Process for the recovery of polyester fabrics with ionic liquid catalysts

Abstract

The application discloses a method for recycling polyester fabric by using an ionic liquid catalyst, and comprises the following steps: providing a recycled polyester fabric; chemically depolymerizing the recycled polyester fabric by using a chemical depolymerization solution to form a depolymerization product containing bis-hydroxyethyl terephthalate (BHET), wherein the chemical depolymerization solution is used to chemically depolymerize the recycled polyester fabric in the presence of a depolymerization catalyst, and the depolymerization catalyst is an ionic liquid catalyst. The method has the advantages of high depolymerization efficiency, high BHET yield and easy recovery of the catalyst.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for recycling polyester fabric, in particular, to a method for recycling polyester fabric using an ionic liquid catalyst. BACKGROUND

[0002] In the prior art, the chemical recycling method of polyester fabric (PET fabric) is mainly to use a chemical depolymerization liquid (such as ethylene glycol) to chemically depolymerize the polyester fabric to form a depolymerization product, and the depolymerization product mainly contains bis(2-hydroxyethyl) terephthalate (abbreviated as BHET). However, the process of the above-mentioned chemical recycling method must go through a complex purification program to remove impurities such as dyes originally present in the polyester fabric, and then the BHET can be repolymerized to form high-quality regenerated polyester particles (r-PET).

[0003] In the above-mentioned chemical recycling method of polyester fabric, the existing chemical depolymerization method is mainly alcoholysis technology, which usually uses organic metal as a catalyst, such as zinc acetate, organic titanium metal, or organic antimony metal. However, the process of using an organic metal catalyst to catalyze the depolymerization reaction to form BHET has the disadvantages of many side reactions and the catalyst cannot be recycled. Therefore, the BHET formed by this method to make regenerated polyester particles (r-PET) has the disadvantages of poor quality and high recycling cost; or using nanoscale catalysts has good depolymerization properties, but it is not easy to recycle the catalyst by solid-liquid separation methods (such as sedimentation, filtration), causing difficulties in mass production.

[0004] U.S. Patent No. 9,255,194 proposes a method for depolymerizing polyester fabric. The method proposed in this patent uses an organic compound with a low boiling point as a catalyst, which can be recovered by evaporation. Compared with existing organic metal catalysts, this method has the advantage that the catalyst can be recycled. However, the purity of the BHET formed by this method is still low. Therefore, the regenerated polyester particles (r-PET) formed by this method still have poor quality compared to virgin polyester particles, and this method also has the disadvantage of high recycling cost.

[0005] Patent CN100344604C proposes a method for depolymerizing polyester fabric. The method proposed in this patent chemically depolymerizes polyester fabric. However, the BHET formed by the method using an organic metal catalyst to catalyze the depolymerization reaction has the disadvantages of many side reactions and the catalyst cannot be recycled. Therefore, the BHET formed by this method to make regenerated polyester particles (r-PET) also has the disadvantages of poor quality and high recycling cost.

[0006] Therefore, the inventor believes that the above-mentioned defects can be improved, and after years of research and application of scientific principles, finally proposes the present application which is reasonable in design and effectively improves the above-mentioned defects. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a method for recycling polyester fabric using an ionic liquid catalyst to solve the problems of the prior art.

[0008] To solve the above technical problems, the present application provides a method for recycling polyester fabric using an ionic liquid catalyst, which includes: performing a preparation operation, which includes: providing a recycled polyester fabric; performing a depolymerization operation, which includes: chemically depolymerizing the recycled polyester fabric using a chemical depolymerization solution to form a depolymerization product mainly containing bis-hydroxyethyleneterephthalate (BHET); wherein the depolymerization operation is performed on the recycled polyester fabric in the presence of a depolymerization catalyst, and the depolymerization catalyst is an ionic liquid catalyst; and performing a separation operation, which includes: separating the ionic liquid catalyst by centrifugation and / or filtration to collect the ionic liquid catalyst.

