Metal organic sulfonic acid-based solid acid catalyst applied to nylon 6 recovery and depolymerization and preparation method of metal organic sulfonic acid-based solid acid catalyst

Abstract

The invention provides a metal organic sulfonic acid-based solid acid catalyst applied to nylon 6 recovery and depolymerization and a preparation method thereof, and realizes upgrading and recovery of waste nylon 6. The main contents are as follows: (1) a structural design and a preparation method of the metal organic framework sulfonic acid-based solid acid catalyst; and (2) the solid acid is used for catalytic depolymerization of nylon 6. The problems that equipment corrosion is aggravated by inorganic acid in the nylon 6 recovery process and a liquid-phase catalyst is difficult to separate and recover are solved, and the application prospect is good.

Description

Technical Field

[0001] The present invention relates to the field of upgrading and recycling of waste nylon 6, and specifically to a metal-organic sulfonic acid-based solid acid catalyst for nylon 6 recycling and depolymerization and a preparation method thereof. Background Art

[0002] Polyamide 6, also known as nylon 6 (PA6), is a polymer material synthesized by polycondensation of the monomer caprolactam and is one of the engineering plastic products with the largest global production and market demand. Along with the booming development of the nylon 6 market, a large amount of nylon 6 waste is also generated. Therefore, the recycling technology of waste nylon 6 has attracted extensive attention.

[0003] The recycling methods of waste nylon 6 mainly include energy recovery, physical recovery and chemical recovery. Among them, chemical recovery conforms to the principle of atom economy and is a relatively thorough and potentially most valuable recycling method. Chemical recovery mainly includes acid-base depolymerization process, high-pressure steam hydrolysis, ammonolysis process and vacuum depolymerization process, and their purpose is to break the amide bond in the main chain of nylon 6 to generate small molecule oligomers and caprolactam monomers.

[0004] Acid-catalyzed depolymerization of nylon 6 is a potential method for upgrading and recycling of nylon 6. However, under high temperature and high pressure, small molecule inorganic acids will aggravate equipment corrosion and it is difficult to separate and recover the liquid phase catalyst. Therefore, solid acid catalysts with less equipment corrosion and simple separation have attracted more and more attention. Summary of the Invention

[0005] The purpose of the present invention is to provide a novel sulfonic acid-based solid acid catalyst for catalytic depolymerization of nylon 6 to realize the upgrading and recycling of waste nylon 6.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions: A preparation method of a sulfonic acid-based solid acid catalyst based on a metal-organic framework, comprising the following steps: Dissolve the catalyst methylene diphosphonic acid in the organic solvent methanol, then mix it with a Co or Ni metal ion precursor, a dicarboxylic acid organic ligand with a sulfonic acid group, and the organic solvent DMF. Stir at room temperature until the solution is clear, then place it in an autoclave and react at 80-120 °C for 48-72 h. After the reaction, wash the solid product with methanol and deionized water and dry it to obtain the sulfonic acid-based solid acid.

[0007] Further, the molar ratio of the used Co or Ni metal ion precursor to the dicarboxylic acid organic ligand with a sulfonic acid group is 1:1-1.5.

[0008] Further, the metal ion precursor is a chloride or nitrate of Ni or Co and its hydrate.

[0009] Further, the dicarboxylic acid organic ligand with a sulfonic acid group includes one of sodium 2-sulfoterephthalate, 5-sulfoisophthalic acid, and 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid.

[0010] Further, the temperature of the heating reaction is 80-120 °C, and the time is 48-72 h.

[0011] The application of the sulfonic acid group solid acid as a catalyst in the catalytic depolymerization and recycling of waste nylon 6.

[0012] Preferably, the application method is to use the sulfonic acid group solid acid as a catalyst, disperse it together with waste nylon 6 in water, and then react at 250-280 °C for 1-3 h in an inert gas atmosphere; wherein, the dosage of the sulfonic acid group solid acid is 20%-40% of the mass of waste nylon 6.

[0013] The novel sulfonic acid group solid acid catalyst for nylon 6 catalytic depolymerization provided by the present invention has the following advantages: (1) The present invention provides a novel sulfonic acid group solid acid catalyst and uses it for catalytic depolymerization of nylon 6. The reaction process is mild, the preparation and production are safe, and the preparation process is simple; (2) The present invention overcomes the disadvantages of traditional inorganic acid catalysts, such as large pollution, strong corrosiveness, inconvenient recovery, and difficult recycling. Description of the Drawings

[0014] Figure 1 Scanning electron microscope image of the Co-MOF sulfonic acid group solid acid prepared in Example 1.

[0015] Figure 2 Scanning electron microscope image of the Ni-MOF sulfonic acid group solid acid prepared in Example 4.

