Method for recycling dyes from waste fabric

Abstract

The application relates to a recycling method of dyes in waste fabric, which can greatly improve the recycling efficiency of the waste fabric, realizes recycling of the waste fabric and the dyes, has extremely high economic benefits, and can save a large amount of resources.

Description

Technical Field

[0001] This invention belongs to the field of waste textiles, and specifically relates to a method for recycling and reusing dyes in waste fabrics. Background Technology

[0002] Denim clothing, with its rugged, simple, and free-spirited style, is widely loved by consumers. With economic development and improved living standards, the demand for denim clothing is increasing, and consequently, the amount of discarded denim is also rising year by year. According to relevant data, my country generates over 26 million tons of waste textiles annually, but its recycling rate is less than 20%, with the recycling rate for discarded denim being even lower at less than 5%. Approximately 20% of discarded denim is typically discarded in landfills or directly incinerated. The incineration process also produces large amounts of carbon dioxide and toxic gases, causing serious pollution problems. Therefore, the recycling of discarded denim clothing is particularly necessary. Discarded denim contains a significant amount of dye, and recovering and reusing this dye is of great importance.

[0003] Existing technologies disclose a method for recycling indigo dye from waste denim. This method utilizes electrochemical technology to reduce the indigo dye in the waste denim and further electrochemically reduces and dyes the dye for reuse. However, this technology requires a reversible redox medium as an electron mediator, and involves large amounts of chemical reagents and electricity consumption, resulting in high recycling costs. Existing technologies also disclose an enzymatic decolorization method for indigo denim, which uses a horseradish peroxidase / hydrogen peroxide catalytic system to decolorize the denim. While this technology causes less fiber damage, its decolorization efficiency still needs improvement. Furthermore, existing technologies disclose a pigment or coating based on waste denim and its preparation method. This method involves cutting waste denim into shreds, grinding it using a ball mill, and then mixing it with a crosslinking agent, thickener, and water to prepare the pigment or coating. However, this method uses waste denim containing a large amount of residual cellulose and chemical reagents, which affects the performance of the pigment or coating. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for recycling and reusing dyes in waste fabrics, so as to improve the economic benefits of recycling and reusing waste fabrics such as denim and promote the development of resource recycling.

[0005] A method for recovering dyes from waste fabrics according to the present invention includes:

[0006] (1) Mix neutral mannanase, auxiliary chemical reagents and water, and then adjust the pH to obtain a pretreatment solution;

[0007] (2) Immerse the waste fabric in the pretreatment solution, mix well, heat treat, wash and dry to obtain the activated fabric.

[0008] (3) the activated fabric is subjected to high-efficiency electro-catalysis treatment, and after electrolysis, the electrolyte is subjected to post-treatment to obtain recovered dyes.

[0009] Preferably, the neutral mannanase in step (1) has a concentration of 1-20% (owf) and an enzyme activity of 20-50 U / mg; the auxiliary chemical reagent includes potassium salt and / or calcium salt and a ligand complexing agent for stabilizing metal ions; and the pH is adjusted to 7-10.

[0010] Preferably, the ligand complexing agent for stabilizing metal ions includes sodium gluconate; the potassium salt in the pretreatment liquid is 5-50 mmol / L and / or the calcium salt is 5-50 mmol / L, and the ligand complexing agent for stabilizing metal ions is 5-100 mmol / L.

[0011] Preferably, in step (2), the bath ratio (mass ratio) of the waste fabric to the pretreatment liquid is 1:10-25; the heat treatment temperature is 40-65°C, and the treatment time is 15-60 min; the dye used for dyeing the waste fabric includes one or more of indigo dye, vat dye and sulfur dye; and the waste fabric is waste denim.

[0012] Preferably, in step (3), the electro-catalysis treatment includes: under the protection of a protective gas, the activated fabric is added to a cathode electrolytic cell, constant-voltage electrolysis is performed at room temperature, and after electrolysis, the waste fabric (such as waste denim) is taken out, and after sufficient water washing and drying, the decolorized fabric (such as denim) is obtained; wherein the electrolysis voltage is 1-15 V, and the electrolysis time is 30-200 min.

[0013] Preferably, the protective gas is nitrogen or argon.

[0014] Preferably, in step (3), the bath ratio (mass ratio) of the waste fabric to the cathode electrolyte is 1:20-50.

[0015] Preferably, in step (3), the system used for electro-catalysis treatment includes a cathode electrolyte, an anode electrolyte, a cathode, an anode and a diaphragm.

[0016] Preferably, the anode electrolyte includes an auxiliary electrolyte and a lye; the content of the auxiliary electrolyte is 0.05-0.4 mol / L, and the content of the lye is 0.5-1 mol / L; the auxiliary electrolyte includes at least one of sodium sulfate and sodium chloride, and the lye includes sodium hydroxide.

[0017] Further, the anode electrolyte is obtained by adding the auxiliary electrolyte to the lye and stirring uniformly.

