Preparation method of alcoholysis catalyst and application of alcoholysis catalyst in regenerated DMT synthesis

Abstract

The invention discloses a preparation method of an alcoholysis catalyst and application of the alcoholysis catalyst in regenerated DMT synthesis. Zinc, nickel and cobalt metal sources are synchronously loaded on a two-dimensional MXene material through an impregnation method, and then through hydrothermal treatment, calcination and carbon nitrogen compound encapsulation treatment, the self-assembled heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt NC catalyst is prepared and used for ethylene glycol alcoholysis reaction of waste polyester textiles. The method comprises the following steps: carrying out ester exchange reaction on an alcoholysis product obtained by carrying out alcoholysis on the waste polyester textiles by using ethylene glycol and methanol to prepare impurity-containing regenerated DMT, and purifying the regenerated DMT through a reduced pressure sublimation method by utilizing the phase change characteristic of DMT crystals, thereby realizing the preparation of the high-purity regenerated DMT. The heterogeneous alcoholysis catalyst prepared by the method is high in catalytic activity, small in pollution, simple to prepare and easy to separate and recover, meanwhile, the purification process of the ester exchange product DMT is simplified, and the energy consumption and the cost are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of DMT synthesis, and more specifically, to a preparation method of an alcoholysis catalyst and its application in the regeneration of DMT synthesis. Background Art

[0002] Polyester fibers are widely used in the fields of clothing, automotive interiors, civil engineering, etc. due to their excellent mechanical properties, chemical stability, and processability. However, with the continuous expansion of the application fields of polyester fibers and the continuous increase in production capacity, the cumulative quantity of waste polyester textiles is also continuously growing, causing serious waste of resources and environmental pollution. Currently, the main methods for recycling waste polyester are physical methods and chemical methods. Among them, physical recycling mainly includes primary recycling and melt regeneration. Primary recycling collects and cleans waste polyester and directly uses it for the processing and preparation of secondary products. The melt regeneration method melts and recreates polyester after crushing, washing, and drying. Physical recycling of waste polyester is simple and easy to operate, with low equipment costs and flexible feeding. However, the recycled polyester is mixed with dyes and other impurities, resulting in a significant reduction in product performance. Chemical recycling methods depolymerize the macromolecular chains of waste polyester into small molecule monomers, and high-performance recycled products can be prepared through processes such as blending and copolymerization in the later stage.

[0003] In the chemical recycling technology, the ethylene glycol alcoholysis method depolymerizes waste polyester into bis(2-hydroxyethyl) terephthalate (BHET). This method has mild reaction conditions, good safety, and high product yields. However, the catalysts for this method are mainly heavy metal salts such as zinc, manganese, cobalt, and antimony. Although the catalytic performance of such catalysts is extremely remarkable, they will dissolve in the ethylene glycol solvent, not only making the depolymerized solution difficult to treat, but also easily causing heavy metal pollution. In order to develop new alcoholysis catalysts, ionic liquids, deep eutectic solvents, organic catalysts, etc. have emerged successively at home and abroad. However, such catalysts not only have low catalytic activity, but also have complex preparation processes, high costs, and are difficult to separate and recycle. In addition, the invention patent with the publication number CN116891410A alcoholyzes waste polyester with an organic solvent mixed depolymerization reagent. However, organic solvents are usually expensive and difficult to separate and recycle in the later stage, increasing the treatment difficulty and cost of the depolymerized waste liquid and products. At the same time, waste polyester textiles have a wide range of sources and often contain impurities such as cotton, oil stains, and dyes. Moreover, BHET is prone to condensation reaction under high temperature conditions, and it is extremely difficult to decolorize and remove impurities, making it difficult for the ethylene glycol alcoholysis method to recycle waste polyester textiles with complex compositions.

[0004] The glycolysis method using ethylene glycol is adopted to depolymerize waste polyester textiles, and then the glycolysis product is subjected to a transesterification reaction with methanol to prepare dimethyl terephthalate (DMT). High-value recycled DMT-based products are prepared through a polymerization process, which has become the most promising process route at present. However, the recycled DMT preliminarily prepared by the glycolysis-transesterification method contains a large amount of impurities, and its hue and purity are difficult to meet the preparation requirements of high-performance DMT-based products. The invention patent with the publication number CN115594581A uses zinc acetate to catalyze the glycolysis of waste polyester textiles with different densification methods, converts each glycolysis product into DMT, and recrystallizes and purifies the DMT-containing impurities and methanol four times according to a mass ratio of 1:30. Only then can the purity of DMT be increased to more than 99%. Although the recrystallization method can effectively separate components by utilizing the solubility differences of each component in the methanol solvent, when purifying recycled DMT, this method has a long process flow, low efficiency, and a huge consumption of methanol, seriously affecting the high-value circular recycling and reuse of waste polyester textiles.

