Preparation method and application of solid acid catalyst for degrading waste PET to prepare TPA

Abstract

The invention belongs to the technical field of waste resource recycling, and discloses a preparation method and application of a solid acid catalyst for degrading waste PET to prepare TPA, and the solid acid catalyst for degrading waste PET to prepare TPA is a heteropolyacid asymmetric biquaternary ammonium salt solid acid catalyst with a phase transfer function. The preparation method comprises the following steps: carrying out an ion exchange reaction on an asymmetric biquaternary ammonium salt surfactant and heteropoly acid according to a molar ratio of (0.5-1.5): 1 to prepare the solid acid catalyst for degrading waste PET to prepare TPA; the application of the solid acid catalyst comprises the following steps: adding the waste PET, the solid acid catalyst and distilled water into a polytetrafluoroethylene or para-polyphenyl lining of a self-pressure-generating reaction kettle according to a certain mass ratio, and reacting at 180-220 DEG C for 4-24 hours by using a homogeneous reactor. The preparation method disclosed by the invention is simple and convenient in process, and the prepared solid acid catalyst has excellent catalytic degradation performance, can be recycled for multiple times, and is environment-friendly and resource-saving.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling of waste resources and relates to a preparation method and application of a solid acid catalyst for degrading waste PET to prepare TPA. Background Art

[0002] Since PET waste is difficult to degrade and recycle at room temperature and pressure, most PET waste is currently treated by incineration, landfill or simple physical recycling and downgrading, which also causes environmental pollution and waste of petrochemical resources, and increases carbon emissions. As people's awareness of environmental safety increases, how to improve the efficient recycling of resources such as waste textiles has become a popular research direction.

[0003] At present, the common chemical recycling methods for PET waste are alcoholysis and hydrolysis.

[0004] The alcoholysis method mainly includes methanol and ethylene glycol alcoholysis. The former needs to be carried out under high temperature and high pressure and has harsh reaction conditions, while the latter is a reversible reaction. Although the PET degradation conversion rate is close to 100%, the yield of the product BHET is low, only about 85%.

[0005] The hydrolysis method is widely used because of its high conversion rate, short time consumption and few by-products. The generated monomer TPA can be used for repolymerization to prepare PET with excellent performance, achieving the goal of efficient recycling of polymer resources. According to the different media, it can be divided into acidic, alkaline and neutral hydrolysis. However, in the liquid acid / alkaline system, the liquid acid / base catalyst after separating TPA will have problems such as how to regenerate, the strong corrosion of the reaction process to the equipment, and the treatment of the large amount of strong acid / base waste liquid caused by the reaction. Neutral hydrolysis is considered to be an environmentally friendly green route, but the reaction needs to be carried out in a high temperature (≥250 ºC) and high pressure subcritical water system, which has high energy consumption and high equipment requirements, limiting the promotion of industrial application.

[0006] In recent years, the use of solid acid catalysts in a neutral hydrolysis system has been proven to be a new green path with low energy consumption, low emissions, low pollution, high performance and high utilization rate in the acid degradation process of waste PET fiber recycling due to its strong acidity, low corrosion and easy regeneration. For example, the literature (Chemical Engineering Journal 2020, 398: 125655) reported a method of using 0.05g ZSM-5 molecular sieve with Si / Al of 25 as a solid acid catalyst to degrade 0.1g of PET bottle flakes under microwave-assisted conditions. After 40 minutes of degradation at 230ºC, the yield of TPA can be close to 100%. However, since the catalyst is solid and the PET waste is also solid, mass transfer between solids is difficult, making it difficult for PET to contact the acid sites on the catalyst, so high temperature and microwave assistance are required for complete degradation, so large-scale production cannot be achieved.

[0007] Therefore, a preparation method and application of a solid acid catalyst for degrading waste PET to produce TPA are needed to solve the above problems, which is of great significance. Summary of the invention

[0008] The purpose of the present invention is to solve the problems existing in the prior art and to provide a preparation method and application of a solid acid catalyst for degrading waste PET to prepare TPA.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A preparation method of a solid acid catalyst for degrading waste PET to prepare TPA, wherein an asymmetric diquaternary ammonium salt surfactant and a heteropoly acid are subjected to an ion exchange reaction at a molar ratio of 0.5 to 1.5:1 to prepare a solid acid catalyst for degrading waste PET to prepare TPA. The catalyst is composed of an asymmetric diquaternary ammonium salt cation and a heteropoly acid anion, and the cation hydrophobic end with lipophilicity in structure brings the heteropoly acid anion into the interface between the organic phase and the aqueous phase, so that the heteropoly acid anion enters the PET organic phase for depolymerization; the cation hydrophilic end can stabilize the heteropoly acid anion structure and improve the catalyst recycling performance.

