Catalytic system for catalytic cracking of polyolefin and method for catalytic cracking of polyolefin

Abstract

The invention relates to the technical field of plastic chemical recovery, and discloses a catalytic system for polyolefin catalytic cracking and a polyolefin catalytic cracking method. The catalytic system comprises a catalyst, a carbocation initiator and a hydrogen donor; the catalyst is selected from a liquid acid catalyst with a sulfonic acid group. The catalytic cracking reaction temperature and pressure of the catalytic system for the polyolefin catalytic cracking reaction are relatively low, the cost is reduced, the economic benefit is improved, and the polyolefin conversion rate is relatively high.

Description

Technical Field

[0001] This invention relates to the field of plastic chemical recycling technology, specifically to a catalytic system for the catalytic cracking of polyolefins and a method for the catalytic cracking of polyolefins. Background Technology

[0002] Global plastic consumption continues to increase, with 32% of waste plastics being directly landfilled, 31% incinerated, and only 30% recycled. This waste plastics discarded into the environment cause serious environmental problems. Polyolefin materials, such as polyethylene, polypropylene, and polystyrene, are widely used in packaging materials and agricultural films due to their excellent performance; polyolefin plastics account for more than half of global plastic production. However, the chemical structure of polyolefins is extremely stable, making them difficult to degrade in the natural environment.

[0003] Unlike physical recycling of waste plastics, chemical recycling primarily targets polyolefins, especially single-monomer polyolefins such as polyethylene, polypropylene, and polystyrene. Chemical recycling involves using technologies such as thermal cracking and hydrocracking to chemically convert polyolefin polymers into monomers or low-carbon hydrocarbons. Existing thermal cracking and catalytic cracking technologies for polyolefin plastics require reactions at temperatures above 300°C, resulting in high energy consumption, high costs, and a high rate of coking during the reaction process.

[0004] The thermal decomposition of polyolefin plastics is a decomposition reaction initiated by reaching the carbon-carbon bond breaking energy barrier at high temperatures (300-900℃), which leads to the breaking of carbon-carbon bonds and the generation of free radicals. The decomposition products are C3-C60 light hydrocarbons, liquid hydrocarbons (including alkanes, olefins, aromatics, etc.), and carbides, with a complex composition.

[0005] Catalytic cracking of polyolefin plastics includes methods such as catalytic pyrolysis, hydrocracking, and hydrogenolysis. Catalytic pyrolysis is a process in which a solid acidic catalyst is added to promote the cracking during thermal cracking. It is a carbocation reaction mechanism, and the products are mainly C5-C15 alkanes, alkenes, cyclic hydrocarbons, and aromatics, with a high degree of isomerization. Hydrocracking uses a solid catalyst with both acidic and metallic sites to achieve the hydrocracking reaction under a certain hydrogen pressure. The products have a high degree of saturation and are C3-C30 alkanes. Hydrogenolysis uses a catalyst with only metallic sites to hydrogenate polyolefins under a certain hydrogen pressure. It is a process in which reactant molecules are adsorbed, bond-broken, and desorbed on the surface of the catalyst's metallic sites. The products are mainly C1-C30 alkanes.

[0006] The above-mentioned reaction conditions all require melting at temperatures above 200℃, and both hydrocracking and hydrogenolysis reactions require hydrogen pressures of 2-6 MPa to proceed, resulting in high energy consumption and the use of expensive hydrogen. Therefore, there is an urgent need to develop a low-temperature, hydrogen-free polyolefin catalytic cracking technology to effectively reduce the energy consumption and cost of chemical recycling of waste plastics, reduce coking rates, and improve economic efficiency. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of high reaction temperature and high cost in the existing polyolefin catalytic cracking process, and to provide a catalytic system and method for polyolefin catalytic cracking. The catalytic system of this invention includes a liquid acid catalyst with sulfonic acid groups, a carbocation initiator, and a hydrogen donor. The catalytic cracking reaction for polyolefins uses a lower temperature and pressure, reducing costs, and achieving a higher polyolefin conversion rate.

[0008] To achieve the above objectives, a first aspect of the present invention provides a catalytic system comprising a catalyst, a carbocation initiator, and a hydrogen donor; wherein the catalyst is selected from liquid acid catalysts containing sulfonic acid groups.

