Method for solvent-assisted efficient recovery of impurity-containing polyester waste

Abstract

The invention belongs to the technical field of PET (Polyethylene Terephthalate) recovery, and particularly relates to a method for efficiently recovering an impurity-containing polyester waste material under the assistance of a solvent. The method for efficiently recovering the impurity-containing polyester waste material with the assistance of the solvent comprises the following steps: S1, sequentially adding methanol, an auxiliary solvent and a catalyst into the waste impurity-containing PET material, performing alcoholysis with methanol, and filtering to obtain filter residues and first filtrate (alcoholysis products); s2, adding activated carbon into the first filtrate, stirring and filtering to obtain second filtrate; s3, performing rotary evaporation treatment on the second filtrate to obtain a rotary evaporation solid product; and S4, washing the rotary evaporation solid product with methanol, filtering to obtain DMT and a third filtrate, and carrying out two-stage reduced pressure distillation on the third filtrate to recover the catalyst, methanol and ethylene glycol. The method provided by the invention realizes recycling of the impurity-containing waste PET, reduces environmental pollution caused by PET polyester, saves petroleum resources, and promotes sustainable development of economy and resources.

Description

Technical Field

[0001] The invention relates to the technical field of PET recycling, in particular to a method for efficiently recycling impure polyester waste materials with the assistance of a solvent. Background Art

[0002] Plastic materials are an indispensable part of our daily lives, but they are mostly consumed as disposable products, which leads to serious environmental pollution worldwide. Plastic materials are mainly composed of polyethylene terephthalate (PET), and about 60 million tons are used for fabric projects worldwide each year, of which about 30 million tons are used for beverage bottles and films. Surveys show that 73% of second-hand textiles are currently incinerated or landfilled in landfills and oceans, and the amount of recyclable polyester waste in the world is estimated to be 42 million tons per year. In order to achieve a circular economy, we urgently need a method that can effectively process waste plastic materials using low energy consumption.

[0003] In the prior art, there are physical and chemical methods for recycling PET. The physical recycling method processes waste PET by sorting, cleaning, crushing and re-granulating. It does not involve molecular degradation, has low cost and simple process, but the recycled materials have many impurities and poor performance, are difficult to use for food contact, and have degraded quality after multiple recycling, eventually becoming a source of white pollution. Because most plastic materials are mixed with other materials and / or colored with dyes, material recycling methods through simple melting and reshaping processes are ineffective. Therefore, in chemical recycling, the original plastic can be infinitely regenerated through depolymerization and repolymerization, which is a promising method for recycling a wide range of polyester fibers.

[0004] However, there are many impurities in waste materials, such as dyes in colored PET, aluminum in ground film, cotton in polyester-cotton blends, and cotton or hemp in fishing nets. These impurities will contaminate the degradation products, making subsequent separation and purification more energy-intensive. Therefore, it is a great challenge to find a feasible and practical way to recycle different polyester wastes. Summary of the invention

[0005] The purpose of the present invention is to provide a solvent-assisted method for efficiently recovering impure polyester waste, so as to solve the problems existing in the above-mentioned prior art and realize resource conversion, treatment and utilization of impure polyester waste.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for efficiently recovering impure polyester waste with the assistance of a solvent, the steps comprising:

[0008] S1, adding methanol, auxiliary solvent and catalyst to the waste PET material containing impurities in sequence, performing alcoholysis with methanol, and filtering to obtain a filter residue and a first filtrate (alcoholysis product);

[0009] S2, adding activated carbon to the first filtrate, stirring, filtering, and obtaining a second filtrate;

[0010] S3, subjecting the second filtrate to rotary evaporation to obtain a rotary evaporation solid product;

[0011] S4, washing the rotary evaporated solid product with methanol, and filtering to obtain DMT.

[0012] Furthermore, the amount of methanol used is 50% to 500% of the mass of the waste PET material containing impurities.

[0013] Furthermore, the auxiliary solvent includes a polar solvent, an alkaline solvent or an acidic solvent.

[0014] Preferably, the polar solvent includes dimethyl sulfoxide; the alkaline solvent includes pyridine or triethylamine; and the acidic solvent includes acetic acid or trifluoroacetic acid.

[0015] Furthermore, the amount of the auxiliary solvent used is 100% to 1000% of the mass of the waste PET material containing impurities.

[0016] Further, the catalyst includes at least one of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), triethanolamine (TEA), N-methylmorpholine (NMM), N,N-diisopropylethylamine (DIPEA) and (tert-butylimino)tri(pyrrolidino)phosphine (BTPP).