[0011] As the preferred technical solution:

[0012] The method for preparing a solid acid catalyst for degrading waste PET to produce TPA as described above comprises the following steps:

[0013] (1) dissolving an asymmetric diquaternary ammonium salt surfactant in ethanol to obtain a mixture I;

[0014] (2) dissolving the heteropoly acid solid powder in water or ethanol to obtain a mixture II;

[0015] (3) Add mixture I into mixture II at a rate of 0.5 ml / min to generate a flocculent precipitate, and stir evenly at room temperature to obtain mixture III;

[0016] (4) The mixture III was stirred and aged for 2 to 6 hours at room temperature, and then washed, centrifuged, and dried in sequence (first washed three times by centrifugation with distilled water, then washed three times by centrifugation with ethanol, and finally dried at 60 °C in vacuum for 12 h) to obtain a solid acid catalyst for degrading waste PET to produce TPA;

[0017] The molar ratio of the asymmetric diquaternary ammonium salt surfactant to ethanol in step (1) is 1-1.5:260, and the molar ratio of the heteropolyacid solid powder to water or ethanol in step (2) is 1-2:260-833.

[0018] The preparation method of the solid acid catalyst for degrading waste PET to prepare TPA as described above, the preparation method of the asymmetric diquaternary ammonium salt surfactant is as follows: first, a long-chain alkyl halide, solvent A and tetramethylhexanediamine are mixed in a molar ratio of 1:40-70:1-10, heated under reflux in a water bath at 45-75°C for 5-12 hours under stirring, filtered, washed with ether and air-dried to obtain an intermediate product, and then a short-chain alkyl halide, solvent B and the intermediate product are mixed in a molar ratio of 1-3:30-55:1, heated under reflux in an oil bath at 80-120°C for 15-50 hours under stirring, the solvent is evaporated and recrystallized with ether to obtain an asymmetric diquaternary ammonium salt surfactant [C m H 2m+1 -N + (CH3)2-C6H 12 -N + (CH3)2-C n H 2n+1 ]-X2 (abbreviated as C m-6-n X2), wherein m=22, 18, 16, or 12; n=4 or 6; X is Cl, Br, or I;

[0019] The long-chain monohaloalkane is chlorodocosanane, chlorooctadecane, chlorohexadecane, chlorododecane, bromodocosanane, bromooctadecane, bromohexadecane, bromododecane, iododocosanane, iodooctadecane, iodohexadecane or iodododecane; the short-chain monohaloalkane is hexyl chloride, chlorobutyl, hexyl bromide, bromobutyl, hexyl iodide or iodobutyl.

[0020] In the above-mentioned method for preparing a solid acid catalyst for degrading waste PET to produce TPA, solvent A is acetone, dimethyl carbonate, diethyl carbonate or acetonitrile; solvent B is n-propanol or ethanol.

[0021] In the above-mentioned method for preparing a solid acid catalyst for degrading waste PET to produce TPA, the heteropoly acid in step (2) is phosphotungstic acid (H3PW 12 O 40 ), silicotungstic acid (H4SiW 12 O 40 ), phosphomolybdic acid (H3PMo 12 O 40 ) or silicomolybdic acid (H4SiMo 12 O 40 ).

[0022] The present invention also provides an application of the solid acid catalyst prepared by the preparation method as described in any one of the above items, wherein waste PET, the solid acid catalyst and distilled water are added to the polytetrafluoroethylene or para-polyphenyl lining of an autoclave in a mass ratio of 1:0.1-0.2:2.5-15, and a homogeneous reactor is used to react at 180-220°C for 4-24 hours.

[0023] As the preferred technical solution:

[0024] According to the application of the solid acid catalyst for degrading waste PET to produce TPA as described above, the solid acid catalyst is recycled for multiple times, and the PET conversion rate during the first use is above 99%, and the TPA yield is above 94%; the PET conversion rate after being recycled for 6 times is above 96.5%, and the TPA yield is above 90.2%.

[0025] In the application of a solid acid catalyst for degrading waste PET to produce TPA as described above, the waste PET is waste PET fiber or PET bottle flakes; the waste PET fiber does not need to be sheared, and the PET bottle flakes need to be crushed into 2mm×2mm×2mm particles.

[0026] Principle of the invention:

[0027] The invention discloses a solid acid catalyst for degrading waste PET to prepare TPA, i.e., a heteropolyacid asymmetric diquaternary ammonium salt solid acid catalyst, which is prepared by ion exchange reaction of heteropolyacid and asymmetric diquaternary ammonium salt according to a certain molar ratio and is combined together by chemical bonds. In the catalyst prepared by the reaction, heteropolyacid anions provide catalytic activity, and quaternary ammonium salt cations provide phase transfer ability. Since the diquaternary ammonium salt cation has a longer chain length and is a hydrophobic group at one end, it has lipophilicity and can bring heteropolyacid anions into the solid-liquid interface of the polyester organic phase and the aqueous phase reaction. The heteropolyacid anions enter the organic phase and attack the surface of the PET macromolecule, and the ester group is attacked and broken into small molecular carboxyl and hydroxyl groups, and the generated monomers are quickly separated and enter the aqueous phase. The diquaternary ammonium salt cation has a shorter chain length and shows hydrophilicity and can be closely combined with the heteropolyacid through ion exchange to stabilize the catalyst structure. After the catalytic reaction ends, the anions and cations in the catalyst recover their original structures.

[0028] The heteropolyacid asymmetric diquaternary ammonium salt solid acid catalyst has a phase transfer function, which can enhance the solid-solid interface mass transfer, reduce the energy consumption required for the degradation of PET macromolecules, and improve the catalytic performance. At the same time, the solid acid catalyst can be recycled many times, avoid the discharge of liquid acid and alkali waste liquids, and has no corrosion to the equipment, thereby extending its service life.

