A nanoscale enzyme catalyst and a process for its use in the hydrothermal degradation of polycaprolactam
By using nanozyme catalysts that combine specific metals with terephthalic acid ligands, the problem of low efficiency in the hydrothermal degradation of polycaprolactam has been solved, achieving efficient, green, and low-energy recovery of polycaprolactam, and the catalyst can be recycled.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YUANTIAN BIOTECHNOLOGY (TIANJIN) CO LTD
- Filing Date
- 2026-02-02
- Publication Date
- 2026-05-29
AI Technical Summary
Existing hydrothermal methods for degrading polycaprolactam are inefficient. Traditional catalysts require harsh reaction conditions under high temperature and pressure, resulting in high energy consumption and low monomer yield, making it difficult to achieve efficient and green recycling.
By combining specific types of single-metal or bimetallic nanozyme catalysts with terephthalic acid ligands, oxygen vacancies are formed through hydrothermal reaction and calcination. The electronic structure of the metal is controlled to improve catalytic efficiency and degrade polycaprolactam into caprolactam monomer.
Complete degradation of polycaprolactam is achieved at a lower temperature with a conversion rate of 100% and a caprolactam yield that is stable at over 94%. This reduces energy consumption and complies with green chemistry principles. The catalyst is also recyclable.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical recycling technology of polymer materials, specifically to a nanoenzyme catalyst and a process for its hydrothermal degradation of polycaprolactam. Background Technology
[0002] Polycaprolactam (PA6), an important engineering plastic, is widely used in textiles, automobiles, and electronics. However, its huge consumption has also led to increasingly serious problems of "white pollution" and resource waste. Traditional landfill and incineration methods not only cause resource loss but also pose environmental risks. Therefore, the development of efficient recycling technologies for PA6 is urgently needed.
[0003] Among numerous recycling methods, chemically degrading PA6 to its monomer caprolactam and reusing it in polymerization production is the most ideal way to achieve a closed-loop cycle. However, traditional pyrolysis or hydrolysis processes suffer from high energy consumption, harsh reaction conditions, low monomer yield, and poor selectivity. In recent years, hydrothermal reaction technology has become an effective means of degrading polymer materials due to its ability to utilize the unique properties of high-temperature and high-pressure water (such as increased ion product and decreased dielectric constant), but the degradation efficiency of hydrothermal reactions needs further improvement.
[0004] Currently, researchers have explored various solid acid / base catalysts to enhance the degradation efficiency of hydrothermal reactions. For example, Keiichi Tomishige et al. used m-ZrO2, which has a higher number of Lewis acid-base sites, as a catalyst to degrade glycine dimers containing amide bonds (model substrate) at 80°C, achieving a glycine dimer degradation rate of 40%. However, when using MgO, which has fewer Lewis acid-base sites, as a catalyst, the glycine yield was only 0.8%. Furthermore, when using m-ZrO2 as a catalyst for a 2-hour hydrothermal reaction of PA6 at 230°C, the caprolactam yield reached 81%. Dionisios G. Vlachos et al. used α-TiO2 as a catalyst for a 2-hour hydrothermal reaction of PA6 at 250°C and 30 bar, achieving a caprolactam yield of up to 80%. It can be seen that there is still significant room for improvement in the degradation efficiency of PA6 using hydrothermal methods. Summary of the Invention
[0005] In view of this, the present invention provides a nanozyme catalyst and a process for its hydrothermal degradation of polycaprolactam. The nanozyme catalyst can efficiently and deeply degrade PA6 at relatively low temperatures, and the catalyst can be recycled, thus achieving complete green recycling of PA6.
[0006] To solve the above technical problems, the first aspect of the present invention provides a single-metal nanozyme catalyst for hydrothermal degradation of polycaprolactam. The single-metal nanozyme catalyst is prepared by hydrothermal reaction of a metal center and an organic ligand. The metal is selected from any one of Zr, Ti, Ce and Mn, Co, Ni, Cu and Zn, and the organic ligand is terephthalic acid.
[0007] Preferably, the single-metal nanozyme catalyst can also be calcined to form oxygen vacancies, thereby obtaining a single-metal nanozyme catalyst containing oxygen vacancies.
