A method for alcohol decolorization of waste polyester textiles

Abstract

The present invention belongs to the technical field of waste polyester regeneration, and particularly relates to a method for alcoholysis decolorization of waste polyester textiles. This method employs a modified ion exchange resin to adsorb and decolorize the alcoholysis product. This method reduces the loss rate of the alcoholysis product (DMT or BHET), effectively improving alcoholysis efficiency. The decolorized alcoholysis product can then be polymerized to produce regenerated polyester chips or directly spun into fibers.

Description

Technical Field

[0001] The invention belongs to the technical field of waste polyester regeneration, and in particular relates to an alcohol decolorization method for waste polyester textiles. Background Art

[0002] Polyester materials have been widely used in textiles and clothing, automotive interiors, civil engineering and other fields due to their high strength and good chemical stability.

[0003] Currently, there are three methods for recycling waste polyester textiles: physical, physicochemical, and chemical. Compared to physical and physicochemical methods, chemical recycling produces higher-quality recycled polyester with better product performance. The most mature and industrially successful chemical recycling method is alcoholysis (e.g., Chinese invention patents CN103145958A, CN103145959A, CN103147162A, and CN103145957A filed by the applicant). However, the alcoholysis products (BHET or DMT) of waste polyester are susceptible to coloration, primarily due to the alcoholysis process and color introduced into the raw materials (the inherent color of the waste polyester textile). Excessive color is a bottleneck hindering the industrialization of waste polyester alcoholysis technology. Therefore, decolorization of the alcoholysis products is particularly important.

[0004] Existing decolorization methods, such as oxidation, are effective but can easily lead to secondary pollution caused by oxidation of alcoholysis products. Membrane separation alone is costly and ineffective, requiring integration with other decolorization technologies. Currently, activated carbon adsorption is the most commonly used decolorization method. However, activated carbon also absorbs the target alcoholysis products (BHET or DMT) during the decolorization process, resulting in product loss. Furthermore, activated carbon lacks regeneration capabilities and is typically single-use, significantly increasing production costs. Therefore, finding a feasible, efficient, and economical method to effectively decolorize polyester alcoholysis products is an urgent challenge in polyester recycling.

[0005] A Chinese invention patent application (publication number: CN109574835A, publication date: April 5, 2019) discloses ion-modification of activated carbon with ferrous, ferric, or trivalent aluminum ions to improve its adsorption of dyes contained in BHET. This method can be used to decolorize ethylene terephthalate (BHET), a polyester alcoholysis product, improving BHET purity and facilitating polyester recycling. While the ion-modified activated carbon prepared in this patented method is regenerated and recyclable, it also adsorbs alcoholysis products, which can lead to product loss and reduced alcoholysis efficiency.

[0006] Ion exchange resins are insoluble, high-molecular-weight compounds with functional groups (active groups that exchange ions), a network structure, and are typically spherical particles. The full name of an ion exchange resin consists of the classification name, the name of the skeleton (or group), and the basic name. Currently, there is a huge demand for ion exchange resins in water treatment, accounting for approximately 90% of ion exchange resin production. They are used to remove various anions and cations from water. They are also used to adsorb colored substances, such as sugar solution decolorization, often using strong basic anion resins. A Chinese invention patent application (publication number: CN112174781A, publication date: January 5, 2021) discloses a method for decolorizing ethylene glycol, comprising the following steps: ethylene glycol recovered from the continuous alcoholysis of waste polyester to produce DMT is decolorized using a recycled adsorption resin. A Chinese invention patent application (publication number: CN114453032A, publication date: May 10, 2022) discloses an ion exchange resin, its preparation method, and its application in polyol dehydration reactions. The modified ion exchange resin contains a large number of B acid centers. After modification, L acid centers are introduced, which can be used as a catalyst in the polyol dehydration reaction, improving the hydrophobicity and electronic properties of the catalyst, thereby showing a better catalytic effect. However, there is currently no document publicly reporting the direct use of ion exchange resins for decolorization of waste polyester alcoholysis. In addition, if ion exchange resins are directly used for decolorization, DMT will still be adsorbed, which will still cause the loss of alcoholysis products and reduce alcoholysis efficiency. Summary of the Invention

[0007] In order to solve the above technical problems, the purpose of the present invention is to provide the application of modified ion exchange resin in the alcoholysis decolorization of waste polyester. This method uses modified ion exchange resin to adsorb and decolorize the alcoholysis product. The loss rate of the alcoholysis product (DMT or BHET) is low, which effectively improves the alcoholysis efficiency. After decolorization, the alcoholysis product can be used to prepare regenerated polyester chips or directly spun through polymerization reaction.

