Selective depolymerization method of polyester in polyester composite material

Abstract

The invention relates to the technical field of polyester degradation, in particular to a selective depolymerization method of polyester in a polyester composite material. The selective depolymerization method comprises the following steps: carrying out a depolymerization reaction on a polyester composite material, a cosolvent, a depolymerization agent and a basic catalyst at normal pressure and a temperature not higher than 65 DEG C, the cosolvent is at least one of an ethylene glycol diether compound, a propylene glycol diether compound and an isobutyl ketone compound. According to the selective depolymerization method, an ethylene glycol diether compound, a propylene glycol diether compound and an isobutyl ketone compound are used as cosolvents, a depolymerization agent is used as a methylation reagent, and directional polyester depolymerization of a polyester composite material can be realized at normal pressure and the temperature not higher than 65 DEG C; when the polyester material is degraded, the non-polyester material is basically not degraded or depolymerized, and the selective depolymerization and separation of the polyester composite material such as a polyester blended fabric can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyester degradation, and in particular to a method for selective depolymerization of polyester in a polyester composite material. BACKGROUND

[0002] The discarded textiles in China each year are usually mixed with various fiber materials. Polyester material is the most used fiber material for clothing, including polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate and other varieties. How to selectively depolymerize and regenerate the polyester fiber in the mixed textile while separating and recycling other fiber materials, or even not affecting the performance of other fiber materials during polyester degradation, is less studied at present.

[0003] Polyester depolymerization includes physical depolymerization and chemical depolymerization. Current chemical depolymerization can be divided into ethylene glycol alcoholysis and methanol alcoholysis, but the reaction conditions of the two are relatively harsh: the reaction temperature of ethylene glycol alcoholysis is 190-250℃, and it is carried out under the action of zinc or alkali metal catalyst; methanol alcoholysis needs to be promoted by a catalyst at 150℃ or above or under supercritical methanol conditions. Under the above conditions, spandex, nylon and other non-polyester fiber materials will also be partially or even completely degraded, resulting in deterioration of fiber performance and affecting the yield and purity of polyester depolymerization monomers.

[0004] The Chinese invention patent with publication number CN116655465A discloses a method for completing PET polyester methanol depolymerization under mild conditions of 40-120℃ and treating polyester blended fabrics. It uses guanidine or amidine organic superbase as the main catalyst, nitrile compounds as the cocatalyst, and methanol as the depolymerization agent. However, such catalysts are expensive and difficult to recover, increasing the cost of the entire process.

[0005] The Chinese invention patent with publication number CN100363410A discloses a method for depolymerization at room temperature, which needs to prepare a nitrogen heterocyclic carbene compound catalyst by reacting an imidazole salt and an alkali metal alcoholate in advance. The catalyst preparation process and depolymerization are carried out under anhydrous and anaerobic conditions, which limits the large-scale application.

[0006] In summary, it is of great application prospect to study how to carry out polyester chemical depolymerization under mild conditions and using conventional catalysts in the field of selective depolymerization and separation of low-value polyester composites. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a method for selective depolymerization of polyester in a polyester composite material under mild conditions and using conventional catalysts.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is: a selective depolymerization method of polyester in polyester composite material, comprising the following steps: carrying out depolymerization reaction of polyester composite material, cosolvent, depolymerization agent and alkaline catalyst under normal pressure and at a temperature not higher than 65 DEG C; the cosolvent is at least one of ethylene glycol diether compound, propylene glycol diether compound and isobutyl ketone compound.

[0009] The beneficial effects of the present application are that: the selective depolymerization method of the present application uses ethylene glycol diether compound, propylene glycol diether compound and isobutyl ketone compound as cosolvent, uses depolymerization agent as methylating agent, and can realize directional depolymerization of polyester in polyester composite material under normal pressure and at a temperature not higher than 65 DEG C, while degrading polyester material and basically not degrading or depolymerizing non-polyester material, so that selective depolymerization and separation of polyester composite material such as polyester blended fabric can be realized. DETAILED DESCRIPTION

[0010] To explain the technical content, purposes and effects of the present application in detail, the following embodiments are combined.

[0011] Polyester composite material refers to a material obtained by blending polyester with cotton, spandex, nylon, polypropylene and other fiber materials.

