A catalyst, a method for preparing the same, and use of the catalyst in catalyzing polystyrene pyrolysis

Abstract

The application provides a catalyst, a preparation method thereof and application of the catalyst in catalyzing polystyrene pyrolysis. The catalyst comprises a molecular sieve and a transition metal element loaded in the molecular sieve; the molecular sieve is H-Beta molecular sieve and / or ZSM-5 molecular sieve; and the transition metal element is selected from one or more of Cu, Zn, Co and Ni, and the transition metal element exists in the form of metal element. The catalyst provided by the application can catalyze polystyrene pyrolysis under relatively mild conditions, and can efficiently and selectively convert polystyrene into styrene; the catalyst is easy to regenerate, has good cycle stability and is conducive to repeated use; and the catalyst has universality in recycling of commercial waste polystyrene plastic and polystyrene mixed plastic.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical catalysis technology, and particularly relates to a catalyst, a preparation method thereof and application of the catalyst in catalyzing polystyrene pyrolysis. BACKGROUND

[0002] Polystyrene (PS) plastics are widely used in food packaging, medical health, building materials and many other fields due to their mechanical durability and easy processability. Unfortunately, the accumulation of PS poses an ecological and economic threat, so it is crucial to develop chemical recycling methods to depolymerize and reuse PS waste.

[0003] Traditional PS depolymerization methods, such as pyrolysis and catalytic hydrogenation, often produce complex hydrocarbon mixtures that are difficult to separate, thereby reducing their usability.

[0004]

[0005] Therefore, avoiding the presence of unwanted hydrocarbons in the target alkane or arene products is an important consideration for PS recycling. Researchers have developed new technologies to recycle PS, such as non-thermal plasma-assisted hydrogenolysis and photocatalytic deconstruction at ambient temperature and atmospheric pressure, but the selectivity is still unsatisfactory. Therefore, how to explore an efficient catalytic system to direct the conversion of polystyrene waste plastics into high-value chemicals still has great challenges. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application aims to provide a catalyst, a preparation method thereof and application of the catalyst in catalyzing polystyrene pyrolysis. The catalyst can catalyze polystyrene pyrolysis under relatively mild conditions, making it efficiently and selectively converted into styrene; the catalyst is easy to regenerate, has good cycle stability and is conducive to repeated use; and it has universality in the recycling of commercial waste polystyrene plastics and polystyrene mixed plastics.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a catalyst precursor, which comprises a molecular sieve and a transition metal element supported in the molecular sieve.

[0009] The molecular sieve is H-Beta molecular sieve and / or ZSM-5 molecular sieve.

[0010] The transition metal element is selected from one or more of Cu, Zn, Co and Ni, and the transition metal element exists in the form of an oxide.

[0011] In some embodiments of the present application, the loading of the transition metal element in the catalyst precursor is 0.1-1 wt%, for example, it can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%, etc.; preferably, it is 0.1-0.8 wt%, more preferably, it is 0.2 wt%. However, the present application is not limited to the listed values, and other values not listed in the range are also applicable.

[0012] In some embodiments of the present application, the transition metal element is Co and / or Ni.

[0013] In some embodiments of the present application, the molecular sieve is H-Beta molecular sieve.

[0014] In some embodiments of the present application, the molar ratio of Si to Al in the molecular sieve is 10-13:1; for example, it can be 10:1, 10.2:1, 10.5:1, 10.8:1, 11:1, 11.2:1, 11.5:1, 11.8:1, 12:1, 12.2:1, 12.5:1, 12.8:1 or 13:1, etc. However, the present application is not limited to the listed values, and other values not listed in the range are also applicable.

[0015] In a second aspect, the present application provides a preparation method of the catalyst precursor according to the first aspect, which comprises the following steps:

[0016] Mixing the aqueous solution of the transition metal salt with the molecular sieve, drying, and then calcining in an oxygen-containing atmosphere to decompose the transition metal salt into an oxide, thereby obtaining the catalyst precursor.

[0017] In some embodiments of the present application, the transition metal salt is a nitrate salt of the transition metal. The nitrate salt of the transition metal is more likely to decompose into a transition metal oxide when calcined in an oxygen-containing atmosphere.

[0018] In some embodiments of the present application, the concentration of the transition metal element in the aqueous solution of the transition metal salt is 0.5-1 mol / L; for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, etc. However, the present application is not limited to the listed values, and other values not listed in the range are also applicable.