[0008] A second aspect of the present invention provides a bimetallic nanozyme catalyst for hydrothermal degradation of polycaprolactam. The bimetallic nanozyme catalyst is prepared by hydrothermal reaction of a bimetallic center and an organic ligand. The bimetallic center is selected from any two of Zr, Ti, and Ce, or the bimetallic center includes a first metal and a second metal. The first metal is any one of Zr, Ti, or Ce, and the second metal is any one of Mn, Co, Ni, Cu, or Zn. The first metal and the second metal are combined in a molar ratio of 0.5-1:0.5-1. The organic ligand is terephthalic acid.
[0009] Preferably, the bimetallic nanozyme catalyst can also be calcined to form oxygen vacancies, thereby obtaining a bimetallic nanozyme catalyst containing oxygen vacancies.
[0010] The inventors discovered that when single-metal nanozymes are prepared using specific types of metals and the organic ligand terephthalic acid as raw materials, or when single-metal nanozymes containing oxygen vacancies are obtained after calcination, their degradation efficiency for PA6 is significantly higher than that of existing catalysts. Furthermore, when bimetallic nanozymes are prepared using specific types of bimetals, or when bimetallic nanozymes containing oxygen vacancies are obtained after calcination, their degradation efficiency for PA6 is further improved, even reaching 100%, indicating that this catalyst can completely degrade PA6, achieving a 100% conversion rate. This is because the combination of specific types of single or bimetals with terephthalic acid ligands can enhance the adsorption and activation capacity of the substrate by regulating the electronic structure of the metal. In particular, the combination of specific bimetals and terephthalic acid can produce a synergistic catalytic effect, further improving the degradation efficiency for PA6. Simultaneously, oxygen vacancies, as an important type of crystal defect, can effectively regulate the Lewis pH of the nanozyme, thereby synergistically improving the degradation efficiency of PA6 with the metal.
[0011] This invention also provides a process for the catalytic degradation of polycaprolactam using a nanozyme catalyst, the steps of which include:
[0012] After cleaning and crushing the polycaprolactam waste to be treated, it is put into the reactor, and the above-mentioned single metal nanozyme catalyst or bimetal nanozyme catalyst and water are added. After deoxygenation, the reactor is sealed and hydrothermal reaction is carried out at 180~230℃. After the reaction is completed, it is cooled to room temperature.
[0013] Solid-liquid separation was performed, and the liquid phase and solid phase were collected separately. The liquid phase was an aqueous solution of caprolactam, and the solid phase contained a nanozyme catalyst.
[0014] The caprolactam aqueous solution was concentrated, distilled under reduced pressure, and recrystallized to obtain caprolactam monomer.
[0015] Preferably, the polycaprolactam waste can be pre-crushed into particles or powder of 0.1~5mm to increase its contact area with the catalyst and promote the catalytic degradation reaction.
[0016] Preferably, the amount of water added is 4 to 20 times the mass of the pulverized polycaprolactam, and the amount of the nanoenzyme catalyst added is 0.1% to 1% of the mass of the pulverized polycaprolactam.
[0017] Preferably, the amount of water added is 7 to 12 times the mass of the pulverized polycaprolactam, and the amount of the nanozyme catalyst added is 0.3% to 0.8% of the mass of the pulverized polycaprolactam.
[0018] The above-mentioned ratio of water and nanozyme can ensure that the pulverized polycaprolactam waste and nanozyme are at a suitable contact concentration, which can guarantee the complete degradation of PA6 without increasing the degradation cost due to excessive nanozyme addition.
[0019] More preferably, the amount of water added is 7 to 10 times the mass of the pulverized polycaprolactam, and the amount of nanozyme added is 0.5% to 0.6% of the mass of the pulverized polycaprolactam.
[0020] Preferably, the hydrothermal reaction is carried out in a high-pressure reaction device, such as a high-pressure reactor.
[0021] Preferably, the hydrothermal reaction temperature is 180~220℃ and the reaction time is 2~20h.
[0022] More preferably, the hydrothermal reaction temperature is 190~210℃, and the reaction time is 8~15h.
[0023] Preferably, the solid-liquid separation is performed by centrifuging or filtering the reaction solution.
[0024] Preferably, the centrifugation speed is 8000~10000 rpm.
[0025] Preferably, the solid phase containing the nanozyme catalyst obtained from the solid-liquid separation step is washed with water, dried, and then recycled for the catalytic degradation of polycaprolactam.