[0005] Therefore, it is urgent to solve the problems that in the process of recycling waste polyester textiles by the glycolysis-transesterification method, the homogeneous metal catalyst for the glycolysis reaction is easily soluble in ethylene glycol, resulting in difficult treatment of the depolymerization solution and a high risk of heavy metal pollution, and the final recycled product DMT is difficult to purify. Based on the depolymerization characteristics of polyester and the characteristics of DMT itself, on the basis of the research on the glycolysis-transesterification method, a new method that can efficiently depolymerize waste polyester textiles and prepare high-purity recycled DMT is developed, so as to reduce environmental pollution, lower the recycling cost, and achieve the high-value circular recycling and upgrading utilization of waste polyester textiles. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art, and provide a preparation method of a glycolysis catalyst and its application in the synthesis of recycled DMT. Zinc salt, nickel salt, and cobalt salt are simultaneously loaded on the two-dimensional material MXene carrier by an impregnation method, and after hydrothermal and calcination treatments, a carbonitride is deposited on its surface and encapsulated to prepare a self-assembled heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt@NC catalyst, which is used as a glycolysis catalyst for waste polyester textiles. Without sacrificing the pore structure of the carrier, this catalyst can greatly increase the metal loading amount, realize the synergistic catalysis of multiple metals and nitrogen sources on polyester molecules, has high catalytic activity and is easy to separate and recycle. After glycolyzing waste polyester textiles, the glycolysis product is subjected to a transesterification reaction with methanol to obtain impure recycled DMT, and then it is purified by vacuum sublimation. The high-efficiency purification of recycled DMT is realized by using the multiple phase transition processes of DMT crystals - melt - gas - solid.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A preparation method of an alcoholysis catalyst, adding two-dimensional material MXene into a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and obtaining dispersion A through ultrasonic dispersion; adding metal complexing agent 8-hydroxyquinoline and a metal source composed of zinc salt, nickel salt and cobalt salt into dispersion A, and performing ultrasonic dispersion again to obtain dispersion B; adding a carbonitride into dispersion B, performing oscillating deposition, and obtaining a self-assembled heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt@NC alcoholysis catalyst through centrifugation, drying and calcination treatments.

[0009] Further, the zinc salt in dispersion A is one of zinc acetate, zinc sulfate and zinc chloride, the nickel salt is one of nickel sulfate and nickel chloride, and the cobalt salt is one of cobalt chloride, cobalt sulfate and cobalt nitrate; the mass ratio of MXene to the metal source is 1:0.1-1, and the mass ratio of the metal complexing agent to the metal source in dispersion B is 0.1-0.3:1.

[0010] Further, the carbonitride in dispersion B is one of melamine, 1,3-dimethylurea, carbamide and 2-(3,4-dihydroxyphenyl)ethylamine, and the mass ratio of the carbonitride to the metal source in dispersion A is 0.1-0.5:1.

[0011] Further, the deposition time after adding the carbonitride in dispersion B is 8-12 h, the calcination temperature is 350-500 °C, the calcination time is 3-5 h, and the protective gas is one of nitrogen or argon.

[0012] An application of an alcoholysis catalyst in the synthesis of recycled DMT, including the following steps:

[0013] (1) The waste polyester textile is densified to obtain a polyester foam, and then it is transported to a depolymerization reactor together with ethylene glycol and the alcoholysis catalyst in proportion, slowly stirred under nitrogen conditions and heated to a preset temperature for depolymerization. After the reaction is completed, the alcoholysis solution is filtered while it is hot, and the filtrate is condensed, crystallized and filtered to obtain an alcoholysis product.

[0014] (2) The alcoholysis product, methanol and transesterification catalyst are transported to a transesterification reactor in proportion, slowly stirred under nitrogen conditions and heated for transesterification reaction. After the reaction is completed, the transesterification product is preliminarily obtained as a recycled DMT containing impurities through filtration, recrystallization and drying steps, and then it is purified by vacuum or atmospheric sublimation and condensed and dried to obtain a recycled DMT with a purity higher than 99.5%.

[0015] Further, in step (1), the mass feeding ratio of the polyester foam, ethylene glycol and the alcoholysis catalyst is 1:2:0.02-0.05; the stirring rate of the reactor is 100-200 r / min; the depolymerization temperature is 170-195 °C, and the reaction time is 40-120 min.

