Method for coupling depolymerization and decoloration of waste polyester fabric

Abstract

The invention provides a method for coupling depolymerization and decoloration of a waste polyester fabric. The method comprises the following steps that pretreated waste polyester fragments are mixed with a depolymerization agent, a catalyst and an adsorbent, a depolymerization and decoloration coupling reaction is carried out under the nitrogen atmosphere, separation and purification are carried out after the reaction is finished, a decoloration and depolymerization solution is obtained, and the adsorbent is selected from amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles or amination modified magnetic nanoparticles. The magnetic nanoparticle is composed of a Fe3O4 core and a mesoporous silica shell layer coated on the surface of the Fe3O4 core. And carrying out reduced pressure distillation and crystallization purification on the decolored and depolymerized liquid to obtain the BHET monomer. By adopting the specific adsorbent, the two steps of depolymerization and decoloration are integrated in the same reaction kettle and are completed in one-step reaction, the technological process and time are greatly shortened, the equipment and operation cost is reduced, meanwhile, synchronous adsorption is conducted in the depolymerization process, secondary pollution of dye molecules to BHET is effectively prevented, and the dye with the chromaticity b value smaller than or equal to 3 and the chromaticity b value smaller than or equal to 3 can be obtained. The heavy metal content of the regenerated monomer is less than or equal to 10ppm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste polyester fabric recycling, in particular to a waste polyester fabric depolymerization and decolorization coupling method. BACKGROUND

[0002] Polyester (polyethylene terephthalate, PET) is one of the largest synthetic fibers in the world, which in turn brings severe environmental pressure caused by a large number of waste polyester textiles. Unlike transparent PET bottles, waste polyester fabric is usually dyed and finished, and the dyes and auxiliaries contained therein affect its recycling.

[0003] At present, the recycling of polyester fabric mainly adopts chemical recycling method, especially alcoholysis method, which can depolymerize polyester into valuable bis-hydroxyethyl terephthalate (BHET) monomer, and is one of the effective ways to recycle and utilize polyester. However, the traditional recycling process usually adopts a separate step of "first depolymerization and then decolorization", that is, after the alcoholysis reaction is completed, the depolymerization solution is treated by decolorization using activated carbon, oxidizing agent or special adsorbent. Depolymerization and decolorization cannot be carried out simultaneously, resulting in long process flow, high energy consumption, and also reducing the yield and purity of the final product. In addition, the traditional adsorbent activated carbon is difficult to separate and regenerate after use, becoming a new solid waste, which does not meet the green and environmental protection principle.

[0004] Therefore, an integrated process capable of realizing depolymerization and decolorization coupling is urgently needed, which can remove dye molecules in situ while the depolymerization reaction occurs, thereby simplifying the process, improving efficiency and product purity, and realizing the recycling of adsorbent and resources. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a waste polyester fabric depolymerization and decolorization coupling method, which solves the problems raised in the background art.

[0006] To achieve the above purpose, the present application realizes the following technical scheme: According to the first aspect of the present application, a waste polyester fabric depolymerization and decolorization coupling method is provided, comprising the following steps: Step 1, mixing the pretreated waste polyester fragments with a depolymerization agent, a catalyst and an adsorbent, carrying out a depolymerization and decolorization coupling reaction under a nitrogen atmosphere, separating and purifying after the reaction is completed to obtain a decolorized depolymerization solution, wherein the adsorbent is selected from amino-modified magnetic nanoparticles, and the magnetic nanoparticles are composed of Fe3O4 core and mesoporous silica shell layer coated on the surface of the Fe3O4 core; Step 2, carrying out vacuum distillation and crystallization purification on the decolorized depolymerization solution to obtain BHET monomer.

