A method for catalytic depolymerization of waste poly(p-dioxanone) to recover monomers

Abstract

This invention discloses a method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers, belonging to the field of heterocyclic compound technology. The method includes: mixing an oxide and / or hydroxide of an alkali metal or alkaline earth metal with a polyol, stirring and reacting under atmospheric pressure (100-180℃) or reduced pressure (10-120℃) while removing moisture to obtain a catalyst; mixing the obtained catalyst with waste poly(p-dioxanone), and carrying out a depolymerization reaction under an absolute pressure of 0.1-30 kPa and a temperature of 120-180℃, the generated poly(p-dioxanone) monomer being continuously distilled off by reduced pressure distillation and collected by condensation; the collected crude distillate being purified by reduced pressure distillation to obtain polymerization-grade poly(p-dioxanone) monomer. Experiments show that the purified monomer yield can reach 99%, with a purity of not less than 99.5%, and the recovered monomer can be used for ring-opening polymerization to synthesize poly(p-dioxanone) with an intrinsic viscosity ≥1.8 dL / g. This invention features a low-cost catalyst raw material, mild depolymerization conditions, good reaction system fluidity, recyclable catalyst, low purification loss, and is easy to implement industrially.

Description

Technical Field

[0001] This invention belongs to the field of heterocyclic compound technology, and more specifically, this invention relates to a method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers. Background Technology

[0002] Poly(p-dioxanone) ketone (PPDO) is an aliphatic polyester with excellent biocompatibility, bioabsorbability, and biodegradability, widely used in medical fields such as surgical sutures, orthopedic fixation materials, tissue repair scaffolds, and drug delivery systems. Furthermore, PPDO's ability to be repeatedly chemically recycled and biodegraded has led to its increasing application in larger-scale single-use plastic products. With the increasing use of PPDO, the accumulation of waste is also putting environmental pressure on the industry. When waste PPDO is collectable, it can be chemically recycled into the monomer p-dioxanone (PDO) for resource recycling.

[0003] A patent published by Sichuan University (CN201410105034.7) proposes to recover monomers by thermally decomposing waste PPDO directly or after mixing it with a catalyst under vacuum conditions at 200-240 °C. While the disclosed method can achieve recovery, the high-temperature operation results in high energy consumption and is prone to side reactions. Research by Wang Yuzhong's team at Sichuan University (DOI: 10.1039 / D2GC00853J, 10.1039 / D3GC00625E) shows that using acidic ionic liquids as a solvent-catalyst bifunctional reagent, PPDO can be depolymerized at temperatures as low as 120 °C to recover PDO monomers with a purity of up to 99.9%. However, the large-scale use of ionic liquids makes this method economically uncompetitive. A study by the team of Shen Yong and Li Zhibo at Qingdao University of Science and Technology (DOI: 10.1021 / acssuschemeng.5c12503) showed that PPDO copolymers can be depolymerized and the monomers recovered at relatively low reaction temperatures, such as 140 °C, under the catalysis of stannous octoate, with a yield of up to 94%. However, stannous octoate is costly for catalytic depolymerization and has poor stability in water and oxygen. Furthermore, organotin catalysts such as stannous octoate cause contamination of the recovered monomers during PDO distillation, and due to their difficulty in removal and high activity, the recovered PDO monomers are prone to self-polymerization, have poor storage stability, and suffer significant purification losses.

[0004] Furthermore, comparative studies on simple catalyst systems show that at lower depolymerization reaction temperatures (120–180 °C), the depolymerization rate of PPDO is extremely low without a catalyst. While adding polyols alone can reduce system viscosity, their catalytic activity is extremely limited. Adding alkali metal or alkaline earth metal oxides or hydroxides alone has some catalytic effect, but the solid particles are poorly dispersed in the PPDO melt, resulting in high system viscosity during the reaction, difficult mass and heat transfer, and a tendency to induce localized overheating and side reactions. Existing methods still have room for improvement in terms of catalyst cost, depolymerization efficiency, process controllability, and the quality of recovered monomers.

[0005] Therefore, it is of great significance to develop a PPDO depolymerization and recovery method that has low catalyst cost, high catalytic activity, good reaction system fluidity, and easy product separation and purification. Summary of the Invention

[0006] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0007] To achieve these objectives and other advantages of the present invention, a method for catalytically depolymerizing waste poly(p-dioxane)hexanone to recover monomers is provided, comprising the following steps: Step 1, Catalyst Preparation: The metal compound is mixed with a polyol, the mixture is stirred and reacted, and the water generated during the reaction is removed to obtain the catalyst; Step 2, Depolymerization reaction: Waste poly(p-dioxanone) and catalyst are added to the reactor, and the depolymerization reaction is carried out under reduced pressure and heated. The p-dioxanone monomer generated during the reaction is continuously distilled off by reduced pressure distillation, collected by condensation, and the crude distillate is obtained. Step 3, Product Refining: The collected crude distillate is refined by vacuum distillation to obtain polymer-grade p-dioxanone monomer.

