Process for the preparation of polycyclohexylethylene by catalytic hydrogenation of polystyrene and catalyst

Abstract

The application relates to the technical field of high polymer materials, and provides a method for preparing polycyclohexyl ethylene by catalytically hydrogenating polystyrene and a catalyst. The catalyst is a graphene-loaded Pd catalyst. The catalyst is applied to the hydrogenation reaction of polystyrene, the amount of the catalyst is small, the catalyst has very high low-temperature reaction activity, and is very suitable for industrial production; and the hydrogenation product polycyclohexyl ethylene does not have obvious chain scission, and the product has good performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a method and catalyst for the catalytic hydrogenation of polystyrene to prepare polycyclohexylethylene. Background Technology

[0002] Polystyrene (PS) is one of the five most widely used general-purpose plastics. It boasts high transparency, good insulation, water resistance, corrosion resistance, high colorability and printability, good processing fluidity, ease of molding, and aesthetically pleasing products. However, due to its poor heat and UV resistance, and brittleness, PS is currently only used in low-end products such as food packaging, toys, clothes hangers, containers, and foam plastics, and may gradually be replaced by the cheaper raw material polypropylene. In high-end applications (such as vehicle parts, optical instruments, new game consoles, and mobile phones), polycarbonate (PC), polymethyl methacrylate (PMMA), and acrylonitrile butadiene styrene (ABS) are widely used, but are expensive.

[0003] When catalytic hydrogenation partially or completely opens the large π bonds of the benzene ring in polystyrene, hydrogenated polystyrene (PCHE) is obtained, and its various properties are significantly improved: the glass transition temperature is greatly increased, the oxidation resistance and heat resistance are better, and it has better regularity and crystallinity, lower density, and lower water absorption. These advantages give PCHE broad application prospects; it can be used as engineering plastics, optical information recording materials, etc., and is expected to replace expensive materials such as PC.

[0004] Current research on catalytic systems for the hydrogenation of polystyrene mainly focuses on supported metal catalysts, including Pd / C, Pd / BaSO4, Pd / CNT, and Raney Ni. However, these catalysts require high concentrations, sometimes reaching 100% or more, and necessitate high reaction temperatures and pressures, as well as molecular chain breakage.

[0005] Graphene, a two-dimensional honeycomb crystal composed of a single layer of tightly packed carbon atoms, possesses a large specific surface area and excellent thermal stability, making it an excellent support for nanomaterials. Currently, researchers have prepared various highly dispersed metal nanoparticles (Pt, Au, Pd, Ag, Fe, etc.) using graphene as a support. However, research on the application of these graphene-supported nanomaterial catalysts is mainly limited to small-molecule reactions, with almost no reports on their application in polymer catalysis. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the catalytic hydrogenation of polystyrene to prepare polycyclohexylethylene and a catalyst, so as to solve the technical problems of low catalyst activity, harsh reaction conditions, and easy molecular chain scission in the prior art for the hydrogenation of polystyrene to prepare polycyclohexylethylene.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention proposes a catalyst, which is a graphene-supported Pd catalyst.

[0009] As a preferred embodiment of the catalyst provided by the present invention, the graphene is reduced graphene oxide.

[0010] As a preferred embodiment of the catalyst provided by the present invention, the mass ratio of Pd to reduced graphene oxide is (0.6-2.4):50.

[0011] Secondly, the present invention proposes a method for preparing the above-mentioned catalyst, comprising: adding graphene oxide to water, then adding palladium chloride solution and a reducing agent, mixing, and obtaining the catalyst.

[0012] As a preferred embodiment of the preparation method of the catalyst provided by the present invention, the mass ratio of palladium chloride to graphene oxide is (1-4):50.

[0013] In another preferred embodiment of the method for preparing the catalyst provided by the present invention, the reducing agent is methanol and / or formaldehyde.

[0014] As another preferred embodiment of the catalyst preparation method provided by the present invention, the method for preparing graphene oxide includes: adding graphite, concentrated sulfuric acid, sodium nitrate and potassium permanganate into a reaction vessel, reacting them successively at low temperature, medium temperature and high temperature, adding deionized water and hydrogen peroxide, filtering, washing and drying to obtain graphene oxide, and ultrasonically exfoliating the graphene oxide in water to obtain graphene oxide.

