Method for preparing dimethyl 2, 5-furandicarboxylate by efficiently catalyzing degradation of polyethylene glycol 2, 5-furandicarboxylate

Abstract

The invention discloses a method for preparing dimethyl 2, 5-furandicarboxylate by efficiently catalyzing degradation of polyethylene glycol 2, 5-furandicarboxylate, and belongs to the technical field of chemical recovery of high polymer materials. The method comprises the following steps: by taking a deep eutectic solvent formed by choline chloride and zinc acetate as a catalyst and a mixed solution of acetonitrile and methanol as a reaction solvent, carrying out catalytic depolymerization on crushed PEF under a mild condition of 80-130 DEG C; and after the reaction is finished, carrying out the steps of concentration, elutriation, methanol-water recrystallization and the like to obtain the high-purity dimethyl furandicarboxylate. The method has the advantages of mild process conditions, effective inhibition of the furan ring side reaction, high product purity (greater than or equal to 99.9%), high yield, recoverable solvent and simple process flow, and provides an efficient, economic and easy-to-industrialize solution for closed-loop circulation and resource utilization of PEF.

Description

Technical Field

[0001] This invention belongs to the field of chemical recycling technology of polymer materials, and relates to a chemical degradation method of bio-based polyester—polyethylene 2,5-furandicarboxylate, and more particularly to a method for efficiently catalyzing its degradation into high-value-added monomer 2,5-furandicarboxylate under mild conditions. Background Technology

[0002] Biomass, as an important renewable carbon source besides fossil resources, plays a crucial role in achieving sustainable energy development and building a low-carbon circular economy. Among numerous bio-based materials, polyethylene 2,5-furandicarboxylate (PEF) is widely considered an ideal alternative to petroleum-based polyester—polyethylene terephthalate (PET)—due to its biomass origin and excellent gas barrier properties, mechanical strength, and thermal properties. However, compared to PET, which has established mature recycling systems (such as alcoholysis and hydrolysis), the chemical structure of PEF makes it difficult to directly utilize existing PET recycling processes. There is still significant room for technological development in efficient and scalable recycling technologies specifically for PEF. To achieve sustainable development and a closed-loop circular economy for PEF materials, it is essential to establish efficient and economical chemical recycling technologies to transform its waste back into valuable monomer raw materials.

[0003] Currently, chemical recycling technologies for PET, such as alcoholysis and hydrolysis, are relatively mature. However, because PEF molecules contain more chemically reactive furan rings, directly applying PET recycling processes (e.g., ethylene glycol alcoholysis at temperatures above 180°C) can lead to ring-opening and degradation of the furan rings at high temperatures, reducing product yield and purity and complicating the recycling process. Some studies (e.g., the microwave-assisted depolymerization technology published by the University of Delaware) have attempted to degrade PEF under high pressure (>2MPa) and relatively high temperature (>120°C), achieving some success. However, microwave conditions place high demands on equipment and consume a lot of energy, increasing the difficulty and cost of industrial scale-up.

[0004] Therefore, developing a method for efficiently and selectively degrading PEF under mild conditions (especially lower temperatures and ambient / low pressure) to obtain high-purity, easily separable monomers is crucial for promoting the large-scale application of PEF and the development of a circular economy. Dimethyl 2,5-furandicarboxylate (FDME), as the target degradation product, is not only a high-quality monomer for the resynthesis of PEF, but also a key platform molecule for the synthesis of various high-performance polymers (such as furanyl polyamides and polyesteramides) and fine chemicals (such as environmentally friendly plasticizers and pharmaceutical intermediates), demonstrating significant value. Summary of the Invention

[0005] To address the shortcomings of existing PEF recovery technologies, such as harsh reaction conditions (high temperature and high pressure), susceptibility to furan ring side reactions, complex equipment, and high energy consumption, this invention aims to provide a highly efficient method for the catalytic degradation of polyethylene 2,5-furandicarboxylate to prepare dimethyl 2,5-furandicarboxylate. This method aims to achieve the following technical effects: (1) Efficient depolymerization of PEF is achieved under relatively mild temperature (80-130℃) and normal / low pressure conditions, which greatly reduces energy consumption and equipment requirements.

[0006] (2) By using innovative catalytic systems and solvent combinations, side reactions such as furan ring opening are suppressed, and reaction kinetics are accelerated through a swelling-ester exchange dual mechanism, thereby improving reaction selectivity and product yield.

[0007] (3) Establish a simple and efficient product separation and purification process to directly obtain high-purity (≥99.9%) FDME crystals to meet the requirements of recycling or high-end applications.

