Process for the alcoholysis of polyester plastics and use thereof

Abstract

The application relates to a glycolysis method of polyester plastics and application thereof. The glycolysis method comprises the following steps: mixing methanol, a catalyst and a cosolvent with polyester plastics, performing a glycolysis reaction to obtain a glycolysis product; and the cosolvent comprises 1,3-dioxolane. Through the design of the glycolysis method, the problems of lack of universality, harsh reaction conditions, high equipment requirement, poor product selectivity, high energy consumption and metal residue in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of polymer solid waste resource recycling technology, and in particular to a method for the alcoholysis of polyester plastics and its application. Background Technology

[0002] With the rapid development of the global plastics industry, polyester materials, due to their excellent mechanical properties, processing performance, and chemical stability, have been widely used in packaging, textiles, electronics, automobiles, medical and other fields. Among them, polylactic acid (PLA) as a bio-based biodegradable polyester, polycarbonate (PC) as an engineering plastic, polybutylene succinate (PBS), polybutylene adipate (PBA), and polyethylene adipate (PEA) as aliphatic polyesters, polybutylene adipate terephthalate (PBAT) as an aromatic-aliphatic copolyester, and polyethylene 2,5-furandicarboxylate (PEF) as a bio-based aromatic polyester have all achieved large-scale industrial production and application.

[0003] In 2024, global polycarbonate (PC) production totaled approximately 6.4 million tons, with China accounting for 2.4 million tons, or 37.5% of global production. Global bio-based biodegradable polyester production totaled approximately 1.44 million tons, including about 680,000 tons of PLA, 1.2 million tons of PBAT, and 175,000 tons of PBS. PEF, as a new generation of bio-based polyester, saw its global commercial production exceed 5,000 tons in 2025, with China producing 2,710 tons, indicating it is in a rapid industrialization phase. However, the large-scale production and use of polyester materials has also brought serious environmental problems and resource waste. In 2024, global plastic waste generation was approximately 350 million tons, with polyester waste accounting for over 25%, totaling nearly 90 million tons. Traditional landfill and incineration methods not only occupy large amounts of land resources but also produce toxic and harmful gases, causing secondary pollution. While mechanical recycling is currently the most commonly used recycling method, it has drawbacks such as decreased product performance, the ability to only reuse downgraded products, and the inability to handle mixed and heavily polluted waste polyester. Globally, the overall recycling rate of plastics is only around 9%, and for polyester materials, with the exception of a few varieties, the chemical recycling rate of most polyesters is less than 1%, resulting in a significant waste of valuable polyester resources. Therefore, developing efficient and environmentally friendly chemical recycling technologies to achieve closed-loop recycling of polyester materials has become a current research hotspot and an urgent need.