[0009] Preferably, in the depolymerization operation, the chemical depolymerization solution is ethylene glycol (EG), and the chemical depolymerization solution is heated to a depolymerization temperature of 180-260°C to chemically depolymerize the recycled polyester fabric.

[0010] Preferably, in the depolymerization operation, the ionic liquid catalyst includes a substrate and an ionic liquid grafted onto the substrate, and a silane coupling agent such as chloropropyl trimethoxysilane is used as a bridge to prepare the ionic liquid catalyst in solid state. First, the silane coupling agent is acidized, then grafted with the substrate (such as carbon, silicon, iron, nickel, and / or cobalt material), and then grafted with the ionic liquid in the presence of a base.

[0011] Preferably, in the ionic liquid catalyst, the grafted amount of the ionic liquid onto the substrate is 10 4 to 10 18 branches of the ionic liquid per gram of the substrate.

[0012] Preferably, the substrate of the ionic liquid catalyst includes carbon, silicon, iron, nickel, and / or cobalt, and the average particle size of the substrate is between 2 microns and 800 microns. The substrate with the above-mentioned average particle size can be separated by mass-produced centrifugal and filtration equipment, and mass production methods include sedimentation and filter bag type filter separation.

[0013] Preferably, in the ionic liquid catalyst, the ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (BMI2ZnCl4), 1-butyl-3-methylimidazolium tetrachloroironate (BMI2FeCl4), 1-butyl-3-methylimidazolium tetrachlorocobaltate (BMI2CoCl4), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF4).

[0014] Preferably, in the separation operation, the ionic liquid catalyst is separated from the depolymerized product by sedimentation due to the high specific gravity of the ionic liquid catalyst and a filtering device, and a catalyst recovery rate of the ionic liquid catalyst is not less than 95%.

[0015] Preferably, after the separation operation, the method for recycling polyester fabric using ionic liquid catalyst further comprises: performing a purification operation to obtain purified ethylene terephthalate from the depolymerized product; and performing a granulation operation to cause the purified ethylene terephthalate to repolymerize and then form regenerated polyester particles (r-PET).

[0016] Preferably, the purification operation comprises an adsorption procedure, which comprises: dissolving the ethylene terephthalate in water to form an aqueous liquid; and adding an activated carbon material and / or an ion exchange resin to the aqueous liquid to cause the activated carbon material and / or the ion exchange resin to adsorb impurities originally present in the recycled polyester fabric.

[0017] Preferably, the aqueous liquid is heated to a liquid temperature of between 70°C and 150°C to increase the solubility of the ethylene terephthalate in water and to enable the activated carbon material and / or the ion exchange resin to adsorb the impurities at the liquid temperature.

[0018] Preferably, after the adsorption procedure, the purification operation further comprises a crystallization procedure comprising cooling the aqueous liquid from the liquid temperature between 70°C to 150°C to a crystallization temperature between 5°C to 25°C to crystallize the ethylene terephthalate from the aqueous liquid, thereby obtaining purified ethylene terephthalate.

[0019] Preferably, the r-PET formed by the granulation operation has an L value no less than 60, an a value between -2 to 2, and a b value between -6 to 6, and the r-PET has a recovery rate no less than 90%.

[0020] The method for recycling polyester fabric using ionic liquid catalyst provided by the present application can improve the recovery quality of r-PET by "providing a recycled polyester fabric; chemically depolymerizing the recycled polyester fabric using a chemical depolymerization liquid to form a depolymerization product containing ethylene terephthalate (BHET), wherein the chemical depolymerization liquid is chemically depolymerized on the recycled polyester fabric in the presence of a depolymerization catalyst, and the depolymerization catalyst is an ionic liquid catalyst; and performing a separation operation comprising separating the ionic liquid catalyst by centrifugation and / or filtration to collect the ionic liquid catalyst".

[0021] Furthermore, the method for recycling polyester fabric using ionic liquid catalyst provided by the present application has the advantages of high depolymerization efficiency, easy mass production, and low cost.

