Method for depolymerizing nylon 6 waste into aminocaproic acid monomer

Abstract

The invention discloses a method for depolymerizing nylon 6 waste into an aminocaproic acid monomer, which comprises the following steps: dispersing the crushed nylon 6 waste into a hydrogen peroxide aqueous solution, adding a titanium silicalite molecular sieve, heating and stirring to depolymerize the nylon 6 to obtain a depolymerization product containing the aminocaproic acid monomer; the mass concentration of the hydrogen peroxide aqueous solution is 0.8%-2.4%; the mass ratio of the titanium silicalite molecular sieve to the nylon 6 waste is (0.02-0.1): 1; the heating temperature is controlled to be 70-90 DEG C. According to the method provided by the invention, the nylon 6 waste can be depolymerized, the reaction condition is mild, the method has the characteristics of low reaction temperature and low pressure, the preparation process is simple and easy to operate, the production cost can be greatly reduced, and the method can be effectively applied to depolymerization of the nylon 6 waste.

Description

Technical Field

[0001] This invention belongs to the field of nylon waste material recycling technology, and particularly relates to a method for depolymerizing nylon 6 waste into aminocaproic acid monomer. Background Technology

[0002] Nylon is a general term for a class of synthetic polyamide fibers, belonging to thermoplastic resins. Nylon 6, also known as PA6, polyamide 6, etc., has the following structural formula: ; Nylon plays a vital role in numerous industries, including textiles, automobiles, electronics, and packaging. As a synthetic polymer, nylon is difficult to degrade naturally, leading to its long-term accumulation in the environment and creating "white pollution," posing a threat to ecosystems and human health. Meanwhile, nylon production relies on non-renewable resources such as petroleum. With resource depletion and increasing environmental awareness, finding sustainable nylon disposal methods has become particularly important. One approach is to use chemical methods to break down nylon waste into monomers or oligomers, thereby achieving its recycling.

[0003] There are three methods for recycling nylon: physical recycling, chemical recycling, and energy recycling. Physical and energy recycling suffer from inefficiency, pollution, and high energy consumption. Therefore, chemical recycling is the most suitable method. Common methods for chemical recycling of nylon include hydrolysis, ammonolysis, and alcoholysis. However, these methods have drawbacks such as excessively high reaction temperatures and pressures. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above and to provide a method for depolymerizing nylon 6 waste into aminocaproic acid monomer.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for depolymerizing nylon 6 waste into aminocaproic acid monomers includes the following steps: The crushed nylon 6 waste was dispersed in an aqueous hydrogen peroxide solution, titanium silicon molecular sieve was added, and the mixture was heated and stirred to depolymerize the nylon 6, resulting in a depolymerized product containing aminocaproic acid monomer. The mass concentration of the hydrogen peroxide aqueous solution is 0.8%-2.4%; the mass ratio of the titanium silicon molecular sieve to nylon 6 waste is (0.02~0.1):1; and the heating temperature is controlled at 70~90℃.

[0006] Furthermore, the mass concentration of the hydrogen peroxide aqueous solution is 1.5-2%.

[0007] Furthermore, the mass of the hydrogen peroxide aqueous solution is 10 to 20 times the mass of the nylon 6 waste.

[0008] Furthermore, the mass of the hydrogen peroxide aqueous solution is 12 to 18 times the mass of the nylon 6 waste.

[0009] Furthermore, the titanium-silicon molecular sieve is TS-1 molecular sieve, and its mass ratio with nylon 6 waste is (0.04~0.08):1.

[0010] Furthermore, the heating temperature is controlled at 80~90℃.

[0011] Furthermore, the depolymerization time is 1 hour to 5 hours.

[0012] Furthermore, the depolymerization time is 2.5 to 3 hours.

[0013] Furthermore, the depolymerization pressure is atmospheric pressure.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The method provided by this invention can depolymerize nylon 6 waste under mild reaction conditions, characterized by low reaction temperature and low pressure. Its preparation process is simple and easy to operate, which can significantly reduce production costs and can be effectively applied to the depolymerization of nylon 6 waste. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 Gas chromatograms of the products reacted for 2 hours (Example 1), 3 hours (Example 2), and 4 hours (Example 3) with aminocaproic acid standard; Figure 2 This is a diagram of the products after the reaction in Example 1; Figure 3 This is a comparison of gel permeation chromatograms of the raw material and the product after hydrogen peroxide treatment in Example 1. Figure 4 The infrared spectra are of the product after the reaction in Example 2 and the standards of caprolactam and 6-aminohexanoic acid. Detailed Implementation

[0017] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0018] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0019] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0020] In some specific embodiments, the method for depolymerizing nylon 6 waste into aminocaproic acid monomers according to the present invention includes the following steps: The crushed nylon 6 waste was dispersed in an aqueous hydrogen peroxide solution, and titanium silicate molecular sieve (such as TS-1 molecular sieve) was added. The mixture was heated and stirred to depolymerize the nylon 6, resulting in a depolymerized product containing aminocaproic acid.

