Acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics

Abstract

This invention discloses an acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics. Using waste polyester or waste polyester-cotton blended fabrics as raw materials, under the action of an acidic catalyst, in a mixed solvent composed of a polar aprotic solvent and water, the method involves heating and degradation, causing the polyester in the waste polyester or polyester-cotton blended fabrics to depolymerize or co-depolymerize, generating organic raw materials. This invention achieves complete depolymerization and recycling of polyester with a relatively low acid dosage, effectively avoiding the corrosion problems of equipment and excessive degradation of cotton fibers caused by existing technologies. It is also more conducive to the generation and recovery of glucose and 5-hydroxymethylfurfural. Furthermore, the separation steps are simple, greatly reducing separation costs, and high-yield recovery of terephthalic acid, glucose, and 5-hydroxymethylfurfural is achieved, realizing high-value recycling and utilization of various components in textiles, reducing waste, and improving resource utilization.

Description

Technical Field

[0001] This invention belongs to the technical field of solid waste recycling methods, specifically relating to an acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics. Background Technology

[0002] Over the past two decades, global fiber production has nearly doubled, increasing from 58 million tons in 2000 to 109 million tons in 2020, with polyester (polyethylene terephthalate fiber) accounting for the largest share. Polyester is a chemical fiber widely used in the clothing industry. Coupled with the current trend of rapid fashion changes in clothing, this has generated a large amount of textile waste. Due to difficulties in recycling, it is mainly disposed of through landfill or incineration, leading to resource waste, environmental pollution, and the potential threat to human health posed by microfibers found in rivers, oceans, and drinking water.

[0003] Currently, the recycling rate of waste polyester textiles is very low, with only 13% of textiles ultimately entering the recycling process. Of these, 12% is reused to manufacture other low-value materials (such as cleaning cloths and carpets), and only 1% is recycled to make new clothes or other high-value products. Physical recycling and chemical recycling are representative recycling methods. Physical methods mainly involve mechanical processing, such as cutting, tearing, opening, and combing, to directly process waste textiles into recycled fibers. However, fibers often suffer performance loss during this physical processing and ultimately cannot be reused. In addition, because textiles are usually woven from multiple polymers and contain additives such as dyes and brighteners, they are difficult to separate and recycle effectively through physical methods.

[0004] The main chemical recycling methods for polyester fibers include alcoholysis, ammonia / amine hydrolysis, and hydrolysis. Compared to other solvation methods, hydrolysis can yield the raw material monomers terephthalic acid (TPA) and ethylene glycol (EG). Currently, the industrial production of polyester mainly involves the direct polymerization of TPA and EG. Therefore, waste polyester can be hydrolyzed to obtain TPA to supplement petroleum-based raw materials. However, the depolymerization process requires harsh reaction conditions, generally requiring temperatures >220℃ and pressures >2MPa (WasteManage., 2021, 135, 267-274; Chem.Eng.J., 2020, 398, 125655). Furthermore, it requires high concentrations of acid and alkali as catalysts, which can easily corrode equipment. Furthermore, for polyester-cotton blended fabrics, due to their complex composition, solvent treatment is often required to separate the components before hydrolysis. This high cost and wastewater discharge limit the competitiveness of this method, leading current research to focus primarily on cotton fibers, which are easily treated with acids or ionic liquids, while neglecting the recovery and conversion of polyester. The yield of 5-hydroxymethylfurfural (HMF) recovered from cotton fiber degradation is often very low (Carbohydr. Polym., 2015, 117, 674-700; CN112574143A). Recently, researchers have turned their attention to the depolymerization of polyester after separating cotton from blended fabrics (GreenChem., 2021, 23, 4065-4073). However, the complex processing steps and wastewater generation make this method economically infeasible.

[0005] Therefore, existing methods for recycling waste polyester-cotton blended fabrics usually rely on the degradation differences in a specific reaction system to recover a specific component of the blended fabric, rather than fully recovering and utilizing all components of the waste polyester-cotton blended fabric. Thus, converting polyester and cotton in waste textiles into high-value chemicals in a one-pot process is more promising and challenging. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing an acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics. This method can achieve both the depolymerization and recycling of pure polyester and the conversion of polyester in polyester-cotton blended fabrics into monomers, while simultaneously converting the cotton into at least one of microcrystalline cellulose, oligosaccharides, glucose, and 5-hydroxymethylfurfural. Furthermore, the degradation products of polyester during the degradation process can also promote the conversion of cotton.

