Method for enhancing methanol alcoholysis of PET (Polyethylene Terephthalate) by using cosolvent

Abstract

The invention provides a method for enhancing methanol alcoholysis of PET (Polyethylene Terephthalate) by using a cosolvent, which comprises the following steps: mixing PET, methanol, a catalyst and the cosolvent, and carrying out alcoholysis reaction to obtain dimethyl terephthalate, the cosolvent comprises any one or a combination of at least two of 1, 3-dioxolame, dichloromethane, anisole or 1, 4-dioxane. The method has the characteristics that the PET alcoholysis temperature is low (0-60 DEG C), the reaction time is short (60-300 minutes), the PET conversion rate is 100%, the DMT monomer yield is high (94.4%), the catalyst does not contain metal, and the product is easy to separate, so that the operation convenience is greatly improved, and the reaction energy consumption and carbon emission are reduced.

Description

Technical Field

[0001] This invention relates to the field of waste PET polyester recycling technology, and in particular to a method for strengthening the methanol alcoholysis of PET with a co-solvent. Background Technology

[0002] Polyethylene terephthalate (PET) possesses core advantages such as high strength, high toughness, excellent chemical stability, light barrier properties, ease of processing, recyclability, and cost-effectiveness. It is widely used in packaging (beverage bottles, food packaging), textiles (polyester fibers), engineering plastics (automotive / electronic components), medical devices, and many other fields, becoming an indispensable basic material for national economic development. Over the past decade, global consumption of PET polymers has experienced sustained and robust growth, with nearly 70 million tons of PET produced globally annually. Of this, only about 9% of plastic waste is recycled, 12% is incinerated, and the remaining 79% ends up in landfills or dispersed into natural habitats. PET degrades at an extremely low rate in the natural environment, causing not only serious environmental pollution but also accumulating and enriching microplastics in soil, marine environments, and in the bodies of animals and plants, ultimately posing a potential threat to human health. On the other hand, the raw materials for PET production come from non-renewable petroleum-based terephthalic acid (TPA) and ethylene glycol. Their indiscriminate disposal not only results in the idle waste of valuable resources, but also further exacerbates the pressure of consuming non-renewable resources. Therefore, the efficient recycling and resource utilization of PET has become an important issue of great concern worldwide.

[0003] PET recycling methods are mainly divided into physical recycling and chemical recycling. Physical recycling methods obtain recycled granules or fibers through steps such as washing, separation, and melt processing. These methods are simple to operate, economical, and efficient, making them the current mainstream. However, this method suffers from drawbacks such as decreased crystallinity and quality of the recycled product during the melting process, and difficulty in removing impurities such as pigments, which makes it difficult to meet the needs of sustainable development. Chemical recycling methods depolymerize PET into monomers such as TPA, dimethyl terephthalate (DMT), and bis(2-hydroxyethyl) terephthalate (BHET) through reactions such as hydrolysis, pyrolysis, and alcoholysis, achieving high-value utilization. Among these, methanol alcoholysis has broad industrial prospects due to its low raw material requirements and the ease of separation and purification of the product DMT. However, existing methanol alcoholysis processes typically involve reactions at high temperatures of 180-280 ℃, high pressures of 2-4 MPa, and large excess methanol, resulting in high operating costs, low energy utilization, and high carbon emissions.

[0004] Therefore, achieving efficient alcoholysis of PET at low temperature and in a short time, while ensuring high PET conversion rate and DMT monomer yield, and with easy product separation and purification, has significant practical implications and broad prospects for industrial application. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for methanol alcoholysis of PET enhanced by a co-solvent, so as to solve the problem of difficulty in removing metal residues in the product when PET is catalyzed by existing metal catalysts. At the same time, it overcomes the technical bottlenecks of traditional methanol alcoholysis methods, such as high reaction temperature, large methanol consumption, high process energy consumption and equipment requirements, and poor product selectivity.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for enhancing the methanol hydrolysis of PET using a co-solvent, the method comprising the following steps:

[0008] PET, methanol, catalyst and cosolvent are mixed and subjected to alcoholysis to obtain dimethyl terephthalate;

[0009] The cosolvent includes any one or a combination of at least two of 1,3-dioxolane, dichloromethane, anisole, or 1,4-dioxane. Typical but non-limiting combinations include combinations of 1,3-dioxolane and dichloromethane, combinations of dichloromethane and anisole, and combinations of anisole and 1,4-dioxane.