[0004] Among numerous chemical recycling methods, methanol hydrolysis is considered one of the most promising polyester recycling technologies for industrialization due to its relatively mild reaction conditions, high product purity, and the ability to directly obtain high-value monomers or intermediates. Methanol hydrolysis refers to the process in which polyester undergoes an transesterification reaction in the presence of methanol and a catalyst, breaking ester bonds to generate the corresponding dimethyl esters and diols. For example, PLA hydrolysis yields methyl lactate (Me-LA), PC hydrolysis yields dimethyl carbonate (DMC) and bisphenol A (BPA), PBS hydrolysis yields dimethyl succinate (DMSu) and 1,4-butanediol (BDO), PBAT hydrolysis yields dimethyl terephthalate (DMT), dimethyl adipate (DMA), and 1,4-butanediol, and PEF hydrolysis yields dimethyl 2,5-furandicarboxylate (FDME) and ethylene glycol (EG). Although there are numerous research reports on polyester methanol hydrolysis technology, several problems still exist. First, a broad-spectrum recovery system is lacking. Polyester plastics exhibit significant structural differences, resulting in marked variations in their physicochemical properties and degradation activity. Existing polyester alcoholysis technologies are mostly developed through research for single polyester varieties. For different polyesters, a new alcoholysis system needs to be established, requiring adjustments to process parameters such as reaction solvents, catalysts, reaction temperature, and reaction time. There is a lack of universally applicable alcoholysis processes for multiple common polyesters. Using differentiated processes for the degradation of various polyesters leads to high costs, complex processes, and poor equipment versatility, hindering the efficient resource utilization of various polyester wastes. Secondly, the reaction conditions are harsh and energy-intensive. Existing technologies often suffer from high temperature and pressure, long reaction times, poor product selectivity, and high energy consumption. Some catalysts are also toxic and corrosive, increasing process costs and environmental risks. Furthermore, existing technologies often require large amounts of organic solvents or additives when processing single pure polyester raw materials, resulting in high energy consumption and poor economic efficiency. Therefore, developing a unified methanol alcoholysis technology applicable to multiple polyester plastic raw materials, with high catalytic activity, mild reaction conditions, easy product separation, and environmental friendliness, is of great significance for promoting the industrial application of polyester chemical recycling technology and achieving the sustainable development of the plastics industry. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for the alcoholysis of polyester plastics and its applications. By designing the alcoholysis method, the problems of existing technologies, such as lack of versatility, harsh reaction conditions, high equipment requirements, poor product selectivity, high energy consumption, and metal residues, are solved.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for the alcoholysis of polyester plastics, the alcoholysis method comprising the following steps: mixing methanol, a catalyst and a co-solvent with polyester plastics to carry out an alcoholysis reaction to obtain an alcoholysis product; wherein the co-solvent comprises 1,3-dioxolane (DOL).

[0007] In this invention, the reason why methanol is chosen as the alcohol and 1,3-dioxolane (DOL) is chosen as the co-solvent to achieve the best alcoholysis effect is as follows: On the one hand, methanol, as a low-carbon alcohol, has a small molecular size and extremely low steric hindrance. As a nucleophile, it has high reactivity when attacking the ester bonds of polyester macromolecules, can efficiently cleave polymer chains, and produces few byproducts in the reaction system. The product has stable boiling point and thermal properties, and is easy to separate and purify. On the other hand, 1,3-dioxolane (DOL), as a cyclic ether solvent, exhibits excellent penetration, swelling, and even dissolution capabilities on polyester plastics with high crystallinity and dense structure.

[0008] More importantly, the combination of these two components breaks through the mass transfer resistance bottleneck of traditional solid-liquid heterogeneous reactions. During the reaction, the 1,3-dioxolane first rapidly opens and expands the aggregated molecular chain network of the polyester, greatly increasing the reaction surface area. At this time, highly active methanol molecules, carrying the catalyst, can easily and uniformly penetrate into the polyester interior, and the two exert a significant synergistic effect. This "first swelling and loosening - then efficient bond breaking" mechanism enables the alcoholysis of this invention to achieve extremely high polyester conversion and monomer yield in a shorter time and under milder conditions.

[0009] The reaction equation of this invention is as follows. Preferably, the catalyst is a non-metallic organic base catalyst.

[0010] Preferably, the catalyst comprises 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0011] The non-metallic organic base catalyst used in this invention is inexpensive, readily available, and has low corrosiveness to equipment, making it easy to promote industrially. Applying it to the methanol alcoholysis reaction of various polyester plastics can significantly reduce the cost of the catalytic system. The catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene and the co-solvent 1,3-dioxolane can achieve efficient, low-temperature, short-time alcoholysis of various polyesters through synergistic effects, balancing high conversion rates and monomer yields. The products are easy to separate and purify, possessing significant practical value and broad prospects for industrial application.

[0012] Preferably, the polyester plastic comprises any one or a combination of at least two of polylactic acid (PLA), polycarbonate (PC), polybutylene succinate (PBS), polybutylene adipate (PBA), polyethylene adipate (PEA), polybutylene terephthalate (PBAT), or polyethylene 2,5-furandicarboxylate (PEF).

