Polyolefin-based waste plastic recycling catalyst, preparation method and application thereof

Abstract

The application discloses a polyolefin waste plastic recycling catalyst and a preparation method and application thereof, and the catalyst takes H-MCM-22 molecular sieve and aluminum oxide as a carrier, and a metal oxide is loaded on the carrier, and the metal does not contain Al. By incorporating the aluminum oxide into the H-MCM-22 molecular sieve, the acid and alkali properties of the catalyst can be effectively adjusted, and in addition, the pore structure of the H-MCM-22 molecular sieve is favorable to the generation of aromatic hydrocarbon compounds. In the preparation process of the catalyst, the addition of a co-impregnation solvent can effectively improve the dispersity of the metal salt compound and the stability of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of high-value treatment and recycling technology of polyolefin waste plastics, specifically relating to a catalyst for recycling polyolefin waste plastics, its preparation method and application. Background Technology

[0002] While plastics bring convenience to human life, they also cause increasingly serious environmental and ecological pollution. Currently, in developing countries, only about 30% of plastics are recycled, and the vast majority of these are through physical recycling. The remaining approximately 70% is usually incinerated, landfilled, or discarded. Because plastics are difficult to degrade naturally, the accumulated waste plastics have caused serious environmental pollution year after year. Inadequate waste plastic disposal will inevitably lead to white pollution from cities to rural areas, and from land to sea. Since 7-8% of global oil is used for plastic production annually, the massive accumulation of waste plastics not only has a serious impact on the ecological environment but also represents a huge waste of resources. Therefore, strengthening the resource recycling and reuse of waste plastics is of paramount importance in mitigating the resource waste and environmental pollution caused by the development of the plastics industry.

[0003] Chemical recycling of waste plastics can break down and recombine waste plastics at the molecular level, yielding small-molecule products of the same quality as petroleum-refined products, which can be applied in high-value fields such as food and medicine. Polyolefin waste plastics, which are polymerized waste plastics, are widely used in agricultural films, household plastic bags, woven bags, and insulation materials, accounting for a large proportion of the total. High-value chemical recycling of polyolefin waste plastics is of great significance, not only meeting the requirements for harmless and resource-based utilization of waste plastics, but also possessing significant advantages such as safety, environmental protection, high efficiency, and energy saving. It aligns better with the principles of waste reduction, harmlessness, and resource recovery in waste treatment, featuring strong processing capacity, high economic value, and environmental friendliness. It meets the social needs of global energy structure adjustment and environmental protection, and is an important direction for the development of a circular economy in the plastics industry, becoming a crucial development strategy for various countries. However, current chemical recycling technologies for polyolefin waste plastics suffer from problems such as complex product composition, low added value, and easy coking and clogging of reaction devices. Therefore, there is an urgent need to develop a catalyst for the chemical recycling of polyolefin waste plastics. Summary of the Invention

[0004] To improve the above-mentioned technical problems, the present invention provides a catalyst for recycling polyolefin waste plastics. The catalyst uses H-MCM-22 molecular sieve and alumina as a support, and the support is loaded with metal oxide, wherein the metal does not contain Al.

[0005] According to an embodiment of the present invention, the particle size of the carrier is 10-1000 mesh, exemplarily 10 mesh, 100 mesh, 200 mesh, 300 mesh, 400 mesh, 500 mesh, 600 mesh, 700 mesh, 800 mesh, 900 mesh or 1000 mesh.

[0006] According to an embodiment of the present invention, the mass ratio of H-MCM-22 molecular sieve to alumina is 1.0:0.005-0.6, preferably 1.0:0.01-0.5, and even more preferably 1.0:0.05-0.2; exemplary ratios are 1:0.01, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, or 1:0.5.

[0007] According to an embodiment of the present invention, the molar ratio of SiO2 to Al2O3 in the H-MCM-22 molecular sieve is 20-40, preferably 28, and exemplaryly 20, 22, 24, 26, 28, 30, 32, 34, 36, 38 or 40; preferably, the alumina is γ crystal form.