[0007] In the process of high-temperature degradation reaction, the polyester polymer chain is degraded under the action of depolymerization agent and catalyst to generate BHET monomer, and at the same time, the dye molecules combined in the fiber are also released into the reaction solution. In the present application, Fe3O4 is selected as the core, mesoporous silica is selected as the shell, and the magnetic nanoparticles modified by amino are selected as the adsorbent. Because of the mesoporous structure and surface modification, the magnetic nanoparticles can timely in-situ adsorb and capture dye molecules in the reaction solution, avoid the side reactions such as decomposition, isomerization or recombination of dye molecules with BHET monomers at high temperature. In addition, the amino functional groups introduced on the surface of the adsorbent itself provide alkaline sites, which can also catalyze the alcoholysis reaction solution of polyester to a certain extent, and cooperate with the catalyst to accelerate the depolymerization process.

[0008] Preferably, the mass ratio of the adsorbent to the waste polyester fragments is 1:10-20.

[0009] Preferably, the preparation method of the adsorbent is as follows: A. First, hexadecyl trimethyl ammonium bromide is mixed with Fe3O4 particles as a template agent for surface adsorption, and then tetraethoxysilane is added dropwise under alkaline conditions for reaction to obtain silica-coated magnetic nanoparticles; B. The magnetic nanoparticles prepared in step A are calcined to obtain magnetic nanoparticles with a shell layer having a mesoporous structure; C. The magnetic nanoparticles prepared in step B are mixed with a modifier and refluxed under a nitrogen atmosphere to obtain the adsorbent, wherein the modifier is selected from p-phenylenediamine and / or 3-aminopropyl triethoxysilane.

[0010] Preferably, in step A, the mass ratio of the hexadecyl trimethyl ammonium bromide to the Fe3O4 particles is 2-6:1; The mass ratio of the tetraethoxysilane to the Fe3O4 particles is 0.5-3:1; The temperature of the reaction is 50-60℃, and the time is 2-8h.

[0011] Preferably, in step B, the calcination temperature is 300-600℃, and the time is 2-6h.

[0012] Preferably, in step C, the mass of the magnetic nanoparticles to the volume of the modifier is 1-40g:1mL; The reflux reaction time is 6-12h.

[0013] Preferably, the depolymerization agent is selected from at least one of methanol, ethylene glycol and ethylenediamine, and the mass ratio of the depolymerization agent to the waste polyester fragments is 2-6:1.

[0014] Preferably, the catalyst is selected from at least one of ferric chloride, zinc acetate, and tetrabutyl titanate, and the mass of the catalyst accounts for 0.5 to 2.0% of the total mass of the waste polyester fragments.

[0015] Preferably, the parameters of the depolymerization and decolorization coupling reaction are: temperature of 180~220℃, time of 0.5~3h, and stirring rate of 200~500rpm.

[0016] Preferably, the temperature of the vacuum distillation is 100~150℃ and the absolute pressure is 10~50kPa; The crystallization purification temperature is 0~10℃, and the crystallization purification time is 2~5h. Beneficial effects

[0017] This invention provides a method for depolymerization and decolorization coupling of waste polyester fabrics. It has the following beneficial effects: (1) The present solution provides a method for depolymerization and decolorization of waste polyester fabric. By using a specific adsorbent, the two steps of depolymerization and decolorization are integrated into the same reactor and completed in one step. This greatly shortens the process flow and time, and reduces equipment and operating costs. At the same time, adsorption is carried out simultaneously during the depolymerization process, which effectively prevents secondary pollution of BHET by dyes. The resulting recycled monomers with a color value b ≤ 3 and heavy metal content ≤ 10 ppm can be obtained.

