Process for the degradation of a composite polyester material

Abstract

This invention provides a degradation process for composite polyester materials, relating to the field of polyester recycling technology. The degradation process involves depolymerizing a reaction system comprising at least raw material components (i) composite polyester material, (ii) organic ester compounds, (iii) a co-solvent, and (iv) an alkaline catalyst at a temperature not exceeding 100°C; the weight ratio of the co-solvent to the organic ester compound is ≥0.5. By adding a certain amount of co-solvent to the depolymerization system, this invention achieves directional depolymerization of polyester-containing composite polyester materials while essentially preventing depolymerization of other materials, such as spandex and nylon.

Description

Technical Field

[0001] This invention belongs to the field of polyester recycling technology and relates to a degradation process method for composite polyester materials. Background Technology

[0002] The annual consumption of polyester materials, represented by PET, reaches tens of millions of tons. The degradation and recycling of polyester materials to produce synthetic raw materials such as dimethyl terephthalate (DMT) and bis(hydroxyethyl) terephthalate (BHET) are generally used for materials with high PET content, such as PET plastic bottles and packaging materials, where PET is even the main component. my country generates tens of millions of tons of waste textiles annually. Textiles are typically blends of various fiber materials. For textiles containing polyester fibers, they are usually blends with other fiber materials (such as cotton, spandex, nylon, and polypropylene). However, research on how to degrade and recycle the polyester fibers in blended textiles while separating and recycling other fiber materials, and even ensuring that the degradation of polyester does not affect the performance of other fiber materials, is currently limited.

[0003] Reference 1 discloses a method for degrading and upgrading polyester materials using aromatic ester solvents. This method employs a solid alkali catalyst and aromatic ester solvents to dissolve and peel PET from tightly interwoven complex textiles in PET-containing textile waste, and then depolymerizes the polyester fibers into dicarboxylic acid esters via transesterification. However, the depolymerization reaction temperature in this technology is as high as 160-240℃, and the reaction time is as long as 10-15 hours. This is detrimental to many textile fibers, such as spandex, as it can lead to the degradation of spandex and other fiber materials. This makes targeted recycling of polyester materials impossible, affecting both the generation and reuse of polyester synthetic raw materials and the recycling of other fiber materials.

[0004] Currently, the targeted recycling and reuse of polyester materials in composite polyester materials is a challenging aspect of polyester recycling, but also a problem that urgently needs to be solved. Therefore, researching targeted degradation processes for polyester-containing composite materials is of great significance.

[0005] Reference 1: Chinese Patent CN119039136A. Summary of the Invention

[0006] This invention provides a degradation process for composite polyester materials, comprising at least one of the following two objectives:

[0007] (1) A mild degradation process for polyester materials is provided, which is suitable for composite polyester material systems.

[0008] (2) A process for the directional degradation of polyester in a composite polyester material is provided, which achieves the separation, recycling and reuse of polyester material and other materials by means of polyester degradation and non-degradation of other materials.

[0009] The technical solution of the present invention is as follows:

[0010] A degradation process for a composite polyester material involves carrying out a depolymerization reaction on a reaction system containing at least the following raw material components (i) to (iv) at a temperature not exceeding 100°C.

[0011] (i) the composite polyester material;

[0012] (ii) Organic ester compounds;

[0013] (iii) Cosolvent;

[0014] and (iv) alkaline catalysts;

[0015] The weight ratio of the cosolvent to the organic ester compound is ≥0.5.

[0016] Preferably, the polyester content in the composite polyester material is not less than 30%.

[0017] More preferably, the polyester is selected from polyethylene terephthalate (PET).

[0018] Preferably, the organic ester compound is selected from one or a combination of two or more of dialkyl carbonate and carboxylic acid ester compounds.

[0019] More preferably, the dialkyl carbonate is selected from one or a combination of two or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate and dibutyl carbonate.

[0020] More preferably, the carboxylic acid ester compound is selected from one or a combination of two or more of methyl propionate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl hexanoate, methyl benzoate, ethyl benzoate and ethyl hexanoate.

[0021] Preferably, the co-solvent is selected from one or a combination of two or more of aromatic solvents, ketone solvents and nitrile solvents.

[0022] Preferably, the alkaline catalyst is selected from one or a combination of two or more inorganic bases and organic bases.

