Method for decoloring supercritical mixed fluid

Abstract

The invention belongs to the field of resource utilization of waste textiles, and discloses a supercritical mixed fluid decolorization method. Comprising the following steps: S1, putting a pretreated to-be-decolored textile into a reaction kettle for vacuum treatment; s2, adding a decolorizing agent into the reaction kettle subjected to vacuum treatment, introducing a supercritical mixed fluid, and pressurizing and heating the reaction kettle to enable the supercritical mixed fluid to circularly flow in the pressurized and heated reaction kettle, so as to decolorize the textile to be decolorized; s3, after the to-be-decolored textile is decolored in the reaction kettle, depressurizing the reaction kettle to separate the dye and the supercritical mixed fluid removed from the to-be-decolored textile; the supercritical mixed fluid is a supercritical CO2-N2 mixed fluid. The invention provides an environment-friendly decolorizing technology which has the removal effects of non-polar and polar dyes and is adaptive to complex vamps, and technical support is provided for high-efficiency and high-quality recovery of waste textiles.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of waste textiles, and specifically relates to a method for decolorization using supercritical mixed fluid. Background Technology

[0002] In the field of athletic and running shoes, polyester fabrics (including mesh, knitted fabrics, and composite fabrics) have become the core material for shoe upper manufacturing due to their lightweight, high abrasion resistance, and excellent breathability. However, resource recycling and carbon emission reduction have become core guiding principles for the development of the manufacturing industry. Therefore, the recycling and reuse of waste shoe uppers is not only a key measure to reduce solid waste pollution but also an inevitable choice for the industry to reduce raw material consumption. However, in the actual recycling process, the diversified decolorization treatment of shoe uppers has become a critical issue that urgently needs to be addressed. When shoe uppers from different batches and of different colors are mixed together, the residual dyes not only cause uneven coloring of the recycled polyester material but also affect the chemical stability and mechanical properties of the recycled material.

[0003] Current decolorization methods are mainly divided into two categories: physical decolorization and chemical decolorization. These methods target either the direct decolorization of recycled fabrics or the decolorization of monomers and intermediate products after depolymerization, respectively. Physical methods primarily include adsorption and dissolution. Adsorption methods operate under mild conditions, but have limited adsorption capacity, requiring frequent replacement of the adsorbent after saturation, thus affecting continuous processing efficiency. Solvent dissolution methods, while technically mature and widely applicable, typically rely on high-temperature and high-pressure equipment and are prone to secondary pollution due to solvent residues. Chemical methods primarily utilize oxidation / reduction, using strong oxidants or reducing agents to destroy the dye structure. While the process is mature, it may damage the physical properties of fibers and generate toxic byproducts during decolorization. Overall, traditional physical and chemical decolorization methods still have significant limitations in terms of environmental friendliness and process cleanliness, making it difficult to meet the current requirements for green and circular development.

[0004] Against this backdrop, supercritical carbon dioxide fluid decolorization technology has shown great potential as an emerging, highly efficient, and environmentally friendly process. This technology utilizes the excellent penetration and extraction capabilities of supercritical carbon dioxide for dyes, achieving efficient decolorization without the need for water or highly reactive chemical auxiliaries, providing a more sustainable technological path for textile recycling. However, the decolorization of waste textiles still faces multiple challenges: the types of dyes in waste textiles are extremely complex, often including not only disperse dyes but also highly polar dyes such as reactive dyes and acid dyes; disperse dyes are tightly bound to polyester fibers through van der Waals forces, hydrogen bonds, and even chemical bonds, and the fibers themselves have high crystallinity and a compact structure, lacking active groups to interact with dyes, making it difficult for dyes to detach and penetrate; oligomers, byproducts of polymerization, form a barrier layer on the fiber surface, further limiting the contact reaction between the decolorizing agent and the dye; traditional reduction cleaning and oxidative stripping methods have limited effectiveness against dyes inside the fibers and may damage the fibers or lead to incomplete decolorization; if the waste textiles are blended materials, the differences in the dyeing properties of different fibers further complicate the decolorization process, requiring consideration of multiple fiber characteristics, otherwise uneven decolorization or fiber damage may occur. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a supercritical mixed fluid decolorization method. It utilizes a supercritical CO2-N2 mixed fluid as the decolorization medium and optimizes the polarity compatibility and solubility characteristics of the mixed fluid. This allows the fluid to retain its efficient extraction capability for non-polar disperse dyes while also exhibiting a significant removal effect on polar dyes such as reactive dyes and acid dyes, thereby improving the adaptability of the technology to waste textiles with complex compositions and diverse dyes.