[0018] Further, the sodium sulfate content in the anolyte is 0.05-0.2 mol / L and / or the sodium chloride content is 0.1-0.4 mol / L, and the sodium hydroxide content is 0.5-1 mol / L.

[0019] Preferably, the catholyte comprises an aqueous solution of caustic soda (caustic soda is dissolved in distilled water and stirred uniformly), and the pH is 11-14.

[0020] Preferably, the cathode electrode comprises a molybdenum disulfide-based catalytic electrode with carbon felt as the substrate.

[0021] Preferably, the anode electrode comprises at least one of a graphite electrode and a stainless steel electrode.

[0022] Preferably, the diaphragm comprises at least one of Nafion-117 and Nafion-324 proton exchange membranes.

[0023] Preferably, the post-processing in step (3) is: the catholyte is subjected to sufficient oxidation, flocculation, filtration, and drying treatment to complete the recovery of the dye; wherein the dosage of the oxidizing agent used in oxidation is 5-15 g / L; the dosage of the flocculating agent used in flocculation is 2-10 g / L; wherein the oxidizing agent comprises hydrogen peroxide (such as hydrogen peroxide with a mass percentage concentration of 30%); and the flocculating agent comprises alum;

[0024] Preferably, the oxidation comprises: oxidation at 30°C for 30-60 min; the flocculation comprises: adjusting the pH of the dye solution to 5.5-7.5 with glacial acetic acid, adding the flocculating agent to the catholyte after sufficient oxidation, stirring uniformly quickly, and then standing for 1-3 hours; the filtration comprises: pouring the catholyte after flocculation into a filter funnel for suction filtration; and the drying comprises: drying the dye filter cake after suction filtration at 80-105°C for 2-6 hours.

[0025] The application provides a pre-reduction liquid based on recovered dye, wherein the pre-reduction liquid is obtained by: adding the recovered dye obtained by the method into a cathode electrolytic tank under the protection of a protective gas, and performing constant-voltage electrolysis to obtain a dye pre-reduction liquid.

[0026] Preferably, the recovered dye comprises at least one of indigo dye, vat dye, and sulfur dye; and the concentration of the dye is 0.005-0.025 mol / L.

[0027] Preferably, the electrolysis voltage in the constant-voltage electrolysis process is 1-15 V, and the electrolysis time is 30-180 min.

[0028] Preferably, the constant-voltage electrolysis system comprises a catholyte, an anolyte, a cathode, an anode, and a diaphragm.

[0029] The anode electrolyte comprises an auxiliary electrolyte and a lye; the content of the auxiliary electrolyte is 0.05-0.4 mol / L, and the content of the lye is 0.5-1 mol / L; the auxiliary electrolyte comprises at least one of sodium sulfate and sodium chloride, and the lye comprises sodium hydroxide;

[0030] Preferably, the cathode electrolyte comprises an aqueous solution of caustic soda with a pH of 11-14.

[0031] Preferably, the cathode electrode comprises a molybdenum disulfide-based catalytic electrode with a carbon felt as a substrate.

[0032] Preferably, the anode electrode comprises at least one of a graphite electrode and a stainless steel electrode.

[0033] Preferably, the diaphragm comprises at least one of Nafion-117 and Nafion-324 proton exchange membranes.

[0034] Further, the molybdenum disulfide-based catalytic electrode with a carbon felt as a substrate is prepared by:

[0035] The carbon felt material is subjected to impurity removal and hydrophilic treatment, then washed and dried to obtain a pretreated carbon felt material; then ammonium molybdate tetrahydrate, thiourea and a solvent are mixed to obtain a mixed solution, the pretreated carbon felt material is put into the mixed solution, and hydrothermal reaction is performed, then washed and vacuum dried to obtain a molybdenum disulfide-carbon felt electrode material; the mass ratio of ammonium molybdate tetrahydrate to deionized water is 1:50-1:150; the mass ratio of thiourea to deionized water is 1:15-1:30; the solvent is a mixed solvent of N,N-dimethylformamide (DMF) and deionized water; the mass ratio of DMF to deionized water is 1:4-1:16. The hydrothermal reaction conditions are 180-240℃ for 3-8 hours. The vacuum drying conditions are 50-80℃ for 6-12 hours. The mass ratio of the carbon felt material area to water in the mixed solution is 0.1 cm 2 / g-0.3 cm 2 / g.

[0036] The pretreated carbon felt material is first soaked in an acetone solution for 5-8 hours to remove surface impurities, then washed with deionized water and dried, further put into a dilute acid with a mass fraction of 10% for hydrophilic treatment at 60-100℃ for 2-6 hours, then washed with deionized water and dried.

[0037] The application provides an application of the pre-reduction liquid in fabric dyeing, which specifically comprises: immersing a fabric (a denim fabric) previously wetted with distilled water into the dye pre-reduction liquid for dyeing for 1-30 minutes, and then performing post-treatment after dyeing through air permeation oxidation, soaping and washing.

