Method for realizing N-methylation of nitrogen-containing compounds by controllable depolymerization of polyformaldehyde and application thereof

Abstract

This invention discloses a method for controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds. N The method and application of methylation belong to the field of solid waste recycling technology. The method includes: constructing a reaction system comprising polyoxymethylene, nitrogen-containing compounds, a supported metal catalyst, and a solvent, and carrying out a depolymerization upgrading reaction at a temperature of 160–240 °C for 0.2–10 h to achieve the methylation of nitrogen-containing compounds. N α-methylation yields the corresponding nitrogen-containing compound. N - Methylated derivatives; the solvent is selected from organic solvents or mixtures of organic solvents and water; the nitrogen-containing compound is an aliphatic amine, an aromatic amine, or an aromatic nitro compound. The method of this invention is simple, and a one-pot process can achieve the conversion of POM-mediated nitrogen-containing compounds to their corresponding derivatives. N The conversion of methylated derivatives, with few side reactions and high product yield, has broad application prospects in the field of POM waste treatment.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycling technology, specifically relating to a method for the controlled depolymerization of polyoxymethylene to realize nitrogen-containing compounds. N Methods and applications of methylation. Background Technology

[0002] Polyoxymethylene (POM), one of the five major engineering plastics, occupies an important position in the automotive and electronics industries due to its excellent mechanical properties, electrical insulation, solvent resistance, and processability. Although its application range is not as wide as that of basic plastics such as polyethylene (PE), polyethylene terephthalate (PET), or polypropylene (PP), POM is an irreplaceable key material in high-end engineering plastics manufacturing. POM causes environmental problems throughout its entire life cycle. The production process of POM has a significant impact on the environment in terms of fossil fuel use, energy consumption, and climate change (CO2 equivalent). Furthermore, due to its higher density and slower degradation rate, and the release of toxic formaldehyde (CH2O) during decomposition, POM as waste has a more persistent polluting effect and poses a greater risk of harm than ordinary plastics. Therefore, conducting effective research on POM recycling is crucial to mitigating its environmental impact.

[0003] Currently, POM waste treatment technologies are mainly divided into two categories: mechanical recycling and chemical recycling. Although mechanical recycling technology for POM waste has been applied on a large scale, degradation occurs during reprocessing, leading to a significant decline in the quality of recycled products. This technological bottleneck means that most POM waste is still disposed of through incineration or landfill, inevitably causing environmental pollution. Given that formaldehyde is a valuable C1 resource and a potential hydrogen source, directly converting POM into high-value-added chemicals through chemical recycling methods has become an important research direction for the efficient utilization of resources.

[0004] However, there are few reports on the value-added utilization of POM in the existing technology, but some studies have disclosed methods for the chemical depolymerization of POM. For example, Chinese patent document CN113582822A discloses a continuous depolymerization method for paraformaldehyde and its application. In this invention, paraformaldehyde is added to a mixing vessel, followed by the addition of an alcohol solvent and a catalyst for thorough mixing and preheating to obtain a solid mixture. The solid mixture is then pumped into a tubular reactor for reaction. After the reaction, a depolymerized liquid is obtained, and the formaldehyde content is determined to be 45-55% by gas chromatography. This continuous depolymerization method for paraformaldehyde can be used in the synthesis process of glyphosate via the glycine method. Chinese patent document CN105199063A discloses a method for preparing phenolic resin from paraformaldehyde. In this invention, phenol and paraformaldehyde are added to a reaction vessel at one time. A catalyst is added uniformly at 70-80°C over a period of 40-80 minutes. The temperature is then raised to 90-95°C and held for 1-4 hours to promote depolymerization. The temperature is then raised to 95-105°C and held for 45-240 minutes. The free aldehyde content is tested and found to be within the standard. Under normal pressure, the temperature is raised to 150-162°C, a phenol-reducing agent is added, and after the index tests are passed, the material is discharged and packaged to obtain phenolic resin.