[0026] For example, the nanozyme solid is washed with deionized water 3 to 5 times and dried at 50 to 60°C, and then recycled for the catalytic degradation of polycaprolactam.
[0027] Preferably, the polycaprolactam waste includes textile fabrics, engineering plastics, fiber products, or film and tube products containing polycaprolactam.
[0028] Compared with existing technologies, the process for the efficient catalytic degradation of polycaprolactam based on nanoenzyme hydrothermal reaction provided by this invention has the following advantages:
[0029] 1. The single-metal or bimetallic nanozyme catalyst prepared by this invention has a high specific surface area and contains high Lewis acid-base sites. The coordination between the metal and oxygen vacancies further adjusts the electronic structure and optimizes the Lewis acid-base properties, which greatly improves the catalytic efficiency. The conversion rate of soluble products of PA6 is as high as 100%. Moreover, this nanozyme catalyst can accurately catalyze the degradation of PA6 to caprolactam in hydrothermal reactions with very few byproducts. The yield of caprolactam monomer can be stably maintained above 94%, and can even approach 100% at its highest.
[0030] 2. Compared with the traditional pyrolysis method (pyrolysis temperature > 300℃), the catalytic degradation process provided by this invention has a milder reaction temperature and greatly reduces production energy consumption.
[0031] 3. The catalytic degradation process provided by this invention is green and environmentally friendly. It uses water as the main reaction medium, avoids the use of highly polluting organic solvents, and realizes the upgraded recycling from "PA6-containing waste" to "renewable caprolactam monomer", which is in line with the principles of green chemistry.
[0032] 4. The nanozyme catalyst provided by this invention has a stable chemical structure and is easy to separate from the reaction system. After separation and recovery, it can be used for the next catalytic degradation after simple cleaning and drying, which greatly reduces the process cost. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0034] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.
[0035] Nanozymes (nanozymes with enzyme-like catalytic activity) have shown great potential in the field of catalysis due to their high activity, high specific surface area, high stability, and designability. Catalysts with Fe and Mg as metal centers, for example, have proven to be highly promising nanozyme catalysts due to their excellent stability, abundant Lewis acid sites, and large specific surface area. However, current research on their application in the degradation of polycaprolactam is limited, and the degradation efficiency of current metal oxide catalysts capable of degrading PA6 is less than 80%, indicating significant room for improvement in degradation efficiency.
[0036] In view of this, the present invention provides a nanozyme catalyst and a process for its use in the hydrothermal degradation of polycaprolactam. Compared with traditional hydrothermal reactions, this process is green and environmentally friendly, using water as the main reaction medium and avoiding the use of toxic organic solvents; moreover, the pyrolysis temperature does not exceed 230°C, the conversion rate of PA6 is as high as 100%, and the yield of polycaprolactam is stably maintained above 96%, showing obvious advantages; at the same time, the nanozyme catalyst used in the present invention has a stable structure and can be recycled, which greatly reduces the degradation cost.
[0037] The preparation method provided by the present invention will be described below through specific embodiments.
[0038] Unless otherwise specified, the raw materials, reagents and equipment used in this invention are all conventional commercially available reagents and equipment.
[0039] Exemplary examples include the nanozyme catalysts Zr@Ti, Ti@Ce, Ce@Zr, and Zr@Ti-O used in this invention. v Ti@Ce-O v and Ce@Zr-O v The preparation method is as follows:
[0040] Zr@Ti and Zr@Ti-O vThe preparation method is as follows: Dissolve 0.5-1 mmol of ZrOCl2·8H2O in 18-27 mL of DMF, denoted as solution A; dissolve 1.0 mmol of terephthalic acid in 18-27 mL of DMF, denoted as solution B; add 0.5-1.0 mL of concentrated hydrochloric acid or acetic acid to solution B; mix solution A and solution B in a hydrothermal reactor, add 0.5-1 mmol of tetraisopropyl titanate dropwise while stirring, heat to 120-150°C, and maintain at this temperature for 12-24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting suspension was then poured into centrifuge tubes and centrifuged at 10,000-12,000 rpm for 5-10 minutes. The precipitate was collected and washed 3-5 times with DMF and 3-5 times with methanol. The washed product was then dried in a vacuum oven at 60°C for at least 12 hours, or vacuum dried at 150°C for 4 hours, to completely remove the solvent from the pores. After drying, the bimetallic nanozyme catalyst Zr@Ti was obtained. The dried Zr@Ti was then calcined in a tube furnace at 150-200°C for 3-5 hours, and then cooled to room temperature under a nitrogen atmosphere to obtain the oxygen-vacant bimetallic nanozyme catalyst Zr@Ti-O. v .