[0008] According to an embodiment of the present invention, the metal is selected from one or more of K, Na, Mg, Ca, Fe, Cu, Co, Ni, Zn, Ce, In, Sn, Ga, La, and Mo; preferably one or more of Cu, Fe, Co, Ni, Zn, and Ce.

[0009] According to an embodiment of the present invention, the metal oxide is obtained by loading a metal salt compound onto a support and then calcining it.

[0010] According to an embodiment of the present invention, the metal salt compound refers to the nitrate of the metal or the hydrochloride of the metal.

[0011] For example, the metal salt compound is selected from at least one of FeCl3, NiCl2·6H2O, ZnCl2, MgCl2, SnCl2, CuCl2·2H2O, CoCl2, In(NO3)3, Cu(NO3)3·3H2O, Ce(NO3)3·6H2O, Co(NO3)3·6H2O, Ga(NO3)3, La(NO3)3·6H2O, Fe(NO3)3, Ni(NO3)2, Zn(NO3)2, and Mg(NO3)2.

[0012] For example, the metal salt compound is selected from FeCl3, NiCl2·6H2O, ZnCl2 and In(NO3)3; or MgCl2, Cu(NO3)3·3H2O, Ce(NO3)3·6H2O; or FeCl3, Co(NO3)3·6H2O, Ce(NO3)3·6H2O; or SnCl2, Cu(NO3)3·3H2O, Ga(NO3)3 and In(NO3)3; or FeCl3, CuCl2·2H2O, CoCl2 and La(NO3)3·6H2O.

[0013] For example, the mass ratio of FeCl3, NiCl2·6H2O, ZnCl2 and In(NO3)3 is 2.9:4:1:0.8.

[0014] For example, the mass ratio of MgCl2, Cu(NO3)3·3H2O and Ce(NO3)3·6H2O is 3.9:3.8:3.1.

[0015] For example, the mass ratio of FeCl3, Co(NO3)3·6H2O and Ce(NO3)3·6H2O is 2.9:3:2.5.

[0016] For example, the mass ratio of SnCl2, Cu(NO3)3·3H2O, Ga(NO3)3 and In(NO3)3 is 0.8:7.6:0.1:0.3.

[0017] For example, the mass ratio of FeCl3, CuCl2·2H2O, CoCl2 and La(NO3)3·6H2O is 2.9:2.7:1.1:4.7.

[0018] According to embodiments of the present invention, the loading amount of the metal is 0.1-20 wt.% of the weight of the carrier, preferably 1-5 wt.%, exemplarily 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, and 5 wt.%. When the metal contains at least two types, the loading amount of each metal does not exceed 2 wt.%.

[0019] The present invention also provides a method for preparing the above-mentioned catalyst for recycling polyolefin waste plastics, the method comprising the following steps:

[0020] The catalyst for recycling polyolefin waste plastics was prepared by mixing and calcining H-MCM-22 molecular sieve, alumina and metal salt compound solution.

[0021] According to an embodiment of the present invention, the preparation method of the catalyst for recycling polyolefin waste plastics includes the following steps:

[0022] H-MCM-22 molecular sieve and alumina were mixed, and the resulting mixture was impregnated in a metal salt compound solution. After calcination, the catalyst for recycling polyolefin waste plastics was prepared.

[0023] According to an embodiment of the present invention, a co-impregnation solvent may also be added to the method; the co-impregnation solvent is an alcohol compound, such as at least one selected from ethylene glycol, propylene glycol, glycerol, butanediol, tert-butanol, cyclohexanol, benzyl alcohol, ethanol or methanol, preferably at least one selected from ethanol, ethylene glycol, propylene glycol, glycerol and butanediol.

[0024] According to an embodiment of the present invention, the amount of the co-impregnation solvent added is 5-50 wt.% of the metal salt compound solution, preferably 10-30 wt.%; exemplary values ​​are 10 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.%, 22 wt.%, 25 wt.%, 28 wt.%, or 30 wt.%.

[0025] According to an embodiment of the present invention, the metal salt compound solution is an aqueous solution of a metal salt compound, and the concentration of the metal salt compound solution is 0.1-30 wt.%, exemplarily 0.1 wt.%, 1 wt.%, 5 wt.%, 10 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.%, 22 wt.%, 25 wt.%, 28 wt.%, or 30 wt.%.