[0023] Preferably, the weight ratio of the composite polyester material, the organic ester compound, the cosolvent, and the alkaline catalyst is 1:0.02-0.2:2-20.

[0024] Preferably, the weight ratio of the cosolvent to the organic ester compound is ≥0.8.

[0025] The beneficial effects of this invention are as follows: This invention uses organic ester compounds as degrading agents and alkylating agents. With the help of a co-solvent, it was found that when the weight ratio of the co-solvent to the organic ester compound exceeds a certain proportion, directional depolymerization of polyester in composite polyester materials (such as waste textiles, which contain not only polyester but also non-polyester materials such as spandex and nylon) can be achieved under relatively mild conditions. While degrading the polyester material, it essentially does not cause degradation or depolymerization of the non-polyester materials. Therefore, the process method of this invention not only recovers terephthalate raw materials from the polyester in composite polyester materials but also avoids the following problems caused by the degradation of non-polyester materials: 1) The degradation products of non-polyester materials dissolve in the degradation products of polyester, affecting the recovery of terephthalate and other raw materials, and adversely affecting the recycling and reuse of polyester; 2) The degradation of non-polyester materials leads to performance deterioration, affecting their recycling and reuse. Attached Figure Description

[0026] Figure 1 The image shows the morphological features of the polyester / ammonia blended fabric before treatment in Example 2.

[0027] Figure 2 The image shows the morphological features of the DMT recovered in Example 2.

[0028] Figure 3 The image shows the external morphology of the spandex collected after processing in Example 2.

[0029] Figure 4 This is an image showing the elasticity of the spandex collected after processing in Example 2.

[0030] Figure 5 The image shows the morphological features of the spandex collected after processing in Comparative Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0032] This invention provides a method for the directional degradation of polyester in composite polyester materials, wherein a reaction system containing at least the following raw material components (i) to (iv) is subjected to a depolymerization reaction at a temperature not exceeding 100°C;

[0033] (i) Composite polyester materials;

[0034] (ii) Organic ester compounds;

[0035] (iii) Cosolvent;

[0036] and (iv) alkaline catalysts;

[0037] The weight ratio of cosolvent to organic ester compound is ≥0.5.

[0038] To achieve the directional degradation of polyester in composite polyester materials, this invention uses organic ester compounds as polyester degrading agents and alkylating agents, and employs a co-solvent. The degradation process is mild, and the weight ratio of the co-solvent to the organic ester compound is not less than a certain value, thus achieving the directional degradation of polyester in composite polyester materials while preventing the degradation of non-polyester components.

[0039] One possible reason for the directional degradation of polyester is that the depolymerization reaction conditions of this invention are relatively mild. The temperature of the depolymerization reaction can be no higher than 90°C, for example, 40-90°C, and the reaction time can be 1-4 hours. Moreover, it does not require high pressure and can be achieved under normal pressure, which has little impact on the non-polyester components in the composite polyester material. Another possible reason is that the added co-solvent can effectively control the solubility parameters of the depolymerization system, thereby improving the selectivity of the depolymerization reaction and avoiding the depolymerization of non-polyester components.

[0040] In this invention, the weight ratio of the cosolvent to the organic ester compound can be any value from 0.5, 0.6, 0.8, 1, 1.2, 1.3, 1.5, 1.7, 1.8, 2, 2.1, 2.3, 2.5, 2.7, 2.8, 3, 3.2, 3.5, 3.8, 4, etc., without any particular limitation.

[0041] In a preferred embodiment of the present invention, the polyester content in the composite polyester material is not less than 30%, and the non-polyester components in the composite polyester material can be spandex, polypropylene, nylon, cotton, linen, silk, satin, etc. For example, the polyester content in the composite polyester material can be any value from 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc., without any particular limitation. In general, the source and form of the composite polyester material are not particularly limited. For example, the source can be waste textiles, and it can be in fiber or fabric form, such as polyester fiber, polyester fabric, polyester blended fabric (polyester / cotton blend, polyester / nylon blend, polyester / spandex blend), etc.

[0042] More preferably, the polyester is selected from polyethylene terephthalate, for example, it may be polyethylene terephthalate (PET), butylene terephthalate (PBT), propylene glycol terephthalate (PDT), etc.