[0022] For a more complete understanding of the features and technical content of the present application, please refer to the following detailed description of the present application and the drawings provided, which are provided for reference and illustration only, and are not intended to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The flowchart of the method for recycling polyester fabric using ionic liquid catalyst provided by the present application is shown in the figure. DETAILED DESCRIPTION

[0024] The present application will be described with respect to the following example, which demonstrates the advantages and benefits of the present application. The present application can be used in other different embodiments and the details described herein can be modified in a variety of ways and can be applied with other applications without departing from the spirit and scope of the present application. In addition, the drawings of the present application are merely simple schematic illustrations and are not drawn to scale. The following embodiments will further illustrate the technical contents of the present application, but the disclosed contents are not intended to limit the scope of the present application.

[0025] It should be understood that although the terms "first", "second", etc. can be used herein to describe various components, these components should not be limited by these terms. These terms are mainly used to distinguish one component from another component. In addition, the term "or" used herein can include any one or a combination of the associated listed items.

[0026] [Method for recycling polyester fabric using ionic liquid catalyst]

[0027] In the prior art, the main method for depolymerizing polyester fabric is to use an organic metal or other organic matter as a catalyst. The depolymerization product formed by the above method mainly includes bis-hydroxyethyl terephthalate (BHET). Then, the depolymerization product is adsorbed by activated carbon material or ion exchange resin to remove impurities such as dyes, or BHET is distilled out by distillation.

[0028] However, the above-mentioned process of using a catalyst to catalyze the depolymerization reaction to form BHET has the disadvantages of many side reactions and the catalyst cannot be recovered. Therefore, the BHET formed by the above-mentioned method has the disadvantages of poor quality and high recovery cost when manufacturing recycled polyester particles (r-PET).

[0029] To solve the above technical problems, please refer to Figure 1 The embodiment of the present application provides a method for recycling polyester fabric using an ionic liquid catalyst, which can improve the recycling quality of recycled polyester particles (r-PET) and has the advantage of low recycling cost. The method for recycling polyester fabric using an ionic liquid catalyst includes steps S110, S120, S130, S140, and S150. It should be pointed out that the order of each step and the actual operation method in the present embodiment can be adjusted according to the needs and is not limited to the present embodiment.

[0030] The step S110 comprises performing a preparation operation. The preparation operation comprises providing a recycled polyester fabric. The recycled polyester fabric has impurities attached thereto, and the impurities can be, for example, dyes and / or water repellents, but the present application is not limited thereto.

[0031] For example, the recycled polyester fabric can have a color, for example, by dyeing. Furthermore, the recycled polyester fabric can have a water repellent function, for example, by water repellent treatment. The dyes can be, for example, at least one of natural dyes and synthetic dyes, or the dyes can be, for example, at least one of physical dyes and chemical dyes. The water repellents can be, for example, water repellents containing silicon (Si), water repellents containing fluorine (F), water repellents containing fluorine and silicon, or water-based polyurethane (PU) water repellents, but the present application is not limited thereto.

[0032] In an embodiment of the present application, the recycled polyester fabric is dyed to have an L value greater than 0 and not greater than 30, that is, the recycled polyester fabric has a darker color, but the present application is not limited thereto. It should be noted that the L value is a parameter value representing brightness (or whiteness of color) in the Lab color space.

[0033] In an embodiment of the present application, the recycled polyester fabric can also be an undyed polyester fabric. That is, the recycled polyester fabric can also be, for example, not attached with dyes, and present the original color of the polyester fabric.

[0034] The step S120 comprises performing a de-polymerization operation. The de-polymerization operation comprises chemically de-polymerizing the recycled polyester fabric by using a chemical de-polymerization solution to form a de-polymerization product. The de-polymerization product mainly comprises bis-2-hydroxylethyl terephthalate (BHET). Furthermore, the de-polymerization product also comprises oligomers, the chemical de-polymerization solution, and the impurities.

