Method for preparing ethylbenzene through alcohol-mediated polystyrene catalytic hydrogenolysis and catalyst thereof

Abstract

The invention discloses a method for preparing ethylbenzene through alcohol-mediated polystyrene catalytic hydrogenolysis and a catalyst thereof. Comprising the following steps: mixing a copper salt solution with an alkaline oxide dispersion liquid, dropwise adding an alkaline precipitator under a heating condition to adjust the pH value to 4-10, centrifuging, washing, drying and calcining to obtain the catalyst. The catalytic hydrogenolysis method comprises the following steps: adding polystyrene, a catalyst and alcohol into a reactor together, and reacting for 1-24 hours at 300-500 DEG C in an inert atmosphere to obtain ethylbenzene. The core of the method is that the alcohol is used as a reaction medium and an in-situ hydrogen source, the hydrogenolysis reaction of polystyrene is realized under the catalytic action, the dependence on high-risk and high-pressure externally supplied hydrogen in the traditional process is avoided, and the process safety is remarkably improved. And the preparation process is simple, low in cost and easy to recycle. By applying the method, the yield of light aromatic hydrocarbon can reach 70% or above, the yield of ethylbenzene can reach 42% or above, and a novel and efficient solution is provided for safe and high-valued recovery of polystyrene waste.

Description

Technical Field

[0001] This invention relates to the fields of catalyst preparation and plastic resource utilization, specifically to a copper-based catalyst for the catalytic hydrogenolysis of polystyrene, its preparation method, and a method for the catalytic hydrogenolysis of polystyrene to ethylbenzene mediated by alcohol without the need for external hydrogen supply. Background Technology

[0002] Polystyrene (PS), as one of the most widely produced general-purpose plastics, is chemically stable and difficult to degrade naturally. Traditional methods of polystyrene recycling include incineration, landfill, and mechanical recycling. However, incineration or landfill processes pollute the natural environment, resulting not only in resource waste but also secondary pollution. Therefore, developing chemical recycling technologies for polystyrene waste to efficiently convert it into high-value basic chemicals such as styrene and ethylbenzene is a key path to achieving a circular economy for plastics.

[0003] Currently, the main pathways for catalytically converting polystyrene into chemicals are catalytic cracking and catalytic hydrogenolysis. However, these existing technologies generally suffer from limitations such as complex processes, poor selectivity, or high safety requirements. In the catalytic cracking pathway, the core technology lies in breaking the long chains of polystyrene through catalytic action to obtain styrene monomers. For example, Chinese invention patent CN117185890A discloses a method for thermally cracking waste polystyrene in a water vapor environment in a semi-batch or continuous manner to produce styrene and ethylbenzene. Although this avoids the use of organic solvents, water vapor at high temperatures is corrosive to the reaction equipment, resulting in high equipment maintenance costs. Patent CN111100325A discloses a microwave high-temperature cracking method for waste polystyrene. Its characteristic is that the waste polystyrene is brought into contact with a porous composite material, and a microwave field is applied to rapidly reach high temperatures, causing the waste polystyrene to crack and allowing for rapid recovery of polystyrene in a short time. However, this method has high energy consumption and requires a large amount of catalyst, which is not conducive to large-scale application. The common problem with this type of catalytic cracking technology is that the reaction process lacks the active intervention of active hydrogen and mainly involves the random breaking of C-C bonds, resulting in a wide product distribution and low selectivity for high-value-added products such as ethylbenzene.

[0004] To obtain more selective ethylbenzene and improve product quality, catalytic hydrogenolysis is a more promising pathway. However, existing technologies require a hydrogen supply to the reaction system. For example, most literature and patented technologies require a high-pressure hydrogen cylinder and other hydrogen supply systems, operating under high temperature and pressure (e.g., reaction pressure often needs to be 2-5 MPa or even higher). This undoubtedly increases the complexity and safety risks of the process, imposes stringent requirements on the pressure resistance and safety protection of the reaction equipment, and also drives up the investment and operating costs of the equipment, limiting its application in a wider range of scenarios. In summary, developing a novel catalytic hydrogenolysis technology that does not rely on an external hydrogen supply, is simple and safe, and can efficiently and selectively convert polystyrene to ethylbenzene has significant practical and economic value. Summary of the Invention

[0005] In view of the deficiencies of the prior art described in the background section, the primary objective of this invention is to provide a copper-based catalyst for the catalytic hydrogenolysis of polystyrene. This catalyst has a simple preparation method, low cost, and uniform dispersion of its active components.