[0010] The reaction equation for this invention is as follows:

[0011]

[0012] As a preferred embodiment of the present invention, the catalyst comprises a non-metallic organic base catalyst.

[0013] As a preferred embodiment of the present invention, the non-metallic organic base catalyst comprises any one or a combination of at least two of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, 1,5-diazabicyclo[4.3.0]non-5-ene, or 1,8-diazabicyclo[5.4.0]undec-7-ene. Typical but non-limiting combinations include combinations of 1,5,7-triazabicyclo[4.4.0]dec-5-ene and 1,1,3,3-tetramethylguanidine, and 1,5,7-triazabicyclo[4.4.0]undec-7-ene. Combinations of azabicyclo[4.4.0]dec-5-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, combinations of 1,5-diazabicyclo[4.3.0]non-5-ene and 1,8-diazabicyclo[5.4.0]undec-7-ene, combinations of 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5,7-triazabicyclo[4.4.0]dec-5-ene, combinations of 1,1,3,3-tetramethylguanidine and 1,8-diazabicyclo[5.4.0]undec-7-ene, etc.

[0014] 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 industrial application. Applying it to the methanolysis reaction of waste PET not only significantly reduces the cost of the catalytic system but also has low requirements for PET raw materials and wide applicability. Furthermore, the catalyst and co-solvent can synergistically achieve low-temperature, short-time, and efficient alcoholysis of PET, balancing high PET conversion rate and DMT monomer yield. The products are easy to separate and purify, possessing significant practical value and broad prospects for industrial application.

[0015] As a preferred technical solution of the present invention, the alcoholysis reaction time is 60-300 min, for example, it can be 60 min, 100 min, 140 min, 180 min, 220 min, 260 min or 300 min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0016] As a preferred technical solution of the present invention, the temperature of the alcoholysis reaction is 0-60℃, for example, it can be 0℃, 20℃, 30℃, 40℃, 50℃ or 60℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] As a preferred technical solution of the present invention, the mass ratio of the co-solvent to PET is (1-7):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1 or 7:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] As a preferred technical solution of the present invention, the mass ratio of methanol to PET is (0.33-5):1, for example, it can be 0.33:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] As a preferred technical solution of the present invention, the mass ratio of the catalyst to PET is (0.01-0.07):1, for example, it can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1 or 0.07:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] As a preferred embodiment of the present invention, the PET includes PET flakes and / or PET fibers.

[0021] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0022] (1) Low-temperature and high-efficiency methanol alcoholysis of waste PET polyester enhanced by co-solvent. The co-solvent and catalyst have a synergistic effect, which can realize the swelling of PET, increase the contact area during alcoholysis reaction, and achieve low alcoholysis temperature (0-60 ℃) and high alcoholysis efficiency (60-300 min).

[0023] (2) Low-temperature and efficient methanol alcoholysis of waste PET polyester reinforced by co-solvent: low amount of methanol and co-solvent used, good product selectivity and high yield (up to 94.4%).

[0024] (3) Low-temperature and high-efficiency methanol alcoholysis of waste PET polyester is carried out using a co-solvent-enhanced method. The co-solvent has the characteristics of low boiling point and easy recovery, which makes it convenient for recycling.

[0025] (4) Low-temperature and high-efficiency methanol alcoholysis of waste PET polyester enhanced by cosolvent is carried out. Non-metallic organic base is used as catalyst to avoid the use of metal catalyst, simplify the purification steps of alcoholysis monomers and reduce production costs.

[0026] (5) Low-temperature and efficient methanol alcoholysis of waste PET polyester reinforced by cosolvent has low requirements for raw material source and is also very applicable to low-quality colored fibers. The obtained monomer is easy to separate and purify, and the product has high purity, which meets the requirements for high-value utilization.

