Method for producing monocyclic aromatic hydrocarbon by promoting polystyrene hydropyrolysis through solvent

Abstract

The invention relates to the field of plastic degradation, in particular to a polystyrene hydropyrolysis method. Comprising the following steps: respectively adding a solvent and polystyrene into a suspended bed reactor, sealing the suspended bed reactor, introducing hydrogen with a certain pressure, and starting a reaction; the polystyrene hydropyrolysis method provided by the invention does not need a catalyst, and the solvent can be recycled, so that the polystyrene hydropyrolysis method is more economical and environment-friendly. According to the invention, the problems of self-cyclization and polycyclic aromatic hydrocarbon formation caused by thermal initiation of polystyrene are solved; meanwhile, the problems of benzene ring hydrogenation and aromatic hydrocarbon selectivity reduction are solved. The method can realize complete degradation of waste polystyrene, and has good economic benefits.

Description

Technical Field

[0001] This invention relates to the field of plastic degradation, and is a method for producing monocyclic aromatic hydrocarbons by solvent-promoted hydrogenation pyrolysis of waste polystyrene. Background Technology

[0002] Polystyrene is widely used in packaging, home appliances, consumer electronics, building materials, and medical supplies. While polystyrene has excellent weather resistance, its accumulation can cause various forms of environmental damage, including visual pollution, soil pollution, and water pollution, posing a lasting threat to the ecological environment. Therefore, it is necessary to develop efficient recycling methods to reuse waste polystyrene plastics.

[0003] Currently, the main methods for treating waste polystyrene include mechanical recycling, energy recovery, and landfill disposal. These methods all have significant negative economic and environmental impacts. Among the developed routes, traditional pyrolysis and catalytic degradation processes for polystyrene are simple, but pyrolysis has low carbon resource utilization, catalytic degradation catalysts suffer from severe carbon buildup, and both methods produce light gases and solid residues. In addition, there are plasma-assisted rapid hydropyrolysis of polystyrene, photocatalytic oxidation of polystyrene, and azide-alkane-assisted degradation routes. While these routes can be carried out at lower temperatures, the yield of high-value oil products is low, and their feasibility is poor. Hydropyrolysis of polystyrene can almost completely convert it into aromatics and alkanes. Currently, there are few reports on the hydropyrolysis of polystyrene. Patent 202311617793.7 discloses a route for the hydropyrolysis of polystyrene into monocyclic aromatics and monocyclic alkanes under the action of a metal sulfide catalyst. Patent 202310316107.6 discloses a route for the hydrogenation and cracking of polystyrene into monocyclic aromatic hydrocarbons and monocyclic alkanes using a supported ruthenium catalyst and methanol. Polystyrene hydrogenation pyrolysis primarily uses precious metals such as Pt and Ru as catalysts, exhibiting excellent catalytic performance; however, these precious metal catalysts are highly susceptible to poisoning. Waste plastics contain numerous impurities that easily poison precious metals. While metal sulfide catalysts are inexpensive and resistant to poisoning, their stability needs further improvement. Therefore, there is an urgent need to develop a feasible method for recycling waste polystyrene, focusing on finding suitable hydrogenation pyrolysis conditions that can completely upgrade waste polystyrene into valuable monocyclic aromatic hydrocarbons under harsh conditions. This invention provides a solvent-promoted method for the hydrogenation pyrolysis of waste polystyrene to produce monocyclic aromatic hydrocarbons. The solvent is divided into a hydrogen-donating solvent and a non-hydrogen-donating solvent. The hydrogen-donating solvent, in addition to possessing strong dissolving, swelling, and dispersing abilities, crucially has excellent hydrogen transfer and donation capabilities. From a structural perspective, hydrogen-donating solvents should be rich in polycyclic aromatic hydrocarbons, especially hydrogenated aromatic hydrocarbons with strong hydrogen-donating properties (such as tetrahydronaphthalene, dihydroanthracene, dihydrophenanthrene, and tetrahydroanthracene), while non-hydrogen-donating solvents are straight-chain alkanes and cycloalkanes with weaker hydrogen-donating capabilities. Various solvents are widely used in the hydrogenation and degradation processes of heavy carbon resources in coal chemical and oil refining industries. Currently, there are no reports of solvents promoting the hydrogenation and pyrolysis of polystyrene to produce light aromatic hydrocarbons. Summary of the Invention

[0004] This invention provides a method for producing monocyclic aromatic hydrocarbons by solvent-promoted hydrogenation pyrolysis of waste polystyrene, which can effectively solve the problems of low polystyrene conversion rate, coking, reactor bed blockage and catalyst deactivation in the polystyrene degradation process.

[0005] This invention provides a method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene, comprising the following steps:

[0006] The solvent and polystyrene were added separately to the slurry bed reactor, which was then sealed and hydrogen gas at a certain pressure was introduced.

[0007] The aforementioned solvants are at least one of hydrogen-donating solvents and non-hydrogen-donating solvents.

[0008] The hydrogen-donating solvent is at least one of tetrahydronaphthalene, tetrahydroanthracene, or octahydroanthracene.