[0041] Ti@Ce and Ti@Ce-O v The preparation method is as follows: Add 1.25 mmol of terephthalic acid to a beaker, then measure DMF and methanol at a volume ratio of 7-9:0.5-1 and add them to the beaker. Mix well, pour the mixed solvent into the inner liner of a hydrothermal reactor, and stir magnetically or sonicate until the terephthalic acid is completely dissolved. Then add 0.5-1 mmol of Ce(NO3)3·6H2O. Under vigorous stirring, slowly add 0.5-1 mmol of tetraisopropyl titanate to the above solution. Place the inner liner into a high-pressure reactor, seal it, and place the reactor in an oven. React at 120-150°C for 12-24 hours. After the reaction is complete, allow it to cool naturally to room temperature. Pour the obtained suspension into centrifuge tubes and centrifuge at 10,000-12,000 rpm for 5-10 minutes. Collect the precipitate, wash it 3-5 times with DMF and 3-5 times with methanol. The washed product was then dried in a vacuum drying oven at 60°C for at least 12 hours, or under vacuum at 150°C for 4 hours, to completely remove the solvent from the pores. After drying, the bimetallic nanoscale enzyme catalyst Ti@Ce was obtained. The dried Ti@Ce was then placed in a tube furnace and calcined at 150-200°C for 3-5 hours, and then cooled to room temperature under a nitrogen atmosphere to obtain the oxygen-vacant bimetallic nanoscale enzyme catalyst Ti@Ce-O. v .
[0042] Ce@Zr and Ce@Zr-O v The preparation method is as follows: Dissolve 0.5-1 mmol Ce(NO3)3·6H2O and 0.5-1 mmol ZrOCl2·8H2O in 10-20 mL DMF, denoted as solution A; dissolve 2.0 mmol terephthalic acid in 10-20 mL DMF, denoted as solution B; add 2-4 mL acetic acid to solution B; mix the metal salt solution and ligand solution in the inner liner of the reaction vessel; seal the reaction vessel; place it in an oven; and react at 120-150℃ for 12-24 hours. After the reaction, allow it to cool naturally to room temperature; pour the obtained suspension into centrifuge tubes; centrifuge at 10,000-12,000 rpm for 5-10 minutes; collect the precipitate; wash 3-5 times with DMF and 3-5 times with methanol. The washed product was then dried in a vacuum drying oven at 60°C for at least 12 hours, or under vacuum at 150°C for 4 hours, to completely remove the solvent from the pores. After drying, the bimetallic nanozyme catalyst Ce@Zr was obtained. The dried Ce@Zr was then placed in a tube furnace and calcined at 150-200°C for 3-5 hours, and then cooled to room temperature under a nitrogen atmosphere to obtain the oxygen-vacant bimetallic nanozyme catalyst Ce@Zr-O. v .
[0043] Other types of nanozyme catalysts, such as single-metal nanozyme catalysts with Zr, Ti, Ce or Mn, Co, Ni, Cu, Zn as the metal center and corresponding single-metal nanozyme catalysts with oxygen vacancies, or bimetallic nanozyme catalysts such as Zr@Mn, Zr@Co, Zr@Ni, Zr@Cu, Zr@Zn, Ti@Mn, Ti@Co, Ti@Ni, Ti@Cu, Ti@Zn, Ce@Mn, Ce@Co, Ce@Ni, Ce@Cu, and Ce@Zn and corresponding bimetallic nanozyme catalysts with oxygen vacancies, can all be prepared by referring to the methods for nanozyme catalysts mentioned above. The only difference is that the metal is replaced with a water-soluble salt such as a chloride or nitrate corresponding to the target metal.
[0044] Example 1
[0045] This embodiment provides a process for using a bimetallic nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam, the steps of which include:
[0046] The polycaprolactam waste to be treated (a mixture of fishing nets, textiles, and industrial waste) was washed, dried, and pulverized into 5g of particles or powder with a particle size of 0.1-0.5mm (denoted as A). This powder was then added to a high-pressure reactor along with 35mL of water and 0.025g (denoted as B) of nanoenzyme Zr@Ti-O. vAfter purging with nitrogen to remove oxygen, the mixture is sealed and then placed in a forced-air drying oven for hydrothermal reaction at 220°C for 10 hours. After the reaction is completed, it is cooled to room temperature.