[0016] Further, in step (2), the transesterification catalyst is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium acetate, and potassium acetate.

[0017] Further, in step (2), the mass feeding ratio of the alcoholysis product, methanol, and the transesterification catalyst is 1:2:0.003 - 0.01; the stirring rate of the reaction kettle is 90 - 150 r / min; the transesterification reaction temperature is 64 - 76 °C, and the reaction time is 60 - 120 min.

[0018] Further, in step (2), the recrystallization temperature of the transesterification product is 4 - 8 °C, and the time is 10 - 12 h.

[0019] Further, in step (2), the vacuum sublimation purification is carried out under the conditions of a temperature of 160 - 230 °C and a vacuum degree of 50 - 200 torr.

[0020] The beneficial effects of the present invention are as follows:

[0021] The heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt@NC catalyst prepared by the present invention can be applied to the glycol alcoholysis of waste polyester. Its supporting carrier MXene is composed of various transition metal carbides, nitrides, or carbonitrides. The active loaded metal ions act as Lewis acids to interact with the carbonyl groups on the polyester molecules. The organic carbonitride further enhances the electronegativity of the oxygen of the glycol hydroxyl group. There is an obvious synergistic effect among the three during the alcoholysis process, with high catalytic activity and easy separation and recovery. In addition, the present invention first utilizes the phase change property of DMT crystals to achieve the effective separation between regenerated DMT and auxiliaries such as dyes and reaction by-products in waste polyester textiles, realizing the preparation of high-quality regenerated DMT. The purity of the purified regenerated DMT can be higher than 99.9%, and it can be directly used as the raw material for downstream high-performance DMT-based products, with broad market application prospects.

[0022] The method provided by the present invention is green and environmentally friendly, simple, easy to operate, economical and efficient, suitable for industrialization, and has significant social and economic benefits. Description of the Drawings

[0023] Figure 1 It is the Fourier infrared spectrum of the alcoholysis product obtained by depolymerizing waste polyester textiles in Example 1;

[0024] Figure 2 It is the gas chromatography-mass spectrometry spectrum of the alcoholysis product obtained by depolymerizing waste polyester textiles in Example 1;

[0025] Figure 3 It is the Fourier infrared spectrum of the high-purity regenerated DMT obtained in Example 11;

[0026] Figure 4Gas chromatogram of the high-purity recycled DMT prepared in Example 11;

[0027] Figure 5 Schematic diagram of the sample of the high-purity recycled DMT prepared in Example 11. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] The overall method for preparing the alcoholysis catalyst of the present invention is as follows:

[0030] Add two-dimensional material MXene (preferably titanium carbide (Ti3C2Tx) MXene multilayer nanosheets, purchased from Jiaxing Hesimer New Materials Co., Ltd.) to tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and obtain dispersion A by ultrasonic dispersion; add metal complexing agent 8-hydroxyquinoline and metal source composed of zinc salt, nickel salt and cobalt salt to dispersion A, and ultrasonically disperse again to obtain dispersion B; add carbonitride to dispersion B, place it in a constant temperature shaker at 25 °C and shake and deposit for 8-12 h, and after centrifugation, drying and calcination (calcination temperature is 350-500 °C, calcination time is 3-5 h, and the protective gas is one of nitrogen or argon), a self-assembled heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt@NC alcoholysis catalyst is prepared.

[0031] The zinc salt in dispersion A is one of zinc acetate, zinc sulfate and zinc chloride, the nickel salt is one of nickel sulfate and nickel chloride, and the cobalt salt is one of cobalt chloride, cobalt sulfate and cobalt nitrate; the mass ratio of MXene to the metal source is 1:0.1-1, and the mass ratio of the metal complexing agent to the metal source in dispersion B is 0.1-0.3:1; the carbonitride in dispersion B is one of melamine, 1,3-dimethylurea, carbamide and 2-(3,4-dihydroxyphenyl)ethylamine, and the mass ratio of the carbonitride to the metal source in dispersion A is 0.1-0.5:1.

[0032] The method for chemically recycling waste polyester textiles to prepare recycled DMT of the present invention, the overall method is as follows:

[0033] (1) The waste polyester textiles are densified to obtain polyester foam materials (obtained by densifying waste polyester textiles, see the preparation of densified waste polyester raw materials in the method for chemically recycling waste textiles to prepare regenerated DMT and its application in preparing flame-retardant polyester chips with the publication number CN115594581 and the patent name A Method for Chemically Recycling Waste Textiles to Prepare Regenerated DMT and Its Application in Preparing Flame-Retardant Polyester Chips). Subsequently, they are transported to a depolymerization reactor in proportion with ethylene glycol and an alcoholysis catalyst (the mass feeding ratio of polyester foam materials, ethylene glycol, and alcoholysis catalyst is 1:2:0.02 - 0.05). Under the condition of nitrogen, it is slowly stirred and heated to a preset temperature for depolymerization. The stirring rate of the reactor is 100 - 200 r / min, the depolymerization temperature is 170 - 195 °C, and the reaction time is 40 - 120 min. After the reaction, the alcoholysis solution is filtered while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product.

