Heterogeneous catalyst for preparing p-xylene through catalytic hydrogenation of waste PET (polyethylene terephthalate) plastic as well as preparation method and application of heterogeneous catalyst

Abstract

The invention discloses a heterogeneous catalyst for preparing p-xylene through catalytic hydrogenation of waste PET and a preparation method and application thereof.The heterogeneous catalyst comprises a carrier and metal and auxiliaries which are precipitated on the carrier, the supported catalyst is used for catalyzing catalytic hydrogenation degradation of waste PET to prepare p-xylene, a green solvent gamma-valerolactone is used, and the environment-friendly effect is achieved. The conversion rate of the waste PET is 100%, the selectivity of p-xylene is as high as 97%, and no obvious deactivation phenomenon is generated after the catalyst is used for five times.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical recycling of PET plastics, and particularly relates to a preparation of a supported catalyst and a method for preparing p-xylene by catalytic hydrogenation of waste PET using the catalyst. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a widely used polyester plastic, with an annual production of 700 million tons, and is widely used to produce fabrics and disposable beverage containers. Most of the products are discarded after use and are difficult to naturally degrade, which causes serious environmental and ecological problems. P-xylene (PX) is an important bulk chemical, usually derived from fossil resources. It is of great significance to develop a technology for synthesizing PX from waste PET.

[0003] Currently, PX is mainly prepared from waste PET using the following methods:

[0004] (1) Under hydrogen conditions, noble metal catalysts are used to prepare PX from PET depolymerization. Chinese patent (CN 105712833 A) discloses a RuSnPt catalyst, the catalyst dosage is 10wt% of the mass percentage of PET, at 350℃, 7MPa hydrogen, reaction for 7h, the PET conversion rate is 100%, and the PX selectivity is 90.1%. Chinese patent (CN 120054614 A) discloses a PtW / MCM-48 bimetallic catalyst, the catalyst dosage is 50wt% of the mass percentage of PET, at 260℃, 2MPa hydrogen, in a phosphotungstic acid aqueous solution (60mL phosphotungstic acid aqueous solution / (1g PET)) at pH=2, reaction for 12h, the PET conversion rate is 100%, and the PX selectivity is 36.4%, and the p-tolylbenzoic acid selectivity is 63.6%.

[0005] (2) Under hydrogen conditions, inexpensive metal catalysts are used to prepare PX from PET depolymerization. Chinese patent (CN 116393139 A) discloses a Cu-MnOX-MgO catalyst, the catalyst dosage is 10wt% of the mass percentage of PET, at 240℃, 4MPa hydrogen, in an ethanol solvent (20mL ethanol / (1g PET)), reaction for 5h, the PET conversion rate is 100%, and the PX selectivity is 98.1%. Chinese patent (CN 118988326 A) discloses a preparation method of a Na-Cu / SiO2 catalyst applied to catalyze waste PET to hydrogenolysis into PX and ethylene glycol, but the performance of the catalyst is not evaluated. +

[0006] ​(3) Under the conditions of hydrogen and carbon dioxide, cheap metal catalysts are used to prepare PX by depolymerization of PET. Chinese patent (CN117816170A) reports a ZIF-67 supported Cu catalyst precursor, which is calcined in nitrogen and ammonia to obtain CuCo@CN-NH3 catalyst. The catalyst dosage is 200wt% of the mass percentage of PET, and the reaction is carried out at 210℃, 3MPa hydrogen, 1MPa carbon dioxide, for 12h. The conversion rate of PET is 100%, and the PX selectivity is 92%.

[0007] (4) Under the conditions of methanol, cheap metal catalysts are used to prepare PX by depolymerization of PET. Chinese patent (CN116655445A) reports a Cu8Ce@CsN-0.6 catalyst, and the catalyst dosage is 100wt% of the mass percentage of PET. In-situ hydrogen production is achieved by using methanol, and the methanol dosage is 200mL / (1g PET). The reaction is carried out at 230℃, 1MPa argon, for 2h. The conversion rate of PET is 100%, and the PX selectivity is 86.94%.