[0008] (4) Provides an industrially scalable closed-loop recycling solution for PEF to support the sustainable development of bio-based materials.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A highly efficient catalytic method for the degradation of polyethylene 2,5-furandicarboxylate to prepare dimethyl 2,5-furandicarboxylate includes the following process steps: S1: Catalyst preparation: Choline chloride (ChCl) and zinc acetate (Zn(OAc)2) are mixed, heated and stirred to form a eutectic solvent (ChCl / Zn(OAc)2 DES), and cooled for later use; S2, PEF depolymerization reaction: Polyethylene 2,5-furandicarboxylate (PEF) fragments and the catalyst (ChCl / Zn(OAc)2 DES) prepared in step S1 are added to a high-pressure reactor, and then a mixed solvent of acetonitrile and methanol is added. The reaction is stirred at 80-130℃. S3. Product separation and purification: After the reaction is completed, the reaction solution is cooled and concentrated, and water is added to crystallize and obtain crude product. Then, it is recrystallized from methanol and water to obtain high-purity dimethyl 2,5-furandicarboxylate (FDME).

[0010] Furthermore, in step S1, the molar ratio of choline chloride to zinc acetate is (0.8-1.2):1, the heating and stirring temperature is 100-120℃, and the time is 20-40 minutes.

[0011] Furthermore, the amount of catalyst used in step S2 is 1-10% of the mass of polyethylene 2,5-furandicarboxylate.

[0012] Furthermore, the volume ratio of acetonitrile to methanol in the mixed solvent is 5:1 to 1:5.

[0013] Furthermore, in step S2, the mass-to-volume ratio of the polyethylene 2,5-furandicarboxylate fragments to the mixed solvent is 1:5-1:15 g / mL, and the particle size of the added polyethylene 2,5-furandicarboxylate fragments is ≤1 mm.

[0014] Furthermore, in step S2, the reaction time is 1-1.5 hours.

[0015] Furthermore, step S3 specifically includes: S31. Cool the reaction solution to 50-70℃ and concentrate it under reduced pressure to 15-25% of the original volume. Add 3-7 times the volume of deionized water to the concentrated solution, stir to precipitate crystals, and filter to obtain a wet filter cake. S32. After washing the wet filter cake with cold water, add 3-10 times its mass of methanol to dissolve it, and then slowly add 1-3 times the volume of deionized water to recrystallize it. S33. The filtered crystals are washed and dried to obtain white dimethyl 2,5-furandicarboxylate crystals.

[0016] Furthermore, in step S33, the drying is performed by vacuum drying at 75-85°C for 4-8 hours.

[0017] Compared with the prior art, the present invention has the following significant advantages and beneficial effects: (1) Mild and efficient reaction conditions: The choline chloride / zinc acetate eutectic solvent catalyst used in this invention has excellent catalytic activity and selectivity. Combined with the synergistic effect of acetonitrile-methanol mixed solvent, the depolymerization reaction of PEF can be carried out efficiently in a low temperature range of 80-130℃, which is much lower than the temperature of traditional PET alcoholysis process (usually >180℃) and also lower than some reported high-pressure depolymerization temperatures of PEF, which significantly reduces energy consumption and the requirements for equipment temperature and pressure resistance.

[0018] (2) Suppressing side reactions and achieving high product purity: The mild reaction conditions effectively suppress side reactions such as ring-opening and degradation of the furan ring in the PEF molecule at high temperatures. The unique catalytic-solvent system promotes the selective methyl esterification reaction pathway. Combined with the subsequently developed water precipitation-recrystallization purification process, the purity of FDME can be easily increased to over 99.9% (HPLC method), which can be directly used for the repolymerization of high-quality PEF or other high-value-added conversions.

[0019] (3) The catalytic and solvent systems are highly innovative: Regarding catalysts: the eutectic solvent (DES) formed by choline chloride and zinc acetate serves not only as a reaction medium but also as a highly efficient catalyst. Among them, Zn... 2+Ions can activate the carbonyl carbon in the ester bond of PEF, promoting its breakage by methanol attack; at the same time, the ionic environment of DES may stabilize the reaction intermediate and reduce the reaction activation energy.

[0020] Regarding solvents: Acetonitrile, as a good solvent and swelling agent, can penetrate and swell the PEF solid, increasing its contact area with the reaction solution and accelerating degradation kinetics. Methanol serves as both a reactant (methyl esterification reagent) and a co-solvent. Together, they create a highly efficient reaction environment for homogeneous / heterogeneous transition.