[0034] (2) The alcoholysis product, methanol, and a transesterification catalyst (one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium acetate, potassium acetate) are transported to a transesterification reactor in proportion. Under the condition of nitrogen, it is slowly stirred and heated for transesterification reaction. The mass feeding ratio of the alcoholysis product, methanol, and transesterification catalyst is 1:2:0.003 - 0.01. The stirring rate of the reactor is 90 - 150 r / min. The transesterification reaction temperature is 64 - 76 °C, and the reaction time is 60 - 120 min. After the reaction is completed, the transesterification product is filtered, recrystallized (the recrystallization temperature is 4 - 8 °C, and the time is 10 - 12 h), and dried to preliminarily obtain the regenerated DMT containing impurities. Subsequently, it is purified by vacuum or atmospheric sublimation (the temperature for vacuum sublimation purification is 160 - 230 °C, and the vacuum degree is 50 - 200 torr; the temperature for vacuum sublimation purification is 160 - 230 °C), condensed, and dried to obtain the regenerated DMT with a purity higher than 99.5%.

[0035] The preferred embodiments are as follows:

[0036] Example 1

[0037] This example is used to illustrate the preparation of the alcoholysis catalyst and its application in the ethylene glycol alcoholysis of polyester textiles.

[0038] 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets were added to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM, and ultrasonically dispersed for 20 min. Then, 0.01 g of 8-hydroxyquinoline was added and ultrasonically dispersed for 25 min to obtain an MXene dispersion; 0.05 g of zinc acetate, 0.02 g of nickel sulfate and 0.03 g of cobalt sulfate were added to the MXene dispersion, and ultrasonically dispersed for another 40 min to obtain an MXene-zinc / nickel / cobalt dispersion. Subsequently, 0.02 g of melamine was added, and the mixture was placed in a constant temperature shaker at 25 °C and shaken for deposition for 8 h. After centrifugation and drying, it was calcined in a tubular furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc / nickel / cobalt@melamine).

[0039] Polyester foam, ethylene glycol, and the alcoholysis catalyst were put into a depolymerization reactor according to a mass feeding ratio of 1:2:0.03, and slowly stirred and heated to a preset temperature for depolymerization under nitrogen protection. The stirring rate of the reactor was 150 r / min, and the reaction was carried out at 185 °C for 90 min; after the reaction, the alcoholysis solution was filtered while it was hot, and the filtrate was condensed, crystallized, and filtered to obtain an alcoholysis product. Under these conditions, the PET depolymerization rate was 98.3%, and the alcoholysis product yield was 86.7%. There were fewer miscellaneous peaks in the infrared absorption spectrum of the alcoholysis product, and all had the characteristic structures of BHET and its oligomers (as Figure 1 shown). Online pyrolysis analysis by pyrolysis gas chromatography-mass spectrometry showed that the main component of the alcoholysis product was BHET (as Figure 2 ).

[0040] Example 2

[0041] This example is used to illustrate the preparation of an alcoholysis catalyst and its application in the glycol alcoholysis of polyester textiles.

[0042] 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets were added to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM, and ultrasonically dispersed for 20 min. Then, 0.01 g of 8-hydroxyquinoline was added and ultrasonically dispersed for 25 min to obtain an MXene dispersion; 0.05 g of zinc acetate, 0.02 g of nickel sulfate and 0.03 g of cobalt sulfate were added to the MXene dispersion, and ultrasonically dispersed for another 40 min to obtain an MXene-zinc / nickel / cobalt dispersion. Subsequently, 0.02 g of 1,3-dimethylurea was added, and the mixture was placed in a constant temperature shaker at 25 °C and shaken for deposition for 10 h. After centrifugation and drying, it was calcined in a tubular furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc / nickel / cobalt@1,3-dimethylurea).

[0043] Put polyester foam, ethylene glycol, and alcoholysis catalyst into the depolymerization reactor according to the mass feeding ratio of 1:2:0.03, slowly stir under nitrogen protection, and heat up to the preset temperature for depolymerization. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min. After the reaction, filter the alcoholysis solution while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 92.5%, and the yield of the alcoholysis product is 82.5%.