[0021] The mass concentration of the hydrogen peroxide aqueous solution is 0.8%-2.4%, preferably 1.5%-2%. The mass of the hydrogen peroxide aqueous solution is 10-20 times the mass of the nylon 6 waste, preferably 12-18 times.

[0022] The mass ratio of TS-1 molecular sieve to nylon 6 waste is (0.02~0.1):1, preferably (0.04~0.08):1.

[0023] The heating temperature is 70~90℃, preferably 80~90℃, and more preferably 90℃.

[0024] The depolymerization time is 1h to 5h, preferably 2h to 4h, more preferably 2.5h to 3h, and most preferably 3h. If the reaction time is too short or too long, the yield of aminocaproic acid will decrease.

[0025] The depolymerization pressure is atmospheric pressure (standard atmospheric pressure), meaning the entire process takes place under atmospheric pressure.

[0026] The mechanism of this invention: Hydrogen peroxide can provide active hydroxyl radicals with unpaired electrons, exhibiting extremely high chemical reactivity (redox potential up to 2.8V), serving as an "active intermediate" in the degradation process. TS-1 molecular sieves can significantly enhance the depolymerization effect of hydrogen peroxide on nylon 6. This promoting effect stems from the synergistic catalytic mechanism between the acidic sites of the molecular sieve and hydrogen peroxide, while the pore structure of the molecular sieve also provides a shape-selective effect, suppressing side reactions. The depolymerization core of nylon 6 (polycaprolactam) is the breaking of the amide bond (-CO-NH-), in which hydrogen peroxide can act as an oxidant and hydrolysis promoter. The Brønsted acid (B acid) center (Si-OH-Al) of TS-1 can provide protons, and the Lewis acid (L acid) center (coordinated unsaturated Al) can provide protons. 3+These electron pairs can accept electrons and work together on the nylon 6 molecular chain. Its main chain is formed by the ring-opening polymerization of caprolactam, with the repeating unit being -[NH(CH2)5CO]-. Its stability depends on the bond energies of the chemical bonds in the chain: carbon-carbon single bonds (CC, bond energy approximately 347 kJ / mol) and carbon-nitrogen bonds (CN, approximately 305 kJ / mol) are relatively stable, while peptide bonds (-CO-NH-) have a bond energy of only 330 kJ / mol. Furthermore, due to the electronegativity of the oxygen atom, the electron cloud distribution is uneven, forming a highly polar bond structure, making it more susceptible to attack by electrophilic reagents. Hydroxyl radicals (·OH) attack the highly electronegative oxygen atom in the peptide bond in two ways: first, by electrophilically attacking the lone pair of electrons and initiating bond breakage; and second, by abstracting hydrogen atoms from the amino group (-NH-→-N•-), forming an unstable nitrogen radical intermediate, ultimately leading to peptide bond breakage. As peptide bonds break down, the long-chain macromolecules of nylon 6 (with molecular weights typically ranging from tens of thousands to hundreds of thousands) are broken down into polyamide oligomers of varying lengths (with molecular weights reduced to below several thousand). The oligomers have a wide molecular weight distribution and usually contain a mixture of monomers, dimers, and even a dozen or more polymers, with the specific composition depending on the degradation time and reaction intensity. Figure 3 The gel permeation chromatogram also confirmed this. Gas chromatography analysis showed that it partially decomposed into aminocaproic acid monomers.

[0027] The present invention will be described in detail below through specific embodiments. All embodiments and comparative examples use the same batch of nylon 6 waste. Example 1

[0028] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution, heat in an oil bath at 80℃, and stir for 2 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 10.2% (where yield = total amount of aminocaproic acid in the product / mass of nylon 6 waste). Example 2

[0029] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution, heat in an oil bath at 80℃, and stir for 3 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 12%. Example 3

[0030] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution, heat in an oil bath at 80℃, and stir for 4 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 7.6%. Example 4

[0031] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.2ml of 30% hydrogen peroxide solution, heat in an oil bath at 80℃, and stir for 3 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 5.4%. Example 5

[0032] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 2.4ml of 30% hydrogen peroxide solution, heat in an oil bath at 80℃, and stir for 4 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 8.1%. Example 6

[0033] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution, heat in an oil bath at 70℃, and stir for 3 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 8.3%. Example 7

[0034] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution, heat in an oil bath at 90℃, and stir for 3 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 12.6%. Example 8

[0035] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution and 0.02g of TS-1 molecular sieve. Heat in an oil bath at 80℃ and stir for 3 hours. After standing for 12 hours, remove the solution and filter it through filter paper. Collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 20.1%. Example 9

[0036] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution and 0.06g of TS-1 molecular sieve. Heat in an oil bath at 80℃ and stir for 3 hours. After standing for 12 hours, remove the solution and filter it through filter paper. Collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 24.2%. Example 10

[0037] Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of distilled water. Add 1.8ml of 30% hydrogen peroxide solution and 0.1g of TS-1 molecular sieve. Heat in an oil bath at 80℃ and stir for 3 hours. After standing for 12 hours, remove the solution and filter it through filter paper. Collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers obtained after depolymerization of nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 22.1%.