[0015] More preferably, the low temperature is 0–5°C and the low temperature reaction time is 0.5–3 h; and / or, the medium temperature is 25–35°C and the medium temperature reaction time is 0.5–1.5 h; and / or, the high temperature is 90–100°C and the high temperature reaction time is 10–60 min.

[0016] As another preferred embodiment of the preparation method of the catalyst provided by the present invention, the mass ratio of concentrated sulfuric acid to graphite is (20-40):1; and / or, the mass ratio of sodium nitrate to graphite is 1:(1-3); and / or, the mass ratio of potassium permanganate to graphite is (2-5):1.

[0017] Thirdly, the present invention proposes the application of the above-mentioned catalyst or the catalyst prepared by the above-mentioned catalyst preparation method in the catalytic hydrogenation of polystyrene to prepare polycyclohexylethylene.

[0018] Fourthly, the present invention proposes a method for catalytic hydrogenation of polystyrene to prepare polycyclohexylethylene, comprising: catalytically hydrogenating polystyrene and hydrogen in a solvent under the action of the above-mentioned catalyst or a catalyst prepared by the above-mentioned catalyst preparation method.

[0019] In a preferred embodiment of the method for preparing polycyclohexylethylene by catalytic hydrogenation of polystyrene provided by the present invention, the amount of catalyst used is 5-10% of the mass of polystyrene; and / or, the solvent is at least one selected from cyclohexane, methylcyclohexane, and N,N-dimethylformamide.

[0020] Another preferred embodiment of the method for preparing polycyclohexylethylene by catalytic hydrogenation of polystyrene provided by the present invention includes:

[0021] S1. Add the catalyst, polystyrene, and solvent together into a high-pressure reactor, replace the reactor with helium and hydrogen gas successively, and set the reaction conditions to carry out the reaction;

[0022] S2. After the reaction is complete, the reactor is allowed to cool naturally to room temperature, the gas inside the reactor is exhausted, the catalyst is separated, the solvent is recovered, and polycyclohexylethylene is obtained.

[0023] More preferably, the reaction conditions include: a reaction temperature of 130–160°C, a reaction pressure of 3–6 MPa, and a reaction time of 3–10 h.

[0024] The beneficial effects of this invention are at least as follows:

[0025] The catalyst provided by this invention is used in the hydrogenation reaction of polystyrene. It requires a small amount, has very high low-temperature reactivity, and is very suitable for industrial production. Furthermore, the hydrogenation product, polycyclohexylethylene, does not exhibit significant chain scission and has good product performance. Attached Figure Description

[0026] Figure 1 This is a transmission electron microscope (TEM) image of the catalyst prepared in Example 6. Detailed Implementation

[0027] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.

[0028] This invention proposes a Pd catalyst supported on graphene.

[0029] The catalyst provided by this invention still exhibits excellent low-temperature reactivity in the hydrogenation reaction of polystyrene when its dosage is reduced to less than 10%. This is because graphene is a polystyrene... 2 The hybrid carbon atoms in the graphene-supported Pd catalyst form strong π-π interactions with the benzene rings on the polystyrene molecule, which facilitates the adsorption of polystyrene onto the catalyst. When the benzene ring is hydrogenated, the π-π interactions disappear, and the product is more easily desorbed from the catalyst surface. Therefore, the graphene-supported Pd catalyst exhibits excellent catalytic activity in the hydrogenation of polystyrene. Furthermore, when using a graphene-supported Pd catalyst, the polystyrene chains do not break during hydrogenation. This is due to the adsorption differences between polystyrene and its products on the unique two-dimensional sheets of graphene, and the elimination of internal diffusion, which accelerates the reaction rate, enabling high reactivity of polystyrene hydrogenation even at low temperatures and avoiding high-temperature pyrolysis of the molecular chains.

[0030] According to some embodiments of the present invention, the graphene is reduced graphene oxide.

[0031] According to some embodiments of the present invention, the mass ratio of Pd to reduced graphene oxide is (0.6 to 2.4): 50.

[0032] The method for preparing the catalyst provided by the present invention includes: adding graphene oxide to water, then adding palladium chloride solution and a reducing agent, mixing, and obtaining the catalyst.

[0033] This invention uses a mixture of graphene oxide and palladium chloride solution and a reducing agent to prepare a catalyst for reducing graphene oxide-supported Pd, instead of directly using a mixture of graphene and palladium chloride solution to prepare a catalyst for graphene-supported Pd. This is mainly because the inventors found during their research that graphene oxide is easier to load with sufficient Pd than graphene.