[0009] The non-hydrogen-donating solvent is at least one of decahydronaphthalene, n-tetrazane, etc.

[0010] The mass ratio of the solvent to polystyrene is 1:100 to 2:1.

[0011] The molar ratio of H2 to polystyrene monomer is 30:1 to 1:2.

[0012] The polystyrene hydrogenation pyrolysis is carried out at a temperature of 300℃~450℃.

[0013] The time for the hydrogenation pyrolysis of the polystyrene is 0.5h to 12h.

[0014] This invention relates to the application of hydrogenation pyrolysis of polystyrene in the aforementioned solvents. Under the above reaction conditions, polystyrene undergoes hydrogenation pyrolysis to generate monocyclic aromatic hydrocarbons (at least one or more of benzene, toluene, ethylbenzene, and cumene). This route is more economical compared to catalyst-catalyzed degradation of polystyrene. This invention proposes a new reaction route to upgrade polystyrene, further optimizing reaction activity and product selectivity by adjusting the solvent type, reaction temperature, and reaction time. Experiments show that, by using different solvents and reacting at 400°C for 2 hours, a comparison between polystyrene pyrolysis under N2 atmosphere and solvent-promoted hydrogenation pyrolysis of polystyrene as described in this invention reveals a trend in the yield of monocyclic aromatic hydrocarbons in polystyrene degradation: solvent-promoted hydrogenation pyrolysis > polystyrene pyrolysis. The yield of monocyclic aromatic hydrocarbons in the solvent-promoted hydrogenation pyrolysis products reaches as high as 89.23 wt%. Under the same conditions, tests were conducted at times of 0.5 h, 2 h, and 8 h, revealing that with prolonged reaction time, the conversion of polystyrene becomes more complete, and the yields of toluene, ethylbenzene, and cumene significantly increase. This invention involves testing different solvents under otherwise identical conditions. By adjusting the type of reaction solvent, not only can the yield of monocyclic aromatic hydrocarbons be changed, but also the selectivity of benzene, toluene, ethylbenzene, and propylbenzene among the monocyclic aromatic hydrocarbons can be altered. It was found that ethylbenzene exhibits the highest selectivity when a hydrogen-donating solvent is used.

[0015] This invention solves the problem of reduced aromatic selectivity due to benzene ring hydrogenation; it also solves the problem of polystyrene easily forming its own rings to produce hydrogen and generate polycyclic aromatic hydrocarbons; and the solvent can be recycled. Therefore, the method provided by this invention is environmentally friendly, can achieve the degradation of polystyrene, successfully avoids the problems of coking and lightweighting during the degradation process, and has very good economic benefits. Detailed Implementation

[0016] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solution of this invention and actual conditions. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages.

[0017] The method for hydrogenating and pyrolyzing polystyrene is carried out as follows: Solvent and polystyrene are separately added to a suspended bed reactor, the reactor is sealed, and hydrogen gas at a certain pressure is introduced. The solvent is at least one of a hydrogen-donating solvent and a non-hydrogen-donating solvent. The mass ratio of polystyrene to solvent is 1:100 to 2:1. The molar ratio of H2 to benzene in the polystyrene is 1:0.8 to 1:2. The hydrogenating and pyrolyzing of polystyrene is carried out at a temperature of 300℃ to 450℃. The time for the hydrogenating and pyrolyzing of polystyrene is 0.5h to 12h. This invention, by employing a suspended bed hydrogenation process, can achieve complete conversion of polystyrene, with a high yield of monocyclic aromatic hydrocarbons, and can realize the hydrogenating and pyrolyzing of polystyrene materials, exhibiting extremely high economic efficiency.

[0018] Example 1:

[0019] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using tetrahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 12 hours; and the hydrogenation pyrolysis product of polystyrene is obtained.

[0020] Example 2:

[0021] The method for hydrogenating and pyrolyzing polystyrene is carried out as follows: using decahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the hydrogenated and pyrolyzed polystyrene product is obtained.

[0022] Example 3:

[0023] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using tridecane as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the hydrogenation pyrolysis product of polystyrene is obtained.

[0024] Example 4:

[0025] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using tetrahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 12 hours; and the hydrogenation pyrolysis product of polystyrene is obtained.

[0026] Example 5:

[0027] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using decahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 8 hours; and the hydrogenation pyrolysis product of polystyrene is obtained.

[0028] Example 6:

[0029] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using tridecane as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 8 hours; and the hydrogenation pyrolysis product of polystyrene is obtained.

[0030] Example 7:

[0031] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using a mixture of tetrahydronaphthalene and decahydronaphthalene as a solvent, with a mass ratio of tetrahydronaphthalene to decahydronaphthalene of 1:9, polystyrene is added to a slurry bed reactor at a mass ratio of the solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and hydrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; the hydrogenation pyrolysis product of polystyrene is obtained.

[0032] Comparative Example 1

[0033] The method for hydrogenating and pyrolyzing polystyrene is carried out as follows: using tetrahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and nitrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the degraded polystyrene product is obtained.