[0008] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0009] The invention discloses an application of modified ion exchange resin in decolorization of waste polyester alcohol. The basic resin skeleton of the modified ion exchange resin is quaternary ammonium salt styrene resin, and the modified ion is a metal cation.

[0010] Preferably, the waste polyester is decomposed by methanol decomposition process, and its decomposition products are mainly dimethyl terephthalate (DMT) and ethylene glycol; or the waste polyester is decomposed by ethylene glycol decomposition process, and its decomposition products are mainly ethylene terephthalate (BHET).

[0011] Preferably, the functional group of the modified ion exchange resin is -N + (CH3)2C2H4OH, - N+ (CH3)3 or -N + (CH3)4OH; the metal cation is Fe 3+ 、Fe 2+ 、Zn 2+ 、Al 3+ 、Ba 2+ and Ca 2+ A mixture of one or more.

[0012] Preferably, the preparation method of the modified ion exchange resin comprises the following steps:

[0013] 1) Soak the selected ion exchange resin in 3 volumes of 0.5 mol / L sulfuric acid and 0.5 mol / L sodium hydroxide solution respectively for 2 hours, then wash with deionized water until it is approximately neutral, and dry at 50°C for pretreatment.

[0014] 2) Blend the modifier, sodium chloride solution, and hydrochloric acid solution to final concentrations of 0.2-0.4 mol / L, 0.1-0.3 mol / L, and 0.3-0.5 mol / L, respectively. Add the pretreated ion exchange resin in a volume-to-mass ratio of 50:1 to 60:1. Ultrasonicate for 2-3 hours, filter, rinse with deionized water, and dry.

[0015] 3) Mix sodium hydroxide solution and sodium chloride solution, wherein the concentration of sodium hydroxide in the mixture is 0.8-1.0 mol / L and the concentration of sodium chloride is 0.4-0.6 mol / L, and then add the modified resin, wherein the volume mass ratio of the mixture to the modified resin is 30:1-40:1. After ultrasonic treatment for 2-3 hours, filter, wash with deionized water to a pH of about 8, and then dry.

[0016] Preferably, the modifier is a mixture of one or more of FeCl3, ZnCl2, AlCl3, BaCl2, and CaCl2.

[0017] Preferably, the modified ion exchange resin has an average pore diameter of 20 to 40 nm and an average pore specific surface area of 400 to 700 m 2 / g, pore volume 0.03~0.20cm 3 / g.

[0018] Furthermore, the present invention also discloses a method for alcohol decolorization of waste polyester textiles, which comprises the following steps:

[0019] 1) subjecting the pretreated waste polyester textiles to alcoholysis to obtain an alcoholysis solution;

[0020] 2) Filter the alcoholysis solution to remove insoluble impurities;

[0021] 3) passing the filtered alcoholysis solution into a multi-stage resin tank for decolorization; the multi-stage resin tank is provided with the modified ion exchange resin;

[0022] 4) After decolorization, the solvent is removed from the alcoholysis solution and then the polymerization reaction is carried out.

[0023] Preferably, the alcoholysis of the waste polyester textiles adopts a methanol alcoholysis process, and its alcoholysis products are mainly dimethyl terephthalate (DMT) and ethylene glycol; or the alcoholysis of the waste polyester textiles adopts an ethylene glycol alcoholysis process, and its alcoholysis products are mainly ethylene terephthalate (BHET).

[0024] Preferably, the decolorization temperature in step 3) is 15-55° C.; and the alcoholysis solution is retained in the multi-stage resin tank for 4-6 hours.