[0018] (2) This solution provides a method for depolymerization and decolorization coupling of waste polyester fabrics. A magnetic adsorbent is selected, and after the reaction, the fabrics can be quickly and thoroughly separated by a simple external magnetic field. After regeneration, the fabrics can be reused, significantly reducing solid waste emissions and raw material costs. In addition, the dyes concentrated by adsorption can be recycled and reused. Detailed Implementation

[0019] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0020] The method for preparing the adsorbent used in this application is as follows: A. Fe3O4 nanoparticles and hexadecyltrimethylammonium bromide were added to a 60℃ water bath and stirred vigorously to dissolve and adsorb onto the surface of Fe3O4 nanoparticles. The mass ratio of Fe3O4 nanoparticles to hexadecyltrimethylammonium bromide was adjusted to 1:2~6. After adding ammonia solution to provide an alkaline environment, tetraethoxysilane was slowly added and stirred for 2~8 hours. A silica shell was coated on the surface of Fe3O4 nanoparticles by coprecipitation sol-gel method. B. Separate the washing product by magnet, and calcine it in a muffle furnace at a temperature of 300~600℃ for 2~6h to remove the template agent hexadecyltrimethylammonium bromide and unclog the surface mesoporous channels. C. Mix p-phenylenediamine and / or 3-aminopropyltriethoxysilane with magnetic nanoparticles having a mesoporous structure, and reflux the mixture under a nitrogen atmosphere for 6-12 hours to obtain modified magnetic nanoparticles with a mesoporous structure.

[0021] The adsorbent prepared in this application has a core of Fe3O4 magnetic nanoparticles and a shell of coated mesoporous silica, which is then modified by amination. The adsorbent obtained by the above preparation method has a specific surface area of ​​200-400 m². 2 / g, with a high specific surface area, and surface modification, can achieve rapid in-situ adsorption of dye molecules.

[0022] In the process of preparing the adsorbent, the mass ratio of Fe3O4 nanoparticles to hexadecyltrimethylammonium bromide is selected from any ratio of 1:2, 1:4, 1:6 or any two ratios. Since the template agent will form micelles on the surface of Fe3O4 nanoparticles, it serves as a template for forming a mesoporous structure. By controlling the amount of hexadecyltrimethylammonium bromide on the surface of Fe3O4 nanoparticles, the mesoporous structure of the mesoporous silica shell can be controlled. Excessive template agent can lead to overly dense micelles or fusion, forming a non-uniform and disordered pore structure, and even generating a large number of amorphous structures, resulting in amorphous and disordered mesopores. During subsequent calcination, excessive template agent will generate too much gas and residue, causing pore collapse or local blockage of the mesoporous silica layer, reducing the overall specific surface area. In addition, excessive template agent will also guide more silica to deposit around it, forming an excessively thick and denser silica shell, increasing mass transfer resistance, making it difficult for dye molecules to quickly enter the pores during the depolymerization reaction, reducing the adsorption rate and efficiency. Conversely, insufficient template agent cannot provide enough pore-forming template sites for silica deposition, resulting in too few mesopores, uneven pore size distribution, and broken and unconnected pores, or even failure to form a complete mesoporous structure. This leads to too low a specific surface area and pore volume of the adsorbent, affecting the adsorption effect of dye molecules. In addition, it can also cause incomplete shell coverage and a reduction in surface modification sites. More preferably, the mass ratio of Fe3O4 nanoparticles to hexadecyltrimethylammonium bromide is 1:3~5.

[0023] In the preparation of modified adsorbents, the combination of p-phenylenediamine and 3-aminopropyltriethoxysilane is preferred as a modifier. Firstly, both p-phenylenediamine and 3-aminopropyltriethoxysilane aminate the surface of mesoporous magnetic nanoparticles, and the amino group can be protonated to -NH3 in the reaction system. +It efficiently adsorbs negatively charged anionic dyes through electrostatic attraction. At the same time, the amino group can form hydrogen bonds with the carbonyl, sulfonic acid, and hydroxyl groups in the dye molecule, enhancing the adsorption strength. Secondly, 3-aminopropyltriethoxysilane mainly adsorbs dyes containing large conjugated systems. The benzene ring structure of p-phenylenediamine and the aromatic ring structure in the dye undergo π-π stacking. Through the strong anchoring of 3-aminopropyltriethoxysilane and the π-π stacking of p-phenylenediamine, high selectivity and high efficiency adsorption of dye molecules in the reaction system are achieved.