[0038] The present application provides a high-efficiency and environmentally-friendly method for recycling dyes in waste fabric (denim). The method can greatly improve the recycling efficiency of waste fabric (denim), realize the recycling of waste fabric (denim) and dyes, has extremely high economic benefits, and can save a large amount of resources.

[0039] Advantages

[0040] The present application adopts a green and environmentally-friendly mannanase enzymatic system to activate and pretreat the waste denim. The neutral mannanase cooperates with alkali metal complexes to swell the cellulose and hemicellulose on the surface of the waste fabric such as waste denim. Meanwhile, the alkali metal has an activating effect on the carbonyl group in the dyes on the waste fabric such as waste denim, which is more conducive to the separation of fibers and dyes in the next step. The electrocatalytic hydrogen reduction technology is adopted to electrolyze the waste fabric such as waste denim in a cathode electrolytic cell. The active hydrogen generated in situ on the cathode electrode of the electrolytic water reduces the reduced dyes on the waste fabric such as waste denim to soluble leuco form, so as to be detached from the fabric such as denim. Further, through sufficient oxidation, the dyes are converted into dyes insoluble in water. After flocculation, filtration and drying, the dyes are recycled. The molybdenum disulfide-based carbon felt catalytic electrode with low price, large specific surface area and excellent conductivity is used as the cathode material for electrocatalytic electrolytic recycling and treatment of the waste fabric such as waste denim. The heterogenization and synergistic effect of the active sites between the metal and non-metal in the catalytic electrode can greatly promote the adsorption of active hydrogen and dyes, and further promote the hydrogen reduction of dyes and improve the decolorization efficiency.

[0041] Compared with the traditional chemical decolorization process, the method for recycling dyes in waste fabric such as waste denim does not damage the structure of the dyes. After recycling, the dyes are further prepared into a pre-reduction solution through electrocatalytic hydrogen reduction, realizing the recycling use of the dyes. The performance damage of the waste fabric such as waste denim after decolorization is small, and the secondary reuse can be realized. The present application avoids the use of reversible oxidation-reduction medium in the traditional indirect electrochemical reduction decolorization, consumes less chemical reagent, has a short processing flow, a simple operation method, a high recycling efficiency, can significantly reduce energy consumption and environmental pollution, and also reduces the comprehensive cost of production, is easy to realize industrialized production, and has a good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The infrared spectrum of the indigo dye recovered in Example 1 is compared with the standard indigo dye;

[0043] Figure 2 Fig. 1 is a comparison of the appearance of waste denim before and after recycling; Fig. 1(a) is the appearance morphology diagram of waste denim without recycling treatment; Fig. 1(b) is the appearance morphology diagram after treatment according to Example 1 of the present application; Fig. 1(c) is the appearance morphology diagram after treatment according to Comparative Example 1; and Fig. 1(d) is the appearance morphology diagram after treatment according to Comparative Example 2;

[0044] Figure 3 Figure (a) is the appearance morphology diagram of the denim fabric after being dyed by the electrocatalytic pre-reduction solution recovered from the treatment of the denim fabric of Example 1; and Figure (b) is the appearance morphology diagram of the denim fabric after being dyed by the cathode reduction solution treated by the treatment of Comparative Example 2.

[0045] Figure 4 Figure is the diagram of the oxidation-reduction potential and the dye reduction rate of the cathode electrolyte in the process of the high-efficiency electrocatalytic recovery treatment of the waste indigo denim of Example 1. DETAILED DESCRIPTION

[0046] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims.

[0047] Raw material sources

[0048] Neutral mannanase, enzyme activity (30 U / mg) (Shanghai Maikelin Biochemical Technology Co., Ltd.)

[0049] Molybdenum disulfide-carbon felt material (laboratory self-made) The specific preparation method is as follows: 1). First, 2 cm x 2 cm carbon felt material is soaked in acetone solution for 8 hours to remove surface impurities; then washed with deionized water and dried. Further, the carbon felt material is subjected to hydrophilic treatment in 10% dilute acid at 80°C for 2 hours, then washed with deionized water and dried. 2). Preparation of molybdenum disulfide-carbon felt material: 0.175 g of ammonium molybdate tetrahydrate and 0.91 g of thiourea are dissolved in a mixed solvent containing 5 g of DMF and 25 g of water, and then transferred to a polytetrafluoroethylene liner after complete dissolution. The pretreated carbon felt is placed in the polytetrafluoroethylene liner, and then the polytetrafluoroethylene liner is transferred to a stainless steel autoclave, and reacted at 240°C for 3 hours. After the reaction, the electrode material is washed with water and ethanol, and then vacuum dried at 50°C for 10 hours to obtain the final molybdenum disulfide-carbon felt electrode material.

[0050] Graphite electrode and carbon felt electrode (Beijing Jinglongte Carbon Technology Co., Ltd.)