[0016] Figure 3 Infrared spectrum of the Co-MOF sulfonic acid group solid acid prepared in Example 1.

[0017] Figure 4 Infrared spectrum of the Ni-MOF sulfonic acid group solid acid prepared in Example 4 Figure 5 Mass spectrum of the liquid phase product obtained after depolymerization of nylon 6 in Example 1.

[0018] Figure 6 Mass spectrum of the liquid phase product obtained after depolymerization of nylon 6 in Example 4. Detailed Description of the Invention

[0019] A sulfonic acid group solid acid based on a metal-organic framework, and its preparation method includes the following steps: 1) Dissolve the catalyst methylenediphosphonic acid in the organic solvent methanol, then add the metal ion precursor and the organic ligand in a molar ratio of the metal ion precursor to the dicarboxylic acid organic ligand with a sulfonic acid group of 1:1 to 1.5, and then add the organic solvent DMF. Stir at room temperature until the solution is clear, then place it in an autoclave and heat and react at 80°C to 120°C for 48 to 72 h. After the reaction is completed, wash the solid product with methanol and deionized water and dry it to obtain the sulfonic acid group solid acid.

[0020] Among them, the metal ion precursor is a chloride or nitrate of Ni or Co. The dicarboxylic acid organic ligand is a dicarboxylic acid with a sulfonic acid group, such as sodium 2-sulfoterephthalate.

[0021] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0022] Example 1 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (17.6 mg, 0.1 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Co(NO3)2·6H2O solution (containing 29.1 mg, 0.1 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (0.1 mmol, 26.8 mg) in an autoclave. React in a drying oven at 80°C for 72 h. After the reaction is completed, cool to room temperature, and then wash with deionized water and methanol and air-dry to obtain the sulfonic acid group solid acid.

[0023] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, and mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle to make the reaction proceed in an inert gas atmosphere; (3) Set the temperature to 250°C and the reaction duration to 1 h; (4) After the reaction is completed, cool to room temperature, filter the product by suction, store the liquid phase product in the refrigerator, and dry and retain the solid phase product.

[0024] Example 2 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (52.8 mg, 0.3 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Co(NO3)2·6H2O solution (containing 87.3 mg, 0.3 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (104.52 mg, 0.39 mmol) in an autoclave. React in an oven at 100 °C for 60 h. After the reaction is completed, cool it to room temperature, and then wash it with deionized water and methanol and air-dry it to obtain a sulfonic acid group solid acid.

[0025] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature to 260 °C and the reaction time to 2 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry the solid-phase product for retention.

[0026] Example 3 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (88 mg, 0.5 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Co(NO3)2·6H2O solution (containing 145.5 mg, 0.5 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (201 mg, 0.75 mmol) in an autoclave. React in an oven at 120 °C for 48 h. After the reaction is completed, cool it to room temperature, and then wash it with deionized water and methanol and air-dry it to obtain a sulfonic acid group solid acid.

[0027] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature to 280 °C and the reaction time to 3 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry the solid-phase product for retention.

[0028] Example 4 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (17.6 mg, 0.1 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Ni(NO3)2·6H2O solution (containing 29 mg, 0.1 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (26.8 mg, 0.1 mmol) in an autoclave. React in an oven at 80 °C for 72 h. After the reaction is completed, cool it to room temperature, and then wash and air-dry it with deionized water and methanol to obtain sulfonic acid group solid acid.

[0029] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, and mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature at 250 °C and the reaction duration at 1 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry and retain the solid-phase product.

[0030] Example 5 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (52.8 mg, 0.3 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Ni(NO3)2·6H2O solution (containing 87 mg, 0.3 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (104.52 mg, 0.39 mmol) in an autoclave. React in an oven at 100 °C for 60 h. After the reaction is completed, cool it to room temperature, and then wash and air-dry it with deionized water and methanol to obtain sulfonic acid group solid acid.

[0031] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, and mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature at 260 °C and the reaction duration at 2 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry and retain the solid-phase product.

[0032] Example 6 1. Preparation of sulfonic acid group solid acid: Dissolve methylenediphosphonic acid H2MDP (88 mg, 0.5 mmol) in 1 mL of methanol, and then mix it with 1 mL of aqueous Ni(NO3)2·6H2O solution (containing 145 mg, 0.5 mmol of Co(NO3)2·6H2O), 2 mL of DMF, and monosodium 2-sulfoterephthalate (0.75 mmol, 201 mg) in an autoclave. React in an oven at 120°C for 48 h. After the reaction is completed, cool it to room temperature, and then wash it with deionized water and methanol and air-dry it to obtain sulfonic acid group solid acid.

[0033] 2. Catalytic depolymerization of nylon 6: (1) Weigh 500 mg of nylon 6 powder dried for 24 h and 100 mg of solid acid catalyst, add them to 100 mL of deionized water, and mix and place them in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature to 280°C and the reaction time to 3 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry and retain the solid-phase product.

