A method for efficiently preparing aromatic hydrocarbon oil from polystyrene by hydrogen-free low-temperature thermal catalytic conversion

Abstract

The application discloses a kind of hydrogen-free low-temperature thermal catalytic conversion polystyrene high-efficiency preparation aromatic hydrocarbon oil method, belong to plastic chemical recycling technical field.The hydrogen-free low-temperature thermal catalytic conversion polystyrene high-efficiency preparation aromatic hydrocarbon oil method includes the following steps: polystyrene is pre-softened, then MgAl-MMO porous catalyst is added to carry out catalytic reaction, and aromatic hydrocarbon oil is obtained;The MgAl-MMO porous catalyst is prepared by magnesium source, aluminum source, sodium carbonate and sodium bicarbonate.The application constructs the core of thermal activation catalyst, low-temperature (280~300 DEG C) atmospheric pressure driven collaborative catalytic system, significantly reduce energy consumption and equipment requirements.At the same time, by optimizing reaction conditions, in the mild environment without solvent and hydrogen, polystyrene (PS) can be efficiently catalytic degradation, and be converted into high value-added aromatic hydrocarbon oil, in addition, the yield of aromatic hydrocarbon oil is high, and high value recovery of polystyrene plastic can be realized.

Description

Technical Field

[0001] This invention belongs to the field of plastic chemical recycling technology, and more specifically relates to a method for the efficient preparation of aromatic oils from polystyrene by hydrogen-free low-temperature thermocatalytic conversion. Background Technology

[0002] Polystyrene (PS) is a common type of foamed plastic. Due to the inherent stability of its chemical bonds and the complexity of its composition, the recycling rate of PS waste remains as low as 1%. In the field of chemical recycling of waste PS, researchers have developed a variety of methods, including thermochemical conversion, photocatalysis, electrocatalysis, and biocatalysis.

[0003] Thermocatalysis is considered one of the most efficient ways to convert organic solid waste into fuel or high-value chemicals. Thermocatalysis does not rely on renewable energy sources (such as solar and wind power) or complex electrochemical devices; it can directly utilize conventional heat sources (such as industrial waste heat or electric heating) to drive the reaction, making it more adaptable and particularly suitable for large-scale continuous production. Simultaneously, the thermocatalytic reaction pathway achieves selective chain breakage of polystyrene through free radical regulation, suppressing coke formation (coke yield <5%), resulting in high product purity and low post-processing costs. Thermocatalytic degradation of polystyrene, with its core competitiveness of low-temperature high efficiency, high-value products, and robust process, provides an economical and environmentally friendly solution for the resource recovery of waste polyolefin plastics, especially suitable for large-scale treatment of mixed plastic waste in industrial settings. However, current thermocatalytic systems face the following key challenges: the catalytic system is prone to sintering deactivation during high-temperature reactions, requiring a reducing atmosphere such as H2 to maintain stability; simultaneously, some catalytic systems require strong adsorption from polar solvents (such as toluene), leading to reaction medium dependence (solvent content >60%), significantly increasing separation energy consumption.

[0004] One common method for polystyrene degradation is pyrolysis. Pyrolysis of polystyrene at high temperatures produces liquid oil, but potential problems include high energy consumption due to the need to maintain high temperatures, such as 400-600°C. Furthermore, high temperatures can lead to coking or carbon buildup, affecting reaction efficiency and equipment lifespan. Unstable product composition can also be a problem; the aromatic oil composition obtained under different conditions may fluctuate significantly, affecting subsequent applications. Catalytic degradation is another option. While catalysts can lower the reaction temperature, the catalysts themselves are prone to deactivation, possibly due to carbon buildup or poisoning (e.g., the influence of impurities). The cost of the catalyst is also an issue, especially for precious metal catalysts, as recovery and reuse can be difficult, increasing overall costs.