[0017] Furthermore, the amount of the catalyst used is 2.5% to 10% of the mass of the waste impurity-containing PET material.

[0018] Furthermore, the temperature of the methanol hydrolysis is 110-140° C., the time is 15-60 min, and the pressure is 0.3-1.0 MPa.

[0019] Furthermore, the amount of activated carbon added is 10% to 300% of the mass of the first filtrate.

[0020] Furthermore, the stirring time is 5 to 60 minutes.

[0021] Furthermore, the temperature of the rotary evaporation treatment is 40-150°C.

[0022] The second technical solution of the present invention is to provide a method for recycling impure polyester waste, the steps comprising:

[0023] S1, adding methanol, auxiliary solvent and catalyst to the waste PET material containing impurities in sequence, performing alcoholysis with methanol, and filtering to obtain a filter residue and a first filtrate (alcoholysis product);

[0024] S2, adding activated carbon to the first filtrate, stirring, filtering, and obtaining a second filtrate;

[0025] S3, subjecting the second filtrate to rotary evaporation to obtain a rotary evaporation solid product, and recovering methanol and auxiliary solvent;

[0026] S4, washing the rotary evaporated solid product with methanol, and filtering to obtain DMT and a third filtrate;

[0027] S5. Recover the third filtrate by a first reduced pressure distillation to obtain methanol, and then recover the catalyst by a second reduced pressure distillation, and the remaining liquid is ethylene glycol.

[0028] Furthermore, the temperature of the first vacuum distillation is 40°C; the temperature of the second vacuum distillation is 120-150°C.

[0029] The purpose of the rotary evaporation in step S3 is to remove methanol and auxiliary solvent; the purpose of the first vacuum distillation in step S5 is to recover methanol, and the purpose of the second vacuum distillation is to recover the catalyst. The remaining product after the second vacuum distillation is ethylene glycol.

[0030] Polyester fibers and other materials in plastics can react in methanol solvent under appropriate conditions to generate dimethyl terephthalate (DMT) and ethylene glycol (EG). The generated DMT and EG can be reused to manufacture other high value-added chemical products, such as recycled polyester fibers and antifreeze. In addition, the commonly used catalysts (such as alkaline catalysts) for methanol hydrolysis require less dosage, are low in cost, and are easy to recycle and reuse.

[0031] The present invention discloses the following technical effects:

[0032] The auxiliary solvent selected in the present invention can promote the dissolution of the PET chain segment and the effective contact with methanol or enhance the nucleophilicity of methanol to promote the alcoholysis reaction so that it can be quickly depolymerized at a lower temperature and pressure, and has better solubility for DMT, while impurities are insoluble in the solvent. After the reaction is completed, the product and impurities can be better separated, and the method is applicable to different raw materials and can realize the recovery of different impurity-containing polyester materials.

[0033] The method of the invention realizes the recycling and reuse of impure waste PET, reduces the environmental pollution caused by PET polyester, saves petroleum resources, and promotes the sustainable development of economy and resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 This is a process flow chart of methanolysis of impure PET materials;

[0036] Figure 2 This is the standard curve of DMT external standard method. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0039] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0040] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0042] The waste and impure PET materials in the present invention include colored polyester fiber cloth, aluminum-containing mulch, polyester-cotton blends, fishing nets, colored bottle flakes, colored films or PET bottles with PP / PVC labels. In the specific implementation scheme, colored bottle flakes are taken as an example to test the technical solution.

[0043] Unless otherwise specified, the “parts” referred to in the specific embodiments of the present invention are all “parts by mass”.

[0044] Example 1

[0045] The steps for solvent-assisted efficient recovery of impure polyester waste include:

[0046] S1, take 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, 30 parts of methanol, and 50 parts of dimethyl sulfoxide, add them into a reactor, heat to 130° C. and react for 0.5 h to obtain a reaction product, and then filter the reaction product to remove impurities to obtain a colored alcoholysis product (first filtrate);

[0047] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove color (second filtrate), and then recovering methanol and dimethyl sulfoxide by rotary evaporation (120° C.), methanol and dimethyl sulfoxide can be further recycled, and the product after rotary evaporation is washed with cold methanol to obtain refined DMT and the third filtrate;

[0048] S3. The third filtrate is heated to 40°C and subjected to reduced pressure distillation to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0049] Example 2

[0050] The steps for solvent-assisted efficient recovery of impure polyester waste include:

