Magnesium-based catalytic recycling process technology of polyester

Abstract

The invention relates to the field of functional materials, in particular to chemical recycling of a series of polyesters represented by PET (Polyethylene Terephthalate) by using a novel and efficient magnesium-based catalyst technology, which is of great significance for treating plastic pollution and realizing green circular economy.

Description

[0001] The present application relates to the field of functional materials, in particular to the use of a new type of efficient magnesium-based catalyst technology to realize the chemical recycling and reuse of a series of polyesters represented by PET, which is of great significance to the management of plastic pollution and the realization of green circular economy.

[0002] Polyesters containing continuous ester

-C(O)-O-

[0003] There are two major categories of polyester recycling, namely physical and chemical methods. From a technical logic point of view, chemical recycling has greater broad-spectrum applicability and economic reuse value, and is the focus of current industry technology research. In particular, by catalytic chemical depolymerization of polyester materials into high-value-added monomer chemicals, not only is environmental pollution eliminated, but the monomer chemicals obtained can be directly reused to produce polyester materials in the polymerization section, which helps to practice efficient circular economy of petrochemical resources.

[0004] Taking PET polyester as an example, it can be decomposed into low molecular weight oligomers or small molecule monomers through catalytic ester decomposition or transesterification, especially to prepare so-called BHET (diethylene glycol terephthalate) or DMT (dimethyl terephthalate), which can be reused as monomers for producing PET or raw materials for manufacturing other chemical products after separation and purification, thereby realizing the recycling of resources.

[0005] Still taking PET polyester as an example, current research activities focus on its alcoholysis method of recycling, i.e. using ethylene glycol or methanol to convert PET into corresponding monomers BHET or DMT, and oligomers. Macromolecular polyesters usually have a relatively complex three-dimensional chemical structure, especially the structure may contain crystalline regions or non-bonding induced associations, which increases the reaction energy barrier of alcoholysis, directly leading to an increase in reaction temperature and a decrease in reaction yield. Therefore, through the use of catalyst technology, it is an important issue to be solved in the field to realize the efficient chemical degradation and recycling of polyesters under mild, safe and environmentally friendly conditions. The latest progress review can be referred to in Green Chem., 2021, 23, 3765.​​

[0006] For example, Fujita Chemicals of Japan disclosed a method for preparing BHEP monomers by alcoholysis of PET in ethylene glycol at approximately 250 degrees Celsius under a nitrogen atmosphere. The catalysts disclosed in the literature primarily utilize Lewis acid-type catalysts to activate the carbonyl group of esters, such as zinc acetate; or their mechanisms primarily involve strong nucleophilic reagents attacking substituted ester alkoxy groups, such as sodium ethoxide (Green Chem., 2023, 25, 1442). Logically, if a catalyst could possess both the function of activating carbonyl groups with Lewis acids and the strong nucleophilic attack properties of (Lewis base) alkoxy groups—integrating these two seemingly contradictory properties—it should theoretically achieve better catalytic reaction efficiency.

[0007] Guided by the aforementioned design principles, this application unexpectedly discovered through experimentation that a novel magnesium-based catalyst system can enable the production of monomer compounds from polyesters such as PET at relatively low temperatures, with faster reaction rates and higher yields. These monomer compounds can be directly recycled into the polyester regeneration process, demonstrating significant cost and efficiency advantages. Furthermore, the discovered magnesium-based catalyst is inexpensive, readily available, and exhibits stable activity, while its introduction and use are environmentally friendly. Considering the widespread application of magnesium-based substances in polymers, particularly as flame retardant additives, this discovery is quite unexpected. [Summary of the Invention]

[0008] This application has now discovered that magnesium-based catalysts have particularly superior catalytic performance for polyester alcoholysis. As shown in reaction formula (I), polyester PET and ethylene glycol EG react in the presence of magnesium-containing catalyst Cat-Mg* under the following reaction conditions to efficiently prepare monomeric diethylene glycol terephthalate (BHET).

[0009]

[0010] The catalyst Cat-Mg* is a single or complex catalytic system containing at least one of the following magnesium-based compound components: a magnesium alkoxy compound in the form of Mg(ORO)2 or Mg(OH)(ORO) (R0 is hydrogen or a hydrocarbon substituent containing 1-12 carbon atoms), or a metal oxide MgO that can react in situ with an alcohol (ethylene glycol) to generate a metal alkoxy compound, or a magnesium carbonate (hydrogen) salt, carboxylate salt, halide salt, or sulfate (hydrogen) salt.