[0008] However, the above-mentioned routes for depolymerization of waste PET to synthesize PX have problems such as the use of noble metal catalysts, high catalyst usage, toxic and volatile solvents, high solvent usage, and low selectivity, resulting in poor economic efficiency of PET hydrogenolysis to synthesize PX. Therefore, it is of great significance to develop a process route for PET hydrogenolysis to synthesize PX using high-efficiency catalysts for the purpose of industrial application. SUMMARY

[0009] The purpose of this section is to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments.

[0010] The present application provides a heterogeneous catalyst for preparing p-xylene by catalytic hydrogenation of waste PET, characterized in that the catalyst is CuReZrAlO x , wherein the mass percentage of copper is 10-40wt%, preferably 13-40wt%, more preferably 13-33wt%; the mass percentage of rhenium is 2-15wt%, preferably 5-15wt%, more preferably 5-10wt%; the mass percentage of zirconium is 5-25wt%, preferably 10-25wt%, more preferably 10-20wt%; and the mass ratio of rhenium to zirconium is 1:(0.5-5), preferably 1:(0.5-3), more preferably 1:(1-3).

[0011] Preferably, the specific surface area of the catalyst is 40-300m 2 / g, preferably 50-300m 2 / g; more preferably 50-250m 2 / g.

[0012] The present invention also provides a method for preparing the heterogeneous catalyst for the catalytic hydrogenation of waste PET to prepare p-xylene, which can be prepared by a co-precipitation method, comprising the following steps: dissolving aluminum precursor, copper precursor, rhenium precursor and zirconium precursor in a solvent, adding a precipitant, aging, washing, drying, calcining, and reducing to obtain the catalyst.

[0013] In this invention, the carrier precursor is one or more of aluminum nitrate, chloride, sulfate, acetate, and acetylacetonate, preferably one or more of aluminum nitrate, chloride, acetate, and acetylacetonate, and more preferably one or more of aluminum nitrate, chloride, and acetate.

[0014] The active component precursor includes one or more of copper nitrates, chlorides, sulfates, acetates, and acetylacetones, preferably one or more of copper nitrates, chlorides, acetates, and acetylacetones, and more preferably one or more of copper nitrates, chlorides, and acetates.

[0015] The rhenium precursor for the additive includes one or more of ammonium perrhenate, sodium perrhenate, potassium perrhenate, and perrhenic acid, preferably one or more of ammonium perrhenate, sodium perrhenate, and potassium perrhenate;

[0016] The auxiliary zirconium precursor includes one or more of zirconium nitrate, zirconium acetate, zirconium ammonium carbonate, zirconium oxychloride, and zirconium sulfate, preferably one or more of zirconium nitrate, zirconium acetate, zirconium ammonium carbonate, and zirconium oxychloride.

[0017] The solvent is one or a mixture of several of the following: water, methanol, ethanol, acetone, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, isopentanol, and tert-pentanol. Preferably, it is one or a mixture of several of the following: water, methanol, ethanol, acetone, isopropanol, tert-butanol, and tert-pentanol. More preferably, it is one or a mixture of several of the following: water, methanol, ethanol, and acetone.

[0018] The precipitant is one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, ammonia, and urea, preferably one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and ammonia.

[0019] As a preferred embodiment of the method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to the present invention, the aging temperature is 25-100°C, preferably 25-80°C, more preferably 25-60°C, and the aging time is 1-24h, preferably 1-12h, more preferably 4-12h.

[0020] As a preferred embodiment of the method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to the present invention, the calcination temperature is 300-900℃, preferably 300-600℃, more preferably 400-600℃, and the calcination time is 1-24h, preferably 1-8h, more preferably 4-8h.

[0021] As a preferred embodiment of the method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to the present invention, the reduction process uses one or more of the following reducing gases: hydrogen, a hydrogen-argon mixture, and a hydrogen-nitrogen mixture; the reduction temperature is 300–800°C, preferably 300–600°C, more preferably 400–600°C; and the reduction time is 1–8 h, preferably 1–6 h, more preferably 4–6 h.