[0005] While chemical recycling can depolymerize POM into formaldehyde monomers for resource conversion, it faces two core challenges: kinetic matching and reaction selectivity. First, there is an order-of-magnitude difference between the depolymerization rate (k1) and the formaldehyde conversion rate (k2). When k1 << k2, insufficient formaldehyde supply leads to conversion stagnation, while when k1 >> k2, excessive formaldehyde accumulation triggers repolymerization or condensation side reactions. Second, while existing strong acid catalytic systems can improve depolymerization efficiency, they also exacerbate equipment corrosion, increase carbon loss (formic acid dehydrogenation to CO2), and decrease product selectivity (generating low-value cyclic acetals or oligomers). Existing research often employs excessive POM feeding to maintain formaldehyde concentration, but this strategy significantly reduces atom economy and is difficult to implement continuously.

[0006] Based on this, there is an urgent need to develop an efficient and green chemical recycling method for POM, which should have the following characteristics: (1) avoid using highly corrosive catalysts to extend equipment life; (2) achieve dynamic matching between depolymerization rate and conversion rate to suppress side reactions; and (3) directly synthesize high-value-added chemicals from POM raw materials in equimolar ratios to improve the atom economy of the process. Breakthroughs in this technology will promote the establishment of a circular economy system for engineering plastics. Summary of the Invention

[0007] This invention addresses the need for depolymerization and targeted upgrading of POM waste plastics, as well as the shortcomings of existing technologies, by providing a method for the controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds. N The methylation method is simple and can achieve POM-mediated methylation of nitrogen-containing compounds to their corresponding derivatives in a one-pot process. NThe conversion of methylated derivatives is efficient with few side reactions and high product yield.

[0008] The specific technical solution adopted is as follows:

[0009] A method for controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds N The method of methylation includes: constructing a reaction system comprising polyoxymethylene, a nitrogen-containing compound, a supported metal catalyst, and a solvent, and carrying out a depolymerization upgrading reaction at a temperature of 160–240 °C for 0.2–10 h (more preferably 0.5–5 h) to achieve the methylation of the nitrogen-containing compound. N -Methylation yields the corresponding nitrogen-containing compound. N -Methylated derivatives;

[0010] The solvent is selected from organic solvents or mixtures of organic solvents and water, wherein the organic solvent is toluene, tetrahydrofuran, etc. N -Methylpyrrolidone, cyclohexane or 1,4-dioxane;

[0011] Nitrogen-containing compounds are aliphatic amines, aromatic amines, or aromatic nitro compounds;

[0012] Supported metal catalysts include a support and the active metal supported thereon; the active metal is copper or nickel, the support is a metal oxide, and the molar ratio of the active metal to the metal in the support is 0.2 to 5:1 (more specifically 2 to 5:1).

[0013] Furthermore, the atmosphere for the depolymerization and upgrading reaction is an air atmosphere or a protective gas atmosphere. The reaction of the present invention does not have strict requirements on the reaction atmosphere, and it is easier to carry out the reaction in an air atmosphere.

[0014] This invention aims to address the technical shortcomings of existing technologies using POM as a formaldehyde source for aniline methylation, including low carbon balance, poor selectivity of target products, and easy catalyst deactivation. The root cause of these shortcomings lies in the mismatch between the POM depolymerization rate and the formaldehyde consumption rate, leading to an increase in free formaldehyde concentration and subsequently triggering an uncontrollable condensation side reaction between formaldehyde and aniline, generating a large amount of tar-like oligomers that cover the catalyst's active sites. This invention discovers that by using a supported metal catalyst (e.g., Cu / Cr2O3) prepared via topological transformation using hydrotalcite (LDH) as a precursor, Lewis acidic sites and methylation active sites can be integrated in the same reaction system. The Lewis acidic sites provided by the support (e.g., Cr2O3) are responsible for activating and orderly depolymerizing the POM molecular chains, releasing formaldehyde monomers as needed; while highly dispersed active metal species such as copper (Cu) exhibit unexpectedly high formaldehyde capture and methylation capabilities, enabling the immediate use of the depolymerized formaldehyde molecules for the stepwise methylation of nitrogen-containing compounds such as aniline. N,N - Dimethylaniline (DMBA), etc.N -Methylated derivatives.

[0015] This invention utilizes a supported metal catalyst to catalyze the depolymerization of POM, slowly releasing formaldehyde monomers, which then undergo methylation with nitrogen-containing compounds. Formaldehyde serves as the methyl source, enabling a one-pot, high-yield preparation process. N Methylated products.