[0019] In some embodiments of the present application, the mixing method is: dropwise adding the aqueous solution of the transition metal salt onto the molecular sieve, and stirring until the surface is dry; or immersing the molecular sieve in the aqueous solution of the transition metal salt for a period of time, and then separating the solid.

[0020] In some embodiments of the present application, the drying is performed at 100-120℃ (for example, it can be 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃, 118℃ or 120℃, etc.).

[0021] As a non-limiting example, the oxygen-containing atmosphere described in the present application can be an air atmosphere, an oxygen atmosphere, etc.

[0022] In some embodiments of the present application, the calcination temperature is 450-650℃; for example, it can be 450℃, 480℃, 500℃, 520℃, 550℃, 580℃, 600℃, 620℃ or 650℃, etc. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0023] In some embodiments of the present application, the calcination time is 4-8h; for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, etc. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0024] In a third aspect, the present application provides a catalyst, which comprises a molecular sieve, and a transition metal element supported in the molecular sieve.

[0025] The molecular sieve is a H-Beta molecular sieve and / or a ZSM-5 molecular sieve.

[0026] The transition metal element is selected from one or more of Cu, Zn, Co and Ni, and the transition metal element is in the form of a metal element.

[0027] A molecular sieve is a silicate-aluminate crystal with a regular pore structure, which is composed of [SiO4] and [AlO4] tetrahedrons by sharing vertex oxygen atoms, and its chemical formula can be represented as M n / m (SiO2)(AlO2) n ·xH2O (M is a cation with a valence of m). The pore structure of the molecular sieve makes it a carrier for loading transition metal elements.

[0028] The present application loads a transition metal in a molecular sieve by selecting a suitable molecular sieve and a transition metal element, thereby obtaining a catalyst with good performance. The catalyst can catalyze the pyrolysis of polystyrene under relatively mild conditions (285-295℃) to convert it into styrene with high efficiency and high selectivity; the catalyst is easy to regenerate, has good cycle stability, and is conducive to repeated use; and it has universality in the recycling of commercial waste polystyrene plastics and mixed polystyrene plastics.

[0029] In some embodiments of the present application, the loading of the transition metal element in the catalyst is 0.1-1 wt%, for example, it can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%, etc.; preferably, it is 0.1-0.8 wt%, more preferably, it is 0.2 wt%. However, the present application is not limited to the listed values, and other values not listed in the range are also applicable.

[0030] In the present application, the loading of the transition metal element is kept in the above range, which is helpful to obtain a catalyst with good performance, and the catalyst has the best performance when the loading of the transition metal element is 0.2 wt%. If the loading of the transition metal element is too low, there are fewer active centers in the catalyst, and the catalyst has a lower catalytic pyrolysis efficiency for polystyrene; if the loading of the transition metal element is too high, the transition metal element occupies more acid sites, which also leads to a lower catalytic pyrolysis efficiency for polystyrene.

[0031] In some embodiments of the present application, the transition metal element is Co and / or Ni.

[0032] In some embodiments of the present application, the molecular sieve is an H-Beta molecular sieve.

[0033] In the present application, when the transition metal element is Co and / or Ni and the molecular sieve is an H-Beta molecular sieve, the obtained catalyst has higher catalytic efficiency.

[0034] The smaller the molar ratio of Si to Al in the molecular sieve, the more Al, the more acid sites in the molecular sieve, and the stronger the catalytic activity; however, if the proportion of Al is too high, the structure of the molecular sieve is unstable. Therefore, in the present application, the molar ratio of Si to Al in the molecular sieve is preferably 10-13:1; for example, it can be 10:1, 10.2:1, 10.5:1, 10.8:1, 11:1, 11.2:1, 11.5:1, 11.8:1, 12:1, 12.2:1, 12.5:1, 12.8:1 or 13:1, etc. However, the present application is not limited to the listed values, and other values not listed in the range are also applicable.

[0035] In a fourth aspect, the present application provides a preparation method of the catalyst according to the third aspect, and the preparation method comprises the following steps:

[0036] The catalyst precursor according to the first aspect or prepared by the preparation method according to the second aspect is heated and reacted in a reducing atmosphere, so that the oxide of the transition metal element in the catalyst precursor is reduced to a metal element, and the catalyst is obtained.

[0037] It should be noted that, since the catalyst provided by the present application contains transition metal elements, the transition metal elements are easily re-oxidized to oxides in an air environment, and therefore the catalyst needs to be stored in a non-oxidizing environment, or in the form of a catalyst precursor, which is prepared into a catalyst by the above method when used.