[0029] Beneficial effects:

[0030] (1) The present invention prepares a heteropolyacid diquaternary ammonium salt solid acid catalyst with phase transfer function, which overcomes the mass transfer limitation between the macromolecular polymer and the solid acid catalyst, effectively improves the catalytic degradation performance, and makes the PET conversion rate as high as more than 99% and the TPA yield as high as more than 94%.

[0031] (2) The heteropolyacid diquaternary ammonium salt solid acid catalyst prepared by the present invention has a stable structure and can be recycled for multiple times compared with liquid acid catalysts. After the sixth recycling, the PET conversion rate can still reach more than 96.5%, and the TPA yield can still be maintained at more than 90.2%. There is no concentrated acid or concentrated alkali waste liquid discharged, which is environmentally friendly. In addition, the entire degradation process is non-corrosive to the equipment and only neutral water is used as the solvent, which is environmentally friendly and saves resources.

[0032] (3) The preparation method of the present invention is simple in process, avoids the discharge of concentrated acid and concentrated alkali waste liquid, significantly reduces environmental pollution, eliminates corrosion to equipment, and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The cation C of the asymmetric diquaternary ammonium salt surfactant prepared in Example 1 of the present invention 18-6-6 2+ Schematic diagram of the molecular formula; in the figure, different numbers represent the types of carbon atoms in different chemical environments;

[0034] Figure 2 The cation prepared in Example 1 of the present invention is C 18-6-6 2+ Heteropolyacid diquaternary ammonium salt solid acid catalyst 1 H NMR spectrum;

[0035] Figure 3 The FT-IR spectrum of the solid acid catalyst for degrading waste PET to produce TPA prepared in Example 1 of the present invention;

[0036] Figure 4 The figure is a standard curve of ultraviolet absorption of TPA purified by the present invention at a wavelength of 240 nm;

[0037] Figure 5This is a comparison diagram of the appearance and purity of the TPA purified by the present invention and commercial TPA; in the figure, a is the appearance and purity diagram of the purified TPA, and b is the appearance and purity diagram of the commercial TPA;

[0038] Figure 6 The X-ray diffraction spectra of TPA and commercial TPA obtained after the solid acid catalyst for preparing TPA by degrading waste PET prepared in Example 1 of the present invention was recycled for 3 and 5 times;

[0039] Figure 7 The solid acid catalyst for degrading waste PET to produce TPA prepared by the present invention degrades waste PET at different cycle times to generate liquid NMR spectra of product TPA; in the figure, a is the liquid of the solid acid catalyst for degrading waste PET to produce TPA at different cycle times to degrade waste PET to generate product TPA 1 H NMR spectrum, b is the liquid of TPA produced by solid acid catalyst degrading waste PET at different cycles 13 C NMR spectrum;

[0040] Figure 8 The solid acid catalyst prepared in Example 1 of the present invention for degrading waste PET to produce TPA is used in the recycling process to show the conversion rate of waste PET and the yield of TPA. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0042] Example 1

[0043] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0044] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0045] (1.1) Tetramethylhexanediamine was dissolved in acetone, and octadecane chloride was added thereto. The mixture was refluxed in a water bath at 58°C for 8 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of octadecane chloride, acetone, and tetramethylhexanediamine was 1:50:10.

[0046] (1.2) The intermediate product was dissolved in n-propanol, and after stirring, hexyl chloride was added thereto, and the mixture was refluxed in an oil bath at 105°C for 36 hours under stirring, and then the solvent was evaporated and recrystallized from ether for 3 times to obtain an asymmetric diquaternary ammonium salt surfactant; wherein the molar ratio of hexyl chloride, n-propanol and the intermediate product was 1.25:52.5:1;

[0047] The prepared asymmetric diquaternary ammonium salt surfactant is [C 18 H 37 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-Cl2, abbreviated as C 18-6-6 Cl2, whose cation has the molecular formula Figure 1 As shown;

[0048] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0049] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 1:833;

[0050] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0051] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA. 1 H NMR spectrum Figure 2 As shown, the H species and peak area correspond to their molecular formulas one by one; the FT-IR spectrum of the solid acid catalyst for degrading waste PET to produce TPA is shown in Figure 3 As shown in the figure, it can be seen that the heteropolyacid diquaternary ammonium salt solid acid catalyst has the characteristic peaks of diquaternary ammonium salt, while retaining the complete characteristic structure of the heteropolyacid, indicating that a high-purity heteropolyacid diquaternary ammonium salt solid acid catalyst has been successfully prepared.

[0052] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0053] (a) Degradation of waste PET;

[0054] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and a homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.1:10;

[0055] (b) TPA purification;

[0056] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0057] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.5% and the TPA yield is 94.3% when it is first used. The purity of the purified TPA is measured by an ultraviolet-visible spectrophotometer at a wavelength of 240 nm, and the results are as follows: Figure 4 , Figure 5 As shown in the figure, it can be seen that the purity of the TPA purified by the present invention is 99%, and it is a pure white powder, which is the same as the purity of commercial TPA;

[0058] (c) The lower solid layer separated in step (b) was taken out, washed and dried in sequence, and steps (a) to (b) were repeated 5 times. The PET conversion rate was 98%, the TPA yield was 91.3%, and the TPA purity was 99% (the PET conversion rate and TPA yield of the solid acid catalyst prepared in this example from the first use to the sixth use are as follows: Figure 8 As shown); wherein, the catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated during the purification process of the previous cycle after washing and drying.