[0044] Example 3

[0045] This example is used to illustrate the preparation of the alcoholysis catalyst and its application in the glycol alcoholysis of polyester textiles.

[0046] Take 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets and add them to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM. Ultrasonically disperse for 20 min, then add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain the MXene dispersion. Add 0.05 g of zinc acetate, 0.02 g of nickel sulfate, and 0.03 g of cobalt sulfate to the MXene dispersion, continue to ultrasonically disperse for 40 min to obtain the MXene-zinc / nickel / cobalt dispersion. Subsequently, add 0.02 g of carbamidine, place it in a constant temperature shaker at 25 °C and shake for deposition for 10 h. After centrifugal drying, calcine it in a tubular furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain the alcoholysis catalyst (MXene-zinc / nickel / cobalt@carbamidine).

[0047] Put polyester foam, ethylene glycol, and alcoholysis catalyst into the depolymerization reactor according to the mass feeding ratio of 1:2:0.03, slowly stir under nitrogen protection, and heat up to the preset temperature for depolymerization. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min. After the reaction, filter the alcoholysis solution while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 90.1%, and the yield of the alcoholysis product is 73.2%.

[0048] Example 4

[0049] This example is used to illustrate the preparation of the alcoholysis catalyst and its application in the glycol alcoholysis of polyester textiles.

[0050] Take 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets and add them to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM. Ultrasonically disperse for 20 min, then add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain an MXene dispersion; add 0.05 g of zinc acetate, 0.02 g of nickel sulfate, and 0.03 g of cobalt sulfate to the MXene dispersion, and continue to ultrasonically disperse for 40 min to obtain an MXene-zinc / nickel / cobalt dispersion. Subsequently, add 0.02 g of 2-(3,4-dihydroxyphenyl)ethylamine, place it in a constant temperature shaker at 25 °C and shake and deposit for 10 h. After centrifugal drying, calcine in a tube furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc / nickel / cobalt@DA).

[0051] Put polyester foam, ethylene glycol, and the alcoholysis catalyst into the depolymerization reactor according to a mass feeding ratio of 1:2:0.03, and slowly stir and heat up to the preset temperature for depolymerization under nitrogen protection. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min; after the reaction, filter the alcoholysis solution while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 88.7%, and the yield of the alcoholysis product is 79.2%.

[0052] Example 5

[0053] This example is used to illustrate the preparation of the alcoholysis catalyst and its application in the glycol alcoholysis of polyester textiles.

[0054] Take 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets and add them to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM. Ultrasonically disperse for 20 min, then add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain an MXene dispersion; add 0.05 g of zinc chloride, 0.02 g of nickel chloride, and 0.03 g of cobalt chloride to the MXene dispersion, and continue to ultrasonically disperse for 40 min to obtain an MXene-zinc / nickel / cobalt dispersion. Subsequently, add 0.02 g of melamine, place it in a constant temperature shaker at 25 °C and shake and deposit for 8 h. After centrifugal drying, calcine in a tube furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc / nickel / cobalt-Cl@melamine).

[0055] Put polyester foam, ethylene glycol, and the alcoholysis catalyst into the depolymerization reactor according to a mass feeding ratio of 1:2:0.03, and slowly stir and heat up to the preset temperature for depolymerization under nitrogen protection. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min; after the reaction, filter the alcoholysis solution while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 96.3%, and the yield of the alcoholysis product is 84.6%.

[0056] Comparative Example 1

[0057] This example is used to illustrate the preparation of an alcoholysis catalyst and its application to the glycol alcoholysis of polyester textiles.

[0058] Take 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets and add them to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM, and ultrasonically disperse for 20 min. Then, add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain an MXene dispersion; add 0.05 g of zinc acetate, 0.02 g of nickel sulfate, and 0.03 g of cobalt sulfate to the MXene dispersion, and continue to ultrasonically disperse for 40 min to obtain an MXene-zinc / nickel / cobalt dispersion. After centrifugal drying treatment, it is calcined in a tube furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc / nickel / cobalt).

[0059] Put polyester foam, ethylene glycol, and the alcoholysis catalyst into the depolymerization reactor according to a mass feed ratio of 1:2:0.03, and slowly stir and heat up to the preset temperature for depolymerization under nitrogen protection. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min; after the reaction, filter the alcoholysis solution while it is hot, and the filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 85.3%, and the yield of the alcoholysis product is 74.5%.