[0038] In some embodiments of the present application, the reducing atmosphere is a hydrogen atmosphere.

[0039] In some embodiments of the present application, the reaction temperature is 350-550℃; for example, it can be 350℃, 380℃, 400℃, 420℃, 450℃, 480℃, 500℃, 520℃ or 550℃, etc. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0040] In some embodiments of the present application, the reaction time is 2-8h; for example, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0041] In a fifth aspect, the present application provides a catalyst prepared by the method of the third aspect or the fourth aspect, which is used in catalyzing polystyrene pyrolysis.

[0042] In a sixth aspect, the present application provides a method for converting polystyrene into styrene, which comprises the following steps:

[0043] The catalyst prepared by the method of the third aspect or the fourth aspect, polystyrene and an organic solvent are mixed, and heated to react in an inert atmosphere, so that polystyrene is pyrolyzed to generate styrene.

[0044] The present application innovatively performs polystyrene pyrolysis reaction in an organic solvent system, and cooperates with the catalyst of the present application, which not only reduces the reaction temperature, but also improves the reaction efficiency and the selectivity of styrene.

[0045] In some embodiments of the present application, the organic solvent is acetonitrile.

[0046] In some embodiments of the present application, the reaction temperature is 285-295℃, for example, it can be 285℃, 286℃, 287℃, 288℃, 289℃, 290℃, 291℃, 292℃, 293℃, 294℃ or 295℃, etc.; preferably, it is 288-292℃, and more preferably, it is 290℃. However, the present application is not limited to the listed values, and other unlisted values within this range are also applicable.

[0047] In some embodiments of the present application, the reaction time is 4-16h, for example, it can be 4h, 5h, 6h, 7h, 8h, 10h, 12h, 13h, 15h or 16h, etc.; preferably 4-8h, more preferably 4h. But the present application is not limited to the listed values, other values not listed in this range are also applicable.

[0048] In some embodiments of the present application, the mass ratio of the catalyst to the polystyrene is 0.5-2:1, for example, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, etc. But the present application is not limited to the listed values, other values not listed in this range are also applicable.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] The catalyst provided by the present application can catalyze the pyrolysis of polystyrene under relatively mild conditions, and convert it into styrene with high efficiency and high selectivity; the catalyst is easy to regenerate, has good cycle stability, and is conducive to repeated use; and it has universality in the recycling of commercial waste polystyrene plastic and polystyrene mixed plastic.

[0051] The method for converting polystyrene into styrene provided by the present application innovatively carries out the pyrolysis reaction of polystyrene in an organic solvent system (especially acetonitrile), in combination with the catalyst of the present application, which not only reduces the reaction temperature, but also improves the reaction efficiency and the selectivity of styrene. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1A TEM and HRTEM images of the Ni-Beta catalyst provided for Example 1 of the present application;

[0053] Figure 1B Energy spectrum surface distribution map of elements in the Ni-Beta catalyst provided for Example 1 of the present application;

[0054] Figure 1C XRD images of the Ni-Beta catalyst and the H-Beta molecular sieve used provided for Example 1 of the present application;

[0055] Figure 1D Nitrogen physical adsorption curve graph of the Ni-Beta catalyst and the H-Beta molecular sieve used provided for Example 1 of the present application;

[0056] Figure 1E Pore size distribution graph of the Ni-Beta catalyst and the H-Beta molecular sieve used provided for Example 1 of the present application;

[0057] Figure 2A NH3-TPD curve of the Ni-Beta catalyst provided in Example 1 of the present application and the H-Beta molecular sieve used;

[0058] Figure 2B Pyridine infrared spectrum of the Ni-Beta catalyst provided in Example 1 of the present application and the H-Beta molecular sieve used;

[0059] Figure 3A Effect diagram of catalytic pyrolysis of polystyrene by H-Beta molecular sieve using different organic solvents;

[0060] Figure 3B Effect diagram of catalytic pyrolysis of polystyrene by different topological structure molecular sieves;

[0061] Figure 4A Effect diagram of catalytic pyrolysis of polystyrene by H-Beta molecular sieve at different reaction temperatures;

[0062] Figure 4B Effect diagram of catalytic pyrolysis of polystyrene by H-Beta molecular sieve at different reaction times;

[0063] Figure 5A Effect diagram of catalytic pyrolysis of polystyrene by catalysts of different metal elements;