[0026] According to an embodiment of the present invention, the immersion temperature is 15-35°C, for example, room temperature; the immersion time is 0.5-48h, preferably 0.5-24h.

[0027] According to an embodiment of the present invention, the calcination temperature is 300-600°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, and the calcination time is 2-72 hours, preferably 4-48 hours.

[0028] Preferably, before roasting, the product can be dried first at a temperature of 60–150°C, preferably 80–120°C, for a time of 0.5–48 h, preferably 1–24 h.

[0029] According to an embodiment of the present invention, the impregnation is a step-by-step co-impregnation method or a one-step co-impregnation method.

[0030] According to an embodiment of the present invention, the impregnation process employs either an excess of solution or an impregnation with a solution of equal volume to the carrier.

[0031] According to an embodiment of the present invention, the stepwise co-impregnation method is as follows: the support is first impregnated with a solution containing a first metal salt compound, then calcined for the first time, the first calcined product is impregnated with a solution containing a second metal salt compound for the second time, and then calcined for the second time to obtain the catalyst;

[0032] The first metal is selected from at least one of K, Na, Mg, Ca, Fe, Cu, Co, and Ni. The first impregnation time is 0.5 to 12 hours, the first calcination temperature is 300 to 600°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C, and the first calcination time is 4 to 24 hours, preferably 6 to 20 hours.

[0033] The second metal is selected from at least one of Zn, Ce, In, Sn, Ga, La, and Mo. The second impregnation time is 0.5 to 12 hours, the second calcination temperature is 400 to 600°C, for example, 400°C, 450°C, 500°C, 550°C, or 600°C, and the second calcination time is 2 to 24 hours, preferably 4 to 20 hours.

[0034] Preferably, before the first roasting, a drying process can be carried out first, with a drying temperature of 60-150℃ and a drying time of 0.5-12h.

[0035] Preferably, before the second roasting, a drying process can be carried out first, with a drying temperature of 60-150℃ and a drying time of 0.5-12h.

[0036] According to an embodiment of the present invention, the one-step co-impregnation method is as follows: the support is impregnated in the metal salt compound solution, dried, and calcined to obtain the catalyst; wherein the impregnation time is 0.5 to 48 h, the drying temperature is 60 to 150 °C, the drying time is 0.5 to 48 h, the calcination temperature is 300 to 600 °C, and the calcination time is 2 to 72 h.

[0037] The present invention also provides the application of the above-mentioned catalyst for recycling polyolefin waste plastics in the preparation of aromatic compounds.

[0038] The present invention also provides a method for preparing aromatic compounds, comprising mixing and reacting the above-mentioned catalyst for recycling polyolefin waste plastics with polyolefin waste plastics to prepare the aromatic compounds.

[0039] According to an embodiment of the present invention, the polyolefin waste plastic is at least one of PP (polypropylene), HDPE (high-density polyethylene), LDPE (low-density polyethylene) and PS (polystyrene).

[0040] According to an embodiment of the present invention, the mass ratio of the catalyst to polyolefin waste plastic is 1.0-10.0:100; preferably 2.0-8.0:100.

[0041] According to an embodiment of the present invention, the reaction is carried out in an inert gas atmosphere such as N2, Ar or He.

[0042] According to an embodiment of the present invention, the reaction temperature is 300-600°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, the reaction heating rate is 5-300°C / s, preferably 50-200°C / s, and the reaction time is 0.1-30 min.

[0043] The beneficial effects of this invention are:

[0044] This invention effectively modulates the acidity and basicity of the catalyst by incorporating alumina into H-MCM-22 molecular sieves. Furthermore, the pore structure of H-MCM-22 molecular sieves is conducive to the formation of aromatic compounds. During the preparation of the catalyst, the addition of a co-impregnation solvent effectively improves the dispersion of the metal salt compound and enhances the catalyst's stability.