[0051] Test method:

[0052] Decolorization rate: The K / S value of the waste denim before and after treatment is measured by Color-i5 color matching instrument (X-Rite Company, USA), and the decolorization rate is calculated by using Formula 1.

[0053]

[0054] In formula (1), K / S0 is the K / S value of the waste denim fabric before treatment, and K / S1 is the K / S value after recycling.

[0055] Strength retention rate: The tensile strength of the discarded denim before and after treatment was tested using a YG365 universal tensile testing machine, and the strength retention rate was calculated using Formula 2.

[0056]

[0057] ORP (Oxidation-Reduction Potential): Refer to the industry standard SL94-1994 for the determination of oxidation-reduction potential. Use an oxidation-reduction potentiometer, place the potentiometer in the dye solution at room temperature, and read the reduction potential value after the value stabilizes.

[0058] Dye conversion rate (reduction rate RE): Dye was weighed at concentrations of 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L and dissolved in a 1.0 M sodium hydroxide solution. The dye was then reduced to its leuco form using excess sodium hydrosulfite or sodium sulfide. The maximum absorption wavelength of the leuco form was determined using a Cary 60 UV spectrophotometer, and a concentration-absorbance standard curve was plotted. The UV spectrophotometer probe was immersed in the catholyte after electrocatalytic reduction, and its absorbance was measured. The dye conversion rate was calculated based on the absorbance. K / S value: The sample was folded into four layers (opaque) and tested using a colorimeter. Measurements were taken at three different locations, and the average value was recorded.

[0059] Example 1

[0060] A method for recycling and reusing dye from waste indigo denim fabric includes the following steps:

[0061] (1) Dissolve 15% (owf) neutral mannanase (enzyme activity 30U / mg), 1 mmol calcium chloride and 2 mmol sodium gluconate in 100 mL of deionized water, stir thoroughly, and then adjust the pH of the solution to 9 with sodium hydroxide.

[0062] (2) Immerse 5g of waste indigo denim in the pretreatment solution, mix evenly, heat treat at 60℃ for 15 minutes, then wash and dry to obtain activated denim.

[0063] (3) The activated denim is subjected to high-efficiency electrocatalytic recovery treatment. Specifically, a molybdenum disulfide-carbon felt material is used as a cathode catalytic electrode, a graphite electrode is used as an anode, and a Nafion-117 proton exchange membrane is used as a diaphragm. An anode electrolyte (100 mL) is composed of 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. A cathode electrolyte (100 mL) is adjusted to a pH of 12 with caustic soda. Under nitrogen protection, the activated denim is added to the cathode electrolytic tank, and constant-voltage (3 V) electrolysis is performed at room temperature for 60 minutes. During the electrolysis, the dye reduction potential and the dye reduction rate in the cathode electrolyte are tested. After the electrolysis is completed, the waste denim is taken out, washed with water, and dried to obtain the decolorized denim. The decolorization rate and the strength retention rate are tested. At the same time, 0.5 g of hydrogen peroxide is added to the cathode electrolyte, which is oxidized at 30°C for 45 minutes. Then, the pH is adjusted to 7.5 with glacial acetic acid, and 0.5 g of alum is added and stirred uniformly. After standing for 2 hours, the flocculated cathode electrolyte is filtered to obtain a filter cake, which is dried at 105°C. Finally, the recovered indigo dye is obtained.

[0064] (4) The recovered indigo dye is subjected to electrocatalytic hydrogenation reduction to prepare a pre-reduction solution. Specifically, a molybdenum disulfide-carbon felt material is used as a cathode catalytic electrode, a graphite electrode is used as an anode, and a Nafion-117 proton exchange membrane is used as a diaphragm. An anode electrolyte (100 mL) is composed of 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. A cathode electrolyte (100 mL) is adjusted to a pH of 12 with caustic soda. Under nitrogen protection, the recovered dye is added to the cathode electrolytic tank, and constant-voltage (6 V) electrolysis is performed for 30 minutes. The oxidation-reduction potential and the dye reduction rate of the cathode electrolyte after electrolysis are tested.

[0065] (5) The denim fabric (5 g) previously wetted with distilled water is immersed in the above-mentioned dye pre-reduction solution for 1 minute. After dyeing is completed, the dyeing after-treatment is completed through air oxidation, soaping, and washing, and the color depth K / S value of the final obtained fabric is tested.

[0066] Example 2

[0067] A method for recycling and reusing dyes in waste indigo denim, comprising the following steps:

[0068] (1) 10% (owf) neutral mannanase (enzyme activity 30 U / mg), 1 mmol calcium chloride, and 2 mmol sodium gluconate are dissolved in 100 mL deionized water, and stirred uniformly. Then, the pH of the above-mentioned solution is adjusted to 9 with sodium hydroxide.

