Process for the co-catalytic conversion of a polyester and co2

Abstract

The application provides a polyester and CO2 co-catalytic conversion method, wherein CO2 reacts with hydrogen to generate methanol under the action of a catalyst, polyester is depolymerized to generate dimethyl terephthalate under the action of methanol, and dimethyl terephthalate is further converted into a hydrogenation product through hydrogenation under the action of a catalyst; the polyester is selected from any one of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The application realizes the co-efficient conversion of CO2 and PET or PBT through the series connection of three reactions of CO2 hydrogenation to generate methanol, polyester methanol depolymerization and dimethyl terephthalate hydrogenation, and chemical waste CO2 and PET or PBT plastic can be recycled at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical recycling degradation, in particular to a polyester and CO2 co-catalytic conversion method. BACKGROUND

[0002] At present, the production of plastics demanded by the market is rapidly increasing, and waste plastics have caused global problems. About 90% of waste plastics are directly landfilled or incinerated, seriously polluting the ecological environment.

[0003] Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are the most commonly used polyester plastics, and their recycling methods are mainly divided into physical recycling and chemical recycling. Among them, chemical recycling is to depolymerize solid polymers into smaller molecules, intermediate raw materials or directly into monomers. Methanol transesterification of PET and PBT is a simple method for degradation of PET and PBT, but the depolymerization of PET and PBT by methanol decomposition has an inherent defect in chemistry: the degradation rate is controlled by thermodynamic limitation, and a large amount of methanol solvent is required. Therefore, it is urgent to develop an efficient and environmentally friendly method for chemical recycling of waste PET and PBT, so as to realize the high value-added conversion and reuse of a large amount of polyester plastics. SUMMARY

[0004] The purpose of the present application is to provide a polyester and CO2 co-catalytic conversion method to realize the efficient conversion of CO2 and polyester plastics. The specific technical solutions are as follows:

[0005] The present application provides a polyester and CO2 co-catalytic conversion method, wherein CO2 reacts with hydrogen under the action of a catalyst to generate methanol, and polyester is depolymerized under the action of the methanol to generate dimethyl terephthalate, and the dimethyl terephthalate is further converted into a hydrogenation product by hydrogenation reaction under the action of the catalyst.

[0006] The polyester is selected from any one of polyethylene terephthalate and polybutylene terephthalate.

[0007] In some embodiments of the present application, the catalyst is selected from a catalyst composed of one or more metals selected from Cu, Fe, Cr, Ag, Mn, In, Mo, Nb, Re, Mg, Pd, Al, Ca, Rh, Zn, Ni, Ga and Zr, preferably a copper-based catalyst.

[0008] In some embodiments of the present application, the copper-based catalyst is a CuFeM composite catalyst, and M is selected from at least one of Mg, Cr, Ag, Mn, In, Mo, Nb and Re.

[0009] In some embodiments of the present application, the mass ratio of the polyester and the catalyst is 1:(0.1-1).

[0010] In some embodiments of the present application, the reaction conditions for the catalytic conversion of the polyester and CO2 are: temperature 220-280℃, time 1.5-48h.

[0011] In some embodiments of the present application, the reaction gas environment for the catalytic conversion of the polyester and CO2 is CO2, hydrogen and argon, and the total pressure of the gas is 0.5-6 MPa.

[0012] In some embodiments of the present application, the pressure of the CO2 and hydrogen is 0.5-6 MPa, and the partial pressure ratio of the CO2 and hydrogen is 1:0.5-1:5 based on the pressure of the CO2 and hydrogen.

[0013] In some embodiments of the present application, the hydrogenation product is at least one of cyclohexane dimethyl dicarboxylate and p-xylene.