[0064] Figure 5B Effect diagram of catalytic pyrolysis of polystyrene by Ni-Beta catalysts with different metal element loadings;

[0065] Figure 6A Effect diagram of catalytic pyrolysis of polystyrene by the Ni-Beta catalyst provided in Example 1 of the present application at different cycle times;

[0066] Figure 6B Effect diagram of catalytic pyrolysis of different commercial polystyrenes by the Ni-Beta catalyst provided in Example 1 of the present application;

[0067] Figure 7A Effect diagram of catalytic pyrolysis of polystyrene in different mixed plastics by the Ni-Beta catalyst provided in Example 1 of the present application;

[0068] Figure 7B H-NMR spectrum of the solution obtained by catalytic pyrolysis of polystyrene by the Ni-Beta catalyst provided in Example 1 of the present application in an enlarged system. 1 H-NMR spectrum. DETAILED DESCRIPTION

[0069] The technical solutions of the present application will be further described below in combination with the drawings and through specific embodiments. Those skilled in the art should understand that the specific embodiments are only used to help understand the present application and should not be regarded as specific limitations to the present application.

[0070] In the embodiments of the present application, the sources of some materials are as follows:

[0071] SAPO-34 molecular sieve: Si / Al molar ratio = 0.25:1, Nankai Catalyst Factory;

[0072] USY molecular sieve: Si / Al molar ratio = 2.5:1, Nankai Catalyst Factory;

[0073] ZSM-5 molecular sieve: Si / Al molar ratio = 12.5:1, Nankai Catalyst Factory;

[0074] H-Beta molecular sieve: Si / Al molar ratio = 12.5:1, 15:1, 30:1, Nankai Catalyst Factory.

[0075] Embodiment 1

[0076] This embodiment provides a catalyst, and the preparation method is as follows:

[0077] (1) A nickel nitrate aqueous solution (100 mg / mL) is added dropwise to H-Beta molecular sieve (Si / Al molar ratio = 12.5:1), the proportion of raw materials is controlled so that the mass content of Ni in the catalyst is 0.2%, stirring is performed until the surface is dry, drying is performed in an oven at 120℃ for 12 h, then calcination is performed in a muffle furnace at 550℃ in an air environment for 6 h, and after being cooled to room temperature, a catalyst precursor is obtained;

[0078] (2) The catalyst precursor is reduced under H2 atmosphere at 450℃ for 2 h, and after being cooled to room temperature, grinding and drying are performed, and a catalyst (named as Ni-Beta catalyst) is obtained.

[0079] Embodiments 2-4

[0080] Embodiments 2-4 respectively provide a catalyst, and the only difference from Embodiment 1 is that the mass content of Ni in the catalyst is 0.1%, 0.8%, 1.5% respectively.

[0081] Embodiments 5-8

[0082] Embodiments 5-8 respectively provide a catalyst, and the only difference from Embodiment 1 is that nickel nitrate is replaced by iron nitrate, copper nitrate, zinc nitrate, and cobalt nitrate, i.e., Fe-Beta catalyst, Cu-Beta catalyst, Zn-Beta catalyst, and Co-Beta catalyst are respectively prepared, and the mass content of the transition metal element is 0.2% in each catalyst.

[0083] Examples 9-14

[0084] Examples 9-14 each provide a catalyst, differing from Example 1 only in that the H-Beta molecular sieve (Si / Al molar ratio = 12.5:1) is replaced with SAPO-34 molecular sieve (Si / Al molar ratio = 0.25:1), USY molecular sieve (Si / Al molar ratio = 2.5:1), ZSM-5 molecular sieve (Si / Al molar ratio = 12.5:1), H-Beta molecular sieve (Si / Al molar ratio = 15:1), and H-Beta molecular sieve (Si / Al molar ratio = 30:1), respectively. Thus, Ni-SAPO-34 catalyst, Ni-USY catalyst, Ni-ZSM-5 catalyst, Ni-Beta catalyst (Si / Al molar ratio = 15:1), and Ni-Beta catalyst (Si / Al molar ratio = 30:1) are prepared respectively.

[0085] Physicochemical property characterization

[0086] 1. The morphology of the Ni-Beta catalyst provided in Example 1 was characterized using transmission electron microscopy (TEM) and high-power transmission electron microscopy (HRTEM), and the results are as follows: Figure 1A As shown in the figure. Figure a is a TEM image, and figure b is an HRTEM image.

