A catalyst for one-pot conversion of waste pet to 1,4-cyclohexanedimethanol

Abstract

The application discloses a catalyst for catalytic conversion of waste PET into 1,4-cyclohexanedimethanol by one-pot method. The catalyst takes spinel oxide AB2O4 as a carrier, and is prepared by a solvothermal method to obtain M / AB2O4 with a heterojunction structure, wherein M is one or more of noble metals Pd, Au, Ru, Ag, Ir and Rh, the loading amount is 2% to 10%; A is one or more of divalent transition metal cations such as Mg, Zn, Ni and Cu; and B is trivalent transition metal cation Al. The M / AB2O4 catalyst with the heterojunction structure designed in the application has high hydrogenation activity and stability in the reaction process of catalytic conversion of waste PET into 1,4-cyclohexanedimethanol by one-pot method, and can be used repeatedly. The application has the advantages that the waste PET is catalytically converted into high-value 1,4-cyclohexanedimethanol by one-pot method, and a high-efficiency and stable M / AB2O4 catalyst is synthesized, and the problem of low efficiency in the PET depolymerization and hydrogenation process is solved.

Description

Technical Field

[0001] This application relates to the field of high-value conversion technology of waste plastics, and in particular to a catalyst for one-pot conversion of waste PET plastics to 1,4-cyclohexanediethanol. Background Technology

[0002] Chemical recycling of waste plastics, upgrading and utilizing their C, H, and O resources to obtain high-value chemical monomers, is one of the ideal methods to solve the growing global plastic waste problem. PET (polyethylene terephthalate) is currently the most consumed polyester plastic, but due to its difficult-to-biodegrade chemical properties, large quantities of post-consumer PET end up in landfills and oceans, causing significant harm to the ecological environment. Current PET chemical recycling methods mainly include alcoholysis, glycolysis, hydrolysis, and ammonolysis, yielding corresponding chemical monomers such as dimethyl terephthalate (DMT), bis(hydroxyethyl) terephthalate (BHET), terephthalic acid (PTA), and terephthalamide.

[0003] Chemical depolymerization of PET can effectively alleviate the white pollution problem caused by waste plastics, but the monomers obtained after depolymerization still have modifiable groups, which can be directionally hydrogenated to upgrade to high-value products. Yan et al. used waste PET as raw material to convert waste plastics into multi-component aromatics through heterogeneous hydrogenation. Chinese patent (CN 109705985A) also reported a method for highly selective one-pot conversion of waste PET to BTX using an inexpensive Cu-based catalyst, realizing the upgrading and utilization of waste PET to fuel. However, hydrogenating waste PET to BTX severely damages the oxygen-containing functional groups of PET monomers, thus reducing the added value of the final hydrogenation product. 1,4-Cyclohexanedimethanol (CHDM) is an important high-value polyester monomer. Due to its elastic cyclohexane backbone, adding it as a monomer to the polyester backbone can effectively improve the toughness and fatigue resistance of polyester plastics. China (CN 104003840B) reported a method for preparing CHDM by tandem hydrogenation of bis(hydroxyethyl) terephthalate (BHET) as a raw material, but it was limited by low catalyst activity (CHDM yield: 43.1%).

[0004] Based on this, the present invention uses spinel oxide with good stability as a support to support noble metals with excellent hydrogenation activity and prepares M / AB2O4 catalyst with heterostructure through in-situ high temperature treatment. This catalyst is applied to the hydrogenation reaction of waste PET to 1,4-cyclohexanediethanol in a one-pot conversion, which solves the problem of low efficiency in the waste PET conversion process. Summary of the Invention

[0005] This application provides a catalyst for one-pot conversion of waste PET plastic into 1,4-cyclohexanediethanol.