[0007] The present invention provides an acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics. The method uses waste polyester or waste polyester-cotton blended fabrics as raw materials. Under the action of an acid catalyst, the waste polyester or polyester-cotton blended fabrics are heated and degraded in a mixed solvent composed of a polar aprotic solvent and water, so that the polyester in the waste polyester or polyester-cotton blended fabrics undergoes depolymerization or polyester-cotton co-depolymerization to generate organic raw materials.

[0008] The present invention provides a method for the acid-catalyzed controlled degradation and recycling of waste polyester and polyester-cotton blended fabrics. The specific process and conditions of this method are as follows:

[0009] 1) Place waste polyester or waste polyester-cotton blended fabric into a mixed solvent consisting of water and a polar aprotic solvent in a mass ratio of 1-3:10-10000. Then add 1-80% of the acidic catalyst based on the mass of the mixed solvent and stir to mix. Perform a depolymerization reaction or co-depolymerization reaction at 100-250℃ for 10-300 minutes. The amount of waste polyester or waste polyester-cotton blended fabric added is 1-50% based on the mass of the mixed solvent.

[0010] 2) After the reaction is complete, cool to room temperature to allow terephthalic acid to precipitate from the reaction solution. Then filter and dry sequentially to obtain the product terephthalic acid and ethylene glycol in the reaction solution. Alternatively, cool to room temperature to allow terephthalic acid to precipitate from the reaction solution, then filter and dry sequentially to obtain the product terephthalic acid and ethylene glycol in the reaction solution, as well as at least one of microcrystalline cellulose, oligosaccharides, glucose, and 5-hydroxymethylfurfural.

[0011] In the above methods, when waste polyester undergoes degradation, the products are terephthalic acid and ethylene glycol; when waste polyester-cotton blended fabrics undergo co-depolymerization, the products are terephthalic acid, ethylene glycol, and at least one of microcrystalline cellulose, oligosaccharides, glucose, and 5-hydroxymethylfurfural.

[0012] In the above method, ethylene glycol or ethylene glycol in the reaction solution, as well as microcrystalline cellulose, oligosaccharides, glucose and 5-hydroxymethylfurfural, can be separated one by one according to the methods disclosed in the prior art (Science, 2014, 343, 277-280; Chem. Eng. J., 2022, 437, 135408) to obtain the final organic raw materials.

[0013] The polar aprotic solvent mentioned in the above methods is at least one of dimethyl sulfoxide, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolinone, hexamethylphosphoric triamine, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone.

[0014] The acidic catalyst mentioned in the above methods is at least one selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, propionic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, terephthalic acid, benzoic acid, heteropoly acid, acidic ionic liquid, aluminum chloride, zinc chloride, solid acid, and molecular sieve. The solid acid is an acidic ion exchange resin, γ-Al₂O₃, or a supported acidic catalyst; the molecular sieve is a Y-type molecular sieve, an H-beta molecular sieve, a ZSM-type molecular sieve, an SBA-type molecular sieve, or an MCM-type molecular sieve.

[0015] In the above method, the mass ratio of water to polar aprotic solvent in the mixed solvent is preferably 1-3:100-1000, more preferably 1-3:10-100.

[0016] The preferred reaction temperature in the above method is 120–200°C.

[0017] The amount of acidic catalyst added in the above method is preferably 1 to 50% based on the mass of the mixed solvent.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. Because the polar aprotic solvent used in the recycling method provided by this invention has a good swelling or dissolving effect on polyester fibers, the mass transfer effect between polyester and catalyst is enhanced during the reaction process. This allows the invention to achieve complete depolymerization and recycling of polyester under conditions of lower acid dosage, effectively avoiding the corrosion problem of equipment caused by existing technologies.

[0020] 2. Since the recycling method provided by this invention uses a polar aprotic solvent, a low-acid catalyst can be used. This avoids the excessive degradation of cotton fibers caused by existing technologies in the recycling of waste polyester-cotton blended textiles, and is more conducive to the generation and recycling of glucose and 5-hydroxymethylfurfural.