[0035] More specifically, the chemical depolymerization solution can be, for example, ethylene glycol (EG), and the method of chemically depolymerizing the recycled polyester fabric can be, for example, an ethylene glycol depolymerization method (or ethylene glycol glycolysis method). Accordingly, the recycled polyester fabric can be depolymerized into a depolymerization product mainly containing bis-hydroxyethyleneterephthalate (BHET). Furthermore, the depolymerization product further contains oligomers formed by depolymerization of the polyester fabric, the chemical depolymerization solution (e.g., ethylene glycol) used for the depolymerization reaction, and impurities originally present in the recycled polyester fabric.

[0036] It is worth mentioning that bis-hydroxyethyleneterephthalate (BHET) is an intermediate of pure terephthalic acid (PTA) and ethylene glycol (EG). Furthermore, bis-hydroxyethyleneterephthalate can also be used as a raw material for synthesizing polyester (PET), and can also form a polyester copolymer with other monomers.

[0037] Further, in an embodiment of the present application, the chemical depolymerization solution is used to chemically depolymerize the recycled polyester fabric in the presence of a depolymerization catalyst. The depolymerization catalyst can be used to assist in reducing the activation energy of the chemical depolymerization solution for chemically depolymerizing the polyester fabric. In other words, the depolymerization catalyst can assist in increasing the reaction rate of the chemical depolymerization solution for chemically depolymerizing the recycled polyester fabric.

[0038] Further, in order to make the depolymerization catalyst easier to be recycled after use, the depolymerization catalyst of the present embodiment is an ionic liquid catalyst. The substrate of the ionic liquid catalyst contains carbon, silicon, iron, nickel, and / or cobalt. The particle size of the substrate is between 2 microns and 800 microns. Furthermore, the ionic liquid catalyst is dispersed in the chemical depolymerization solution in a micron-sized particle size, thereby effectively catalyzing the depolymerization reaction of the recycled polyester fabric.

[0039] In an embodiment of the present application, the chemical depolymerization solution is heated to a depolymerization temperature to chemically depolymerize the recycled polyester fabric. The depolymerization temperature is preferably between 180°C and 260°C, and more preferably between 210°C and 240°C, but the present application is not limited thereto. At the above depolymerization temperature, the efficiency of the chemical depolymerization solution for chemically depolymerizing the recycled polyester fabric can be more effectively improved, and the ionic liquid catalyst can play a greater catalytic role.

[0040] In an embodiment of the present application, the ionic liquid catalyst can be, for example, a substrate grafted with ionic liquid, comprising: a substrate and ionic liquid grafted on the substrate, the steps comprising: first acidizing the surface of the substrate comprising carbon, silicon, iron, nickel, and / or cobalt to form OH functional groups, synthesizing with Silane and OH groups, and then synthesizing ionic liquid with the end of Silane. The substrate is used to separate the solid-liquid after the ionic liquid catalyst is used up, so that the ionic liquid catalyst can be recycled. Furthermore, the ionic liquid is used to catalyze the chemical depolymerization reaction rate of the chemical depolymerization solution on the recycled polyester fabric in the depolymerization operation. It should be noted that the substrate comprises non-magnetic materials such as carbon and / or silicon, and / or magnetic materials such as iron, nickel, and / or cobalt.

[0041] In an embodiment of the present application, the substrate is a particulate material with a micron-level size. The average particle size of the substrate is preferably between 2 microns and 800 microns, and more preferably between 5 microns and 200 microns, but the present application is not limited thereto.

[0042] In an embodiment of the present application, the number of ionic liquid grafts on the substrate in the ionic liquid catalyst is preferably 10 4 to 10 18 grams of ionic liquid per gram of substrate, and more preferably 10 5 to 10 15 grams of ionic liquid, but the present application is not limited thereto.

[0043] In an embodiment of the present application, the PET weight ratio of the ionic liquid catalyst to the chemical depolymerization solution is preferably between 1:100-1000. That is, in the depolymerization operation, the PET weight of the chemical depolymerization solution is 100 to 1000 times the weight of the ionic liquid catalyst, but the present application is not limited thereto.