[0006] The core objective of this invention is to provide an alcohol-mediated method for the catalytic hydrogenolysis of polystyrene to ethylbenzene. This method uses alcohol as the reaction medium and an in-situ hydrogen source, achieving highly efficient and selective conversion of polystyrene without the need for additional high-pressure hydrogen gas. This fundamentally avoids the safety risks and equipment costs associated with external hydrogen supply, providing a novel solution for the safe and high-value recycling of polystyrene waste.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution: A copper-based catalyst for the catalytic hydrogenolysis of polystyrene, wherein the catalyst is composed of copper species supported on an alkaline oxide support, and is prepared by the following steps: S1. Add copper salt to deionized water and stir evenly at 25~90°C to obtain solution A; disperse alkaline oxide in deionized water to obtain suspension B; add sodium salt to deionized water and stir to obtain solution C; S2. Mix the solution A and the suspension B, and add solution C dropwise to it under stirring at 25~90°C until the pH of the system is 4~10 to obtain the mixed slurry D; S3. After the reaction is completed, the mixed slurry D is centrifuged, separated into solid and liquid, washed and dried to obtain the catalyst precursor, and then calcined in air at 200~500°C for 2~8 h to obtain the copper-based catalyst.

[0008] Preferably, in step S1, the liquid-to-solid ratio of deionized water to copper salt in solution A is (100~500):1mL / g; the mass ratio of copper salt to alkaline oxide is (0.25~1):1; and the liquid-to-solid ratio of deionized water to sodium salt in solution C is (10~30):1mL / g.

[0009] Preferably, in step S1, the copper salt is selected from at least one of copper acetate, copper nitrate, copper chloride, or copper sulfate; the alkaline oxide is selected from one of zirconium oxide, cerium oxide, lanthanum oxide, or molybdenum oxide; and the sodium salt is selected from at least one of sodium carbonate, sodium sulfate, sodium chloride, or sodium bicarbonate.

[0010] Preferably, in step S3, the calcination temperature is 300~500°C and the calcination time is 2~8 h.

[0011] An alcohol-mediated catalytic hydrogenolysis method for the production of ethylbenzene from polystyrene, using the aforementioned copper-based catalyst, includes the following steps: Polystyrene, the copper-based catalyst, and the alcohol were placed together in a pressure-resistant reactor. After the air inside the reactor was replaced with an inert atmosphere, the reaction was carried out at 350-450°C for 3-24 hours to obtain the product ethylbenzene. The alcohol serves as the reaction medium and in-situ hydrogen source, eliminating the need for additional hydrogen gas.

[0012] Preferably, the alcohol is a C2-C6 fatty alcohol or alicyclic alcohol, preferably at least one of ethanol, ethylene glycol, isopropanol or cyclohexanol.

[0013] Preferably, the inert atmosphere is nitrogen or argon, and the initial pressure of the reaction system is 0.1~2 MPa.

[0014] Preferably, the mass ratio of the alcohol to polystyrene is (2~20):1; and the mass ratio of the copper-based catalyst to polystyrene is (0.2~3):1.

[0015] Preferably, the reaction temperature is 360~420 °C and the reaction time is 4~24 hours.

[0016] Preferably, the method further includes: after the reaction is completed, separating and recovering the copper-based catalyst, and using it directly or after regeneration for the next batch of reaction.

[0017] The products were characterized by gas chromatography. The yields of the light aromatic hydrocarbons (a mixture of benzene, toluene, xylene, ethylbenzene, and styrene) and ethylbenzene were calculated using the following formulas:

[0018] The amount of polystyrene before the reaction is expressed as the relative molecular mass of C8H8.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. The innovation and advantage of this invention lies in the fact that by using alcohol as an in-situ hydrogen source, it completely avoids the dependence of traditional technology on high-pressure external hydrogen supply, eliminates major safety hazards from the source, and significantly reduces the requirements for equipment pressure resistance and operating costs.

[0020] 2. The method of this invention achieves highly efficient synergy between polystyrene pyrolysis and in-situ hydrogenation (hydrogenolysis), effectively guiding the reaction towards ethylbenzene production while suppressing the generation of light gases and coke, thereby significantly improving the selectivity of the target product. Using this method, the yield of light aromatics can reach over 70%, and the yield of ethylbenzene can reach over 42%.

[0021] 3. The copper-based catalyst used has the dual function of activating C-C bonds and alcohol molecules, allowing cracking and hydrogen donation to proceed synergistically on the same catalyst without the need to introduce other promoters or complex steps.