[0021] 3. Because the solvent system and catalyst in the recovery method provided by the present invention are matched and designed, the TPA product after polyester depolymerization can be directly precipitated by self-precipitation and can be separated by simple filtration. Therefore, not only is the separation step simple, greatly reducing the separation steps and separation cost, but also high-yield TPA (95%) can be recovered, and the total yield of glucose and 5-hydroxymethylfurfural obtained by depolymerization can be greater than 70%.

[0022] 4. Because the reaction solvent used in the recycling method provided by this invention not only enables the depolymerization of polyester under low acidity through swelling and dissolution, but also has a positive promoting effect on the conversion to 5-hydroxymethylfurfural. At the same time, the polyester product TPA can also have a positive promoting effect on the conversion of cotton fibers due to its own acidity. Therefore, it can not only produce a positive promoting effect between each other, but also realize the high-value recycling of various components in textiles, reduce waste, and improve the utilization rate of resources. Attached Figure Description

[0023] Figure 1 The image shows a comparison of the 1H NMR spectra of TPA obtained by depolymerization and recovery of polyester-cotton blended fabrics using the method provided in this invention, and commercially available TPA. The image shows that the peak positions and integrals of the 1H NMR spectra of the recovered TPA are basically consistent with those of the commercially available TPA, indicating that the polyester depolymerization and recovery process not only yielded TPA but also achieved high purity.

[0024] Figure 2 The image shows the 1H NMR spectrum of the degradation solution obtained after degrading polyester-cotton blended fabrics using the method provided by this invention. The image shows the presence of 5-hydroxymethylfurfural in the degradation solution, indicating that cotton can be effectively converted into 5-hydroxymethylfurfural after depolymerization.

[0025] Figure 3 This invention provides an HPLC study to detect glucose in the degradation solution of polyester-cotton blended fabrics at different reaction times during the depolymerization reaction. The figures show that glucose was detected at all reaction time points, indicating that the glycosidic bonds in the cotton fibers of the polyester-cotton blended fabric had broken, generating glucose products.

[0026] Figure 4 This invention provides an HPLC method for the detection of HMF in the degradation solution obtained from polyester-cotton blended fabrics at different depolymerization reaction times. The figure shows that HMF was detected at all reaction time points, indicating that cotton in the polyester-cotton blended fabric can be effectively converted into HMF. Detailed Implementation

[0027] The following embodiments are provided to further illustrate the present invention. It should be noted that the following embodiments should not be construed as limiting the scope of protection of the present invention. If those skilled in the art make some non-essential improvements and adjustments to the present invention based on the above description, they shall still fall within the scope of protection of the present invention.

[0028] It is worth noting that:

[0029] 1) The degradation rate of waste polyester in the examples and comparative examples was calculated using the following formula:

[0030] D p= (W0-W1) / W0×100%

[0031] In the formula: D p W0 represents the degradation rate; W1 represents the mass of waste polyester; and W2 represents the mass of undegraded polyester obtained after filtration and separation of the degradation liquid, followed by washing and drying.

[0032] 2) The degradation rates of polyester and cotton in the waste polyester-cotton blended fabrics in the examples and comparative examples were calculated using the following formula:

[0033] D p =W3 / βW2×100%

[0034] D c =W4 / (1-β)W2×100%

[0035] In the formula: D p D represents the polyester degradation rate. c W1 represents the cotton degradation rate; W2 represents the mass of waste polyester-cotton blended fabric; W3 represents the mass of undegraded polyester obtained after filtration and separation of the degradation liquid after the reaction, followed by washing and drying; W4 represents the mass of undegraded cotton obtained after filtration and separation of the degradation liquid after the reaction, followed by washing and drying; β represents the proportion of polyester in waste polyester-cotton blended fabric.

[0036] 3) The monomer yields and product recoveries in the examples and comparative examples were calculated using the following formulas:

[0037] Y TPA =W5 / W6 × 100%

[0038] Y c =W7 / W8 × 100%

[0039] In the formula: Y TPA Y represents the monomer recovery rate. c W5 represents the recovery rate of microcrystalline cellulose; W6 represents the mass of TPA recovered; W7 represents the mass of theoretical TPA; W8 represents the mass of microcrystalline cellulose recovered; and W9 represents the mass of cellulose.