[0006] The objective of this invention is achieved through the following technical solution: This invention provides a method for decolorizing supercritical mixed fluids, the method comprising the following steps: S1, the pretreated textiles to be decolorized are placed in a reaction vessel for vacuum treatment; S2, after adding a decolorizing agent to the vacuum-treated reactor, a supercritical mixed fluid is introduced, and the reactor is pressurized and heated so that the supercritical mixed fluid circulates in the pressurized and heated reactor, thereby decolorizing the textiles to be decolorized. S3, after the textile to be decolorized has been decolorized in the reactor, the pressure in the reactor is reduced to separate the dye removed from the textile to be decolorized from the supercritical mixed fluid. The supercritical mixed fluid is a supercritical CO2-N2 mixed fluid.

[0007] In some embodiments, in step S1, the pretreatment method is to sequentially crush, wash and dry the textile to be decolorized; the drying temperature is 60-80℃.

[0008] In some embodiments, in step S1, the moisture content of the pretreated textile to be decolorized is less than 1%.

[0009] In some embodiments, in step S2, the decolorizing agent is at least one of dimethylformamide and dimethyl sulfoxide; the mass ratio of the decolorizing agent to the pretreated textile to be decolorized is 5%-15%.

[0010] In some embodiments, in step S2, the mass ratio of N2 to CO2 in the supercritical mixed fluid is 5%-15%.

[0011] In some embodiments, in step S2, the pressure of the reactor after pressurization is 10-30 MPa; the temperature of the reactor after heating is 80-120°C.

[0012] In some embodiments, in step S2, the supercritical mixed fluid circulates within the reactor at a flow rate of 20-40 L / h for a duration of 1-4 h.

[0013] In some embodiments, in step S3, the pressure reduction method is to reduce the pressure inside the reactor to atmospheric pressure in a segmented manner while controlling the temperature change.

[0014] Furthermore, the segmented depressurization includes at least a first stage and a second stage: the first stage maintains the reactor temperature at 80-100℃ and reduces the reactor pressure to 10 MPa at a rate of 2-4 MPa / min; the second stage reduces the reactor temperature from the first stage reactor temperature to 60-80℃ at a rate of 1-2℃ / min and reduces the 10 MPa pressure after the first stage to atmospheric pressure at a rate of 1 MPa / min.

[0015] In some embodiments, in step S3, the separated supercritical mixed fluid is purified and then recycled.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) This invention introduces N2 to regulate the physicochemical properties of the supercritical CO2 system, enhances its solubility spectrum, and acts as a dispersant, penetration promoter and morphology regulator to effectively prevent the redeposition of dye molecules desorbed from the fiber, ensuring the uniformity of decolorization; reduces fluid viscosity, strengthens the swelling effect on the fiber, and releases the dye wrapped inside the waste textiles; optimizes the precipitation morphology of dye particles in the separation stage, making them easy to collect, and improving the stability and closed-loop recovery efficiency of the system. (2) The supercritical mixed fluid decolorization method provided by the present invention has a decolorization rate of over 90% for both non-polar and polar dyes, and the decolorization rate of the mixed dye system is stable at 92%-95%. No toxic byproducts are generated in the whole process. (3) The supercritical mixed fluid decolorization method provided by the present invention can flexibly deal with various waste textiles such as light-colored fabrics, dark-colored fabrics with high load, and polar / non-polar mixed dyes by adjusting the circulation time (to adapt to fabrics with different color depths), the mass ratio of N2 to CO2 (to adapt to mixed systems of different dye types), and the mass ratio of decolorizing agent to pretreated textiles to be decolorized, thus solving the pain point of "poor adaptability of single system" in the existing technology.