[0087] from Figure 1A As can be seen, Ni is uniformly dispersed in atomic form on the Beta molecular sieve.

[0088] 2. The elemental distribution of the Ni-Beta catalyst provided in Example 1 was tested using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and the results are as follows: Figure 1B As shown.

[0089] from Figure 1B As can be seen, the Ni metal loaded on the molecular sieve support is uniformly dispersed without significant agglomeration or the formation of large nanoparticles.

[0090] 3. The Ni-Beta catalyst provided in Example 1 and the H-Beta molecular sieve used were tested using an X-ray diffractometer, and the X-ray diffraction spectra (XRD patterns) were obtained, as shown below. Figure 1C As shown.

[0091] from Figure 1C As can be seen, the loading of Ni metal did not affect the topology of the Beta molecular sieve support itself. At the same time, no obvious nickel diffraction peaks were found in the XRD pattern, which preliminarily indicates that the obtained nickel species has a small particle size.

[0092] 4. The specific surface area and pore size distribution of the Ni-Beta catalyst provided in Example 1 and the H-Beta molecular sieve used were tested using nitrogen physical adsorption method. The nitrogen physical adsorption curve and pore size distribution diagram are shown below. Figure 1D , Figure 1E As shown.

[0093] from Figure 1D and Figure 1E As can be seen from the above, the Ni-Beta catalyst provided in Example 1 has a high specific surface area and obvious microporous structure, indicating that the microporous structure of the Beta molecular sieve was not changed after Ni was loaded.

[0094] 5. The Ni-Beta catalyst provided in Example 1 and the H-Beta molecular sieve used were tested using ammonia-programmed temperature desorption (NH3-TPD), and the NH3-TPD curves were obtained, as shown in the figure. Figure 2A As shown.

[0095] from Figure 2A As can be seen, Ni loading has little effect on the density of the weak acid in the catalyst. However, the desorption peak temperature of the weak acid shifts to a lower temperature region after Ni loading, indicating that the strength of the weak acid in the catalyst decreases.

[0096] 6. The Ni-Beta catalyst provided in Example 1 and the H-Beta molecular sieve used were tested using pyridine infrared spectroscopy (PyFT-IR), and the pyridine infrared spectra were obtained, as shown below. Figure 2B As shown.

[0097] from Figure 2B It can be seen that Ni-Beta exhibits more Lewis acid / The acid ratio indicates that the Ni metal loading affects the distribution and number of acidic sites in the molecular sieve.

[0098] Catalytic performance test

[0099] 1. The effect of different solvents on catalytic performance

[0100] Experimental method: 200 mg of polystyrene (purchased from Acros, M) was added to the reaction vessel. w =260000), 30 mL of organic solvent (cyclohexane, toluene, tetrahydrofuran, chlorobenzene, mesitylene, acetonitrile) was used as the reaction solvent, and then 200 mg of H-Beta molecular sieve (Si / Al molar ratio = 12.5:1) was added. The mixture was heated to 290 °C under Ar atmosphere and reacted for 4 hours to obtain a styrene solution.

[0101] Gas chromatography, mass spectrometry and 1H-NMR was used to analyze the reaction system qualitatively and quantitatively, and the conversion of polystyrene and the selectivity of each decomposition product (including styrene, ethylbenzene, methylstyrene, cumene, toluene, dimer) were obtained.

[0102] The yield of styrene using different organic solvents is shown in Figure 3A Figure. It can be seen from the figure that the yield of styrene using acetonitrile as the reaction solvent is much higher than that using other organic solvents.

[0103] 2, Effect of different types of molecular sieves on catalytic performance

[0104] Experimental method: 200 mg of polystyrene (purchased from Acros Company, M w = 260000), 30 mL of acetonitrile as the reaction solvent, and then 200 mg of molecular sieve (SAPO-34, USY, ZSM-5, H-Beta (Si / Al molar ratio = 12.5:1)) or catalyst (catalysts provided in Examples 1 and 9-14) were added. Under Ar atmosphere, heated to 290°C, and reacted for 4 hours to obtain a solution of styrene in acetonitrile. The conversion of polystyrene and the selectivity of each decomposition product (including styrene, ethylbenzene, methylstyrene, cumene, toluene, dimer) were tested, and the results are shown in Figure 3B . Among them, the column represents the selectivity, the column height represents the selectivity value, the dot represents the conversion rate, and the number after the molecular sieve and catalyst name represents the Si / Al molar ratio.