[0012] A selective depolymerization method of polyester in polyester composite material, comprising the following steps: carrying out depolymerization reaction of polyester composite material, cosolvent, depolymerization agent and alkaline catalyst under normal pressure and at a temperature not higher than 65 DEG C; the cosolvent is at least one of ethylene glycol diether compound, propylene glycol diether compound and isobutyl ketone compound.

[0013] From the above description, the beneficial effects of the present application are that: the present application uses ethylene glycol diether compound, propylene glycol diether compound and isobutyl ketone compound as cosolvent, uses depolymerization agent as methylating agent, and can realize directional depolymerization of polyester in polyester composite material under normal pressure and at a temperature not higher than 65 DEG C. Not only can the polyester in polyester composite material be depolymerized to recover terephthalate raw material, but also the problems of low recovery purity and performance degradation caused by degradation of non-polyester material are avoided, and the utilization of recovery is improved.

[0014] The cosolvent of the present application is stable under alkaline conditions and does not react with depolymerization product DMT (dimethyl terephthalate), especially EG (ethylene glycol). After separation and purification of the depolymerization product, it can be re-polymerized into r-PET (recycled polyethylene terephthalate) material according to the existing polymerization process, which meets the closed-loop cycle requirement.

[0015] Further, the reaction temperature of the depolymerization reaction is 35-65 DEG C.

[0016] From the above description, it can be seen that the use of the present application of the cosolvent promotes the reaction to move in the direction of depolymerization, reduces the reaction temperature, and realizes the directional depolymerization of the polyester at a lower temperature, which is beneficial to popularization and use.

[0017] Further, the content of the polyester in the polyester composite material is not less than 30wt%.

[0018] Further, the cosolvent is at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-propanediol dimethyl ether, 1,2-propanediol dimethyl ether, methyl isobutyl ketone and ethyl isobutyl ketone.

[0019] Further, the polyester in the polyester composite material is polyglycol terephthalate or polyglycol furan dicarboxylate.

[0020] Further, the depolymerization agent is methanol.

[0021] Further, the basic catalyst is an alkali metal alcoholate or an alkaline earth metal alcoholate.

[0022] From the above description, it can be seen that the alkali metal alcoholate and the alkaline earth metal alcoholate are used as the catalyst, and the catalytic effect is good.

[0023] Further, the basic catalyst is at least one of sodium methoxide, potassium methoxide, lithium methoxide, sodium ethoxide and magnesium methoxide.

[0024] Further, the mass ratio of the polyester composite material and the cosolvent is 1:1~20.

[0025] Preferably, the mass ratio of the polyester composite material and the cosolvent is 1:10~20.

[0026] From the above description, it can be seen that the cosolvent can promote the reaction, so a larger proportion is adopted to improve the reaction rate.

[0027] Further, the mass ratio of the polyester composite material and the depolymerization agent is 1:1~10.

[0028] Preferably, the mass ratio of the polyester composite material and the depolymerization agent is 1:5~10.

[0029] From the above description, it can be seen that the proportion of the depolymerization agent is larger to avoid the phenomenon of incomplete depolymerization.

[0030] Further, the mass ratio of the polyester composite material and the basic catalyst is 1:0.03~0.1.

[0031] Preferably, the mass ratio of the polyester composite material and the basic catalyst is 1:0.05~0.1.

[0032] From the above description, the amount of basic catalyst is too small, the depolymerization rate is slow, and the time is long; the amount of catalyst is too much, which will increase the cost, and will cause the problem of metal residue in the product after treatment and the increase of side reaction; therefore, the mass ratio of polyester composite material and basic catalyst is controlled to be 1:0.03-0.1.

[0033] Further, it further comprises the steps of filtering after the reaction, washing the insoluble substances with acetonitrile, and then combining the washing liquid and the filtrate and drying.

[0034] Embodiment 1 of the present application is a selective depolymerization method of polyester in a polyester composite material, and the specific steps are as follows: Take 4 g of dry polyester / cotton blended fabric (polyester / cotton component weight ratio 63 / 37), 0.2 g of sodium methoxide (5 wt%), 13 g of methanol, and 47 g of ethylene glycol dimethyl ether, mix them, and then react at 65℃ for 4 h. After the reaction is completed, the reaction system is filtered while hot, the insoluble substance is cotton fiber, the structure is complete, the insoluble substance is washed with acetonitrile, then the washing liquid and the filtrate are combined, the solvent is evaporated by rotary evaporation, the precipitated solid is washed with methanol, the filter cake is collected and dried at 60℃ until the weight is constant. Analysis of the product shows that the product is DMT, the yield of DMT is 78.3%, and the purity is 98.1%. The insoluble cotton fiber is washed with water and dried at 60℃ until the weight is constant, the recovery rate is 95.2%, and the infrared spectrum shows that there is no absorption at 1720 cm -1 (PET (polyester) carbonyl absorption peak), indicating that the polyester has been completely depolymerized.