[0060] Comparative Example 2

[0061] This example is used to illustrate the preparation of an alcoholysis catalyst and its application to the glycol alcoholysis of polyester textiles.

[0062] Take 0.1 g of titanium carbide (Ti3C2Tx) MXene multi-layer nanosheets and add them to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM, and ultrasonically disperse for 20 min. Then, add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain an MXene dispersion; add 0.1 g of zinc acetate to the MXene dispersion, and continue to ultrasonically disperse for 40 min to obtain an MXene-zinc dispersion. Subsequently, add 0.02 g of melamine, place it in a constant temperature shaker at 25 °C and shake and deposit for 8 h. After centrifugal drying treatment, it is calcined in a tube furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain an alcoholysis catalyst (MXene-zinc@melamine).

[0063] Put polyester foam, ethylene glycol, and alcoholysis catalyst into the depolymerization reactor according to the mass feeding ratio of 1:2:0.03, slowly stir under nitrogen protection, and heat up to the preset temperature for depolymerization. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min. After the reaction, filter the alcoholysis solution while it is hot. The filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 83.3%, and the yield of the alcoholysis product is 73.7%.

[0064] Comparative Example 3

[0065] This example is used to illustrate the preparation of the alcoholysis catalyst and its application in the glycol alcoholysis of polyester textiles.

[0066] Take 0.1 g of activated carbon fiber (ACF) and add it to 25 mL of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 50 mM. Ultrasonically disperse for 20 min, then add 0.01 g of 8-hydroxyquinoline and ultrasonically disperse for 25 min to obtain an ACF dispersion. Add 0.05 g of zinc acetate, 0.02 g of nickel sulfate, and 0.03 g of cobalt sulfate to the ACF dispersion, continue to ultrasonically disperse for 40 min to obtain an ACF-zinc / nickel / cobalt dispersion. Subsequently, add 0.02 g of melamine, place it in a constant temperature shaker at 25 °C and shake for deposition for 8 h. After centrifugal drying treatment, calcine it in a tube furnace at 400 °C for 4 h under a nitrogen atmosphere to obtain the alcoholysis catalyst (ACF-zinc / nickel / cobalt@melamine).

[0067] Put polyester foam, ethylene glycol, and alcoholysis catalyst into the depolymerization reactor according to the mass feeding ratio of 1:2:0.03, slowly stir under nitrogen protection, and heat up to the preset temperature for depolymerization. The stirring rate of the reactor is 150 r / min, and the reaction is carried out at 185 °C for 90 min. After the reaction, filter the alcoholysis solution while it is hot. The filtrate is condensed, crystallized, and filtered to obtain the alcoholysis product. Under these conditions, the PET depolymerization rate is 80.3%, and the yield of the alcoholysis product is 71.7%.

[0068] Example 6

[0069] This example is used to illustrate the transesterification reaction of the alcoholysis product with methanol to prepare recycled DMT.

[0070] Put the alcoholysis product obtained by depolymerizing polyester in Example 1, methanol, and the transesterification catalyst sodium hydroxide into the transesterification reactor according to the mass feeding ratio of 1:2:0.003. Slowly stir under nitrogen conditions and heat up for transesterification reaction. The stirring rate of the reactor is 110 r / min, and the reaction is carried out at 70 °C for 110 min. After the reaction, the transesterification product is filtered, recrystallized (temperature is 5 °C, time is 10 h), and dried to preliminarily obtain recycled DMT containing impurities. The yield of recycled DMT is 78.5%.

[0071] Example 7

[0072] This example is used to illustrate the preparation of regenerated DMT by transesterifying the alcoholysis product with methanol.

[0073] The alcoholysis product obtained by depolymerizing the polyester in Example 1, methanol, and the transesterification catalyst potassium carbonate were charged into a transesterification reactor at a mass feed ratio of 1:2:0.007. Under nitrogen conditions, it was slowly stirred and heated to carry out the transesterification reaction. The stirring rate of the reactor was 110 r / min, and the reaction was carried out at 70 °C for 120 min. After the reaction was completed, the transesterification product was preliminarily prepared into regenerated DMT containing impurities through filtration, recrystallization (temperature of 5 °C, time of 10 h), and drying steps. The yield of regenerated DMT was 74.5%.

[0074] Example 8

[0075] This example is used for the purification of regenerated DMT.

