A method for recycling high-crystallinity tin-containing waste polyester material

Abstract

The present application relates to a kind of high crystallinity tin-containing waste polyester material recycling method, comprising, high crystallinity tin-containing waste polyester material is treated to remove tin, and the tin-removing material is obtained;Tin-removing material is mixed with swelling agent, swelling treatment is obtained, and the swelling material is obtained;Swelling material is mixed with alcoholysis agent and catalyst, and alcoholysis reaction is carried out, and the alcoholysis monomer is obtained.The present application provides a targeted recycling method for high crystallinity tin-containing waste polyester material, through the steps of removing tin and swelling, effectively removing the residual organotin in the original raw material, and reducing the crystallinity.Ensure that the residual organotin in alcoholysis monomer is low, which essentially solves the problem of difficult penetration of alcoholysis agent.In addition, swelling agent and alcoholysis agent can be recycled, and material utilization is high, without a large amount of high-salt wastewater generation.

Description

Technical Field

[0001] This invention relates to the field of waste polyester material recycling and processing technology, specifically to a method for recycling highly crystalline tin-containing waste polyester materials. Background Technology

[0002] Polyester (polyethylene terephthalate, PET) is the most produced synthetic fiber material, widely used in fibers, textiles, clothing, polyester bottles, films, sheets, and other products. Based on the need for sustainable development, how to handle the scraps generated during polyester product manufacturing and the waste generated after polyester products are used has become a major direction for green development. Methanol hydrolysis is the mainstream process for recycling dimethyl terephthalate (DMT) from waste PET.

[0003] However, unlike ordinary waste polyester (such as bottle flakes, films, and conventional clothing fabrics), the processing of highly crystalline tin-containing waste polyester materials, such as waste marine fishing nets and ropes, presents the following technical challenges: First, the crystallinity is significantly higher. Fishing nets / ropes undergo high-stretching and heat-setting processes during manufacturing, resulting in a fiber crystallinity of 45%-55%, far exceeding the 30%-40% of ordinary PET fibers. High crystallinity means that the molecular chains are arranged more regularly and densely, making it difficult for alcoholysis agents to penetrate into the fiber interior, leading to a significantly lower conversion rate for this type of material in conventional alcoholysis processes.

[0004] Secondly, the fabric structure is thick and dense. Fishing nets and ropes are thick, high-twist fabrics with tightly twisted yarns and a dense structure, which further increases the difficulty of contact between the alcoholysis agent and the polyester molecular chains. Under conventional alcoholysis conditions, the alcoholysis reaction mainly occurs on the fiber surface and cannot penetrate deep into the fiber, resulting in an incomplete reaction.

[0005] Thirdly, there is pollution from organotin antifouling agents. Organotin antifouling agents (such as tributyltin and triphenyltin) are commonly added during the processing of fishing nets. After prolonged immersion in seawater, the surface becomes contaminated with large amounts of salt, oil, and marine organisms. Organotin compounds have strong biotoxicity; if not removed during recycling, they will remain in DMT products, affecting the quality and safety of downstream polyester synthesis.

[0006] Currently, several publicly available methods for the alcoholysis recycling of waste polyester materials are available, but all use general waste polyester as raw materials and do not offer specific technical solutions for the high crystallinity, high twist structure, and organotin pollution issues of fishing nets / ropes. Some patents involve fishing net recycling, but mainly focus on the physical or chemical recycling of polyamide fishing nets, and do not address the methanol alcoholysis of PET fishing nets to prepare DMT. Existing research has reported the use of an ethylene glycol-zinc acetate catalytic system to depolymerize PET material in waste marine fishing nets, but similarly, it does not provide specific crystallinity control pretreatment for the high crystallinity characteristics of fishing nets.

[0007] Therefore, developing an alcoholysis recovery method capable of systematically treating highly crystalline tin-containing waste polyester materials has significant industrial application value and environmental significance. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for recycling highly crystalline tin-containing waste polyester materials, comprising: Tin-free material is obtained by removing tin from highly crystalline tin-containing waste polyester material. The tin-removing material is mixed with a swelling agent and subjected to swelling treatment to obtain a swollen material; The swollen material is mixed with an alcoholysis agent and a catalyst to carry out an alcoholysis reaction, yielding alcoholysis monomers.