[0025] Preferably, in step 3), three-stage adsorption kettles are connected in series for decolorization, the resin adsorption capacity of the first adsorption kettle is controlled at 80-100 mg / g, the resin adsorption capacity of the second adsorption kettle is controlled at 50-80 mg / g, and the resin adsorption capacity of the third adsorption kettle is controlled at 20-60 mg / g.

[0026] The present invention has the following advantages:

[0027] 1) Compared with the currently widely used activated carbon adsorption, the use of ion exchange resin as an adsorbent has a low loss rate of alcoholysis products (DMT or BHET), which is less than 7%, effectively improving the alcoholysis efficiency.

[0028] 2) Using resin as adsorbent, it can effectively remove unsaturated compounds with double bonds such as aldehydes, ethers, and sulfides during the alcoholysis process, with high decolorization efficiency.

[0029] 3) As a decolorizing agent, the resin can be regenerated and recycled through an eluent. The adsorbed resin can be reused after being eluted with an eluent. The resin can be recycled 5 to 10 times according to actual usage needs; it is more green and economical and also reduces production costs.

[0030] 4) Through metal ion modification, the adsorption sites of ion exchange resin are increased, the adsorption capacity is improved, and the decolorization effect is enhanced. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0032] The modified ion exchange resin preparation process of the present invention:

[0033] 1) Immerse the ion exchange resin in 3 volumes of 0.5 mol / L sulfuric acid and 0.5 mol / L sodium hydroxide solution, stirring for 2 hours, then wash with deionized water until it is approximately neutral, and dry at 50°C for pretreatment.

[0034] 2) A modifier (one or a mixture of FeCl3, ZnCl2, ALCl3, BaCl2, CaCl2), sodium chloride solution, and hydrochloric acid solution are mixed to a final concentration of 0.2-0.4 mol / L, 0.1-0.3 mol / L, and 0.3-0.5 mol / L, respectively. The pretreated ion exchange resin is then added at a volume-to-mass ratio of 50:1 to 60:1. After ultrasonic treatment for 2-3 hours, the mixture is filtered, washed with deionized water, and then dried.

[0035] 3) Mix sodium hydroxide solution and sodium chloride solution, wherein the concentration of sodium hydroxide in the mixture is 0.8-1.0 mol / L and the concentration of sodium chloride is 0.4-0.6 mol / L, and then add the modified resin, wherein the volume mass ratio of the mixture to the modified resin is 30:1-40:1. After ultrasonic treatment for 2-3 hours, filter, wash with deionized water to a pH of about 8, and then dry.

[0036] Example 1

[0037] The recycled waste polyester textiles were sorted and then densified. Methanol was used as the alcoholysis solution. The alcoholysis products were mainly dimethyl terephthalate (DMT) and ethylene glycol. The alcoholysis solution was filtered to remove insoluble impurities and then cooled to 25 ° C. It was passed into the three-stage resin adsorption kettle. The resin was a strong alkaline anion exchange resin with a functional group of -N + (CH3)3 was modified with FeCl3. The modification process was the same as the above-mentioned modified ion exchange resin preparation process. The average pore diameter of the modified resin was 29.12 nm, and the average pore specific surface area was 565 m 2 / g, pore volume 0.0484cm 3 / g, the alcoholysis solution was retained in the resin tank for 6 h, and the DMT loss rate and color value after decolorization were calculated as shown in Table 1.

[0038] The modified ion exchange resin after adsorption is eluted with hydrochloric acid (water and ethanol 1:1.5), in which the mass concentration of hydrochloric acid is 10-20%. It can be recycled, and the decolorization rate of DMT by the modified ion exchange resin after 5 repeated adsorptions can still reach 85.7%.