[0040] 4) The yields of glucose and 5-hydroxymethylfurfural were obtained by quantitative analysis using 1H NMR spectroscopy with benzyl benzoate as an internal standard; the yields of oligosaccharides were obtained by quantitative analysis using 5mM sulfuric acid aqueous solution as the mobile phase.

[0041] 5) The waste polyester-cotton blended fabrics used in the examples and comparative examples all contained 80% polyester and 20% cotton. The waste polyester or waste polyester-cotton blended fabrics used in the examples and comparative examples were all cut into 2mm×2mm fragments before the recycling reaction.

[0042] Example 1

[0043] Waste polyester-cotton blended fabric fragments were added to a mixed solvent of water and methyl ethyl ketone at a mass ratio of 1:10000 (1% by mass of the mixed solvent). Then, 1% hydrochloric acid (based on the mass of the mixed solvent) was added, and the mixture was reacted at 180℃ for 60 min. After the reaction, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. The precipitate was then filtered and dried to obtain terephthalic acid. The degradation rate of polyester was 20%, and the recovery rate of terephthalic acid was 15%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 30% and 5%, respectively.

[0044] Example 2

[0045] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of N-methylpyrrolidone and water, with a water-to-N-methylpyrrolidone mass ratio of 1:10000. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. Nitric acid was added at 10% of the mass of the mixed solvent. The reaction was carried out at 100℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 93%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 25% and 6%, respectively.

[0046] Example 3

[0047] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of acetonitrile and water, with a water-to-acetonitrile mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. Sulfuric acid was added at 1% of the mass of the mixed solvent. The reaction was carried out at 250℃ for 10 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 70%, and the yield of terephthalic acid was 63%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 18% and 8%, respectively.

[0048] Example 4

[0049] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of hexamethylphosphoric acid (HPA) and water, with a mass ratio of water to HPA of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. The amount of phosphoric acid added was 5% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 91%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 20% and 7%, respectively.

[0050] Example 5

[0051] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of hexamethylphosphoric acid (HPA) and water, with a mass ratio of water to HPA of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. The amount of phosphoric acid added was 30% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 30 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 86%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 17% and 5%, respectively.

[0052] Example 6

[0053] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of 1,3-dimethyl-2-imidazolinone and water, with a mass ratio of water to 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. Formic acid was added at 10% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 85%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 28% and 7%, respectively.

[0054] Example 7

[0055] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of N,N-dimethylacetamide and water, with a water-to-N,N-dimethylacetamide mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 50% of the mass of the mixed solvent. Acetic acid was added at 40% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 83%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 26% and 6%, respectively.

[0056] Example 8

[0057] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of N,N-dimethylformamide and water, with a water-to-N,N-dimethylformamide mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 25% of the mass of the mixed solvent. Propionic acid was added at 40% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 87%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 25% and 6%, respectively.

[0058] Example 9

[0059] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-butyrolactone and water, with a mass ratio of water to gamma-butyrolactone of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 120 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 89%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 36% and 15%, respectively.

[0060] Example 10

[0061] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a mass ratio of water to gamma-valerol of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 93%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 46% and 20%, respectively.

[0062] Example 11

[0063] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of delta-valerolactone and water, with a water-to-delta-valerolactone mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 60 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 90%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 43% and 17%, respectively.

[0064] Example 12

[0065] Waste polyester-cotton blended fabric fragments were added to a 20 mL mixture of acetone and water (mass ratio of water to acetone: 1:100), with the polyester-cotton blended fabric accounting for 5% of the mixed solvent mass. Methanesulfonic acid was added at 10% of the mixed solvent mass. The reaction was carried out at 100℃ for 300 min. After the reaction, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 60%, and the yield of terephthalic acid was 52%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC, with a cotton degradation rate of 100%. The yields of glucose and 5-hydroxymethylfurfural were 31% and 10%, respectively.

[0066] Example 13

[0067] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of tetrahydrofuran and water, with a water-to-tetrahydrofuran mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. Ethylenesulfonic acid was added at 10% of the mass of the mixed solvent. The reaction was carried out at 150 °C for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 70%, and the yield of terephthalic acid was 63%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 34% and 11%, respectively.