[0059] The crystal structure of the TPA obtained by purifying the solid acid catalyst prepared in this example after being reused 3 times and 5 times was compared with that of the commercial TPA. Figure 6 As shown, its XRD diffraction peak position is the same as that of commercial TPA; at the same time, the solid acid catalyst prepared in this example was recycled 1 time, 3 times, 5 times, and 6 times to obtain purified TPA. 1 H.13 C liquid NMR characterization, the results are as follows Figure 7 As shown in the figure, it can be seen that the product obtained by recycling the solid acid catalyst to degrade PET is high-purity, high-crystallinity TPA.

[0060] Example 2

[0061] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0062] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0063] (1.1) Tetramethylhexanediamine was dissolved in dimethyl carbonate, and octadecane bromide was added thereto. The mixture was refluxed in a water bath at 60°C for 7 hours under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of octadecane bromide, dimethyl carbonate, and tetramethylhexanediamine was 1:50:5.

[0064] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then bromohexane was added. The mixture was heated under reflux in an oil bath at 85°C for 48 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium surfactant. The molar ratio of bromohexane, ethanol and the intermediate product was 1.25:50:1.

[0065] The prepared asymmetric diquaternary ammonium salt surfactant is [C 18 H 37+1 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-Br2, abbreviated as C 18-6-6 Br2;

[0066] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1.5:260;

[0067] (3) dissolving phosphomolybdic acid in ethanol to obtain a mixture II, wherein the molar ratio of phosphomolybdic acid to ethanol is 1:260;

[0068] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0069] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0070] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0071] (a) Degradation of waste PET;

[0072] First, PET bottle flakes (waste mineral water bottles, the manufacturer is Nongfu Spring) are crushed into 2mm×2mm×2mm particles, and then the granular PET bottle flakes, the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and the homogeneous reactor is used to react at a speed of 10 r / min at 190 ºC for 15 hours, and then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of PET bottle flakes, solid acid catalyst and distilled water is 1:0.125:12.5;

[0073] (b) TPA purification;

[0074] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0075] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.2%, the TPA yield is 94.6%, and the TPA purity is 99% when it is first used;

[0076] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.4%, the TPA yield is 90.9%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0077] Example 3

[0078] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0079] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0080] (1.1) Tetramethylhexanediamine was dissolved in diethyl carbonate, and iodooctadecane was added thereto. The mixture was refluxed in a water bath at 75°C for 5 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of iodooctadecane, diethyl carbonate, and tetramethylhexanediamine was 1:50:3.

[0081] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then iodine hexane was added. The mixture was heated under reflux in an oil bath at 80°C for 48 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium surfactant; wherein the molar ratio of iodine hexane, ethanol and the intermediate product was 1.5:50:1;

[0082] The prepared asymmetric diquaternary ammonium salt surfactant is [C 18 H 37 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-I2, abbreviated as C 18-6-6 I2;

[0083] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0084] (3) dissolving phosphotungstic acid in ethanol to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to ethanol is 2:260;

[0085] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0086] (5) Mixture III was stirred and aged for 4 hours at 25°C, then washed by centrifugation with distilled water for 3 times, then washed by centrifugation with ethanol for 3 times, and finally dried in vacuo at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0087] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0088] (a) Degradation of waste PET;

[0089] First, PET bottle flakes (waste mineral water bottles, the manufacturer is Nongfu Spring) are crushed into 2mm×2mm×2mm particles, and then the granular PET bottle flakes, the solid acid catalyst prepared by degrading waste PET to produce TPA, and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and the homogeneous reactor is used to react at 180 ºC at a speed of 10 r / min for 24 hours, and then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of PET bottle flakes, solid acid catalyst and distilled water is 1:0.125:12.5;

[0090] (b) TPA purification;

[0091] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0092] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.3%, the TPA yield is 94%, and the TPA purity is 99% when it is first used;

[0093] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.7%, the TPA yield is 90.6%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0094] Example 4

[0095] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0096] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0097] (1.1) Tetramethylhexanediamine was dissolved in acetone, and iododecane was added thereto. The mixture was refluxed in a water bath at 60°C for 8 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of iododecane, acetone, and tetramethylhexanediamine was 1:40:10.

[0098] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then iodine butane was added. The mixture was heated under reflux in an oil bath at 85°C for 40 h under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant; wherein the molar ratio of iodine butane, ethanol and the intermediate product was 1.5:55:1;

[0099] The prepared asymmetric diquaternary ammonium salt surfactant is [C 12 H 25 -N + (CH3)2-C6H 12 -N + (CH3)2-C4H9]-I2, abbreviated as C 12-6-4 I2;

[0100] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0101] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:550;

[0102] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0103] (5) Mixture III was stirred and aged for 4 hours at 25°C, then washed by centrifugation with distilled water for 3 times, then washed by centrifugation with ethanol for 3 times, and finally dried in vacuo at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0104] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0105] (a) Degradation of waste PET;

[0106] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and a homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.1:15;

[0107] (b) TPA purification;

[0108] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0109] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.2%, the TPA yield is 94.2%, and the TPA purity is 99% when it is first used;

[0110] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.6%, the TPA yield is 90.2%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0111] Example 5

[0112] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0113] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0114] (1.1) Tetramethylhexanediamine was dissolved in acetonitrile, and then chlorodocosane was added thereto. The mixture was refluxed in a water bath at 70°C for 10 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of chlorodocosane, acetonitrile and tetramethylhexanediamine was 1:55:7.