[0039] Example 2

[0040] The recycled waste polyester textiles are sorted and then densified. Ethylene glycol is used as the alcoholysis liquid. The alcoholysis product is mainly ethylene terephthalate (BHET). The alcoholysis liquid is filtered to remove insoluble impurities, then cooled to 25°C and passed into a three-stage resin adsorption kettle. The resin is an ion exchange resin. A strong alkaline anion exchange resin with a functional group of -N + (CH3)3 was modified with FeCl3. The modification process was the same as the above-mentioned modified ion exchange resin preparation process. The average pore diameter of the modified resin was 29.12 nm, and the average pore specific surface area was 565 m 2 / g, pore volume 0.0484cm 3 / g, the alcoholysis solution was retained in the resin tank for 6 h, and the BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0041] Example 3

[0042] The recycled waste polyester textiles are sorted and then densified. Ethylene glycol is used as the alcoholysis liquid. The alcoholysis product is mainly ethylene terephthalate (BHET). The alcoholysis liquid is filtered to remove insoluble impurities, then cooled to 25°C and passed into a three-stage resin adsorption kettle. The resin is an ion exchange resin. A strong alkaline anion exchange resin with a functional group of -N + (CH3)2C2H4OH was modified with BaCl2. The modification process was the same as the above-mentioned modified ion exchange resin preparation process. The average pore diameter of the modified resin was 25.34 nm, and the average pore specific surface area was 638 m 2 / g, pore volume 0.0625cm 3 / g, the alcoholysis solution was retained in the resin tank for 6 h, and the BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0043] Example 4

[0044] The recycled waste polyester textiles are sorted and then densified. Ethylene glycol is used as the alcoholysis liquid. The alcoholysis product is mainly ethylene terephthalate (BHET). The alcoholysis liquid is filtered to remove insoluble impurities, then cooled to 50℃ and passed into the resin tank. The resin is an ion exchange resin. Strong alkaline anion exchange resin is selected, and the functional group is -N + (CH3)3 was modified with FeCl3. The modification process was the same as the above-mentioned modified ion exchange resin preparation process. The average pore diameter of the modified resin was 29.12 nm, and the average pore specific surface area was 565 m 2 / g, pore volume 0.0484cm 3 / g, the alcoholysis solution was retained in the resin tank for 4h, and the BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0045] Example 5

[0046] The recycled waste polyester textiles are sorted and then densified. Ethylene glycol is used as the alcoholysis liquid. The alcoholysis product is mainly ethylene terephthalate (BHET). The alcoholysis liquid is filtered to remove insoluble impurities, then cooled to 25°C and passed into the resin tank. The resin is an ion exchange resin. A strong alkaline anion exchange resin with a functional group of -N + (CH3)3 was modified with FeCl3. The modification process was the same as the above-mentioned modified ion exchange resin preparation process. The resin used was a regenerated resin after being used four times and regenerated with an eluent. The alcoholysis solution was retained in the resin tank for 6 hours. The BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0047] Comparative Example 1

[0048] The recycled waste polyester textiles were sorted and densified. Ethylene glycol was used as the alcoholysis liquid. The alcoholysis product was mainly ethylene terephthalate (BHET). The alcoholysis liquid was filtered to remove insoluble impurities, then cooled to 25°C and passed into an activated carbon adsorption tank. The alcoholysis liquid was retained in the adsorption tank for 6 hours. The BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0049] Comparative Example 2

[0050] The recycled waste polyester textiles are sorted and then densified. Ethylene glycol is used as the alcoholysis liquid. The alcoholysis product is mainly ethylene terephthalate (BHET). The alcoholysis liquid is filtered to remove insoluble impurities, then cooled to 25°C and passed into a three-stage resin adsorption kettle. The resin is an ion exchange resin. A strong alkaline anion exchange resin with a functional group of -N + (CH3)3, ion exchange resin is not modified, the average pore diameter of the resin is 28.22nm, and the average pore specific surface area is 588m 2 / g, pore volume 0.0524cm 3 / g, the alcoholysis solution was retained in the resin tank for 6 h, and the BHET loss rate and color value after decolorization were measured and shown in Table 1.

[0051] Comparative Example 3

[0052] The recycled waste polyester textiles were sorted and then densified. Ethylene glycol was used as the alcoholysis solution. The alcoholysis product was mainly ethylene terephthalate (BHET). The alcoholysis solution was filtered to remove insoluble impurities, then cooled to 25°C and passed into a three-stage modified activated carbon adsorption kettle. The modified activated carbon used was the trivalent iron ion modified activated carbon prepared in Example 6 of the Chinese invention patent application (publication number: CN109574835A, publication date: 2019-04-05). The alcoholysis solution was retained in the resin tank for 6 hours. The BHET loss rate and color value after decolorization are shown in Table 1.