[0006] The technical solution adopted in this application is as follows:

[0007] Using spinel oxide AB₂O₄ as a support, a heterojunction-structured M / AB₂O₄ catalyst was prepared via solvothermal reaction and applied to the hydrogenation reaction of waste PET to 1,4-cyclohexanediol in a one-pot catalytic conversion. The specific reaction process is as follows: First, waste PET is alcoholyzed at high temperature to obtain the corresponding monomer and ethylene glycol. Then, under high pressure and with the catalyst, the plastic monomer undergoes benzene ring hydrogenation to cyclohexanedimethyl ester. Finally, cyclohexanedimethyl ester undergoes selective ester group hydrogenation to obtain 1,4-cyclohexanediol. After the hydrogenation reaction is completed, the catalyst and reaction solution are separated. The reaction solution is analyzed, and the catalyst is then added back into the reaction. The reaction route is as follows:

[0008]

[0009] A method for preparing a catalyst for the one-pot catalytic conversion of waste PET to 1,4-cyclohexanediethanol. The catalyst is characterized by the following preparation method: using spinel oxide AB₂O₄ as a support, a heterojunction structure M / AB₂O₄ is prepared via solvothermal reaction and applied to the hydrogenation reaction of the one-pot catalytic conversion of waste PET to 1,4-cyclohexanediethanol, wherein M is a noble metal additive; A is a divalent transition metal cation; and B is a trivalent transition metal cation Al.

[0010] The specific reaction process is as follows: Recycled waste PET plastic bottles, solvent, and catalyst are added to a high-pressure reactor. After sealing the reactor, high-pressure nitrogen is introduced to replace the air inside, and this cycle is repeated three times. Then, under programmed temperature control and a high-pressure hydrogen atmosphere, PET depolymerization is carried out at 120–200°C. After the waste PET depolymerization is complete, the temperature is lowered to 90–160°C to hydrogenate the benzene ring of the intermediate DMT (dimethyl terephthalate). After the DMT hydrogenation is completed, the reactor temperature is raised to 180–220°C to hydrogenate the ester bond of DMCD (dimethyl 1,4-cyclohexanedimethyl ester), achieving a one-pot catalytic conversion of waste PET to 1,4-cyclohexanediethanol. After the reaction, the high-pressure reactor is cooled and the gas is released. The catalyst is filtered to separate the reaction liquid, which is then analyzed and tested. The catalyst is dried and added to the next reaction batch.

[0011] Furthermore, the catalyst is prepared by using Al2O4 as a support, and the noble metal additive M is one or more of Pd, Au, Ru, Ag, Ir and Rh, with a loading of 2% to 10%. A is one or more of Mg, Zn, Ni and Cu.

[0012] Furthermore, the preparation method of CO(NH2)2 is a co-precipitation method-solvothermal method, and the precipitant is one or both of ammonia and CO(NH2)2.

[0013] Furthermore, in the preparation method of the catalyst, the loading of A in the spinel oxide is 10-30%, preferably 15%.

[0014] Furthermore, the solvent in the solvothermal preparation method of the catalyst is water, ethanol, or isopropanol, with ethanol being preferred.

[0015] Furthermore, the loading of noble metal additives in the preparation of the catalyst is 2% to 10%, preferably 5%.

[0016] Furthermore, the volume ratio of PET plastic to solvent in the catalytic reaction process is 1:10-10:1, preferably 1:7.

[0017] Furthermore, the reaction solvent is one or a combination of methanol, ethanol, and isopropanol.

[0018] Furthermore, the catalytic reaction process for PET alcoholysis is carried out at a temperature of 180-250°C, preferably 150°C; the two-step hydrogenation temperatures are 90-160°C and 180-220°C, preferably 150°C and 240°C, respectively.

[0019] Furthermore, the one-pot catalytic reaction time is 2-10 hours, preferably 4 hours.

[0020] Furthermore, the high-pressure hydrogen pressure is 2-10.0 MPa, preferably 5 MPa.