[0017] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0018] This invention provides a method for decolorizing supercritical mixed fluids, the method comprising the following steps: Pretreatment: The fabric to be decolorized (waste polyester shoe uppers, textile production waste, clothing, home textiles and other polyester fabrics) is mechanically crushed into irregular, loose fabric fragments; then the fabric fragments are rinsed with deionized water to remove surface dust and water-soluble stains; after rinsing, the fabric fragments are placed in a vacuum drying oven and dried at 60-80℃ for 2-3 hours to ensure that their moisture content is less than 1% to avoid moisture affecting the polarity and stability of the supercritical fluid; Vacuum preparation: Evenly pack the dried fabric scraps into the high-pressure reactor to facilitate fluid penetration. Then open the vacuum valve to perform a vacuum operation on the reactor, and pump the pressure inside the reactor to below -0.1 MPa. Maintain this pressure for 10-15 minutes to completely remove the air and prevent air from interfering with the supercritical state of the mixed fluid. Then close the vacuum valve. Decolorization preparation: Add the decolorizing agent (at least one of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)) into the reactor. The mass ratio of the decolorizing agent to the pretreated textile to be decolorized is 5%-15%. Open the valves of the CO2 and N2 storage tanks. Control the mass ratio of N2 to CO2 to 5%-15% by mass flow counting to form a supercritical CO2-N2 mixed gas. Condense the mixed gas into a liquid state through a condenser. Temporarily store the mixed fluid in a gas storage tank. Open the gas storage tank and introduce the mixed fluid into the sealed reactor. Start the pressure pump to adjust the pressure. Maintain the system pressure at 10-30 MPa at a pressurization rate of 1-2 MPa / min. Gradually raise the temperature inside the reactor to 80-120℃ through the heating device at a heating rate of 5-10℃ / min. Decolorization: Start the circulation pump to dynamically circulate the supercritical CO2-N2 mixture in the reactor at a flow rate of 20-40 L / h for 1-4 hours; Separation: The pressure inside the reactor is reduced to atmospheric pressure in stages while temperature changes are controlled. First stage: Maintain the reactor temperature at 80-100℃, and reduce the pressure from the operating pressure to 10MPa at a rate of 2-4 MPa / min to avoid premature phase change of the mixed fluid due to a sudden temperature drop; In the first stage, control the temperature within a relatively constant range of 80-100℃ to avoid premature phase change of the mixed fluid due to a sudden temperature drop. The second stage involves slowly reducing the temperature to 60-80℃ (cooling rate 1-2℃ / min) and reducing the pressure from 10 MPa to atmospheric pressure at a rate of 1 MPa / min to promote the stable precipitation of dye particles. The precipitated dye particles are carried by the mixed fluid gas flow into the separation vessel, where gas-solid separation is completed through a filter screen. The separated CO2-N2 mixed fluid is recycled to the gas storage tank through a purification device for recycling. The second stage involves slow pressure reduction to promote the stable precipitation of dye particles, ensure thorough decolorization, and facilitate gas-solid separation.

[0019] Post-processing: Turn off the heating system and wait for the reactor to cool to a safe temperature below 40°C before opening the reactor. Take out the decolorized textiles and vacuum dry them at 80-100°C for 1-2 hours to remove residual mixed fluids and decolorizing agents.

[0020] It should be noted that the introduction of N2 is not only to adjust the polarity of the supercritical fluid to enhance its solubility spectrum, but also to produce multiple synergistic effects in the specific reverse process of decolorization: First, as a dispersant, it effectively prevents the redeposition of dye molecules desorbed from the fiber, ensuring the uniformity of decolorization; second, as a penetration promoter, it reduces the fluid viscosity, enhances the swelling effect on the fiber, thereby releasing the dye encapsulated inside; third, as a morphology regulator, it optimizes the precipitation morphology of dye particles in the separation stage, making them easier to collect and improving the stability of the system and the closed-loop recovery efficiency.