[0076] The regenerated DMT containing impurities prepared in Example 6 was put into a vacuum sublimator, slowly heated to 230 °C, and no vacuum pumping treatment was carried out. The sublimation environment was at normal pressure. After the charged regenerated DMT was sublimated at normal pressure, the device was allowed to cool naturally. The regenerated DMT enriched on the condensation receiver was taken out, and the normal pressure sublimation purification and condensation operations were repeated twice each, and then dried to obtain high-purity regenerated DMT. After three consecutive vacuum sublimation operations for purification, the purities of the regenerated DMT were 96.25%, 98.91%, and 99.42% respectively.

[0077] Example 9

[0078] This example is used for the purification of regenerated DMT.

[0079] The regenerated DMT containing impurities preliminarily prepared in Example 6 was put into a vacuum sublimator, slowly heated to 220 °C, and the vacuum degree environment was 200 torr. After the charged regenerated DMT was sublimated under reduced pressure, the device was allowed to cool naturally. The regenerated DMT enriched on the condensation receiver was taken out, and the reduced pressure sublimation purification and condensation operations were repeated twice each, and then dried to obtain high-purity regenerated DMT. After three consecutive vacuum sublimation operations for purification, the purities of the regenerated DMT were 97.64%, 98.32%, and 99.56% respectively.

[0080] Example 10

[0081] This example is used for the purification of regenerated DMT.

[0082] The regenerated DMT containing impurities obtained initially in Example 6 was put into a vacuum sublimator, and the temperature was slowly raised to 210 °C with a vacuum degree of 100 torr. After the vacuum sublimation of the input regenerated DMT was completed, the device was allowed to cool naturally, and the regenerated DMT enriched on the condensation receiver was taken out. The vacuum sublimation purification and condensation operations were repeated twice each, and then dried to obtain high-purity regenerated DMT. After three consecutive vacuum sublimation operations for purification, the purities of the regenerated DMT were 98.74%, 99.63%, and 99.90% respectively.

[0083] Example 11

[0084] This example is used for the purification of regenerated DMT.

[0085] The regenerated DMT containing impurities obtained initially in Example 6 was put into a vacuum sublimator, and the temperature was slowly raised to 200 °C with a vacuum degree of 50 torr. After the vacuum sublimation of the input regenerated DMT was completed, the device was allowed to cool naturally, and the regenerated DMT enriched on the condensation receiver was taken out. The vacuum sublimation purification and condensation operations were repeated twice each, and then dried to obtain high-purity regenerated DMT. The products obtained after three consecutive purifications were recorded in sequence as: DMT 1, DMT 2, DMT 3.

[0086] Infrared spectrum analysis was performed on the purified regenerated DMT (as Figure 3 shown), and it was found that the three products had peak type characteristics similar to those of the native DMT. The -OH characteristic peak corresponding to 3430 cm -1 was very weak, and there were trace amounts of hydroxyl products in the DMT after purification treatment. And through gas chromatography - internal standard method, a detailed quantitative analysis was carried out on the trace impurities and the components of DMT in the vacuum sublimation products (as Figure 4 shown). After three consecutive vacuum sublimation operations for purification, organic impurities such as 2-hydroxyethyl methyl terephthalate, monomethyl terephthalate, and dimethyl isophthalate were effectively removed, and the purities of the regenerated DMT were 99.26%, 99.84%, and 99.91% respectively. Among them, DMT 3 presented as white crystals, with a melting chroma of 10 and excellent hue (as Figure 5 shown).

[0087] Comprehensive comparative analysis

[0088] By comparing the results of Examples 1 to 4, it was found that when melamine was added as a carbon-nitrogen compound to the heterogeneous alcoholysis catalyst, the depolymerization rate of PET and the yield of BHET were significantly improved. In the comparison between Example 1 and Example 5, it was observed that the difference in the acid radical ions contained in the metal salt of the heterogeneous alcoholysis catalyst had a slight effect on the catalytic effect. Further comparing Examples 1 to 5 with Comparative Example 1, it was found that the heterogeneous alcoholysis catalyst without the addition of carbon-nitrogen compounds had a poor catalytic effect. In the comparison of Examples 1 to 5 and Comparative Example 2, the heterogeneous alcoholysis catalyst containing only a single metal loading also showed a poor catalytic effect. Comparing Examples 1 to 5 and Comparative Example 3, the heterogeneous alcoholysis catalyst with MXene as the carrier showed better catalytic performance than the catalyst prepared from ACF.

[0089] By comparing Example 6 with Example 7, it was found that when preparing recycled DMT through transesterification reaction, the weaker the basicity of the basic catalyst, the more amount needed to be added, and at the same mass addition ratio, the catalytic activity of the weakly basic catalyst was lower, and the yield of recycled DMT was relatively low under the condition of the same reaction time.

