US-12624183-B2 - Polyamide recycling process and polyamide obtained by recycling process

Abstract

A recycling process for a polyamide waste material includes the following steps: adding a polyamide waste material into a mixed solvent to obtain a solution, heating the solution to 50° C. to a reflux temperature of the solution, conducting stirring for dissolution, and then conducting decolorization treatment and filtration to obtain a polyamide solution; and adding the polyamide solution into water, precipitating polyamide as a solid in deionized water, and conducting separation to obtain recycled polyamide. The mixed solvent includes, in parts by weight, 10-30 parts of phenol and 15-40 parts of toluene.

Inventors

• Huan Chang
• Nanbiao YE
• Cheng Li
• Wohua ZHOU
• Xinxin Liu
• Xiumei ZHU
• Yujun SU
• Lei Tang
• Xianbo Huang

Assignees

• KINGFA SCI. & TECH. CO., LTD.

Dates

Publication Date

20260512

Application Date

20201229

Priority Date

20200630

Claims (8)

1. 1 . A polyamide recycling process, comprising following steps: adding a polyamide waste material into a mixed solvent to obtain a solution, heating the solution to 50° C. to a reflux temperature of the solution, conducting stirring for dissolution, and then conducting decolorization treatment and filtration to obtain a polyamide solution; and adding the polyamide solution into deionized water, precipitating polyamide in the deionized water, and conducting separation to obtain recycled polyamide; wherein the mixed solvent comprises, in parts by weight, 10-30 parts of phenol and 15-40 parts of toluene; and a weight ratio of the polyamide waste material to the mixed solvent is 1:10 to 1:2, wherein a decolorizing agent is added during the decolorization treatment, and a weight ratio of the decolorizing agent to the polyamide waste material is 1:8 to 1:12; and the solution is heated to 50° C. to the reflux temperature of the solution, subjected the solution to heat preservation for 0.5-2 hours, cooled the solution to a temperature of less than 50° C., and then filtered the solution to obtain the polyamide solution.
2. 2 . The polyamide recycling process according to claim 1 , wherein after the polyamide waste material is added into the mixed solvent to obtain the solution, the solution is heated to 100° C. to the reflux temperature of the solution, and stirred for dissolution, and then the decolorization treatment and the filtration treatment are subsequently conducted.
3. 3 . The polyamide recycling process according to claim 1 , wherein a weight ratio of the polyamide solution to the deionized water is 1:5 to 1:50.
4. 4 . The polyamide recycling process according to claim 1 , wherein the mixed solvent further comprises, in parts by weight, one or more of 0-5 parts of methanol, 0-20 parts of o-cresol, or 0-20 parts of benzyl alcohol.
5. 5 . The polyamide recycling process according to claim 1 , wherein a temperature in the step of precipitating the polyamide in the deionized water is 0-50° C.
6. 6 . The polyamide recycling process according to claim 1 , wherein the decolorizing agent is at least one selected from activated carbon and activated clay.
7. 7 . The polyamide recycling process according to claim 1 , wherein the polyamide waste material is at least one selected from an aliphatic polyamide waste material and a semi-aromatic polyamide waste material; the aliphatic polyamide waste material is at least one selected from a PA6 waste material, a PA66 waste material, a PA12 waste material, a PA1010 waste material, and a PA1012 waste material; and the semi-aromatic polyamide waste material is at least one selected from a PA6T waste material, a PA10T waste material, a PA10T10I waste material, a PA10T1010 waste material, a PA10T1012 waste material, and a PA10T6T waste material.
8. 8 . The polyamide recycling process according to claim 1 , wherein further comprising a step of pulverization before the polyamide waste material is added into the mixed solvent.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a 371 application of International PCT application serial no. PCT/CN2020/140812 filed on Dec. 29, 2020, which claims the priority benefit of China application no. 202010611058.5, filed on Jun. 30, 2020. The entirety of each of the above mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. BACKGROUND Technical Field The present invention relates to the technical field of environment-friendly polymer materials, and in particular to a polyamide recycling process and polyamide obtained by the recycling process. Description of Related Art As one of four engineering plastics, polyamide has been widely used. However, after use, polyamide wastes are usually discarded directly as garbage in a large amount, resulting in energy waste and environmental pollution. Therefore, a cyclic utilization topic for recycling of the polyamide has been put forward all over the world. However, current recycling methods are still very simple. Except that some of the polyamide wastes with greatly reduced properties are used in the field of low-end products after granulation, the other polyamide wastes are usually burnt, and heat energy released during burning is used. On the one hand, the energy utilization efficiency is low. On the other hand, since a polyamide molecule contains the element N, nitrogenous compounds are released during burning, resulting in serious environmental pollution. However, according to a solution method for recycling of the polyamide, energy of polymers can be used to a maximum extent while it is ensured that properties are not reduced, the method is environmentally friendly, and little pollution is caused. According to CN109810284A, a PA12 recycling method is provided. The method includes: S1, adding a PA12 waste material into a composite solvent system, and conducting stirring for dissolution; S2, heating the reaction system to 60-90° C., and conducting heat preservation in a water bath at constant temperature for 2-5 hours to make the PA12 waste material fully dissolved; S3, subjecting the solution obtained after a reaction to centrifugal separation, and adding deionized water into an upper supernatant for precipitation to obtain a PA12 precipitate; and S4, drying the PA12 precipitate under vacuum to thoroughly remove a solvent so as to obtain a PA12 powder. According to the invention, the solvent system includes 5-28% of formic acid, 1-10% of hydrochloric acid, 25-35% of acetic acid, and the balance of deionized water, and is a typical strong protic solvent. The polyamide is dissolved by a hydrogen bond formed by the polyamide, a strong polar hydrogen ion, and an acid radical ion. However, all the formic acid, the hydrochloric acid, and the acetic acid have extremely high corrosivity and volatility and high acidity, so that corrosion of equipment is likely to be caused. Moreover, in the step of adding the deionized water to precipitate out the polyamide, produced wastewater has extremely high acidity, and needs to be neutralized with an alkali before sewage treatment, so that environmental protection is not facilitated. During dissolution in a strong acidic environment, a part of amide bonds are hydrolyzed, so that a main chain of the polyamide is destroyed and converted into polyamide with low molecular weight, and properties of the recycled polyamide are greatly reduced. A centrifugation process is used as a solid separation method, which is not suitable for production in a large scale, and is high in cost. According to a Chinese patent CN101058695A, a paint for metals is disclosed. A main curing substance includes any one of polyamide (PA), polyamide (PA6), polyamide (PA66), polyamide (PA610), polyamide (PA1010), and polyamide (PA12). A main solvent includes one or more of m-cresol, m-para-cresol, tricresol, and phenol. A co-solvent includes one or more of xylene, toluene, dimethylformamide, butanol, ethylene glycol ethyl ether, and ethylene glycol butyl ether. The polyamide can be well dissolved in the mixed solvent. However, since the solvent is used for not only dissolving the polyamide, but also dissolving other paint compositions, the amount of the main solvent is greater than that of the co-solvent. When the mixed solvent is used for recycling of the polyamide, a small amount of the polyamide cannot be precipitated out during precipitation, so that the yield is reduced. SUMMARY An objective of the present invention is to provide a recycling method for a polyamide waste material and polyamide obtained by the method. Phenol and toluene are used as main components of a mixed solvent, which has low volatility and irritation, environmental friendliness, little pollution, and low corrosivity to equipment, and is conducive to precipitation of polyamide. The obtained polyamide has good crystallization properties, the end-capping rate (with phenol as an end-capping agent) is increased, and