[0009] Furthermore, the ratio of the tin-removing material to the swelling agent is 1:5-10 g / mL; The swelling treatment is carried out at a temperature of 120-140℃ for 1-2 hours.

[0010] Furthermore, the feeding ratio of the swollen material to the alcoholysis agent is 1:5-10 g / mL; The amount of catalyst used is 0.5%-2.0% of the mass of the swollen material; The alcoholysis reaction was carried out under a protective atmosphere, at a pressure of 1.5-2.5 MPa and a temperature of 180-200℃ for 2-5 hours.

[0011] Further, the detinning process includes, Immerse the highly crystalline tin-containing waste polyester material in a composite decontamination agent solution at 40-60℃ and shake and clean for 30-60 minutes. The composite detergent is composed of AEO-9 and sodium citrate in a mass ratio of 1-3:1. The total mass concentration of AEO-9 and sodium citrate in the composite detergent solution is 0.5%-2.0%.

[0012] Furthermore, the oscillation cleaning is performed using ultrasonic oscillation cleaning with an ultrasonic frequency of 30-50kHz and a power of 200-500W.

[0013] Furthermore, the swelling agent is ethylene glycol; The alcoholysis agent is methanol; The catalyst is zinc acetate.

[0014] Further, the obtained alcoholysis monomer includes, The mixture after alcoholysis was subjected to solid-liquid separation while hot to obtain the filtrate; The filtrate was collected by vacuum distillation to obtain the alcoholysis agent, and the residue was cooled and crystallized to obtain the crude product and the mother liquor for crystallization. The crude product was recrystallized, decolorized, and dried to obtain high-purity alcoholysis monomer.

[0015] Furthermore, the vacuum degree of the reduced pressure distillation is -0.095 MPa to -0.098 MPa; The temperature for cooling crystallization is 0-10℃; The recrystallization uses a solvent composed of alcoholysis agent and water in a volume ratio of 3-4:1. After recrystallization, the recrystallization mother liquor is also separated by vacuum distillation to remove the alcoholysis agent. The decolorization is carried out using activated carbon at a temperature of 60-80℃, and the amount of activated carbon used is 0.5%-1.5% of the crude product weight.

[0016] Furthermore, the high-crystallinity tin-containing waste polyester material contains ≥60% polyester by mass and has a crystallinity of 45%-55%; After swelling treatment, the swollen material is rinsed at a temperature of 60-80°C, using an alcoholysis agent as the rinsing agent to remove the swelling agent adsorbed on the surface and in the micropores of the swollen material; the rinsing agent after washing is also collected and distilled to separate the alcoholysis agent.

[0017] The present invention also provides alcoholysis monomers obtained by the above-mentioned method for recycling highly crystalline tin-containing waste polyester materials.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) A specific swelling and activation scheme for high-crystallinity waste polyester materials: Targeting the structural characteristics of high-crystallinity (45%-55%) polyester materials used in fishing nets / ropes, this invention employs ethylene glycol for swelling treatment within a specific temperature window of 120-140℃. This temperature is higher than the glass transition temperature of PET (approximately 75℃), allowing ethylene glycol molecules to enter the amorphous region and increase the inter-chain spacing. Simultaneously, it is lower than the cold crystallization temperature peak (approximately 130-140℃), avoiding the induction of new crystal formation. After swelling, the crystallinity can be reduced to 30%-38%, fundamentally solving the technical problem of the difficulty in penetrating the alcoholysis agent due to high crystallinity, ensuring a conversion rate of ≥96% in subsequent alcoholysis reactions.