[0034] The mixing process in the above preparation method can be carried out by conventional stirring or by ultrasonic dispersion.

[0035] According to some embodiments of the present invention, the mass ratio of palladium chloride to graphene oxide is (1-4):50. For example, the mass ratio of palladium chloride to graphene oxide can be 1:50, 2:50, 2.5:50, 3:50, 4:50, etc.

[0036] According to some embodiments of the present invention, the reducing agent is methanol and / or formaldehyde.

[0037] The catalyst provided by this invention uses graphene as a support to highly disperse Pd nanoparticles, and uses relatively mild reducing agents such as methanol and formaldehyde in the preparation process. The Pd in ​​the obtained catalyst is highly dispersed, and its particle size is 2-4 nm.

[0038] According to some embodiments of the present invention, the ratio of the amount of graphene oxide to the reducing agent is 1g:(1.5-3)mL, for example, it can be 1g:1.5mL, 1g:2mL, 1g:2.5mL, 1g:3mL, etc.

[0039] According to some embodiments of the present invention, the method for preparing graphene oxide includes: adding graphite, concentrated sulfuric acid, sodium nitrate and potassium permanganate into a reaction vessel, reacting them successively at low temperature, medium temperature and high temperature, terminating the reaction by adding deionized water and hydrogen peroxide, filtering, washing with dilute hydrochloric acid and water in sequence, drying to obtain graphene oxide, and ultrasonically exfoliating the graphene oxide in water to obtain graphene oxide.

[0040] According to some embodiments of the present invention, the low temperature is 0–5°C, and the low-temperature reaction time is 0.5–3 h; and / or, the medium temperature is 25–35°C, and the medium-temperature reaction time is 0.5–1.5 h; and / or, the high temperature is 90–100°C, and the high-temperature reaction time is 10–60 min. For example: the low temperature can be 0°C, 1°C, 2°C, 4°C, 5°C, etc.; the low-temperature reaction time can be 0.5 h, 1 h, 1.2 h, 1.5 h, 2 h, 2.5 h, 3 h, etc. The medium temperature can be 25°C, 28°C, 30°C, 35°C, etc.; the medium-temperature reaction time can be 0.5 h, 0.8 h, 1 h, 1.1 h, 1.2 h, 1.5 h, etc. The high temperature can be 90°C, 91°C, 95°C, 97°C, 100°C, etc.; the high-temperature reaction time can be 10 min, 15 min, 30 min, 35 min, 45 min, 60 min, etc.

[0041] In this invention, the temperature and time of ultrasonic exfoliation are preferably set to ensure sufficient exfoliation while simultaneously preserving the morphology of the resulting graphene oxide. For example, the ultrasonic exfoliation temperature can be 30-50°C, and the time can be 1-3 hours.

[0042] According to some embodiments of the present invention, the mass ratio of concentrated sulfuric acid to graphite is (20-40):1; and / or, the mass ratio of sodium nitrate to graphite is 1:(1-3); and / or, the mass ratio of potassium permanganate to graphite is (2-5):1. For example, the mass ratio of concentrated sulfuric acid to graphite can be 20:1, 25:1, 30:1, 32:1, 36:1, 40:1, etc. The mass ratio of sodium nitrate to graphite can be 1:1, 1:1.2, 1:1.5, 1:2, 1:2.8, 1:2.9, 1:3, etc. The mass ratio of potassium permanganate to graphite can be 2:1, 2.5:1, 3:1, 4:1, 4.4:1, 5:1, etc.

[0043] The method for preparing polycyclohexylethylene by catalytic hydrogenation of polystyrene proposed in this invention includes: catalytically hydrogenating polystyrene and hydrogen in a solvent under the action of the above-mentioned catalyst or the catalyst prepared by the above-mentioned catalyst preparation method.

[0044] According to some embodiments of the present invention, the amount of catalyst used is 5-10% of the mass of polystyrene; and / or, the solvent is at least one selected from cyclohexane, methylcyclohexane, and N,N-dimethylformamide. For example, the amount of catalyst used can be 5%, 6%, 7%, 8%, 9%, 10% of the mass of polystyrene, etc. The solvent can be selected from cyclohexane, methylcyclohexane, or N,N-dimethylformamide alone, or two or three of them can be used together.