[0013] Preferably, the mass ratio of the co-solvent to the polyester plastic is (1-7):1, for example, it can be 2:1, 3:1, 4:1, 5:1 or 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the mass ratio of methanol to polyester plastic is (0.25-5):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or 4.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the mass ratio of the catalyst to the polyester plastic is (0.01-0.07):1, for example, it can be 0.02:1, 0.03:1, 0.04:1, 0.05:1 or 0.06:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the temperature of the alcoholysis reaction is 25-60°C, for example, it can be 30°C, 35°C, 40°C, 45°C, 50°C or 55°C, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the alcoholysis reaction time is 5-240 min, for example, it can be 10 min, 20 min, 40 min, 80 min, 120 min, 160 min, 180 min, 200 min or 210 min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the alcoholysis method includes the following steps: Methanol, catalyst, and co-solvent are mixed with polyester plastic and subjected to alcoholysis reaction at 25-60℃ for 5-240 min to obtain alcoholysis product.

[0019] Secondly, the present invention provides an application of the alcoholysis method as described in the first aspect in polyester recycling.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Broad-spectrum unified process: One reaction system can process multiple types of polyester PLA, PC, PBS, PBA, PEA, PBAT and PEF, with strong versatility.

[0021] (2) Low temperature and high efficiency: TBD is an organic strong base that works synergistically with 1,3-dioxolane to activate methanol and promote ester bond cleavage at low temperature. It reacts at normal pressure, has a low alcoholysis temperature (25-60℃), and high alcoholysis efficiency (5-240min).

[0022] (3) High conversion rate and yield: 100% polyester conversion rate, good product selectivity and high yield (up to 81.7%-95.0%).

[0023] (4) The cosolvent is easy to recover: the cosolvent 1,3-dioxolane has a low boiling point, is easy to recover, and can be recycled.

[0024] (5) Metal-free catalysis: Non-metallic organic bases are used as catalysts to avoid the use of metal catalysts, simplify the purification steps of alcoholysis monomers, and reduce production costs.

[0025] (6) Simple process: atmospheric pressure reaction, low equipment requirements, easy to scale up industrially. Attached Figure Description

[0026] Figure 1 This is the GC spectrum of the alcoholysis product obtained in Example 1 of the present invention; Figure 2 This is the HPLC spectrum of the alcoholysis product obtained in Example 2 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0028] The sources of some of the raw materials used in the following examples are as follows: PLA (Mw~80000) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0029] PC (Mw~45000) was purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0030] PBS (extrusion grade) was purchased from Shanghai Maclean Biotechnology Co., Ltd.

[0031] PBA (Mw~3000) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0032] PEA (Mw~1000) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0033] PBAT (Mn~120000) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0034] PEF (≥99%) was purchased from Shanghai Maclean Biotechnology Co., Ltd.

[0035] Example 1 A method for alcoholysis of polyester plastic, the method comprising the following steps: PLA, non-metallic organic-base catalyst TBD, methanol, and co-solvent 1,3-dioxolane were added to a reactor and subjected to alcoholysis at 25°C for 210 min to obtain the alcoholysis product. After the reaction, the conversion rate of PLA and the yield of Me-LA were calculated by analyzing the mass of the remaining PLA and the mass of the product Me-LA in the alcoholysis product.

[0036] The mass ratio of TBD to PLA is 0.07:1, the mass ratio of methanol to PLA is 2.5:1, and the mass ratio of 1,3-dioxolane to PLA is 5:1.

[0037] GC analysis was performed using the alcoholysis product obtained in Example 1, and the results are as follows: Figure 1 As shown in the figure, the obtained product is a relatively pure Me-LA monomer.

[0038] Example 2 A method for the alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, and the alcoholysis reaction time is changed to 240 min; otherwise, the method is the same as in Example 1.

[0039] The alcoholysis product obtained in Example 2 was analyzed by HPLC, and the results are as follows: Figure 2 As shown in the figure, the obtained product is a relatively pure BPA monomer.

[0040] Example 3 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PBS, the alcoholysis reaction temperature is changed to 60°C, and the alcoholysis reaction time is changed to 20 min. After the reaction, the conversion rate of PBS and the yield of DMSu are calculated by analyzing the mass of the remaining PBS and the mass of the product DMSu. All other aspects are the same as in Example 1.