[0005] Therefore, developing novel catalytic systems that combine low-temperature activity (<300℃), compatibility with solvent-free systems, and hydrogen-free systems has become an innovative breakthrough direction for industrial application in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the efficient preparation of aromatic oils from polystyrene by hydrogen-free low-temperature thermocatalytic conversion, in order to solve the problems existing in the prior art. The thermocatalytic method provided by this invention can achieve efficient catalytic degradation of polystyrene (PS) at low temperature and normal pressure under mild conditions without solvents and hydrogen, and convert it into high-value-added aromatic oils.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One of the technical solutions of this invention is to provide a method for the efficient preparation of aromatic oils from polystyrene through hydrogen-free low-temperature thermocatalytic conversion, comprising the following steps:

[0009] Polystyrene was pre-softened, and then a MgAl-MMO porous catalyst was added for catalytic reaction to obtain aromatic oil.

[0010] The MgAl-MMO porous catalyst has a sheet-like array structure and is prepared using magnesium source, aluminum source, sodium carbonate and sodium bicarbonate as raw materials.

[0011] Preferably, the pre-softening temperature is 200°C.

[0012] Preferably, the mass ratio of the polystyrene to the MgAl-MMO porous catalyst is 1.2–2:0.2–1.

[0013] Preferably, the temperature of the catalytic reaction is 280–300°C, the heating rate is 2–10°C / min, the pressure is 101.325 kPa, and the time is 8–16 h.

[0014] Preferably, the catalytic reaction is carried out under a nitrogen atmosphere.

[0015] Furthermore, the process includes a step of introducing nitrogen gas into the catalytic reaction system to remove air before the catalytic reaction.

[0016] Preferably, the preparation steps of the MgAl-MMO porous catalyst include:

[0017] Magnesium and aluminum sources are dissolved in water to obtain solution A; sodium carbonate and sodium bicarbonate are dissolved in water to obtain solution B; solutions A and B are mixed and subjected to a hydrothermal reaction to obtain a MgAl-LDHs precursor; the MgAl-LDHs precursor is calcined to obtain a MgAl-MMO porous catalyst.

[0018] Preferably, the molar ratio of the magnesium source to the aluminum source is 3:1; in solution B, the concentration of sodium carbonate is 0.48–0.56 mol / L and the concentration of sodium bicarbonate is 0.2–0.4 mol / L; in the solution after mixing solution A and solution B, the concentration of the magnesium source is 0.03–0.06 mol / L and the concentration of the aluminum source is 0.01–0.02 mol / L.

[0019] Preferably, the hydrothermal reaction is carried out at a temperature of 80–120°C for 8–16 hours.

[0020] Preferably, the calcination temperature is 400–700°C, the heating rate is 2–10°C / min, and the time is 0.5–4h.

[0021] In the preparation of MgAl-MMO porous catalysts, different preparation conditions affect the catalyst's performance. The main factors are the hydrothermal reaction temperature and the calcination temperature. Hydrothermal temperature: affects crystal structure and crystallinity. Low temperature: low crystallinity: LDH layers do not grow sufficiently, resulting in numerous crystal defects and disordered interlayer anion arrangement. Loose layer stacking: leads to a higher specific surface area but weaker mechanical strength, making it prone to collapse after calcination. Suitable temperature: high crystallinity: orderly stacking of layers, forming a typical hexagonal plate structure, with uniform distribution of interlayer anions (such as CO32-). Calcination temperature: Mechanism of influence: Calcination temperature directly affects the crystal structure, dispersion, and pore structure of the catalyst's active components and the support. Specific manifestations: Too low a temperature: the precursor is not completely decomposed, and the active components do not form a stable crystalline phase, resulting in insufficient exposure of active sites (e.g., incomplete formation of metal oxides). Too high a temperature: active components sinter and agglomerate, reducing the specific surface area (e.g., collapse of molecular sieve channels); some metals may undergo irreversible oxidation changes, reducing reducibility.