[0115] (1.2) The intermediate product was dissolved in n-propanol, stirred evenly, and then hexyl chloride was added. The mixture was heated under reflux in an oil bath at 100°C for 48 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant. The molar ratio of hexyl chloride, n-propanol and the intermediate product was 1.25:55:1.

[0116] The prepared asymmetric diquaternary ammonium salt surfactant is [C 22 H 45 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H13 ]-Cl2, abbreviated as C 22-6-6 Cl2;

[0117] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1.5:260;

[0118] (3) dissolving phosphotungstic acid in ethanol to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to ethanol is 1:260;

[0119] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0120] (5) Mixture III was stirred and aged for 6 hours at 25°C, then washed by centrifugation with distilled water for 3 times, then washed by centrifugation with ethanol for 3 times, and finally dried in vacuo at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0121] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0122] (a) Degradation of waste PET;

[0123] First, PET bottle flakes (waste mineral water bottles, the manufacturer is Nongfu Spring) are crushed into 2mm×2mm×2mm particles, and then the granular PET bottle flakes, the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and the homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, and then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of PET bottle flakes, solid acid catalyst and distilled water is 1:0.125:10;

[0124] (b) TPA purification;

[0125] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0126] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.3%, the TPA yield is 94.1%, and the TPA purity is 99% when it is first used;

[0127] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 96.8%, the TPA yield is 91.2%, and the TPA purity is 99%; wherein the catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0128] Example 6

[0129] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0130] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0131] (1.1) Tetramethylhexanediamine is dissolved in dimethyl carbonate, and then docosane bromide is added thereto. The mixture is refluxed in a water bath at 70°C for 7 hours under stirring, and then cooled to 25°C. The mixture is then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of docosane bromide, dimethyl carbonate, and tetramethylhexanediamine is 1:70:1.

[0132] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then bromohexane was added. The mixture was heated under reflux in an oil bath at 80°C for 48 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium surfactant. The molar ratio of bromohexane, ethanol and the intermediate product was 3:50:1.

[0133] The prepared asymmetric diquaternary ammonium salt surfactant is [C 22 H 45 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-Br2, abbreviated as C 22-6-6 Br2;

[0134] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0135] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:550;

[0136] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0137] (5) Mixture III was stirred and aged for 6 hours at 25°C, then washed by centrifugation with distilled water for 3 times, then washed by centrifugation with ethanol for 3 times, and finally dried in vacuo at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0138] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0139] (a) Degradation of waste PET;

[0140] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the para-polyphenyl lining of the autogenous pressure reactor, and a homogeneous reactor is used to react at a speed of 10 r / min at 205 ºC for 10 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.1:7.5;

[0141] (b) TPA purification;

[0142] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0143] According to the mass calculation of TPA and impurities obtained after the above purification, the solid acid catalyst for degrading waste PET to produce TPA has a PET conversion rate of 99.4%, a TPA yield of 94%, and a TPA purity of 99% when used for the first time;

[0144] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.4%, the TPA yield is 91.2%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0145] Example 7

[0146] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0147] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0148] (1.1) Tetramethylhexanediamine was dissolved in acetone, and hexadecane chloride was added thereto. The mixture was refluxed in a water bath at 45°C for 12 h under stirring, and then cooled to 25°C. The mixture was filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of hexadecane chloride, acetone, and tetramethylhexanediamine was 1:50:10.

[0149] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then chlorobutane was added. The mixture was heated under reflux in an oil bath at 80°C for 50 h under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium surfactant. The molar ratio of chlorobutane, ethanol and the intermediate product was 2:40:1.

[0150] The prepared asymmetric diquaternary ammonium salt surfactant is [C 16 H 33 -N + (CH3)2-C6H 12 -N + (CH3)2-C4H9]-Cl2, abbreviated as C 16-6-4 Cl2;

[0151] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0152] (3) dissolving silicotungstic acid in ethanol to obtain a mixture II, wherein the molar ratio of silicotungstic acid to ethanol is 1:260;

[0153] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0154] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0155] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0156] (a) Degradation of waste PET;

[0157] Waste PET fiber (oil-free semi-dull PET waste silk, manufactured by Tongkun Group Co., Ltd., with a TiO2 content of 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA, and distilled water were added to the polytetrafluoroethylene liner of an autoclave, and a homogeneous reactor was used to react at a speed of 10 r / min at 220 ºC for 4 hours, then cooled to room temperature, and the solid was separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water was 1:0.125:5;

[0158] (b) TPA purification;

[0159] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0160] According to the mass calculation of TPA and impurities obtained after the above purification, the solid acid catalyst for degrading waste PET to produce TPA has a PET conversion rate of 99%, a TPA yield of 94.1%, and a TPA purity of 99% when used for the first time;

[0161] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 96.5%, the TPA yield is 90.2%, and the TPA purity is 99%; wherein the catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0162] Example 8

[0163] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0164] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0165] (1.1) Tetramethylhexanediamine was dissolved in acetone, and then dodecane bromide was added thereto. The mixture was refluxed in a water bath at 60°C for 10 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of dodecane bromide, acetone, and tetramethylhexanediamine was 1:50:10.