[0044] In an embodiment of the present application, the ionic liquid in the ionic liquid catalyst is at least one selected from the group consisting of 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (BMI2ZnCl4), 1-butyl-3-methylimidazolium tetrachloroironate (BMI2FeCl4), 1-butyl-3-methylimidazolium tetrachlorocobaltate (BMI2CoCl4), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF4), but the present application is not limited thereto. The above-mentioned ionic liquid has a good effect on catalytic recovery of polyester fabric.

[0045] In an embodiment of the present application, the substrate in the ionic liquid catalyst is at least one selected from the group consisting of iron microparticle, nickel microparticle, carbon microparticle, silicon microparticle, and cobalt microparticle.

[0046] The step S130 comprises performing a separation operation, which comprises separating the ionic liquid catalyst by a centrifugal method and / or a filtration method to collect the ionic liquid catalyst. In the separation operation, the ionic liquid catalyst is separated from the depolymerization product by sedimentation due to its high specific gravity and filtration separation, and the catalyst recovery rate of the ionic liquid catalyst is not less than 95%.

[0047] Alternatively, the step S130 comprises performing a centrifugal sedimentation and filtration operation. The centrifugal operation comprises separating the depolymerization liquid and the catalyst by a cyclone separator, and then separating the catalyst from the depolymerization liquid by a filtration device to collect the ionic liquid catalyst.

[0048] More specifically, in the centrifugal sedimentation and filtration operation, the ionic liquid catalyst can be separated from the depolymerization product by specific gravity difference, and the catalyst recovery rate is preferably not less than 70%; then, the depolymerization liquid is separated from the residual catalyst by a filtration device. Preferably, the catalyst recovery rate of the ionic liquid catalyst is not less than 95%, and more preferably not less than 96%.

[0049] In an embodiment of the present application, the depolymerization product and the ionic liquid catalyst are separated by natural gravity, centrifugal gravity, etc., and the filtrate is separated by filter pressing, centrifugal filtration, etc., and then the ionic liquid catalyst is collected, but the present application is not limited thereto.

[0050] According to the above configuration, the process of forming purified terephthalic acid glycol ester (BHET) by using the ionic liquid catalyst to catalyze the depolymerization reaction has the advantages of less side reaction, high conversion rate, high selectivity, and recyclable catalyst, etc. Therefore, the regenerated polyester particles (r-PET) formed subsequently can have higher recycling quality and lower recycling cost.

[0051] The step S140 comprises: performing a purification operation to obtain purified terephthalic acid glycol ester (BHET) from the depolymerization product.

[0052] In an embodiment of the present application, the purification operation comprises an adsorption procedure and a crystallization procedure in sequence.

[0053] Further, the adsorption procedure comprises: dissolving the terephthalic acid glycol ester in water to form an aqueous liquid; and adding an activated carbon material and / or an ion exchange resin to the aqueous liquid, so that the activated carbon material and / or the ion exchange resin adsorb impurities (such as dyes) originally present in the recycled polyester fabric.

[0054] Preferably, the aqueous liquid is heated to a liquid temperature of 70-150°C to increase the solubility of the terephthalic acid glycol ester in water, and the activated carbon material and / or the ion exchange resin can adsorb the impurities at the liquid temperature, but the present application is not limited thereto.

[0055] Further, the crystallization procedure comprises: cooling the aqueous liquid from the liquid temperature between 70°C and 150°C to a crystallization temperature between 5°C and 25°C to crystallize the ethylene terephthalate from the aqueous liquid, thereby obtaining the purified ethylene terephthalate.

[0056] The step S150 comprises: performing a granulation operation to make the purified ethylene terephthalate re-polymerize, and then form regenerated polyester particles (r-PET). For example, the regenerated polyester particles can be formed by performing a granulation operation on the polymerized ethylene terephthalate by a single-screw granulator or a double-screw granulator.

