Chemical separation method of polyester-cotton composite material

Abstract

The invention relates to the technical field of waste fabric recovery, in particular to a chemical separation method of a polyester-cotton composite material. The chemical separation method comprises the following steps: adding an alcohol solvent and NH4OH into the polyester-cotton composite material for reaction. According to the chemical separation method, NH4OH is used for replacing sodium hydroxide used in traditional alkali treatment, terephthalic acid diamine salt is obtained through depolymerization, the thermal stability of the terephthalic acid diamine salt is poor, the terephthalic acid diamine salt can be directly decomposed into terephthalic acid and recyclable ammonia gas through thermal cracking, use of acid and byproduct salt generated by acid-base neutralization are avoided, and recycling of the polyester-cotton composite material is better facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste fabric recycling, and particularly relates to a chemical separation method of polyester-cotton composite material. BACKGROUND

[0002] Polyester-cotton blended fabric is one of the most common clothing fabrics, and the amount and stock of waste textiles in China are huge, but the utilization rate of waste textiles is less than 20%.

[0003] Component separation is a prerequisite for realizing high-value regeneration and utilization of polyester-cotton composite material, and selective removal of a component through chemical depolymerization is a feasible and effective method. The prior art such as Chinese invention patents with publication numbers CN111868316A and CN119384453A selectively depolymerizes polyester fibers in polyester-cotton waste into water-soluble terephthalate and ethylene glycol through alkali treatment, and the remaining cotton fibers can be used as raw materials for preparing regenerated cellulose fibers such as viscose or lyocell after further stripping and purification.

[0004] The polyester depolymerate after alkali treatment contains sodium terephthalate, and dilute sulfuric acid or hydrochloric acid is added to the alkali treatment waste liquid containing sodium terephthalate salt, and the pH is adjusted to about 2-3, and the sodium terephthalate salt will be converted into terephthalic acid and precipitated, realizing the collection of terephthalic acid. Since the alkali used in the alkali treatment is often excessive, in the acid precipitation process, the added acid will first neutralize the excess alkali, and after the alkali is consumed, it will react with sodium terephthalate to make it acid-precipitated and precipitated. In this way, the amount of acid and alkali used is huge, and the waste salt by-products such as sodium sulfate and sodium chloride formed after the neutralization of acid and alkali far exceed the amount of product terephthalic acid, making it difficult to recycle the polyester alkali depolymerate. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a chemical separation method of polyester-cotton composite material which is beneficial to the recycling of polyester alkali depolymerate.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows: a chemical separation method of polyester-cotton composite material, comprising the following steps: adding an alcohol solvent and NH4OH to the polyester-cotton composite material for reaction.

[0007] The present application has the advantages that in the recycling of polyester-cotton composite material, NH4OH is used instead of sodium hydroxide used in traditional alkali treatment, and p-phenylenediamine terephthalate is obtained by depolymerization, which has poor thermal stability and can be directly decomposed into terephthalic acid (TPA) and recyclable ammonia gas through thermal cracking, avoiding the use of acid and the generation of by-product salt after the neutralization of acid and alkali, and being more beneficial to the recycling of polyester-cotton composite material. DETAILED DESCRIPTION

[0008] To make the technical contents of the present application, the purposes and effects achieved more clear, the following will be described in conjunction with the embodiments.

[0009] A chemical separation method of polyester-cotton composite material, comprising the following steps: adding alcohol solvent and NH4OH into the polyester-cotton composite material to react.

[0010] From the above description, the beneficial effects of the present application are that: when recycling the polyester-cotton composite material, the present application uses NH4OH to replace sodium hydroxide used in traditional alkali treatment, and the obtained polyester depolymerization product is terephthalic acid diamine salt, which is an unconventional terephthalic acid salt. Terephthalic acid diamine salt has poor thermal stability and can be directly decomposed into TPA and recyclable ammonia gas through thermal cracking at about 190℃. There is no need to convert terephthalic acid salt into TPA through acid precipitation method, thereby avoiding the use of acid and the by-product salt generated by acid-base neutralization, and being more conducive to polyester-cotton composite material recycling.

[0011] Further, the alcohol solvent is at least one of methanol, ethanol and ethylene glycol.

[0012] Further, the alcohol solvent is ethanol.

[0013] From the above description, the present application uses alcohol solvent to replace water as the reaction medium, which can effectively reduce the reaction temperature and improve the reaction rate.

[0014] Further, the mass ratio of the alcohol solvent to the polyester-cotton composite fabric is 10-20:1.

[0015] From the above description, the alcohol solvent needs to effectively soak the polyester-cotton composite fabric to ensure that the reaction proceeds effectively.

[0016] Further, the mass ratio of NH4OH to the polyester-cotton composite fabric is 0.5-2.0:1.

[0017] From the above description, a slight excess of NH4OH can ensure a relatively high conversion rate of the reaction.

[0018] Further, the NH4OH is added in the form of ammonia water.

[0019] From the above description, the NH4OH is added in the form of ammonia water, which does not require an additional dissolution step. The solute can quickly contact with the reactants and participate in the reaction process, so the reaction rate is relatively fast.

[0020] Further, the concentration of the ammonia water is 10-28 wt%.

[0021] Further, the reaction temperature of the reaction is 120-160℃.

[0022] Further, the reaction time of the reaction is 2-5h.

[0023] Furthermore, the reaction takes place under closed conditions.

[0024] As can be seen from the above description, the reaction is carried out under closed conditions to avoid solvent evaporation.

[0025] Furthermore, it also includes the step of condensing and collecting the vapor after the reaction.

[0026] As can be seen from the above description, the vapors produced after the reaction are methanol and ammonia. The collected material can be used to replenish the consumed NH4OH and can be used for the next depolymerization.