[0068] Example 14

[0069] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of dimethyl sulfoxide and water, with a water-to-dimethyl sulfoxide mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. Ethylene sulfonic acid was added at 10% of the mass of the mixed solvent. The reaction was carried out at 150 °C for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 65%, and the yield of terephthalic acid was 60%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 36% and 11%, respectively.

[0070] Example 15

[0071] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of p-toluenesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 170℃ for 100 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 94%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 45% and 25%, respectively.

[0072] Comparative Example 1

[0073] Waste polyester-cotton blended fabric fragments were added to 20 mL of water, with the amount of polyester-cotton blended fabric added being 5% of the water mass. Toluenesulfonic acid was added at 10% of the water mass. The reaction was carried out at 170℃ for 100 min. After the reaction, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 2.1%, and the yield of terephthalic acid was 2%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 18% and 3%, respectively.

[0074] Comparative Example 2

[0075] Waste cotton fabric fragments were added to a mixed solvent of gamma-valerol and water in 20 mL, with a mass ratio of water to gamma-valerol of 1:100 and the amount of cotton fabric added being 5% of the mass of water. The amount of p-toluenesulfonic acid added was 10% of the mass of water. The reaction was carried out at 170 °C for 100 min. After the reaction was completed, the cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 28% and 18%, respectively.

[0076] Example 16

[0077] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of aluminum chloride added was 40% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 89%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 38% and 14%, respectively.

[0078] Example 17

[0079] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:10. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. Zinc chloride was added at 80% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 88%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 36% and 15%, respectively.

[0080] Example 18

[0081] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-butyrolactone and water, with a mass ratio of water to gamma-butyrolactone of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of Y-type molecular sieve added was 20% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 30%, and the yield of terephthalic acid was 22%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 20% and 5%, respectively.

[0082] Example 19

[0083] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-butyrolactone and water, with a mass ratio of water to gamma-butyrolactone of 3:10. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of Y-type molecular sieve added was 20% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 19%, and the yield of terephthalic acid was 14%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 16% and 3%, respectively.

[0084] Example 20

[0085] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a mass ratio of water to gamma-valerol of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of ZSM molecular sieve added was 20% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 200 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 25%, and the yield of terephthalic acid was 21%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 22% and 5%, respectively.

[0086] Example 21

[0087] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. ZSM molecular sieves were added at 50% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 65%, and the yield of terephthalic acid was 61%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 29% and 6%, respectively.

[0088] Example 22

[0089] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of methyl ethyl ketone and water, with a water-to-methyl ethyl ketone mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. SBA molecular sieves were added to make the mass concentration 20% of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 15%, and the yield of terephthalic acid was 12%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 19% and 4%, respectively.

[0090] Example 23

[0091] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of methyl ethyl ketone and water, with a water-to-methyl ethyl ketone mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of MCM molecular sieve added was 20% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 20%, and the yield of terephthalic acid was 16%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 22% and 6%, respectively.

[0092] Example 24

[0093] Waste polyester-cotton blended fabric fragments were added to a mixed solvent of acetonitrile and water in a mass ratio of 1:100, with the amount of polyester-cotton blended fabric added being 1% of the mass of the mixed solvent. Sulfuric acid was added at 1% of the mass of the mixed solvent. The reaction was carried out at 130℃ for 30 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, a mixture of terephthalic acid and microcrystalline cellulose was obtained. The mixture was treated with sodium hydroxide solution and then filtered to obtain microcrystalline cellulose. The filtrate was acidified and filtered to obtain terephthalic acid. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The degradation rate of polyester was 10%, the yield of terephthalic acid was 8%, the degradation rate of cotton was 100%, and the yields of microcrystalline cellulose and glucose were 22% and 5%, respectively.

[0094] Example 25

[0095] Waste polyester fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a mass ratio of water to gamma-valerol of 1:1000. The amount of polyester added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 300 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 93%.

[0096] Comparative Example 3

[0097] Waste polyester fragments were added to 20 mL of water, with the amount of polyester added being 5% of the mass of the mixed solvent; the amount of methanesulfonic acid added was 10% of the mass of water. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 4%, and the yield of terephthalic acid was 3%.