[0166] (1.2) The intermediate product was dissolved in n-propanol, stirred evenly, and then butyl bromide was added. The mixture was heated under reflux in an oil bath at 120°C for 15 h under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant; wherein the molar ratio of butyl bromide, n-propanol and the intermediate product was 1:30:1;

[0167] The prepared asymmetric diquaternary ammonium salt surfactant is [C 12 H 25 -N + (CH3)2-C6H 12 -N + (CH3)2-C4H9]-Br2, abbreviated as C 12-6-4 Br2;

[0168] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0169] (3) dissolving silicomolybdic acid in distilled water to obtain a mixture II, wherein the molar ratio of silicomolybdic acid to distilled water is 2:833;

[0170] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0171] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0172] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0173] (a) Degradation of waste PET;

[0174] Waste PET fiber (oil-free semi-dull PET waste silk, manufactured by Tongkun Group Co., Ltd., with a TiO2 content of 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA, and distilled water were added to the para-polyphenyl lining of the autogenous pressure reactor, and a homogeneous reactor was used to react at a speed of 10 r / min at 210 ºC for 8 h, then cooled to room temperature, and the solid was separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water was 1:0.1:10;

[0175] (b) TPA purification;

[0176] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0177] According to the mass calculation of TPA and impurities obtained after the above purification, the solid acid catalyst for degrading waste PET to produce TPA has a PET conversion rate of 99.4%, a TPA yield of 94.5%, and a TPA purity of 99% when used for the first time;

[0178] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.2%, the TPA yield is 90.9%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0179] Example 9

[0180] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0181] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0182] (1.1) Tetramethylhexanediamine was dissolved in dimethyl carbonate, and then chlorododecane was added thereto. The mixture was refluxed in a water bath at 65°C for 8 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of chlorododecane, dimethyl carbonate and tetramethylhexanediamine was 1:40:5.

[0183] (1.2) The intermediate product was dissolved in n-propanol, stirred evenly, and then hexyl chloride was added. The mixture was heated under reflux in an oil bath at 108°C for 36 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant. The molar ratio of hexyl chloride, n-propanol and the intermediate product was 1.25:30:1.

[0184] The prepared asymmetric diquaternary ammonium salt surfactant is [C 12 H 25 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-Cl2, abbreviated as C 12-6-6 Cl2;

[0185] (2) dissolving the asymmetric diquaternary ammonium salt surfactant prepared in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1.25:260;

[0186] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:833;

[0187] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0188] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0189] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0190] (a) Degradation of waste PET;

[0191] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and a homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.15:10;

[0192] (b) TPA purification;

[0193] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0194] According to the mass calculation of TPA and impurities obtained after the above purification, the solid acid catalyst for degrading waste PET to produce TPA has a PET conversion rate of 99.4%, a TPA yield of 94.4%, and a TPA purity of 99% when used for the first time;

[0195] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.4%, the TPA yield is 90.7%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0196] Example 10

[0197] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0198] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0199] (1.1) Tetramethylhexanediamine was dissolved in acetone, and hexadecane bromide was added thereto. The mixture was refluxed in a water bath at 55°C for 9 hours under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of hexadecane bromide, acetone, and tetramethylhexanediamine was 1:60:10.

[0200] (1.2) The intermediate product was dissolved in ethanol, stirred evenly, and then bromohexane was added. The mixture was refluxed in an oil bath at 80°C for 50 h under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium surfactant. The molar ratio of bromohexane, ethanol and the intermediate product was 1.5:40:1.

[0201] The prepared asymmetric diquaternary ammonium salt surfactant is [C 16 H 33 -N + (CH3)2-C6H 12 -N+ (CH3)2-C6H 13 ]-Br2, abbreviated as C 16-6-6 Br2;

[0202] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0203] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:550;

[0204] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0205] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0206] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0207] (a) Degradation of waste PET;

[0208] Waste PET fiber (oil-free semi-dull PET waste yarn, manufactured by Tongkun Group Co., Ltd., with a TiO2 content of 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA, and distilled water were added to the polytetrafluoroethylene liner of an autoclave, and a homogeneous reactor was used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid was separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst, and distilled water was 1:0.1:2.5;

[0209] (b) TPA purification;

[0210] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0211] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.6%, the TPA yield is 94.5%, and the TPA purity is 99% when it is first used;

[0212] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.8%, the TPA yield is 91%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0213] Embodiment 11

[0214] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0215] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0216] (1.1) Tetramethylhexanediamine was dissolved in diethyl carbonate, and then iododecane was added thereto. The mixture was refluxed in a water bath at 75°C for 6 hours under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of iododecane, diethyl carbonate, and tetramethylhexanediamine was 1:50:5.

[0217] (1.2) The intermediate product was dissolved in n-propanol, stirred evenly, and then iodine butane was added. The mixture was heated under reflux in an oil bath at 110°C for 32 hours under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant. The molar ratio of iodine butane, n-propanol and the intermediate product was 2:50:1.