[0014] The method for the catalytic conversion of the polyester and CO2 provided by the present application overcomes the thermodynamic limitation by using a hydrogenation catalyst, and uses the greenhouse gas CO2 as a solvent precursor to convert PET or PBT into high-value chemicals. The synergistic coupling of CO2 hydrogenation and PET or PBT methanolysis in this method is a double-promotion effect. The presence of PET or PBT can promote CO2 hydrogenation because the product methanol is consumed in situ by PET or PBT methanolysis. The product obtained by PET or PBT methanolysis under the action of the hydrogenation catalyst can be further hydrogenated, promoting PET or PBT methanolysis. Compared with the yield of non-coupled reactions, this one-pot catalytic process improves the yield of CO2 hydrogenation or PET or PBT methanolysis.

[0015] The present application provides a new method for simultaneously recycling two challenging chemical wastes, polyester plastics and carbon dioxide. At the same time, the double-promotion catalytic process is suitable for the recycling of commercial PET or PBT waste and other other polyester plastics, and can realize the conversion of a large amount of polyester plastics into high-value chemicals.

[0016] Of course, the implementation of any product or method of the present application does not necessarily require the simultaneous achievement of all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0018] Figure 1 A reaction scheme of the one-pot catalytic system of the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the present application will be described clearly and completely in combination with the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0020] In order to avoid direct use of a large amount of methanol, methanol can be generated from the precursor chemical CO2 by hydrogenation. Carbon dioxide is a waste gas related to global warming, and catalytic hydrogenation of CO2 into high-value chemicals has become one of the most promising methods to establish a global economy. However, the yield of CO2 hydrogenation is also limited by the thermodynamic equilibrium. Under the conditions of 250℃, 3MPa and H2 / CO2 pressure ratio of 1, the methanol yield of CO2 hydrogenation can only reach 3.5C-mol%. If the generated methanol is consumed in situ by PET or PBT methanolysis, the CO2 hydrogenation yield can be improved. At the same time, the hydrogenation catalyst used for CO2 conversion can carry out the hydrogenation of terephthalic acid dimethyl ester (DMT), thereby improving the yield of PET or PBT methanolysis.

[0021] Therefore, the present application provides a simple and sustainable catalytic method for converting PET or PBT into high-value chemicals by overcoming the thermodynamic limitations involved and using CO2 as a solvent precursor. Specifically, the present application combines CO2 hydrogenation, PET or PBT methanolysis and DMT hydrogenation in a one-pot catalytic system, as shown in the reaction scheme Figure 1 Due to the double promotion of the reaction, the yield of PET or PBT degradation and CO2 hydrogenation is significantly improved.

[0022] The present application provides a method for co-catalytic conversion of a polyester and CO2, wherein CO2 reacts with hydrogen under the action of a catalyst to generate methanol, the polyester is depolymerized under the action of the methanol to generate terephthalic acid dimethyl ester, and the terephthalic acid dimethyl ester is further converted into a hydrogenation product by hydrogenation under the action of the catalyst.

[0023] The polyester is selected from any one of polyethylene terephthalate and polybutylene terephthalate.

[0024] In some embodiments of the present application, the catalyst is selected from a catalyst composed of one or more metals selected from Cu, Fe, Cr, Ag, Mn, In, Mo, Nb, Re, Pd, Mg, Al, Ca, Rh, Zn, Ni, Ga and Zr, preferably a copper-based catalyst.

[0025] In some embodiments of the present application, the copper-based catalyst is a CuFeM composite catalyst, wherein M is at least one selected from Mg, Cr, Ag, Mn, In, Mo, Nb and Re.

[0026] In some embodiments of the present application, the mass ratio of the polyester and the catalyst is 1:(0.1-1), preferably 1:1.

[0027] In some embodiments of the present application, the reaction conditions for the catalytic conversion of the polyester and CO2 are: temperature 220℃ -280℃, time 1.5h-48h, preferably: temperature 240℃-260℃, 12h-48h.

[0028] In some embodiments of the present application, the reaction gas environment for the catalytic conversion of the polyester and CO2 is CO2, hydrogen and argon, and the total pressure of the gas is 0.5MPa-6MPa, preferably 3MPa.