[0021] (4) The process is green and easy to scale up: the reagents used in the entire process are inexpensive and readily available, the reaction and post-processing steps are simple, and the solvents (acetonitrile, methanol) can be efficiently recovered and reused through distillation (recovery rate >90%), which is in line with the principles of green chemistry. The reaction does not require ultra-high pressure and can be carried out in a conventional pressure vessel. The process flow is simple and is very conducive to scaling up to industrial production scale, providing a practical and feasible technical solution for the large-scale resource utilization of PEF waste.

[0022] (5) Achieving a closed-loop cycle of PEF: This invention successfully converts waste PEF into high-purity FDME monomers, which can be directly used as raw materials to resynthesize PEF, realizing the upgrading and reconstruction from "waste" to "high-value raw materials", and connecting the complete cycle path of bio-based PEF materials "from cradle to cradle", which has significant economic value and environmental benefits. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the reaction route for preparing FDME from PEF via alcoholysis according to the present invention; Figure 2 The 1H NMR spectrum of the FDME product prepared in Example 1; Figure 3 This is a high-performance liquid chromatography purity analysis chromatogram of the FDME product prepared in Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] Example 1

[0026] A highly efficient catalytic method for the degradation of polyethylene 2,5-furandicarboxylate to prepare dimethyl 2,5-furandicarboxylate includes the following process steps: (1) Catalyst preparation: In a 50 mL reaction flask, add 10.0 g of choline chloride and 13.14 g of zinc acetate (molar ratio of about 1:1), turn on the stirrer and heat in an oil bath to 110 °C. Continue stirring for about 30 minutes until the system is completely melted into a homogeneous transparent liquid. Stop heating and cool to room temperature to obtain the ChCl / Zn(OAc)2 eutectic solvent catalyst for later use.

[0027] (2) PEF depolymerization reaction: In a 500 mL high-pressure reactor equipped with a stirrer and a heater, add 10 g of PEF fragments with a particle size ≤1 mm, and then add 0.5 g of the catalyst prepared in step (1) (accounting for 5 wt% of the PEF mass). Measure 25 mL of acetonitrile and 25 mL of methanol (volume ratio 1:1) and add them to the reactor to make the solid-liquid ratio approximately 1:5 g / mL. Seal the reactor, turn on the stirrer, and heat to 120 °C. React at this temperature for 1 hour, and observe that the reaction solution becomes basically clear.

[0028] (3) Separation and purification: After the reaction was completed, the reaction solution was transferred to a rotary evaporator and concentrated to about 10 mL under reduced pressure in a 60°C water bath. 50 mL of deionized water was added to the concentrate, and the mixture was stirred for 30 minutes, resulting in the precipitation of a large amount of white solid. The solid was filtered to obtain a wet filter cake of about 12.6 g. The wet filter cake was transferred to a 250 mL reaction flask, and 37.8 mL of methanol (3 times the mass of the wet filter cake) was added and stirred to dissolve. While stirring, 75.6 mL of deionized water (2 times the volume of methanol) was slowly added dropwise, and the mixture was stirred at room temperature for 1 hour after the addition was complete. The mixture was filtered again, and the resulting filter cake was washed with cold water at 5°C. The filter cake was placed in a vacuum drying oven and dried at 80°C for 6 hours to obtain 9.0 g of white crystalline product (FDME).

[0029] The reaction route for the preparation of FDME by PEF alcoholysis is shown in the diagram below. Figure 1 As shown; the calculated yield of FDME was 90%. A small amount of the product was analyzed by 1H NMR spectroscopy, and the spectrum is shown in the figure. Figure 2 ) and standard FDME spectrum Figure 1 The product structure was confirmed to be correct. Its purity was determined using high-performance liquid chromatography (HPLC) with area normalization, and the result was 99.9%. Figure 3 ).

[0030] Example 2-11

[0031] The PEF depolymerization experiment was conducted according to the conditions listed in Table 1 and the steps of Example 1 were followed. Only a single variable, such as reaction temperature, catalyst dosage, solvent ratio, or recrystallization solvent ratio, was changed. The results are listed in Table 1.

[0032] Table 1 Reaction conditions and results of Examples 2-11

[0033] The preferred embodiment of the present invention has the following parameters: catalyst dosage is 5 wt%, reaction temperature is 120°C, acetonitrile:methanol volume ratio is 1:1, and purified recrystallized methanol:water volume ratio is 1:2.

[0034] Comparative Example 1 (simulating traditional high-temperature alcoholysis conditions)

[0035] 10g of PEF fragments were added to 100 mL of ethylene glycol as solvent and reactant, along with 0.5 g of zinc acetate as catalyst. The mixture was heated to 190℃ for 4 hours under nitrogen protection. After the reaction, the mixture was cooled and poured into a large amount of water. A solid precipitated, but the product composition was complex. Preliminary HPLC analysis showed a very low FDME content, with the main byproducts being small molecules resulting from furan ring opening and further degradation. High-purity FDME could not be obtained by simple recrystallization.