[0041] Example 4 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PBA, the alcoholysis reaction time is changed to 10 min, and after the reaction is completed, the conversion rate of PBA and the yield of DMA are calculated by analyzing the mass of the remaining PBA and the mass of the product DMA. All other aspects are the same as in Example 1.

[0042] Example 5 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PEA, the alcoholysis reaction time is changed to 10 min, and after the reaction is completed, the conversion rate of PEA and the yield of DMA are calculated by analyzing the mass of the remaining PEA and the mass of the product DMA. All other aspects are the same as in Example 1.

[0043] Example 6 A method for alcoholysis of polyester plastics, which differs from Example 1 only in that PLA is replaced with the same mass of PBAT. After the reaction is completed, the conversion rate of PBAT and the yield of DMA and DMT are calculated by analyzing the mass of the remaining PBAT and the mass of the products DMA and DMT, respectively. DMA and DMT are analyzed by GC and HPLC, respectively. All other aspects are the same as in Example 1.

[0044] Example 7 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PEF, the alcoholysis reaction time is changed to 10 min, and after the reaction is completed, the conversion rate of PEF and the yield of FDME are calculated by analyzing the mass of the remaining PEF and the mass of the product FDME. FDME is analyzed by HPLC, and the rest are the same as in Example 1.

[0045] Example 8 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the amount of TBD is changed to 1% of the mass of PC, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction, the conversion rate of PC and the yield of BPA are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC. All other methods are the same as in Example 1.

[0046] Example 9 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction, the conversion rate of PC and the yield of BPA are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC, and the rest are the same as in Example 1.

[0047] Example 10 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the mass ratio of cosolvent to PC is changed to 1:1, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction, the conversion rate of PC and the yield of BPA are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC, and the rest are the same as in Example 1.

[0048] Example 11 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the mass ratio of cosolvent to PC is changed to 7:1, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction, the conversion rate of PC and the yield of BPA are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC, and the rest are the same as in Example 1.

[0049] Example 12 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the mass ratio of methanol to PC is changed to 0.25:1, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction is completed, the conversion rate of PC and the yield of BPA are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC, and the rest are the same as in Example 1.

[0050] Example 13 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the mass ratio of methanol to PC is changed to 5:1, the alcoholysis reaction temperature is changed to 40°C, and the alcoholysis reaction time is changed to 90 min. After the reaction, the PC conversion rate and BPA yield are calculated by analyzing the mass of the remaining PC and the mass of the product BPA. BPA is analyzed by HPLC, and the rest are the same as in Example 1.

[0051] Example 14 A method for alcoholysis of polyester plastics, differing from Example 1 only in that the catalyst is replaced by the same mass of the non-metallic organic base catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) instead of TBD.

[0052] Comparative Example 1 A method for alcoholysis of polyester plastics differs from Example 1 only in that no co-solvent is added; all other aspects are the same as in Example 1.

[0053] Comparative Example 2 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PC, the alcoholysis reaction time is changed to 240 min, and no co-solvent is added; otherwise, it is the same as Example 1.

[0054] Comparative Example 3 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PBS, the alcoholysis reaction temperature is changed to 60°C, the alcoholysis reaction time is changed to 20 min, and no co-solvent is added; all other aspects are the same as in Example 1.

[0055] Comparative Example 4 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PBA, the alcoholysis reaction time is changed to 10 min, and no co-solvent is added; otherwise, it is the same as Example 1.

[0056] Comparative Example 5 A method for alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PEA, the alcoholysis reaction time is changed to 10 min, and no co-solvent is added; otherwise, it is the same as Example 1.

[0057] Comparative Example 6 A method for the alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PBAT and no co-solvent is added; otherwise, the method is the same as Example 1.

[0058] Comparative Example 7 A method for the alcoholysis of polyester plastics differs from Example 1 only in that PLA is replaced with the same mass of PEF, the alcoholysis reaction time is changed to 10 min, and no co-solvent is added; otherwise, it is the same as Example 1.