[0043] In a preferred embodiment of the present invention, the organic ester compound is selected from one or a combination of two or more of dialkyl carbonate and carboxylic acid ester compounds. In this invention, the organic ester compound can not only act as a polyester degrading agent under the action of a catalyst, but also further act as an alkylating agent to react with the depolymerization products of polyester, thereby converting the polyester degradation products into terephthalic acid esters (such as dimethyl terephthalate, diethyl terephthalate, etc.), which can then be reused as raw materials in the synthesis of polyester (such as PET).

[0044] More preferably, the dialkyl carbonate is selected from one or a combination of two or more of dimethyl carbonate (DMC), ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate. From the perspective of dimethyl terephthalate, the synthetic raw material for obtaining PET, the dialkyl carbonate is further preferably dimethyl carbonate.

[0045] More preferably, the carboxylic acid ester compound is selected from one or a combination of two or more of methyl propionate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl hexanoate, methyl benzoate, ethyl benzoate, and ethyl hexanoate. From the perspective of obtaining dimethyl terephthalate as a synthetic raw material for PET, the carboxylic acid ester compound is further preferably a methyl propionate, methyl butyrate, methyl hexanoate, methyl benzoate, or other methyl carboxylic acids.

[0046] In a preferred embodiment of the present invention, the co-solvent is selected from one or a combination of two or more of aromatic solvents, ketone solvents, and nitrile solvents. For example, aromatic solvents may be toluene, xylene, ethylbenzene, etc., ketone solvents may be acetone, methyl ethyl ketone, cyclohexanone, etc., and nitrile solvents may be acetonitrile, propionitrile, benzonitrile, etc.

[0047] In a preferred embodiment of the present invention, the alkaline catalyst is selected from one or a combination of two or more inorganic bases and organic bases. In this invention, there are no particular limitations on the inorganic and organic bases. Specifically, the inorganic base can be one or a combination of two or more of sodium aluminate, potassium aluminate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, sodium methoxide, lithium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide. The organic base can be one or a combination of two or more of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,5-diazabicyclo[4.3.0]-5-nonene (DBN), 1,1,3,3-tetramethylguanidine (TMG), 4-dimethylaminopyridine (DMAP), and triethylamine.

[0048] In a preferred embodiment of the present invention, the weight ratio of the composite polyester material, the organic ester compound, the cosolvent, and the alkaline catalyst is 1:0.02-0.2:2-20. For example, the weight ratio of the composite polyester material, the organic ester compound, the cosolvent, and the alkaline catalyst can be 1:0.02:2, 1:0.2:20, 1:0.02:20, 1:0.2:2, 1:0.07:5, 1:0.1:10, 1: Any value from 0.12:15, 1:0.15:10, 1:0.15:15, 1:0.15:20, 1:0.1:20, 1:0.08:12, 1:0.12:12, 1:0.06:10, 1:0.06:12, 1:0.05:2, 1:0.05:5, 1:0.05:10, 1:0.05:15, 1:0.2:5, 1:0.2:10, 1:0.2:12, etc., without any particular restrictions.

[0049] In a preferred embodiment of the present invention, the weight ratio of the cosolvent to the organic ester compound is ≥0.8. For example, the weight ratio of the cosolvent to the organic ester compound may be 0.8, 1, 1.2, 1.3, 1.5, 1.7, 1.8, 2, 2.1, 2.3, 2.5, 2.7, 2.8, 3, 3.2, 3.5, 3.8, 4, etc. More preferably, the weight ratio of the cosolvent to the organic ester compound is ≥1.

[0050] The technical solutions of the present invention will be further described and explained below with reference to various embodiments.

[0051] Example 1 (Examining the selectivity of the depolymerization system)

[0052] Pure polyester fabric, pure nylon fabric, and pure spandex filament were used as raw materials, sodium methoxide as the catalyst, and dimethyl carbonate as the depolymerization agent. In the presence or absence of a co-solvent (the weight ratio of raw material:sodium methoxide:[dimethyl carbonate + co-solvent] was 1:0.05:6), the above-mentioned pure polyester fabric, pure nylon fabric, and pure spandex filament were stirred at 65°C for 2 hours. After treatment, the mixture was filtered while hot, and the insoluble matter was washed sequentially with dimethyl carbonate and water, and then dried at 60°C to constant weight. The depolymerization of different raw materials is shown in Table 1 below. The greater the weight loss rate of nylon fabric and spandex fabric, the more severe the degradation, and the worse the selectivity and directional degradation of polyester.