[0016] Specifically, aliphatic amines include cyclohexylamine, diisopropylamine, or octylamine; aromatic amines include aniline, p-methylaniline, 4-isopropylaniline, 4-bromoaniline, or benzylamine; and aromatic nitro compounds include nitrobenzene, 4-ethylnitrobenzene, 4-methoxynitrobenzene, p-isopropylnitrobenzene, p-chloronitrobenzene, or p-nitrophenol.

[0017] Specifically, the supported metal catalyst is Cu / Cr2O3, Cu / Al2O3, Cu / Ga2O3, Cu / In2O3 or Ni / Al2O3, with Cu / Cr2O3 being more preferred. Experiments have shown that Cu / Cr2O3 has better catalytic performance.

[0018] The supported metal catalyst can be synthesized by the following method: preparing a mixed solution containing a first soluble metal salt, a second soluble metal salt, sodium hydroxide, and sodium carbonate; precipitating, aging, washing, and drying the mixed solution; and reducing the obtained product in a reducing atmosphere to obtain the supported metal catalyst; the first soluble metal salt is a soluble copper salt or a soluble nickel salt; the second soluble metal salt is a soluble chromium salt, a soluble aluminum salt, a soluble gallium salt, or a soluble indium salt.

[0019] Furthermore, the molar ratio of the metal elements in the first soluble metal salt and the second soluble metal salt is 0.2 to 5:1 (and even further, 2 to 5:1).

[0020] Furthermore, the pH value is maintained at an alkaline level during the precipitation process.

[0021] Furthermore, the aging conditions are 30–70℃ for 2–20 hours.

[0022] Furthermore, the reducing atmosphere is a mixture of hydrogen and argon, the reduction temperature is 200–500℃, and the reduction time is 4–8 hours.

[0023] Preferably, in the reaction system, polyoxymethylene and nitrogen-containing compounds are fed in a molar ratio of 2 to 10:1, and more preferably in a molar ratio of 2.5 to 4:1.

[0024] Preferably, in the reaction system, the supported metal catalyst is Cu / Cr2O3, and the amount of the supported metal catalyst added is 0.002 to 0.1 g / mmol of nitrogen-containing compound, more preferably 0.02 to 0.1 g / mmol of nitrogen-containing compound.

[0025] Preferably, in the reaction system, the solvent is a mixture of water and 1,4-dioxane, and the amount of water and 1,4-dioxane mixed solvent added is 0.5 to 10 mL / mmol of nitrogen-containing compound.

[0026] More preferably, in the mixed solvent of water and 1,4-dioxane, the volume ratio of water to 1,4-dioxane is 0.02–8:1, more preferably 0.02–2:1. The addition of water can promote the depolymerization of POM.

[0027] This invention also provides the controllable depolymerization of polyoxymethylene to achieve nitrogen-containing compounds. N The application of methylation in waste plastics treatment, where waste plastics are made of polyoxymethylene (POM) material, including but not limited to POM connector clips, POM faucets, POM buttons, POM toy parts, etc.

[0028] The method of this invention is applicable to various forms of POM waste samples, and the nitrogen-containing compounds mediated by POM waste samples to... N Transformation of methylation products, N The recovery rate of methylation products is ≥90%, and further ≥95%, which is highly efficient and realizes the high-value utilization of waste plastics.

[0029] Waste plastics need to be pre-crushed into centimeter- or millimeter-sized flakes, granules, or powder before undergoing depolymerization and upgrading reactions to ensure the resource utilization effect of POM waste, thereby achieving targeted upgrading with high yield. N Methylated products.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The supported metal catalyst used in this invention has excellent stability and recyclability. It can suppress side reactions and optimize reaction kinetic balance, delay the release rate of formaldehyde generated by POM depolymerization, realize efficient breaking of CO bonds in POM and directional conversion of C1 resources. The supported metal catalyst can be recycled. Experiments have shown that after six cycles, the reaction yield still remains above 90%.