[0029] In some embodiments of the present application, the pressure of CO2 and hydrogen is 0.5MPa-3MPa, and the partial pressure ratio of CO2 and hydrogen is 1:0.5-1:5, preferably 1:1-1:3, based on the pressure of CO2 and hydrogen.

[0030] In some embodiments of the present application, the hydrogenation product is at least one selected from cyclohexane dimethyl dicarboxylate and p-xylene.

[0031] In the present application, the argon (Ar) in the reaction gas environment does not participate in the reaction and is used to adjust the gas pressure.

[0032] In the present application, the reaction vessel used is a high-pressure reactor, and the vessel used can be any vessel that can achieve the purpose of the present application, and exemplary stainless steel autoclave reactors can be used.

[0033] In some embodiments of the present application, the catalytic conversion reaction is carried out in a solvent, and the solvent is at least one selected from dioxane, n-heptane and tetrahydrofuran, preferably dioxane.

[0034] In the present application, the catalyst can be recovered after the reaction by washing with a solvent. Exemplarily, the catalyst is washed with dioxane for 3 times and can be added to the next cycle of reaction for repeated use.

[0035] In the present application, the atmosphere environment of the reaction needs to be free of air, and the present application does not limit the operation mode of the process as long as the purpose of the present application can be achieved. Exemplarily, the reactor is filled to the total reaction pressure after being washed with the reaction gas three times.

[0036] The inventors found that the CuFeM catalyst derived from the layered double hydroxide (LDHs) precursor has a unique structure that can distribute Cu 2+ , Fe 3+ and M x+ cations in the hydroxide layer at the atomic level and improve the stability of the catalyst through structural topology conversion. In the present application, the method for obtaining the catalyst is not limited as long as the purpose of the present application can be achieved.

[0037] The inventors also found that when PET exists in the reaction system, CO2 reacts with hydrogen to generate methanol (MeOH) under the action of the catalyst Cu4Fe1Mg1Cr1, and the productivity is as high as 11.9 mmol g cat -1 , which is about twice as high as that without adding PET (6.5 mmol g cat -1 ). PET is converted through ester exchange and DMT hydrogenation to obtain cyclohexane dimethyl dicarboxylate (DMCD) and p-xylene (PX), and a high yield of ethylene glycol (EG, 88.6%), and the yield of EG directly reflects the degree of PET depolymerization and can be used as an indicator of PET degradation. The detection of EG shows that methanol decomposition is the main way of PET degradation in the presence of H2. At the same time, in the absence of H2, PET is decomposed in a large amount of methanol solvent, and the yield of EG is only 12.1%, that is, H2 promotes the methanol decomposition reaction of PET through the hydrogenation of DMT.

[0038] In the present application, the term "yield" means the ratio of the actual yield of a product to the theoretical yield; in the present application, the calculation formula of the methanol yield is: methanol yield = the number of moles of methanol obtained + the number of moles of ethylene glycol x 2. In the present application, the calculation formula of the yield of EG, DMT, DMCD and PX is: EG / DMT / DMCD / PX yield = (the number of moles of detected EG / DMT / DMCD / PX) / (the number of moles of PET monomer used) x 100%.

[0039] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the present application.

[0040] Test method and equipment:

[0041] The yield of each component in the target solution is determined by Agilent 8860 HP-innowax chromatographic column.

[0042] Catalyst synthesis and source:

[0043] The catalysts employed in the various embodiments of the present application are prepared by the following procedures.

[0044] Synthesis procedure: Cu4Fe1Mg 2-x Cr x -LDH quaternary precursor. First, 0.016 mol Cu(N03)2-6H20, 0.004 mol Fe(N03)3-9H20, (0.008-0.004x) mol Mg(N03)2-3H20 and 0.004x mol Cr(N03)3-9H20 are dissolved in 50 mL deionized water to form a mixed salt solution. Then, 0.09 mol NaOH is dissolved in 50 mL deionized water and added to the above mixed salt solution under vigorous stirring, adjusting the pH to 9.5. After aging in a 60 °C water bath for 24 h, the precipitate is washed to neutral pH and then dried at 60 °C to obtain the quaternary precursor Cu4Fe1Mg 2-x Cr x -LDH.