[0022] 4. The catalyst preparation raw materials are readily available, the method is simple, and the reaction product is easy to separate and recover. The entire process route is concise, avoiding precious metals and hazardous hydrogen, providing an economical and feasible new approach for the resource utilization of polystyrene waste. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of copper-supported alkaline oxide catalysts.

[0024] Figure 2 The image shows the XRD pattern of the copper-supported alkaline oxide catalyst obtained in Example 4.

[0025] Figure 3 (ab) Scanning electron microscope image of the CuO / La2O3 catalyst obtained in Example 4; (cf) SEM-EDS elemental mapping diagram.

[0026] Figure 4 Example 42 shows the results of the catalyst recycling verification test. Detailed Implementation

[0027] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0028] Example 1: A method for preparing a Cu / ZrO2 catalyst, comprising the following steps:

[0029] 1.0 g of copper acetate monohydrate was weighed and added to a 500 mL round-bottom flask. 100 mL of deionized water was slowly added, and the mixture was stirred at 50 °C to obtain a clear solution A. Simultaneously, a 100 mL beaker was filled with 30 mL of deionized water, and 2.0 g of zirconium oxide was dispersed in it. The mixture was sonicated to obtain a suspension B. Another 100 mL beaker was filled with 0.5 g of sodium carbonate and 50 mL of deionized water, and the mixture was stirred to obtain solution C. Solution A and suspension B were mixed at 70 °C with stirring. Solution C was added dropwise to the mixture using a constant-pressure dropping funnel, and the pH was monitored until it stabilized at 6, yielding a mixed slurry D. Heating was stopped, and the mixture was stirred and aged for 1 hour. The slurry was then centrifuged, and the precipitate was washed with deionized water until the eluent was neutralized. The eluent was then dried in an oven for 12 hours to obtain the precursor. The precursor was placed in a muffle furnace and calcined at 300 °C for 4 hours to obtain a Cu / ZrO2 catalyst.

[0030] Example 2: A method for preparing a Cu / CeO2 catalyst, comprising the following steps: 1.5 g of copper nitrate trihydrate was weighed and added to a 500 mL round-bottom flask. 300 mL of deionized water was slowly added, and the mixture was stirred at 60°C to obtain solution A. Simultaneously, a 100 mL beaker was filled with 60 mL of deionized water, and 1.0 g of cerium oxide was dispersed in it. The mixture was sonicated to obtain suspension B. Another 100 mL beaker was filled with 1.0 g of sodium bicarbonate and 80 mL of deionized water, and the mixture was stirred to obtain solution C. Solution A and suspension B were mixed at 40°C with stirring. Solution C was added dropwise to the mixture using a constant-pressure dropping funnel until the pH reached 5. Subsequent centrifugation, washing, and drying procedures were the same as in Example 1. The dried precursor was calcined at 400°C for 8 hours to obtain the Cu / CeO2 catalyst.

[0031] Example 3: A method for preparing a Cu / La2O3 catalyst, comprising the following steps:

[0032] 1.5 g of copper nitrate trihydrate was weighed and added to a 500 mL round-bottom flask. 300 mL of deionized water was slowly added, and the mixture was stirred at 60°C to obtain solution A. Simultaneously, a 100 mL beaker was filled with 60 mL of deionized water, and 1.8 g of cerium oxide was dispersed in it. The mixture was then sonicated to obtain suspension B. Another 100 mL beaker was filled with 1.0 g of sodium bicarbonate and 80 mL of deionized water, and the mixture was stirred to obtain solution C. Solution A and suspension B were mixed at 40°C with stirring. Solution C was added dropwise to the mixture using a constant-pressure dropping funnel until the pH reached 9. Subsequent centrifugation, washing, and drying procedures were the same as in Example 1. The dried precursor was calcined at 400°C for 8 hours to obtain the Cu / La₂O₃ catalyst.