[0027] (6) Recycling and reusing waste PET polyester can reduce environmental pollution and resource waste caused by waste PET polyester and achieve sustainable economic development. Attached Figure Description

[0028] Figure 1 This is the DMT obtained in specific embodiment 1 of the present invention. 1 H-NMR;

[0029] Figure 2 This is the DMT obtained in specific embodiment 1 of the present invention. 13 C-NMR;

[0030] Figure 3 This is the liquid phase spectrum of DMT obtained in specific embodiment 1 of the present invention. Detailed Implementation

[0031] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0032] In one specific embodiment, the present invention provides a method for enhancing the methanol hydrolysis of PET with a co-solvent, the method comprising the following steps:

[0033] Waste PET bottle flakes and 1-7% by mass of non-metallic organic-base catalysts TBD, TMG, DBN, and DBU, along with methanol and a co-solvent in a mass ratio of (0.33-5):1 and (1-7):1, were added to a reactor and reacted at (0-60) °C for (60-300) min. After the reaction, the conversion rate of PET and the yield of DMT were calculated by analyzing the mass of the remaining PET and the mass of the product DMT.

[0034] It should be clarified that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0035] Example 1

[0036] This embodiment provides a method for co-solvent-enhanced methanol alcoholysis of PET, the method comprising the following steps:

[0037] Waste PET bottle flakes and 7% (by mass) of the non-metallic organic-base catalyst TBD, along with methanol in a mass ratio of 2.5:1 and a co-solvent 1,3-dioxolane in a mass ratio of 5:1, were added to a reactor and reacted at 25°C for 180 min. After the reaction, the conversion rate of PET and the yield of DMT were calculated by analyzing the mass of the remaining PET and the mass of the product DMT.

[0038] The DMT sample obtained in Example 1 was subjected to 1H NMR, 1C NMR, and liquid chromatography analyses, and the results are as follows: Figure 1-3 As shown in the figure, the obtained product is a relatively pure DMT monomer.

[0039] Example 2

[0040] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the non-metallic organic base catalyst TBD is replaced with TMG, and the alcoholysis reaction temperature is changed to 35°C. All other aspects are the same as in Example 1.

[0041] Example 3

[0042] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the non-metallic organic base catalyst TBD is replaced with DBN, the alcoholysis reaction temperature is changed to 30°C, and the alcoholysis reaction time is changed to 240 min. All other aspects are the same as in Example 1.

[0043] Example 4

[0044] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the non-metallic organic base catalyst TBD is replaced with DBU, and the alcoholysis reaction temperature is changed to 45°C. All other aspects are the same as in Example 1.

[0045] Example 5

[0046] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the amount of the non-metallic organic base catalyst TBD is changed to 1% of the mass of waste PET bottle flakes, while the rest is the same as in Example 1.

[0047] Example 6

[0048] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the amount of the non-metallic organic base catalyst TBD is changed to 3% of the mass of the waste PET bottle flakes, while the rest is the same as in Example 1.

[0049] Example 7

[0050] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the amount of the non-metallic organic base catalyst TBD is changed to 5% of the mass of waste PET bottle flakes, while the rest is the same as in Example 1.

[0051] Example 8

[0052] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with dichloromethane; all other aspects are the same as in Example 1.

[0053] Example 9

[0054] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with anisole; all other aspects are the same as in Example 1.

[0055] Example 10

[0056] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with 1,4-dioxane, while all other aspects are the same as in Example 1.

[0057] Example 11

[0058] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the mass ratio of the co-solvent 1,3-dioxolane to waste PET bottle flakes is changed to 1:1. All other aspects are the same as in Example 1.

[0059] Example 12

[0060] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the mass ratio of the co-solvent 1,3-dioxolane to waste PET bottle flakes is changed to 3:1. All other aspects are the same as in Example 1.

[0061] Example 13

[0062] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the mass ratio of the co-solvent 1,3-dioxolane to waste PET bottle flakes is changed to 7:1. All other aspects are the same as in Example 1.

[0063] Example 14

[0064] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis reaction temperature is changed to 0°C, while the rest is the same as in Example 1.

[0065] Example 15

[0066] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis reaction temperature is changed to 10°C, while the rest is the same as in Example 1.

[0067] Example 16

[0068] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis reaction temperature is changed to 20°C, while the rest is the same as in Example 1.

[0069] Example 17

[0070] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis reaction temperature is changed to 35°C, while the rest is the same as in Example 1.

[0071] Example 18

[0072] This embodiment provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the alcoholysis reaction temperature is changed to 60°C and the alcoholysis reaction time is changed to 60 min. All other aspects are the same as in Example 1.

[0073] Example 19

[0074] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis time is changed to 120 min, while the rest is the same as Example 1.