[0069] (2) 5 g of waste indigo denim is immersed in the pretreatment solution, mixed uniformly, and heat-treated at 60°C for 15 minutes. Then, it is washed with water and dried to obtain the activated denim.

[0070] (3) The activated denim is subjected to high-efficiency electrocatalytic recovery treatment. Specifically, a molybdenum disulfide-carbon felt material is used as a cathode catalytic electrode, a graphite electrode is used as an anode, and a Nafion-117 proton exchange membrane is used as a diaphragm. An anode electrolyte (100 mL) is composed of 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. A cathode electrolyte (100 mL) is adjusted to a pH of 12 with caustic soda. Under nitrogen protection, the activated denim is added to a cathode electrolytic tank, and constant voltage (3 V) electrolysis is performed at room temperature for 60 minutes. During the electrolysis, the dye reduction potential and the dye reduction rate in the cathode electrolyte are tested. After the electrolysis is completed, the waste denim is taken out, washed with water, and dried to obtain decolorized denim. The decolorization rate and the strength retention rate are tested. At the same time, 0.5 g of hydrogen peroxide is added to the cathode electrolyte, which is fully oxidized at 30°C for 45 minutes. Then, 0.5 g of alum is added and fully stirred to obtain a uniform mixture. The mixture is left to stand for 2 hours. Finally, the cathode electrolyte after flocculation treatment is suction filtered, the filter cake is dried at 105°C, and finally the recovered indigo dye is obtained.

[0071] Example 3

[0072] A method for recycling dyes in waste indigo denim includes the following steps:

[0073] The waste indigo denim is subjected to high-efficiency electrocatalytic recovery treatment. Specifically, a molybdenum disulfide-carbon felt material is used as a cathode catalytic electrode, a graphite electrode is used as an anode, and a Nafion-117 proton exchange membrane is used as a diaphragm. An anode electrolyte (100 mL) is composed of 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. A cathode electrolyte (100 mL) is adjusted to a pH of 12 with caustic soda. Under nitrogen protection, the waste indigo denim is added to a cathode electrolytic tank, and constant voltage (3 V) electrolysis is performed at room temperature for 60 minutes. During the electrolysis, the dye reduction potential and the dye reduction rate in the cathode electrolyte are tested. After the electrolysis is completed, the waste denim is taken out, washed with water, and dried to obtain decolorized denim. The decolorization rate and the strength retention rate are tested. At the same time, 0.5 g of hydrogen peroxide is added to the cathode electrolyte, which is fully oxidized at 30°C for 45 minutes. Then, 0.5 g of alum is added and fully stirred to obtain a uniform mixture. The mixture is left to stand for 2 hours. Finally, the cathode electrolyte after flocculation treatment is suction filtered, the filter cake is dried at 105°C, and finally the recovered indigo dye is obtained.

[0074] Example 4

[0075] A method for recycling dyes in waste indigo denim includes the following steps:

[0076] (1) Dissolve 15% (owf) neutral mannanase (enzyme activity 30 U / mg), 1 mmol calcium chloride and 2 mmol sodium gluconate in 100 mL of deionized water, fully stir to uniform, then use sodium hydroxide to adjust the pH of the above solution to 9.

[0077] (2) Soak 5 g of discarded indigo denim in the pretreatment solution, mix well, heat treat at 60°C for 15 minutes, then wash with water and dry to obtain the activated denim.

[0078] (3) The activated denim is subjected to high-efficiency electrocatalytic recovery treatment. Specifically, carbon felt electrode is used as cathode, graphite electrode as anode, and Nafion-117 proton exchange membrane as separator. The composition of the anode electrolyte (100 mL) is 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. The cathode electrolyte (100 mL) is adjusted to pH 12 with caustic soda. Under nitrogen protection, the activated denim is added to the cathode electrolytic tank, and constant voltage (3V) electrolysis is carried out at room temperature for 60 minutes. During the electrolysis, the dye reduction potential and dye reduction rate in the cathode electrolyte are tested. After the electrolysis is completed, the discarded denim is taken out, washed with water and dried to obtain the decolorized denim. The decolorization rate and strength retention rate are tested. At the same time, 0.5 g of hydrogen peroxide is added to the cathode electrolyte, which is oxidized at 30°C for 45 minutes. Then, 0.5 g of alum is added and fully stirred to uniform. After standing for 2 hours, the flocculated cathode electrolyte is filtered to obtain a filter cake, which is dried at 105°C. Finally, the recovered indigo dye is obtained.

[0079] (4) The recovered indigo dye is subjected to electrocatalytic hydrogenation reduction to prepare a pre-reduction solution. Specifically, molybdenum disulfide-carbon felt material is used as the cathode catalytic electrode, graphite electrode as the anode, and Nafion-117 proton exchange membrane as the separator. The composition of the anode electrolyte (100 mL) is 0.5 mol / L sodium hydroxide and 0.1 mol / L sodium sulfate. The cathode electrolyte (100 mL) is adjusted to pH 12 with caustic soda. Under nitrogen protection, the recovered dye is added to the cathode electrolytic tank, and constant voltage (6V) electrolysis is carried out for 30 minutes. The oxidation-reduction potential and dye reduction rate of the cathode electrolyte after electrolysis are tested.

