10% of the mass of CeO2, and the molar ratio of Pd to In is 1-10:1-10.

4. The preparation method according to claim 1, characterized in that: In step (1), the soluble palladium salt is selected from palladium acetylacetonate, ammonium tetrachloropalladate, palladium acetate, palladium nitrate, palladium sulfate, diammonium dichloropalladium or palladium tetraaminonitrate.

5. The preparation method according to claim 1, characterized in that: In step (2), the soluble indium salt is selected from indium nitrate, indium chloride, indium iodide, indium fluoride, indium sulfate, indium acetate or indium phosphate, and the soluble tungsten salt is selected from ammonium metatungstate, ammonium paratungstate, phosphotungstic acid or tungsten pentachloride.

6. The preparation method according to claim 1, characterized in that: The sample calcination parameters in step (3) are: heating rate 0.8~20℃ / min; the parameters for the reduction process in step (4) are: heating rate 1~20℃ / min, reducing gas 5~10 vol% hydrogen-argon mixture.

7. The Pd prepared by the method according to claim 1 x In y WO3 / CeO2 catalyst.

8. The application of the catalyst according to claim 7 in the degradation of polyethylene to produce ethylene.

9. The application according to claim 8, characterized in that... The steps and conditions for the polyethylene degradation reaction are as follows: (1) Add a catalyst and polyethylene of a catalyst amount to the reactor, wherein the polyethylene is selected from one or more of low-density polyethylene, linear low-density polyethylene and high-density polyethylene, and purge with nitrogen gas for protection. (2) Increase the temperature to 200~350℃ to allow the reaction to proceed fully; (3) Collect gaseous products and use gas chromatograph to perform quantitative analysis of gaseous products. The conversion rate of polyethylene is 25-58%, and the selectivity of ethylene is 81%.

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