[0011] Preferably, the magnesium-based compound components include: Mg(OEt)2, Mg(OMe)2, Mg(OH)(OEt), Mg(OH)(OMe), Mg(On-Pr)2, Mg(Oi-Pr)2, Mg(OCH2CH2O), Mg(OH)(OCH2CH2OH), Mg(OCH2CH2OH)2, MgO, Mg(OAc)2, Mg(OH)2, MgCl2, MgSO4, or MgCO3.

[0012] The conditions are at least one of solvent, temperature, pressure (or vacuum), and additives.

[0013] Additives are catalysts or accelerators.

[0014] Preferably, based on the PET equivalent of the reactant, the amount of additive used is 0.001-1000% of the reactant; more preferably 0.01-300%, more preferably 0.1-100%, and even more preferably 0.1-50%.

[0015] The temperature ranges from -25 to 450 degrees Celsius, preferably from -20 to 300 degrees Celsius; more preferably from 10 to 250 degrees Celsius.

[0016] Pressure refers to the pressure under which the reaction system is carried out, or under a certain degree of vacuum. The pressure of the reaction process is 0.001-200 atmospheres, preferably 0.01-100 atmospheres, and more preferably 0.1-10 atmospheres.

[0017] The solvent is selected from at least one of substituted or unsubstituted aromatic hydrocarbons, straight or branched aliphatic hydrocarbons, (sulfoxides), amides, ethers, alcohols, esters, ketones, nitriles, carboxylic acids, water, amines, carbonates, ionic liquids, and supercritical carbon dioxide containing 1 to 24 carbons; or the liquid or molten substrate (including mixtures thereof) itself acts as a solvent medium.

[0018] Preferably, ethylene glycol serves as both a reactant and a reaction solvent. This simplifies the post-processing of the reaction system and the separation and purification of the products BHEP and oligomers.

[0019] The use of solvents is preferred but not essential. Under certain conditions, it is preferable not to use solvents, i.e., to use the dissolved or melted form of the reactants, or to directly mix the reactants and then react them under heating, grinding, or gas-phase conditions; and to use supercritical carbon dioxide as the reaction medium. The advantages of using supercritical carbon dioxide as the reaction medium are that it is environmentally friendly and facilitates the occurrence of the reaction and the separation of products, advantages well known to professionals in this field.

[0020] Compared with known results in the literature, the outstanding advantages of the novel magnesium-based catalyst system disclosed in this invention are that it achieves the chemical recycling of polyester with faster reaction rates, higher product yields, and milder operating conditions. Furthermore, the magnesium-based catalyst material is non-toxic, harmless, safe, convenient, inexpensive, and readily available, making it highly environmentally friendly and application-friendly. This technology is widely applicable to the recycling of polyester (PET) or PET-containing compounded or modified polymer systems.

[0021] This invention further discloses that the magnesium-based catalyst Cat-Mg* has extremely wide applicability in catalyzing the alcoholysis reaction of polyester materials. As shown in the following general reaction formula (II), the polyester material described by general structural formula A reacts with an alcohol (or water) ROH with structure B in the presence of the magnesium-containing catalyst Cat-Mg* under the following reaction conditions to efficiently recover and prepare the monomer or oligomer shown in structural formula C, as well as the alcohol shown in structural formula D, thereby achieving the green recycling of materials C and D.

[0022]

[0023] Substrate A is a polyester material containing an ester functional group in a straight or branched polymer chain, and R is a hydrogen or a straight or branched hydrocarbon group containing 1-12 carbons, substituted or unsubstituted, containing 0-6 discontinuous hydroxyl, carboxyl, or halogen substituents.

[0024] Exemplary, and not limiting, examples of substrate A are commercially known polyesters such as PBAT, PBS, PLA, PGA, PHA, PCL, and composite or blended polymeric materials containing at least one of the aforementioned polyesters.

[0025] A preferred method for performing general formula (II) is to use PBAT, which is difficult to degrade naturally, as a polyester substrate, and mix it with 1,4-butanediol BDO in the presence of a magnesium-based catalyst Cat-Mg* under reaction conditions to carry out alcoholysis recovery and recycling to obtain the corresponding monomer materials dibutyl terephthalate and dibutyl adipate.

[0026]

[0027] We will explain further in the embodiments.