[0045] This invention utilizes a catalyst for recycling polyolefin waste plastics in the catalytic pyrolysis reaction of polyolefin waste plastics, exhibiting good catalytic activity and stability, high yield of aromatic compounds, and effectively increasing the added value of polyolefin waste plastic pyrolysis products, thus achieving efficient chemical recycling of polyolefin waste plastics. Attached Figure Description

[0046] Figure 1 This is the XRD pattern of Cat I in Example 1;

[0047] Figure 2 This is the GC-MS spectrum of the pyrolysis products in Example 1;

[0048] Figure 3 This is the FT-IR spectrum of the pyrolysis product in Example 1. Detailed Implementation

[0049] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0050] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0051] Unless otherwise stated, the parts in the following examples are by weight.

[0052] Example 1

[0053] I) Preparation of Catalyst I

[0054] The preparation process of Cat I is as follows: 99 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 1.0 parts of alumina are weighed, mixed and ground to 500 mesh. The mixture is then added to a mixing vessel containing 2.89 parts of FeCl3 solid, 4.05 parts of NiCl2·6H2O solid, 500 parts of water and 80 parts of ethylene glycol. The mixture is stirred and mixed evenly, impregnated for 12 h, dried at 100℃ for 12 h in a N2 atmosphere, and calcined at 350℃ for 8.0 h to obtain Cat I-Pre.

[0055] Weigh 100 parts of Cat I-Pre, 1.04 parts of ZnCl2 solid, 0.79 parts of In(NO3)3 solid, 300 parts of water and 50 parts of propylene glycol, add them to a mixing vessel, stir and mix evenly, impregnate for 12 hours, dry at 100°C for 12 hours in a N2 atmosphere, and calcine at 500°C for 8.0 hours to obtain Cat I. Figure 1 This is the XRD pattern of Cat I in Example 1.

[0056] 2) Evaluation of Catalyst I

[0057] A method for preparing an aromatic compound, the method comprising:

[0058] A mixture of PP and HDPE (mass ratio 2:1, wherein the PP and HDPE are derived from polyolefin waste plastics) was crushed and then mixed with Cat I at a mass ratio of 100:3. This mixture was then added to a fixed-bed reactor, where the temperature was rapidly increased to 500℃ at a heating rate of 200℃ / s for pyrolysis. The pyrolysis products were then analyzed in situ online by GC-MS and FT-IR. The GC-MS spectrum is shown in the attached figure. Figure 2 As shown, the FT-IR spectrum is attached. Figure 3 As shown. From Figure 2 and Figure 3 It can be seen that when using Cat I for mixed catalytic pyrolysis of PP and HDPE, aromatic compounds account for 87% of the pyrolysis products.

[0059] Example 2

[0060] 1) Preparation of Catalyst II

[0061] The preparation process of Cat II is as follows: 85 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 15 parts of alumina are weighed, mixed and ground to 300 mesh. The mixture is then added to a mixing vessel containing 3.92 parts of MgCl2 solid, 3.80 parts of Cu(NO3)3·3H2O solid, 3.10 parts of Ce(NO3)3·6H2O solid, 500 parts of water and 70 parts of butanediol. The mixture is stirred and mixed evenly, impregnated for 12 h, dried at 120 °C for 12 h in a N2 atmosphere, and calcined at 450 °C for 8.0 h to obtain Cat II.

[0062] 2) Evaluation of Catalyst II

[0063] A method for preparing an aromatic compound, the method comprising:

[0064] A mixture of PP and PS (mass ratio 8:2, the PP and PS being derived from polyolefin waste plastics) was crushed and then mixed with Cat II at a mass ratio of 95:5. This mixture was then added to a fixed-bed reactor, where the temperature was rapidly increased to 450℃ at a heating rate of 150℃ / s for pyrolysis. The resulting pyrolysis products were analyzed in situ online by GC-MS and FT-IR. The analysis showed that, using Cat II for the mixed catalytic pyrolysis of PP and PS, aromatic compounds accounted for 93% of the pyrolysis products.