[0033] Example 4: A method for preparing a Cu / La2O3 catalyst, comprising the following steps: 0.5 g of anhydrous copper chloride was weighed and added to a 500 mL round-bottom flask. 200 mL of deionized water was slowly added, and the mixture was stirred at 25°C to obtain solution A. Simultaneously, a 100 mL beaker was filled with 60 mL of deionized water, and 1.8 g of cerium oxide was dispersed in it. The mixture was then sonicated to obtain suspension B. Another 100 mL beaker was filled with 0.5 g of sodium sulfate and 70 mL of deionized water, and the mixture was stirred to obtain solution C. Solution A and suspension B were mixed at 30°C with stirring. Solution C was added dropwise to the mixture using a constant-pressure dropping funnel until the pH reached 9. Subsequent centrifugation, washing, and drying steps were the same as in Example 1. The dried precursor was calcined at 500°C for 3 hours to obtain the Cu / La₂O₃ catalyst. The XRD pattern of the catalyst is shown below. Figure 2 As shown. From Figure 2 As can be seen, the diffraction peaks of the copper-supported alkaline oxide catalyst and the standard substance correspond, indicating that the copper-supported alkaline oxide catalyst was successfully prepared. Furthermore, the absence of obvious peaks at the copper sites indicates uniform loading. The scanning electron microscope image of the catalyst is shown below. Figure 3 As shown in (a,b), the CuO / La2O3 catalyst is composed of wide and short rod-shaped units stacked together to form a porous structure. This structure can increase the surface reaction area and improve the efficiency of in-situ hydrogenolysis of polystyrene. Figure 3 (cf) The SEM-EDS spectrum of the CuO / La2O3 catalyst shows that Cu elements are uniformly distributed on the La2O3 surface. The high degree of Cu element dispersion can improve the surface reaction activity of the CuO / La2O3 catalyst.

[0034] Example 5: A method for preparing a Cu / MoO3 catalyst, comprising the following steps: 0.8 g of copper was weighed and added to copper nitrate trihydrate in a 500 mL round-bottom flask. 240 mL of deionized water was slowly added, and the mixture was stirred at 60°C to obtain solution A. Simultaneously, a 100 mL beaker was filled with 60 mL of deionized water, and 1.0 g of molybdenum oxide was dispersed in it. The mixture was sonicated to obtain suspension B. Another 100 mL beaker was filled with 0.8 g of sodium carbonate and 24 mL of deionized water, and the mixture was stirred to obtain solution C. Solution A and suspension B were mixed at 70°C with stirring. Solution C was added dropwise to the mixture using a constant-pressure dropping funnel until the pH reached 8. Subsequent centrifugation, washing, and drying procedures were the same as in Example 1. The dried precursor was calcined at 400°C for 5 hours to obtain the Cu / MoO3 catalyst.

[0035] Examples 6-11: Effects of different catalysts on the catalytic hydrogenolysis of polystyrene to ethylbenzene This set of examples aims to illustrate the effect of different catalysts on the performance of alcohol-mediated catalytic hydrogenolysis of polystyrene to ethylbenzene, including the following steps: 500 mg of polystyrene powder, 200 mg of the Cu / La₂O₃ catalyst obtained in Example 4, and 1.0 g of cyclohexanol were added sequentially to a 50 mL reactor. The reactor was sealed, and the air inside was repeatedly purged with nitrogen three times. Finally, nitrogen was introduced until the initial pressure was 0.3 MPa. The reactor was placed in a heater, and the temperature was increased to 390 °C at a rate of 10 °C / min. The reaction was carried out at this temperature for 6 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The product was washed out several times with 80 mL of dichloromethane. The washings were collected and diluted to volume with a 100 mL volumetric flask. The product was sampled and analyzed by gas chromatography, and the product was quantified using the external standard method. The results showed that the copper-supported basic oxide catalyst of the present invention can be used for the efficient catalytic cracking of polystyrene to prepare light aromatic hydrocarbons, including benzene, toluene, ethylbenzene, and styrene, with ethylbenzene showing the highest selectivity.

[0036] Table 1. Effects of different catalysts

[0037] Examples 11-16: Effects of different reaction temperatures and times In this set of examples, the Cu / La2O3 obtained in Example 4 was used as a catalyst to investigate the effects of reaction temperature and time on the yields of light aromatics and ethylbenzene. The operating procedures were the same as in Example 6, only the reaction temperature and time were changed. The results are summarized in Table 2. The data show that this method can effectively catalytically hydrogenate polystyrene to obtain high-value products at 360~410°C for 4~24 h.

[0038] Table 2. Effects of reaction temperature and time

[0039] Examples 17-19: The effect of the type of alcohol on the reaction In this set of examples, the Cu / La2O3 obtained in Example 4 was used as the catalyst to systematically compare the effects of different alcohols on the yields of polystyrene catalytic hydrogenolysis to light aromatics and ethylbenzene. The operation was the same as in Example 6, only the alcohol was changed, and the results are shown in Table 3.

[0040] Table 3. Effects of different alcohols

[0041] Examples 20-28: Effect of the mass ratio of isopropanol and catalyst to polystyrene on the reaction In this set of examples, the Cu / La2O3 obtained in Example 4 was used as the catalyst and isopropanol as the hydrogen source. The effects of alcohol / styrene (mass ratio) and catalyst / styrene (mass ratio) on the yield of polystyrene catalytic hydrogenolysis to light aromatics and ethylbenzene were compared systematically. The operation was the same as in Example 6, and the results are shown in Table 4.