[0034] Comparative Example 2

[0035] The method for hydrogenating and pyrolyzing polystyrene is carried out as follows: using decahydronaphthalene as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and nitrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the degraded polystyrene product is obtained.

[0036] Comparative Example 3

[0037] The method for hydrogenating and pyrolyzing polystyrene is carried out as follows: using tridecane as a solvent, polystyrene is added to a slurry bed reactor at a mass ratio of 10:1; the slurry bed reactor is sealed, and nitrogen gas at 8 MPa is introduced. The reaction is carried out at a temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the degraded polystyrene product is obtained.

[0038] Comparative Example 4

[0039] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using a mixture of tetrahydronaphthalene and tridecane as a solvent, with a mass ratio of tetrahydronaphthalene to decahydronaphthalene of 3:1, polystyrene is added to a slurry bed reactor at a mass ratio of the solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and nitrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the degraded polystyrene product is obtained.

[0040] Comparative Example 5

[0041] The method for the hydrogenation pyrolysis of polystyrene is carried out as follows: using a mixture of tetrahydronaphthalene and decahydronaphthalene as a solvent, with a mass ratio of tetrahydronaphthalene to decahydronaphthalene of 3:1, polystyrene is added to a slurry bed reactor at a mass ratio of the solvent to polystyrene of 10:1; the slurry bed reactor is sealed, and nitrogen gas at 8 MPa is introduced. The reaction is carried out at a reaction temperature of 400°C; the residence time of the mixture in the slurry bed reactor is 2 hours; and the degraded polystyrene product is obtained.

[0042] In this invention, the results of the hydrogenation pyrolysis of polystyrene in Examples 1 to 7 and Comparative Examples 1 to 5 are shown in Table 1. Table 1 shows that this invention has very good implementation effects. After the hydrogenation reaction of polystyrene, the yield of monocyclic aromatic hydrocarbons can reach as high as 89.24%. The monocyclic aromatic hydrocarbons are composed of at least one or more of benzene, toluene, ethylbenzene, and propylbenzene (n-propylbenzene and isopropylbenzene). The hydrogenation pyrolysis method for polystyrene provided by this invention is more economical; this invention solves the problem of reduced aromatic hydrocarbon selectivity due to benzene ring hydrogenation; it solves the problem of polystyrene easily forming its own rings to produce hydrogen and form polycyclic aromatic hydrocarbons; and it also solves the problem of easy catalyst deactivation. It can achieve efficient degradation of waste polystyrene and has good economic benefits.

[0043] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0044] Table 1 Results of Hydrogenation Pyrolysis of Polystyrene

[0045]

[0046] The present invention provides a method for producing monocyclic aromatic hydrocarbons by promoting the hydrogenation and pyrolysis of waste polystyrene using a solvent. The solvent can be recycled, making it more economical and environmentally friendly. It solves the problem of polystyrene easily forming its own rings to produce hydrogen and generate polycyclic aromatic hydrocarbons; it also solves the problem of reduced aromatic hydrocarbon selectivity due to benzene ring hydrogenation, achieving a monocyclic aromatic hydrocarbon yield of up to 89.23%. It enables highly efficient degradation of waste polystyrene and has significant economic benefits.

Claims

1. A method for solvent-promoted hydrogenation of polystyrene to prepare monocyclic aromatic hydrocarbons, characterized in that, It includes the following steps: Polystyrene is hydrogenated and pyrolyzed under the action of solvent and H2.

2. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 1, characterized in that, The solvent is at least one or more of a hydrogen-donating solvent and a non-hydrogen-donating solvent.

3. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 1, characterized in that, The non-hydrogen-donating solvent is at least one or more of decahydronaphthalene, n-tetrazane, etc. Preferably, the solvent is a hydrogen-donating solvent, which is a hydrogenated aromatic hydrocarbon, such as at least one or more of tetrahydronaphthalene, dihydroanthracene, dihydrophenanthrene, and tetrahydroanthracene.

4. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 1, characterized in that, The mass ratio of polystyrene to solvent is 1:100 to 2:1, preferably 1:50 to 1:1, and more preferably 1:20 to 1:

1.

5. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 1, characterized in that, The molar ratio of H2 to benzene in polystyrene is 30:1 to 1:2, preferably 10:1 to 1:2, and more preferably 10:1 to 2:

1.

6. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 1, characterized in that, The specific process involves adding the solvent and polystyrene separately into a slurry bed reactor, sealing the slurry bed reactor, and introducing hydrogen gas at a certain pressure to start the reaction; the reaction pressure is 2 MPa to 20 MPa, preferably 6 MPa to 15 MPa, and more preferably 8 MPa to 12 MPa.

7. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to any one of claims 1 to 6, characterized in that, The polystyrene hydrogenation pyrolysis is carried out at a temperature of 300℃ to 450℃, preferably at 380℃ to 420℃, and more preferably at 400℃; the polystyrene hydrogenation pyrolysis time is 0.5h to 12h, preferably 2h to 12h, and more preferably 4h to 8h.

8. The method for preparing monocyclic aromatic hydrocarbons by hydrogenation of polystyrene according to claim 7, characterized in that, The polystyrene in question is waste polystyrene plastic.

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