[0045] Activation procedure: The obtained Cu4Fe1Mg 2-x Cr x -LDH is reduced in a dilute hydrogen atmosphere consisting of 10% H2+90% N2, heating at a rate of 2 °C min -1 to 350 °C and reducing for 3 h to obtain the activated Cu4Fe1Mg 2-x Cr x .

[0046] Cu4Fe1Mg 2-x N x is derived from Cu4Fe1Mg 2-x N x -LDH by changing N to Ag, Mn, In, Mo, Nb and Re, prepared according to the above synthesis and activation procedures.

[0047] The preparation procedure of Cu4Fe1Mg1is the same as that of Cu4Fe1Mg 2-x Cr x except that Cr(N03)3-9H20 is not added.

[0048] The preparation procedure of Cu4Mg2Al1is the same as that of Cu4Fe1Mg 2-x Crx The synthesis and activation process are the same as Cu4Mg2Al1.

[0049] The preparation process of Cu4Mg2Ga1 is the same as Cu4Mg2Al1 except that Al(NO3)3·9H2O is replaced by Ga(NO3)3·9H2O.

[0050] The preparation process of Cu4Ni2Zn1 is the same as Cu4Mg2Al1 except that 0.008 mol Mg(NO3)2·3H2O and 0.004 mol Al(NO3)3·9H2O are replaced by 0.008 mol Ni(NO3)2·6H2O and 0.004 mol Zn(NO3)2·6H2O.

[0051] The preparation process of Cu4Ca1Mg1Al1 is the same as Cu4Mg2Al1 except that 0.008 mol Mg(NO3)2·3H2O is replaced by 0.004 mol Ca(NO3)2·4H2O and 0.004 mol Mg(NO3)2·3H2O.

[0052] The preparation process of ZrO2-Cu is that 0.016 mol Cu(NO3)2·6H2O and 0.008 mol Zr(NO3)4 are co-precipitated in oxalic acid solution, and after washing and drying, ZrO2-Cu-oxalic acid precursor is obtained, and then activated, and the activation process is the same as Cu4Fe1Mg 2-x Cr x .

[0053] The preparation process of Cu4Mg2Al1Rh 0.2 catalyst is that Cu4Mg2Al1 catalyst is impregnated in 5% Rh(NO3)3 aqueous solution, and after washing and drying, Cu4Mg2Al1Rh 0.2 -LDH precursor is obtained, and then activated, and the activation process is the same as Cu4Fe1Mg 2-x Cr x .

[0054] The CuZnAl, Pd / C and Ru / C catalysts used in the examples and comparative examples of the present application are commercial catalysts.

[0055] Example 1

[0056] Into a 250 mL stainless autoclave reactor, 100 mL of dioxane solvent and 0.5 g of PET were added, then 0.5 g of catalyst Cu4Fe1Mg1Cr1was quickly added without passivation or exposure to air. CO2+H2(gas pressure ratio 1 / 1) was used as the reaction gas, the reactor was washed with the reaction gas three times and then filled to a total reaction pressure of 3 MPa, and reacted at 240°C and a stirring speed of 500 rpm for 12 hours.

[0057] 0.1 g of n-heptane was added as an internal standard to the uniformly mixed solution after the reaction, and the amount of each product in the mixed solution was determined by chromatography.

[0058] Example 2

[0059] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1.

[0060] Example 3

[0061] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1Ag1.

[0062] Example 4

[0063] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1Mn1.

[0064] Example 5

[0065] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1In1.

[0066] Example 6

[0067] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1Nb1.

[0068] Example 7

[0069] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1Re1.

[0070] Example 8

[0071] The rest was the same as Example 1 except that the catalyst was Cu4Fe1Mg1Mo1.