[0022] The present invention also provides the application of the heterogeneous catalyst in the hydrogenolysis of PET to prepare p-xylene, which includes adding PET and the catalyst in a certain proportion to a high-temperature and high-pressure reactor, then adding a solvent, and introducing a certain amount of hydrogen gas to carry out a hydrogenation reaction.

[0023] The mass ratio of PET to catalyst is 1:(0.1-0.5), preferably 1:(0.1-0.4), and more preferably 1:(0.1-0.3);

[0024] The solvent is one or more of γ-valerolactone, methanol, and 1,4-dioxane;

[0025] The mass ratio of PET to solvent is 1:(1-20), preferably 1:(1-15), and more preferably 1:(1-10);

[0026] The pressure of the hydrogen gas is 4-8 MPa, preferably 4-8 MPa;

[0027] The reaction temperature is 180–250°C, preferably 200–250°C, and more preferably 200–240°C;

[0028] The reaction time is 0.5 to 12 hours, preferably 4 to 12 hours; more preferably 4 to 6 hours. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0030] Figure 1 CuReZrAlO in this invention x Gas chromatogram of the preparation of p-xylene by catalytic hydrogenolysis of PET. Detailed Implementation

[0031] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0032] The reaction route for the hydrogenation of PET to synthesize p-xylene is as follows:

[0033]

[0034] Example 1:

[0035] The method for preparing CuOx catalyst by hydrogenolysis of PET to p-xylene includes the following steps:

[0036] (1) Preparation of metal salt solution: Add 1.208g Cu(NO3)2·3H2O to 50mL of deionized water to obtain metal salt solution;

[0037] (2) Preparation of precipitant: Take 0.795g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0038] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0039] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuOx catalyst.

[0040] Example 2:

[0041] The method for preparing ZrOx catalyst by hydrogenolysis of PET to p-xylene includes the following steps:

[0042] (1) Preparation of metal salt solution: Add 1.695g of Zr(NO3)4 to 50mL of deionized water to obtain metal salt solution;

[0043] (2) Preparation of precipitant: Take 1.59g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0044] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0045] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain the ZrOx catalyst.

[0046] Example 3:

[0047] The method for preparing the catalyst AlOx for the hydrogenolysis of PET to p-xylene includes the following steps:

[0048] (1) Preparation of metal salt solution: Add 1.875g Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0049] (2) Preparation of precipitant: Take 1.19g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0050] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0051] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain the AlOx catalyst.

[0052] Example 4:

[0053] The method for preparing CuZrOx catalyst by hydrogenolysis of PET to p-xylene includes the following steps:

[0054] (1) Preparation of metal salt solution: Add 0.484g of Cu(NO3)2·3H2O and 0.678g of Zr(NO3)4 to 50mL of deionized water to obtain metal salt solution;

[0055] (2) Preparation of precipitant: Take 0.954g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0056] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0057] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuZrOX catalyst.

[0058] Example 5:

[0059] The method for preparing CuZrAlOx catalyst by hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0060] (1) Preparation of metal salt solution: Add 0.484g Cu(NO3)2·3H2O, 0.676g Zr(NO3)4, and 1.4g Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0061] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0062] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0063] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuZrAlOx catalyst.

[0064] Example 6:

[0065] The preparation method of CuReAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0066] (1) Preparation of metal salt solution: Add 0.484g Cu(NO3)2·3H2O, 0.0536g NH4ReO4, and 1.4g Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0067] (2) Preparation of precipitant: Take 1.98g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0068] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0069] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuReAlOx catalyst.

[0070] Example 7:

[0071] The preparation method of CuReZrAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0072] (1) Preparation of metal salt solution: Add 0.484g Cu(NO3)2·3H2O, 0.0536g NH4ReO4, 0.676g Zr(NO3)4, and 1.4g Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0073] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0074] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0075] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuReZrAlOX catalyst.