[0024] The process for depolymerization and decolorization coupling of waste polyester fabric using the above-mentioned adsorbent in this application is as follows: Step 1: After washing and drying the colored waste polyester fabric, mechanically crush it to obtain polyester fragments with a size of 0.5~2.0cm. 2 ; Step 2: Mix waste polyester fragments with depolymerization agent, catalyst and adsorbent, and carry out depolymerization coupling decolorization reaction at 180~220℃ for 1~3 hours under nitrogen atmosphere and stirring at 200~500 rpm. After the reaction, use an external magnetic field to magnetically separate the adsorbent that adsorbs dye molecules to obtain decolorization depolymerization solution. Step 3: First, the decolorized and depolymerized solution is subjected to vacuum distillation at 100~150℃ and 10~50kPa absolute pressure, and then crystallized at 0~10℃ for 2~5h to obtain BHET monomer.

[0025] In a specific embodiment, the mass ratio of adsorbent to waste polyester fragments is 1:10 to 20. Optionally, the mass ratio of adsorbent to waste polyester fragments is selected from any ratio or range between any two values ​​of 1:10, 1:13, 1:15, 1:18, and 1:20. More preferably, the mass ratio of adsorbent to waste polyester fragments is 1:15 to 18.

[0026] In a specific embodiment, the depolymerizing agent is selected from at least one of methanol, ethylene glycol, and ethylenediamine, wherein the mass ratio of the depolymerizing agent to the waste polyester fragments is 2 to 6:1.

[0027] In a specific embodiment, the catalyst is selected from at least one of ferric chloride, zinc acetate, and tetrabutyl titanate, wherein the mass of the catalyst accounts for 0.5 to 2.0% of the total mass of the waste polyester fragments.

[0028] The following detailed embodiments illustrate the method for depolymerization and decolorization coupling of waste polyester fabric provided by the present invention.

[0029] Example 1 Preparation of adsorbent: In an aqueous solution at 60℃, 1g of Fe3O4 nanoparticles and 4g of hexadecyltrimethylammonium bromide were weighed and dissolved in the solution with vigorous stirring until fully dissolved and adsorbed onto the surface of the Fe3O4 nanoparticles. Ammonia was added dropwise to adjust the pH to alkalinity, and then 2g of tetraethoxysilane was slowly added dropwise while stirring continuously for 4 hours. A silica shell was coated onto the surface of the Fe3O4 nanoparticles using a co-precipitation sol-gel method. The product was separated and washed using a magnet, and then calcined in a muffle furnace at 500℃ for 4 hours. After removing the template, Fe3O4@mSiO2 magnetic nanoparticles were obtained. Finally, 1g of Fe3O4@mSiO2 magnetic nanoparticles were mixed with 0.5mL of a mixture of p-phenylenediamine and 3-aminopropyltriethoxysilane, and refluxed at 80℃ for 8 hours under a nitrogen atmosphere. After magnetic separation, washing, and drying, a product with a specific surface area of ​​355m² was obtained. 2 / g of adsorbent X-Fe3O4@mSiO2.

[0030] Depolymerization and decolorization coupling process: 2g of waste polyester fragments were mixed with 8.0g of ethylene glycol, 0.02g of zinc acetate, and 0.133g of adsorbent X-Fe3O4@mSiO2. The mixture was subjected to a depolymerization and decolorization coupling reaction at 200℃ for 30min under a nitrogen atmosphere and stirring at 300rpm. After the reaction, the adsorbent adsorbing the dye molecules was separated using an external magnetic field to obtain a decolorized and depolymerized solution. The obtained decolorized and depolymerized solution was then subjected to vacuum distillation at 120℃ and 40kPa, and then crystallized at 5℃ for 3h to obtain BHET monomer.