[0035] Embodiment 2 of the present application is a selective depolymerization method of polyester in a polyester composite material, and the specific steps are as follows: Take 4 g of dry polyester / cotton blended fabric (polyester / cotton component weight ratio 63 / 37), 0.2 g of sodium methoxide (5 wt%), 13 g of methanol, and 47 g of ethylene glycol dimethyl ether, mix them, and then react at 65℃ for 4 h. After the reaction is completed, the reaction system is filtered while hot, the insoluble substance is cotton fiber, the structure is complete, the insoluble substance is washed with acetonitrile, then the washing liquid and the filtrate are combined, the solvent is evaporated by rotary evaporation, the precipitated solid is washed with methanol, the filter cake is collected and dried at 60℃ until the weight is constant. Analysis of the product shows that the product is DMT, the yield of DMT is 78.3%, and the purity is 98.1%. The insoluble cotton fiber is washed with water and dried at 60℃ until the weight is constant, the recovery rate is 95.2%, and the infrared spectrum shows that there is no absorption at 1720 cm -1 (PET carbonyl absorption peak), indicating that the polyester has been completely depolymerized.

[0036] Embodiment 3 of the present application is a selective depolymerization method of polyester in a polyester composite material, and the specific steps are as follows: Take the dry polyester / nylon blended fabric (polyester / nylon component weight ratio 87 / 13) 4g, lithium methoxide 0.16g (4wt%), methanol 5g, ethylene glycol diethyl ether 19g, after mixing, react at 60℃ for 5h. After the reaction is completed, the reaction system is filtered while hot, the insoluble is nylon fiber, the structure is complete, after washing the insoluble with acetonitrile, combine the washing liquid with the filtrate, rotary evaporate to dryness, wash the precipitated solid with methanol, collect the filter cake and dry at 60℃ to constant weight. Analysis of the product shows that the product is DMT, the yield of DMT is 76.7%, and the purity is 97.6%. The insoluble nylon fiber is washed with water and dried at 60℃ to constant weight, the recovery rate is 90.8%.

[0037] Embodiment 4 of the present application is a method for selectively depolymerizing polyester in a polyester composite material, the specific steps are as follows: Take the dry poly (ethylene furandicarboxylate) / nylon blended fabric (poly (ethylene furandicarboxylate) / nylon component weight ratio 80 / 20) 4g, sodium ethoxide 0.4g (10wt%), methanol 4g, 1,3-propanediol dimethyl ether 2g, 1,2-propanediol dimethyl ether 2g, after mixing, react at 35℃ for 10h. After the reaction is completed, the reaction system is filtered while hot, the insoluble is nylon fiber, the structure is complete, after washing the insoluble with acetonitrile, combine the washing liquid with the filtrate, rotary evaporate to dryness, wash the precipitated solid with methanol, collect the filter cake and dry at 60℃ to constant weight. Analysis of the product shows that the product is furandicarboxylic acid dimethyl ester (FDME), the yield of FDME is 80.6%, and the purity is 98.1%. The insoluble nylon fiber is washed with water and dried at 60℃ to constant weight, the recovery rate is 98.9%.

[0038] Embodiment 5 of the present application is a method for selectively depolymerizing polyester in a polyester composite material, the specific steps are as follows: Take the dry polyester / nylon blended fabric (polyester / nylon component weight ratio 80 / 20) 4g, magnesium methoxide 0.16g (4wt%), methanol 40g, ethyl isobutyl ketone 80g, after mixing, react at 45℃ for 8h. After the reaction is completed, the reaction system is filtered while hot, the insoluble is nylon fiber, the structure is complete, after washing the insoluble with acetonitrile, combine the washing liquid with the filtrate, rotary evaporate to dryness, wash the precipitated solid with methanol, collect the filter cake and dry at 60℃ to constant weight. Analysis of the product shows that the product is DMT, the yield of DMT is 79.4%, and the purity is 97.9%. The insoluble nylon fiber is washed with water and dried at 60℃ to constant weight, the recovery rate is 99.3%.