[0019] (2) Detoxification and decontamination pretreatment ensures product safety: In response to the problem of residual organotin antifouling agents in tin-containing waste polyester materials, this invention uses a composite decontaminant compounded with AEO-9 and sodium citrate to remove tin. The organotin removal rate is ≥95%, ensuring that the residual organotin in the alcoholysis monomer is ≤0.5mg / kg, which meets the safety standards for polyester synthesis raw materials.

[0020] (3) Rinsing to remove alcohol to ensure high product purity: After swelling, a large amount of free ethylene glycol is adsorbed on the surface and in the micropores of the material. This invention completely removes residual ethylene glycol through a methanol rinsing step, avoiding the transesterification reaction between ethylene glycol and DMT during the subsequent methanol alcoholysis process to generate mixed ester impurities such as methyl terephthalate (MET), ensuring that the purity of the alcoholysis monomer is ≥99.5%.

[0021] (4) Solvent closed-loop recycling, green and environmentally friendly: Methanol is recovered by vacuum distillation (recovery rate ≥92%), and ethylene glycol is recovered by distillation. Both can be recycled, with high material utilization and no large amount of high-salt wastewater generated, which meets the requirements of green chemistry. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0023] Figure 1 A flowchart illustrating a method for recycling highly crystalline tin-containing waste polyester materials is shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] The design concept of this invention is to first remove tin from highly crystalline tin-containing waste polyester materials to eliminate organic tin residues at the source; before alcoholysis, the tin-removed material is also swollen to reduce crystallinity, fundamentally solving the problem of poor penetration of the alcoholysis agent.

[0028] Accordingly, the present invention provides a method for recycling highly crystalline tin-containing waste polyester materials, comprising, Tin-free material is obtained by removing tin from highly crystalline tin-containing waste polyester material. The tin-removing material is mixed with a swelling agent and subjected to swelling treatment to obtain a swollen material; The swollen material is mixed with an alcoholysis agent and a catalyst to carry out an alcoholysis reaction, yielding alcoholysis monomers.

[0029] In some preferred embodiments, the ratio of the tin-removing material to the swelling agent is 1:5-10 g / mL; The swelling treatment is carried out at a temperature of 120-140℃ for 1-2 hours.

[0030] In some preferred embodiments, the feeding ratio of the swollen material to the alcoholysis agent is 1:5-10 g / mL; The amount of catalyst used is 0.5%-2.0% of the mass of the swollen material; The alcoholysis reaction was carried out under a protective atmosphere, at a pressure of 1.5-2.5 MPa and a temperature of 180-200℃ for 2-5 hours.

[0031] In some preferred embodiments, the detinning process includes, Immerse the highly crystalline tin-containing waste polyester material in a composite decontamination agent solution at 40-60℃ and shake and clean for 30-60 minutes. The composite detergent is composed of AEO-9 and sodium citrate in a mass ratio of 1-3:1. The total mass concentration of AEO-9 and sodium citrate in the composite detergent solution is 0.5%-2.0%.

[0032] In some preferred embodiments, the oscillation cleaning is performed using ultrasonic oscillation cleaning with an ultrasonic frequency of 30-50kHz and a power of 200-500W.

[0033] In some preferred embodiments, the swelling agent is ethylene glycol; The alcoholysis agent is methanol; The catalyst is zinc acetate.

[0034] In some preferred embodiments, the obtained alcoholysis monomer comprises, The mixture after alcoholysis was subjected to solid-liquid separation while hot to obtain the filtrate; The filtrate was collected by vacuum distillation to obtain the alcoholysis agent, and the residue was cooled and crystallized to obtain the crude product and the mother liquor for crystallization. The crude product was recrystallized, decolorized, and dried to obtain high-purity alcoholysis monomer.

[0035] In some preferred embodiments, the vacuum degree of the reduced pressure distillation is -0.095 MPa to -0.098 MPa; The temperature for cooling crystallization is 0-10℃; The recrystallization uses a solvent composed of alcoholysis agent and water in a volume ratio of 3-4:1. After recrystallization, the recrystallization mother liquor is also separated by vacuum distillation to remove the alcoholysis agent. The decolorization is carried out using activated carbon at a temperature of 60-80℃, and the amount of activated carbon used is 0.5%-1.5% of the crude product weight.