[0009] Preferably, the catalyst has the chemical formula R-SO3H, wherein R is selected from substituted or unsubstituted C1-C4 alkyl groups, and is preferably an F-substituted C1-C4 alkyl group.

[0010] Preferably, the catalyst is trifluoromethanesulfonic acid.

[0011] A second aspect of the present invention provides a method for catalytic cracking of polyolefins, the method comprising: adding polyolefins and the catalytic system described in the first aspect above in the presence of a solvent to carry out a catalytic cracking reaction.

[0012] During their research, the inventors of this invention discovered that when using carbocation initiators and hydrogen donors for the catalytic cracking reaction of polyolefins, replacing the solid acids and / or supported metal catalysts conventionally used in the prior art with liquid acid catalysts containing sulfonic acid groups significantly reduces the reaction temperature and enables the obtained products to be saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons. The catalytic system of this invention achieves lower catalytic cracking reaction temperatures and pressures for polyolefin catalytic cracking reactions, while maintaining a higher polyolefin conversion rate, avoiding the high temperatures and high hydrogen pressures of the prior art, and resulting in lower costs.

[0013] Through the above technical solution, the present invention has the following beneficial effects:

[0014] (1) The catalytic system provided by the present invention includes a liquid acid catalyst with sulfonic acid groups, a carbocation initiator and a hydrogen donor. The liquid catalyst and the carbocation initiator initiate the generation of reactive carbocations, and the hydrogen donor saturates the generated olefins, resulting in C3-C12 alkanes, cycloalkanes and benzene ring hydrocarbons, which are basically free of olefins and effectively prevent olefins from repolymerizing.

[0015] (2) The catalytic system provided by the present invention avoids the addition of hydrogen when used for the catalytic cracking of polyolefins. The catalytic cracking reaction temperature and pressure are low, which greatly reduces the cost, effectively reduces energy consumption, and improves economic benefits. In preferred cases, the conversion rate of polyolefins reaches 100%.

[0016] (3) The method for catalytic cracking of polyolefins provided by the present invention pretreats the polyolefins so that the polymer chain ends are more fully exposed, thereby improving the conversion rate of the subsequent catalytic cracking reaction of polyolefins; after the pretreated polyolefins are dissolved, they are brought into contact with the catalytic system, thereby avoiding side reactions that passivate the surface and reduce the dissolution effect when the polyolefins are in contact with the catalyst before they are dissolved. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] The first aspect of the present invention provides a catalytic system comprising a catalyst, a carbocation initiator, and a hydrogen donor; wherein the catalyst is selected from liquid acid catalysts containing sulfonic acid groups.

[0019] In this invention, the catalytic system utilizes a liquid acid catalyst with sulfonic acid groups, a carbocation initiator, and a hydrogen donor. The liquid catalyst and carbocation initiator initiate the generation of reactive carbocations, while the hydrogen donor saturates the generated olefins. The resulting products are saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons. When used for the catalytic cracking of polyolefins, the catalytic system eliminates the need for hydrogen, resulting in lower catalytic cracking reaction temperatures and pressures, thus reducing costs and energy consumption.

[0020] In this invention, the type of liquid acid catalyst with sulfonic acid groups is not particularly limited, and various liquid acid catalysts with sulfonic acid groups known in the art can be used. Preferably, the chemical formula of the catalyst is R-SO3H, wherein R is selected from substituted or unsubstituted C1-C4 alkyl groups, and R is preferably an F-substituted C1-C4 alkyl group. The C1-C4 alkyl group mentioned in this invention can be methane, ethane, propane, and butane.

[0021] In this invention, unless otherwise specified, substitution refers to the substitution of at least one hydrogen atom in a C1-C4 alkyl group by a halogen atom, preferably, at least one hydrogen atom in a C1-C4 alkyl group by F.

[0022] In some embodiments of the present invention, preferably, the catalyst is trifluoromethanesulfonic acid.

[0023] In this invention, a catalytic system consisting of a liquid acid catalyst with sulfonic acid groups that satisfies the above chemical formula, a carbocation initiator, and a hydrogen donor is used. This system is advantageous for reducing the temperature and pressure of the polyolefin catalytic cracking reaction and avoiding the addition of hydrogen, thereby reducing costs and energy consumption, improving economic efficiency, and also for producing saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons.