[0076] Example 8:

[0077] The method for preparing the NiReZrAlOX catalyst for the hydrogenolysis of PET to p-xylene includes the following steps:

[0078] (1) Preparation of metal salt solution: Add 0.58g of Ni(NO3)2·6H2O, 0.0536g of NH4ReO4, 0.676g of Zr(NO3)4, and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0079] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0080] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0081] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain the NiReZrAlOX catalyst.

[0082] Example 9:

[0083] The preparation method of FeReZrAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0084] (1) Preparation of metal salt solution: Add 0.808g of Fe(NO3)3·9H2O, 0.0536g of NH4ReO4, 0.676g of Zr(NO3)4, and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0085] (2) Preparation of precipitant: Take 2.32g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0086] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0087] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain the FeReZrAlOx catalyst.

[0088] Example 10:

[0089] The preparation method of CuMnZrAlOX catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0090] (1) Preparation of metal salt solution: Add 0.484g of Cu(NO3)2·3H2O, 0.05g of Mn(NO3)2·4H2O, 0.676g of Zr(NO3)4, and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0091] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0092] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0093] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuMnZrAlOx catalyst.

[0094] Example 11:

[0095] The preparation method of CuCoZrAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0096] (1) Preparation of metal salt solution: Add 0.484g of Cu(NO3)2·3H2O, 0.0582g of Co(NO3)2·6H2O, 0.676g of Zr(NO3)4, and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0097] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0098] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0099] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuCoZrAlOx catalyst.

[0100] Example 12:

[0101] The preparation method of CuReCeAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0102] (1) Preparation of metal salt solution: Add 0.484g of Cu(NO3)2·3H2O, 0.0536g of NH4ReO4, 0.868g of Ce(NO3)3·6H2O, and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0103] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0104] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0105] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuReCeAlOx catalyst.

[0106] Example 13:

[0107] The preparation method of CuReMgAlOx catalyst for the hydrogenolysis of PET to prepare p-xylene includes the following steps:

[0108] (1) Preparation of metal salt solution: Add 0.484g of Cu(NO3)2·3H2O, 0.0536g of NH4ReO4, 0.512g of Mg(NO3)3·6H2O and 1.4g of Al(NO3)3·9H2O to 50mL of deionized water to obtain metal salt solution;

[0109] (2) Preparation of precipitant: Take 2.02g Na2CO3 and add it to 50mL of deionized water to obtain precipitant solution;

[0110] (3) Co-precipitation: Under stirring conditions, the precipitant solution obtained in step (2) is added dropwise to the metal salt solution obtained in step (1); after the addition is completed, the mixture is stirred vigorously, and then aged at 60°C for 6 hours. The resulting suspension is washed with deionized water by centrifugation until neutral, and dried at 120°C overnight.

[0111] (4) Activation: The dried solid was first calcined at 450℃ for 4h, and then reduced at 600℃ under a hydrogen-argon mixture with a hydrogen molar concentration of 5% at a flow rate of 20mL / min for 2h to finally obtain CuReMgAlOx catalyst.

[0112] Examples 14-26:

[0113] The supported catalysts prepared in Examples 1-13 were used for the selective hydrogenolysis of PET to produce p-xylene. The specific steps are as follows:

[0114] PET particles, one of the catalysts obtained in Examples 1-13, and solvent (γ-valerolactone) were added to a high-temperature and high-pressure reactor. The mass ratio of PET:catalyst:γ-valerolactone was 1:0.2:5. After sealing the high-temperature and high-pressure reactor, it was purged with argon gas at 0.5 MPa three times, followed by the introduction of hydrogen gas to 6.0 MPa. The temperature was set at 225°C, and the reaction was carried out for 6.5 h. After the reaction was completed, it was cooled to room temperature. The liquid product was collected by centrifugation, and the product distribution was analyzed by gas chromatography.

[0115] Table 1. Study on PET hydrogenolysis performance using different supported catalysts, different reduction temperatures, hydrogen pressures, and reaction temperatures in Examples 14-26.