[0090] By comparing Examples 8 to 11, it was observed that after continuously purifying DMT three times under negative pressure conditions, its purity gradually increased; while during sublimation at atmospheric pressure, although the purity of DMT also increased with the increase in the number of continuous purification times, the relatively high sublimation temperature caused trace by-products to sublime together with impurities, thus slightly reducing the purity of DMT.

[0091] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing an alcoholysis catalyst, characterized in that: The two-dimensional material MXene is added to tris(hydroxymethylaminomethane)-hydrochloric acid buffer and ultrasonically dispersed to obtain dispersion A; metal chelating agent 8-hydroxyquinoline and metal sources consisting of zinc salt, nickel salt and cobalt salt are added to dispersion A and ultrasonically dispersed again to obtain dispersion B; carbon and nitrogen compounds are added to dispersion B, shaken and deposited, and after centrifugation, drying and calcination, a self-assembled heterogeneous nitrogen-doped MXene-zinc / nickel / cobalt@NC alcoholysis catalyst is obtained.

2. A method for preparing an alcoholysis catalyst as claimed in claim 1, characterized in that: The zinc salt in dispersion A is one of zinc acetate, zinc sulfate, and zinc chloride, the nickel salt is one of nickel sulfate and nickel chloride, and the cobalt salt is one of cobalt chloride, cobalt sulfate, and cobalt nitrate; the mass ratio of the MXene to the metal source is 1:0.1-1, and the mass ratio of the metal complexing agent to the metal source in dispersion B is 0.1-0.3:

1.

3. The method for preparing an alcoholysis catalyst according to claim 1, characterized in that: The carbon nitrogen compound in the dispersion B is one of melamine, 1,3-dimethylurea, carbonyl diamide, and 2-(3,4-dihydroxyphenyl)ethylamine, and the mass ratio of the carbon nitrogen compound to the metal source in the dispersion A is 0.1-0.5:

1.

4. The method for preparing an alcoholysis catalyst according to claim 1, characterized in that: The deposition time after adding carbonitride to dispersion B is 8 to 12 hours, the calcination temperature is 350 to 500° C., the calcination time is 3 to 5 hours, and the protective gas is one of nitrogen or argon.

5. Use of an alcoholysis catalyst prepared according to the method of any one of claims 1 to 4 in the synthesis of regenerated DMT, characterized in that: The following steps are involved: (1) Waste polyester textiles are subjected to densification treatment to obtain polyester foam, which is then transported to a depolymerization reactor with ethylene glycol and an alcoholysis catalyst in proportion, slowly stirred under nitrogen conditions and heated to a preset temperature for depolymerization. After the reaction is completed, the alcoholysis liquid is filtered while hot, and the filtrate is condensed, crystallized, and filtered to obtain an alcoholysis product; (2) The alcoholysis product, methanol, and transesterification catalyst are transported to the transesterification reactor in proportion, slowly stirred and heated under nitrogen to carry out the transesterification reaction. After the reaction is completed, the transesterification product is filtered, recrystallized, and dried to initially obtain the impure regenerated DMT, which is then purified by reduced pressure or atmospheric pressure sublimation, condensed, and dried to obtain the regenerated DMT with a purity higher than 99.5%.

6. The use of an alcoholysis catalyst in regenerated DMT synthesis as claimed in claim 5, characterized in that: In step (1), the mass feed ratio of the polyester foam material, ethylene glycol and alcoholysis catalyst is 1:2:0.02-0.05; the stirring rate of the reactor is 100-200 r / min; the depolymerization temperature is 170-195° C., and the reaction time is 40-120 min.

7. The use of an alcoholysis catalyst in regenerated DMT synthesis as claimed in claim 5, characterized in that: In step (2), the transesterification catalyst is one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium acetate and potassium acetate.

8. The use of an alcoholysis catalyst in regenerated DMT synthesis as claimed in claim 5, characterized in that: In step (2), the mass feed ratio of alcoholysis product, methanol and ester exchange catalyst is 1:2:0.003-0.01; the stirring rate of the reactor is 90-150 r / min; the ester exchange reaction temperature is 64-76° C., and the reaction time is 60-120 min.

9. The use of an alcoholysis catalyst in regenerated DMT synthesis as claimed in claim 5, characterized in that: In step (2), the recrystallization temperature of the transesterification product is 4 to 8° C. and the time is 10 to 12 hours.

10. The use of an alcoholysis catalyst in regenerated DMT synthesis as claimed in claim 5, characterized in that: In step (2), the reduced pressure sublimation purification is carried out at a temperature of 160 to 230° C. and a vacuum degree of 50 to 200 torr.

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