[0027] Furthermore, it also includes the step of washing the reaction product with water.

[0028] As can be seen from the above description, after the product is washed with water, the generated diamine terephthalate salt can be dissolved, and the remaining solid is the separated cotton fiber.

[0029] The detection methods and standards involved in the following examples and comparative examples are as follows: Infrared spectroscopy was used to confirm whether the separated cotton fibers contained polyester residues: the molecular structure of polyester fibers contains a carbonyl absorption peak at 1720 cm⁻¹. -1 Around 1720 cm⁻¹, cotton cellulose does not show an absorption peak at this location. Therefore, the infrared spectrum of the separated cotton fibers can be used to determine the absorption peak at 1720 cm⁻¹. -1 The presence of absorption peaks can be used to confirm the presence of polyester residue.

[0030] The polyester-cotton composition ratio was tested according to GB / T2910.11-2009.

[0031] Example 1 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2 300g of ethanol and 80g of 25 wt% ammonia were depolymerized at 130℃ for 3 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate. The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 11.7g, with no polyester residue (yield 92.9%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed several times with water, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.34g (yield 83.5%).

[0032] Example 2 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2 200g of ethylene glycol and 100g of 25 wt% ammonia solution were depolymerized at 160℃ for 4 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate. The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 11.4g, with no polyester residue (yield 92.1%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed with water several times, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.27g (yield 82.4%).

[0033] Example 3 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2 300g of ethanol and 60g of 25 wt% ammonia were depolymerized at 130℃ for 4 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate. The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 11.8g, with no polyester residue (yield 93.6%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed with water several times, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.36g (yield 83.8%).

[0034] Example 4 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2300g of ethanol and 80g of 25 wt% ammonia were depolymerized at 130℃ for 3 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate. The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 12.0g, with no polyester residue (yield 95.2%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed several times with water, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.38g (yield 83.8%).

[0035] Example 5 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2 400g of methanol and 400g of 28 wt% ammonia were depolymerized at 120℃ for 5 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate. The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 11.9g, with no polyester residue (yield 94.4%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed several times with water, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.05g (yield 81.3%).

[0036] Example 6 of the present invention is: a chemical separation method for polyester-cotton composite material, the specific steps of which are as follows: 20g of polyester-cotton composite material (cotton content 63%, polyester content 37%, woven fabric, weight 160 g / m²) is added to a 1L sealed reaction vessel. 2100g methanol, 150g ethanol, and 35.7g 10 wt% ammonia solution were depolymerized at 160℃ for 2 hours. After depolymerization, the exhaust valve at the top of the reactor was opened to discharge the methanol and ammonia vapors, which were then condensed and collected. After collection, when the temperature inside the reactor dropped to 60℃, the reactor lid was opened, the material inside was removed, and the material was washed with water to dissolve the generated diamine terephthalate (TPA). The remaining solid was the separated cotton fiber, which was dried and weighed to obtain 11.7g, with no polyester residue (yield 92.9%). The washing liquid was collected in a flask, and the water was first evaporated under vacuum at 80℃, then evaporated at 200℃ for 1 hour and cooled to room temperature. The remaining solid in the flask was washed several times with water, and the insoluble matter was TPA, which was collected, dried, and weighed to obtain 5.3g (yield 85.3%).

[0037] Comparative Example 1 of the present invention is: The only difference between Comparative Example 1 and Example 1 is that ethanol was replaced with an equal amount of water. The separated cotton fibers, after drying, weighed 16.3 grams, with a yield of 129.4%. The infrared spectrum showed polyester residue, indicating incomplete depolymerization and incomplete separation.

[0038] Comparative Example 2 of the present invention is: The only difference between Comparative Example 2 and Example 1 is that the depolymerization temperature was changed to 110°C. The separated cotton fibers, after drying, weighed 15.2 grams, with a yield of 120.8%. The infrared spectrum showed polyester residue, indicating that the depolymerization was incomplete and the separation was not thorough.

[0039] In summary, the chemical separation method for polyester-cotton composite materials provided by this invention has the following advantages: 1. Replacing sodium hydroxide with NH4OH in traditional alkali treatment solves the drawbacks of traditional alkali treatment methods, which require a large amount of acid to regenerate polyester depolymers and generate a large amount of neutralization waste salt.

[0040] 2. The product obtained by depolymerizing polyester with NH4OH is diamine terephthalate, which can be directly decomposed into TPA and recyclable ammonia through thermal cracking, with higher efficiency and better TPA purity.

[0041] 3. Using alcohol solvents instead of water as the reaction medium effectively lowers the reaction temperature and increases the reaction rate.

[0042] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A chemical separation method of polyester-cotton composite material, characterized by, The method comprises the following steps: adding an alcohol solvent and NH4OH to the polyester-cotton composite material to react.

2. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The alcohol solvent is at least one of methanol, ethanol and ethylene glycol.

3. The method of claim 2, wherein the chemical separation of the polyester-cotton composite material is characterized by, The alcohol solvent is ethanol.

4. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The mass ratio of the alcohol solvent to the polyester-cotton composite fabric is 10-20:

1.

5. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The mass ratio of the NH4OH to the polyester-cotton composite fabric is 0.5-2.0:

1.

6. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The NH4OH is added in the form of ammonia water.

7. The method of claim 6, wherein the chemical separation of the polyester-cotton composite material is characterized by, The concentration of the ammonia water is 10-28 wt%.

8. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The reaction temperature of the reaction is 120-160°C.

9. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The reaction time of the reaction is 2-5h.

10. The method of claim 1, wherein the chemical separation of the polyester-cotton composite material is characterized by, The method further comprises a step of washing the product after the reaction.