[0098] Comparative Example 4

[0099] Waste polyester fragments were added to 20 mL of water, with the amount of polyester added being 5% of the water mass; methanesulfonic acid was added at 80% of the water mass. The reaction was carried out at 180℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 91%.

[0100] Example 26

[0101] Waste polyester fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a mass ratio of water to gamma-valerol of 1:500. The amount of polyester added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 100 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 91%.

[0102] Example 27

[0103] Waste polyester fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a mass ratio of water to gamma-valerol of 3:10. The amount of polyester added was 5% of the mass of the mixed solvent. The amount of p-toluenesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 100 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 60%, and the yield of terephthalic acid was 53%.

[0104] Example 28

[0105] Waste polyester fragments were added to a mixed solvent of hexamethylphosphoric acid and water in 20 mL, wherein the mass ratio of water to hexamethylphosphoric acid was 1:10, and the amount of polyester added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180℃ for 100 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 80%, and the yield of terephthalic acid was 73%.

[0106] Example 29

[0107] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of methyl ethyl ketone and water, with a water-to-methyl ethyl ketone mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. The amount of terephthalic acid added was 20% of the mass of the mixed solvent. The reaction was carried out at 220℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to allow the terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 70%, and the yield of terephthalic acid was 63%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 18% and 5%, respectively.

[0108] Example 30

[0109] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. Benzoic acid was added at 20% of the mass of the mixed solvent. The reaction was carried out at 220℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 90%, and the yield of terephthalic acid was 83%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 26% and 6%, respectively.

[0110] Example 31

[0111] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. The amount of heteropoly acid added was 20% of the mass of the mixed solvent. The reaction was carried out at 220℃ for 300 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 90%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 21% and 7%, respectively.

[0112] Example 32

[0113] Waste polyester fragments were added to 20 mL of a mixed solvent of N-methylpyrrolidone and water, with a mass ratio of water to N-methylpyrrolidone of 1:100. The amount of polyester added was 1% of the mass of the mixed solvent. The amount of acidic ionic liquid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 300 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 93%.

[0114] Example 33

[0115] Waste polyester fragments were added to a mixed solvent of N-methylpyrrolidone and water in 20 mL, with a mass ratio of water to N-methylpyrrolidone of 1:100. The amount of polyester added was 1% of the mass of the mixed solvent. The amount of acidic ion exchange resin added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 180 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, the product terephthalic acid was obtained. The degradation rate of polyester was 73%, and the yield of terephthalic acid was 65%.

[0116] Example 34

[0117] Waste polyester fragments were added to 20 mL of a mixed solvent of delta-valerolactone and water, with a water-to-delta-valerolactone mass ratio of 1:100. The amount of polyester added was 1% of the mass of the mixed solvent. The amount of γ-Al₂O₃ added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 180 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. A certain amount of potassium hydroxide was added, and the mixture was filtered. The filtrate was acidified to obtain a solid product, which was then filtered to obtain terephthalic acid. The degradation rate of polyester was 68%, and the yield of terephthalic acid was 63%.

[0118] Example 35

[0119] Waste polyester fragments were added to 20 mL of a mixed solvent of delta-valerolactone and water, with a water-to-delta-valerolactone mass ratio of 1:100. The amount of polyester added was 1% of the mass of the mixed solvent. The amount of the supported acidic catalyst added was 20% of the mass of the mixed solvent. The reaction was carried out at 200℃ for 180 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. A certain amount of potassium hydroxide was added, and the mixture was filtered. The filtrate was acidified to obtain a solid product, which was then filtered to obtain terephthalic acid. The degradation rate of polyester was 88%, and the yield of terephthalic acid was 85%.

[0120] Example 36

[0121] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 1% of the mass of the mixed solvent. The amount of H-beta molecular sieve added was 20% of the mass of the mixed solvent. The reaction was carried out at 200℃ for 180 min. After the reaction was completed, the mixture was cooled to room temperature to precipitate terephthalic acid from the reaction solution. A certain amount of potassium hydroxide was added, and the mixture was filtered. The filtrate was acidified to obtain a solid product, which was terephthalic acid. The degradation rate of polyester was 90%, and the yield of terephthalic acid was 83%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yields of glucose and 5-hydroxymethylfurfural were 22% and 5%, respectively.

