Disclosure of Invention
The invention provides a method for efficiently catalyzing polyolefin aromatization by a double-catalyst serial system, which aims to overcome the problems of the prior art in the aromatization reaction of polyolefin, and adopts a double-bed serial catalytic route to convert polyolefin into low-carbon olefin and then carry out olefin aromatization reaction, so that the reaction temperature and the heavy aromatic content are successfully reduced, the catalyst for catalyzing olefin aromatization reaction at the lower bed layer is different from the traditional supported metal-molecular sieve catalyst, and the metal nano particles are encapsulated in zeolite crystals to form a stable catalytic system, so that the aromatic yield and the service life of the catalyst can be improved.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
A low-temperature aromatization method of polyolefin based on zeolite-encapsulated metal catalyst comprises taking zeolite-encapsulated metal catalyst as lower bed layer, taking mixture of polyolefin plastic and lamellar ZSM-5 molecular sieve as upper bed layer, and heating and melting to perform aromatization reaction;
The zeolite encapsulated metal catalyst comprises a matrix and metal encapsulated in the matrix, wherein the matrix is an HZSM-5 molecular sieve with a silicon-aluminum ratio of 20-30, the metal is one or more of Ga, cu, fe, zn, cr, and the molar ratio of metal atoms to silicon in the HZSM-5 molecular sieve is 0.01-0.1;
the preparation method of the zeolite-encapsulated metal catalyst comprises the steps of dissolving a silicon source, an aluminum source, a template agent and metal salt in water to form a mixed solution, then carrying out hydrothermal crystallization reaction, and roasting the product to obtain the zeolite-encapsulated metal catalyst.
The method designs a double-bed series catalytic route, firstly enables polyolefin to react with the upper-bed lamellar HZSM-5 molecular sieve, enables the lamellar ZSM-5 molecular sieve to crack the polyolefin into low-carbon olefin with high efficiency, and then enables the zeolite of the lower bed to encapsulate a metal catalyst for olefin aromatization reaction, so that the reaction temperature and the content of heavy aromatics can be reduced successfully. The method can successfully realize the high-selectivity preparation of the methylated aromatics by using the polyolefin at a lower reaction temperature (below 400 ℃), and the serial catalytic system has excellent stability and can not obviously reduce the activity after long-term use.
The zeolite-encapsulated metal catalyst used in the lower bed layer is different from the traditional supported metal-molecular sieve catalyst, and the metal nano particles are encapsulated in zeolite crystals to form a stable catalytic system, so that the aromatic hydrocarbon yield can be improved, obvious progress is made in the aspect of carbon deposition resistance, and the long-term use of the catalyst is facilitated. The zeolite encapsulated metal catalyst has metal encapsulated in zeolite pores and has regular and homogeneous active site distribution, and pore canal limiting effect to avoid the formation of large size carbon precursor. In contrast, the active sites of the traditional supported catalyst are unevenly distributed on the surface of the carrier, so that the situation of overhigh local activity easily occurs, and the carbon deposition precursor is accumulated and deposited. In addition, due to the limitation of the pore canal, the diffusion speed of reactant and product molecules entering the zeolite pore canal is relatively slow, which makes the reaction process milder, and is beneficial to inhibiting the excessive reaction and the generation of carbon deposit. The reaction on the surface of the traditional supported catalyst is relatively more severe, and deep reaction is easier to initiate to generate carbon deposit.
Preferably, the molar ratio of SiO2、Al2O3, template agent, metal atoms and water in the mixed solution is 1:0.02-0.03:0.45-0.47:0.01-0.1:30-35.
Preferably, when preparing the zeolite-encapsulated metal catalyst, the metal salt is coordinated with EDTA to form a complex, and then added to the mixed solution.
Preferably, the silicon source is TEOS, the aluminum source is aluminum nitrate, and the template agent is TPAOH.
Preferably, the temperature of the hydrothermal crystallization reaction is 150-200 ℃ and the time is 36-60 h.
Preferably, the roasting temperature of the product is 500-600 ℃ and the roasting time is 3-5 h.
Preferably, the mass ratio of the polyolefin plastic to the lamellar ZSM-5 molecular sieve to the zeolite-encapsulated metal catalyst is 1:0.05-0.2:0.1-0.3.
Preferably, quartz sand is added between the upper bed layer and the lower bed layer as a separation.
Preferably, the temperature of the aromatization reaction is 350-450 ℃ and the reaction time is 2-4 hours.