[0031] Example 2 The preparation method of the adsorbent in this embodiment is the same as that in Example 1. The difference is that in the depolymerization and decolorization coupling process, 2g of waste polyester fragments are mixed with 8.0g of ethylene glycol, 0.02g of zinc acetate, and 0.111g of adsorbent X-Fe3O4@mSiO2. The depolymerization and decolorization coupling reaction is carried out at 200℃ for 30min under nitrogen atmosphere and stirring at 300rpm. After the reaction, the adsorbent adsorbing the dye molecules is separated by an external magnetic field to obtain a decolorized and depolymerized solution. The obtained decolorized and depolymerized solution is then subjected to vacuum distillation at 120℃ and 40kPa, and then crystallized at 5℃ for 3h to obtain BHET monomer.

[0032] Example 3

[0033] This embodiment is the same as the depolymerization and decolorization coupling process in Example 1. The difference is that, in the preparation of the adsorbent, only p-phenylenediamine is used to modify the Fe3O4@mSiO2 magnetic nanoparticles.

[0034] Example 4

[0035] This embodiment is the same as the depolymerization and decolorization coupling process in Example 1. The difference is that, in the preparation of the adsorbent, Fe3O4@mSiO2 magnetic nanoparticles are modified only by 3-aminopropyltriethoxysilane.

[0036] Comparative Example 1 2g of waste polyester fragments were mixed with 8.0g of ethylene glycol and 0.02g of zinc acetate. The mixture was subjected to depolymerization at 200℃ for 30min under nitrogen atmosphere and stirring at 300rpm. After cooling to room temperature, 0.2g of activated carbon was added for decolorization treatment for 30min to obtain a decolorized depolymerization solution. The decolorized depolymerization solution was then subjected to vacuum distillation at 120℃ and 40kPa, and then crystallized at 5℃ for 3h to obtain BHET monomer.

[0037] Comparative Example 2 The comparative example uses the same method as the adsorbent in Example 1, except that in the depolymerization and decolorization coupling process, 2g of waste polyester fragments are mixed with 8.0g of ethylene glycol, 0.02g of zinc acetate, and 0.08g of adsorbent X-Fe3O4@mSiO2. The mixture is then subjected to a depolymerization and decolorization coupling reaction at 200°C for 30min under a nitrogen atmosphere and stirring at 300rpm. After the reaction, the adsorbent adsorbing the dye molecules is separated using an external magnetic field to obtain a decolorized and depolymerized solution. The obtained decolorized and depolymerized solution is then subjected to vacuum distillation at 120°C and 40kPa, and then crystallized at 5°C for 3h to obtain BHET monomer.

[0038] Comparative Example 3 This comparative example uses the same depolymerization and decolorization coupling process as in Example 1, except that the amount of hexadecyltrimethylammonium bromide added during the preparation of the adsorbent is 1g, resulting in a specific surface area of ​​125m². 2 / g of adsorbent X-Fe3O4@mSiO2.

[0039] Comparative Example 4 This comparative example uses the same depolymerization and decolorization coupling process as Example 1, except that 7g of hexadecyltrimethylammonium bromide is added during the preparation of the adsorbent, resulting in a specific surface area of ​​185m². 2 / g of adsorbent X-Fe3O4@mSiO2.

[0040] The yield, color b-value, and heavy metal content of the BHET monomers prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 1.

[0041] Table 1

[0042] According to the data in Table 1, comparing Example 1 with Comparative Example 1, the product yield and purity of BHET monomers prepared by the coupling process in this application are better than those of the traditional stepwise process, and the process flow is simpler.

[0043] As can be seen from the comparison between Example 1 and Examples 3-4, the adsorbent X-Fe3O4@mSiO2, which is co-modified with p-phenylenediamine and 3-aminopropyltriethoxysilane, has a significantly better decolorization effect than the adsorbent modified by a single agent. The co-modified adsorbent combines the stability of covalent anchoring with the strong adsorption force of π-π conjugation.