[0045] According to some embodiments of the present invention, it includes:

[0046] S1. Add the catalyst, polystyrene, and solvent together into a high-pressure reactor, replace the reactor with helium and hydrogen gas successively, and set the reaction conditions to carry out the reaction;

[0047] S2. After the reaction is complete, the reactor is allowed to cool naturally to room temperature, the gas inside the reactor is exhausted, the catalyst is separated, the solvent is recovered, and polycyclohexylethylene is obtained.

[0048] According to some embodiments of the present invention, the reaction conditions include: a reaction temperature of 130–160°C, a reaction pressure of 3–6 MPa, and a reaction time of 3–10 h. For example, the reaction temperature can be 130°C, 140°C, 150°C, 160°C, etc.; the reaction pressure can be 3 MPa, 4 MPa, 5 MPa, 6 MPa, etc.; and the reaction time can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc.

[0049] The method and catalyst for the catalytic hydrogenation of polystyrene to prepare polycyclohexylethylene provided by the present invention will be described in detail below with reference to specific embodiments.

[0050] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0051] In the embodiments and comparative examples of this invention, the dilute hydrochloric acid used is 5% hydrochloric acid, the concentrated sulfuric acid is 100% sulfuric acid, the sodium nitrate and potassium permanganate are analytical grade, and the hydrogen peroxide is 30% hydrogen peroxide.

[0052] The number-average molecular weight of the polystyrene used in the various embodiments and comparative examples of this invention is 12.2 × 10⁻⁶. 4 g / mol.

[0053] Example 1

[0054] 2g of graphite, 40g of concentrated sulfuric acid, 2g of sodium nitrate, and 4g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 0.5h, 25℃ for 0.5h, and 90℃ for 10min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.02g palladium chloride) and 2mL methanol.

[0055] 0.05 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of cyclohexane were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 150 °C and 6 MPa for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0056] Example 2

[0057] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphene oxide. 1g of graphene oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.04g palladium chloride) and 2mL methanol.

[0058] 0.08 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of cyclohexane were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 150 °C and 4 MPa for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside the reactor was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0059] Example 3

[0060] 2g of graphite, 80g of concentrated sulfuric acid, 0.7g of sodium nitrate, and 10g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 4℃ for 2h, 30℃ for 1h, and 95℃ for 60min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.08g palladium chloride) and 2mL methanol.

[0061] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of cyclohexane were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 150 °C and 4 MPa for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0062] Example 4

[0063] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphene oxide. 1g of graphene oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL methanol.

[0064] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of cyclohexane were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 6 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0065] Example 5

[0066] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL of formaldehyde.

[0067] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of methylcyclohexane were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside the reactor was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0068] Example 6

[0069] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphene oxide. 1g of graphene oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL formaldehyde. The transmission electron microscope (TEM) image of the catalyst prepared in this example is shown below. Figure 1 As shown, Figure 1 The results show that Pd is highly uniformly dispersed on the graphene sheets.

[0070] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0071] Example 7

[0072] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL of formaldehyde.

[0073] 0.05 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0074] Example 8

[0075] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL of formaldehyde.

[0076] 0.2 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0077] Example 9

[0078] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL of formaldehyde.

[0079] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 3 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0080] Example 10

[0081] 2g of graphite, 60g of concentrated sulfuric acid, 1g of sodium nitrate, and 8g of potassium permanganate were weighed and added to a flask. The mixture was reacted successively at 0℃ for 1.5h, 30℃ for 1h, and 95℃ for 30min. 300mL of deionized water and 20mL of 30% hydrogen peroxide were added, followed by filtration. The mixture was washed successively with 5% dilute hydrochloric acid and water, and dried to obtain graphite oxide. 1g of graphite oxide was ultrasonically exfoliated in water to obtain graphene oxide. A graphene-supported Pd catalyst was prepared by adding palladium chloride solution (0.06g palladium chloride) and 2mL of formaldehyde.

[0082] 0.1 g of the prepared catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 6 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0083] Compare with Example 1

[0084] 1g of commercial Pd / C catalyst, 1g of polystyrene, and 30mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 160℃ and 4MPa for 4h. After the reaction was completed, the reactor was allowed to cool to room temperature and the gas inside was purged. The solid catalyst was separated by a high-speed centrifuge, and the solvent was recovered by a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0085] Compare with Example 2

[0086] 1g of carbon nanotubes were ultrasonically dispersed in water, and then a palladium chloride solution (0.06g of palladium chloride) and 2mL of formaldehyde were added to prepare a carbon nanotube-supported Pd catalyst.