[0105] As can be seen from Figure 3B , compared with H-Beta molecular sieve (Si / Al molar ratio = 12.5:1), the conversion of polystyrene of Ni-Beta catalyst (Si / Al molar ratio = 12.5:1) under the same conditions increased from 75% to 99%, and the selectivity of styrene did not change significantly (about 87%). Compared with other molecular sieve catalysts, the catalytic performance of Ni-Beta catalyst (Si / Al molar ratio = 12.5:1) is the best. And the catalytic activity of Ni-Beta catalyst decreases with the increase of Si / Al molar ratio.

[0106] 3, Effect of different reaction temperatures on catalytic performance

[0107] Experimental method: 200 mg of polystyrene (purchased from Acros Company, M w= 260,000), 30 mL of acetonitrile as a reaction solvent, and then 200 mg of H-Beta molecular sieve (Si / Al molar ratio = 12.5:1) was added. The reaction was heated to 270-300°C under an Ar atmosphere, and the reaction was carried out for 4 hours to obtain a solution of styrene in acetonitrile. The conversion of polystyrene and the selectivity of styrene were tested, and the results are shown in Figure 4A . Among them, red corresponds to the conversion, and blue corresponds to the selectivity.

[0108] As can be seen from Figure 4A , in the range of 270-300°C, the conversion of polystyrene increases with the increase of the reaction temperature; the selectivity of styrene increases first and then decreases with the increase of the reaction temperature, and the selectivity of styrene is the largest at 290°C.

[0109] 4. Effect of different reaction times on catalytic performance

[0110] Experimental method: 200 mg of polystyrene (purchased from Acros Company, M w = 260,000) was added to the reaction kettle, 30 mL of acetonitrile was used as a reaction solvent, and then 200 mg of H-Beta molecular sieve (Si / Al molar ratio = 12.5:1) was added. The reaction was heated to 290°C under an Ar atmosphere, and the reaction was carried out for 1-16 hours to obtain a solution of styrene in acetonitrile. The conversion of polystyrene and the selectivity of styrene were tested, and the results are shown in Figure 4B . Among them, red corresponds to the conversion, and blue corresponds to the selectivity.

[0111] As can be seen from Figure 4B , the conversion of polystyrene gradually increases with the extension of the reaction time, and reaches about 75% at 4h; the selectivity of styrene fluctuates within a certain range with the extension of the reaction time, and the selectivity of styrene decreases when the reaction time exceeds 4h. Therefore, from Figure 4A and Figure 4B , it can be seen that the comprehensive catalytic effect is the best when the reaction temperature is 290°C and the reaction time is 4h.

[0112] 5. Effect of different metal element types on catalytic performance

[0113] Experimental method: 200 mg of polystyrene (purchased from Acros Company, M w = 260,000) was added to the reaction kettle, 30 mL of acetonitrile was used as a reaction solvent, and then 200 mg of H-Beta molecular sieve (Si / Al molar ratio = 12.5:1) was added. The reaction was heated to 290°C under an Ar atmosphere, and the reaction was carried out for 1-16 hours to obtain a solution of styrene in acetonitrile. The conversion of polystyrene and the selectivity of styrene were tested, and the results are shown in Figure 5AAs shown in the figure. Here, the bars represent selectivity, the bar height represents the selectivity value, and the points represent conversion rates.

[0114] from Figure 5A As can be seen, there is no significant difference in styrene selectivity among the various catalysts; the polystyrene conversion rates of Cu-Beta, Zn-Beta, Co-Beta, and Ni-Beta catalysts are significantly higher than those of Fe-Beta catalyst; Co-Beta and Ni-Beta catalysts have the best catalytic performance, with a polystyrene conversion rate of approximately 99% and a styrene selectivity of approximately 87%.

[0115] 6. Effect of different metal element loadings on catalytic performance

[0116] Experimental method: 200 mg of polystyrene (purchased from Acros, M) was added to the reaction vessel. w =260000), 30 mL of acetonitrile was used as the reaction solvent, and then 200 mg of catalyst (the catalyst provided in Examples 1-4) was added. The mixture was heated to 290 °C under an Ar atmosphere and reacted for 4 hours to obtain a styrene acetonitrile solution. The conversion rate of polystyrene and the selectivity of each decomposition product (including styrene, ethylbenzene, methylstyrene, cumene, toluene, and dimer) were tested, and the results are as follows: Figure 5B As shown in the figure. Here, the bars represent selectivity, the bar height represents the selectivity value, and the points represent conversion rates.