[0024] In this invention, preferably, the mass ratio of the catalyst to the carbocation initiator is 1:0.004-0.04, more preferably 1:0.005-0.015. This preferred embodiment is more conducive to the rapid generation of carbocations at low temperatures.

[0025] In this invention, preferably, the mass ratio of the catalyst to the hydrogen donor is 1:0.01-0.2, more preferably 1:0.02-0.1. This preferred embodiment is more conducive to the saturation of olefins generated during the cracking process, yielding saturated hydrocarbons and cycloalkanes.

[0026] In this invention, the type of carbocation initiator is not particularly limited and can be any carbocation initiator known in the art. Preferably, the carbocation initiator is selected from at least one of tert-butane chloride, tert-butane bromide, and tert-butane iodoformide, and more preferably tert-butane chloride. The carbocation initiator of this invention is advantageous for co-initiating the generation of reactive carbocations with the catalyst.

[0027] In this invention, the type of hydrogen donor is not particularly limited, as long as it can provide hydrogen for the reaction, saturating the olefins generated in the catalytic cracking reaction to obtain saturated low-carbon hydrocarbons, cycloalkanes, and benzene-containing hydrocarbon products. Preferably, the hydrogen donor is selected from partially hydrogenated polycyclic aromatic hydrocarbons, more preferably from tetrahydronaphthalene and / or 9,10-dihydroanthracene, and even more preferably tetrahydronaphthalene. The hydrogen donor of this invention, together with a liquid acid catalyst with a sulfonic acid group and a carbocation initiator, forms a catalytic system that facilitates obtaining saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons, ensuring that the olefin content in the products obtained from the catalytic cracking reaction is less than 5 wt%, and effectively preventing the re-polymerization of olefins.

[0028] In this invention, unless otherwise specified, the composition and content of the polyolefin catalytic cracking products are tested using gas chromatography-mass spectrometry.

[0029] A second aspect of the present invention provides a method for catalytic cracking of polyolefins, the method comprising: adding polyolefins and the catalytic system described in the first aspect above in the presence of a solvent to carry out a catalytic cracking reaction.

[0030] In this invention, the ratio of the polyolefin to the catalytic system is not particularly limited, as long as a catalytic cracking reaction can occur. Preferably, the mass ratio of the polyolefin to the catalytic system (based on the catalyst) is 1:3-12, for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, or any value within any range of two such values, preferably 1:6-8.

[0031] In this invention, the type of polyolefin is not particularly limited and can be any polyolefin known in the art. Preferably, the polyolefin is selected from monomonomer polyolefins, more preferably from at least one of low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, and polystyrene, and even more preferably from at least one of low-density polyethylene, polypropylene, and polystyrene.

[0032] In this invention, the polyolefin can directly undergo catalytic cracking with the catalytic system, or it can be pretreated before undergoing catalytic cracking with the catalytic system. Preferably, the polyolefin is pretreated before the catalytic cracking reaction. The method of polyolefin pretreatment is not particularly limited, but preferably, the method includes: melt stirring and / or melt spinning the polyolefin to obtain the pretreated polyolefin. The polyolefin pretreatment described in this invention helps to expose more polymer chain ends in the polyolefin, thereby improving the conversion rate of the subsequent catalytic cracking reaction.

[0033] In this invention, the method of melting and stirring is not particularly limited; it can be to melt the polyolefin and then stir it, or to stir it simultaneously with melting. The melting conditions are not particularly limited. Preferably, the melting temperature is 120-160°C, more preferably 140-150°C.

[0034] In this invention, the stirring method and conditions are not particularly limited, and methods and conditions conventionally used in the art can be employed. For example, the stirring can be performed using magnetic stirring and / or a glass rod, preferably using a glass rod. Preferably, the stirring time is 2-30 minutes.

[0035] In this invention, the method and conditions for melt spinning are not particularly limited, and conventional melt spinning methods and conditions used in the art can be employed. In this invention, the polyolefin is melted and then spun. The spinning can be performed using a spinning machine and / or by repeatedly stretching the molten polyolefin with tools. The melting conditions are not particularly limited. Preferably, the melting temperature is 120-160°C.