[0044] As can be seen from the comparison between Examples 1-2 and Comparative Example 2, in the depolymerization coupling adsorption process, the amount of adsorbent is insufficient, which cannot effectively adsorb all dye molecules, resulting in incomplete decolorization, interference from dye by-products, and a decrease in yield.

[0045] The comparison between Example 1 and Comparative Examples 3-4 shows that if too little template agent is added during the preparation of the adsorbent, the mesoporous structure of the adsorbent will be underdeveloped and the specific surface area will be small. If too much template agent is added, the channels will be blocked and disordered, both of which will result in poor adsorption performance and poor decolorization effect.

[0046] In summary, this invention achieves efficient coupling of depolymerization and decolorization by preparing a composite modified magnetic mesoporous silica adsorbent with a specific structure and optimizing process parameters, thereby obtaining regenerated BHET monomers with high yield, high purity and low impurities.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for coupled depolymerization and decolorization of waste polyester fabric, characterized in that: Includes the following steps: Step 1: The pretreated waste polyester fragments are mixed with depolymerization agent, catalyst and adsorbent. Under nitrogen atmosphere, depolymerization and decolorization coupling reaction is carried out. After the reaction is completed, separation and purification are performed to obtain decolorization and depolymerization liquid. The adsorbent is selected from aminated magnetic nanoparticles. The magnetic nanoparticles are composed of Fe3O4 core and mesoporous silica shell covering the surface of Fe3O4 core. Step 2: The decolorized and depolymerized solution is subjected to vacuum distillation and crystallization purification to obtain BHET monomer.

2. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The mass ratio of the adsorbent to the waste polyester fragments is 1:10~20.

3. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The adsorbent is prepared as follows: A. First, hexadecyltrimethylammonium bromide was mixed with Fe3O4 particles as a template agent for surface adsorption. Then, tetraethoxysilane was added dropwise under alkaline conditions to react and obtain silica-coated magnetic nanoparticles. B. The magnetic nanoparticles prepared in step A are calcined to obtain magnetic nanoparticles with a mesoporous shell structure. C. The magnetic nanoparticles prepared in step B are mixed with a modifier and refluxed under a nitrogen atmosphere to obtain the adsorbent, wherein the modifier is selected from p-phenylenediamine and / or 3-aminopropyltriethoxysilane.

4. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 3, characterized in that: In step A, the mass ratio of hexadecyltrimethylammonium bromide to Fe3O4 particles is 2~6:1; The mass ratio of the tetraethoxysilane to the Fe3O4 particles is 0.5~3:1; The reaction is carried out at a temperature of 50-60°C for 2-8 hours.

5. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 3, characterized in that: In step B, the roasting temperature is 300~600℃ and the time is 2~6h.

6. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 3, characterized in that: In step C, the mass ratio of the magnetic nanoparticles to the volume ratio of the modifier is 1~40g:1mL; The reflux reaction time is 6-12 hours.

7. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The depolymerizing agent is selected from at least one of methanol, ethylene glycol, and ethylenediamine, and the mass ratio of the depolymerizing agent to the waste polyester fragments is 2~6:

1.

8. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The catalyst is selected from at least one of ferric chloride, zinc acetate, and tetrabutyl titanate, and the mass of the catalyst accounts for 0.5 to 2.0% of the total mass of the waste polyester fragments.

9. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The parameters for the depolymerization and decolorization coupling reaction are: temperature 180~220℃, time 0.5~3h, and stirring rate 200~500rpm.

10. The method for depolymerization and decolorization coupling of waste polyester fabric according to claim 1, characterized in that: The temperature of the vacuum distillation is 100~150℃, and the absolute pressure is 10~50kPa; The crystallization purification temperature is 0~10℃, and the crystallization purification time is 2~5h.

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