[0117] from Figure 5B As can be seen, within the Ni loading range of 0.1-1.5%, the polystyrene conversion rate first increases and then decreases with increasing Ni loading, reaching its maximum at a Ni loading of 0.2%. The styrene selectivity shows relatively little change with Ni loading. This indicates that the catalyst exhibits the best catalytic performance at a Ni loading of 0.2%.

[0118] 7. Cyclic stability of the catalyst

[0119] Experimental method: 200 mg of polystyrene (purchased from Acros, M) was added to the reaction vessel. w =260000), 30 mL of acetonitrile was used as the reaction solvent, and then 200 mg of the catalyst provided in Example 1 was added. The mixture was heated to 290 °C under an Ar atmosphere and reacted for 4 hours to obtain a styrene acetonitrile solution. After the reaction, the catalyst was centrifuged and calcined in an air environment at 550 °C in a muffle furnace for 6 hours, followed by reduction at 450 °C under an H2 atmosphere for 2 hours to regenerate the catalyst, which was then used again to catalyze the pyrolysis of polystyrene. The above experiment was repeated cyclically, and the conversion rate of polystyrene and the selectivity of styrene in each cycle were tested. The results are as follows: Figure 6A As shown in the image. Red represents conversion rate, and blue represents selectivity.

[0120] From Figure 6A It can be seen that the polystyrene conversion rate and styrene selectivity do not change significantly after 5 cycles, indicating that the catalyst provided by the present application has good cycle stability.

[0121] 8. Catalytic effect of different polystyrene plastics

[0122] Experimental method: 200 mg of polystyrene (one-time cup, coffee cup cover, foam, doll filler) was added to the reaction kettle, 30 mL of acetonitrile was used as the reaction solvent, then 200 mg of the catalyst provided in Example 1 was added, heated to 290°C under Ar gas atmosphere, and reacted for 4 hours to obtain a styrene acetonitrile solution. The conversion rate of polystyrene and the selectivity of styrene were tested, and the results are shown in Figure 6B .

[0123] From Figure 6B It can be seen that the catalyst provided by the present application has good catalytic pyrolysis effect on different commercial polystyrene.

[0124] 9. Catalytic effect of different types of mixed plastics

[0125] Experimental method: 200 mg of mixed plastic (PS+2% PET, PS+2% PP, PS+2% PVC, PS+2% PE) was added to the reaction kettle, 30 mL of acetonitrile was used as the reaction solvent, then 500 mg of the catalyst provided in Example 1 was added, heated to 290°C under Ar gas atmosphere, and reacted for 12 hours to obtain a styrene acetonitrile solution. The conversion rate of polystyrene and the selectivity of styrene were tested, and the results are shown in Figure 7A .

[0126] From Figure 7A It can be seen that the mixing of other plastics in polystyrene will cause the catalytic effect of the catalyst of the present application to decrease, but the conversion rate of polystyrene can still reach more than 90%, and the selectivity of styrene can still reach more than 67%.

[0127] 10. Influence of scale-up system on catalytic performance

[0128] Experimental method: 4 g of polystyrene was added to the reaction kettle, 50 mL of acetonitrile was used as the reaction solvent, then 2 g of the catalyst provided in Example 1 was added, heated to 290°C under Ar gas atmosphere, and reacted for 12 hours to obtain a styrene acetonitrile solution. The nuclear magnetic hydrogen spectrum of the solution was tested, and the results are shown in Figure 7B .

[0129] From Figure 7B It can be seen that the styrene product obtained in the solution is relatively pure, indicating that the scale-up system can still maintain a high selectivity of styrene.

[0130] The foregoing is merely illustrative of the various implementations of the present disclosure and the general principles thereof. Numerous modifications can be made to these illustrations, and equivalents can be substituted therefor, without departing from the scope of the present disclosure. The specific embodiments commensurate with the specific application are intended to be illustrative only and not limiting of the scope of the application as set forth in the following claims.

Claims

1. A catalyst precursor for catalyzing the pyrolysis of polystyrene, characterized in that, The catalyst precursor includes a molecular sieve and a transition metal element supported in the molecular sieve. The molecular sieve is H-Beta molecular sieve and / or ZSM-5 molecular sieve; The transition metal element is selected from one or more of Cu, Zn, Co and Ni, and the transition metal element exists in the form of an oxide; The loading of the transition metal element in the catalyst precursor is 0.1-1 wt%; The molar ratio of Si to Al in the molecular sieve is 10-13:

1.

