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CN-122010813-A - Method for catalyzing depolymerization of waste nylon 6 into caprolactam

CN122010813ACN 122010813 ACN122010813 ACN 122010813ACN-122010813-A

Abstract

The invention discloses a method for catalyzing depolymerization of waste nylon 6 into caprolactam, and belongs to the technical field of depolymerization of polyamide waste materials. The invention solves the problems that the existing method for depolymerizing nylon 6 lacks a cheap and easily available high-efficiency catalytic system and the purity of caprolactam monomer obtained by catalyzing the depolymerization of nylon 6 is low. The method has the advantages of low cost, easy obtainment, low cost, and no need of participation of additional solvents such as water, etc., and can be used as a depolymerization catalyst by caprolactam sodium or potassium caprolactam prepared by simple process steps such as sodium hydroxide/potassium hydroxide, sodium alkoxide/potassium alkoxide, etc., and nylon 6 is depolymerized into caprolactam under the condition of reduced pressure and heating, so that the catalyst is prevented from remaining in the product, the purity of the recovered monomer is high, the monomer product can be directly recycled, and the recycling efficiency of the nylon 6 is improved.

Inventors

  • WANG QINGGANG
  • XU GUANGQIANG
  • WANG LIANG
  • YANG RULIN
  • ZHU GUANGQIAN
  • YU MINGJIA

Assignees

  • 中国科学院青岛生物能源与过程研究所

Dates

Publication Date
20260512
Application Date
20260107

Claims (10)

  1. 1. A method for catalyzing waste nylon 6 to depolymerize into caprolactam is characterized in that nylon 6 is depolymerized under the catalysis of caprolactam salt under the conditions of no solvent, heating and decompression to obtain depolymerized product caprolactam.
  2. 2. The method of claim 1, wherein the caprolactam salt is sodium caprolactam or potassium caprolactam having the following structural formula: 。
  3. 3. The method of claim 1, wherein the depolymerization temperature is 250-320 ℃.
  4. 4. A process according to claim 3, wherein the depolymerization temperature is 280 ℃.
  5. 5. A method according to claim 3, wherein the depolymerization temperature is 300 ℃.
  6. 6. The method of claim 1, wherein the depolymerization pressure is 0.01-100 mbar.
  7. 7. The method of claim 6, wherein the depolymerization pressure is 0.1 mbar.
  8. 8. The method according to claim 1, wherein the caprolactam salt is added in an amount of 2-20 wt% by mass of nylon 6.
  9. 9. The method of claim 1, wherein the waste nylon 6 is produced reject material derived from nylon 6, process scrap, and product recycle.
  10. 10. Caprolactam obtained by the process according to any one of claims 1 to 9.

Description

Method for catalyzing depolymerization of waste nylon 6 into caprolactam Technical Field The invention relates to a method for catalyzing depolymerization of waste nylon 6 into caprolactam, and belongs to the technical field of depolymerization of polyamide waste materials. Background Nylon 6 (PA 6) is an important polyamide engineering plastic, and is widely applied to the fields of textile, automobile, electronic and electric, packaging and the like by virtue of excellent mechanical strength, wear resistance, chemical resistance and good processability. The annual production energy is huge worldwide, however, large-scale production is accompanied by the generation of a large amount of wastes, such as waste fishing nets, carpets and industrial waste silk, which are difficult to degrade in natural environment and pose a threat to ecological environment. Therefore, the development of efficient recovery techniques is critical to the sustainable development of the nylon 6 industry. At present, three plastic recycling modes mainly comprise physical recycling, energy recycling and chemical recycling. Nylon 6 is physically recycled by melt remodeling because high temperature melting can cause partial degradation, which typically results in reduced performance, and nylon 6 can be physically recycled for a limited number of times. Energy recovery refers to heat recovery through combustion, however nylon 6 releases toxic HCN, CO, CO 2 and NH 3 when burned, which not only causes air pollution problems, but also makes the produced small molecules difficult to be converted into high-value products. In contrast, it is more practical to obtain polymerized monomers or high value chemicals by chemical recovery. At present, the hydrolysis method is a main mode of nylon 6 chemical recovery, and water is used as a reaction medium at high temperature and high pressure to break amide bonds in nylon 6 polymer chains to produce caprolactam monomers. However, this method generally requires high temperature and high pressure water or steam, and the product is often accompanied by-products such as aminocaproic acid, and complicated purification steps are required. And the depolymerized product caprolactam can be obtained more efficiently by the decompression directional pyrolysis to the monomer. Although some directional pyrolysis systems have been disclosed at present, such as lanthanum metal complex catalysis (Angew. Chem. Int. Ed. 2023, 135, e202212543; chem 2024, 10, 172-189), they suffer from the problems of cumbersome and costly preparation of the catalytic system and the possibility of catalyst ingress into the product affecting monomer purity. Patent CN 202410248101.4 reports that catalytic depressurization directional pyrolysis under the action of a metal amide catalyst is also costly and that the catalyst may enter caprolactam monomer. There remains a need in the art to develop inexpensive, readily available, efficient catalytic systems for the depolymerization of nylon 6 to high purity caprolactam monomers. Disclosure of Invention The invention provides a method for catalyzing depolymerization of waste nylon 6 into caprolactam, which aims to solve the problems that the existing method for depolymerizing nylon 6 lacks a cheap and easily available high-efficiency catalytic system and the purity of caprolactam monomer obtained by catalyzing depolymerization of nylon 6 is low. The technical scheme of the invention is as follows: The invention aims to provide a method for catalyzing depolymerization of waste nylon 6 into caprolactam, which is to depolymerize nylon 6 under the catalysis of caprolactam salt under the conditions of no solvent, heating and decompression to obtain depolymerized product caprolactam. Further defined, the caprolactam salt is sodium caprolactam or potassium caprolactam, and has the following structural formula: 。 further defined, the depolymerization temperature is 250-320 ℃. Further defined, the depolymerization temperature is 280 ℃. Further defined, the depolymerization temperature is 300 ℃. Further defined, the depolymerization pressure is 0.01-100 mbar. Further defined, the depolymerization pressure is 0.1 mbar. Further defined, the addition amount of caprolactam salt is 2-20 wt% of the mass of nylon 6. Further limited, the waste nylon 6 is produced unqualified nylon 6, processed leftover materials and product reclaimed materials. Further, the number average molecular weight of the waste nylon 6 is 10 2-107 g/mol. The beneficial effects are that: (1) The catalyst system used in the invention is cheap and easy to obtain, has low cost, can be prepared from caprolactam, sodium hydroxide/potassium, sodium alkoxide/potassium and the like through simple flow steps, and has good economic benefit in the depolymerization process. (2) The catalyst system used in the invention can depolymerize nylon 6 with high efficiency, and caprolactam monomer, aminocaproic acid, oligomer and other byproducts are less. The