[0053] Table 1

[0054]

[0055] As shown in Table 1, without the use of a co-solvent, the depolymerization system exhibits poor selectivity, depolymerizing not only polyester fabric but also non-polyester fibers such as nylon and spandex. Introducing a co-solvent into the depolymerization system increases the depolymerization selectivity of polyester with increasing co-solvent proportion. When the weight ratio of co-solvent to depolymerizing agent reaches a certain level, directional depolymerization of polyester can be achieved. For example, when the weight ratio of co-solvent to depolymerizing agent reaches 0.5 or higher, directional depolymerization of polyester can be considered achieved.

[0056] Example 2

[0057] 50 g of polyester / spandex blended fabric (polyester to spandex weight ratio 85:15) was taken. The weight ratio of polyester / spandex blended fabric, catalyst (potassium carbonate), depolymerizing agent (dimethyl carbonate) + cosolvent (acetonitrile) was 1:0.06:7, and the weight ratio of cosolvent to depolymerizing agent was 1:1. The reaction was carried out at 70℃ for 2 hours. After the reaction was completed, the reaction system was filtered while hot. The insoluble matter was spandex. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. The product analysis showed that the product was DMT, with a yield of 80.5% and a purity of 97.0%. The insoluble spandex was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried spandex had an intact structure and was still elastic.

[0058] The morphology of the polyester / ammonia blended fabric before treatment is shown in the attached figure. Figure 1 As shown in the attached figure, the morphology of the recovered DMT is as follows. Figure 2 As shown in the attached figure, the morphology of the treated spandex is as follows. Figure 3 As shown, attached Figure 4 The results show that the treated spandex still retains good elasticity. (Comparison attached) Figure 1 and attached Figure 3 It can be seen that the spandex basically maintains the original shape and structure of the polyester / spandex blended fabric, indicating that the spandex has basically not undergone degradation or depolymerization.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 2 is that in Example 2, the weight ratio of the cosolvent and depolymerizing agent was adjusted from 1:1 to 1:3, while the other steps remained unchanged. The results showed that: (1) the purity of the collected DMT product was 86.3%; (2) the recovery rate of the insoluble spandex was 60.7% after washing with water and drying at 60°C to constant weight. The morphology of the dried spandex is shown in the attached figure. Figure 5 As shown, the spandex structure is destroyed and its elasticity is basically lost.

[0061] Example 3

[0062] 50 g of polyester / spandex blended fabric (polyester to spandex weight ratio 85:15) was taken. The weight ratio of polyester / spandex blended fabric, catalyst (DBU), depolymerizing agent (dimethyl carbonate) + cosolvent (acetone) was 1:0.1:7, and the weight ratio of cosolvent to depolymerizing agent was 1:1. The reaction was carried out at 60℃ for 2 hours. After the reaction was completed, the reaction system was filtered while hot. The insoluble matter was spandex. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. The product analysis showed that the product was DMT, with a yield of 81.3% and a purity of 97.5%. The insoluble spandex was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried spandex had an intact structure and was still elastic.

[0063] Example 4

[0064] 50 g of polyester / spandex blended fabric (polyester to spandex weight ratio 70:30) was used. The weight ratio of polyester / spandex blended fabric, catalyst (DBU), depolymerizing agent (dimethyl carbonate) + cosolvent (acetone) was 1:0.12:10, and the weight ratio of cosolvent to depolymerizing agent was 2:1. The reaction was carried out at 60℃ for 2 hours. After the reaction was completed, the reaction system was filtered while hot. The insoluble matter was spandex. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. The product analysis showed that the product was DMT, with a yield of 84.5% and a purity of 97.2%. The insoluble spandex was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried spandex had an intact structure and was still elastic.

[0065] Example 5

[0066] 50 g of polyester / nylon blended fabric (polyester to nylon weight ratio 80:20) was used. The weight ratio of polyester / nylon blended fabric, catalyst (DBN), depolymerizing agent (dimethyl carbonate) + cosolvent (toluene) was 1:0.15:7, and the weight ratio of cosolvent to depolymerizing agent was 1:1. The reaction was carried out at 55℃ for 4 hours. After the reaction was completed, the reaction system was filtered while hot. The insoluble matter was nylon. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. The product analysis showed that the product was DMT, with a DMT yield of 79.4% and a purity of 98.0%. The insoluble nylon was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried nylon had an intact structure.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 5 is that in Example 5, the weight ratio of the cosolvent and depolymerizing agent was adjusted from 1:1 to 1:3, while the other steps remained unchanged. The results showed that: (1) the purity of the collected DMT product was 83.8%; (2) the recovery rate of the insoluble nylon was 83.6% after washing with water and drying at 60°C to constant weight. The structure of the dried nylon was destroyed and its strength was lost.