[0087] 1g of carbon nanotube-supported Pd catalyst, 1g of polystyrene, and 30mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140℃ and 4MPa for 4h. After the reaction was completed, the reactor was allowed to cool to room temperature and the gas inside was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0088] Compare with Example 3

[0089] 0.1 g of commercial Pd / C catalyst, 1 g of polystyrene, and 30 mL of N,N-dimethylformamide were added to a stainless steel high-pressure reactor. The reactor was purged with helium and then hydrogen, and the reaction was carried out at 140 °C and 4 MPa for 4 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the gas inside the reactor was purged. The solid catalyst was separated using a high-speed centrifuge, and the solvent was recovered using a rotary evaporator. The polystyrene conversion rate and the molecular weight of the hydrogenation product were determined by ultraviolet spectrophotometry and gel permeation chromatography, respectively.

[0090] The conversion rate and chain scission of the polystyrene obtained in the above examples and comparative examples are shown in Table 1.

[0091] Table 1. Conversion rate and chain scission of polystyrene

[0092]

[0093]

[0094] The above experimental results show that, compared with commercial Pd / C and carbon nanotube-supported Pd catalysts, the amount of graphene-supported Pd catalyst used is only 1 / 10 of the control catalysts (commercial Pd / C catalyst and carbon nanotube-supported Pd catalyst), yet it still exhibits high polystyrene hydrogenation activity. Furthermore, the product obtained from the catalytic hydrogenation of graphene-supported Pd shows almost no chain breakage. In contrast, the control catalysts require a larger amount, resulting in lower polystyrene conversion and some degree of chain breakage in the molecules.

[0095] Under relatively low reaction conditions (140℃, 4MPa, 4h), graphene-supported Pd catalysts can achieve a conversion rate of 99.7% for the catalytic hydrogenation of PS.

[0096] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing polycyclohexylethylene by catalytic hydrogenation of polystyrene, characterized in that, include: In the presence of a catalyst, polystyrene and hydrogen are subjected to a catalytic hydrogenation reaction in a solvent; The catalyst is a graphene-supported Pd catalyst. The graphene is reduced graphene oxide; the mass ratio of Pd to reduced graphene oxide is (0.6~2.4):50; The reaction conditions include: a reaction temperature of 130~160℃, a reaction pressure of 3~6MPa, and a reaction time of 3~10h.

2. The method according to claim 1, characterized in that, The amount of catalyst used is 5-10% of the mass of polystyrene; and / or, the solvent is at least one of cyclohexane, methylcyclohexane, and N,N-dimethylformamide.

3. The method according to claim 1 or 2, characterized in that, include: S1. Add the catalyst, polystyrene, and solvent together into a high-pressure reactor, replace the reactor with helium and hydrogen gas successively, and set the reaction conditions to carry out the reaction; S2. After the reaction is complete, the reactor is allowed to cool naturally to room temperature, the gas inside the reactor is exhausted, the catalyst is separated, the solvent is recovered, and polycyclohexylethylene is obtained.

4. The method according to claim 1 or 2, characterized in that, The catalyst is prepared by adding graphene oxide to water, then adding palladium chloride solution and a reducing agent, mixing them, and obtaining the catalyst.

5. The method according to claim 4, characterized in that, The mass ratio of palladium chloride to graphene oxide is (1~4):50; And / or, the reducing agent is methanol and / or formaldehyde.

6. The method according to claim 4, characterized in that, The method for preparing graphene oxide includes: adding graphite, concentrated sulfuric acid, sodium nitrate and potassium permanganate into a reaction vessel, reacting them successively at low temperature, medium temperature and high temperature, adding deionized water and hydrogen peroxide, filtering, washing and drying to obtain graphene oxide, and then ultrasonically exfoliating the graphene oxide in water to obtain graphene oxide.

7. The method according to claim 6, characterized in that, The low temperature is 0~5℃, and the low temperature reaction time is 0.5~3h; And / or, the intermediate temperature is 25~35℃, and the intermediate temperature reaction time is 0.5~1.5h; And / or, the high temperature is 90~100℃, and the high temperature reaction time is 10~60min.

8. The method according to claim 6, characterized in that, The mass ratio of concentrated sulfuric acid to graphite is (20~40):1; And / or, the mass ratio of sodium nitrate to graphite is 1:(1~3); And / or, the mass ratio of potassium permanganate to graphite is (2~5):1.

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