[0036] In this invention, the polyolefin can be added alone or in the form of a solution. Preferably, the polyolefin is added in the form of a solution, which facilitates contact with the catalyst and initiator and enables catalytic cracking reaction, avoiding side reactions such as surface passivation and reduced solubility caused by undissolved polyolefin contacting the catalyst.

[0037] In this invention, the ratio of solvent to polyolefin has a wide range of selection. Preferably, the mass ratio of polyolefin to solvent is 1:2-32, more preferably 1:20-25. In this invention, controlling the mass ratio of polyolefin to solvent within the above range is beneficial for the polyolefin to dissolve fully, making it easier to interact with the catalyst system to generate carbocations and initiate the reaction, thereby achieving a faster reaction rate.

[0038] In this invention, the type of solvent is not particularly limited, and various solvents conventionally used in the art are applicable to this invention. The solvent in this invention is an organic solvent, preferably selected from at least one of dichloromethane, trichloromethane, isobutane, isopentane, cyclohexane, benzene, toluene, p-xylene, and trichlorobenzene, more preferably dichloromethane, cyclohexane, and toluene.

[0039] In some embodiments of the present invention, preferably, the method for catalytic cracking of polyolefins specifically includes: dissolving the polyolefin by contacting it with a solvent, and then contacting the dissolved polyolefin with the catalytic system to carry out a catalytic cracking reaction. More preferably, the polyolefin is pretreated as described above before contacting it with the solvent.

[0040] In this invention, the manner in which the polyolefin and the solvent come into contact is not particularly limited and can be any conventional solution preparation method used in the art, which will not be elaborated further here. The polyolefin and the solvent can come into contact in a pressure-resistant test tube.

[0041] In this invention, the dissolution conditions are not particularly limited; for example, the dissolution can be carried out under stirring conditions. The dissolution temperature has a wide selection range; preferably, the dissolution temperature is 70-120°C, more preferably 70-90°C. The stirring method and conditions are not particularly limited; stirring methods and conditions known in the art can be used, as long as the polyolefin dissolves in the solvent. Preferably, magnetic stirring is used, and stirring can be carried out in a constant temperature water bath magnetic stirrer.

[0042] In this invention, the order in which the polyolefin and the catalytic system are added is not particularly limited. The polyolefin can be added to the catalytic system, or the catalytic system can be added to the dissolved polyolefin, as long as the dissolved polyolefin and the catalytic system come into contact and a catalytic cracking reaction occurs. Preferably, the catalytic system is added to the polyolefin for contact. The polyolefin and the catalytic system can come into contact in a pressure-resistant test tube.

[0043] In this invention, the conditions for the catalytic cracking reaction can be carried out according to conventional methods for the catalytic cracking of polyolefins. Preferably, the reaction temperature of the catalytic cracking reaction is 50-120°C, for example, it can be any value within the range of 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or any two of these values, more preferably 50-80°C.

[0044] In this invention, preferably, the reaction pressure of the catalytic cracking reaction is 0-2 MPa, for example, it can be 0 MPa, 0.2 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, or any value within a range of any two values, preferably 0-0.2 MPa. In this invention, the reaction pressure of the catalytic cracking reaction refers to the pressure in the pressure-resistant test tube during the reaction.

[0045] In this invention, the reaction time of the catalytic cracking reaction is not particularly limited, as long as the catalytic cracking reaction can be completed. Preferably, the reaction time of the catalytic cracking reaction is 1-10 hours, more preferably 5-7 hours.

[0046] In this invention, a catalytic system comprising a liquid acid catalyst with sulfonic acid groups, a carbocation initiator, and a hydrogen donor is used for the catalytic cracking of polyolefins. The catalytic cracking reaction temperature and pressure are low, which greatly reduces costs, effectively reduces energy consumption, and improves economic efficiency. In preferred cases, the conversion rate of polyolefins reaches 100%.

[0047] The present invention will be described in detail below through embodiments.

[0048] In this invention, unless otherwise specified, the room temperature mentioned in the following examples and comparative examples refers to 25°C.

[0049] The composition and content of polyolefin catalytic cracking products in the following examples and comparative examples were tested using gas chromatography-mass spectrometry.

[0050] Selectivity of polyolefin catalytic cracking products = (total yield of C3-C12 saturated low-carbon alkanes, cycloalkanes and benzene ring-containing hydrocarbons / polyolefin catalytic cracking conversion) × 100%.