Detailed Implementation Methods

[0028] The essence of the invention is further illustrated below with reference to specific embodiments:

[0029] Example:

[0030]

[0031] Raw material pretreatment: Wash and cut the polyester PET plastic bottles, wash with ethanol, and dry at 50℃ for later use;

[0032] Experimental procedure: Weigh 1 gram of the above-mentioned PET material, 3-6% magnesium-based catalyst Cat-Mg*, and 5 grams of dry ethylene glycol EG. After mixing, the reaction system was reacted at 195℃. After a certain period of time, the reaction system was observed to be homogeneous and clear, and the endpoint was monitored by TLC. After the reaction was completed, the system was allowed to return to room temperature, and mesitylene was added as an internal standard. The reaction yield was quantitatively evaluated by nuclear magnetic resonance (NMR).

[0033] Post-processing: The reaction mixture was distilled under reduced pressure at 135°C to recover ethylene glycol. Hot water was added for washing, and the mixture was filtered. The filtrate was placed in a refrigerator overnight for crystallization. After crystallization, the mixture was washed with cold water and filtered. The filter cake was dried to obtain pure BHET product.

[0034] Item 1: 6% Mg(OEt)2, PET completely dissolved in 1.5 hours, BHET yield 92%;

[0035] Item 2: 6% MgO, PET completely dissolved in 2.5 hours, yield 83%;

[0036] Serial No. 3: 3% Mg(OEt)2 + 3% NaOH, PET completely dissolved in 2.5 hours, yield 76%;

[0037] Serial No. 4: 3% Mg(OEt)2 + 3% CaO, PET completely dissolved in 2.5 hours, yield 72%;

[0038] Serial No. 5: 1% Mg(OEt)2 + 5% MgO, PET completely dissolved in 2.5 hours, yield 80%;

[0039] Serial number 6: 2% Mg(OEt)2 + 4% MgO, PET completely dissolved in 2.5 hours, yield 83%;

[0040] Item 7: 3% Mg(OEt)2 + 3% MgO, PET completely dissolved in 2 hours, yield 86%;

[0041] Item 8: 4% Mg(OEt)2 + 2% MgO, PET completely dissolved in 2 hours, yield 86%;

[0042] Item 9: 3% MgO + 3% EtONa, PET remains in large quantity after 2.5 hours, yield 35%;

[0043] Serial No. 10: 1% Mg(OEt)2 + 3% EtONa, with a large amount of PET remaining after 2.5 hours, yield 41%;

[0044] Serial No. 11: 3% Mg(OEt)2 + 1% EtONa, PET completely dissolved in 2.5 hours, yield 78%;

[0045] Serial number 12: 3% Mg(OEt)2, PET completely dissolved in 2.5 hours, yield 80%;

[0046] Item 13: 3% Mg(OAc)2, PET completely dissolved in 2.5 hours, yield 72%;

[0047] Item 14: 3% Mg(OH)2, PET completely dissolved in 3 hours, yield 68%;

[0048] Serial No. 15: 3% MgCl2 + 3% EtONa, PET completely dissolved in 2.5 hours, yield 71%;

[0049] Serial No. 16: 3% Mg(OEt)2 + 3% Mg(OH)2, PET completely dissolved in 2 hours, yield 82%;

[0050] Comparative Example 17:3% EtONa, with a significant amount of PET remaining after 4 hours, yield was 46%.

[0051] Comparative Example 18: 3% Zn(OAc)2, PET was completely dissolved in 4 hours, yield 64%;

[0052] Comparative Example 19: Without catalyst, a large amount of PET remained after 8 hours, with a yield of 7%.

[0053] The above experimental results clearly demonstrate the superior performance of magnesium-based catalysts, particularly in terms of faster reaction efficiency and higher product yield.

[0054] Example:

[0055]

[0056] Weigh 1 gram of PBAT polyester powder, 3% magnesium-based catalyst Cat-Mg*, and 8 grams of butanediol (BDO). Mix the mixture and react at 195°C. After a certain period of time, observe that the reaction system becomes homogeneous and clear, and then monitor the endpoint using TLC. After the reaction is complete, allow the system to return to room temperature, remove butanediol under reduced pressure, and elute the residue by silica gel column chromatography with a hexane / ethyl acetate gradient to obtain the products dibutylene terephthalate and dibutylene adipate.

[0057] Serial number 20: 3% Mg(OEt)2, PBAT was completely dissolved in 2 hours to obtain 0.43 g of dibutyl terephthalate and 0.46 g of dibutyl adipate;

[0058] Serial number 21: 3% MgO, PBAT completely dissolved in 2.5 hours to obtain 0.38 g of dibutyl terephthalate and 0.42 g of dibutyl adipate.