[0036] In some preferred embodiments, the high-crystallinity tin-containing waste polyester material contains ≥60% polyester by mass and has a crystallinity of 45%-55%. After swelling treatment, the swollen material is rinsed at a temperature of 60-80°C, using an alcoholysis agent as the rinsing agent to remove the swelling agent adsorbed on the surface and in the micropores of the swollen material; the rinsing agent after washing is also collected and distilled to separate the alcoholysis agent.

[0037] The test methods mentioned in this invention are described below: PET crystallinity: determined by X-ray diffraction (XRD) with a scanning range of 2θ = 5°-40° and a scanning speed of 2° / min.

[0038] PET intrinsic viscosity: determined by capillary viscometer method in national standard GB / T 14190-2017 "Test Method for Fiber Grade Polyester (PET) Chips", with a solvent mass ratio of 60:40.

[0039] PET conversion rate: calculated by combining the difference in the mass of polyester fragments before and after the reaction and the DMT content in the filtrate determined by HPLC.

[0040] DMT yield: The ratio of the actual quality of DMT obtained to the theoretically expected quality of DMT after complete conversion.

[0041] DMT purity: determined by HPLC. Chromatographic conditions: C18 reversed-phase column (4.6×250mm, 5μm), mobile phase: methanol:water (70:30), detection wavelength: 254nm, flow rate: 1.0mL / min, column temperature: 30℃.

[0042] Acid value: determined according to national standard GB / T14189-2008 "Fiber Grade Polyester Chips (PET)".

[0043] Ash content: determined in accordance with the national standard GB / T7531-2008 "Determination of ignition residue of organic chemical products".

[0044] Organotin residue: determined by ICP-MS.

[0045] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0046] Example 1 A method for recycling highly crystalline tin-containing waste polyester materials, such as Figure 1 As shown, it includes the following steps: S1. Grading and Pretreatment: Waste aquaculture nets from a certain sea area were taken. The PET content was measured to be 82wt%, and the fiber crystallinity was 52%. Metal, sand, and other impurities were manually removed. The nets were then immersed in a 50℃ aqueous solution of a composite decontaminant (AEO-9 to sodium citrate mass ratio 2:1, total concentration 1.5%) and ultrasonically cleaned (40kHz, 300W) for 45 minutes. ICP-MS analysis showed that the initial organotin content in the nets before cleaning was 8.5mg / kg, which decreased to 0.3mg / kg after cleaning, achieving a 96.5% organotin removal rate. After cleaning, the nets were rinsed twice with deionized water, dried in a forced-air dryer at 60℃, and crushed into 3mm×3mm fragments to obtain the detin-removed material. A 500-mesh double-layer polypropylene filter membrane was installed at the drainage end of the crushing and cleaning process, achieving a microplastic interception rate of 99.2%.

[0047] S2. Crystallinity-Controlled Swelling Activation: 100g of the tin-removed material obtained from S1 was mixed with 600mL of ethylene glycol and transferred to a closed reactor. The mixture was heated to 130℃ and stirred for 1.5h to induce swelling. XRD analysis showed that the crystallinity of the polyester decreased from 52% to 33% after swelling. The intrinsic viscosity of PET before swelling was 0.68 dL / g, and after swelling it was 0.66 dL / g, a decrease of only 2.9%, proving that this step was merely physical swelling and no significant chemical depolymerization reaction occurred.

[0048] S3. Rinsing to remove alcohol: After swelling, cool to 70℃ and rinse three times with 500mL of anhydrous methanol, stirring for 5 minutes each time. Filter to remove free ethylene glycol, obtaining the swollen material. Further distillation of the rinsing solution yields ethylene glycol.

[0049] S4, alcoholysis reaction: 100g of the swollen material obtained from S2, 800g of methanol, and 1.5g of zinc acetate were added to a high-pressure reactor, purged with nitrogen three times, pressurized to 2.0MPa, heated to 195℃, and reacted at a constant temperature for 3.5h.