Preferably, inert atmosphere is provided by carrier gas in the aromatization reaction, and the flow rate of the carrier gas is 4-6 mL/min.
Preferably, the polyolefin plastic is one or more of polyethylene, polypropylene and polystyrene, and the weight average molecular weight (Mw) is 150000-260000 Da.
Therefore, the invention has the following beneficial effects:
(1) Compared with the prior art, the method has the advantages that the reaction temperature is lower, the yield of methylated aromatic hydrocarbon is higher, and reducing reaction gases CO, H2 and the like are not required to be added in the reaction process;
(2) The catalyst is cheap and easy to obtain, avoids the use of noble metals, greatly reduces the preparation cost of the catalyst, and is beneficial to realizing the large-scale production of the catalyst;
(3) Compared with the traditional supported metal-zeolite catalyst, the zeolite-encapsulated metal catalyst adopted by the invention has obvious progress in the aspect of carbon deposit resistance, and is beneficial to the long-term use of the catalyst.
Detailed Description
The invention is further described below with reference to the drawings and detailed description.
In the present invention, all the equipment and raw materials are commercially available or commonly used in the industry, and the methods in the following examples are conventional in the art unless otherwise specified.
General examples:
A low-temperature aromatization method of polyolefin based on zeolite-encapsulated metal catalyst comprises taking zeolite-encapsulated metal catalyst as lower bed layer, taking mixture of polyolefin plastic and lamellar ZSM-5 molecular sieve as upper bed layer, and heating and melting to perform aromatization reaction;
The zeolite encapsulated metal catalyst comprises a matrix and metal encapsulated in the matrix, wherein the matrix is an HZSM-5 molecular sieve with a silicon-aluminum ratio of 20-30, the metal is one or more of Ga, cu, fe, zn, cr, and the molar ratio of metal atoms to silicon in the HZSM-5 molecular sieve is 0.01-0.1;
the preparation method of the zeolite-encapsulated metal catalyst comprises the steps of dissolving a silicon source, an aluminum source, a template agent and metal salt in water to form a mixed solution, then carrying out hydrothermal crystallization reaction, and roasting the product to obtain the zeolite-encapsulated metal catalyst.
As a specific implementation, the molar ratio of SiO2、Al2O3, the template agent, the metal atoms and water in the mixed solution is 1:0.02-0.03:0.45-0.47:0.01-0.1:30-35, and preferably, the molar ratio of SiO2、Al2O3, the template agent, the metal atoms and water in the mixed solution is 1:0.02:0.46:0.01-0.1:32.
As a specific embodiment, when preparing the zeolite-encapsulated metal catalyst, the metal salt is coordinated with EDTA to form a complex, and then added into the mixed solution.
As a specific embodiment, the silicon source is TEOS, the aluminum source is aluminum nitrate, and the template agent is TPAOH.
As a specific implementation, the temperature of the hydrothermal crystallization reaction is 150-200 ℃ and the time is 36-60 h.
As a specific implementation mode, the roasting temperature of the product is 500-600 ℃ and the roasting time is 3-5 h.
As a specific embodiment, the mass ratio of the polyolefin plastic to the lamellar ZSM-5 molecular sieve to the zeolite-encapsulated metal catalyst is 1:0.05-0.2:0.1-0.3, and preferably, the mass ratio of the polyolefin plastic to the lamellar ZSM-5 molecular sieve to the zeolite-encapsulated metal catalyst is 1:0.1:0.2.
As a specific implementation mode, quartz sand is added between the upper bed layer and the lower bed layer to serve as separation.
As a specific embodiment, the temperature of the aromatization reaction is 350-450 ℃ and the reaction time is 2-4 hours.
As a specific implementation mode, inert atmosphere is provided by carrier gas in the aromatization reaction, and the flow rate of the carrier gas is 4-6 mL/min.
In one specific embodiment, the polyolefin plastic is one or more of polyethylene, polypropylene and polystyrene, and the weight average molecular weight (Mw) is 150000-260000 Da.
The catalyst for catalyzing the olefin aromatization reaction at the lower bed layer is different from the traditional supported metal-molecular sieve catalyst, and the stable catalytic system is formed by encapsulating metal nano particles in zeolite crystals, so that the aromatic hydrocarbon yield and the service life of the catalyst can be improved.
