A method for preparing cycloalkanes from polystyrene plastics by one-step hydrocracking

Abstract

This invention discloses a method for preparing cycloalkanes from polystyrene plastic via one-step hydrocracking, belonging to the fields of waste plastic resource upgrading and catalytic hydrocracking technology. The invention first prepares a bifunctional catalyst of Pd supported on molecular sieve HY, and then carries out a one-step hydrocracking reaction in a batch reactor under a hydrogen atmosphere, converting polystyrene into a liquid product mainly composed of cycloalkanes. The Pd loading in the catalyst is 0.1–0.9 wt%, the catalyst operating temperature is 240–300℃, the reaction time is 2–10 h, and the hydrogen pressure is 0.1–5 MPa. This method is simple, with relatively mild reaction conditions, and can achieve efficient conversion of polystyrene plastic waste into high-value-added cycloalkane liquid fuel components, showing good prospects for resource utilization.

Description

Technical Field

[0001] This invention relates to the fields of waste plastic resource utilization and catalytic hydrocracking technology, specifically to a method for preparing cycloalkane liquid fuel by one-step hydrocracking of polystyrene waste plastic using a Pd / HY catalyst. Background Technology

[0002] Polystyrene is a common type of plastic in daily life, widely used in foam packaging, disposable lunch boxes, food containers, insulation materials, and other daily plastic products. However, polystyrene polymers contain stable aromatic ring side chain structures and a main chain structure formed by C-C bonds, making them chemically inert and difficult to degrade in the natural environment, resulting in serious resource waste and environmental pollution. Currently, polystyrene recycling methods mainly include mechanical recycling, incineration, pyrolysis, catalytic cracking, and hydrocracking. Among these, mechanical recycling requires high purity and cleanliness of raw materials and often involves partial degradation during the recycling process, leading to a decline in the quality of recycled plastics and downgrading. Incineration causes large amounts of carbon emissions and pollutant release. Pyrolysis and catalytic cracking typically require high reaction temperatures (>350 ℃), resulting in high energy consumption during the degradation process, complex product composition, and product yields below 80%. Therefore, developing efficient and targeted chemical upgrading and conversion methods for waste polystyrene plastics is of great significance.

[0003] Cycloalkanes are an important class of saturated cyclic hydrocarbons with applications in liquid fuels, industrial solvents, and liquid organic hydrogen carriers. Traditionally, cycloalkanes are mainly derived from fossil resources such as coal and petroleum. For example, the petroleum route typically requires complex processes such as atmospheric and vacuum distillation, catalytic reforming, aromatics separation, and hydrogenation to obtain cycloalkanes, which presents problems such as unsustainable resources, complex processes, high energy consumption, and environmental pollution. In recent years, the preparation of cycloalkanes using biomass or polyester plastics has become a new research direction. For instance, oxygen-containing raw materials such as lignin and polyethylene terephthalate can be converted into cycloalkanes through hydrodeoxygenation reactions. However, in this process, the removal of oxygen reduces the utilization efficiency of the raw materials.

[0004] Polystyrene polymers are formed by the polymerization of styrene monomers, consisting only of carbon and hydrogen elements, and rich in aromatic ring structures, making them more suitable as raw materials for the preparation of cycloalkanes from both composition and structure perspective. Therefore, developing a one-step catalytic degradation method for the hydrocracking of polystyrene waste plastics with low metal loading and relatively mild conditions has significant application value for the resource utilization of polystyrene waste plastics and the preparation of high-value-added cycloalkane liquid fuels. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing cycloalkanes by one-step hydrogenation cracking of polystyrene plastic. The prepared Pd / HY bifunctional catalyst efficiently achieves the breaking of C-C bonds in the polystyrene main chain and the hydrogenation of aromatic rings in a batch reactor under solvent-free conditions, hydrogen atmosphere, and relatively low temperature, thereby achieving highly selective preparation of cycloalkanes as liquid products.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing cycloalkanes from polystyrene plastic via one-step hydrogenation cracking involves adding molten polystyrene plastic substrate and catalyst into a batch reactor and carrying out a hydrogenation cracking reaction under a hydrogen atmosphere, thereby directly converting polystyrene into a liquid product containing cycloalkanes in one step. The catalyst is a Pd / HY bifunctional catalyst, comprising a metal active component Pd and a HY molecular sieve support, wherein the content of palladium in the catalyst accounts for 0.1–0.9 wt%.