[0021] The mass ratio of nitrogen (N2) in the supercritical fluid mixture affects the decolorization rate of the fabric to be decolored. When the N2 content is less than 5%, the decolorization rate is low for both polar and non-polar dyes, especially for polar dyes due to insufficient solubility. When the N2 content exceeds 15%, the concentration of CO2 in the fluid mixture decreases significantly. Since supercritical CO2 is the core carrier for removing non-polar dyes, its solubility saturation for non-polar dyes decreases accordingly. Moreover, the desorbed dye molecules cannot be quickly carried to the separation vessel by CO2 and are prone to reversible adsorption on the fiber surface. Furthermore, due to the poor compatibility between polar dyes and CO2, efficient desorption relies on the dual synergy of "N2 penetration promotion + DMSO decolorizing agent solubilization": N2 molecules can reduce the viscosity of the fluid mixture, enhance the swelling effect of the fluid on the polyester fibers, and help polar dyes diffuse from the fiber interior to the surface. However, when the N2 content exceeds 15%, this penetration promotion effect becomes "excessive." Excessively swollen fibers form micropores, and some desorbed polar dyes become trapped in these pores and cannot be carried out by the fluid. Furthermore, due to insufficient CO2 concentration, the polar dyes within the pores cannot be effectively carried to the separation vessel, ultimately leading to dye redeposition and a decrease in the decolorization rate of polar dyes. In addition, the maintenance of the supercritical state depends on the coordinated matching of fluid density, pressure, and temperature. The supercritical density of N2 is much lower than that of CO2. Excess N2 will reduce the density of the mixed fluid, and slight pressure / temperature fluctuations may cause the mixed fluid to undergo a phase transition from the supercritical state to the gaseous state. However, the mass transfer efficiency of the gaseous fluid is only 1 / 3 to 1 / 2 of that of the supercritical state, which is insufficient to continuously penetrate the fiber gaps and desorb the encapsulated dye molecules.

[0022] It should be noted that the ratio of decolorization cycle time to dyeing depth (based on dye loading owf) is 0.8-1.2% owf / hour : 1% owf; specifically, a dye loading of 2% owf (medium dyeing depth) corresponds to a decolorization cycle time of 2-2.5 hours; a dye loading of 5% owf (dark color, high loading) corresponds to a decolorization cycle time of 3-4 hours. The core is to extend the time to match higher dye removal requirements and ensure a stable decolorization rate of ≥90%.

[0023] The total amount of supercritical mixed fluid used needs to be matched with the weight of the fabric and the amount of bleaching agent. The more fabric there is and the higher the amount of bleaching agent, the more the total amount of fluid needs to be increased to ensure that the bleaching agent is fully dissolved and the dye is efficiently extracted. Otherwise, insufficient fluid may lead to incomplete bleaching.

[0024] The total amount of supercritical mixed fluid used consists of the system's basic filling volume and the dynamic circulation replenishment volume, which are determined as follows: 1. System basic filling volume: refers to the minimum total amount of mixed fluid required to fill the closed-loop system formed by all pressure-bearing components such as the high-pressure reactor, connecting pipelines, separation vessel, and gas storage tank; 2. Dynamic circulation replenishment volume: refers to the total amount of mixed fluid that needs to be continuously circulated above the basic filling volume to achieve efficient dye desorption and carryover. It is determined by adapting the circulation flow rate (20-40 L / h), circulation time, and dye loading (owf). The core adaptation principle is: the higher the dye loading and the longer the circulation time, the greater the dynamic circulation replenishment volume should be, ensuring that the desorbed dye is not re-adsorbed and that the dispersion and penetration promoting effect of N2 can be fully utilized. The circulation replenishment volume should be no less than 3-6 times the basic filling volume (3-4 times for low dyeing depth ≤2% owf, and 5-6 times for high dyeing depth ≥4% owf).

[0025] The preferred total amount of supercritical mixed fluid used in this application is 45~105 kg. Among them, the basic filling amount of the system is calculated to be 7.6-9.5 kg based on the set process conditions (80-120℃, 10-30MPa) and the density of CO2-N2 mixed fluid in the supercritical state (0.7-0.85 g / mL) (to ensure the formation of a stable supercritical environment). The dynamic circulation replenishment amount is determined to be 27.2-95.0 kg based on the circulation flow rate (20-40 L / h), circulation time and dye loading (owf).

[0026] The method for determining the decolorization rate in this invention is as follows: using a colorimeter to measure the CIELAB values ​​(L, a, b*) at multiple points on the fabric surface before and after decolorization, and calculating the average color difference value (ΔE); The formula for calculating the decolorization rate is: Decolorization rate (%) = (ΔE) / (ΔE) 脱色前 -ΔE 脱色后 )×100% / ΔE 脱色前 .

[0027] The present invention will be further described in detail with reference to specific embodiments. The following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention, but do not limit the present invention in any way.