Example 1:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite-encapsulated metal catalyst, namely mixing and stirring TEOS, al (NO3)3·9H2O、TPAOH、Ga(NO3)3·9H2 O and water to obtain a mixed solution with the SiO2:Al2O3:TPAOH:Ga2O3:H2 O mole ratio of 1:0.02:0.46:0.05:32, carrying out hydrothermal crystallization reaction at 180 ℃ to obtain a product, and then roasting the product at 550 ℃ by air for 4h to obtain the zeolite-encapsulated metal catalyst, namely Ga@HZSM-5 (Ga/Si=0.1), wherein XRD is shown in figure 1;
(2) The catalytic polyethylene aromatization reaction comprises the steps of weighing 0.2g of prepared Ga@HZSM-5 (Ga/Si=0.1) catalyst, mixing with 0.2g of quartz sand, filling into a quartz tube, fixing with quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing 1g of polyethylene powder (Mw =150000Da) with 0.1g of lamellar ZSM-5 molecular sieve, grinding and granulating, uniformly mixing with 1g of quartz sand, filling into the upper layer of the quartz tube, introducing N2 carrier gas, reacting for 2 hours at a carrier gas flow rate of 5mL/min and a fixed bed at 400 ℃, condensing the product, and then testing by a gas chromatograph, wherein the polyethylene conversion rate is 100%, the aromatic hydrocarbon yield is 54.8%, the methylated aromatic hydrocarbon content is 94.5%, the carbon content of the catalyst after the reaction is 2.1%, and the thermogravimetric data are shown in figure 2.
Example 2:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite-encapsulated metal catalyst, namely firstly coordinating Fe (NO3)3·9H2 O and sodium ethylenediamine tetraacetate (EDTA) to obtain an Fe-EDTA complex to avoid agglomeration of Fe in an alkaline medium, then adding the Fe-EDTA complex into mixed gel containing TEOS, al (NO3)3·9H2 O, TPAOH and H2 O) to obtain a mixed solution with the SiO2:Al2O3:TPAOH:Fe-EDTA:H2 O mole ratio of 1:0.02:0.46:0.03:32, carrying out hydrothermal crystallization reaction at 150 ℃ for 60H, and then roasting the product at 500 ℃ by air for 5H to prepare the zeolite-encapsulated metal catalyst, wherein the zeolite-encapsulated metal catalyst is marked as Fe@HZSM-5 (Fe/Si=0.03), and a scanning electron microscope chart is shown in figure 3;
(2) The method comprises the steps of weighing 0.2g of prepared Fe@HZSM-5 (Fe/Si=0.03) catalyst, mixing with 0.2g of quartz sand, loading into a quartz tube, fixing with quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing, grinding and granulating 1g of polypropylene powder (Mw =200000 Da) and 0.1g of lamellar ZSM-5 molecular sieve, uniformly mixing with 1g of quartz sand, loading into the upper layer of the quartz tube, introducing N2 carrier gas, reacting for 2 hours at a carrier gas flow rate of 5mL/min under a fixed bed temperature of 400 ℃, condensing the product, and then testing by a gas chromatograph, wherein the polypropylene conversion rate is 100%, the aromatic hydrocarbon yield is 47.8%, methylated aromatic hydrocarbon accounts for 92.4%, the liquid product distribution is shown in fig. 4, and the carbon content of the catalyst after the reaction is 2.5%.
Example 3:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Mixing TEOS、Al(NO3)3·9H2O、TPAOH、Zn(NO3)2·6H2O、Ga(NO3)3·9H2O and water, stirring to obtain a mixed solution with a SiO2:Al2O3:TPAOH:ZnO:Ga2O3:H2 O mol ratio of 1:0.02:0.46:0.02:0.015:32, carrying out hydrothermal crystallization reaction at 200 ℃ to obtain a product, and then carrying out air roasting on the product at 600 ℃ to obtain 3 h, wherein the zeolite-encapsulated metal catalyst is recorded as ZnGa@HZSM-5 (Zn/Si=0.02, ga/Si=0.03);
(2) The catalytic polystyrene aromatization reaction comprises the steps of weighing 0.2g of prepared ZnGa@HZSM-5 (Zn/Si=0.02, ga/Si=0.03) catalyst, mixing with 0.2g of quartz sand, loading into a quartz tube, fixing by quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing 1g of polystyrene powder (Mw =260000 Da) with 0.1g of lamellar ZSM-5 molecular sieve, grinding and granulating, uniformly mixing with 1g of quartz sand, loading into an upper layer of the quartz tube, introducing N2 carrier gas, enabling the carrier gas flow rate to be 4mL/min, reacting for 2 hours at a fixed bed 450 ℃, condensing the product, and testing by a gas chromatograph, wherein the result is shown in table 1, the polystyrene conversion rate is 100%, the arene yield is 62.5%, the methylated arene accounts for 96.4%, and the carbon content of the catalyst after the reaction is 1.8%.