[0075] Example 20

[0076] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the alcoholysis time is changed to 240 min, while the rest is the same as Example 1.

[0077] Example 21

[0078] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the alcoholysis time is changed to 300 min, while the rest is the same as Example 1.

[0079] Example 22

[0080] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the mass ratio of methanol to PET is changed to 0.33:1, while all other aspects are the same as in Example 1.

[0081] Example 23

[0082] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the mass ratio of methanol to PET is changed to 1:1, while all other aspects are the same as in Example 1.

[0083] Example 24

[0084] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the mass ratio of methanol to PET is changed to 5:1, while all other aspects are the same as in Example 1.

[0085] Example 25

[0086] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with waste colored PET bottle flakes, the alcoholysis reaction temperature is changed to 60°C, and the alcoholysis reaction time is changed to 90 min. All other aspects are the same as in Example 1.

[0087] Example 26

[0088] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with white fibers and the alcoholysis reaction time is changed to 90 min. All other aspects are the same as in Example 1.

[0089] Example 27

[0090] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with orange fiber and the alcoholysis reaction time is changed to 150 min. All other aspects are the same as in Example 1.

[0091] Example 28

[0092] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with yellow fibers and the alcoholysis reaction time is changed to 150 min. All other aspects are the same as in Example 1.

[0093] Example 29

[0094] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with blue fibers and the alcoholysis reaction time is changed to 150 min. All other aspects are the same as in Example 1.

[0095] Example 30

[0096] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with purple fibers and the alcoholysis reaction time is changed to 150 min. All other aspects are the same as in Example 1.

[0097] Example 31

[0098] This embodiment provides a method for methanol alcoholysis of PET enhanced by a cosolvent. The only difference between this method and Example 1 is that the waste PET bottle flakes are replaced with brown fibers and the alcoholysis reaction time is changed to 150 min. All other aspects are the same as in Example 1.

[0099] Example 32

[0100] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the non-metallic organic base catalyst TBD is replaced with a metal catalyst ZnAc2. All other aspects are the same as in Example 1.

[0101] Example 33

[0102] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the mass ratio of the co-solvent to PET is changed to 0.5:1, while the rest is the same as in Example 1.

[0103] Example 34

[0104] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that the mass ratio of the co-solvent to PET is changed to 7.5:1, while all other aspects are the same as in Example 1.

[0105] Example 35

[0106] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the mass ratio of methanol to PET is changed to 0.3:1, while all other aspects are the same as in Example 1.

[0107] Example 36

[0108] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the mass ratio of methanol to PET is changed to 5.5:1, while all other aspects are the same as in Example 1.

[0109] Example 37

[0110] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the amount of catalyst used is changed to 0.8% of the mass of PET, while the rest is the same as in Example 1.

[0111] Example 38

[0112] This embodiment provides a method for enhancing the methanol alcoholysis of PET with a cosolvent. The only difference between this method and Example 1 is that the amount of catalyst used is changed to 7.2% of the mass of PET, while the rest is the same as in Example 1.

[0113] Comparative Example 1

[0114] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that methanol is replaced with ethylene glycol; otherwise, the methods are the same as in Example 1.

[0115] Comparative Example 2

[0116] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with tetrahydrofuran, while the rest is the same as in Example 1.

[0117] Comparative Example 3

[0118] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with acetonitrile, while all other aspects are the same as in Example 1.

[0119] Comparative Example 4

[0120] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with N,N-dimethylformamide, while the rest is the same as in Example 1.

[0121] Comparative Example 5

[0122] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with cyclopentanone; all other aspects are the same as in Example 1.

[0123] Comparative Example 6

[0124] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with 2-methyltetrahydrofuran, while the rest is the same as in Example 1.

[0125] Comparative Example 7

[0126] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with dimethyl sulfoxide, while the rest is the same as in Example 1.

[0127] Comparative Example 8

[0128] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the cosolvent 1,3-dioxolane is replaced with cyclohexanone; all other aspects are the same as in Example 1.

[0129] Comparative Example 9

[0130] This comparative example provides a method for enhancing the methanol alcoholysis of PET with a co-solvent. The only difference between this method and Example 1 is that no co-solvent is added; all other aspects are the same as in Example 1.