[0116]

[0117] As shown in Table 1, CuReMgAlOx is the optimal catalyst.

[0118] Examples 27-34:

[0119] Using the catalyst CuReMgAlOx from Example 20, and other reaction conditions identical to those in Example 20, the hydrogenation and depolymerization of PE into p-xylene was investigated under different reaction temperatures, ammonia pressures, hydrogen pressures, and reaction times. The results are listed in Table 2.

[0120] Table 2. Study on the hydrodepolymerization performance of PET using different solvents, reaction temperatures, hydrogen pressures, and reaction times (Examples 27-34)

[0121]

[0122] Examples 35-39:

[0123] Using the catalyst CuReMgAlOx from Example 20, and under the same reaction conditions as in Example 20, the synthesis of cyclohexylamine by phenol reduction amination was investigated with different number of repetitions. The results are listed in Table 3.

[0124] Table 3. Study on the number of times the catalyst for PET hydrogenolysis performance was applied in Examples 36-40.

[0125]

[0126] As can be seen from the above examples, the CuReMgAlOx catalyst designed in this invention uses the green solvent γ-valerol, has a simple preparation process, requires a small amount of catalyst for hydrogenation reaction, has strong resistance to carbon deposition, good cycle stability, and has good prospects for industrial application.

[0127] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A heterogeneous catalyst for the catalytic hydrogenation of waste PET plastic to prepare p-xylene, characterized in that: The catalyst is CuReZrAlO x The copper content is 10–40 wt%; the rhenium content is 2–15 wt%; the zirconium content is 5–25 wt%; and the mass ratio of rhenium to zirconium is 1:(0.5–5).

2. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 1, characterized in that: The process includes dissolving aluminum precursor, copper precursor, rhenium precursor and zirconium precursor in a solvent, adding a precipitant, aging, washing, drying, calcining, and reducing to obtain the catalyst.

3. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2, characterized in that: The aluminum precursor includes one or more of aluminum nitrates, chlorides, sulfates, acetates, and acetylacetones. The copper precursor includes one or more of copper nitrates, chlorides, sulfates, acetates, and acetylacetones. The rhenium precursor includes one or more of ammonium perperurate, sodium perperurate, potassium perperurate, and perperuric acid; The zirconium precursor includes one or more of zirconium nitrate, zirconium acetate, ammonium zirconium carbonate, zirconium oxychloride, and zirconium sulfate.

4. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2 or 3, characterized in that: The solvent is one or a mixture of several of the following: water, methanol, ethanol, acetone, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, isopentanol, and tert-pentanol.

5. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2 or 3, characterized in that: The precipitant is one or more of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, ammonia, and urea.

6. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2 or 3, characterized in that: The aging temperature is 25–100℃, and the aging time is 1–24 hours.

7. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2 or 3, characterized in that: The calcination temperature is 300–900℃, and the calcination time is 1–24 h.

8. The method for preparing a heterogeneous catalyst for the catalytic hydrogenation of waste PET to p-xylene according to claim 2 or 3, characterized in that: The reduction process uses one or more of the following reducing gases: hydrogen, hydrogen-argon mixture, and hydrogen-nitrogen mixture; the reduction temperature is 300–800°C, and the reduction time is 1–8 hours.

9. The application of the heterogeneous catalyst according to claim 1 in the catalytic hydrogenation of waste PET to produce p-xylene, characterized in that: Polyethylene terephthalate and the catalyst were added to a reaction vessel, along with a reaction solvent and hydrogen gas, to carry out a hydrogenation reaction.

10. The application according to claim 9, characterized in that: The mass ratio of polyethylene terephthalate to the catalyst is 1:(0.1-0.5); the reaction solvent is one or more of γ-valerolactone, methanol, and 1,4-dioxane; the mass ratio of polyethylene terephthalate to the reaction solvent is 1:(1-20); the hydrogen pressure is 4-8 MPa; the reaction temperature is 180-250°C; and the reaction time is 0.5-12 h.

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