[0022] This invention proposes a method for the efficient preparation of aromatic oils from polystyrene through a hydrogen-free, low-temperature thermocatalytic conversion based on a thermocatalytic system, for the efficient chemical recycling of waste polystyrene plastics. By adjusting the ratio of polystyrene to MgAl-MMO porous catalyst, the conversion rate of polystyrene is effectively improved. The mass ratio of polystyrene to MgAl-MMO porous catalyst is 1.2–2:0.2–1. When the mass ratio is higher than this range, a small amount of catalyst cannot provide sufficient surface active sites to adsorb and activate polystyrene, resulting in a slow reaction rate and low conversion rate. When the mass ratio is lower than this range, excessive catalyst leads to excessive accumulation of catalyst particles, which lengthens the diffusion path of reactant molecules on the catalyst surface, hindering the reactant molecules from reaching the active sites and reducing mass transfer efficiency.

[0023] In the thermocatalytic system described in this invention, the conversion rate of polystyrene and the yield of aromatic oils are improved by adjusting the reaction temperature. The catalytic reaction temperature is 280–300°C, and the degradation temperature of polystyrene begins at 260°C. Although gradually increasing the temperature can improve the conversion rate of polystyrene, the gas yield also increases with increasing temperature, which will affect the yield of aromatic oils. Within the catalytic reaction temperature range of 280–300°C described in this invention, the conversion rate of polystyrene and the yield of aromatic oils can be significantly improved.

[0024] In the degradation of plastics, the core role of adding a catalyst is to significantly reduce the required temperature by altering the reaction pathway and lowering the activation energy. Catalysts provide new reaction pathways (such as surface adsorption-activation mechanisms), allowing chemical bonds that would otherwise require high temperatures to break (such as C-C bonds and CH bonds) to be broken at lower temperatures. The reaction mechanism of the thermocatalytic system described in this invention is as follows: 1. Adsorption and activation of polystyrene: Polystyrene chains are physically adsorbed and fixed on the MMO surface. MgO basic sites weaken the electron cloud density of adjacent CH bonds through polarization, activating the CH bonds. 2. CH bond cleavage: Mg-O basic sites on the catalyst surface attack the CH bonds in the polystyrene chains through nucleophilic interactions, abstracting hydrogen atoms to form H-Mg-O intermediates, leading to heterolytic cleavage of the CH bonds and the generation of unstable carbon radical intermediates. 3. C-C bond cleavage: The radical intermediate triggers a β-cleavage mechanism: C-C bonds at the β-position of the radical site break, generating styrene monomers and short-chain radical fragments. 4. Chain pyrolysis and short-chain product generation: Hydrogen species (H*) adsorbed by MMO participate in the reaction as a hydrogen source, converting free radical intermediates into short-chain aromatics (such as toluene and ethylbenzene). This invention achieves the degradation of polystyrene at relatively low temperatures (280–300°C), at atmospheric pressure, and without the participation of hydrogen gas. It not only achieves efficient degradation of polystyrene under mild conditions but also significantly improves the yield of aromatic oils. The mild conditions of this invention can significantly reduce equipment costs, energy consumption, and safety risks, possessing unique industrial application value.

[0025] Compared to conventional catalysts (such as MgO, CaO, and ZnO), the thermocatalytic system of this invention uses the composite metal hydroxide MgAl-LDH as a precursor, which, after calcination, becomes the composite metal oxide MgAl-MMO, exhibiting basic sites. During the reaction mechanism, the MgAl-MMO catalyst possesses both strongly basic and moderately basic sites. Strongly basic sites facilitate the breaking of CH bonds, while moderately basic sites promote the breaking of C / C bonds. Analysis of the gas and liquid oil produced by the catalytic reaction revealed that the liquid oil contains aromatic substances such as styrene and toluene, with a high selectivity for styrene. Although single solid basic catalysts (MgO, CaO, and ZnO) can activate CH bonds by abstracting hydrogen atoms, their limited active sites make it difficult for PS molecules to effectively adsorb onto the catalyst surface. Furthermore, their relatively simple crystal structures and limited types of surface basic sites result in insufficient adsorption and activation capacity for polystyrene molecules, hindering efficient initiation of polystyrene chain breakage and limiting the conversion rate.