[0007] The Pd / HY bifunctional catalyst uses palladium as the active metal hydrogenation component and HY molecular sieve to provide acidic sites. Palladium is dispersed in atomically dispersed clusters on the HY molecular sieve support. Through the synergistic effect of acidic sites and metal sites, highly selective conversion of polystyrene to cycloalkanes is achieved.

[0008] In this catalyst, the palladium loading is 0.1-0.9 wt.%, and the SiO2 / Al2O3 ratio in the HY molecular sieve support is 2.5-80.

[0009] The preparation method of the Pd / HY bifunctional catalyst includes the following steps: (1) First, HY molecular sieve carrier materials were prepared using HY molecular sieve as raw material; (2) The palladium species were impregnated onto the HY molecular sieve support material by impregnation method to obtain the HY molecular sieve supported palladium catalyst precursor; (3) The HY molecular sieve supported palladium catalyst precursor is placed in a quartz tube and reduced in a hydrogen atmosphere to obtain the Pd / HY bifunctional catalyst.

[0010] The preparation process of the HY molecular sieve carrier in step (1) is as follows: the HY molecular sieve raw material is subjected to high-temperature calcination treatment to obtain the HY molecular sieve without template agent, which is the HY molecular sieve carrier; the high-temperature calcination treatment process is as follows: the HY molecular sieve raw material is placed in an air atmosphere at 400-600℃ for treatment for 1-4 hours, and the HY molecular sieve carrier is obtained after calcination treatment.

[0011] In step (2), the impregnation process is as follows: Take 200-1000 ml of the HY molecular sieve support obtained after calcination in step (1) and place it in a beaker. Add 1-5 mL of anhydrous ethanol. Calculate the amount of palladium nitrate solution to be used based on the palladium loading in the catalyst. Then add it to an aqueous palladium nitrate solution with a Pd concentration of 5-15 mg / mL to meet the required palladium loading of the catalyst. Stir until dry to obtain the catalyst precursor.

[0012] Preparation of the palladium nitrate aqueous solution: Dissolve palladium nitrate in deionized water to obtain a palladium nitrate aqueous solution with a Pd concentration of 5-15 mg / mL. Add 1 drop of concentrated hydrochloric acid (36-38% by mass) to the solution using a dropper to acidify it, thereby inhibiting the hydrolysis of palladium species. Stir until homogeneous. Then, add the obtained acidified palladium nitrate aqueous solution to the HY molecular sieve carrier dispersion for impregnation.

[0013] In step (3) during the reduction process, the hydrogen gas integral in the hydrogen atmosphere is 99.99%, the gas flow rate is 30-60 mL / min, the reduction temperature is 250~450℃, and the reduction time is 1-3 hours. After the reduction process, the HY molecular sieve supported palladium catalyst, i.e., Pd / HY bifunctional catalyst, is obtained after cooling to room temperature in the hydrogen atmosphere.

[0014] The palladium catalyst supported on the HY molecular sieve was used as a catalyst for the one-step hydrogenation cracking of polystyrene to prepare cycloalkanes. The SiO2 / Al2O3 ratio in the HY molecular sieve was 2.5-80, and the Pd loading in the catalyst was 0.1-0.9 wt%.

[0015] The process for preparing cycloalkanes by one-step hydrocracking of waste polystyrene plastics is as follows: The hydrocracking reaction is carried out under solvent-free conditions. Polystyrene plastic is weighed and preheated to 50-200℃ to melt it. A weighed catalyst is then added to the reaction vessel, with a polystyrene substrate to catalyst mass ratio of 5-15:1. At room temperature, the vessel is first filled with nitrogen and its airtightness is checked. If the airtightness is good, the reaction vessel is purged with hydrogen three times. After purging, hydrogen is introduced to the specified pressure, and the temperature is increased at a rate of 5℃ / min to the specified temperature. The reaction is then carried out under stirring.

[0016] The reaction temperature is 240–300°C.

[0017] The reaction time is 2 to 10 hours.