[0080] (5) Further, the denim fabric (5 g) pre-wetted with distilled water is soaked in the above dye pre-reduction solution for 1 minute. After dyeing is completed, the dyeing aftertreatment is completed by air oxidation, soaping and washing, and the color depth K / S value of the final obtained fabric is tested.

[0081] Example 5

[0082] A method for recycling and reusing dyes in discarded indigo denim, comprising the following steps:

[0083] (1) 15% (owf) of neutral mannanase (enzyme activity 30 U / mg), 1 mmol of calcium chloride and 2 mmol of sodium gluconate were dissolved in 100 mL of deionized water, and stirred uniformly, and then the solution was adjusted to pH 9 with sodium hydroxide.

[0084] (2) 5 g of discarded indigo denim was immersed in the pretreatment solution, mixed uniformly, and decolorized at 60°C for 15 min, and after the decolorization was completed, washed with water and dried to obtain the denim after decolorization, and the decolorization rate and strength retention rate were tested. At the same time, 0.5 g of hydrogen peroxide was added to the stripping solution, and oxidized at 30°C for 45 min, and then 0.5 g of alum was added after the pH was adjusted to 7.5 with lye, and stirred uniformly, and stood for 2 hours, and finally filtered, and the filter cake was dried at 105°C to obtain the recovered indigo dye.

[0085] Comparative Example 1

[0086] An enzyme washing and decolorizing method for discarded indigo denim, comprising the following steps:

[0087] The indigo denim was immersed in a buffer solution (consisting of acetic acid, sodium acetate and penetrant JFC, mass ratio 10:5:1) with pH 4.5 at a bath ratio of 1:10, and then 3% (owf) of cellulase was added, and stirred for 5 min to mix uniformly to obtain a mixture; then the mixture was heated to 60°C at a heating rate of 2°C / min, and decolorized for 60 min, and after the decolorization was completed, washed with water and dried to obtain the denim after decolorization, and the decolorization rate and strength retention rate were tested. At the same time, 0.5 g of hydrogen peroxide was added to the stripping solution, and oxidized at 30°C for 45 min, and then 0.5 g of alum was added after the pH was adjusted to 7.5 with lye, and stirred uniformly, and stood for 2 hours, and finally filtered, and the filter cake was dried at 105°C to obtain the recovered indigo dye.

[0088] Comparative Example 2

[0089] A method for recovering dyes from discarded indigo denim, comprising the following steps:

[0090] (1) 100 ml of 0.1 mol / L citric acid solution was prepared, and cellulase was added to the citric acid solution so that the concentration of cellulase was 1 g / L;

[0091] (2) 5 g of discarded denim was placed in the citric acid solution containing cellulase, and soaked at 40°C for 30 min;

[0092] (3) The waste jeans soaked in the citric acid solution are subjected to electrolytic recovery treatment, specifically as follows: the cathode electrode material and the anode electrode material are both nickel mesh, the diaphragm is Nafion-117 proton exchange membrane, the anode electrolyte (100 mL) is 40 g / L sodium hydroxide, the cathode electrolyte (100 mL) is 15 g / L ferric sulfate, 30 g / L triethanolamine, 21.5 g / L sodium hydroxide, 1 g / L indigo blue, and 1.5 g / L safety powder, the waste jeans soaked in the citric acid solution are immersed into the cathode electrolytic tank for constant-current electrolysis, wherein the electrolysis current is 1 A, the electrolysis time is 30 minutes, and the electrolysis temperature is 60°C. After the electrolysis is completed, the waste jeans are taken out, and after being fully washed with water and dried, the decolorized jeans are obtained. The decolorization rate and the strength retention rate are tested. Meanwhile, the jeans fabric (5 g) previously wetted with distilled water is immersed in the cathode electrolyte for dyeing for 1 minute, after the dyeing is completed, the dyeing aftertreatment is completed through air permeation oxidation, soaping and washing, and the color depth K / S value of the finally obtained fabric is tested. Finally, 0.5 g of hydrogen peroxide is added into the cathode electrolyte, and the oxidation is carried out at 30°C for 45 minutes, then the pH value is adjusted to 7.5 by using glacial acetic acid, and then 0.5 g of alum is added and fully stirred, and after being placed for 2 hours, the cathode electrolyte subjected to the flocculation treatment is filtered, the filter cake is dried at 105°C, and finally the recovered indigo blue dye is obtained.

[0093] The specifications of the waste indigo blue jeans used in the examples are as follows: warp and weft yarn count 6s x 10s, warp density 237 roots / 10 cm, weft density 178 roots / 10 cm, fabric organization 3 / 1 right oblique, extra dark blue, width 150 / 155 cm (Guangdong Qianjin Jeans Co., Ltd.).