[0047] The cooled reaction solution was centrifuged at 8000 rpm to obtain a supernatant and a precipitate. The supernatant was an aqueous solution of caprolactam, and the precipitate consisted of incompletely degraded and insoluble PA6 oligomers and the nanozyme Zr@Ti-O. v The precipitate was washed five times with deionized water, dried at 60°C, and weighed (denoted as C). The precipitate mass was 0.025g (indicating that the obtained precipitate was entirely nanozyme, and also indicating that PA6 had been completely degraded, with a PA6 conversion rate of 100%). It was stored at room temperature for later use.
[0048] The caprolactam aqueous solution was concentrated, distilled under reduced pressure, and recrystallized to obtain 4.98 g of high-purity caprolactam monomer (denoted as D). The monomer purity was tested to be >97%, and the yield was 99.6%.
[0049] PA6 conversion rate (%) = [A - (CB)] / A × 100%, caprolactam yield (%) = (D / 113.16) / theoretical amount of caprolactam × 100%; where 113.16 is the relative molecular mass of caprolactam, and the theoretical amount of caprolactam is 0.0442 mol (retain 4 decimal places).
[0050] Example 2
[0051] This embodiment provides a process for using a bimetallic nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam, the steps of which include:
[0052] The polycaprolactam waste to be treated (a mixture of fishing nets, textiles, and industrial waste) was washed, dried, and pulverized into 5g of particles or powder with a particle size of 1-2mm (denoted as A). This powder was then added to a high-pressure reactor along with 25mL of water and 0.015g (denoted as B) of nanozyme Ti@Ce-O. v After purging with nitrogen to remove oxygen, the mixture is sealed and then placed in a forced-air drying oven for hydrothermal reaction at 180°C for 20 hours. After the reaction is completed, it is cooled to room temperature.
[0053] The cooled reaction solution was centrifuged at 9000 rpm to obtain a supernatant and a precipitate. The supernatant was an aqueous solution of caprolactam, and the precipitate consisted of incompletely degraded and insoluble PA6 oligomers and the nanozyme Ti@Ce-O. v The precipitate was washed four times with deionized water, dried at 60°C, and weighed (denoted as C). The precipitate mass was 0.015g (indicating that the obtained precipitate was entirely nanozyme, and also indicating that PA6 had been completely degraded, with a PA6 conversion rate of 100%). It was stored at room temperature for later use.
[0054] The caprolactam aqueous solution was concentrated, distilled under reduced pressure, and recrystallized to obtain 4.84 g of high-purity caprolactam monomer (denoted as D). The monomer purity was tested to be >97%, and the yield was 96.8%.
[0055] The calculation methods for PA6 conversion rate and caprolactam yield are the same as in Example 1.
[0056] Example 3
[0057] This embodiment provides a process for using a bimetallic nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam, the steps of which include:
[0058] The polycaprolactam waste (a mixture of fishing nets and textiles) to be treated was washed, dried, and pulverized into 5g of particles or powder with a particle size of 2-4mm (denoted as A). This powder was then added to a high-pressure reactor along with 80mL of water and 0.04g (denoted as B) of nanoenzyme Ce@Zr-O. v After purging with nitrogen to remove oxygen, the mixture is sealed and then placed in a forced-air drying oven for hydrothermal reaction at 200°C for 15 hours. After the reaction is completed, it is cooled to room temperature.
[0059] The cooled reaction solution was centrifuged at 10,000 rpm to obtain a supernatant and a precipitate. The supernatant was an aqueous solution of caprolactam, and the precipitate consisted of incompletely degraded and insoluble PA6 oligomers and the nanozyme Ce@Zr-O. v The precipitate was washed four times with deionized water, dried at 60°C, and weighed (denoted as C). The precipitate mass was 0.04 g (indicating that the obtained precipitate was entirely nanozyme, and also indicating that PA6 had been completely degraded, with a PA6 conversion rate of 100%). It was stored at room temperature for later use.