[0051] Polypropylene powder: purchased from Macklin, molecular weight 4000±500;

[0052] Polystyrene powder: purchased from Innochem, general purpose type I;

[0053] Low-density polyethylene powder: purchased from Macklin, melt index: 20-30 g / 10 min, particle size 100 mesh;

[0054] High-density polyethylene powder: purchased from Macklin, melt index: 6-9 g / 10 min, particle size 200 mesh.

[0055] Example 1

[0056] (1) Place 10g of polypropylene powder in a beaker, place it on an electric heating table and heat it to 140°C. After the polypropylene powder is completely melted, stir it in one direction for 2 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0057] (2) At room temperature, add 0.4g of the pretreated polypropylene solid and 8g of dichloromethane to a pressure-resistant test tube; add 3.1g of trifluoromethanesulfonic acid, 0.08g of tetrahydronaphthalene and 0.016g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0058] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the pretreated polypropylene in the solvent.

[0059] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0060] Tests showed that the catalytic cracking conversion rate of polypropylene was 100%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene ring-containing hydrocarbons was 97.2%.

[0061] Example 2

[0062] (1) Place 10g of polypropylene powder in a beaker, place it on an electric heating table and heat it to 140°C. After the polypropylene powder is completely melted, stir it in one direction for 2 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0063] (2) At room temperature, add 0.4g of the pretreated polypropylene solid, 8.17g of dichloromethane and 1.6g of isopentane to a pressure-resistant test tube; add 2.7g of trifluoromethanesulfonic acid, 0.08g of tetrahydronaphthalene and 0.015g of tert-chlorobutane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0064] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0065] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0066] Tests showed that the catalytic cracking conversion rate of polypropylene was 100%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 98.1%.

[0067] Example 3

[0068] (1) Place 5g of polystyrene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction for 5 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0069] (2) At room temperature, add 0.41g of the pretreated polypropylene solid and 8.3g of dichloromethane to a pressure-resistant test tube; add 3.1g of trifluoromethanesulfonic acid, 0.08g of tetrahydronaphthalene and 0.03g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0070] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0071] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0072] Tests showed that the catalytic cracking conversion rate of polystyrene was 100%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 96.5%.

[0073] Example 4

[0074] (1) Place 5g of polystyrene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction for 5 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0075] (2) At room temperature, add 0.1g of the pretreated polypropylene solid and 3g of dichloromethane to a pressure-resistant test tube; add 1g of trifluoromethanesulfonic acid, 0.1g of tetrahydronaphthalene and 0.01g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0076] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0077] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 50°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0078] Tests showed that the catalytic cracking conversion rate of polystyrene was 100%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 95.4%.

[0079] Example 5

[0080] (1) Place 5g of low-density polyethylene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction with a glass rod for 10 minutes, cool it, and obtain the pretreated polypropylene solid.

[0081] (2) At room temperature, add 0.4g of the pretreated polypropylene solid and 10g of dichloromethane to a pressure-resistant test tube; add 2.4g of trifluoromethanesulfonic acid, 0.2g of tetrahydronaphthalene and 0.032g of chlorotert-butane to a small glass bottle and float them above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0082] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0083] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 50°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0084] Tests showed that the catalytic cracking conversion rate of low-density polyethylene was 100%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene ring-containing hydrocarbons was 97.4%.

[0085] Example 6

[0086] (1) Place 5g of low-density polyethylene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction with a glass rod for 10 minutes, cool it, and obtain the pretreated polypropylene solid.

[0087] (2) At room temperature, add 0.21g of the pretreated polypropylene solid and 3.95g of dichloromethane to a pressure-resistant test tube; add 1.51g of trifluoromethanesulfonic acid, 0.04g of tetrahydronaphthalene and 0.031g of tert-chlorobutane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0088] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0089] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0090] Tests showed that the catalytic cracking conversion rate of low-density polyethylene was 90.2%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene ring-containing hydrocarbons was 96.6%.

[0091] Example 7

[0092] (1) Place 5g of low-density polyethylene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction with a glass rod for 10 minutes, cool it, and obtain the pretreated polypropylene solid.