[0094] Table 1 Dyeing K / S value and breaking strength of the waste indigo blue jeans before and after treatment in different examples

[0095]

[0096] Figure 1 As shown in the infrared spectrum of the recovered indigo blue dye obtained in Example 1 and the infrared spectrum of the standard indigo blue dye, it can be seen that the infrared spectra of the recovered indigo blue dye obtained by the treatment in Example 1 and the standard indigo blue dye are basically the same. Figure 4 As shown in the figure of the redox potential of the cathode electrolyte and the dye reduction rate in the process of the efficient electrocatalytic recovery treatment of the waste indigo blue jeans in Example 1, it can be seen that with the progress of the electrolysis process, the absolute value of the reduction potential of the dye gradually reaches the potential of the leuco form of the indigo blue dye, the indigo blue dye on the waste jeans is gradually reduced into the leuco form of the dye, and further forms a soluble leuco form sodium salt with sodium ions in the electrolyte to be detached from the jeans.

[0097] The K / S value and breaking strength of the waste indigo denim before and after the recycling treatment in different embodiments are shown in Table 1, wherein the K / S value of the waste indigo denim before the treatment in each embodiment is 18.7532, and the breaking strength is 1319.8 N. The mass of the indigo dye recovered, the decolorization rate and the strength retention rate in different embodiments are shown in Table 2.

[0098] In the embodiments 1, 2 and 3, the effects of the neutral mannanase on the dye decolorization and recycling treatment of the waste denim are compared, and it can be seen that after the waste denim is activated and pretreated by the mannanase enzyme system, the recycling efficiency of the dye and the decolorization rate are higher. The neutral mannanase cooperates with the alkali metal complex to swell and loosen the cellulose and hemicellulose on the surface of the waste denim, and the alkali metal has an activating effect on the carbonyl in the mannanase and the dye on the waste denim, which is more conducive to the separation of the fiber and the dye in the next step, and thus the recycling efficiency of the dye can be greatly improved. In the embodiments 1, 3 and 5, the effects of the synergistic action between the enzyme hydrolysis and activation pretreatment and the molybdenum disulfide-carbon felt electrocatalytic reduction on the dye decolorization and recycling treatment of the waste denim are compared, and it can be seen that the decolorization rate in the case of the synergistic treatment of the mannanase enzyme hydrolysis decolorization and the molybdenum disulfide-carbon felt electrocatalytic reduction is much higher than that in the case of the single use of the mannanase enzyme hydrolysis decolorization or the single use of the molybdenum disulfide-carbon felt electrocatalytic reduction, and the high-efficiency recycling of the dye in the waste denim can be realized under the synergistic action.

[0099] In the embodiments 1 and 4, the effects of the molybdenum disulfide-carbon felt catalytic electrode and the ordinary carbon felt electrode on the electrochemical decolorization and recycling treatment are compared, and it can be seen that after the molybdenum disulfide catalyst is loaded on the carbon felt, the decolorization efficiency of the dye on the waste indigo denim can be greatly improved. This is because the nanoscale metal phase molybdenum disulfide catalyst has excellent conductivity, which can greatly improve the electron mobility and ion diffusion rate on the surface of the electrode. In addition, the higher specific surface area of the catalyst shortens the ion diffusion path, and as the cathode material for the electrocatalytic electrolysis recycling treatment of the waste denim, the catalyst can greatly promote the adsorption of active hydrogen and dye, and thus improve the dye recycling efficiency.

[0100] In addition, from Figure 2 , it can be seen from Table 1 and Table 2 that the high-efficiency electrocatalytic recycling treatment method of the dye in the waste denim according to the present application has the advantages of higher recycling mass of the dye, higher decolorization rate, higher strength retention rate, less use of chemical reagents, higher decolorization rate of more than 90%, higher strength retention rate, and can meet the requirements of the decolorization and finishing of the denim fabric, from Figure 3It can be seen that the denim fabric treated by the application has deeper color after electrocatalytic pre-reduction liquid dyeing, K / S is 15.7545, can reach 84.01% of the original dyeing depth, realizes secondary reuse, the application can significantly reduce energy consumption and environmental pollution, also reduces the comprehensive cost of production, is easy to realize industrialized production, and has good application prospect.