[0034] Comparative example (1) Weigh 500 mg of nylon 6 powder dried for 24 h, add it to 100 mL of deionized water, and mix and place it in an autoclave; (2) Purge with argon for 30 s to displace the residual air in the reaction kettle, and make the reaction proceed in an inert gas atmosphere; (3) Set the temperature to 260°C and the reaction time to 1 h; (4) After the reaction is completed, cool it to room temperature, filter the product by suction, store the liquid-phase product in the refrigerator, and dry and retain the solid-phase product.

[0035] Figure 1 is the scanning electron microscope image of the Co-MOF sulfonic acid group solid acid prepared in Example 1. It can be seen from the figure that it is a stacked lamellar structure.

[0036] Figure 2 is the scanning electron microscope image of the Ni-MOF sulfonic acid group solid acid prepared in Example 4. It can be seen from the figure that it is a discrete lamellar structure.

[0037] Figure 3 is the infrared spectrum of the Co-MOF sulfonic acid group solid acid prepared in Example 1. As can be seen from the figure, at 1172 cm -1 are the symmetric and asymmetric stretching vibration peaks of O=S=O respectively, indicating that the sulfonic acid group is successfully introduced.

[0038] Figure 4 The infrared spectrum of the Ni-MOF sulfonic acid solid acid prepared in Example 4. As can be seen from the figure, the symmetric and asymmetric stretching vibration peaks of O=S=O are at 1172 cm -1 respectively, indicating the successful introduction of the sulfonic acid group.

[0039] Figure 5 The mass spectrum of the liquid-phase product obtained by depolymerizing nylon 6 in Example 1. In the figure, the mass spectrum peak of caprolactam is at m / z = 114.1, and the other peaks are the peaks of 6-aminocaproic acid and small-molecule oligomers.

[0040] Figure 6 The mass spectrum of the liquid-phase product obtained by depolymerizing nylon 6 in Example 4. In the figure, the mass spectrum peak of caprolactam is at m / z = 114.1, and the other peaks are the peaks of 6-aminocaproic acid and small-molecule oligomers.

[0041] The performance of the sulfonic acid solid acid in catalyzing the depolymerization of nylon 6 is mainly indicated by the yield of water-soluble small molecules in the product. The calculation method of the yield is as follows: Yield = (mass of original nylon 6 - mass of remaining nylon 6) / mass of original nylon 6 × 100% The comparison of the effects of different metal ion sulfonic acid solid acids prepared in Examples 1-6 on catalyzing the depolymerization of nylon 6 is shown in Table 1.

[0042] Table 1. Data on the depolymerization effect of nylon 6 in Examples 1-6 and comparative examples The above examples are only detailed examples for explaining the present invention and are not limitations on the implementation manners of the present invention. For other relevant workers, various forms of changes or modifications can be made without departing from the technical idea of the present invention. Any equivalent changes or modifications made according to the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A preparation method of a sulfonic acid-based solid acid catalyst based on metal-organic framework, characterized in that, Steps: Dissolve the catalyst methylenediphosphonic acid in the organic solvent methanol. Then, for the Co or Ni metal ion precursor, add a dicarboxylic acid organic ligand with a sulfonic acid group to the organic solvent DMF. Stir at room temperature until the solution is clear, then place it in an autoclave and react at 80 - 120 °C for 48 - 72 h. After the reaction, wash the solid product with methanol and deionized water and dry it to obtain the sulfonic acid group solid acid.

2. The method for preparing a sulfonic acid group solid acid according to claim 1, characterized in that: The metal ion precursor includes metal chlorides, metal nitrates, and their hydrates.

3. The method for preparing a sulfonic acid group solid acid according to claim 1, wherein: The dicarboxylic acid ligand with a sulfonic acid group includes one of sodium 2-sulfoterephthalate, 5-sulfoisophthalic acid, and 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid.

4. The method for preparing sulfonic acid group solid acid according to claim 1, wherein: The molar ratio of the metal ion precursor to the dicarboxylic acid organic ligand with a sulfonic acid group is 1:1 - 1.

5.

5. The sulfonic acid group solid acid prepared by the preparation method according to any one of claims 1 - 4.

6. Use of the sulfonic acid group solid acid according to claim 5 as a catalyst in the depolymerization and recycling of waste nylon 6.

7. The application according to claim 6, wherein: Use the sulfonic acid group solid acid as a catalyst, disperse it together with waste nylon 6 in water, and then react at 250 - 280 °C for 1 - 3 h in an inert gas atmosphere; wherein, the dosage of the sulfonic acid group solid acid is 20% - 40% of the mass of waste nylon 6.

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