[0093] (2) At room temperature (25°C), add 0.4g of the pretreated polypropylene solid and 8.12g of dichloromethane to a pressure-resistant test tube; add 2.51g of trifluoromethanesulfonic acid, 0.04g of tetrahydronaphthalene and 0.02g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0094] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0095] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0096] Tests showed that the catalytic cracking conversion rate of low-density polyethylene was 76.3%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 97.2%.

[0097] Example 8

[0098] (1) Place 5g of low-density polyethylene powder in a beaker, place it on an electric heating table and heat it to 120°C. After the polypropylene powder is completely melted, stir it in one direction with a glass rod for 10 minutes, cool it, and obtain the pretreated polypropylene solid.

[0099] (2) At room temperature, add 0.8g of the pretreated polypropylene solid and 8.02g of dichloromethane to a pressure-resistant test tube; add 2.76g of trifluoromethanesulfonic acid, 0.08g of tetrahydronaphthalene and 0.015g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0100] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0101] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0102] Tests showed that the catalytic cracking conversion rate of low-density polyethylene was 75.8%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 96.4%.

[0103] Example 9

[0104] (1) Place 5g of polystyrene powder in a beaker, place it on an electric heating table and heat it to 160°C. After the polypropylene powder is completely melted, stir it in one direction for 30 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0105] (2) At room temperature, add 2g of the pretreated polystyrene solid and 4g of dichloromethane to a pressure-resistant test tube; add 1g of trifluoromethanesulfonic acid, 0.2g of tetrahydronaphthalene and 0.04g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0106] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 100℃ and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0107] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 120°C for 2 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0108] Tests showed that the catalytic cracking conversion rate of polystyrene was 80%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 95.2%.

[0109] Example 10

[0110] (1) Place 5g of high-density polyethylene powder in a beaker, place it on an electric heating table and heat it to 160°C. After the polypropylene powder is completely melted, stir it in one direction for 5 minutes with a glass rod, cool it, and obtain the pretreated polypropylene solid.

[0111] (2) At room temperature, add 0.41g of the pretreated polypropylene solid and 8.44g of dichloromethane to a pressure-resistant test tube; add 3.17g of trifluoromethanesulfonic acid, 0.08g of tetrahydronaphthalene and 0.026g of tert-chlorobutane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0112] (3) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0113] (4) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 80°C for 6 hours to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0114] Tests showed that the catalytic cracking conversion rate of high-density polyethylene was 43.5%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 98.1%.

[0115] Example 11

[0116] (1) At room temperature, add 0.41g of untreated low-density polyethylene and 8.37g of dichloromethane to a pressure-resistant test tube; add 2.77g of trifluoromethanesulfonic acid, 0.04g of tetrahydronaphthalene and 0.02g of chlorotert-butane to a small glass bottle and float it above the liquid surface in the pressure-resistant test tube; add a magnetic stir bar and tighten the test tube cap.

[0117] (2) Place the pressure-resistant test tube in a constant temperature water bath magnetic stirrer, maintain the water bath temperature at 70°C and perform magnetic stirring for 2 hours to dissolve the polypropylene in the solvent.

[0118] (3) Pour the pressure-resistant test tube to completely mix the trifluoromethanesulfonic acid and chlorotert-butane in the small glass bottle with the solution in the pressure-resistant test tube. Stir at 70°C for 6.5 h to carry out the catalytic cracking reaction. After the reaction is completed, take out the pressure-resistant test tube, cool it, and evaporate the solvent to obtain the polyolefin catalytic cracking product.

[0119] Tests showed that the catalytic cracking conversion rate of low-density polyethylene was 67.2%, and the selectivity for C3-C12 saturated low-carbon alkanes, cycloalkanes, and benzene-containing hydrocarbons was 96.8%.

[0120] Comparative Example 1

[0121] The method described in Example 1 is different except that in step (2), trifluoromethanesulfonic acid is replaced with sulfuric acid by mass; after the reaction, no catalytic cracking reaction was detected.

[0122] Comparative Example 2

[0123] The method described in Example 1 is different except that tetrahydronaphthalene is not added in step (2); polyolefin catalytic cracking product is obtained; the polypropylene catalytic cracking conversion rate is 100% and the selectivity of C3-C12 saturated low carbon alkanes, cycloalkanes and benzene ring hydrocarbons is 42%.