[0026] This invention also provides the reaction system used in the above-mentioned method for the efficient preparation of aromatic oils from polystyrene through hydrogen-free low-temperature thermocatalytic conversion, as detailed below:

[0027] The reaction system consists of: a reactor, a heating and temperature control device, an inert gas device, and a product collection and separation device.

[0028] The reactor is a quartz reactor, which is resistant to high temperature and corrosion and is suitable for normal and low pressure conditions.

[0029] The heating and temperature control device is provided by the heating reaction device. The temperature is controlled by a PID temperature controller (accuracy ±1℃) connected to the quartz reactor through thermocouple detection.

[0030] An inert gas device is used to supply nitrogen.

[0031] The product collection and separation device is used for product collection and separation. Product collection includes connecting a condenser to the outlet of the quartz reactor to condense gaseous aromatics into liquid aromatic oil, with the liquid product collected in a sealed glass bottle. Product separation involves using an Erlenmeyer flask and rubber tubing. The condensed liquid product is collected through the Erlenmeyer flask, while the gas is connected to a gas bag through the rubber tubing. Uncondensed gases (such as methane and ethylene) are collected through a gas bag or gas sampling bag for subsequent component analysis.

[0032] The present invention discloses the following technical effects:

[0033] This invention constructs a synergistic catalytic system driven by a thermally activated catalyst at low temperature (280–300°C) and ambient pressure, significantly reducing energy consumption and equipment requirements. Simultaneously, by optimizing reaction conditions, highly efficient catalytic degradation of polystyrene (PS) can be achieved in a mild environment without solvents or hydrogen, converting it into high-value aromatic oils. Furthermore, the high yield of the aromatic oils enables high-value recovery of polystyrene plastics. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method described in this invention;

[0035] Figure 2 The X-ray diffraction patterns of MgAl-LDH and MgAl-MMO described in Example 1 are shown below.

[0036] Figure 3 The image shown is a scanning electron microscope (SEM) image of the MgAl-MMO described in Example 1.

[0037] Figure 4 The image shown is a scanning electron microscope (SEM) energy dispersive spectroscopy (EDS) spectrum of MgAl-MMO described in Example 1.

[0038] Figure 5 This is a scanning electron microscope image of MgO as described in Example 2;

[0039] Figure 6 This is a scanning electron microscope image of the CaO described in Example 2;

[0040] Figure 7 The image shown is a scanning electron microscope (SEM) image of ZnO as described in Example 2.

[0041] Figure 8 A photograph of the resulting liquid product (aromatic oil);

[0042] Figure 9 Selectivity of gaseous, liquid and solid products for the thermocatalytic conversion of polystyrene under different catalysts (MgO, CaO, ZnO, and MgAl-MMO obtained in Example 1);

[0043] Figure 10 This is a graph showing the selectivity of gaseous, liquid, and solid products in the thermal catalytic conversion of polystyrene under different magnesium-aluminum molar ratios during catalyst preparation.

[0044] Figure 11 Selectivity of gaseous, liquid, and solid products for the thermocatalytic conversion of polystyrene at different temperatures;

[0045] Figure 12 Selectivity of gaseous, liquid and solid products for the thermocatalytic conversion of polystyrene under different catalyst dosages;

[0046] Figure 13The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene with / without a catalyst is shown in the graph.

[0047] Figure 14 This is a carbon number distribution diagram of the liquid product obtained in Example 1;

[0048] Figure 15 The infrared spectrum of the liquid product obtained in Example 1;

[0049] Figure 16 The 1H NMR spectrum of the liquid product obtained in Example 1;

[0050] Figure 17 This is a selectivity diagram for different components in the liquid product obtained in Example 1. Detailed Implementation

[0051] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0052] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0053] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0054] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0055] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0056] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0057] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0058] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0059] Unless otherwise specified, the atmospheric pressure involved in this invention is 101.325 kPa.