[0018] The pressure of the hydrogen gas is 0.1–5 MPa. The polystyrene plastic mentioned is waste polystyrene plastic.

[0019] The present invention has the following advantages and beneficial effects: 1. This invention uses waste polystyrene plastics as raw materials and conducts a one-step hydrocracking reaction in a batch reactor using a Pd / HY bifunctional catalyst under a hydrogen atmosphere. This method simplifies the polystyrene resource utilization process, reduces energy consumption in the traditional polystyrene waste plastic treatment process, and simultaneously produces high-value-added cycloalkane liquid fuels, promoting the development of a circular economy.

[0020] 2. In the Pd / HY catalyst used in this invention, the HY molecular sieve provides acidic sites, which can promote the breaking of C-C bonds in the polystyrene backbone; the Pd species provides metal hydrogenation sites, which can promote hydrogen activation, aromatic ring hydrogenation, and hydrogenation of unsaturated intermediates. The interaction between the acidic sites and the metal sites can effectively improve the polystyrene conversion efficiency and promote the formation of cycloalkanes.

[0021] 3. The Pd loading in the Pd / HY catalyst of the present invention is 0.1-0.9 wt%. By adjusting the Pd loading, the matching relationship between the metal hydrogenation sites and the acidic sites of the HY molecular sieve can be adjusted, so that the catalyst can still achieve polystyrene hydrogenation cracking and cycloalkane generation with a lower amount of precious metal, which is beneficial to improving the utilization efficiency of precious metal and reducing the cost of catalyst.

[0022] 4. This invention enables the conversion of polystyrene to cycloalkanes at relatively low temperatures (240–300°C). At a reaction temperature of 260°C, the yield of liquid fuel can reach 90%. Furthermore, the lower temperature helps reduce reaction energy consumption and minimizes problems such as complex product distribution and increased side reactions caused by high-temperature cracking.

[0023] 5. This invention converts polystyrene into high-value-added cycloalkanes liquid products, which helps reduce environmental pollution caused by polystyrene waste and expands the application scenarios for converting waste plastics into liquid fuels and chemicals. Attached Figure Description

[0024] Figure 1 The XRD patterns are for HY, 001Pd / HY, 03Pd / HY, and 3Pd / HY.

[0025] Figure 2 This is a performance graph showing the yield and selectivity of cycloalkanes and aromatics in polystyrene waste plastics of the present invention under different reaction times (2h, 4h, 6h, 8h and 10h) under the conditions of Example 1. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] Preparation Example 1: The catalyst preparation process in this embodiment is as follows: HY molecular sieve raw material was calcined in a muffle furnace at 550 °C for 2 h to obtain a HY molecular sieve support with template agent removed. 300 mg of the calcined HY molecular sieve support was weighed and placed in a beaker, and 2 mL of anhydrous ethanol was added to fully disperse the HY molecular sieve support. Palladium nitrate was dissolved in deionized water to obtain a palladium nitrate aqueous solution with a Pd concentration of 10 g / L. One drop of 37% concentrated hydrochloric acid was added dropwise to the solution for acidification. Based on the target catalyst Pd loading of 0.3 wt%, the required amount of palladium nitrate aqueous solution was added to the HY molecular sieve support dispersion. Stirring continued until dry to obtain a Pd / HY bifunctional catalyst precursor. The obtained Pd / HY bifunctional catalyst precursor was placed in a quartz tube and reduced in a hydrogen atmosphere. The hydrogen gas integral was 99.99%, the gas flow rate was 30 mL / min, the reduction temperature was 350 ℃, and the reduction time was 1 h. After the reduction was completed, the catalyst was cooled to room temperature in a hydrogen atmosphere to obtain a Pd / HY bifunctional catalyst with a Pd loading of 0.3 wt%, denoted as 03Pd / HY.

[0028] Example 1: This example demonstrates the catalytic performance test of the catalyst prepared in Example 1 in the one-step hydrogenation cracking of polystyrene to prepare cycloalkanes: Weigh 1.0 g of waste polystyrene plastic and preheat it to 150 °C to melt it. Add 200 mg of the reduced catalyst and place it in a reactor. At room temperature, first fill the reactor with nitrogen and check the airtightness. If the airtightness is good, purge the reactor three times with hydrogen. After purging, introduce hydrogen at 3 MPa and raise the temperature to 260 °C at a rate of 5 °C / min. React for 10 h with stirring at 500 rpm. After the reaction, cool to room temperature and analyze the liquid phase products. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of waste polystyrene plastic is >99%, the total yield of cycloalkanes and aromatics is 90%, and the selectivity of cycloalkanes is 95%.