[0028] Example 1: This embodiment provides a method for decolorizing supercritical mixed fluids, the method comprising the following steps: Pretreatment: 500g of waste light pink and white polyester mesh shoe upper (containing Disperse Red 3B (non-polar, 1% owf) + Acid Red G (polar, 0.5% owf), a mixed dye system) was pretreated using a mechanical crushing device to break it into irregular, loose fabric fragments. Surface dust and water-soluble stains were rinsed off with deionized water. After rinsing, the fabric fragments were placed in a vacuum drying oven and dried at 70℃ for 2.5 hours, yielding a dry weight of 495g. Testing showed a moisture content of 0.6%. Vacuum preparation: Evenly load the pre-treated fabric fragments into the high-pressure reactor. Open the vacuum valve to evacuate the reactor, reducing the pressure inside to below -0.1 MPa, and maintain this pressure for 12 minutes to completely remove the air. Then close the vacuum valve. Decolorization preparation: Add 49.5g DMSO (the mass ratio of decolorizing agent to pretreated textiles to be decolorized is 10%) to the reactor through the decolorizing agent supply system; open the valves of the CO2 and N2 storage tanks, and control the mass ratio of N2 to CO2 to 10% through the mass flow meter to form a CO2-N2 mixed gas; the total amount of the mixed fluid is 54.82kg, of which N2 is 5.48kg and CO2 is 49.34kg (this amount consists of the system basic filling amount of 8.62kg and the dynamic circulation replenishment amount of 46.20kg); condense the mixed gas into liquid through the condenser and temporarily store it in the gas storage tank; open the gas storage tank and introduce the mixed fluid into the sealed reactor, start the pressure pump to adjust the pressure, and maintain the system pressure at 20 MPa at a pressurization rate of 1.5 MPa / min; at the same time, start the heating device and gradually raise the temperature inside the reactor to 90℃ at a heating rate of 7℃ / min; Decolorization: Start the circulation pump to dynamically circulate the supercritical CO2-N2 mixture in the reactor at a flow rate of 30 L / h for 2 hours; Separation: The pressure inside the reactor is reduced to atmospheric pressure in stages while temperature changes are controlled. First stage: Maintain the reactor temperature at 90℃, and reduce the pressure from 20 MPa to 10 MPa at a rate of 3 MPa / min (takes 3.3 minutes) to avoid premature phase change of the mixed fluid due to a sudden drop in temperature; The second stage involves slowly reducing the temperature to 70℃ at a rate of 1.5℃ / min, while simultaneously reducing the pressure from 10MPa to atmospheric pressure at a rate of 1 MPa / min (taking 10 minutes) to promote the stable precipitation of dye particles. The precipitated dye particles are then carried by the mixed fluid gas flow into the separation vessel, where gas-solid separation is completed through a filter screen. The separated CO2-N2 mixed fluid is then purified and recycled to a gas storage tank for reuse. Post-processing: Turn off the heating system and wait for the reactor to cool to a safe temperature below 40°C before opening the reactor. Take out the decolorized polyester fabric and vacuum dry it at 90°C for 1.5 hours to remove residual mixed fluid and decolorizing agent.

[0029] Analysis showed that the decolorization rate of nonpolar disperse red was 94.6%, while that of polar acid red was 91.7%.

[0030] Example 2: This embodiment provides a method for decolorizing with a supercritical mixed fluid. Compared with Embodiment 1, the object processed in this embodiment is waste orange-brown color-blocked polyester shoe upper (disperse orange S-4RL (non-polar, 2% owf) + acid brown RH (polar, 1% owf), resulting in a higher color depth), with a dry weight of 495 g and a moisture content of 0.6% after pretreatment. The decolorization cycle time is 3 hours, and the total amount of supercritical CO2-N2 mixed fluid used is 77.92 kg, of which N2 is 7.79 kg and CO2 is 69.13 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 69.30 kg, with other conditions remaining the same.

[0031] Analysis showed that the decolorization rate of nonpolar disperse orange was 95.2%, while that of polar acid brown was 91.7%.

[0032] Example 3: This embodiment provides a method for decolorization using a supercritical mixed fluid. Compared to Embodiment 1, the material processed in this embodiment is waste dark purple and black polyester shoe upper (disperse purple HFRL (non-polar, 3% owf) + acid purple 4BNS (polar, 2% owf), a mixture of dye types), with a dry weight of 495g and a moisture content of 0.6% after pretreatment. The decolorization cycle time is 4 hours, and the total amount of supercritical CO2-N2 mixed fluid used is 101.02kg, of which N2 is 10.10kg and CO2 is 90.92kg. This amount consists of a system base filling amount of 8.62kg and a dynamic circulation replenishment amount of 92.40kg, with other conditions remaining the same.