[0072] Example 9

[0073] The rest was the same as Example 1 except that the catalyst was Cu4Mg2Al1.

[0074] Example 10

[0075] The rest was the same as Example 1 except that the catalyst was Cu4Mg2Ga1.

[0076] Example 11

[0077] The same as Example 1 except that the catalyst was Cu4Ca1Mg1Al1.

[0078] Example 12

[0079] The same as Example 1 except that the catalyst was Cu4Ni2Zn1.

[0080] Example 13

[0081] The same as Example 1 except that the catalyst was Zr02-Cu.

[0082] Example 14

[0083] The same as Example 1 except that the catalyst was Cu4Mg2Al1Rh 0.2 .

[0084] Example 15

[0085] The same as Example 1 except that the catalyst was CuZnAl.

[0086] Example 16

[0087] The same as Example 1 except that the catalyst was Pd / C.

[0088] Example 17

[0089] The same as Example 1 except that the catalyst was Cu4Fe1Mg1Cr 0.05 .

[0090] Example 18

[0091] The same as Example 1 except that the catalyst was Cu4Fe1Mg1Cr 0.1 .

[0092] Example 19

[0093] The same as Example 1 except that the catalyst was Cu4Fe1Mg1Cr 0.5 .

[0094] Example 20

[0095] The same as Example 1 except that the reaction temperature was 220°C.

[0096] Example 21

[0097] The same as Example 1 except that the reaction temperature was 260°C.

[0098] Example 22

[0099] The same as Example 1 except that the reaction temperature was 280°C.

[0100] Example 23

[0101] The same as Example 1 except that the total pressure of the reaction was 1 MPa.

[0102] Example 24

[0103] The same as Example 1 except that the total pressure of the reaction was 2 MPa.

[0104] Example 25

[0105] The same as Example 1 except that the total pressure of the reaction was 4 MPa.

[0106] Example 26

[0107] The same as Example 1 except that the reaction atmosphere was 0.5 MPa (50% CO2+ 50% H2) + 2.5 MPa Ar.

[0108] Example 27

[0109] The same as Example 1 except that the reaction atmosphere was 1 MPa (50% CO2+ 50% H2) + 2 MPa Ar.

[0110] Example 28

[0111] The same as Example 1 except that the reaction atmosphere was 1.5 MPa (50% CO2+ 50% H2) + 1.5 MPa Ar.

[0112] Example 29

[0113] The same as Example 1 except that the reaction atmosphere was 3 MPa CO2+ H2, CO2 / H2 pressure ratio = 1 / 3.

[0114] Example 30

[0115] The same as Example 1 except that 1.0 g of PET was added and the reaction time was 1.5 h.

[0116] Example 31

[0117] The same as Example 1 except that 1.0 g of PET was added and the reaction time was 3 h.

[0118] Example 32

[0119] The same as Example 1 except that 1.0 g of PET was added and the reaction time was 6 h.

[0120] Example 33

[0121] The same as Example 1 except that 1.0 g of PET was added and the reaction time was 24 h.

[0122] Example 34

[0123] The same as Example 1 except that 1.0 g of PET was added and the reaction time was 48 h.

[0124] Example 35

[0125] Cycling experiment: the catalyst after the reaction of Example 1 (first reaction) was collected by immersion in solvent dioxane, and then the catalyst was washed with dioxane for 3 times to obtain the catalyst for the second cycling experiment, denoted as Cu4Fe1Mg1Cr1-α.

[0126] The same as Example 1 except that the catalyst was replaced by Cu4Fe1Mg1Cr1-α.

[0127] Example 36

[0128] Cycling experiment: the catalyst after the reaction of Example 33 (second reaction) was collected by immersion in solvent dioxane, and then the catalyst was washed with dioxane for 3 times to obtain the catalyst for the third cycling experiment, denoted as Cu4Fe1Mg1Cr1-β.