[0124] The results of the examples show that the catalytic system of the present invention has excellent catalytic effect when used in the catalytic cracking reaction of polyolefins. In the preferred case, the conversion rate of polyolefins is 100%, and the selectivity of C3-C12 saturated low-carbon alkanes, cycloalkanes and benzene ring hydrocarbons is greater than 95%.

[0125] By comparing Example 1 and Comparative Example 1, it can be seen that the liquid acid catalyst with sulfonic acid group used in this invention is more acidic and less oxidizing than sulfuric acid, which can effectively avoid oxidation reaction and promote the generation of carbocations. By comparing Example 1 and Comparative Example 2, it can be seen that the tetrahydronaphthalene used in this invention can improve the selectivity of polyolefin catalytic cracking into C3-C12 saturated low-carbon alkanes, cycloalkanes and benzene ring hydrocarbons.

[0126] This invention uses inexpensive raw materials, avoids the addition of hydrogen, and has a low catalytic cracking reaction temperature and pressure, resulting in a low-cost catalytic system and effectively reducing energy consumption.

[0127] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalytic system, characterized in that, The catalytic system includes a catalyst, a carbocation initiator, and a hydrogen donor; the catalyst is selected from liquid acid catalysts with sulfonic acid groups.

2. The catalytic system according to claim 1 or 2, wherein, The catalyst has the chemical formula R-SO3H, wherein R is selected from substituted or unsubstituted C1-C4 alkyl groups, preferably F-substituted C1-C4 alkyl groups; Preferably, the catalyst is trifluoromethanesulfonic acid.

3. The catalytic system according to claim 1 or 2, wherein, The mass ratio of the catalyst to the carbocation initiator is 1:0.004-0.04, preferably 1:0.005-0.015; Preferably, the mass ratio of the catalyst to the hydrogen donor is 1:0.01-0.2, and more preferably 1:0.02-0.

1.

4. The catalytic system according to any one of claims 1-3, wherein, The carbocation initiator is selected from at least one of tert-butane chloride, tert-butane bromide, and tert-butane iodide, preferably tert-butane chloride; Preferably, the hydrogen donor is selected from partially hydrogenated polycyclic aromatic hydrocarbons, more preferably from tetrahydronaphthalene and / or 9,10-dihydroanthracene, and more preferably from tetrahydronaphthalene.

5. A method for catalytic cracking of polyolefins, characterized in that, The method includes: in the presence of a solvent, adding a polyolefin and the catalytic system according to any one of claims 1-4 to carry out a catalytic cracking reaction.

6. The method according to claim 5, wherein, The mass ratio of the polyolefin to the catalytic system, based on the catalyst, is 1:3-12, preferably 1:6-8; Preferably, the mass ratio of the polyolefin to the solvent is 1:2-32, more preferably 1:20-25.

7. The method according to claim 5 or 6, wherein, The polyolefin is selected from a single monomer polyolefin, preferably from at least one of low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene and polystyrene, and more preferably from at least one of low-density polyethylene, polypropylene and polystyrene; Preferably, the solvent is selected from at least one of dichloromethane, trichloromethane, isobutane, isopentane, cyclohexane, benzene, toluene, p-xylene, and trichlorobenzene, and more preferably from at least one of dichloromethane, cyclohexane, and toluene.

8. The method according to any one of claims 5-7, wherein, The method further includes pretreating the polyolefin before the catalytic cracking reaction. The pretreating method includes: melting and stirring the polyolefin and / or melting and spinning it to obtain the pretreated polyolefin. Preferably, the melting temperature is 120-160°C; Preferably, the stirring time is 2-30 minutes.

9. The method according to any one of claims 5-8, wherein, The method specifically includes: dissolving the polyolefin by contacting it with a solvent, and then contacting the dissolved polyolefin with the catalytic system to carry out a catalytic cracking reaction; Preferably, the melting temperature is 70-120℃, and more preferably 70-90℃.

10. The method according to any one of claims 5-9, wherein, The reaction temperature of the catalytic cracking reaction is 50-120℃, preferably 50-80℃; Preferably, the reaction pressure of the catalytic cracking reaction is 0-2 MPa, more preferably 0-0.2 MPa; Preferably, the reaction time of the catalytic cracking reaction is 1-10 h, and more preferably 5-7 h.