[0057] In an embodiment of the present application, the regenerated polyester particles (r-PET) formed by the granulation operation have an L value not less than 60, an a value between -2 and 2, and a b value between -6 and 6, and the regenerated polyester particles have a recovery rate not less than 90%.

[0058] [Experimental data and test results]

[0059] To verify the method for recycling polyester fabric provided by the embodiments of the present application using an ionic liquid catalyst, which has good recycling effect and improved yield, the following will be illustrated by Examples 1 to 5 and Comparative Examples 1 to 5.

[0060] Example 1:

[0061] The activated carbon (average particle size 61.3 um, particle size range 5-284 um), chloropropyl trimethoxysilane, and 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) synthesized solid ionic liquid catalyst is used as a depolymerization catalyst (referred to as SDX1).

[0062] 1 kg of PET fabric, 6 kg of ethylene glycol, and 20 g of ionic liquid (SDX1) catalyst are put into a 10 L three-neck glass bottle and heated to 190°C, and the PET fabric is depolymerized by stirring for 3 hours. The reaction liquid is cooled to 120°C, and then centrifuged at 300 rpm for 1 minute. The upper layer of the reaction liquid is taken out to separate from the catalyst. The upper layer of the reaction liquid is filtered with 1 um filter cloth, and the catalyst is separated from the reaction liquid. The catalyst separated in two stages is recycled, and the catalyst recovery rate is 96.7%.

[0063] Under an absolute pressure of 3 torr, the reaction liquid is heated from 120°C to 170°C, and excess EG and other substances are distilled off, so that the residual amount of EG in the reaction liquid is <5%.

[0064] The reaction solution was cooled to 90°C, then 7 kg of water was added, and the temperature was raised to 90°C to dissolve the BHET in water. 30 g of activated carbon was added, and the temperature was maintained at 90°C for 1 hr to adsorb impurities such as dyes. The activated carbon was then removed by filtration.

[0065] The BHET-containing aqueous solution at 90°C was cooled to 50°C with cooling water to precipitate BHET crystals. The cooling rate was 6°C / min, and the solid BHET was removed by filtration. The liquid mother liquor was subjected to a second-stage cooling crystallization. The BHET-containing aqueous solution at 50°C was cooled to 5°C with chilled water to precipitate BHET crystals. The cooling rate was 0.2°C / min, and the solid BHET was removed by filtration.

[0066] After the first-stage and second-stage BHET were mixed and dried, the BHET was repolymerized into r-PET at 270°C and 0.5 torr. The r-PET quality was L=61%, a=0.8, and b=3.5, and the yield was 93.0%. The catalyst recovery rate was 96.7%.

[0067] Example 2:

[0068] Example 1, using silicon (average particle size 55.4 um, particle size range 6-275 um), chloropropyltrimethoxysilane, and 1-butyl-3-methylimidazolium hexafluorophosphate to synthesize a solid ionic liquid catalyst as the depolymerization catalyst (SDX2). The remaining conditions were the same as in Example 1.

[0069] The r-PET quality was L=62%, a=0.9, and b=4.6, and the yield was 95.4%. The catalyst recovery rate was 98.4%.

[0070] Example 3:

[0071] Example 1, using nickel (average particle size 64.3 um, particle size range 4-223 um), chloropropyltrimethoxysilane, and 1-butyl-3-methylimidazolium hexafluorophosphate to synthesize a solid ionic liquid catalyst as the depolymerization catalyst (SDX3). The remaining conditions were the same as in Example 1.

[0072] The r-PET quality was L=63%, a=0.6, and b=4.8, and the yield was 96.4%. The catalyst recovery rate was 99.2%.

[0073] Example 4:

[0074] Example 1, using the recovered catalyst (19.34 g) from Example 1 and adding 0.66 g of SDX1 catalyst as the depolymerization catalyst. The remaining conditions were the same as in Example 1.

[0075] The r-PET quality was L=63%, a=0.5, and b=4.9, and the yield was 96.1%. The catalyst recovery rate was 96.5%.