[0218] The prepared asymmetric diquaternary ammonium salt surfactant is [C 22 H 45 -N + (CH3)2-C6H 12 -N + (CH3)2-C4H9]-I2, abbreviated as C 22-6-4 I2;

[0219] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0220] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:833;

[0221] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0222] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0223] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0224] (a) Degradation of waste PET;

[0225] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and a homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.2:10;

[0226] (b) TPA purification;

[0227] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0228] According to the mass calculation of TPA and impurities obtained after the above purification, the solid acid catalyst for degrading waste PET to produce TPA has a PET conversion rate of 99.3%, a TPA yield of 94.3%, and a TPA purity of 99% when used for the first time;

[0229] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97.2%, the TPA yield is 90.5%, and the TPA purity is 99%; wherein the catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0230] Example 12

[0231] A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, comprising the following steps:

[0232] (1) Preparation of asymmetric diquaternary ammonium salt surfactants;

[0233] (1.1) Tetramethylhexanediamine was dissolved in acetonitrile, and hexadecane iodide was added thereto. The mixture was refluxed in a water bath at 60°C for 12 h under stirring, and then cooled to 25°C. The mixture was then filtered, washed with ether for three times, and air-dried to obtain an intermediate product. The molar ratio of hexadecane iodide, acetonitrile, and tetramethylhexanediamine was 1:70:10.

[0234] (1.2) The intermediate product was dissolved in n-propanol, stirred evenly, and then iodine hexane was added. The mixture was heated under reflux in an oil bath at 105°C for 40 h under stirring. The solvent was then evaporated and recrystallized from ether three times to obtain an asymmetric diquaternary ammonium salt surfactant. The molar ratio of iodine hexane, n-propanol and the intermediate product was 2.5:55:1.

[0235] The prepared asymmetric diquaternary ammonium salt surfactant is [C 16 H 33 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 ]-I2, abbreviated as C 16-6-6 I2;

[0236] (2) dissolving the asymmetric diquaternary ammonium salt surfactant obtained in step (1) in ethanol and stirring the mixture to obtain a mixture I; wherein the molar ratio of the asymmetric diquaternary ammonium salt surfactant to the ethanol is 1:260;

[0237] (3) dissolving phosphotungstic acid in distilled water to obtain a mixture II, wherein the molar ratio of phosphotungstic acid to distilled water is 2:550;

[0238] (4) At 25°C, under magnetic stirring, mixture I was added dropwise to mixture II at a rate of 0.5 ml / min. A white flocculent precipitate was generated during the addition, and mixture III was obtained after the addition was completed. The addition time was 0.5 h.

[0239] (5) Mixture III was stirred and aged for 2 hours at 25°C, then centrifuged and washed three times with distilled water, then centrifuged and washed three times with ethanol, and finally vacuum dried at 60°C for 12 hours to obtain a solid acid catalyst for degrading waste PET to produce TPA.

[0240] An application of a solid acid catalyst for degrading waste PET to produce TPA, the steps are as follows:

[0241] (a) Degradation of waste PET;

[0242] Waste PET fiber (oil-free semi-dull PET waste silk, the manufacturer is Tongkun Group Co., Ltd., TiO2 content is 0.225%), the solid acid catalyst prepared by degrading waste PET to produce TPA and distilled water are added to the polytetrafluoroethylene liner of the autoclave, and a homogeneous reactor is used to react at a speed of 10 r / min at 200 ºC for 12 h, then cooled to room temperature, and the solid is separated by filtration; wherein the mass ratio of waste PET fiber, solid acid catalyst and distilled water is 1:0.1:10;

[0243] (b) TPA purification;

[0244] The solid product obtained in step (a) is dissolved in a 1 mol / L NaOH aqueous solution and stirred at 25°C for 0.5 hours, and then centrifuged at 9000 rpm for 10 minutes in a high-speed centrifuge. After the centrifugation, the upper layer is a clear liquid, and the lower solid layer is a catalyst and trace impurities. The upper clear liquid is then taken out, and 1 mol / L dilute sulfuric acid is added thereto under stirring until the pH of the solution becomes acidic. Stirring is continued for 1 hour until TPA is completely precipitated, then filtered, washed, dried and weighed.

[0245] According to the mass calculation of TPA and impurities obtained after the above purification, the PET conversion rate of the solid acid catalyst for degrading waste PET to produce TPA is 99.1%, the TPA yield is 94.2%, and the TPA purity is 99% when it is first used;

[0246] (c) The lower layer solid separated in step (b) is taken out, washed and dried in sequence, and steps (a) to (b) are repeated 5 times. The PET conversion rate is 97%, the TPA yield is 90.3%, and the TPA purity is 99%. The catalyst used when repeating steps (a) to (b) 5 times is the product of the lower layer solid separated in the purification process of the previous cycle after washing and drying.

[0247] Comparative Example 1

[0248] An application of a solid acid catalyst for degrading waste PET to produce TPA is basically the same as Example 1, except that the solid acid catalyst for degrading waste PET to produce TPA in step (a) is replaced by an equal mass of phosphotungstic acid.