[0050] S5. Separation and Purification: After the reaction, the temperature was lowered to 80℃, and the mixture was filtered while hot. The filtrate was distilled under reduced pressure at -0.096 MPa to recover methanol, with a recovery rate of 93.2%. The residue was cooled to 5℃ and allowed to stand for crystallization for 5 hours, then filtered to obtain crude DMT. The crude product was recrystallized from methanol-water (volume ratio 4:1). After recrystallization, the recrystallization mother liquor was distilled under reduced pressure at -0.096 MPa to separate methanol. Subsequently, 1.0% (by weight) of activated carbon was added to decolorize at 70℃ for 30 minutes, and then dried under vacuum at 50℃ for 4 hours to obtain high-purity DMT.

[0051] In this embodiment, the final measured values ​​were: PET conversion rate 97.2%, DMT yield 91.5%, product purity 99.6%, acid value 0.12 mg KOH / g, ash content 0.006%, and organotin residue 0.3 mg / kg.

[0052] Example 2 The difference compared to Example 1 is that in S2, the temperature is heated to 120°C and stirred to swell for 2 hours.

[0053] As the swelling temperature drops to 120°C, the thermal mobility of ethylene glycol molecules weakens, reducing the swelling activation effect on the crystallization region. After swelling, the crystallinity decreases from 52% to 38% (compared to 33% in Example 1 at 130°C / 1.5h), showing a significantly smaller decrease in the rate of crystallinity reduction.

[0054] Test results showed that the PET conversion rate was 95.8%, the DMT yield was 89.8%, and the product purity was 99.4%. Although this was still better than Comparative Example 1 (conversion rate 72.3%) which was not swollen and activated, the overall effect was lower than Example 1 (conversion rate 97.2%), proving that although 120°C was within the effective swelling temperature window, the swelling efficiency was lower than the optimized condition of 130°C.

[0055] Example 3 The difference compared to Example 1 is that in S2, the temperature was heated to 140°C and stirred to induce swelling for 1 hour. After swelling, the crystallinity decreased from 53% to 31%.

[0056] Test results showed that the PET conversion rate was 97.5%, the DMT yield was 91.8%, and the product purity was 99.5%.

[0057] Example 4 The difference compared to Example 1 is that the S4 alcoholysis reaction was carried out at a constant temperature for 2 hours.

[0058] Test results showed that the PET conversion rate was 96.0%, the DMT yield was 90.1%, and the product purity was 99.5%.

[0059] Example 5 The difference compared to Example 1 is that the S4 alcoholysis reaction was carried out at a constant temperature for 5 hours.

[0060] Test results showed that the PET conversion rate was 97.8%, the DMT yield was 92.0%, and the product purity was 99.5%.

[0061] Example 6 In Example 1, ethylene glycol was recovered by distillation in S3, and methanol was recovered by vacuum distillation in S5. These were used for subsequent batches of recovery, with additional methanol added if necessary. Five batches were run consecutively, and the test data are shown in Table 1.

[0062] Table 1

[0063] After 5 cycles, all indicators remained at an excellent level, proving the stability of the solvent cycling system.

[0064] Comparative Example 1 Compared to Example 1, without the crystallinity-controlled swelling activation of S2, the tin-removed material is directly subjected to alcoholysis reaction. Test results showed that the PET conversion rate was only 72.3%, and the DMT yield was only 65.4%. This is because the high crystallinity of fishing nets (52%) prevented the alcoholysis agent from effectively penetrating the fiber interior, and the reaction only occurred on the fiber surface. This demonstrates the necessity of swelling activation for thick, highly crystalline fabrics such as fishing nets / ropes.

[0065] Comparative Example 2 The difference compared to Example 1 is that in S2, the temperature was heated to 100°C and stirred for 2 hours to induce swelling. After swelling, the crystallinity only decreased from 52% to 47%.