Example 4:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite encapsulated metal catalyst, namely firstly coordinating Cr (NO3)3·9H2 O and ethylenediamine tetraacetic acid (EDTA) to obtain a Cr-EDTA complex to avoid Cr agglomeration in an alkaline medium, then adding the Cr-EDTA complex into mixed gel containing TEOS, al (NO3)3·9H2 O, TPAOH and H2 O) to obtain a mixed solution with the SiO2:Al2O3:TPAOH: Cr-EDTA:H2 O mole ratio of 1:0.02:0.46:0.03:32, carrying out hydrothermal crystallization reaction at 180 ℃ for 60H, and then roasting the product at 550 ℃ for 4H to prepare the zeolite encapsulated metal catalyst, wherein the zeolite encapsulated metal catalyst is denoted as Cr@HZSM-5 (Cr/Si=0.03), and a transmission electron microscope chart of the zeolite encapsulated metal catalyst is shown in figure 5;
(2) The catalytic polyethylene aromatization reaction comprises the steps of weighing 0.2g of prepared Cr@HZSM-5 (Cr/Si=0.03) catalyst, mixing with 0.2g of quartz sand, loading into a quartz tube, fixing with quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing 1g of polyethylene powder (Mw =150000Da) with 0.1g of lamellar ZSM-5 molecular sieve, grinding and granulating, uniformly mixing with 1g of quartz sand, loading into the upper layer of the quartz tube, introducing N2 carrier gas, reacting for 3 hours at a carrier gas flow rate of 4mL/min at a fixed bed of 400 ℃, condensing the product, and then testing by a gas chromatograph, wherein the polyethylene conversion rate is 100%, the aromatic hydrocarbon yield is 52.8%, the methylated aromatic hydrocarbon accounts for 94.5%, and the carbon content of the catalyst after the reaction is 2.0%.
Example 5:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite-encapsulated metal catalyst, namely firstly, coordinating CuSO4 and sodium ethylenediamine tetraacetate (EDTA) to obtain a Cu-EDTA complex to avoid Cu agglomeration in an alkaline medium, then adding the Cu-EDTA complex into mixed gel containing TEOS, al (NO3)3·9H2 O, TPAOH and H2 O) to obtain a mixed solution with the SiO2:Al2O3:TPAOH:Cu-EDTA:H2 O mole ratio of 1:0.02:0.46:0.05:32, and carrying out hydrothermal crystallization reaction at 180 ℃ for 48: 48H, and then, roasting the product at 550 ℃ by air for 4H to prepare the zeolite-encapsulated metal catalyst, wherein the Cu@HZSM-5 (Cu/Si=0.05);
(2) The catalytic polyethylene aromatization reaction comprises the steps of weighing 0.2g of prepared Cu@HZSM-5 (Cu/Si=0.05) catalyst, mixing with 0.2g of quartz sand, loading into a quartz tube, fixing with quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing 1g of polyethylene powder (Mw =150000Da) with 0.1g of lamellar ZSM-5 molecular sieve, grinding and granulating, uniformly mixing with 1g of quartz sand, loading into the upper layer of the quartz tube, introducing N2 carrier gas, reacting for 4 hours at a carrier gas flow rate of 6mL/min and a fixed bed of 350 ℃, condensing the product, and then testing by a gas chromatograph, wherein the polyethylene conversion rate is 100%, the aromatic hydrocarbon yield is 43.5%, the methylated aromatic hydrocarbon accounts for 91.4%, and the carbon content of the catalyst after the reaction is 2.7%.