[0060] The caprolactam aqueous solution was concentrated, distilled under reduced pressure, and recrystallized to obtain 4.91 g of high-purity caprolactam monomer (denoted as D). The monomer purity was tested to be >97%, and the yield was 98.2%.
[0061] The calculation methods for PA6 conversion rate and caprolactam yield are the same as in Example 1.
[0062] Example 4
[0063] This embodiment provides a process for using a bimetallic nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 1, except that the oxygen-vacant bimetallic nanozyme catalyst Zr@Ti-O is used. v The catalyst was replaced with an equal mass of Zr@Ti catalyst without oxygen vacancies, and the remaining steps were the same as in Example 1.
[0064] Example 5
[0065] This embodiment provides a process for using a bimetallic nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 2, except that the oxygen-vacant bimetallic nanozyme catalyst Ti@Ce-O is used. v The catalyst was replaced with an equal mass of Ti@Ce catalyst without oxygen vacancies, and the remaining steps were the same as in Example 2.
[0066] Example 6
[0067] This embodiment provides a process for using a bimetallic nanozyme catalyst in the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 3, except that the oxygen-vacant bimetallic nanozyme catalyst Ce@Zr-O is used. v The catalyst was replaced with an equal mass of Ce@Zr catalyst without oxygen vacancies, and the remaining steps were the same as in Example 3.
[0068] Example 7
[0069] This embodiment provides a process for using a single-metal nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 1, except that a bimetallic nanozyme catalyst containing oxygen vacancies, Zr@Ti-O, is used. v Replace with an equal mass of oxygen-vacant single-metal nanozyme catalyst Zr-O v The remaining steps are the same as in Example 1.
[0070] Example 8
[0071] This embodiment provides a process for using a single-metal nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 2, except that a bimetallic nanozyme catalyst containing oxygen vacancies, Ti@Ce-O, is used. v Replace with an equal mass of oxygen-vacant single-metal nanozyme catalyst Ti-O v The remaining steps are the same as in Example 2.
[0072] Example 9
[0073] This embodiment provides a process for using a single-metal nanozyme catalyst containing oxygen vacancies for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 3, except that a double-metal nanozyme catalyst containing oxygen vacancies, Ce@Zr-O, is used. v Replace with an equal mass of Ce-O monometallic nanozyme catalyst containing oxygen vacancies v The remaining steps are the same as in Example 3.
[0074] Example 10
[0075] This embodiment provides a process for using a single-metal nanozyme catalyst in the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 7, except that the oxygen-vacant single-metal nanozyme catalyst Zr-O is used.v The catalyst was replaced with an equal mass of a single-metal nanozyme catalyst with Zr as the metal center, and the remaining steps were the same as in Example 7.
[0076] Example 11
[0077] This embodiment provides a process for using a single-metal nanozyme catalyst in the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 8, except that the oxygen-vacant single-metal nanozyme catalyst Ti-O is used. v The catalyst was replaced with an equal mass of Ti-centered single-metal nanozyme catalyst, and the remaining steps were the same as in Example 8.
[0078] Example 12
[0079] This embodiment provides a process for using a single-metal nanozyme catalyst in the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 9, except that the oxygen-vacant single-metal nanozyme catalyst Ce-O is used. v The catalyst was replaced with an equal mass of Ce-centered monometallic nanozyme catalyst, and the remaining steps were the same as in Example 9.
[0080] Examples 13-17
[0081] Examples 13-17 provide a process for using a single-metal nanozyme catalyst for hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 10, except that the single-metal nanozyme catalyst with Zr as the metal center is replaced by an equal mass of single-metal nanozyme catalysts with Mn, Co, Ni, Cu and Zn as the metal centers. The remaining steps are the same as in Example 10.
[0082] Examples 18-22
[0083] Examples 18-22 respectively provide a process for using a single-metal nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 7, except that the oxygen-vacant single-metal nanozyme catalyst Zr-O is used. v The catalysts were successively replaced with equal masses of single-metal nanozyme catalysts containing oxygen vacancies, Mn-O. v Co-O v Ni-O v Cu-O v and Zn-O v The remaining steps are the same as in Example 7.