[0051] S1, take 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, 30 parts of methanol, and 50 parts of pyridine, add them into a reactor, heat to 130° C. and react for 0.5 h to obtain a reaction product, and then filter the reaction product to remove impurities to obtain a colored alcoholysis product (first filtrate);

[0052] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove the color (second filtrate), and then recovering methanol and pyridine by rotary evaporation (90° C.), which can be further recycled, and washing the product after rotary evaporation with cold methanol to obtain refined DMT and the third filtrate;

[0053] S3. The third filtrate is heated to 40°C and subjected to reduced pressure distillation to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0054] Example 3

[0055] The steps for solvent-assisted efficient recovery of impure polyester waste include:

[0056] S1, take 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, 30 parts of methanol, and 50 parts of triethylamine, add them into a reactor, heat to 130° C. and react for 0.5 h to obtain a reaction product, and then filter the reaction product to remove impurities to obtain a colored alcoholysis product (first filtrate);

[0057] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove color (second filtrate), and then recovering methanol and triethylamine by rotary evaporation (40° C.), methanol and triethylamine can be further recycled, and the product after rotary evaporation is washed with cold methanol to obtain refined DMT and the third filtrate;

[0058] S3. The third filtrate is heated to 40°C and subjected to reduced pressure distillation to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0059] Example 4

[0060] The steps for solvent-assisted efficient recovery of impure polyester waste include:

[0061] S1, taking 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, 30 parts of methanol, and 50 parts of acetic acid, adding them into a reactor, heating to 130° C. and reacting for 0.5 h to obtain a reaction product, and then filtering the reaction product to remove impurities to obtain a colored alcoholysis product (first filtrate);

[0062] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove color (second filtrate), and then recovering methanol and acetic acid by rotary evaporation (60° C.), which can be further recycled, and washing the product after rotary evaporation with cold methanol to obtain refined DMT and a third filtrate;

[0063] S3, the third filtrate is heated to 40°C and distilled under reduced pressure to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0064] Example 5

[0065] The steps for solvent-assisted efficient recovery of impure polyester waste include:

[0066] S1, take 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, 30 parts of methanol, and 50 parts of trifluoroacetic acid, add them into a reactor, heat to 130° C. and react for 0.5 h to obtain a reaction product, and then filter the reaction product to remove impurities to obtain a colored alcoholysis product (first filtrate);

[0067] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove color (second filtrate), and then recovering methanol and trifluoroacetic acid by rotary evaporation (40° C.), methanol and trifluoroacetic acid can be further recycled, and the product after rotary evaporation is washed with cold methanol to obtain refined DMT and the third filtrate;

[0068] S3. The third filtrate is heated to 40°C and subjected to reduced pressure distillation to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0069] Example 6

[0070] Compared with Example 1, the only difference is that the PET bottle flakes are replaced by an equal amount of PET film.

[0071] Example 7

[0072] Compared with Example 1, the only difference is that the PET bottle flakes are replaced by an equal amount of PET fiber cloth.

[0073] Example 8

[0074] Compared with Example 1, the only difference is that the PET bottle flakes are replaced by an equal amount of PET aluminum-containing ground film.

[0075] Example 9

[0076] Compared with Example 1, the only difference is that the PET bottle flakes are replaced with an equal amount of polyester-cotton blended fabric.

[0077] Example 10

[0078] Compared with Example 1, the only difference is that the PET bottle flakes are replaced by an equal amount of PET fishing nets.

[0079] Comparative Example 1

[0080] The treatment steps of impure polyester waste include:

[0081] S1, 10 parts of washed and dried colored PET bottle flakes, 0.5 parts of 1,5-diazabicyclo[4.3.0]non-5-ene, and 30 parts of methanol are added into a reactor, heated to 130° C. and reacted for 0.5 h to obtain a reaction product, and then the reaction product is filtered and impurities are removed to obtain a colored alcoholysis product (first filtrate);

[0082] S2, adding 0.5 parts of activated carbon to the alcoholysis product, stirring for 15 minutes and then filtering to remove the color (second filtrate), and then recovering methanol by rotary evaporation (40°C), the methanol can be further recycled, and the product after rotary evaporation is washed with cold methanol to obtain refined DMT and the third filtrate;

[0083] S3. The third filtrate is heated to 40°C and subjected to reduced pressure distillation to recover methanol, and then the temperature is further raised to 130°C to recover 1,5-diazabicyclo[4.3.0]non-5-ene, and the remaining liquid portion is ethylene glycol.