[0065] Example 3

[0066] 1) Preparation of Catalyst III

[0067] The preparation process of Cat III is as follows: 70 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 30 parts of alumina are weighed, mixed and ground to 500 mesh. The mixture is then added to a mixing vessel containing 2.89 parts of FeCl3 solid, 2.96 parts of Co(NO3)3·6H2O solid, 2.48 parts of Ce(NO3)3·6H2O solid, 400 parts of water and 40 parts of glycerol. The mixture is stirred and mixed evenly, impregnated for 8 hours, dried at 100℃ for 12 hours in a N2 atmosphere, and calcined at 400℃ for 8.0 hours to obtain Cat III.

[0068] 2) Evaluation of Catalyst III

[0069] A method for preparing an aromatic compound, the method comprising:

[0070] PP (derived from polyolefin waste plastics) was crushed and mixed with Cat III at a mass ratio of 95:5. The mixture was then added to a fixed-bed reactor and rapidly heated to 400℃ at a heating rate of 60℃ / s for pyrolysis. The pyrolysis products were prepared and analyzed in situ online by GC-MS and FT-IR. The results showed that when Cat III was used for catalytic pyrolysis of PP, aromatic compounds accounted for 83% of the pyrolysis products.

[0071] Example 4

[0072] 1) Preparation of catalyst IV

[0073] The preparation process of Cat IV is as follows: 90 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 10 parts of alumina are weighed, mixed and ground to 500 mesh. The mixture is then added to a mixing vessel containing 0.80 parts of SnCl2 solid, 7.60 parts of Cu(NO3)3·3H2O solid, 0.11 parts of Ga(NO3)3 and 0.26 parts of In(NO3)3 solid, 300 parts of water and 30 parts of butanediol. The mixture is stirred and mixed evenly, impregnated for 12 h, dried at 120 °C for 12 h in a N2 atmosphere, and calcined at 450 °C for 8.0 h to obtain Cat IV.

[0074] 2) Evaluation of Catalyst IV

[0075] A method for preparing an aromatic compound, the method comprising:

[0076] PP and LDPE (mass ratio 5:1, the PP and LDPE being derived from polyolefin waste plastics) were mixed with Cat IV at a mass ratio of 90:7 and added to a fixed-bed reactor. The mixture was rapidly heated to 400℃ at a heating rate of 60℃ / s to carry out a pyrolysis reaction, and the pyrolysis products were prepared. The pyrolysis products were analyzed in situ online by GC-MS and FT-IR. The analysis results showed that when Cat IV was used for the catalytic pyrolysis of PP and LDPE, the proportion of aromatic compounds in the pyrolysis products was 82%.

[0077] Example 5

[0078] 1) Preparation of catalyst V

[0079] The preparation process of Cat V is as follows: 95 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 5.0 parts of alumina are weighed, mixed and ground to 500 mesh. The mixture is then added to a mixing vessel containing 2.89 parts of FeCl3 solid, 2.68 parts of CuCl2·2H2O solid, 300 parts of water and 50 parts of ethanol. The mixture is stirred and mixed evenly, impregnated for 12 h, dried at 100℃ for 12 h in a N2 atmosphere, and calcined at 350℃ for 8.0 h to obtain Cat V-Pre.

[0080] Weigh 100 parts of Cat V-Pre, 1.10 parts of CoCl2 solid, 4.68 parts of La(NO3)3·6H2O solid, 500 parts of water and 50 parts of ethylene glycol, add them to a mixing vessel, stir and mix evenly, impregnate for 12 hours, dry at 100°C for 12 hours in a N2 atmosphere, and calcine at 500°C for 8.0 hours to obtain Cat V.

[0081] 2) Evaluation of catalyst V

[0082] A method for preparing an aromatic compound, the method comprising:

[0083] PP, PS, HDPE, and LDPE (in a mass ratio of 5:1:2:2, wherein the PP, PS, HDPE, and LDPE are derived from polyolefin waste plastics) were mixed with Cat V at a mass ratio of 90:7 and then added to a fixed-bed reactor. The mixture was rapidly heated to 500℃ at a heating rate of 100℃ / s to carry out a pyrolysis reaction, thereby preparing pyrolysis products. The pyrolysis products were analyzed in situ online by GC-MS and FT-IR. The analysis results showed that when using Cat V for the catalytic pyrolysis of mixed waste plastics of PP, PS, HDPE, and LDPE, the proportion of aromatic compounds in the pyrolysis products was 90%.