[0059] It should be emphasized that the above embodiments are merely exemplary and not limiting. Based on the disclosure of this application, any adjustments or changes to the reaction conditions or parameters that a person skilled in the art might normally adopt will not deviate from the spirit of the invention. The scope of protection of this patent shall be determined by the relevant claims.

Claims

1. A novel process technology for the degradation, recycling, and reuse of polyester PET catalyzed by a magnesium-based catalyst, as shown in reaction formula (I), wherein polyester PET and ethylene glycol EG react in the presence of a magnesium-containing catalyst (Cat-Mg*) under certain reaction conditions to efficiently prepare the monomer diethylene glycol terephthalate (BHET): The catalyst Cat-Mg* is a single or complex catalytic system containing at least one of the following magnesium-based compound components: a magnesium alkoxy compound in the form of Mg(ORO)2 or Mg(OH)(ORO) (R0 is hydrogen or a hydrocarbon group containing 1-12 carbon atoms), or a magnesium metal oxide MgO, or a magnesium carbonate (hydrogen) salt, carboxylate salt, halide salt, or sulfate (hydrogen) salt; conditions are at least one of solvent, temperature, pressure (or vacuum), and additives; the additives are reaction catalysts or promoters.

2. A novel process technology for the degradation, recycling, and reuse of ester-containing functional polymers catalyzed by a magnesium-based catalyst, as shown in the general reaction formula (II), involves the reaction of a polyester substance described by general formula A with an alcohol (or water) ROH of structure B under the presence of a magnesium-containing catalyst (Cat-Mg*) under specific reaction conditions. This process efficiently recovers and prepares monomers or oligomers as shown in structure C, as well as an alcohol as shown in structure D, thereby achieving the green recycling of materials C and D. Substrate A is a polyester material containing an ester functional group in its straight or branched polymer chain; R is hydrogen or a straight or branched hydrocarbon group containing 1-12 carbons, substituted or unsubstituted, containing 0-6 discontinuous hydroxyl, carboxyl, or halogen substituents; Catalyst Cat-Mg* is a single or complex catalytic system containing at least one of the following magnesium-based compound components: a magnesium alkoxy compound in the form of Mg(ORO)2 or Mg(OH)(ORO), or a magnesium metal oxide MgO, or a magnesium carbonate (hydrogen) salt, carboxylate, halide salt, or sulfate (hydrogen) salt; conditions are at least one of solvent, temperature, pressure (or vacuum), and additives; the additive is a reaction catalyst or promoter.

3. According to claims (I) and (II), preferably, the magnesium-based catalyst compound component includes at least one of Mg(OEt)2, Mg(OMe)2, Mg(OH)(OEt), Mg(OH)(OMe), Mg(On-Pr)2, Mg(Oi-Pr)2, Mg(OCH2CH2O), Mg(OH)(OCH2CH2OH), Mg(OCH2CH2OH)2, MgO, MgCl2, Mg(OAc)2, Mg(OH)2, Mg(HCO3)2, MgSO4, or MgCO3.

4. According to claims (I) and (II), the amount of the additive used is 0.001-1000% of the reactant, based on the raw material equivalent; preferably 0.01-300%, more preferably 0.1-100%, and even more preferably 0.1-50%.

5. According to claims (I) and (II), the temperature is -25 to 450 degrees Celsius, preferably -20 to 300 degrees Celsius; more preferably 10 to 250 degrees Celsius.

6. According to claims (I) and (II), pressure refers to the reaction system being carried out under pressurized or vacuum conditions, and the pressure of the reaction process is 0.001-200 atmospheres, preferably 0.01-100 atmospheres, and more preferably 0.1-10 atmospheres.

7. According to claims (I) and (II), the solvent is selected from at least one of substituted or unsubstituted aromatic hydrocarbons containing 1-24 carbons, straight-chain or branched aliphatic hydrocarbons, (sulfoxides), amides, ethers, alcohols, esters, ketones, nitriles, carboxylic acids, water, amines, carbonates, ionic liquids, and supercritical carbon dioxide; or the liquid or molten substrate (including mixtures thereof) itself simultaneously serves as the solvent medium. Preferably, ethylene glycol in formula (I) or ROH in formula (II) serves as both the reactant and the reaction solvent medium.

8. According to claim (II), a preferred embodiment of formula (II) is to use PBAT, which is difficult to biodegrade, as a polyester substrate, and mix it with 1,4-butanediol (BDO) under the presence of a magnesium-based catalyst (Cat-Mg*) for alcoholysis recovery and recycling to obtain the corresponding monomer materials dibutylene terephthalate and dibutylene adipate:

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