[0033] Analysis showed that the decolorization rate of nonpolar disperse violet was 94.8%, and the decolorization rate of polar acid violet was 92.0%.

[0034] Example 4: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 2, the mass ratio of N2 to CO2 in the mixed gas is reduced to 5% in this embodiment. The total amount of supercritical CO2-N2 mixed fluid used is 78.94 kg, of which N2 accounts for 3.95 kg and CO2 accounts for 74.99 kg. This amount consists of a system base filling amount of 8.74 kg and a dynamic circulation replenishment amount of 70.20 kg, with other conditions remaining the same.

[0035] Analysis showed that the decolorization rate of nonpolar disperse orange was 92.2%, while that of polar acid brown was 84.5%.

[0036] Example 5: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 3, the decolorization cycle time in this embodiment is 3 hours, and the total amount of supercritical CO2-N2 mixed fluid used is 77.92 kg, of which N2 is 7.79 kg and CO2 is 69.13 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 69.30 kg, with other conditions remaining the same.

[0037] Analysis showed that the decolorization rate of nonpolar disperse violet was 91.0%, while the decolorization rate of polar acid violet was 85.8%.

[0038] Example 6: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the mass ratio of N2 to CO2 in the mixed fluid in this embodiment is 15%, and the total amount of supercritical CO2-N2 mixed fluid is 53.40 kg, of which N2 accounts for 8.01 kg and CO2 accounts for 45.39 kg. This amount consists of the system's basic filling amount of 8.40 kg and the dynamic circulation replenishment amount of 45.00 kg, with other conditions remaining the same.

[0039] Analysis showed that the decolorization rate of nonpolar disperse red was 94.1%, while that of polar acid red was 92.1%.

[0040] Example 7: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the mass ratio of N2 to CO2 in the mixed fluid in this embodiment is 5%, and the total amount of supercritical CO2-N2 mixed fluid is 55.54 kg, of which N2 accounts for 2.78 kg and CO2 accounts for 52.76 kg. This amount consists of a system base filling amount of 8.74 kg and a dynamic circulation replenishment amount of 46.80 kg, with other conditions remaining the same.

[0041] Analysis showed that the decolorization rate of nonpolar disperse red was 91.5%, while that of polar acid red was 84.5%.

[0042] Example 8: This embodiment provides a method for decolorization using a supercritical mixed fluid. Compared to Embodiment 1, the mass ratio of the decolorizing agent to the pretreated textile to be decolorized in this embodiment is 5%, and the total amount of the supercritical CO2-N2 mixed fluid is 54.82 kg, of which 5.48 kg is N2 and 49.34 kg is CO2. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 46.20 kg, with other conditions remaining the same.

[0043] Analysis showed that the decolorization rate of nonpolar disperse red was 90.8%, while that of polar acid red was 86.3%.

[0044] Example 9: This embodiment provides a method for decolorization using a supercritical mixed fluid. Compared to Embodiment 1, the mass ratio of the decolorizing agent to the pretreated textile to be decolorized in this embodiment is 15%, and the total amount of the supercritical CO2-N2 mixed fluid is 54.82 kg, of which 5.48 kg is N2 and 49.34 kg is CO2. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 46.20 kg, with other conditions remaining the same.

[0045] Analysis showed that the decolorization rate of nonpolar disperse red was 95.1%, while that of polar acid red was 93.2%.

[0046] Example 10: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the circulation flow rate of the supercritical CO2-N2 mixed fluid in this embodiment is adjusted to 20 L / h; the total amount of the supercritical CO2-N2 mixed fluid is 39.42 kg, of which N2 is 3.94 kg and CO2 is 49.34 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 30.80 kg, with other conditions remaining the same.

[0047] Analysis showed that the decolorization rate of nonpolar disperse red was 91.2%, while that of polar acid red was 87.5%.

[0048] Example 11: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the circulation flow rate of the supercritical CO2-N2 mixed fluid in this embodiment is adjusted to 40 L / h; the total amount of the supercritical CO2-N2 mixed fluid is 70.22 kg, of which N2 is 7.02 kg and CO2 is 63.20 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 61.60 kg, with other conditions remaining the same.