[0084] Test example

[0085] The methanolysis effect of the impure PET materials in Examples 1 to 10 and Comparative Example 1 was tested by the following method. The results are shown in Table 1.

[0086] Detection method:

[0087] The obtained filtrate was analyzed by high performance liquid chromatography. The high performance liquid chromatography used a Waters AQ-C18 (5um, 4.6×250mm) column, with a mobile phase of methanol: ultrapure water (70:30 (v / v)) at a flow rate of 1 mL / min and a column temperature of 35°C. By injecting a standard sample of known concentration (such as Figure 2 The retention time and calibration value of the observed product were determined and quantified using the external standard method.

[0088] Among them, the calculation formulas for PET conversion rate, DMT yield and ethylene glycol yield are as follows:

[0089] PET conversion rate = (total PET amount - PET balance) / total PET amount;

[0090] DMT yield = actual DMT output / theoretical DMT output;

[0091] Ethylene glycol yield = actual ethylene glycol production / theoretical ethylene glycol production.

[0092] Table 1 Effect of methanolysis of colored PET bottle flakes assisted by different solvents

[0093]

[0094] Table 2 Effect of dimethyl sulfoxide-assisted methanolysis of different impurity-containing PET materials

[0095]

[0096]

[0097] It can be seen from Table 1 that, compared with not adding solvent, chemical recovery of PET waste can be achieved at lower temperature and pressure by solvent-assisted PET methanolysis. This is because the solvent can promote the swelling of PET, allowing it to fully contact with the alcoholysis agent and thus accelerate the depolymerization rate. In addition, it can be seen from Table 2 that this method is suitable for different commercial impurity-containing PET materials, and this method can realize the resource utilization of PET waste.

[0098] Figure 1 This is the process flow chart of methanol hydrolysis of impure PET materials.

[0099] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for efficiently recovering impure polyester waste with solvent assistance, characterized in that the steps include: S1. Adding methanol, an auxiliary solvent and a catalyst in sequence to the waste PET material containing impurities, performing methanolysis, and filtering to obtain a filter residue and a first filtrate; S2, adding activated carbon to the first filtrate, stirring, filtering, and obtaining a second filtrate; S3, subjecting the second filtrate to rotary evaporation to obtain a rotary evaporation solid product; S4, washing the rotary evaporated solid product with methanol, and filtering to obtain refined DMT.

2. The method according to claim 1, characterized in that The amount of methanol used is 50% to 500% of the mass of the waste PET material containing impurities; the amount of the auxiliary solvent used is 100% to 1000% of the mass of the waste PET material containing impurities; and the amount of the catalyst used is 2.5% to 10% of the mass of the waste PET material containing impurities.

3. The method according to claim 1, characterized in that The auxiliary solvent includes a polar solvent, a basic solvent or an acidic solvent.

4. The method according to claim 3, characterized in that The polar solvent includes dimethyl sulfoxide; the alkaline solvent includes pyridine or triethylamine; and the acidic solvent includes acetic acid or trifluoroacetic acid.

5. The method according to claim 1, characterized in that The catalyst includes at least one of DBN, TMG, DBU, TBD, TEA, NMM, DIPEA and BTPP.

6. The method according to claim 1, characterized in that The temperature of the methanol hydrolysis is 110-140° C., the time is 15-60 min, and the pressure is 0.3-1.0 MPa.

7. The method according to claim 1, characterized in that The amount of activated carbon added is 10% to 300% of the mass of the first filtrate; and the stirring time is 5 to 60 minutes.

8. The method according to claim 1, characterized in that The temperature of the rotary evaporation treatment is 40-150°C.

9. A method for recycling impure polyester waste, characterized in that the steps include: S1. Adding methanol, an auxiliary solvent and a catalyst in sequence to the waste PET material containing impurities, performing methanolysis, and filtering to obtain a filter residue and a first filtrate; S2, adding activated carbon to the first filtrate, stirring, filtering, and obtaining a second filtrate; S3, subjecting the second filtrate to rotary evaporation to obtain a rotary evaporation solid product, and recovering methanol and auxiliary solvent; S4, washing the rotary evaporated solid product with methanol, and filtering to obtain DMT and a third filtrate; S5. Recover the third filtrate by a first reduced pressure distillation to obtain methanol, and then recover the catalyst by a second reduced pressure distillation, and the remaining liquid is ethylene glycol.

10. The method according to claim 9, characterized in that The temperature of the first vacuum distillation is 40°C; the temperature of the second vacuum distillation is 120-150°C.

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