[0066] Test results showed that the PET conversion rate was 78.6%, while the DMT yield was only 71.2%. This is because 100℃ is below the effective swelling temperature window of PET, resulting in insufficient molecular mobility of ethylene glycol, which cannot effectively open the amorphous region and reduce crystallinity.

[0067] Comparative Example 3 The difference compared to Example 1 is that in S2, the temperature was raised to 160°C and stirred for 2 hours to induce swelling. After swelling, the tin-free material showed obvious adhesion and partial dissolution, and the crystallinity only decreased to 49%.

[0068] Test results showed that the PET conversion rate was 81.3%, while the DMT yield was only 74.5%. This is because 160℃ exceeds the peak range of PET's cold crystallization temperature, inducing the formation of new crystals; at the same time, the excessively high temperature caused excessive swelling and surface dissolution of polyester by ethylene glycol, which destroyed the morphology of the detin-removed material and was not conducive to subsequent uniform alcoholysis.

[0069] Comparative Example 4 The difference from Example 1 is that S3 is not performed, and the swollen material is directly subjected to alcoholysis reaction.

[0070] Test results showed a PET conversion rate of 94.8%, a DMT yield of 85.3%, and a product purity reduced to 96.2%. HPLC analysis revealed the formation of a large amount of mixed ester impurities, including ethylene glycol terephthalate (MET). This demonstrates that residual ethylene glycol must be removed after swelling to ensure DMT purity.

[0071] Comparative Example 5 Using the conventional methanol alcoholysis process for waste polyester commonly used in existing technologies, fishing net fragments were directly reacted with methanol and zinc acetate at 195°C and 2.0 MPa for 3.5 h. After the alcoholysis reaction was completed, the same operation as in Example S5 was used for separation and purification.

[0072] Test results showed that the PET conversion rate was only 78.6%, the DMT yield was 68.3%, the product purity was 94.7%, and the organotin residue was 8.7 mg / kg. This demonstrates that the conventional waste polyester alcoholysis process is significantly less effective when directly applied to highly crystalline tin-containing fishing nets.

[0073] Comparative Example 6 Compared with Example 1, the difference is that in S1, the object of treatment is changed from waste aquaculture nets to ordinary PET bottle flakes (35% crystallinity, no organotin contamination).

[0074] Test results showed a PET conversion rate of 99.1% and a DMT yield of 94.2%. Although the method in Example 1 also achieved high conversion and recovery rates for ordinary PET bottle flakes, similar results can be achieved through direct alcoholysis in existing technologies, which indirectly demonstrates that this invention is a suitable solution for highly crystalline tin-containing waste polyester materials.

[0075] Comparative Example 7 Compared with Example 1, the difference is that in S1, a composite decontaminating agent aqueous solution is used for cleaning, and the material is directly crushed to obtain fragments. The fragments are then used to replace the detinning material for subsequent processing.

[0076] Test results showed that the PET conversion rate was 96.8% and the DMT yield was 90.9%. The alcoholysis effect was basically comparable to that of Example 1, but the residual organotin in the DMT was as high as 8.7 mg / kg, far exceeding the safety limit for polyester synthesis raw materials. This demonstrates the necessity of detoxification pretreatment to ensure product safety.

[0077] Comparative Example 8 Compared with Example 1, the difference is that in S4, potassium carbonate, calcium acetate, and zinc chloride were used in place of zinc acetate in equal masses. The corresponding test results are shown in Table 2.

[0078] Table 2

[0079] The results showed that using zinc acetate as a catalyst for the alcoholysis reaction was more effective than that used in current technologies.

[0080] During the swelling process, the glass transition temperature (Tg) of PET is approximately 75℃, and the cold crystallization temperature is approximately 130-140℃. This invention selects 120-140℃ as the swelling temperature window. Higher than the Tg allows ethylene glycol molecules to enter the amorphous region, increasing the interchain spacing and reducing crystallinity; simultaneously, lower than the cold crystallization temperature avoids inducing new crystal formation. This temperature window can reduce the crystallinity from 45%-55% to 30%-38%, while the change in the intrinsic viscosity of PET before and after swelling is minimal (decreased by ≤5%), proving that this step is purely physical swelling and does not involve chemical depolymerization. After swelling, free ethylene glycol is removed by rinsing with methanol to prevent transesterification with DMT, thus avoiding the formation of mixed ester impurities and ensuring high product purity.