[0076] Example 5:

[0077] The same as example 4, the catalyst (19.30 g) recovered from example 4 was added with SDX1 catalyst (0.70 g) as depolymerization catalyst. The rest of the conditions were the same as example 1.

[0078] r-PET quality L = 62%, a = 0.3, b = 4.7, yield 96.3%. Catalyst recovery rate 96.7%.

[0079] Comparative example 1:

[0080] Take 1 kg of PET fabric, 6 kg of ethylene glycol and 20 g of zinc acetate catalyst, put it into a 10 L three-necked glass bottle and heat to 190°C, stir for 6 hr, then heat to maintain boiling (195-210) of the reaction liquid, distill the excess EG, and make the residual amount of EG in the reaction liquid <5%.

[0081] After cooling the reaction liquid to 90°C, add 7 kg of water, and heat to 90°C to dissolve BHET in water, add 30 g of activated carbon, and stir at 90°C for 1 hr to adsorb impurities such as dyes, then remove the activated carbon by filtration.

[0082] The BHET-containing aqueous solution at 90°C is cooled to 50°C with cold water to precipitate BHET crystals, the cooling rate is 6°C / min, and the solid BHET is removed by filtration; the liquid mother liquor will be subjected to a second stage of cooling crystallization.

[0083] The BHET-containing aqueous solution at 50°C is cooled to 5°C with chilled water to precipitate BHET crystals, the cooling rate is 0.2°C / min, and the solid BHET is removed by filtration.

[0084] After mixing and drying the BHET from the first and second stages, the BHET is repolymerized into r-PET at 270°C and 0.5 torr.

[0085] r-PET quality L = 55%, a = 1.6, b = 5.1, yield 81.3%. Catalyst recovery rate 0%; in addition, the catalyst is not easy to recover because it dissolves in water.

[0086] Comparative example 2:

[0087] The same as comparative example 1, only sodium acetate is used instead of zinc acetate as catalyst, and the rest of the process conditions are the same as comparative example 1. r-PET quality L = 57%, a = 1.4, b = 6.2, yield 77.9%. Catalyst recovery rate 0%; in addition, the catalyst is not easy to recover because it dissolves in water.

[0088] Comparative example 3:

[0089] The same as Comparative Example 1, only change the stirring time from 6 hours to 4 hours, and the rest of the process conditions are the same as Comparative Example 1. The r-PET quality L = 56%, a = 1.9, b = 7.1, and the yield is 58.3%. The catalyst recovery rate is 0%; in addition, the catalyst is not easy to recover, and the ionic liquid catalyst is high in cost.

[0090] Comparative Example 4:

[0091] The same as Comparative Example 1, only replace zinc acetate with 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) as the catalyst, and the rest of the process conditions are the same as Comparative Example 1. The r-PET quality L = 61%, a = 1.4, b = 6.2, and the yield is 87.8%. The catalyst recovery rate is 0%; in addition, the catalyst is not easy to recover because it dissolves in water.

[0092] Comparative Example 5:

[0093] The same as Comparative Example 1, only replace zinc acetate with 1-butyl-3-methylimidazolium zinc tetrachloride (abbreviated as BMI2ZnCl4) as the catalyst, and the rest of the process conditions are the same as Comparative Example 1. The r-PET quality L = 60%, a = 1.1, b = 6.7, and the yield is 89.7%. The catalyst recovery rate is 0%; in addition, the catalyst is not easy to recover because it dissolves in water, and the ionic liquid catalyst is high in cost.

[0094] [Advantages of the embodiments]

[0095] One of the advantages of the present application is that the method for recycling polyester fabric using ionic liquid catalyst provided by the embodiments of the present application can improve the recycling quality of r-PET by the technical solution of "providing a recycled polyester fabric; chemically depolymerizing the recycled polyester fabric using a chemical depolymerization liquid to form a depolymerization product containing bis-hydroxyethyleneterephthalate (BHET), wherein the chemical depolymerization of the recycled polyester fabric is carried out in the presence of a depolymerization catalyst, and the depolymerization catalyst is an ionic liquid catalyst; and performing a separation operation, which includes separating the ionic liquid catalyst by centrifugation and / or filtration to collect the ionic liquid catalyst". Furthermore, the method for recycling polyester fabric using ionic liquid catalyst provided by the present application has the advantage of low cost.