[0029] Example 2:

[0030] The catalyst was prepared according to the method of Preparation Example 1. The operation of Example 1 was followed, except that the reaction temperature was 300°C and the reaction time was 3 hours; all other conditions remained unchanged. After the reaction, the liquid phase products were analyzed at room temperature. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was >99%, the total yield of cycloalkanes and aromatics was 95%, and the selectivity of cycloalkanes was 92%.

[0031] Example 3: The catalyst was prepared according to the method of Preparation Example 1, except that a Pd / HY bifunctional catalyst with a Pd loading of 0.7 wt% was prepared by adjusting the amount of palladium nitrate aqueous solution added, denoted as 07Pd / HY.

[0032] Following the procedure of Example 1, except that the catalyst was 07Pd / HY, all other conditions remained unchanged. After the reaction was completed, the liquid phase products were analyzed at room temperature. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was >99%, the total yield of cycloalkanes and aromatics was 85%, and the selectivity of cycloalkanes was 96%.

[0033] Comparative Example 1: Catalyst preparation: HY molecular sieve raw material was calcined in a muffle furnace at 550 °C for 2 h to obtain a HY molecular sieve support with template agent removed. 300 mg of the calcined HY molecular sieve support was weighed and placed in a beaker, and 2 mL of anhydrous ethanol was added to fully disperse the HY molecular sieve support. Chloroplatinic acid was dissolved in deionized water to obtain a chloroplatinic acid aqueous solution with a Pt concentration of 20 g / L. Based on the target catalyst Pt loading of 0.3 wt%, the required amount of chloroplatinic acid aqueous solution was added to the HY molecular sieve support dispersion. Stirring continued until dry to obtain a Pt / HY bifunctional catalyst precursor. The obtained Pt / HY bifunctional catalyst precursor was placed in a quartz tube and reduced in a hydrogen atmosphere. The hydrogen gas integral was 99.99%, the gas flow rate was 30 mL / min, the reduction temperature was 350 °C, and the reduction time was 1 h. After reduction, the catalyst was cooled to room temperature in a hydrogen atmosphere to obtain the Pt / HY bifunctional catalyst. By adjusting the amount of chloroplatinic acid solution added, a Pt / HY bifunctional catalyst with a Pt loading of 0.3 wt% could be prepared, denoted as 03Pt / HY.

[0034] Following the procedure of Example 1, except that the catalyst was 03Pt / HY, all other conditions remained unchanged. After the reaction was completed, the liquid phase products were analyzed. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was >90%, the total yield of cycloalkanes and aromatics was 61%, and the selectivity of cycloalkanes was 96%.

[0035] Comparative Example 2: Catalyst preparation: Hβ molecular sieve raw material was calcined in a muffle furnace at 550 °C for 2 h to obtain Hβ molecular sieve support with template agent removed. 300 mg of the calcined HY molecular sieve support was weighed and placed in a beaker, and 2 mL of anhydrous ethanol was added to fully disperse the Hβ molecular sieve support. Palladium nitrate was dissolved in deionized water to obtain a palladium nitrate aqueous solution with a Pd concentration of 10 g / L. One drop of 37% concentrated hydrochloric acid was added dropwise to the solution for acidification. Based on the target catalyst Pd loading of 0.3 wt%, the required amount of palladium nitrate aqueous solution was added to the Hβ molecular sieve support dispersion. Stirring continued until dry to obtain the Pd / Hβ bifunctional catalyst precursor. The obtained Pd / Hβ bifunctional catalyst precursor was placed in a quartz tube and reduced under a hydrogen atmosphere. The hydrogen gas integral was 99.99%, the gas flow rate was 30 mL / min, the reduction temperature was 350 ℃, and the reduction time was 1 h. After the reduction was completed, the catalyst was cooled to room temperature in a hydrogen atmosphere to obtain a Pd / Hβ bifunctional catalyst with a Pd loading of 0.3 wt%, denoted as 03Pd / Hβ.