[0084] Comparative Example 1

[0085] 1) Preparation of catalyst VI

[0086] The preparation process of Cat VI is as follows: i) Weigh 85 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28), grind it to 300 mesh, and add it to a mixing vessel containing 3.92 parts of MgCl2 solid, 3.80 parts of Cu(NO3)3·3H2O solid, 3.10 parts of Ce(NO3)3·6H2O solid, 500 parts of water and 70 parts of butanediol. Stir and mix evenly, impregnate for 12 h, dry at 120℃ for 12 h in N2 atmosphere, and calcine at 450℃ for 8.0 h to obtain Pre-1. ii) Weigh 15 parts of alumina, grind it to 300 mesh, and add it to a mixing vessel containing 3.92 parts of MgCl2 solid, 3.80 parts of Cu(NO3)3·3H2O solid, 3.10 parts of Ce(NO3)3·6H2O solid, 500 parts of water and 70 parts of butanediol. Stir and mix evenly, impregnate for 12 h, dry at 120 °C for 12 h in a N2 atmosphere, and calcine at 450 °C for 8.0 h to obtain Pre-2. iii) Mix Pre-1 and Pre-2 evenly to prepare Cat-VI.

[0087] 2) Evaluation of Catalyst VI

[0088] A method for preparing an aromatic compound, the method comprising:

[0089] A mixture of PP and PS (mass ratio 8:2, the PP and PS being derived from polyolefin waste plastics) was crushed and then mixed with Cat VI at a mass ratio of 95:5. This mixture was then added to a fixed-bed reactor, where the temperature was rapidly increased to 450℃ at a heating rate of 150℃ / s for pyrolysis. The resulting pyrolysis products were analyzed in situ online by GC-MS and FT-IR. The analysis showed that, using Cat VI for the mixed catalytic pyrolysis of PP and PS, aromatic compounds accounted for 67% of the pyrolysis products.

[0090] Comparative Example 2

[0091] 1) Preparation of catalyst VII

[0092] The preparation process of Cat VII is as follows: i) Weigh 85 parts of H-MCM-22 molecular sieve (n(SiO2) / n(Al2O3)=28) and 15 parts of alumina, mix and grind to 300 mesh, add it to a mixing vessel containing 3.92 parts of MgCl2 solid, 3.80 parts of Cu(NO3)3·3H2O solid, 3.10 parts of Ce(NO3)3·6H2O solid and 570 parts of water, stir and mix evenly, impregnate for 12 h, dry at 120℃ for 12 h in N2 atmosphere, calcine at 450℃ for 8.0 h to prepare Cat-VII.

[0093] 2) Evaluation of Catalyst VII

[0094] A method for preparing an aromatic compound, the method comprising:

[0095] A mixture of PP and PS (mass ratio 8:2, the PP and PS being derived from polyolefin waste plastics) was crushed and then mixed with Cat VII at a mass ratio of 95:5. This mixture was then added to a fixed-bed reactor, where the temperature was rapidly increased to 450℃ at a heating rate of 150℃ / s for pyrolysis. The resulting pyrolysis products were analyzed in situ online by GC-MS and FT-IR. The analysis showed that, using Cat VII for the mixed catalytic pyrolysis of PP and PS, aromatic compounds accounted for 71% of the pyrolysis products.

[0096] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a catalyst for recycling polyolefin waste plastics in the preparation of aromatic compounds, characterized in that, The catalyst uses H-MCM-22 molecular sieve and alumina as a support, and the support is loaded with a metal oxide, the metal of which does not contain Al; The metal is selected from one or more of K, Na, Mg, Ca, Fe, Cu, Co, Ni, Zn, Ce, In, Sn, Ga, La, and Mo; The mass ratio of H-MCM-22 molecular sieve to alumina is 1.0:0.005-0.6; The catalyst preparation method includes the following steps: mixing H-MCM-22 molecular sieve, alumina and metal salt compound solution, and calcining to prepare the catalyst for recycling polyolefin waste plastics; The method also includes a co-impregnation solvent; the co-impregnation solvent is an alcohol compound selected from at least one of ethylene glycol, propylene glycol, glycerol, butanediol, tert-butanol, cyclohexanol, benzyl alcohol, ethanol, or methanol.