Example 6:
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite-encapsulated metal catalyst, namely firstly coordinating CuSO4 and Cr (NO3)3·9H2 O respectively with sodium ethylenediamine tetraacetate (EDTA) to obtain a Cu-EDTA complex and a Cr-EDTA complex, avoiding metal agglomeration in an alkaline medium, then adding the Cu-EDTA complex and the Cr-EDTA complex into mixed gel containing TEOS, al (NO3)3·9H2 O, TPAOH and H2 O) to obtain a mixed solution of SiO2:Al2O3, TPAOH, cu-EDTA, cr-EDTA complex and H2 O in a molar ratio of 1:0.02:0.46:0.01:0.03:32, carrying out hydrothermal crystallization at 180 ℃ to obtain a product, and then roasting the product at 550 ℃ under air of 4H to obtain the zeolite-encapsulated metal catalyst, wherein the zeolite-encapsulated metal catalyst is marked as CuCr@HZSM-5 (Cu/Si=0.01, cr/Si=0.03);
(2) The method comprises the steps of weighing 0.2g of prepared CuCr@HZSM-5 (Cu/Si=0.01, cr/Si=0.03) catalyst, mixing with 0.2g of quartz sand, loading into a quartz tube, fixing by quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing 1g of polyolefin powder (polyethylene 0.5g, Mw =150000Da; polypropylene 0.5g, Mw =200000 Da) with 0.1g of lamellar ZSM-5 molecular sieve, grinding and granulating, uniformly mixing with 1g of quartz sand, loading into the upper layer of the quartz tube, introducing N2 carrier gas, reacting for 2 hours at a carrier gas flow rate of 5mL/min at a fixed bed of 400 ℃, condensing the product, testing by a gas chromatograph, wherein the product has a polyethylene conversion rate of 100%, an aromatic hydrocarbon yield of 57.9%, and the carbon content of the catalyst after the reaction is 1.9%.
Comparative example 1 (no metal encapsulated in zeolite molecular sieve):
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing zeolite molecular sieve, namely mixing and stirring TEOS, al (NO3)3·9H2 O, TPAOH and water to obtain a mixed solution with the SiO2:Al2O3:TPAOH:H2 O molar ratio of 1:0.02:0.46:32, carrying out hydrothermal crystallization reaction at 180 ℃ for 48 and h, and then air-roasting the product at 550 ℃ for 4h to obtain the zeolite molecular sieve, namely HZSM-5;
(2) The catalytic polyethylene aromatization reaction comprises the steps of weighing 0.2g of prepared HZSM-5 and 0.2g of quartz sand, mixing and loading the mixture into a quartz tube, fixing the quartz tube by quartz wool, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing, grinding and granulating 1g of polyethylene powder (Mw =150000Da) and 0.1g of lamellar ZSM-5 molecular sieve, uniformly mixing the mixture with 1g of quartz sand, loading the mixture into the upper layer of the quartz tube, introducing N2 carrier gas, reacting the mixture for 2 hours at a carrier gas flow rate of 5mL/min in a fixed bed at 400 ℃, condensing the product, and then testing the product by a gas chromatograph, wherein the result is shown in a table 1, the conversion rate of polyethylene is 100%, the aromatic hydrocarbon yield is 36.8%, the methylated aromatic hydrocarbon accounts for 89.7%, and the carbon content of the catalyst after the reaction is 8.1%.
Comparative example 2 (using a supported metal-molecular sieve catalyst):
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a supported metal-molecular sieve catalyst, namely mixing TEOS, al (NO3)3·9H2 O, TPAOH and water, stirring to obtain a mixed solution with the SiO2:Al2O3:TPAOH:H2 O molar ratio of 1:0.02:0.46:32, carrying out hydrothermal crystallization at 180 ℃ and then carrying out air roasting on the product at 550 ℃ for 4h to obtain a zeolite molecular sieve, namely HZSM-5, mixing the HZSM-5 with Zn (NO3)2·6H2 O aqueous solution) with the concentration of 1.7mol/L, wherein the volume ratio of the HZSM-5 to the Zn (NO3)2·6H2 O aqueous solution is 1:1, carrying out ultrasonic drying and carrying out air roasting at 400 ℃ for 2h to obtain the supported metal-molecular sieve catalyst, namely Zn/HZSM-5, and the transmission electron microscopic image of the supported metal-molecular sieve catalyst is shown in FIG. 6;
(2) The catalytic polyethylene aromatization reaction comprises the steps of weighing 0.2g of prepared Zn/HZSM-5 and 0.2g of quartz sand, mixing and loading the mixture into a quartz tube, fixing the quartz tube with quartz cotton, adding 0.5g of quartz sand to separate an upper bed layer from a lower bed layer, mixing and grinding 1g of polyethylene powder (Mw =150000Da) and 0.1g of lamellar ZSM-5 molecular sieve, granulating the mixture, uniformly mixing the mixture with 1g of quartz sand, loading the upper layer of the quartz tube, introducing N2 carrier gas, reacting the mixture for 2 hours at a carrier gas flow rate of 5mL/min at a fixed bed of 400 ℃, condensing the product, testing the condensed product by a gas chromatograph, wherein the result is shown in a table 1, the conversion rate of polyethylene is 100%, the aromatic hydrocarbon yield is 42.5%, the methylated aromatic hydrocarbon accounts for 91.3%, and the carbon deposition content of the catalyst after the reaction is 5.1%.