[0039] Comparative Example 1 of the present application is that the cosolvent is equal amount of ethylene glycol, the specific steps are as follows: Take dry polyester / cotton blended fabric (polyester / cotton component weight ratio 63 / 37) 4g, sodium methoxide 0.2g (5wt%), methanol 13g, glycol 47g, reaction at 65℃ for 4h. After the reaction, the reaction system is filtered while hot, the insoluble material is cotton fiber, the structure is complete, the insoluble material is washed with acetonitrile, then the washing liquid and the filtrate are combined, the solvent is evaporated to dryness by rotary evaporation, the precipitated solid is washed with methanol, the filter cake is collected and dried at 60℃ to constant weight. Analysis of the product shows that the product is DMT, and the yield of DMT is <1%.

[0040] The comparative example 2 of the present application is that the cosolvent is an equal amount of glycerol, and the specific steps are as follows: Take dry polyester / cotton blended fabric (polyester / cotton component weight ratio 63 / 37) 4g, sodium methoxide 0.2g (5wt%), methanol 13g, glycol 47g, reaction at 65℃ for 4h. After the reaction, the reaction system is filtered while hot, the insoluble material is cotton fiber, the structure is complete, the insoluble material is washed with acetonitrile, then the washing liquid and the filtrate are combined, the solvent is evaporated to dryness by rotary evaporation, the precipitated solid is washed with methanol, the filter cake is collected and dried at 60℃ to constant weight. Analysis of the product shows that the product is DMT, and the yield of DMT is <1%.

[0041] The comparative example 3 of the present application is that the cosolvent is an equal amount of benzyl alcohol, and the specific steps are as follows: Take dry polyester / cotton blended fabric (polyester / cotton component weight ratio 63 / 37) 4g, sodium methoxide 0.2g (5wt%), methanol 13g, glycol 47g, reaction at 65℃ for 4h. After the reaction, the reaction system is filtered while hot, the insoluble material is cotton fiber, the structure is complete, the insoluble material is washed with acetonitrile, then the washing liquid and the filtrate are combined, the solvent is evaporated to dryness by rotary evaporation, the precipitated solid is washed with methanol, the filter cake is collected and dried at 60℃ to constant weight. Analysis of the product shows that the product is DMT, and the yield of DMT is <1%.

[0042] In summary, the selective depolymerization method of polyester in the polyester composite material provided by the present application has the following advantages: 1. A mild degradation process for polyester material is provided, which is suitable for composite polyester material system; 2. A directional degradation process for polyester in composite polyester material is provided, which realizes the separation and recycling of polyester material and other materials by the method of polyester degradation and non-degradation of other materials.

[0043] 3. A cosolvent that is stable in alkaline conditions is used, which does not react with the depolymerization product, meeting the closed-loop recycling requirement.

[0044] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for selective depolymerization of polyester in a polyester composite material, characterized in that, The process includes the following steps: carrying out a depolymerization reaction of a polyester composite material, a cosolvent, a depolymerizing agent, and an alkaline catalyst at atmospheric pressure and a temperature not exceeding 65°C; wherein the cosolvent is at least one of ethylene glycol diether compounds, propylene glycol diether compounds, and isobutyl ketone compounds.

2. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The polyester composite material contains no less than 30 wt% polyester.

3. The method for selective depolymerization of polyester in the polyester composite material according to claim 1, characterized in that, The co-solvent is at least one selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-propanediol dimethyl ether, 1,2-propanediol dimethyl ether, methyl isobutyl ketone, and ethyl isobutyl ketone.

4. The method for selective depolymerization of polyester in the polyester composite material according to claim 1, characterized in that, The polyester in the polyester composite material is poly(terephthalate) or poly(furandicarboxylate).

5. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The depolymerization agent is methanol.

6. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The alkaline catalyst is an alkali metal alkoxide or an alkaline earth metal alkoxide.

7. The method for selective depolymerization of polyester in a polyester composite material according to claim 6, characterized in that, The alkaline catalyst is at least one of sodium methoxide, potassium methoxide, lithium methoxide, sodium ethoxide, and magnesium methoxide.

8. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The mass ratio of the polyester composite material to the co-solvent is 1:1 to 20.

9. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The mass ratio of the polyester composite material to the depolymerizing agent is 1:1 to 10.

10. The method for selective depolymerization of polyester in a polyester composite material according to claim 1, characterized in that, The mass ratio of the polyester composite material to the alkaline catalyst is 1:0.03~0.1.