[0049] Analysis showed that the decolorization rate of nonpolar disperse red was 95.3%, while that of polar acid red was 93.0%.

[0050] Example 12: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the circulation time of the supercritical CO2-N2 mixed fluid in this embodiment is adjusted to 1 hour; the total amount of the supercritical CO2-N2 mixed fluid is 31.72 kg, of which N2 is 3.17 kg and CO2 is 28.55 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 23.10 kg, with other conditions remaining the same.

[0051] Analysis showed that the decolorization rate of nonpolar disperse red was 88.5%, while that of polar acid red was 82.3%.

[0052] Example 13: This embodiment provides a method for decolorizing a supercritical mixed fluid. Compared with Embodiment 1, the circulation time of the supercritical CO2-N2 mixed fluid in this embodiment is adjusted to 3 hours; the total amount of the supercritical CO2-N2 mixed fluid is 77.92 kg, of which N2 is 7.79 kg and CO2 is 70.13 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 69.30 kg, with other conditions remaining the same.

[0053] Analysis showed that the decolorization rate of nonpolar disperse red was 95.5%, while that of polar acid red was 93.8%.

[0054] Example 14: This embodiment provides a method for decolorization using a supercritical mixed fluid. Compared to Embodiment 1, the object processed in this embodiment is waste dark blue polyester knitted shoe upper (same type of disperse blue 2BLN, non-polar, dyeing depth 5% owf, higher color depth), with a dry weight of 495 g and a moisture content of 0.6% after pretreatment. The decolorization cycle time is 4 hours, and the total amount of supercritical CO2-N2 mixed fluid used is 101.02 kg, of which N2 is 10.10 kg and CO2 is 90.92 kg. This amount consists of a system base filling amount of 8.62 kg and a dynamic circulation replenishment amount of 92.40 kg, with other conditions remaining the same.

[0055] Analysis showed a decolorization rate of 95.1%. Example 15: This embodiment provides a method for decolorization using a supercritical mixed fluid. Compared to Embodiment 1, the object processed in this embodiment is waste purple-dyed polyester composite shoe upper (containing disperse violet HFRL (non-polar, 2% owf) + acid violet 4BNS (polar, 2% owf), a mixture of dye types), with a dry weight of 495 g and a moisture content of 0.6% after pretreatment. The mass ratio of N2 to CO2 in the mixed fluid is 15%, and the total amount of supercritical CO2-N2 mixed fluid used is 53.40 kg, of which N2 accounts for 8.01 kg and CO2 accounts for 45.39 kg. This amount consists of a system base filling amount of 8.40 kg and a dynamic circulation replenishment amount of 45.00 kg, with other conditions remaining the same.

[0056] Analysis showed that the decolorization rate of nonpolar disperse violet was 93.9%, and the decolorization rate of polar acid violet was 93.4%.

[0057] Comparative Example 1: This comparative example provides a method for decolorization using supercritical fluid. Compared to Example 1, the supercritical fluid in this comparative example is only CO2 (without N2), and the total amount used is 57.67 kg. This amount consists of a system base filling amount of 9.07 kg and a dynamic circulation replenishment amount of 48.60 kg, with other conditions remaining the same.

[0058] Analysis showed that the decolorization rate of nonpolar disperse red was 87.9%, while that of polar acid red was 64.8%.

[0059] Comparative Example 2: This comparative example provides a method for decolorization using supercritical fluids. Compared to Example 1, the mass ratio of N2 to CO2 in the mixed fluid in this comparative example is 20%, and the total amount of the supercritical CO2-N2 mixed fluid is 51.98 kg, of which N2 accounts for 10.40 kg and CO2 accounts for 41.58 kg. This amount consists of a system base filling amount of 8.18 kg and a dynamic circulation replenishment amount of 43.80 kg, with other conditions remaining the same.

[0060] Analysis showed that the decolorization rate of nonpolar disperse red was 87.2%, while that of polar acid red was 82.0%.

[0061] The decolorization rates obtained by using the method described in this application to decolorize waste textiles are shown in Table 1. The supercritical mixed fluid used in this invention has a good decolorization effect on waste textiles containing various types of dyes. Furthermore, comparing Example 1 with the comparative example, it was found that compared with simply using supercritical CO2 treatment, adding N2 to the supercritical fluid for decolorizing waste textiles significantly improves the decolorization rate.