Comparative example 3 (packing of platelet ZSM-5 molecular sieve and zeolite encapsulated metal catalyst):
A polyolefin low-temperature aromatization method based on zeolite-encapsulated metal catalyst comprises the following steps:
(1) Preparing a zeolite-encapsulated metal catalyst, namely mixing and stirring TEOS, al (NO3)3·9H2O、TPAOH、Ga(NO3)3·9H2 O and water to obtain a mixed solution with the SiO2:Al2O3:TPAOH:Ga2O3:H2 O mol ratio of 1:0.02:0.46:0.2:32, carrying out hydrothermal crystallization reaction at 180 ℃ to obtain a product, and then carrying out air roasting on the product at 550 ℃ to obtain the zeolite-encapsulated metal catalyst, namely Ga@HZSM-5 (Ga/Si=0.1);
(2) Catalytic polyethylene aromatization reaction 1g polyethylene powder (Mw =150000Da) is mixed with 0.1g lamellar ZSM-5 molecular sieve, 0.2g prepared Ga@HZSM-5 (Ga/Si=0.05) catalyst, ground and granulated, uniformly mixed with 1.5g quartz sand, loaded into the upper layer of a quartz tube, N2 carrier gas is introduced, the carrier gas flow rate is 5mL/min, the fixed bed is 400 ℃ for 2h, the product is condensed and then tested by a gas chromatograph, the result is shown in table 1, the polyethylene conversion rate is 100%, the aromatic hydrocarbon yield is 38.8%, wherein methylated aromatic hydrocarbon accounts for 79.5%, the carbon deposition content of the catalyst after reaction is 3.9%, and the physical diagram is shown in figure 7.
TABLE 1 polyolefin aromatization reaction test results
As can be seen from the data in Table 1, the method of the present invention adopted in examples 1-6 can significantly improve the aromatic hydrocarbon yield and methylated aromatic hydrocarbon selectivity by serially connecting the lamellar ZSM-5 molecular sieve and the zeolite-encapsulated metal catalyst. Fully illustrates that the double-bed series catalytic system changes the traditional one-step aromatization route of polyolefin in the process of catalyzing the aromatization of polyolefin plastics, splits the aromatization reaction of polyolefin into two steps of series reactions, and successfully reduces the reaction temperature.
As can be seen from the experimental results of comparative examples 1 and 2, the presence of metal greatly improves the catalytic performance of the olefin aromatization reaction of the lower bed layer and reduces the carbon content compared with the pure ZSM-5 molecular sieve.
From the experimental results of example 1 and comparative example 2, it can be seen that the aromatic hydrocarbon yield is reduced due to the significant increase of the carbon deposition content when the conventional supported metal-zeolite catalyst is adopted in comparative example 2, and the aromatization activity and stability of the zeolite-encapsulated metal catalyst of the invention are significantly higher than those of the supported metal-molecular sieve catalyst.
From the experimental results of comparative example 3, it can be seen that the aromatic hydrocarbon yield is significantly reduced and the heavy aromatic hydrocarbon content is increased by replacing the double bed packing mode of the two catalysts with the mixed packing mode. The double-bed filling mode is critical to the tandem aromatization reaction, and the ideal two-step aromatization route cannot be realized by mixing the filled lamellar ZSM-5 molecular sieve and the zeolite-encapsulated metal catalyst, so that the selectivity of methylated aromatics is reduced.
From the experimental results of examples 3 to 5, it can be seen that the aromatic hydrocarbon yield is gradually increased and improved with the increase of the reaction temperature.
Compared with the prior art, the method has the advantages of lower reaction temperature, higher methylated arene yield, no need of adding reducing reaction gases CO, H2 and the like in the reaction process. Meanwhile, the catalyst disclosed by the invention is low in cost and easy to obtain, avoids the use of noble metals, greatly reduces the preparation cost of the catalyst, and is favorable for realizing the large-scale production of the catalyst. Compared with the traditional supported metal catalyst, the zeolite-encapsulated metal catalyst can fully exert the pore canal limiting function to avoid generating large-size carbon deposition precursors, and adjust the diffusion speed of reactants and product molecules to inhibit deep reaction, thereby improving the aromatization performance.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.