[0060] The conversion rate, yield of liquid product (aromatic oil), solid yield, and gas yield of polystyrene in the following examples and comparative examples of the present invention were calculated using the following formula:

[0061] Conversion rate of polystyrene = (mass of polystyrene before reaction - mass of polystyrene after reaction) / mass of polystyrene before reaction × 100%;

[0062] Yield of liquid product (aromatic oil) = mass of liquid product (aromatic oil) / mass of polystyrene before reaction × 100%;

[0063] The yield of solids = mass of solid product / mass of polystyrene before reaction × 100%;

[0064] Gas yield = 100% - yield of liquid product (aromatic oil) - yield of solid.

[0065] Example 1

[0066] Preparation of MgAl-MMO catalysts:

[0067] Step 1: Weigh 17.69g of magnesium nitrate and 8.63g of aluminum nitrate, add 230mL of deionized water to prepare solution A. Weigh 4.42g of sodium carbonate and 4.88g of sodium bicarbonate, add 230mL of deionized water to prepare solution B. Prepare magnesium-aluminum hydrotalcite using a colloid mill. Mix solutions A and B and transfer to a polytetrafluoroethylene hydrothermal reactor for hydrothermal reaction at 100℃ for 12h. After cooling to room temperature, collect the resulting white solid product by centrifugation, wash with water and anhydrous ethanol at least three times, and dry in an oven at 60℃ for 12h to obtain MgAl-LDH.

[0068] Step 2: Place MgAl-LDH in a sintering furnace and heat it to 450℃ for 3 hours, controlling the heating rate to be 5℃ / min, to obtain MgAl-MMO.

[0069] Figure 2The X-ray diffraction patterns of MgAl-LDH and MgAl-MMO described in Example 1 are shown below. Figure 3 The image shown is a scanning electron microscope (SEM) image of the MgAl-MMO described in Example 1. Figure 4 The image shows the scanning electron microscope energy dispersive spectroscopy (SEM) spectrum of the MgAl-MMO described in Example 1.

[0070] Depend on Figures 2-4 It is evident that the structure of calcined magnesium-aluminum layered double hydroxide (MgAl-MMO) undergoes significant changes. With the loss of interlayer anions and water molecules, the layers collapse, and the characteristic diffraction peaks such as 003 and 006, reflecting the interlayer structure, disappear. This indicates that the unique layered structure of MgAl-MMO is disrupted, and characteristic diffraction peaks of magnesium-aluminum mixed oxides appear. This also confirms the successful preparation of the MgAl-MMO catalyst. SEM analysis of the catalyst morphology shows that MgAl-MMO exhibits a typical hexagonal plate-like stacked morphology. The energy dispersive spectroscopy (EDS) spectrum reveals that Mg, Al, and O elements are uniformly distributed within the catalyst.

[0071] A method for the efficient preparation of aromatic oils from polystyrene via hydrogen-free, low-temperature thermocatalytic conversion is described below:

[0072] The crushed polystyrene particles were evenly spread on top of the catalyst bed in a quartz reactor, and the prepared MgAl-MMO was placed in the catalyst bed. The mass ratio of polystyrene particles to MgAl-MMO was 2:0.6. The inert gas system was turned on, and nitrogen gas was introduced into the quartz reactor at a rate of 5 L / min for 30 min to purge air. Then, the nitrogen gas introduction rate was adjusted to 50 mL / min, and the heating and temperature control system was adjusted to pre-soften the polystyrene particles at atmospheric pressure by raising the temperature to 200 °C at a rate of 5 °C / min for 30 min. Then, the nitrogen gas was continuously introduced at a rate of 50 mL / min, and the temperature was raised to 280 °C at a rate of 5 °C / min (the temperature fluctuation was monitored in real time (±1 °C)). The thermocatalytic conversion was carried out at atmospheric pressure for 12 h. Finally, the product was collected. The nitrogen gas carried the product through a condenser, and the liquid product (aromatic oil) was collected in a sealed bottle. At the same time, dichloromethane was used to collect the product generated at the connection points of each device, and the uncondensed gas was introduced into a gas bag.