[0129] The same as Example 1 except that the catalyst was replaced by Cu4Fe1Mg1Cr1-β.

[0130] The reaction conditions of Examples 1 to 36 and the yield results of each product in the mixed solution after reaction are shown in Table 1.

[0131]

[0132]

[0133] Comparative Examples 1 to 9

[0134] The same as Example 1 except that the catalyst type and the substrate were adjusted according to Table 2.

[0135] The catalyst type and the substrate of Comparative Examples 1 to 9 and the yield results of each product in the mixed solution after reaction are shown in Table 2.

[0136] Table 2

[0137]

[0138] Notes: a" / " in Table 2 indicates that the substance is not generated in the mixed solution after the reaction.

[0139] b The yield indicates the remaining unreacted portion of the DMT raw material.

[0140] Comparative Examples 10 to 14

[0141] The same as Example 1 except that PET is not added and the reaction time is adjusted according to Table 3.

[0142] The reaction time and the yield of each product in the mixed solution after the reaction of Comparative Examples 10 to 14 are shown in Table 3.

[0143] Table 3

[0144] Comparative Example Reaction time [h] MeOH [mmol] MeOH yield [%] CO yield [%] CHx yield [%] 10 1.5 1.82 2.8 0.07 0.03 11 3 2.09 3.2 0.06 0.03 12 6 2.14 3.3 0.07 0.04 13 24 2.67 4.1 0.21 0.09 14 48 3.29 5.1 0.3 0.46

[0145] Comparative Example 15

[0146] In a 250 mL stainless steel autoclave reactor, 100 mL of dioxane solvent, 0.5 g of PET, and 0.19 g of methanol were added, and then 0.5 g of catalyst Cu4Fe1Mg1Cr1 was quickly added without passivation or exposure to air, argon (Ar) was used as the reaction gas, the reactor was washed three times with Ar, and then filled to a total reaction pressure of 3 MPa, and reacted at 240°C and 500 rpm for 12 hours.

[0147] 0.1 g of n-heptane was added as an internal standard to the mixed solution after the reaction, and the amount of each product in the mixed solution was measured by a chromatographic column.

[0148] Comparative Example 16

[0149] The same as Comparative Example 15 except that the reaction time is 48 h.

[0150] The yield of each product in the mixed solution after the reaction of Comparative Examples 15 and 16 is shown in Table 4.

[0151] Table 4

[0152] Comparative Example EG yield [%] DMT yield [%] 15 10 2 16 12.1 2.9

[0153] Example 37

[0154] The same as Example 1 except that PET is replaced with polybutylene terephthalate (PBT).

[0155] Comparative Example 17

[0156] The same as Example 1 except that PET is replaced with polyhexamethylene adipate (PHA).

[0157] The yield results of each product in the mixed solution after the reaction of Example 37 and Comparative Example 17 are shown in Table 5.

[0158] Table 5

[0159] Substrate BD yield [%] DMT / DMA yield [%] DMCD yield [%] PX yield [%] Example 37 PBT 33.6 6.2 a ]]> 9.1 13.4 Comparative Example 17 PHA 26.0 13.4 b ]]> c ]]> ​ c ]]> ​

[0160] Note: a Dimethyl terephthalate (DMT)

[0161] b Dimethyl adipate (DMA)

[0162] c " / " in Table 5 indicates that no such substance is generated in the mixed solution after the reaction.

[0163] As can be seen from the yield data of Examples 1 to 16 given in Table 1, the catalysts provided in the present application can all achieve the PET and CO2 co-catalytic conversion reaction. Among the copper-based catalysts, CuFeMgN (N = Cr, Ag, Mn, In) has better catalytic effect on PET depolymerization and DMT hydrogenation. Considering factors such as PET degradation yield and DMCD selectivity, CuFeMgCr is selected as the best catalyst of the present application.