[0036] Following the procedure of Example 1, except that the catalyst was O3Pd / Hβ, all other conditions remained unchanged. After the reaction was completed, the liquid phase products were analyzed. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was <80%, the total yield of cycloalkanes and aromatics was 35%, and the selectivity of cycloalkanes was 96%.

[0037] Comparative Example 3: Catalyst preparation: HY molecular sieve raw material was calcined in a muffle furnace at 550 °C for 2 h to obtain a HY molecular sieve support with template agent removed. 300 mg of the calcined HY molecular sieve support was weighed and placed in a beaker, and 2 mL of anhydrous ethanol was added to fully disperse the HY molecular sieve support. Palladium nitrate was dissolved in deionized water to obtain a palladium nitrate aqueous solution with a Pd concentration of 10 g / L. One drop of 36–38% concentrated hydrochloric acid was added dropwise to the solution for acidification. Based on the target catalyst Pd loading of 0.01 wt%, the required amount of palladium nitrate aqueous solution was added to the HY molecular sieve support dispersion. Stirring continued until dry to obtain a Pd / HY bifunctional catalyst precursor. The obtained Pd / HY bifunctional catalyst precursor was placed in a quartz tube and reduced under a hydrogen atmosphere. The hydrogen gas integral was 99.99%, the gas flow rate was 30 mL / min, the reduction temperature was 250–450 °C, and the reduction time was 1–3 h. After reduction, the catalyst was cooled to room temperature in a hydrogen atmosphere to obtain the Pd / HY bifunctional catalyst. By adjusting the amount of palladium nitrate solution added, a Pd / HY bifunctional catalyst with a Pd loading of 0.01 wt% can be prepared, denoted as 001Pd / HY.

[0038] Following the procedure of Example 1, except that the catalyst was 001Pd / HY, all other conditions remained unchanged. After the reaction, the liquid phase products were analyzed. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was <80%, the total yield of cycloalkanes and aromatics was 41%, and the selectivity of cycloalkanes was 32%.

[0039] Comparative Example 4: Catalyst preparation: The method of Comparative Example 1 is the same, except that by adjusting the amount of palladium nitrate solution added, a Pd / HY bifunctional catalyst with a Pd loading of 3 wt% can be prepared, denoted as 3Pd / HY.

[0040] Following the procedure of Example 1, except that the catalyst was 3Pd / HY and other conditions remained unchanged, the liquid phase products were analyzed after the reaction was completed. In the one-step hydrogenation cracking products of polystyrene, the conversion rate of polystyrene waste plastic was <80%, the total yield of cycloalkanes and aromatics was 55%, and the selectivity of cycloalkanes was 95%.

[0041] A comparison of Comparative Example 1 and Example 1 shows that, under the same support, metal loading, and reaction conditions, the 03Pd / HY catalyst exhibits higher cycloalkane yield and selectivity than the 03Pt / HY catalyst, indicating that Pd species are more suitable for the hydrogenation stabilization of polystyrene cracking intermediates and the hydrogenation of aromatic rings. A comparison of Comparative Example 2 and Example 1 shows that, under the same active metal, metal loading, and reaction conditions, the 03Pd / HY catalyst exhibits higher cycloalkane yield and selectivity than the 03Pd / Hβ catalyst, indicating that the acidic site distribution and pore structure of the HY molecular sieve are more favorable for polystyrene main chain cracking and intermediate product conversion. A comparison of Comparative Examples 3, 4, and Example 1 shows that, by using a palladium catalyst supported on HY molecular sieve (03Pd / HY), this application can further improve the yield and selectivity of one-step hydrogenation cracking of polystyrene to cycloalkanes compared to 001Pd / HY and 3Pd / HY, under the same reaction conditions.

[0042] By utilizing the Pd / HY bifunctional catalyst of this invention, the hydrogenation capability of Pd metal sites and the pyrolysis capability of HY molecular sieve acidic sites are effectively synergistically combined. This enables a one-step hydrocracking process from polystyrene waste plastics to produce high-value-added cycloalkane liquid fuels with high selectivity and high yield, at relatively low noble metal loading and reaction temperatures. This one-step hydrocracking catalytic method for polystyrene waste plastics helps reduce environmental pollution and resource waste caused by plastic waste and expands the application scenarios for converting waste plastics into liquid fuels and high-value chemicals.