[0062] Furthermore, by comparing Examples 4 and 2 with Comparative Examples 1 and 7, it can be seen that for the same textile dye, increasing the mass ratio of N2 in the mixed fluid can improve the decolorization rate of the dye, with a more significant improvement in the decolorization rate for polar dyes. When the mass ratio of N2 in the mixed fluid is further increased to 15%, the decolorization rate of polar dyes is slightly improved, while the decolorization rate of non-polar dyes is slightly decreased (comparison between Examples 1 and 6). When the mass ratio of N2 in the mixed fluid is further increased to 20%, the decolorization rates of both polar and non-polar dyes are significantly reduced (Example 1 and Comparative Example 2), proving that a mass ratio of N2 in the mixed fluid of 10%-15% results in a better decolorization rate.

[0063] By comparing Examples 5 and 3 with Examples 1, 12 and 13, it can be seen that for the same textile dye, increasing the decolorization cycle time can increase the decolorization rate of the dye, with a more significant increase in the decolorization rate for polar dyes. By comparing the decolorization rates of Examples 1, 8 and 9, it can be seen that increasing the mass ratio of the decolorizing agent to the pretreated textile to be decolorized can increase the decolorization rate of the dye, with a more significant increase in the decolorization rate for polar dyes.

[0064] In summary, in the supercritical mixed fluid decolorization system of this application, the mass ratio of N2 in the mixed fluid, the decolorization cycle time, and the mass ratio of the decolorizing agent to the pretreated textiles to be decolorized work synergistically to affect the polar dyes, and their interaction effect significantly influences the decolorization efficiency. Precise control of these ternary parameters can improve the decolorization rate of polar dyes.

[0065] Table 1

[0066] Although embodiments of the present invention have been shown and described above, it is understood that these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from its principles and spirit. Where techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

Claims

1. A method for decolorizing supercritical mixed fluids, characterized in that, The method includes the following steps: S1, the pretreated textiles to be decolorized are placed in a reaction vessel for vacuum treatment; S2, after adding a decolorizing agent to the vacuum-treated reactor, a supercritical mixed fluid is introduced, and the reactor is pressurized and heated so that the supercritical mixed fluid circulates in the pressurized and heated reactor, thereby decolorizing the textiles to be decolorized. S3, after the textile to be decolorized has been decolorized in the reactor, the pressure in the reactor is reduced to separate the dye removed from the textile to be decolorized from the supercritical mixed fluid. The supercritical mixed fluid is a supercritical CO2-N2 mixed fluid.

2. The method according to claim 1, characterized in that, In step S1, the pretreatment method is to sequentially crush, wash and dry the textiles to be decolorized; the drying temperature is 60-80℃.

3. The method according to claim 1, characterized in that, In step S1, the moisture content of the pretreated textile to be decolorized is less than 1%.

4. The method according to claim 1, characterized in that, In step S2, the decolorizing agent is at least one of dimethylformamide and dimethyl sulfoxide; the mass ratio of the decolorizing agent to the pretreated textile to be decolorized is 5%-15%.

5. The method according to claim 1, characterized in that, In step S2, the mass ratio of N2 to CO2 in the supercritical mixed fluid is 5%-15%.

6. The method according to claim 1, characterized in that, In step S2, the pressure of the reactor after pressurization is 10-30 MPa; the temperature of the reactor after heating is 80-120℃.

7. The method according to claim 1, characterized in that, In step S2, the supercritical mixed fluid circulates within the reactor at a flow rate of 20-40 L / h for a duration of 1-4 h.

8. The method according to claim 1, characterized in that, In step S3, the pressure reduction method is to reduce the pressure inside the reactor to atmospheric pressure in a segmented manner while controlling the temperature change.

9. The method according to claim 8, characterized in that, The segmented depressurization includes at least a first stage and a second stage: the first stage maintains the reactor temperature at 80-100℃ and reduces the reactor pressure to 10 MPa at a rate of 2-4 MPa / min; the second stage reduces the reactor temperature from the first stage reactor temperature to 60-80℃ at a rate of 1-2℃ / min and reduces the 10 MPa pressure after the first stage to atmospheric pressure at a rate of 1 MPa / min.

10. The method according to claim 1, characterized in that, In step S3, the separated supercritical mixed fluid is purified and then recycled.

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