[0081] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for recycling highly crystalline tin-containing waste polyester material, characterized in that, include, Tin-free material is obtained by removing tin from highly crystalline tin-containing waste polyester material. The tin-removing material is mixed with a swelling agent and subjected to swelling treatment to obtain a swollen material; The swollen material is mixed with an alcoholysis agent and a catalyst to carry out an alcoholysis reaction, yielding alcoholysis monomers.

2. The method for recycling highly crystalline tin-containing waste polyester material according to claim 1, characterized in that, The ratio of the tin-removing material to the swelling agent is 1:5-10 g / mL; The swelling treatment is carried out at a temperature of 120-140℃ for 1-2 hours.

3. The method for recycling highly crystalline tin-containing waste polyester material according to claim 1, characterized in that, The feeding ratio of the swollen material to the alcoholysis agent is 1:5-10 g / mL; The amount of catalyst used is 0.5%-2.0% of the mass of the swollen material; The alcoholysis reaction was carried out under a protective atmosphere, at a pressure of 1.5-2.5 MPa and a temperature of 180-200℃ for 2-5 hours.

4. The method for recycling highly crystalline tin-containing waste polyester material according to claim 1, characterized in that, The detinning process includes, Immerse the highly crystalline tin-containing waste polyester material in a composite decontamination agent solution at 40-60℃ and shake and clean for 30-60 minutes. The composite detergent is composed of AEO-9 and sodium citrate in a mass ratio of 1-3:

1. The total mass concentration of AEO-9 and sodium citrate in the composite detergent solution is 0.5%-2.0%.

5. The method for recycling highly crystalline tin-containing waste polyester material according to claim 4, characterized in that, The oscillation cleaning is performed using ultrasonic oscillation cleaning, with an ultrasonic frequency of 30-50kHz and a power of 200-500W.

6. The method for recycling highly crystalline tin-containing waste polyester material according to claim 1, characterized in that, The swelling agent is ethylene glycol; The alcoholysis agent is methanol; The catalyst is zinc acetate.

7. The method for recycling highly crystalline tin-containing waste polyester material according to claim 1, characterized in that, The obtained alcoholysis monomers include, The mixture after alcoholysis was subjected to solid-liquid separation while hot to obtain the filtrate; The filtrate was collected by vacuum distillation to obtain the alcoholysis agent, and the residue was cooled and crystallized to obtain the crude product and the mother liquor for crystallization. The crude product was recrystallized, decolorized, and dried to obtain high-purity alcoholysis monomer.

8. The method for recycling highly crystalline tin-containing waste polyester material according to claim 7, characterized in that, The vacuum degree of the vacuum distillation is -0.095 MPa to -0.098 MPa; The temperature for cooling crystallization is 0-10℃; The recrystallization uses a solvent composed of alcoholysis agent and water in a volume ratio of 3-4:

1. After recrystallization, the recrystallization mother liquor is also separated by vacuum distillation to remove the alcoholysis agent. The decolorization is carried out using activated carbon at a temperature of 60-80℃, and the amount of activated carbon used is 0.5%-1.5% of the crude product weight.

9. The method for recycling highly crystalline tin-containing waste polyester material according to any one of claims 1-8, characterized in that, The high-crystallinity tin-containing waste polyester material contains ≥60% polyester by mass and has a crystallinity of 45%-55%. After swelling treatment, the swollen material is rinsed at a temperature of 60-80°C, using an alcoholysis agent as the rinsing agent to remove the swelling agent adsorbed on the surface and in the micropores of the swollen material; the rinsing agent after washing is also collected and distilled to separate the alcoholysis agent.

10. The alcoholysis monomer obtained by the recycling method of highly crystalline tin-containing waste polyester material according to any one of claims 1-9.

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