[0073] The collected liquid products were analyzed using a combination of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gas chromatography-mass spectrometry.

[0074] Figure 14 This is a carbon number distribution diagram of the liquid product obtained in Example 1; Figure 15 The infrared spectrum of the liquid product obtained in Example 1; Figure 16 The 1H NMR spectrum of the liquid product obtained in Example 1; Figure 17 This is a selectivity diagram for different components in the liquid product obtained in Example 1.

[0075] Depend on Figure 17 It can be seen that the liquid product contains aromatic substances such as styrene and toluene, with a high selectivity for styrene.

[0076] Example 2

[0077] The selectivity of different catalysts for the thermocatalytic conversion of polystyrene towards gaseous, liquid, and solid products was verified using the following methods:

[0078] In Example 1, MgAl-MMO was replaced with MgO, CaO, and ZnO (MgO was purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd., CaO was purchased from Xilong Chemical, and ZnO was from Hushi). A case was set up in which the addition of MgAl-MMO was omitted. The rest was the same as in Example 1.

[0079] Morphological diagrams of MgO, CaO, and ZnO are shown below. Figures 5-7 As shown.

[0080] The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene under different catalysts is as follows: Figure 9 As shown.

[0081] The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene with or without a catalyst is as follows: Figure 13 As shown.

[0082] Figure 9 Selectivity of gaseous, liquid and solid products for the thermocatalytic conversion of polystyrene under different catalysts (MgO, CaO, ZnO, and MgAl-MMO obtained in Example 1).

[0083] Depend on Figure 9 It is evident that, compared with conventional catalysts (such as MgO, CaO, and ZnO), the MgAl-MMO porous catalyst in the thermocatalytic system described in this invention can significantly improve the yield of aromatic oils.

[0084] Figure 13 This is a graph showing the selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene with and without a catalyst.

[0085] Depend on Figure 13 It is known that more liquid products can be produced in the presence of a catalyst.

[0086] Example 3

[0087] The selectivity of the thermocatalytic conversion of polystyrene to gaseous, liquid, and solid products during the preparation of MgAl-MMO under different magnesium-aluminum molar ratios was verified. The specific method is as follows:

[0088] The molar ratio of magnesium nitrate and aluminum nitrate described in Example 1 was adjusted to 2:1 or 4:1, and the rest was the same as in Example 1.

[0089] The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene under different magnesium-aluminum molar ratios during catalyst preparation is as follows: Figure 10 As shown.

[0090] Figure 10 This is a graph showing the selectivity of gaseous, liquid, and solid products in the thermal catalytic conversion of polystyrene under different magnesium-aluminum molar ratios during catalyst preparation.

[0091] Depend on Figure 10 It is known that the catalyst prepared under the magnesium-aluminum molar ratio specified in this invention can significantly improve the selectivity of polystyrene for aromatic oil in thermocatalytic conversion and can significantly improve the yield of aromatic oil.

[0092] Example 4

[0093] The selectivity of the thermocatalytic conversion of polystyrene at different temperatures for gaseous, liquid, and solid products was verified using the following method:

[0094] The thermocatalytic conversion temperature in Example 1 was adjusted to 260°C or 300°C, and the rest was the same as in Example 1.

[0095] The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene at different temperatures is as follows: Figure 11 As shown.

[0096] Figure 11 Selectivity diagrams for gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene at different temperatures.

[0097] Depend on Figure 11 It is known that at the thermocatalytic conversion temperature defined in this invention, polystyrene can be efficiently degraded, while the yield of aromatic oils is effectively improved.