[0032] (2) The formaldehyde controllable slow-release strategy developed in this invention drives the high efficiency of nitrogen-containing compounds mediated by polyoxymethylene. N The -methylation method has the advantages of simple conditions and high catalytic efficiency, and can achieve the conversion of aniline to methylated aniline under standard reaction conditions. N,NThe complete conversion of dimethylaniline and the efficient targeted upgrading and conversion of various forms of POM waste can be achieved in a short period of time.

[0033] (3) The method of the present invention has a wide range of applications and is applicable to the targeted upgrading and transformation of various aromatic compounds containing amino or nitro functional groups, and the products are the corresponding N Methylated high-value chemicals.

[0034] (4) This invention simultaneously completes the depolymerization of POM and the directional upgrading and efficient conversion of nitrogen-containing compounds in a single reaction system. It has low equipment requirements and energy consumption, high product yield, and the supported metal catalyst can be quickly recovered and reused after the reaction is completed through simple centrifugal separation.

[0035] (5) The method of the present invention achieves extremely high carbon atom economy and environmental friendliness. By using solid POM to replace the traditional toxic and volatile formaldehyde aqueous solution, and combined with a carbon balance rate of up to 97.8%, the present invention greatly improves the utilization rate of reaction raw materials, reduces the generation of waste from the source, and conforms to the development direction of green chemistry.

[0036] (6) This invention successfully and efficiently couples POM depolymerization and methylation reactions. Taking aniline methylation as an example, 95.7% methylation was achieved under optimal conditions. N,N The significantly high yield of dimethylaniline is directly attributable to the bifunctional catalyst's efficient promotion of the main reaction pathway and effective inhibition of side reactions, thus solving the core challenge of reaction selectivity.

[0037] (7) The supported metal catalyst used in this invention exhibits excellent resistance to deactivation. Thermogravimetric analysis shows that the amount of carbon deposit on the optimal catalyst is extremely low (only 1.88%), which proves that the strategy of preventing catalyst coking by controlling the reaction path is successful and indicates that the catalyst has a long service life and good industrial application potential. Attached Figure Description

[0038] Figure 1 for N,N -1H NMR spectrum of dimethylaniline.

[0039] Figure 2 for N,N - Carbon NMR spectrum of dimethylaniline.

[0040] Figure 3 This is a graph showing the reusability of supported metal catalysts. Detailed Implementation

[0041] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0042] The Cu / Cr₂O₃ catalyst was synthesized as follows: At room temperature, two aqueous solutions—copper nitrate and chromium nitrate solutions (molar ratio Cu:Cr = 4:1) and a mixed solution of sodium hydroxide and sodium carbonate (molar ratio NaOH:Na₂CO₃ = 5:1)—were simultaneously added dropwise to 100 mL of deionized water under vigorous stirring. The pH was maintained at 10 ± 0.2 during precipitation. The precipitate was aged at 60 °C for 16 hours, filtered, and thoroughly washed with deionized water. The filter cake was dried in a vacuum oven at 50 °C for 10 hours, followed by overnight drying. The resulting Cu / Cr-LDH was then heated at 300 °C at a heating rate of 2 °C / min. -1 Under these conditions, with a 5% H2 / Ar gas flow (60 mL·min) -1 The catalyst was reduced in the solution for 6 hours and labeled as Cu / Cr2O3. The preparation methods of other catalysts were the same as those described above, except for the type of metal salt. Supported metal catalysts Cu / Al2O3, Cu / Ga2O3, Cu / In2O3, and Ni / Al2O3 were prepared.

[0043] The catalyst recovery process involved: filtration to recover the catalyst, washing with deionized water and ethanol, and drying at 60°C. The catalyst was then calcined in a muffle furnace at 550°C for 6 h, followed by reduction at 300°C for 6 h in a 5% H₂ / Ar atmosphere (gas flow rate 60 mL / min). -1 Heating rate 2℃·min -1 ), and then reuse it.

[0044] Example 1

[0045] A reaction system was constructed by adding POM powder (1.5 mmol), aniline (0.5 mmol), Cu / Cr₂O₃ (0.05 g), 1,4-dioxane (3 mL), and water (1.5 mL) to a high-pressure reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. The reaction system was placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction was completed, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the product yield was determined by GC. The results showed that... N,N The yield of dimethylaniline was 95.7%.