[0038] Comparative Example 1 Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of 15% sulfuric acid solution. Heat in an oil bath at 80℃ and stir for 2 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yielded small molecule monomers after depolymerization of the nylon 6 waste. Gas chromatography analysis showed that the yield of aminocaproic acid was 7%.

[0039] Comparative Example 2 Weigh 2g of nylon 6 waste, cut it into small pieces, and place it in 30ml of a 15% sulfuric acid solution. Add 1.8ml of a 30% hydrogen peroxide solution to the sulfuric acid solution. Heat in an oil bath at 80℃ and stir for 3 hours. After standing for 12 hours, remove the solution, filter it through filter paper, and collect the filtrate. Rotary evaporation of the filtrate yields the small molecule monomers after depolymerization of the nylon 6 waste. This comparative example does not yield aminocaproic acid (aminocaproic acid is not detectable by gas chromatography).

[0040] Figure 1 The images show gas chromatograms of the products from reactions 2 hours (Example 1), 3 hours (Example 2), and 4 hours (Example 3) with aminohexanoic acid standards. (a) Chromatograms from top to bottom are for reactions 2 / 3 / 4 hours; (b) is the chromatogram of the aminohexanoic acid standard. It can be seen that aminohexanoic acid was obtained from all three reactions.

[0041] Figure 2 The image shows the product after the reaction in Example 1. As can be seen, 2g of nylon 6 waste was completely decomposed into a transparent solution.

[0042] Figure 3This is a comparison of gel permeation chromatography (GPC) images of the raw material (nylon 6 waste) from Example 1 (a) and the product after hydrogen peroxide treatment (b). It can be seen that the weight-average molecular weights (Mw) of the raw material components are 16800 and 559, respectively. After hydrogen peroxide treatment, the molecular weights decreased to 1405, 581, and 126, respectively, indicating that most of the polymers were depolymerized.

[0043] Figure 4 The images show the infrared spectra of the product after the reaction in Example 2, along with caprolactam and 6-aminohexanoic acid standards. The values ​​are in the range of 3000–2500. -1 The peak shape at 1500–1000 cm⁻¹ is highly similar to that of 6-aminohexanoic acid (black), exhibiting a broad and gentle absorption band, indicating the presence of a carboxyl (-COOH) functional group, which is completely different from the peak shape of caprolactam. -1 The sample did not exhibit the strong amide bimodal peaks characteristic of caprolactam; instead, the peak shape was closer to that of 6-aminohexanoic acid (black), indicating the absence of abundant cyclic amide structures. The hydrogen peroxide-treated sample showed broad peaks at the carboxyl group (yellow region) and amino group (3500–3000). -1 The infrared signature of the double peak (cm) is highly consistent with that of 6-aminocaproic acid, and the typical amide double peak (red area) of caprolactam is not present. Therefore, it can be proved that its structure is closer to 6-aminocaproic acid than caprolactam.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for depolymerizing nylon 6 waste into aminocaproic acid monomer, characterized in that, Includes the following steps: The crushed nylon 6 waste was dispersed in an aqueous hydrogen peroxide solution, titanium silicon molecular sieve was added, and the mixture was heated and stirred to depolymerize the nylon 6, resulting in a depolymerized product containing aminocaproic acid monomer. The mass concentration of the hydrogen peroxide aqueous solution is 0.8%-2.4%; the mass ratio of the titanium silicon molecular sieve to nylon 6 waste is (0.02~0.1):1; and the heating temperature is controlled at 70~90℃.

2. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1, characterized in that, The mass concentration of the hydrogen peroxide aqueous solution is 1.5-2%.

3. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1 or 2, characterized in that, The mass of the hydrogen peroxide aqueous solution is 10 to 20 times the mass of the nylon 6 waste.

4. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 3, characterized in that, The mass of the hydrogen peroxide aqueous solution is 12 to 18 times the mass of the nylon 6 waste.

5. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1 or 2, characterized in that, The titanium-silicon molecular sieve is TS-1 molecular sieve, and its mass ratio with nylon 6 waste is (0.04~0.08):

1.

6. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1 or 2, characterized in that, The heating temperature is controlled at 80~90℃.

7. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1 or 2, characterized in that, The depolymerization time is 1 hour to 5 hours.

8. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 7, characterized in that, The depolymerization time is 2.5 to 3 hours.

9. The method for depolymerizing nylon 6 waste into aminocaproic acid monomer according to claim 1 or 2, characterized in that, The depolymerization pressure is atmospheric pressure.

Images