2. The catalyst precursor according to claim 1, characterized in that, The loading of the transition metal element in the catalyst precursor is 0.1-0.8 wt%.

3. The catalyst precursor according to claim 2, characterized in that, The loading of the transition metal element in the catalyst precursor is 0.2 wt%.

4. The catalyst precursor according to any one of claims 1-3, characterized in that, The transition metal element is Co and / or Ni.

5. The catalyst precursor according to any one of claims 1-3, characterized in that, The molecular sieve is an H-Beta molecular sieve.

6. A method for preparing a catalyst precursor as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: An aqueous solution of a transition metal salt is mixed with a molecular sieve, dried, and then calcined in an oxygen-containing atmosphere to decompose the transition metal salt into an oxide, thereby obtaining the catalyst precursor.

7. The preparation method according to claim 6, characterized in that, The transition metal salt is a nitrate of a transition metal.

8. The preparation method according to claim 6 or 7, characterized in that, The concentration of the transition metal element in the aqueous solution of the transition metal salt is 0.5-1 mol / L.

9. The preparation method according to claim 6, characterized in that, The mixing method is as follows: an aqueous solution of transition metal salt is added dropwise to the molecular sieve and stirred until it is surface dry; or, the molecular sieve is immersed in an aqueous solution of transition metal salt for a period of time and the solid is separated.

10. The preparation method according to claim 6, characterized in that, The drying method is as follows: drying at 100-120℃.

11. The preparation method according to claim 6, characterized in that, The roasting temperature is 450-650℃, and the roasting time is 4-8 h.

12. A catalyst for catalyzing the pyrolysis of polystyrene, characterized in that, The catalyst comprises a molecular sieve and a transition metal element supported in the molecular sieve; The molecular sieve is H-Beta molecular sieve and / or ZSM-5 molecular sieve; The transition metal element is selected from one or more of Cu, Zn, Co and Ni, and the transition metal element exists in the form of a metallic element. The loading of the transition metal element in the catalyst is 0.1-1 wt%; The molar ratio of Si to Al in the molecular sieve is 10-13:

1.

13. The catalyst according to claim 12, characterized in that, The loading of the transition metal element in the catalyst is 0.1-0.8 wt%.

14. The catalyst according to claim 13, characterized in that, The catalyst has a loading of 0.2 wt% for the transition metal element.

15. The catalyst according to any one of claims 12-14, characterized in that, The transition metal element is Co and / or Ni.

16. The catalyst according to any one of claims 12-14, characterized in that, The molecular sieve is an H-Beta molecular sieve.

17. A method for preparing a catalyst according to any one of claims 12-16, characterized in that, The preparation method includes the following steps: The catalyst precursor according to any one of claims 1-5, or the catalyst precursor prepared by the preparation method according to any one of claims 6-11, is heated and reacted in a reducing atmosphere to reduce the oxide of the transition metal element in the catalyst precursor to a metallic element, thereby obtaining the catalyst.

18. The preparation method according to claim 17, characterized in that, The reducing atmosphere is a hydrogen atmosphere.

19. The preparation method according to claim 17, characterized in that, The reaction temperature is 350-550℃, and the reaction time is 2-8 h.

20. The application of a catalyst according to any one of claims 12-16 or a catalyst prepared by any one of claims 17-19 in the catalytic pyrolysis of polystyrene.

21. A method for converting polystyrene into styrene, characterized in that, The method includes the following steps: The catalyst according to any one of claims 12-16 or the catalyst prepared by any one of claims 17-19, polystyrene, and an organic solvent are mixed and heated in an inert atmosphere to pyrolyze the polystyrene to produce styrene.

22. The method according to claim 21, characterized in that, The organic solvent is acetonitrile.

23. The method according to claim 21, characterized in that, The reaction temperature is 285-295℃.

24. The method according to claim 23, characterized in that, The reaction temperature is 288-292℃.

25. The method according to claim 24, characterized in that, The reaction was carried out at a temperature of 290°C.

26. The method according to claim 21 or 23, characterized in that, The reaction time is 4-16 h.

27. The method according to claim 26, characterized in that, The reaction time is 4-8 hours.

28. The method according to claim 27, characterized in that, The reaction time was 4 hours.

29. The method according to claim 21, characterized in that, The mass ratio of the catalyst to the polystyrene is 0.5-2:1.

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