[0131] Comparative Example 10

[0132] This comparative example provides a method for enhancing the methanol alcoholysis of PET using a cosolvent. The only difference between this method and Example 1 is that the non-metallic organic base catalyst TBD is replaced with triethylamine; all other aspects are the same as in Example 1.

[0133] Performance testing

[0134] After the reactions provided in the examples and comparative examples were completed, the conversion rate of PET and the yield of DMT were calculated by analyzing the mass of the remaining PET and the mass of the product DMT. The PET polyester conversion rate and the product DMT yield were calculated by the following formulas:

[0135]

[0136] The effects of different variables on low-temperature, high-efficiency methanol alcoholysis waste PET polyester enhanced by cosolvents are shown in Table 1.

[0137] Table 1

[0138]

[0139] As can be seen from Table 1, the method provided in this application has the characteristics of low PET alcoholysis temperature (0-60 ℃), short reaction time (60-300 min), high PET conversion rate (100%) and DMT monomer yield (94.4%), metal-free catalyst, and easy product separation, which greatly improves the convenience of operation and reduces reaction energy consumption and carbon emissions.

[0140] A comprehensive comparison of Examples 1 and 33-38 shows that excessive amounts of methanol and cosolvent reduce the catalyst concentration in the reaction system, leading to a decrease in the density of active sites and a decline in catalytic efficiency. Conversely, insufficient amounts of methanol and cosolvent increase the concentration of the byproduct ethylene glycol, resulting in increased byproducts and a decreased product yield. Similarly, excessive catalyst dosage exacerbates transesterification side reactions, while insufficient catalyst dosage reduces the density of active sites, leading to decreased reaction efficiency and product yield. A comprehensive comparison of Examples 1 and Comparative Examples 1-10 shows that when the alcoholysis solvent is changed from methanol to ethylene glycol, the reaction efficiency and product yield decrease due to the greater steric hindrance and weaker nucleophilicity of ethylene glycol. When the types of catalyst and cosolvent are changed, or when there is no cosolvent, the coupling effect between the cosolvent and catalyst changes, reducing the number of hydrogen bonds and interactions, thus decreasing the methanol alcoholysis effect.

[0141] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for enhancing the methanol alcoholysis of PET using a co-solvent, characterized in that, The method includes the following steps: PET, methanol, catalyst and cosolvent are mixed and subjected to alcoholysis to obtain dimethyl terephthalate; The cosolvent includes any one or a combination of at least two of 1,3-dioxolane, dichloromethane, anisole, or 1,4-dioxane.

2. The method according to claim 1, characterized in that, The catalyst includes a non-metallic organic base catalyst.

3. The method according to claim 2, characterized in that, The non-metallic organic base catalyst includes any one or a combination of at least two of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, 1,5-diazabicyclo[4.3.0]non-5-ene, or 1,8-diazabicyclo[5.4.0]undec-7-ene.

4. The method according to any one of claims 1 to 3, characterized in that, The alcoholysis reaction takes 60-300 minutes.

5. The method according to any one of claims 1 to 4, characterized in that, The alcoholysis reaction is carried out at a temperature of 0-60℃.

6. The method according to any one of claims 1 to 5, characterized in that, The mass ratio of the co-solvent to PET is (1-7):

1.

7. The method according to any one of claims 1 to 6, characterized in that, The mass ratio of methanol to PET is (0.33-5):

1.

8. The method according to any one of claims 1 to 7, characterized in that, The mass ratio of the catalyst to PET is (0.01-0.07):

1.

9. The method according to any one of claims 1 to 8, characterized in that, The PET includes PET flakes and / or PET fibers.

10. The method according to any one of claims 1 to 9, characterized in that, The method includes the following steps: PET bottle flakes and / or PET fibers, methanol, catalyst and co-solvent are mixed and subjected to alcoholysis reaction at 0-60℃ for 60-300 min. The mass ratio of the co-solvent to PET is (1-7):1, the mass ratio of methanol to PET is (0.33-5):1, and the mass ratio of the catalyst to PET is (0.01-0.07):1, to obtain dimethyl terephthalate. The co-solvent includes any one or a combination of at least two of 1,3-dioxolane, dichloromethane, anisole, or 1,4-dioxane; The non-metallic organic base catalyst includes any one or a combination of at least two of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine, 1,5-diazabicyclo[4.3.0]non-5-ene, or 1,8-diazabicyclo[5.4.0]undec-7-ene.

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