[0084] Examples 23-37
[0085] Examples 23-37 provide a process for using a bimetallic nanozyme catalyst for hydrothermal degradation of polycaprolactam, with steps similar to those in Example 4, except that the bimetallic nanozyme catalyst Zr@Ti is replaced sequentially with equal masses of bimetallic nanozyme catalysts Zr@Mn, Zr@Co, Zr@Ni, Zr@Cu, Zr@Zn, Ti@Mn, Ti@Co, Ti@Ni, Ti@Cu, Ti@Zn, Ce@Mn, Ce@Co, Ce@Ni, Ce@Cu, and Ce@Zn, respectively. All other steps are the same as in Example 4.
[0086] Examples 38-52
[0087] Examples 38-52 respectively provide a process for using a bimetallic nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 1, except that the oxygen-vacant bimetallic nanozyme catalyst Zr@Ti-O is used. v The catalysts were successively replaced with equal masses of bimetallic nanozyme catalysts containing oxygen vacancies, namely Zr@Mn-O. v Zr@Co-O v Zr@Ni-O v Zr@Cu-O v Zr@Zn-O v Ti@Mn-O v Ti@Co-O v Ti@Ni-O v Ti@Cu-O v Ti@Zn-O v Ce@Mn-O v Ce@Co-O v Ce@Ni-O v Ce@Cu-O v and Ce@Zn-O v The remaining steps are the same as in Example 1.
[0088] Comparative Example 1
[0089] This comparative example provides a process for using a single-metal nanozyme catalyst for hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 10, except that the Zr-centered single-metal nanozyme catalyst is replaced with an equal mass of Fe-centered single-metal nanozyme catalyst. All other steps are the same as in Example 10.
[0090] Comparative Example 2
[0091] This comparative example provides a process for using a single-metal nanozyme catalyst for hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 10, except that the Zr-centered single-metal nanozyme catalyst is replaced with an equal mass of Mg-centered single-metal nanozyme catalyst. All other steps are the same as in Example 10.
[0092] Comparative Example 3
[0093] This comparative example provides a process for using a bimetallic nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 4, except that the Zr@Ti bimetallic nanozyme catalyst is replaced with an equal mass of Mn@Ti bimetallic nanozyme catalyst. All other steps are the same as in Example 4.
[0094] Comparative Example 4
[0095] This comparative example provides a process for using a bimetallic nanozyme catalyst for the hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 5, except that the Ti@Ce bimetallic nanozyme catalyst is replaced with an equal mass of Fe@Ce bimetallic nanozyme catalyst. All other steps are the same as in Example 5.
[0096] Comparative Example 5
[0097] This comparative example provides a process for using a bimetallic nanozyme catalyst containing oxygen vacancies for hydrothermal degradation of polycaprolactam. The steps are similar to those in Example 11, except that when preparing the Ti single-metal nanozyme catalyst, the organic ligand terephthalic acid is replaced with p-aminobenzoic acid. All other steps are the same as in Example 11.
[0098] Test Example
[0099] The specific surface area and number of Lewis acid / base sites of the nanozymes used in Examples 1-17 and Comparative Examples 1-5 of this application, as well as the conversion rate of PA6 and the yield of caprolactam (CPL), are shown in Table 1 below.
[0100] Table 1
[0101]
[0102] As can be seen from the results in Table 1, compared with Comparative Examples 1-5, all nanozymes of the present invention with Zr, Ti, and Ce as metal centers (i.e., Examples 1-12, including monometallic nanozymes and bimetallic nanozymes, regardless of whether they contain oxygen vacancies) achieved complete conversion of PA6 (conversion rate reached 100%), and the caprolactam (CPL) yield was consistently 94% or higher. Among them, the bimetallic nanozymes containing oxygen vacancies (such as Zr@Ti-O) v Ti@Ce-O v Ce@Zr-O vThe performance of the nanozyme catalysts provided in Examples 13-52 is the most outstanding, with CPL yields reaching 97%-100%, and they also possess high specific surface area (1100-1300 m² / g) and abundant Lewis acid-base sites (acid sites 2467-3679 μmol / g, base sites 572-742 μmol / g). Furthermore, although the specific surface area and Lewis acid / base sites of the nanozyme catalysts provided in Examples 1-12 are lower than those in Examples 1-12, they still exhibit a positive effect on PA6 degradation, with PA6 conversion rates still above 80%, even reaching above 90%, and CPL yields exceeding 66%.