[0096] The above disclosure is only the preferred feasible embodiments of the present application, and does not limit the scope of the patent application of the present application, so any equivalent technical changes made by applying the content of the specification and drawings of the present application are included in the scope of the patent application of the present application.

Claims

1. A method for recycling polyester fabrics using an ionic liquid catalyst, characterized by, The method for recycling polyester fabric by using ionic liquid catalyst comprises: a preparation operation including providing a recycled polyester fabric; a depolymerization operation including chemically depolymerizing the recycled polyester fabric by using a chemical depolymerization solution to form a depolymerization product mainly including ethylene terephthalate; wherein the chemical depolymerization solution is ethylene glycol and is heated to 180-260°C; wherein the depolymerization operation is performed on the recycled polyester fabric in the presence of a depolymerization catalyst, and the depolymerization catalyst is an ionic liquid catalyst in solid state; wherein the ionic liquid catalyst comprises a substrate and ionic liquid grafted on the substrate; wherein the average particle size of the substrate is 2-800 microns, and the substrate is selected from at least one of the following material group: micron iron particles, micron nickel particles, micron carbon particles, micron silicon particles, and micron cobalt particles; The ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrachlorozincate, 1-butyl-3-methylimidazolium tetrachloroferrate, 1-butyl-3-methylimidazolium tetrachlorocobaltate, and 1-butyl-3-methylimidazolium tetrafluoroborate; wherein the number of grafts of the ionic liquid onto the substrate is 10 per gram of the substrate. 4 Up to 10 18 The ionic liquid of the branch; and a separation operation including separating the ionic liquid catalyst by centrifugation and / or filtration to collect and recycle the ionic liquid catalyst.

2. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 1, characterized by, In the ionic liquid catalyst, the ionic liquid is grafted on the substrate by using silane coupling agent as a bridge; wherein the preparation method is to first acidize the silane coupling agent, then perform grafting reaction with the substrate, and then graft the ionic liquid on the silane coupling agent in an alkaline environment, thereby forming the ionic liquid catalyst in solid state.

3. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 1, wherein, In the separation operation, the ionic liquid catalyst can be separated from the depolymerization product by sedimentation due to its high specific gravity; wherein the catalyst recovery rate of the ionic liquid catalyst is not less than 95%.

4. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 1, wherein, After the separation operation, the method for recycling polyester fabric by using ionic liquid catalyst further comprises a purification operation to obtain purified ethylene terephthalate from the depolymerization product, and a granulation operation to make the purified ethylene terephthalate polymerize again to form regenerated polyester particles having an L value not less than 60, an a value between -2 and 2, and a b value between -6 and 6, and the regenerated polyester particles have a recovery rate not less than 90%.

5. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 4, characterized by, The purification operation includes an adsorption procedure including dissolving the ethylene terephthalate in water to form an aqueous liquid, and adding an activated carbon material and / or an ion exchange resin into the aqueous liquid to enable the activated carbon material to adsorb impurities originally present in the recycled polyester fabric.

6. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 5, wherein, The aqueous liquid is heated to a liquid temperature of 70-150°C to increase the solubility of the ethylene terephthalate in water, and enable the activated carbon material and / or the ion exchange resin to adsorb the impurities at the liquid temperature.

7. The method for recovering polyester fabrics using an ionic liquid catalyst according to claim 6, wherein, After the adsorption procedure, the purification process further comprises a crystallization procedure comprising: cooling the aqueous liquid from the liquid temperature of between 70 °C to 150 °C to a crystallization temperature of between 5 °C to 25 °C to crystallize the terephthalic acid ethylene glycol ester out of the aqueous liquid, thereby obtaining the purified terephthalic acid ethylene glycol ester.

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