[0036] Comparative Example 2 (without acetonitrile swelling agent)

[0037] Following Example 1, but without acetonitrile, only 50 mL of methanol was used as the solvent, and all other conditions were the same. After reacting at 120°C for 2 hours, the reaction system was still very turbid, indicating incomplete PEF degradation. After filtration and further processing, the final FDME yield was only about 35%, with a purity of 99.0%.

[0038] As can be seen from the above examples and comparative examples, the catalyst system, acetonitrile-methanol mixed solvent, and optimized process conditions (temperature, ratio) provided by this invention are crucial for achieving efficient and highly selective degradation of PEF under mild conditions. The method of this invention significantly reduces the reaction temperature while ensuring high yield and high purity, demonstrating excellent comprehensive performance and technological innovation.

[0039] In summary, the main innovations of the technical solution of this invention are as follows: (1) Innovation of low-temperature eutectic catalytic system Zn in DES catalyst 2+ The carbon groups on the long chain of PEF are attacked to form carbocations, while the acetate anion attacks the hydroxyl groups in methanol. This causes the oxygen in the methanol hydroxyl group to carry a greater negative charge and better combine with the carbocation on the furan ring. The O on the methanol hydroxyl group attaches to the C on the CO of the PEF polyester to form a new ester group. During degradation, the PEF polyester first transforms into short-chain oligomers, and then continues to produce FDME monomers.

[0040] (2) Lowering the reaction temperature (80-130℃) can suppress the ring-opening side reaction of furan ring and avoid the formation of by-products.

[0041] (3) Synergistic mechanism of acetonitrile / methanol mixed solvent: Acetonitrile acts as a co-solvent, causing the surface of PEF to expand, increasing the specific surface area of ​​PEF, lowering the reaction temperature, and accelerating the degradation of PEF; methanol provides methyl esterification groups, which react with Zn in DES. 2+ [Zn(OCH3)4] is formed. 2- Intermediates accelerate transesterification.

[0042] (4) Water displacement purification technology: Utilizing the different solubilities of FDME in methanol and water, a recrystallization process is developed to improve the purity of FDME; (5) Acetonitrile / methanol is soluble in water, and the solvent recovery rate is >90% by vacuum distillation.

[0043] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate, characterized in that, The process includes the following steps: S1: Catalyst preparation: Choline chloride and zinc acetate are mixed, heated and stirred to form a eutectic solvent, and then cooled for later use; S2, PEF depolymerization reaction: A certain proportion of polyethylene 2,5-furandicarboxylate fragments and the catalyst prepared in step S1 are added to a high-pressure reactor, and then a mixed solvent of acetonitrile and methanol is added. The reaction is stirred at 80-130℃. S3. Product separation and purification: After the reaction is completed, the reaction solution is cooled and concentrated, and water is added to crystallize and obtain crude product. Then, it is recrystallized by methanol-water to obtain high-purity dimethyl 2,5-furandicarboxylate.

2. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, In step S1, the molar ratio of choline chloride to zinc acetate is (0.8-1.2):1, the heating and stirring temperature is 100-120℃, and the time is 20-40 minutes.

3. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, The amount of catalyst used in step S2 is 1-10% of the mass of polyethylene 2,5-furandicarboxylate.

4. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, The volume ratio of acetonitrile to methanol in the mixed solvent is 5:1 to 1:

5.

5. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, In step S2, the mass-to-volume ratio of the polyethylene 2,5-furandicarboxylate fragments to the mixed solvent is 1:5-1:15 g / mL.

6. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, In step S2, the reaction time is 1-1.5 hours.

7. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, The particle size of the polyethylene 2,5-furandicarboxylate fragments added in step S2 is ≤1 mm.

8. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 1, characterized in that, Step S3 specifically includes: S31. Cool the reaction solution to 50-70℃ and concentrate it under reduced pressure to 15-25% of the original volume. Add 3-7 times the volume of deionized water to the concentrated solution, stir to precipitate crystals, and filter to obtain a wet filter cake. S32. After washing the wet filter cake with cold water, add 3-10 times its mass of methanol to dissolve it, and then slowly add 1-3 times the volume of deionized water to recrystallize it. S33. The filtered crystals are washed and dried to obtain white dimethyl 2,5-furandicarboxylate crystals.

9. The method for preparing dimethyl 2,5-furandicarboxylate by efficient catalytic degradation of polyethylene 2,5-furandicarboxylate according to claim 8, characterized in that, In step S33, the drying is performed by vacuum drying at 75-85°C for 4-8 hours.

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