[0101] Table 2 mass of indigo dye recovered under different examples, decolorization rate and strength retention rate

[0102] Sample Recovered dye mass / mg Decolorization rate / % Strength retention / % Example 1 189.5 95.27 93.16 Example 2 166.3 92.15 93.39 Example 3 50.1 68.28 95.45 Example 4 66.7 72.46 94.23 Example 5 36.6 50.12 96.72 Comparative Example 1 33.2 56.49 85.52 Comparative Example 2 100.4 82.13 89.68

[0103] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recovering dyes from waste fabric, comprising: (1) mixing neutral mannanase, auxiliary chemical reagent and water, adjusting pH to obtain a pretreatment solution; wherein the auxiliary chemical reagent comprises potassium salt and / or calcium salt, and ligand complexing agent for stabilizing metal ions;the ligand complexing agent for stabilizing metal ions comprises sodium gluconate; (2) immersing the waste fabric in the pretreatment solution, mixing, heat treatment, washing and drying to obtain activated fabric; (3) performing electro-catalytic treatment on the activated fabric, and after electrolysis, post-treating the electrolyte to obtain recovered dyes;the cathode electrode used in the electro-catalytic treatment comprises a molybdenum disulfide-based catalytic electrode with carbon felt as substrate;the post-treatment comprises oxidation, flocculation, filtration and drying of the cathode electrolyte to complete the recovery of dyes.

2. The method of claim 1, wherein, In step (1), the concentration of neutral mannanase is 1-20% owf, and the enzyme activity is 20-50 U / mg;the pH is adjusted to 7-10.

3. The method of claim 1, wherein, In step (1), the potassium salt in the pretreatment solution is 5-50 mmol / L and / or the calcium salt is 5-50 mmol / L, and the ligand complexing agent for stabilizing metal ions is 5-100 mmol / L.

4. The method of claim 1, wherein, In step (2), the bath ratio of waste fabric to pretreatment solution is 1:10-25;the heat treatment temperature is 40-65℃, and the treatment time is 15-60 min;the dyes used for dyeing the waste fabric include one or more of vat dyes and sulfur dyes;the waste fabric is waste denim.

5. The method of claim 1, wherein, In step (3), the electro-catalytic treatment comprises adding the activated fabric into a cathode electrolytic cell under the protection of protective gas, and performing constant voltage electrolysis at room temperature. In step (3), the electrolytic voltage is 1-15 V, the electrolysis time is 30-200 min, the bath ratio of waste fabric to cathode electrolyte is 1:20-50, and the waste fabric is taken out after electrolysis to obtain decolorized fabric.

6. The method of claim 1, wherein, In step (3), the system used in the electro-catalytic treatment comprises cathode electrolyte, anode electrolyte, cathode, anode and diaphragm. The anode electrolyte comprises auxiliary electrolyte and alkali solution;the content of the auxiliary electrolyte is 0.05-0.4 mol / L, and the content of the alkali solution is 0.5-1 mol / L;the auxiliary electrolyte comprises at least one of sodium sulfate and sodium chloride, and the alkali solution comprises sodium hydroxide; The cathode electrolyte comprises aqueous solution of caustic soda, and the pH is 11-14; The anode electrode comprises at least one of graphite electrode and stainless steel electrode; The diaphragm comprises at least one of Nafion-117 and Nafion-324 proton exchange membrane.

7. The method according to claim 1, wherein the amount of the oxidizing agent used in the oxidation in step (3) is 5-15 g / L, and the amount of the flocculating agent used in the flocculation is 2-10 g / L. The oxidant comprises hydrogen peroxide;the flocculant comprises alum; The oxidation comprises oxidizing the oxidant at 30℃ for 30-60 min;the flocculation comprises adjusting the pH of the dye solution to 5.5-7.5 with glacial acetic acid, adding the flocculant to the oxidized cathode electrolyte, stirring uniformly, and then standing for 1-3 hours;the filtration comprises suction filtration of the flocculated cathode electrolyte;and the drying comprises drying the dye filter cake at 80-105℃ for 2-6 hours.

8. A pre-reduction solution based on recycled dyes, characterized in that, The pre-reduction solution is obtained by adding the recovered dye obtained by the method of claim 1 into a cathode electrolytic cell under the protection of a protective gas, and performing constant voltage electrolysis to obtain the dye pre-reduction solution.

9. The pre-reduction solution of claim 8, wherein, The recovered dye comprises at least one of a vat dye and a sulfur dye, and the concentration of the dye is 0.005-0.025 mol / L. The voltage in the constant voltage electrolysis process is 1-15 V, and the electrolysis time is 30-180 min. The constant voltage electrolysis system comprises a cathode electrolyte, an anode electrolyte, a cathode, an anode, and a diaphragm. The anode electrolyte comprises an auxiliary electrolyte and a lye, the content of the auxiliary electrolyte is 0.05-0.4 mol / L, and the content of the lye is 0.5-1 mol / L; the auxiliary electrolyte comprises at least one of sodium sulfate and sodium chloride, and the lye comprises sodium hydroxide. The cathode electrolyte comprises an aqueous solution of caustic soda, and the pH is 11-14. The cathode electrode comprises a molybdenum disulfide-based catalytic electrode with carbon felt as a substrate. The anode electrode comprises at least one of a graphite electrode and a stainless steel electrode. The diaphragm comprises at least one of Nafion-117 and Nafion-324 proton exchange membranes.

10. The application of the pre-reduction solution of claim 8 in fabric dyeing.

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