[0046] Example 2

[0047] POM powder (1.5 mmol), aniline (0.5 mmol), and different supported metal catalysts (Cu / Al₂O₃, Cu / Ga₂O₃, Cu / In₂O₃, Mg / Al₂O₃, Ni / Al₂O₃, Co / Al₂O₃, Fe / Al₂O₃) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively, to construct multiple reaction systems. 1,4-Dioxane and water (3 mL: 1.5 mL) were used as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 81%, 81%, 67%, 10%, 18%, 4%, and 4%, respectively.

[0048] Example 3

[0049] POM powder (1.5 mmol), aniline (0.5 mmol), and different masses of Cu / Cr₂O₃ (0.01, 0.02, 0.03, 0.04 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively, to construct multiple reaction systems. 1,4-Dioxane and water (3 mL : 1.5 mL) were used as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,NThe yields of dimethylaniline were 28%, 66%, 75%, and 83%, respectively.

[0050] Example 4

[0051] POM powder (1.5 mmol), aniline (0.5 mmol), and Cu / Cr2O3 (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively. The solutions were then prepared using toluene (TOL, 4.5 mL) and acetonitrile (MeCN, 4.5 mL), respectively. N,N -Dimethylformamide (DMF, 4.5 mL), Tetrahydrofuran (THF, 4.5 mL) N Multiple reaction systems were constructed using methylpyrrolidone (NMP, 4.5 mL) and cyclohexane (CYH, 4.5 mL) as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted with continuous stirring for 5 hours. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 61%, 0%, 2%, 68%, 29%, and 39%, respectively.

[0052] Example 5

[0053] Different molar ratios of POM powder and aniline (POM powder to aniline molar ratios of 1.5:1, 2.5:1, and 4:1, with aniline at 0.5 mmol in each ratio) and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers. 1,4-Dioxane and water (3 mL : 1.5 mL) were used as solvents to construct multiple reaction systems. These reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 35%, 73%, and 96%, respectively.

[0054] Example 6

[0055] POM powder (1.5 mmol), aniline (0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively. Multiple reaction systems were constructed using mixed solutions of 1,4-dioxane and water (4.4 mL : 0.1 mL, 2.25 mL : 2.25 mL, 1.5 mL : 3 mL, 0.1 mL : 4.4 mL, 0 mL : 4.5 mL) in different mass ratios as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 42%, 61%, 20%, 11%, and 11%, respectively.

[0056] Example 7

[0057] POM powder (1.5 mmol), aniline (0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers. A reaction system was constructed using 1,4-dioxane and water (3 mL: 1.5 mL) as solvents. The reaction system was placed in oil baths preheated to 160 °C, 180 °C, 200 °C, and 240 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 10%, 36%, 63%, and 88%, respectively.

[0058] Example 8

[0059] Multiple reaction systems were constructed by adding 0.06 g of centimeter-sized POM waste fragments (interface clamps, faucets, buttons, gears, approximately 1.5 mmol), aniline (0.5 mmol), and Cu / Cr₂O₃ (0.05 g) to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively. 1,4-Dioxane and water (3 mL : 1.5 mL) were used as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 95%, 92%, 95%, and 93%, respectively.

[0060] Example 9

[0061] POM powder (1.5 mmol), different aromatic amine compounds (p-methylaniline, p-isopropylaniline, and benzylamine, each 0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively. Multiple reaction systems were constructed using 1,4-dioxane and water (3 mL: 1.5 mL) as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of -dimethyl were 91%, 89%, and 81%, respectively.

[0062] Example 10

[0063] POM powder (1.5 mmol), aniline (0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to multiple high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers. A reaction system was constructed using 1,4-dioxane and water (3 mL : 1.5 mL) as solvents. The reaction system was placed in an oil bath preheated to 220 °C under air atmosphere and reacted continuously for 15 min, 30 min, 45 min, 1 h, 2 h, 3 h, and 4 h. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,NThe yields of dimethylaniline were 6%, 62%, 70%, 78%, 84%, 85%, and 88%, respectively.

[0064] Example 11

[0065] POM powder (2.5 mmol), different aromatic nitro compounds (nitrobenzene, p-isopropylnitrobenzene, and p-ethylnitrobenzene, each 0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively, to construct multiple reaction systems. 1,4-Dioxane and water (3 mL : 1.5 mL) were used as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N The yields of the methylated derivatives were 78%, 74%, and 89%, respectively.