[0122] Example 37

[0123] Waste polyester fragments were added to a mixed solvent of acetone, tetrahydrofuran, and water in 20 mL, where the mass ratio of water to acetone to tetrahydrofuran was 1:10:10, and the amount of polyester added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 10% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 100 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 93%.

[0124] Example 38

[0125] Waste polyester fragments were added to a mixed solvent of acetone, tetrahydrofuran, and water in 20 mL, where the mass ratio of water to acetone to tetrahydrofuran was 1:10:10. The amount of polyester added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was 5% of the mass of the mixed solvent, and the amount of p-methanesulfonic acid added was 5% of the mass of the mixed solvent. The reaction was carried out at 180 °C for 100 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 100%, and the yield of terephthalic acid was 91%.

[0126] Example 39

[0127] Waste polyester-cotton blended fabric fragments were added to 20 mL of a mixed solvent of gamma-valerol and water, with a water-to-gamma-valerol mass ratio of 1:100. The amount of polyester-cotton blended fabric added was 5% of the mass of the mixed solvent. The amount of methanesulfonic acid added was also 5% of the mass of the mixed solvent. The reaction was carried out at 160℃ for 200 min. After the reaction was completed, the mixture was cooled to room temperature to allow terephthalic acid to precipitate from the reaction solution. After filtration and drying, terephthalic acid was obtained. The degradation rate of polyester was 55%, and the yield of terephthalic acid was 50%. The cotton conversion products in the reaction solution were quantified by NMR and HPLC. The cotton degradation rate was 100%, and the yield of oligosaccharides was 33%.

Claims

1. A method for the acid-catalyzed controlled degradation and recycling of waste polyester and polyester-cotton blended fabrics, wherein the method uses waste polyester or waste polyester-cotton blended fabrics as raw materials, and under the action of an acidic catalyst, in a mixed solvent composed of a polar aprotic solvent and water, the materials are heated and degraded, causing the polyester in the waste polyester or polyester-cotton blended fabrics to depolymerize or the polyester and cotton to co-depolymerize and generate organic raw materials. The specific process and conditions of this method are as follows: 1) Place waste polyester or waste polyester-cotton blended fabrics into a mixed solvent consisting of water and a polar aprotic solvent in a mass ratio of 1~3:10~10000. Then add 1~80% of the acidic catalyst based on the mass of the mixed solvent and stir to mix. Perform a depolymerization reaction or co-depolymerization reaction at 100~250℃ for 10~300 min. The amount of waste polyester or waste polyester-cotton blended fabrics added is 1~50% based on the mass of the mixed solvent. 2) After the reaction is complete, cool to room temperature to allow terephthalic acid to precipitate from the reaction solution. Then, filter and dry sequentially to obtain the product terephthalic acid and ethylene glycol in the reaction solution. Alternatively, cool to room temperature to allow terephthalic acid to precipitate from the reaction solution, then filter and dry sequentially to obtain the product terephthalic acid and ethylene glycol in the reaction solution, as well as at least one of microcrystalline cellulose, oligosaccharides, glucose, and 5-hydroxymethylfurfural. The polar aprotic solvent mentioned therein is at least one selected from dimethyl sulfoxide, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolinone, hexamethylphosphoric triamine, N-methylpyrrolidone, acetonitrile, methyl ethyl ketone, gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone. The acidic catalyst is at least one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, propionic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, terephthalic acid, benzoic acid, heteropoly acid, acidic ionic liquid, aluminum chloride, zinc chloride, acidic ion exchange resin, and molecular sieve.

2. The acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics according to claim 1, wherein the molecular sieve in the method is a Y-type molecular sieve, an H-beta molecular sieve, a ZSM-type molecular sieve, an SBA-type molecular sieve, or an MCM-type molecular sieve.

3. The acid-catalyzed controlled degradation and recycling method for waste polyester and polyester-cotton blended fabrics according to claim 1 or 2, wherein the mass ratio of water to polar aprotic solvent in the mixed solvent is 1~3:100~1000; the reaction temperature is 120~200℃; and the amount of acid catalyst added is 1~50% based on the mass of the mixed solvent.

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