[0164] As can be seen from the reaction results of Example 1 and Examples 17 to 19 given in Table 1, adjusting the molar ratio of metal elements in the CuFeMgCr composite catalyst can adjust the conversion rate of PET and the selectivity of products. Among them, Cu4Fe1Mg1Cr1 catalyst has the best depolymerization performance, with the highest EG yield (75.5%) and the lowest DMT selectivity (9.0%), which is conducive to obtaining more high value-added product DMCD.

[0165] In Comparative Examples 1-9, Cu4Fe1Mg1Cr1, traditional CO2 hydrogenation catalysts (e.g., Pd / C and CuZnAl) and aromatic hydrogenation catalysts (e.g., Pd / C and Ru / C) were compared, as shown in Table 2. In combination with Examples 1 and 15-16, CuZnAl and Pd / C catalysts can convert CO2 to methanol with better reactivity than Cu4Fe1Mg1Cr1. Pd / C, CuZnAl and Ru / C can all hydrogenate DMT in the presence of CO2 to produce DMCD and / or PX with comparable reactivity to Cu4Fe1Mg1Cr1. However, Ru / C cannot produce methanol from CO2 and thus cannot depolymerize PET. For CuZnAl and Pd / C, although they promote the hydrogenation of both CO2 and DMT, their methanol production is significantly inhibited in the presence of PET. In addition, PX is produced as a major byproduct along with DMT, indicating that the catalytic performance of CuZnAl and Pd / C is affected by the dissolved PET in the solution. Considering factors such as product selectivity and tolerance to adverse conditions, CuFeMgCr composite catalysts are the preferred catalysts for the dual-promoted reaction system.

[0166] As can be seen from Table 1, in Examples 1 and 20-22, as the temperature increases, PET methanolysis and subsequent DMT hydrogenation exhibit better performance at higher temperatures due to the exothermic reaction of CO2 hydrogenation to synthesize methanol. The best performance of PET methanolysis is obtained at 240°C. At 220°C, PET methanolysis cannot proceed effectively because methanol cannot be generated quickly. At 240-280°C, methanol synthesis is inhibited.

[0167] In Examples 1 and 23-25, the total reaction pressure was adjusted from 1 MPa to 4 MPa. The yield of each product in Table 1 changes slightly between 3 MPa and 4 MPa, indicating that increasing the pressure does not promote methanol production. When the pressure is lowered, the EG yield at 1 MPa is only half of that at 3 MPa. At the same time, the total yield of DMT, DMCD and PX under different pressures is very close to the EG yield, indicating that DMT hydrogenation is not sensitive to the total pressure or H2 partial pressure.

[0168] Further, in Examples 1 and 26 to 28, the present application adjusted the partial pressure of CO2+H2from 0.5 MPa to 3 MPa. When the partial pressure of CO2+H2was 1.5 MPa, the EG yield was 57.5%, which was similar to the yield at a total reaction pressure of 2 MPa, indicating that methanol was still effectively produced at this time. However, unexpectedly, when the partial pressure of CO2+H2was 1 MPa, the yield of EG decreased to 11.5%, which was much lower than the yield at a total reaction pressure of 1 MPa. This result indicates that the CO2concentration plays a crucial role in methanol synthesis. In Example 29, by adjusting the CO2 / H2ratio to 1 / 3 to lower the CO2partial pressure, the EG yield decreased to 58.3%, even though CO2 / H2= 1 / 3 is generally the optimal ratio for methanol synthesis.

[0169] For Comparative Examples 10 to 14, it can be seen from Table 3 that CO2was rapidly hydrogenated to methanol without PET in the first 3 h. In the next 45 h, the yield slowly increased and approached the thermodynamic equilibrium limit of 5.0% (formation rate of 1.4 mmol g cat -1 h -1 ).