[0059] Comparative Example 8 A method for alcoholysis of polyester plastics differs from Example 1 only in that methanol is replaced with the same mass of ethylene glycol; all other aspects are the same as in Example 1.

[0060] Comparative Example 9 A method for alcoholysis of polyester plastics, differing from Example 1 only in that 1,3-dioxolane is replaced with the same mass of 1,4-dioxane.

[0061] Test method: After the reaction was completed in the examples and comparative examples, the conversion rate of the polyester plastic and the corresponding product yield were calculated by analyzing the mass of the remaining polyester plastic and the product. The polyester conversion rate and the product yield were calculated by the following formulas. The effects of different variables on low-temperature, high-efficiency methanol hydrolysis of PLA, PC, PBS, PBA, PEA, PBAT, and PEF polyester plastics reinforced by cosolvents are shown in Table 1.

[0062] Table 1 The test results show that: (1) As can be seen from Examples 1-14, the present invention solves the problems of lack of universality, harsh reaction conditions, high equipment requirements, poor product selectivity, high energy consumption and metal residue in the prior art by designing the alcoholysis method.

[0063] (2) By comparing Example 1 and Example 14, it can be seen that the present invention improves polyester conversion rate and product yield by further limiting the type of catalyst.

[0064] (3) By comparing Example 1 and Comparative Example 1, it can be seen that when no co-solvent is added, the methanol alcoholysis effect is greatly reduced due to the disappearance of the mutual coupling effect between the co-solvent and the catalyst.

[0065] The comparison between Example 1 and Comparative Example 8 shows that when the alcoholysis solvent is changed from methanol to ethylene glycol, the reaction cannot occur due to the large steric hindrance and weak nucleophilicity of ethylene glycol, and no alcoholysis products are produced.

[0066] A comparison of Example 1 and Comparative Example 9 shows that if the specific type of co-solvents used in this application is not used, the conversion rate and product yield of the polyester are significantly reduced.

[0067] In summary, the method provided by this invention has the advantages of low alcoholysis temperature (25-60℃), short reaction time (5-240min), high polyester conversion rate (100%) and product monomer yield (81.7%-95.0%), metal-free catalyst, and easy product separation, which greatly improves the convenience of operation and reduces reaction energy consumption and carbon emissions.

[0068] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for the alcoholysis of polyester plastics, characterized in that, The alcoholysis method includes the following steps: Methanol, catalyst, and co-solvent are mixed with polyester plastic to carry out an alcoholysis reaction, yielding the alcoholysis product; The co-solvent comprises 1,3-dioxolane.

2. The alcoholysis method according to claim 1, characterized in that, The catalyst is a non-metallic organic base catalyst. Preferably, the catalyst comprises 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

3. The alcoholysis method according to claim 1 or 2, characterized in that, The polyester plastic includes any one or a combination of at least two of polylactic acid, polycarbonate, polybutylene succinate, polybutylene adipate, polyethylene adipate, polybutylene adipate-terephthalate, or polyethylene 2,5-furandicarboxylate.

4. The alcoholysis method according to any one of claims 1-3, characterized in that, The mass ratio of the co-solvent to the polyester plastic is (1-7):

1.

5. The alcoholysis method according to any one of claims 1-4, characterized in that, The mass ratio of methanol to polyester plastic is (0.25-5):

1.

6. The alcoholysis method according to any one of claims 1-5, characterized in that, The mass ratio of the catalyst to the polyester plastic is (0.01-0.07):

1.

7. The alcoholysis method according to any one of claims 1-6, characterized in that, The alcoholysis reaction is carried out at a temperature of 25-60℃.

8. The alcoholysis method according to any one of claims 1-7, characterized in that, The alcoholysis reaction takes 5-240 min.

9. The alcoholysis method according to any one of claims 1-8, characterized in that, The alcoholysis method includes the following steps: Methanol, catalyst, and co-solvent are mixed with polyester plastic and subjected to alcoholysis reaction at 25-60℃ for 5-240 min to obtain alcoholysis product.

10. The application of the alcoholysis method as described in any one of claims 1-9 in polyester recycling.

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