[0098] Example 5

[0099] The selectivity of the thermocatalytic conversion of polystyrene to gaseous, liquid, and solid products under different catalyst dosages was verified using the following method:

[0100] The mass ratio of polystyrene to MgAl-MMO in Example 1 was adjusted to 2:0.2 or 2:1, and the rest was the same as in Example 1.

[0101] The selectivity of gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene under different catalyst dosages is as follows: Figure 12 As shown.

[0102] Figure 12 Selectivity diagrams for gaseous, liquid, and solid products in the thermocatalytic conversion of polystyrene under different catalyst dosages.

[0103] As shown in 12, when the mass ratio of plastic to catalyst is increased to an appropriate range, the heat generated selectively on the catalyst can be better distributed to the plastic, forming a solid-liquid contact state and reducing the contact opportunities between the "catalyst" or "active site" and the plastic intermediate, which helps to reduce excessive depolymerization and gas formation.

[0104] This invention discloses a method for the degradation of polystyrene under mild conditions based on a thermocatalytic system, enabling efficient chemical recycling of polystyrene plastics. This method constructs a synergistic catalytic system with a thermally activated catalyst as the core, driven by low temperature (280℃) and normal pressure, significantly reducing energy consumption and equipment requirements. By precisely controlling the reaction pathway and suppressing side reactions, highly selective cleavage of the polystyrene molecular chain and directional enrichment of aromatic products are achieved. Simultaneously, by optimizing reaction conditions, efficient catalytic degradation of polystyrene (PS) at low temperature and normal pressure is achieved in a mild environment without solvents or hydrogen, converting it into high-value-added aromatic oils. Compared to traditional chemical recycling technologies, the system described in this invention can effectively initiate the cracking reaction of polystyrene at a low temperature of 280℃, achieving a maximum conversion rate of 96.5% and a maximum liquid (aromatic oil) yield of 89.5%, significantly superior to traditional pyrolysis processes, while also exhibiting high selectivity and stability. This method can be applied to the resource recovery of waste plastics (such as food packaging, electronic device casings, etc.), providing an economical and environmentally beneficial solution for the control of "white pollution," while also providing a renewable source of aromatic raw materials for the petrochemical industry.

[0105] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0106] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing aromatic oil from polystyrene by hydrogen-free low-temperature thermocatalytic conversion, characterized in that, Includes the following steps: Polystyrene was pre-softened, and then a porous catalyst of composite metal oxide MgAl-MMO was added to carry out a catalytic reaction to obtain aromatic oil. The MgAl-MMO porous catalyst has a sheet-like array structure and is prepared using magnesium source, aluminum source, sodium carbonate and sodium bicarbonate as raw materials. The pre-softening temperature is 200°C; The mass ratio of the polystyrene to the MgAl-MMO porous catalyst is 2:0.6; The catalytic reaction was carried out at a temperature of 280℃, a heating rate of 2–10℃ / min, a pressure of 101.325 kPa, and a time of 8–16 h. The catalytic reaction was carried out under a nitrogen atmosphere; The preparation steps of the MgAl-MMO porous catalyst include: Step 1, weighing 17.69g of magnesium nitrate and 8.63g of aluminum nitrate, adding 230mL of deionized water to prepare solution A; weighing 4.42g of sodium carbonate and 4.88g of sodium bicarbonate, adding 230mL of deionized water to prepare solution B; mixing solutions A and B and transferring them to a polytetrafluoroethylene hydrothermal reactor for hydrothermal reaction at 100℃ for 12h; cooling to room temperature, collecting the obtained white solid product by centrifugation, washing it with water and anhydrous ethanol more than 3 times, and drying it in an oven at 60℃ for 12h to obtain MgAl-LDH; Step 2, placing MgAl-LDH in a sintering furnace and heating it to 450℃ for 3h, controlling the heating rate at 5℃ / min to obtain the MgAl-MMO porous catalyst.

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