[0042] Table 4. Effects of alcohol / styrene (mass ratio) and catalyst / styrene (mass ratio)

[0043] Examples 29-33: Effects of Reaction Atmosphere and Pressure In this set of examples, the Cu / La2O3 obtained in Example 4 was used as the catalyst, and isopropanol was used as the hydrogen source to explore the effects of inert atmosphere and pressure on the yield of polystyrene catalytic hydrogenolysis to light aromatics and ethylbenzene. The operation was the same as in Example 6, and the results are shown in Table 5.

[0044] Table 5. Effects of Atmosphere and Pressure

[0045] Example 42: Validation of catalyst recovery This set of examples is based on the reaction conditions of Example 9, completing the first reaction. After the reaction was completed, the reaction vessel was cooled, and the entire reaction mixture was transferred to a centrifuge tube. The solid catalyst was washed three times with ethanol by centrifugation. The recovered solid was dried at 80°C for 4 hours and used directly in the next reaction without any regeneration treatment. The second reaction was carried out under the same reaction conditions. This process was repeated for a total of five experiments. The operation was the same as in Example 6, and the results are shown in Example 9. Figure 4 The results showed that after five catalytic cycles, the ethylbenzene yield was 50%. This indicates that the catalyst of the present invention has good recyclability and reusability, with minimal decrease in activity.

Claims

1. A copper-based catalyst for the catalytic hydrogenolysis of polystyrene, characterized in that, The catalyst is composed of copper species supported on an alkaline oxide support and is prepared by the following steps: S1. Add copper salt to deionized water and stir evenly at 25~90°C to obtain solution A; disperse alkaline oxide in deionized water to obtain suspension B; add sodium salt to deionized water and stir to obtain solution C; S2. Mix the solution A and the suspension B, and add solution C dropwise to it under stirring at 25~90°C until the pH of the system is 4~10 to obtain the mixed slurry D; S3. After the reaction is completed, the mixed slurry D is centrifuged, separated into solid and liquid, washed and dried to obtain the catalyst precursor, and then calcined in air at 200~500°C for 2~8 h to obtain the copper-based catalyst.

2. The method for preparing the copper-based catalyst according to claim 1, characterized in that, In step S1, the liquid-to-solid ratio of deionized water to copper salt in solution A is (100~500):1 mL / g; the mass ratio of copper salt to alkaline oxide is (0.25~1):1; and the liquid-to-solid ratio of deionized water to sodium salt in solution C is (10~30):1 mL / g.

3. The method for preparing the copper-based catalyst as described in claim 1, characterized in that, In step S1, the copper salt is selected from at least one of copper acetate, copper nitrate, copper chloride, or copper sulfate; the alkaline oxide is selected from one of zirconium oxide, cerium oxide, lanthanum oxide, or molybdenum oxide; and the sodium salt is selected from at least one of sodium carbonate, sodium sulfate, sodium chloride, or sodium bicarbonate.

4. The method for preparing the copper-based catalyst as described in claim 1, characterized in that, In step S3, the calcination temperature is 300~500°C and the calcination time is 2~8 h.

5. A method for the catalytic hydrogenolysis of polystyrene mediated to produce ethylbenzene, characterized in that, The method of using the copper-based catalyst according to any one of claims 1-4 includes the following steps: Polystyrene, the copper-based catalyst, and alcohol were placed together in a pressure-resistant reactor. After the air inside the reactor was replaced with an inert atmosphere, the reaction was carried out at 300-450°C for 3-24 hours to obtain the product ethylbenzene.

6. The method as described in claim 5, characterized in that, The alcohol is a C2-C6 fatty alcohol or alicyclic alcohol, preferably at least one of ethanol, ethylene glycol, isopropanol or cyclohexanol.

7. The method as described in claim 5, characterized in that, The inert atmosphere is nitrogen or argon, and the initial pressure of the reaction system is 0.1~2 MPa.

8. The method of claim 5, wherein, The mass ratio of the alcohol to polystyrene is (2~20):1; the mass ratio of the copper-based catalyst to polystyrene is (0.2~3):

1.

9. The method of claim 5, wherein, The reaction temperature is 360~410 °C, and the reaction time is 4~24 hours.

10. The method of claim 5, wherein, The method further includes: after the reaction is completed, separating and recovering the copper-based catalyst, and using it directly or after regeneration for the next batch of reaction.

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