2. The application according to claim 1, characterized in that, The molar ratio of SiO2 to Al2O3 in the H-MCM-22 molecular sieve is 20-40.

3. The application according to claim 1, characterized in that, The alumina is in the γ-crystal form.

4. In the application according to claim 1, the metal oxide is obtained by loading a metal salt compound onto a carrier and then calcining it; the metal salt compound refers to the nitrate of the metal or the hydrochloride of the metal.

5. The application according to claim 4, wherein the metal salt compound is selected from at least one of FeCl3, NiCl2·6H2O, ZnCl2, MgCl2, SnCl2, CuCl2·2H2O, CoCl2, In(NO3)3, Cu(NO3)3·3H2O, Ce(NO3)3·6H2O, Co(NO3)3·6H2O, Ga(NO3)3, La(NO3)3·6H2O, Fe(NO3)3, Ni(NO3)2, Zn(NO3)2, and Mg(NO3)2.

6. In the application according to claim 1, the loading amount of the metal is 0.1-20 wt.% of the weight of the carrier, and when the metal contains at least two kinds, the loading amount of each metal does not exceed 2 wt.%.

7. In the application according to claim 1, the amount of the co-impregnation solvent added is 5-50 wt.% of the metal salt compound solution.

8. In the application according to claim 1, the metal salt compound solution is an aqueous solution of the metal salt compound, and the concentration of the metal salt compound solution is 0.1-30 wt.%.

9. The application according to claim 1, characterized in that, The preparation method of catalysts for recycling polyolefin waste plastics includes the following steps: H-MCM-22 molecular sieve and alumina were mixed, and the resulting mixture was impregnated in a metal salt compound solution. After calcination, the catalyst for recycling polyolefin waste plastics was prepared.

10. The application according to claim 9, characterized in that, The immersion temperature is 15-35℃; the immersion time is 0.5-48h.

11. The application according to claim 1, characterized in that, The roasting temperature is 300–600℃, and the roasting time is 2–72 hours.

12. The application according to claim 9, characterized in that, The impregnation is either a step-by-step co-impregnation method or a one-step co-impregnation method.

13. The application according to claim 12, characterized in that, The stepwise co-impregnation method is as follows: first, the support is impregnated for the first time with a solution containing a first metal salt compound, then calcined for the first time, and the first calcined product is impregnated for the second time with a solution containing a second metal salt compound, and then calcined for the second time to obtain the catalyst; The first metal is selected from at least one of K, Na, Mg, Ca, Fe, Cu, Co, and Ni. The first impregnation time is 0.5 to 12 hours, the first calcination temperature is 300 to 600°C, and the first calcination time is 4 to 24 hours. The second metal is selected from at least one of Zn, Ce, In, Sn, Ga, La, and Mo. The second impregnation time is 0.5 to 12 hours, the second calcination temperature is 400 to 600°C, and the second calcination time is 2 to 24 hours.

14. The application according to claim 13, characterized in that, Before the first roasting, the product is dried at a temperature of 60–150°C for 0.5–12 hours.

15. The application according to claim 13, characterized in that, Before the second roasting, the product is dried at a temperature of 60–150°C for 0.5–12 hours.

16. The application according to claim 12, characterized in that, The one-step co-impregnation method is as follows: the support is impregnated in the metal salt compound solution, dried, and calcined to obtain the catalyst; wherein the impregnation time is 0.5-48 h, the drying temperature is 60-150 °C, the drying time is 0.5-48 h, the calcination temperature is 300-600 °C, and the calcination time is 2-72 h.

17. A method for preparing an aromatic compound, characterized in that, The method is as follows: The aromatic compound is prepared by mixing and reacting the catalyst for recycling polyolefin waste plastics described in any one of claims 1-16 with polyolefin waste plastics.

18. The method according to claim 17, characterized in that, The polyolefin waste plastics are at least one of PP, HDPE, LDPE and PS.

19. The method according to claim 17, characterized in that, The mass ratio of the catalyst to polyolefin waste plastics is 1.0-10.0:100.

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