[0069] Example 6

[0070] 50 g of polyester / nylon blended fabric (polyester to nylon weight ratio 50:50) was used. The weight ratio of the polyester / nylon blended fabric, catalyst (sodium ethoxide and DBN weight ratio 1:2), depolymerizing agent (dimethyl carbonate) + cosolvent (acetone) was 1:0.12:10, and the weight ratio of cosolvent to depolymerizing agent was 3:2. The reaction was carried out at 80℃ for 2.5 hours. After the reaction was completed, the reaction system was filtered while hot. The insoluble matter was nylon. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. The product analysis showed that the product was DMT, with a DMT yield of 81.4% and a purity of 97.7%. The insoluble nylon was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried nylon had an intact structure.

[0071] Example 7

[0072] 50g of mixed fibers (composed of 20g polyester and 30g spandex fibers) were cut to a length not exceeding 2cm. The weight ratio of the mixed fibers, catalyst (sodium ethoxide and DBN in a 1:1 weight ratio), depolymerizing agent (dimethyl carbonate) + cosolvent (acetone) was 1:0.15:20, and the weight ratio of cosolvent to depolymerizing agent was 2:1. The reaction was carried out at 70℃ for 3 hours. After the reaction, the reaction system was filtered while hot. The insoluble matter was spandex fiber. After washing the insoluble matter with a small amount of dimethyl carbonate, the washing liquid and filtrate were combined, the solvent was evaporated by rotary evaporation, and the precipitated solid was washed with methanol. The filter cake was collected and dried at 60℃ to constant weight. Product analysis showed that the product was DMT, with a yield of 85.1% and a purity of 97.3%. The insoluble spandex fiber was washed with water and dried at 60℃ to constant weight, with a recovery rate >99%. The dried spandex fiber had an intact structure and remained elastic.

[0073] The results of the above embodiments and comparative examples confirm that when a cosolvent is added to the depolymerization system and the weight ratio of the cosolvent to the depolymerizing agent is not less than a certain value, directional depolymerization of composite polyester materials can be achieved.

[0074] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A degradation process for a composite polyester material, characterized in that, The reaction system containing at least the following raw material components (i) to (iv) is subjected to a depolymerization reaction at a temperature not exceeding 100°C; (i) the composite polyester material; (ii) Organic ester compounds; (iii) Cosolvent; and (iv) alkaline catalysts; The weight ratio of the cosolvent to the organic ester compound is ≥0.

5.

2. The degradation process of polyester material according to claim 1, characterized in that, The polyester content in the composite polyester material is not less than 30%.

3. The degradation process method for polyester materials according to claim 2, characterized in that, The polyester is selected from polyethylene terephthalate (PET).

4. The degradation process method for polyester materials according to claim 1, characterized in that, The organic ester compounds are selected from one or a combination of two or more of dialkyl carbonate and carboxylic acid ester compounds.

5. The degradation process method for polyester materials according to claim 4, characterized in that, The dialkyl carbonate is selected from one or a combination of two or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate.

6. The degradation process method for polyester materials according to claim 4, characterized in that, The carboxylic acid ester compound is selected from one or a combination of two or more of methyl propionate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl hexanoate, methyl benzoate, ethyl benzoate, and ethyl hexanoate.

7. The degradation process method for polyester materials according to claim 1, characterized in that, The co-solvent is selected from one or a combination of two or more of aromatic solvents, ketone solvents and nitrile solvents.

8. The degradation process method for polyester materials according to claim 1, characterized in that, The alkaline catalyst is selected from one or a combination of two or more inorganic bases and organic bases.

9. The degradation process method for polyester materials according to claim 1, characterized in that, The weight ratio of the composite polyester material, the organic ester compound, the cosolvent, and the alkaline catalyst is 1:0.02-0.2:2-20.

10. The degradation process method for polyester material according to claim 1, characterized in that, The weight ratio of the cosolvent to the organic ester compound is ≥0.8.

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