[0170] For Examples 30 to 34, the methanol formation rate in the first 3.0 h remained at 1.4 mmol g cat -1 h -1 However, a high yield of methanol was obtained in 48 h (Table 1, 5.94 mmol, 9.4%), which was about twice as high as the reaction system without PET (Table 1, 3.29 mmol, 5.0%), and the methanol yield exceeding the original thermodynamic equilibrium limit confirmed the significant promotion of CO2hydrogenation in the presence of PET. In addition, the Cu4Fe1Mg1Cr1 catalyst showed high selectivity (95%) for the synthesis of methanol from CO2hydrogenation, regardless of whether PET was added.

[0171] For Comparative Examples 15 to 16, from Table 4, it can be seen that when excess methanol was mixed with PET under Ar atmosphere (no H2), only 2.9% DMT and 12.1% EG were obtained after 48 h. Therefore, PET was not fully depolymerized into monomers, but likely to be microplastics and oligomers. From the data of Example 32 in Table 1, it can be seen that with CO2 and H2 instead of methanol, the yield of PET degradation product EG reached 88.6% after 48 h. The degradation products included 3.7% DMT, 28.6% DMCD, and 49.3% PX. The total yield of these products was 81.6%, close to the stoichiometric ratio of monomer units in PET. Therefore, the degradation of PET was promoted in the presence of CO2 hydrogenation. Overall, the synergistic coupling of CO2 hydrogenation and PET degradation led to a double promotion.

[0172] Examples 35 and 36 evaluated the stability of the catalyst. The catalyst after the first reaction was washed and recycled for reuse. After three cycles, the EG yield of PET degradation catalyzed by Cu4Fe1Mg1Cr1 remained at a high level, and had similar product selectivity as Example 1.

[0173] Examples 37 and Comparative Example 17 evaluated the transferability (to other substrates) of the one-pot catalytic reaction, which extended the substrates of this application to other polyester plastics. For PBT, the yield of butanediol (BD) after the catalytic reaction by Cu4Fe1Mg1Cr1 was 33.6%, and the selectivity of the depolymerization products was similar to PET (Table 5). Therefore, the double promotion between CO2 hydrogenation and polyester methanol decomposition also applied to PBT degradation. However, for the degradation of polyhexamethylene adipate (PHA), the BD yield was only 26.0%, because dimethyl adipate (DMA) could not be converted by hydrogenation. Therefore, to achieve the double promotion effect of CO2 hydrogenation and polyester methanol decomposition, hydrogenation of the degradation products is a necessary condition.

[0174] The above descriptions are only preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the co-catalytic conversion of a polyester and CO2, wherein, CO2 reacts with hydrogen under the action of a catalyst to generate methanol, the polyester is depolymerized under the action of the methanol to generate terephthalic acid dimethyl ester, and the terephthalic acid dimethyl ester is further converted into a hydrogenation product through hydrogenation under the action of the catalyst; The polyester is selected from any one of polyethylene terephthalate and polybutylene terephthalate; The catalyst is selected from at least one of Cu4Mg2Al1, Cu4Mg2Ga1, Cu4Ca1Mg1Al1, Cu4Ni2Zn1, ZrO2-Cu, Cu4Mg2Al1Rh 0.2 , CuZnAl or CuFeM complex catalysts, M being selected from at least one of Mg, Cr, Ag, Mn, In, Mo, Nb and Re.

2. The conversion process of claim 1, wherein, The mass ratio of the polyester to the catalyst is 1:(0.1-1).

3. The conversion process of claim 1, wherein, The reaction conditions of the catalytic conversion of the polyester and CO2 are as follows: temperature 220-280 ℃, and time 1.5-48 h.

4. The conversion process of claim 1, wherein, The reaction gas environment of the catalytic conversion of the polyester and CO2 is CO2, hydrogen and argon, and the total pressure of the gas is 0.5-6 MPa.

5. The conversion process of claim 4, wherein, The pressure of the CO2 and hydrogen is 0.5-6 MPa, and the partial pressure ratio of the CO2 and hydrogen is 1:0.5-1:5 based on the pressure of the CO2 and hydrogen.

6. The conversion process of claim 1, wherein, The hydrogenation product is at least one of cyclohexane dimethyl ester and p-xylene.

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