[0066] Example 12

[0067] POM powder (1.5 mmol), different aromatic nitro compounds (cyclohexylamine, diisopropylamine, and octylamine, each 0.5 mmol), and Cu / Cr₂O₃ (0.05 g) were added to several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, respectively, to construct multiple reaction systems. 1,4-Dioxane and water (3 mL: 1.5 mL) were used as solvents. The reaction systems were placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring. After the reaction, the reaction mixture was rapidly transferred to an ice-water bath and cooled to room temperature. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N The yields of the methylated derivatives were 76%, 57%, and 33%, respectively.

[0068] Comparative Example 1

[0069] The only difference between this comparative example and Example 1 is that the reduced copper-chromium supported metal catalyst was not added; all other reaction conditions and parameters were the same. After the reaction, a mixture was obtained. Trimethylbenzene was used as an internal standard, the organic phase was extracted with dichloromethane, and the yield was determined by GC. The results showed that the corresponding... N,N The yields of dimethylaniline were 2%.

[0070] Comparative Example 2

[0071] The only difference between this comparative example and Example 1 is that the POM powder was replaced with an aqueous formaldehyde solution (equimolar amount of 1.5 mmol POM powder in Example 1). All other reaction conditions and parameters were the same. After the reaction, a mixture was obtained. Trimethylbenzene was used as an internal standard, and the organic phase was extracted with dichloromethane. The yield was determined by GC. The results showed that the corresponding... N, N The yield of dimethylaniline was 52%.

[0072] Sample Analysis

[0073] Product obtained in Example 1 N,N The 1H and 1C NMR spectra of dimethylaniline are as follows: Figure 1-2 As shown, the specific data is as follows: 1 H NMR (500 MHz, CDCl3) δ = 7.21-7.24 (m, 2H), 6.69-6.73 (m, 3H), 2.91 (s, 6H); 13 C NMR (151 MHz, CDCl3) δ = 150.8, 129.2, 116.7, 112.8, 40.7.

[0074] The Cu / Cr2O3 catalyst from Example 1 was recovered by filtration, washed with deionized water and ethanol, and dried at 60°C. It was then calcined in a muffle furnace at 550°C for 6 h and reduced at 300°C for 6 h in a 5% H2 / Ar atmosphere (gas flow rate 60 mL / min). -1 Heating rate 2℃·min -1 ), and then reuse it. Figure 3 This is a graph showing the reusability of the catalyst. Under the standard conditions of Example 1, it was recycled 6 times, yielding... N,N- The yield of dimethylaniline remains at 90%.

[0075] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds N The method of methylation is characterized by... A reaction system was constructed by adding 1.5 mmol of POM powder, 0.5 mmol of aniline, 0.05 g of Cu / Cr₂O₃, 3 mL of 1,4-dioxane, and 1.5 mL of water to a high-pressure reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. The reaction system was placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring to obtain… N,N -Dimethylaniline.

2. A method for controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds N The method of methylation is characterized by... In several high-pressure reactors equipped with electromagnetic stirrers, thermocouples, and programmable temperature controllers, 1.5 mmol of POM powder, 0.5 mmol of different aromatic amine compounds, and 0.05 g of Cu / Cr₂O₃ were added, respectively. Multiple reaction systems were constructed using 1,4-dioxane and water in a 3 mL:1.5 mL solvent. These reaction systems were then placed in an oil bath preheated to 220 °C under air atmosphere and reacted for 5 hours with continuous stirring to obtain the corresponding... N -Methylated derivatives; The aromatic amine compounds are p-methylaniline, p-isopropylaniline, or benzylamine.

3. The controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds according to claim 1 or 2. N The application of methylation in waste plastic treatment is characterized by, Waste plastic is made of polyoxymethylene (POM) material.

4. The controlled depolymerization of polyoxymethylene to achieve nitrogen-containing compounds according to claim 3. N The application of methylation in waste plastic treatment is characterized by, Waste plastics need to be crushed into centimeter- or millimeter-sized powders before undergoing depolymerization and upgrading reactions.

Images