[0053] Table 1 Loss rate and color value of alcoholysis product after decolorization

[0054]

[0055] The above is a description of the embodiments of the present invention. The above description of the disclosed embodiments will enable professionals in the field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of modified ion exchange resin in decolorization of waste polyester alcohol, wherein the basic resin skeleton of the modified ion exchange resin is a quaternary ammonium salt styrene resin, and the modified ion is a metal cation; the metal cation is Fe 3+ and Ba 2+ One or a mixture of two.

2. The use according to claim 1, characterized in that The waste polyester is decomposed by using a methanol decomposition process, and its decomposition products are mainly dimethyl terephthalate and ethylene glycol; or the waste polyester is decomposed by using an ethylene glycol decomposition process, and its decomposition products are mainly ethylene terephthalate.

3. The use according to claim 1, characterized in that The functional group of the modified ion exchange resin is -N + (CH3)2C2H4OH or - N + (CH3)3.

4. The use according to any one of claims 1 to 3, characterized in that: The preparation method of the modified ion exchange resin comprises the following steps: 1) Soak the selected ion exchange resin in 3 volumes of 0.5 mol / L sulfuric acid and 0.5 mol / L sodium hydroxide solution respectively for 2 hours, then wash with deionized water until neutral, dry at 50°C, and pre-treat for later use; 2) Blend the modifier, sodium chloride solution, and hydrochloric acid solution to final concentrations of 0.2-0.4 mol / L, 0.1-0.3 mol / L, and 0.3-0.5 mol / L, respectively. Add the pretreated ion exchange resin in a volume-to-mass ratio of 50:1 to 60:

1. Ultrasonicate for 2-3 hours, filter, rinse with deionized water, and dry. 3) Mix sodium hydroxide solution and sodium chloride solution, wherein the concentration of sodium hydroxide in the mixture is 0.8-1.0 mol / L and the concentration of sodium chloride is 0.4-0.6 mol / L, and then add the modified resin, wherein the volume mass ratio of the mixture to the modified resin is 30:1-40:

1. After ultrasonic treatment for 2-3 hours, filter, wash with deionized water to a pH of 8, and then dry.

5. The use according to claim 4, characterized in that The modifier is FeCl3, BaCl2 or a mixture of the two.

6. The use according to any one of claims 1 to 3, characterized in that: The average pore size of the modified ion exchange resin is 20-40 nm, and the specific surface area is 400-700 m 2 / g, pore volume 0.03~0.20cm 3 / g.

7. A method for alcohol decolorization of waste polyester textiles, characterized in that: The method comprises the following steps: 1) subjecting the pretreated waste polyester textiles to alcoholysis to obtain an alcoholysis solution; 2) Filter the alcoholysis solution to remove insoluble impurities; 3) passing the filtered alcoholysis solution into a multi-stage resin tank for decolorization; the multi-stage resin tank is provided with the modified ion exchange resin according to any one of claims 1, 3, 4, 5 and 6; 4) After decolorization, the solvent is removed from the alcoholysis solution and then the polymerization reaction is carried out.

8. The method according to claim 7, characterized in that The alcoholysis of waste polyester textiles adopts a methanol alcoholysis process, and its alcoholysis products are mainly dimethyl terephthalate and ethylene glycol; or the alcoholysis of waste polyester textiles adopts an ethylene glycol alcoholysis process, and its alcoholysis products are mainly ethylene terephthalate.

9. The method according to claim 7, characterized in that Step 3) The decolorization temperature is 15-55°C; the alcoholysis solution is retained in the multi-stage resin tank for 4-6 hours.

10. The method according to claim 7, characterized in that Step 3) Decolorization is performed using three adsorption kettles in series, with the resin adsorption capacity of the first adsorption kettle controlled at 80-100 mg / g, the resin adsorption capacity of the second adsorption kettle controlled at 50-80 mg / g, and the resin adsorption capacity of the third adsorption kettle controlled at 20-60 mg / g.

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