[0249] In step (b), phosphotungstic acid is used as a catalyst. The PET conversion rate is 97% and the TPA yield is 91.3% when it is used for the first time. However, phosphotungstic acid is not recyclable and cannot be recycled.

[0250] Comparing Comparative Example 1 with Example 1, it can be seen that when Comparative Example 1 uses phosphotungstic acid as a catalyst, the PET conversion rate and TPA yield at the initial use are reduced and cannot be recycled. This is because compared with the heteropolyacid asymmetric diquaternary ammonium salt solid acid catalyst prepared in Example 1, phosphotungstic acid is soluble in water and the generated H + It is evenly distributed in water and has no phase transfer catalytic function, while the heteropolyacid asymmetric diquaternary ammonium salt solid acid catalyst has a phase transfer function. The hydrophobic end of the quaternary ammonium cation is lipophilic, which can bring the heteropolyacid anion into the solid-liquid interface of the polyester organic phase and the aqueous phase reaction, which is beneficial for the heteropolyacid anion to enter the organic phase to attack the surface of the PET macromolecule. Therefore, the PET conversion rate and TPA yield of phosphotungstic acid as a catalyst are lower than those of solid acid catalysts; in addition, since phosphotungstic acid is highly soluble in water, phosphotungstic acid will dissolve in the aqueous solution (including ethylene glycol and trace impurities) after the degradation reaction is completed, making it difficult to recover and recycle at room temperature.

Claims

1. A method for preparing a solid acid catalyst for degrading waste PET to produce TPA, characterized in that: An asymmetric diquaternary ammonium salt surfactant and a heteropoly acid are subjected to an ion exchange reaction at a molar ratio of 0.5-1.5:1 to obtain a solid acid catalyst for degrading waste PET to produce TPA.

2. The method for preparing a solid acid catalyst for degrading waste PET to produce TPA according to claim 1, characterized in that: The steps include: (1) dissolving an asymmetric diquaternary ammonium salt surfactant in ethanol to obtain a mixture I; (2) dissolving the heteropoly acid solid powder in water or ethanol to obtain a mixture II; (3) Add mixture I into mixture II at a rate of 0.5 ml / min to generate a flocculent precipitate, and stir evenly at room temperature to obtain mixture III; (4) stirring and aging the mixture III at room temperature for 2 to 6 hours, and then washing, centrifuging, and drying in sequence to obtain a solid acid catalyst for degrading waste PET to produce TPA; The molar ratio of the asymmetric diquaternary ammonium salt surfactant to ethanol in step (1) is 1-1.5:260, and the molar ratio of the heteropolyacid solid powder to water or ethanol in step (2) is 1-2:260-833.

3. The method for preparing a solid acid catalyst for degrading waste PET to produce TPA according to claim 2, characterized in that: The preparation method of the asymmetric diquaternary ammonium salt surfactant comprises the following steps: firstly, a long-chain alkyl halide, a solvent A and tetramethylhexanediamine are mixed in a molar ratio of 1:40-70:1-10, refluxed in a water bath at 45-75° C. for 5-12 hours under stirring, and air-dried to obtain an intermediate product; then, a short-chain alkyl halide, a solvent B and the intermediate product are mixed in a molar ratio of 1-3:30-55:1, refluxed at 80-120° C. for 15-50 hours under stirring, the solvent is evaporated and recrystallized from ether to obtain an asymmetric diquaternary ammonium salt surfactant [C m H 2m+1 -N + (CH3)2-C6H 12 -N + (CH3)2-C n H 2n+1 ]-X2, wherein m=22, 18, 16, or 12; n=4 or 6; X is Cl, Br, or I; The long-chain monohaloalkane is chlorodocosanane, chlorooctadecane, chlorohexadecane, chlorododecane, bromodocosanane, bromooctadecane, bromohexadecane, bromododecane, iododocosanane, iodooctadecane, iodohexadecane or iodododecane; the short-chain monohaloalkane is hexyl chloride, chlorobutyl, hexyl bromide, bromobutyl, hexyl iodide or iodobutyl.

4. The method for preparing a solid acid catalyst for degrading waste PET to produce TPA according to claim 3, characterized in that: Solvent A is acetone, dimethyl carbonate, diethyl carbonate or acetonitrile; solvent B is n-propanol or ethanol.

5. The method for preparing a solid acid catalyst for degrading waste PET to produce TPA according to claim 2, characterized in that: In step (2), the heteropoly acid is phosphotungstic acid, silicotungstic acid, phosphomolybdic acid or silicomolybdic acid.

6. The use of a solid acid catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The waste PET, the solid acid catalyst and distilled water are added into the polytetrafluoroethylene or para-polyphenyl liner of the autoclave in a mass ratio of 1:0.1-0.2:2.5-15, and the reaction is carried out at 180-220 ºC for 4-24 hours using a homogeneous reactor.

7. The use of a solid acid catalyst for degrading waste PET to produce TPA according to claim 6, characterized in that: The solid acid catalyst was recycled for multiple times, and the PET conversion rate was above 99% and the TPA yield was above 94% when it was used for the first time; the PET conversion rate was above 96.5% and the TPA yield was above 90.2% when it was recycled for 6 times.

8. The use of a solid acid catalyst for degrading waste PET to produce TPA according to claim 6, characterized in that: Waste PET refers to waste PET fibers or PET bottle flakes.

Images