[0043] The above examples are for reference only. Any technical solutions that are similar to or derived from the concept of this patent are within the scope of protection of this invention.

Claims

1. A method for preparing cycloalkanes from polystyrene plastic via one-step hydrogenation cracking, characterized in that: The molten polystyrene plastic substrate and catalyst are added to a batch reactor and subjected to a hydrocracking reaction under a hydrogen atmosphere, so that polystyrene can be directly converted into a liquid product containing cycloalkane in one step. The catalyst is a Pd / HY molecular sieve bifunctional catalyst, which includes a metal active component Pd and a HY molecular sieve support. The content of palladium in the catalyst accounts for 0.1 to 0.9 wt%.

2. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 1, characterized in that: In the Pd / HY molecular sieve bifunctional catalyst, the HY molecular sieve support provides acidic sites to promote the CC cleavage of polystyrene; the Pd species provides metal hydrogenation sites to promote the hydrogenation of aromatic rings and the hydrogenation of unsaturated intermediates, thereby achieving highly selective conversion of polystyrene to cycloalkanes.

3. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 1, characterized in that: The SiO2 / Al2O3 ratio in the HY molecular sieve support is 2.5-80.

4. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 1, characterized in that: The preparation method of Pd / HY molecular sieve bifunctional catalyst includes the following steps: (1) First, HY molecular sieve carriers were prepared by calcination using HY molecular sieve as raw material; (2) Palladium species were impregnated onto the HY molecular sieve support by impregnation method to obtain Pd / HY molecular sieve bifunctional catalyst precursor; (3) The Pd / HY molecular sieve bifunctional catalyst precursor is placed in a quartz tube and reduced in a hydrogen atmosphere to obtain the Pd / HY bifunctional catalyst.

5. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 4, characterized in that: The preparation process of the HY molecular sieve carrier in step (1) is as follows: the HY molecular sieve raw material is subjected to high-temperature calcination treatment to obtain the HY molecular sieve without template agent, which is the HY molecular sieve carrier; the high-temperature calcination treatment process is as follows: the HY molecular sieve raw material is placed at 400-600℃ for treatment for 1 to 4 hours, and the HY molecular sieve carrier is obtained after calcination treatment.

6. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 4, characterized in that: In step (2), the impregnation process is as follows: 200~1000 mg of the HY molecular sieve support obtained after calcination treatment in step (1) is placed in a beaker, 1~5 mL of anhydrous ethanol is added, and then an aqueous solution of palladium nitrate with a Pd concentration of 5~15 mg / mL is added to meet the palladium loading requirements of the catalyst. The mixture is stirred at room temperature until dry to obtain the Pd / HY bifunctional catalyst precursor.

7. The method for preparing cycloalkanes from polystyrene plastic by one-step hydrogenation cracking according to claim 4, characterized in that: In step (3) during the reduction process, the hydrogen gas integral in the hydrogen atmosphere is 99.99%, the gas flow rate is 30-60 mL / min, the reduction temperature is 250~450℃, and the reduction time is 1-3 hours. After the reduction process, the Pd / HY bifunctional catalyst is obtained by cooling the hydrogen atmosphere to room temperature.

8. The one-step hydrogenation cracking of polystyrene to prepare cycloalkanes according to claim 1, characterized in that: The hydrocracking reaction is carried out under solvent-free conditions.

9. The one-step hydrogenation cracking of polystyrene to prepare cycloalkanes according to claim 1 or 8, characterized in that: In the one-step hydrogenation cracking process for preparing cycloalkanes from polystyrene, the mass ratio of polystyrene plastic substrate to catalyst is 5-15:1, the reaction temperature is 240-300℃, the reaction time is 2-10 h, and the hydrogen pressure is 0.1-5 MPa.

10. The method according to claim 1, characterized in that: The cycloalkane includes one or more of methylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, and dimethylcyclohexane, wherein the dimethylcyclohexane includes one or more of 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohexane.

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