[0103] In summary, this invention systematically investigated the performance of nanozyme catalysts with different metal compositions, structural states (containing or without oxygen vacancies), and ligand types in the hydrothermal degradation of PA6. Data show that the choice of metal center is the primary factor determining catalytic efficiency, with Zr, Ti, and Ce exhibiting excellent degradation activity due to their suitable Lewis acidity / basicity. Further introducing a second metal to form a bimetallic system can modulate the electronic structure and enhance the synergistic catalytic effect; especially after the formation of oxygen vacancies, the surface acidity and reaction selectivity of the catalyst are further improved. Furthermore, this invention also found that the ligand structure has a crucial influence on the construction of the metal active center; for example, terephthalic acid is more conducive to the formation of a highly active and stable catalytic interface than p-aminobenzoic acid.
[0104] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. The application of a metal nanozyme catalyst in the hydrothermal degradation of polycaprolactam, characterized in that, The metal nanozyme catalyst is a single-metal nanozyme catalyst, wherein the single-metal nanozyme catalyst is prepared by a hydrothermal reaction of a metal center and an organic ligand, wherein the metal is selected from any one of Zr, Ti, Ce and Mn, Co, Ni, Cu, Zn, and the organic ligand is terephthalic acid; the specific application of the metal nanozyme catalyst in the hydrothermal degradation of polycaprolactam is as follows: The polycaprolactam waste to be treated was cleaned, crushed and put into the reactor. The metal nanozyme catalyst and water were added, and after deoxygenation, the reactor was sealed and hydrothermal reaction was carried out at 180~230℃. After the reaction was completed, the reactor was cooled to room temperature. Solid-liquid separation was performed, and the liquid phase and solid phase were collected separately. The liquid phase was an aqueous solution of caprolactam, and the solid phase contained a nanozyme catalyst. The caprolactam aqueous solution was concentrated, distilled under reduced pressure, and recrystallized to obtain caprolactam monomer.
2. The application of the metal nanozyme catalyst as described in claim 1 in the hydrothermal degradation of polycaprolactam, characterized in that, The single-metal nanozyme catalyst is calcined to form oxygen vacancies, thus obtaining a single-metal nanozyme catalyst containing oxygen vacancies.
3. The application of the metal nanozyme catalyst as described in claim 1 in the hydrothermal degradation of polycaprolactam, characterized in that, The metal nanozyme catalyst is a bimetallic nanozyme catalyst, wherein the bimetallic nanozyme catalyst is prepared by hydrothermal reaction of a bimetallic center and an organic ligand. The bimetallic center is Zr and Ti, or Ce and Ti, or any one of Zr, Ti or Ce as the first metal and any one of Mn, Co, Ni, Cu or Zn as the second metal. The first metal and the second metal are combined in a molar ratio of 0.5-1:0.5-1. The organic ligand is terephthalic acid.
4. The application of the metal nanozyme catalyst as described in claim 3 in the hydrothermal degradation of polycaprolactam, characterized in that, The bimetallic nanozyme catalyst is calcined to form oxygen vacancies, thus obtaining a bimetallic nanozyme catalyst containing oxygen vacancies.
5. The application of the metal nanozyme catalyst as described in claim 1 in the hydrothermal degradation of polycaprolactam, characterized in that, The amount of water added is 4 to 20 times the mass of the pulverized polycaprolactam, and the amount of the nanozyme catalyst added is 0.1% to 1% of the mass of the pulverized polycaprolactam.
6. The application of the metal nanozyme catalyst as described in claim 5 in the hydrothermal degradation of polycaprolactam, characterized in that, The amount of water added is 7 to 12 times the mass of the pulverized polycaprolactam, and the amount of the nanozyme catalyst added is 0.3% to 0.8% of the mass of the pulverized polycaprolactam.
7. The application of the metal nanozyme catalyst as described in claim 1 in the hydrothermal degradation of polycaprolactam, characterized in that, The hydrothermal reaction is carried out at a temperature of 180~220℃ for 2~20h.
8. The application of the metal nanozyme catalyst as described in claim 1 in the hydrothermal degradation of polycaprolactam, characterized in that, The solid phase containing the nanozyme catalyst obtained from the solid-liquid separation step is washed with water, dried, and then recycled for the catalytic degradation of polycaprolactam.
9. The application of the metal nanozyme catalyst according to any one of claims 1 to 8 in the hydrothermal degradation of polycaprolactam, characterized in that, The polycaprolactam waste includes engineering plastics or fiber products containing polycaprolactam.