[0021] Compared with the prior art, the beneficial effects of this application are as follows:

[0022] This application utilizes catalyst design to prepare a heterostructured M / AB₂O₄ catalyst by supporting a noble metal with excellent hydrogenation activity on a stable spinel oxide as a support and preparing it through in-situ high-temperature treatment. This catalyst is then applied to the one-pot hydrogenation reaction of waste PET to 1,4-cyclohexanediethanol, simultaneously solving the problems of catalyst deactivation and poor stability during the HDO reaction of waste plastics. Furthermore, the heterostructured catalyst exhibits high stability and recyclability while achieving a high concentration of waste PET converted to high-value-added 1,4-cyclohexanediethanol in a one-pot process. This invention can significantly promote the conversion of waste PET plastics in urban areas into the high-value economic product 1,4-cyclohexanediethanol, thereby promoting waste plastic recycling, solving environmental pollution problems, and driving urban economic development. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Example 1

[0025] Preparation method of PdRu3Sn / MgAl2O4 (coprecipitation method): 2 mmol of magnesium nitrate and 4 mmol of aluminum nitrate were dissolved in 100 mL of deionized water. After stirring for 30 min until the metal salts were completely dissolved, noble metals Pd and Ru were added, with the noble metal loading controlled at 2%. Then, tin chloride (Ru:Sn = 3:1) was added as an auxiliary agent. After stirring for 20 min, ammonia water was added dropwise until the solution pH was maintained at 10. After the addition was complete, the solution was stirred for 1 h, and the precipitate was centrifuged and washed until the filtrate was neutral. The precipitate was then transferred to an 80℃ oven and dried for 12 h to obtain the PdRu3Sn / MgAl2O4 precursor. The dried sample was then thoroughly ground and calcined in a muffle furnace at 600℃ for 8 h, followed by reduction in a hydrogen atmosphere for 2 h to obtain the PdRu3Sn / MgAl2O4 catalyst.

[0026] The catalyst prepared in Example 1 was used to conduct waste PET conversion experiments.

[0027] 1.0 g of physically cut waste PET plastic was placed in a 100 mL high-pressure reactor, followed by the addition of 30 mL of methanol and 0.1 g of PdRu3Sn / MgAl2O4 catalyst. After sealing the reactor, high-pressure nitrogen was introduced to replace the air in the reactor, and this cycle was repeated three times. Finally, 3 MPa of H2 was introduced into the reactor. The temperature was controlled by a program: first, the reactor temperature was raised to 180 °C, and the reaction was carried out for 3 hours to depolymerize PET into monomers. After depolymerization, the reactor temperature was lowered to 80 °C and maintained for 4 hours for the hydrogenation of the aromatic ester benzene ring. After 3 hours of benzene ring hydrogenation, the reactor temperature was raised to 210 °C and maintained for 6 hours for the hydrogenation of dimethyl cyclohexane to 1,4-cyclohexanediethanol. After the reaction, the reaction solution and catalyst were separated by filtration, and the catalyst could be added back into the reaction for plastic conversion.

[0028] The reaction results and catalyst cycle performance are as follows:

[0029]

[0030] Example 2

[0031] Pd / Mg 0.4 Cu 0.4 Ni0.2 Preparation method of Al2O4 (hydrothermal method): Dissolve 1 mmol copper nitrate, 1 mmol magnesium nitrate, 0.5 mmol nickel nitrate, and 5 mmol aluminum nitrate in 100 mL deionized water. Stir for 30 min until the reagents are completely dissolved. Then add 10 mmol CO(NH2)2 and stir for 30 min until the solution is clear. Add the noble metal Pd, controlling the Pd loading at 4%. Continue stirring for 5 min, then transfer the solution to an 80 mL hydrothermal reactor and react at 140 °C for 12 h. After the hydrothermal reactor cools, centrifuge and wash the precipitate. After the filtrate is neutral, transfer the precipitate to an 80 °C oven and dry for 12 h. The p-Pd / Mg ratio of the dried precipitate is calculated. 0.4 Cu 0.4 Ni 0.2 Al2O4. Then the sample p-Pd / Mg 0.4 Cu 0.4 Ni 0.2 Pd / Mg can be obtained by calcining Al2O4 at 800℃ for 6 hours in a muffle furnace and then reducing it in a hydrogen atmosphere for 4 hours. 0.4 Cu 0.4 Ni 0.2 Al2O4 catalyst.

[0032] The catalyst prepared in Example 2 was used to conduct waste PET conversion experiments.

[0033] Take 2.0g of physically cut waste PET plastic and place it in a 100mL high-pressure reactor. Then add 30mL of a mixed solution of methanol and ethanol, and 0.1g of Pd / Mg. 0.4 Cu 0.4 Ni 0.2 Al₂O₄ catalyst. After sealing the reactor, high-pressure nitrogen gas is introduced to replace the air in the reactor, and this cycle is repeated three times. Finally, 5 MPa of H₂ is introduced into the reactor. The temperature is controlled by a program: first, the reactor temperature is raised to 200°C, and after 1 hour, PET is depolymerized into monomer. After depolymerization, the reactor temperature is lowered to 120°C and maintained for 3 hours for the hydrogenation of the aromatic ester benzene ring. After the 3-hour benzene ring hydrogenation is completed, the reactor temperature is raised to 240°C and maintained for 3 hours for the hydrogenation of dimethyl cyclohexane to 1,4-cyclohexanediethanol. After the reaction is complete, the reaction solution and catalyst are filtered and separated. The catalyst can be added back into the reaction for plastic conversion.

[0034] The reaction results and catalyst cycle performance are as follows:

[0035]

[0036] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. The application of a catalyst in the one-pot catalytic conversion of waste PET to 1,4-cyclohexanediethanol, characterized in that, The catalyst is prepared by using spinel oxide AB2O4 as a support and then preparing an M / AB2O4 catalyst with a heterojunction structure by solvothermal method. The catalyst is then applied to the one-pot catalytic conversion of waste PET to 1,4-cyclohexanediethanol. M is a noble metal additive; A is a divalent transition metal cation; and B is a trivalent transition metal cation Al. In the M / AB2O4 catalyst, the noble metal additive M is one or more of Pd, Au, Ru, Ag, Ir and Rh, with a loading of 2% to 10%; A is one or more of Mg, Zn, Ni and Cu. The specific reaction process is as follows: recycled waste PET plastic bottles, solvents, and catalysts are added to a high-pressure reactor. After sealing the reactor, high-pressure nitrogen is introduced to replace the air inside the reactor, and the process is repeated three times. Subsequently, PET depolymerization is carried out under a high-pressure hydrogen atmosphere at 120–200°C through programmed temperature control. After the waste PET depolymerization is completed, the temperature is lowered to 90–160°C to carry out the hydrogenation reaction of the benzene ring on the intermediate DMT dimethyl terephthalate. After the hydrogenation of DMT dimethyl terephthalate is completed, the reactor is heated to 180–220°C to carry out the hydrogenation reaction of the ester bond of DMCD 1,4-cyclohexanedimethyl ester, thus realizing the one-pot catalytic conversion of waste PET into 1,4-cyclohexanediethanol.

2. The application according to claim 1, characterized in that, The M / AB2O4 catalyst is prepared by co-precipitation-solventothermal method, and the precipitant is one or both of ammonia and CO(NH2)2.

3. The application according to claim 1, characterized in that, The content of A in the application of the catalyst is 10-30%.

4. The application according to claim 1, characterized in that, The solvent used in the solvothermal preparation method of the M / AB2O4 catalyst is one or more of water, ethanol, and isopropanol.

5. The application according to claim 1, characterized in that, In the reaction test, the volume ratio of PET plastic to solvent was 1:10-10:

1.

6. The application according to claim 1, characterized in that, The solvent required for the depolymerization process is one or a combination of methanol, ethanol, and isopropanol.

7. The application according to claim 1, characterized in that, The depolymerization temperature of PET is 180-250℃, the first step of benzene ring hydrogenation reaction temperature is 90-160℃, and the second step of ester bond selective hydrogenation reaction temperature is 180-260℃.

8. The application according to claim 1, characterized in that, The reaction time for one-pot catalytic conversion of PET is 2-10 hours.

9. The application according to claim 1, characterized in that, The hydrogen pressure for the one-pot catalytic conversion of PET is 2-10.0 MPa.

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