[0008] Preferably, in step one, the metal compound includes one or more of the following: alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides, and alkaline earth metal hydroxides.

[0009] Preferably, the alkali metal is one or more of lithium, sodium, and potassium; and the alkaline earth metal is one or two of magnesium and calcium.

[0010] Preferably, in step one, the polyol is a diol and / or a triol, including but not limited to one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, glycerol, and trimethylolpropane; more preferably, ethylene glycol, diethylene glycol, and glycerol.

[0011] Preferably, in step one, the molar ratio of the metal compound to the polyol is 1:(1~25).

[0012] Preferably, in step one, the metal compound is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, magnesium oxide, and calcium oxide; more preferably, it is calcium oxide, or a combination of calcium oxide and potassium hydroxide, or a combination of calcium oxide and sodium hydroxide.

[0013] Preferably, in step one, the specific conditions for the stirring reaction include: (1) Under normal pressure, the reaction temperature is 100~180℃ and the reaction time is 1~8 hours; Or, (2) Under reduced pressure conditions, the working pressure is 0.1~30 kPa, the reaction temperature is 10~120℃, and the reaction time is 2~12 hours.

[0014] Preferably, in step two, the amount of catalyst used, in terms of the molar amount of metal ions, is 0.2% to 5% of the molar amount of waste polydioxanone repeating units.

[0015] Preferably, in step two, the pressure of the decompression condition is 0.1~30 kPa.

[0016] Preferably, in step two, the temperature of the depolymerization reaction is 120~180℃.

[0017] Preferably, in step three, the pressure of vacuum distillation is 0.05~1 kPa and the temperature is 60~80℃.

[0018] The present invention has at least the following beneficial effects: (1) The catalyst is inexpensive and flexible in preparation: The oxides, hydroxides and polyols of alkali metals or alkaline earth metals used are all bulk chemical raw materials, which are widely available and inexpensive. The catalyst can be prepared by heating under normal pressure or under reduced pressure, which is flexible, does not require complicated equipment, and is easy to implement in industrial applications.

[0019] (2) High depolymerization efficiency, mild conditions, and high product purity: Depolymerization can be completed rapidly at a low temperature of 120℃ (as short as 0.5 hours), with a purified monomer yield of up to 99% and a purity of 99.9%. The reaction system has good fluidity, avoiding high viscosity and local overheating caused by solid catalysts. The intrinsic viscosity of poly(p-dioxanone) obtained by ring-opening polymerization of the recovered monomer is generally not less than 1.8 dL / g, and some can reach 2.5 dL / g.

[0020] (3) Low purification loss and good stability of recovered monomers: The catalyst of this invention does not distill off with the monomers. High-purity monomers can be obtained from the crude distillate through a single vacuum distillation. The purification process has extremely low loss (usually less than 1%). Compared with organotin catalytic systems, the recovered monomers are less prone to self-polymerization, and the storage stability is significantly improved.

[0021] (4) The catalyst is recyclable and has good process economy: The catalyst remains in the liquid phase throughout the depolymerization process and can be recycled multiple times. When using waste polydioxanone residue as raw material, the single-refined monomer yield is still over 98.5% after 30 cycles, and the cumulative total yield is close to 99%. Kilogram-scale scale-up experiments also obtained a yield of over 97% and a purity of 99.9%, showing good industrialization prospects.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is the gas chromatogram of the crude distillate in Example 4 of the present invention; Figure 3 This is a gas chromatogram of the purified monomer in Example 4 of the present invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0025] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0026] The names and abbreviations of the materials used in the following examples and comparative examples are shown in Table 1.

[0027] Table 1 category Chinese name Chemical formula / molecular formula Common abbreviations Alkaline earth metal oxides magnesium oxide MgO — Alkaline earth metal oxides Calcium oxide CaO — Alkaline earth metal hydroxides calcium hydroxide <![CDATA[Ca(OH)2]]> — Alkali metal hydroxides Lithium hydroxide LiOH — Alkali metal hydroxides Sodium hydroxide NaOH — Alkali metal hydroxides potassium hydroxide KOH — Diol Ethylene glycol <![CDATA[C2H6O2]]> EG Diol Diethylene glycol (diethylene glycol) <![CDATA[C4H 10 O3]]> DEG Triol Glycerin (glycerol) <![CDATA[C3H8O3]]> Gly Diol 1,2-Propanediol <![CDATA[C3H8O2]]> 1,2-PDO Diol 1,4-Butanediol <![CDATA[C4H 10 O2]]> 1,4-BDO Example 1 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 62 g (1.0 mol) of EG and 14 g (0.25 mol, molar ratio 4:1) of CaO to a reaction flask, heat to 140℃ under normal pressure, stir and react for 4 hours, continuously separating the generated water until no water is distilled off, and obtain an orange-red mixture, which is the catalyst. Step 2, Depolymerization Reaction: Take 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g, approximately 0.49 mol repeating units), add the above catalyst (calcium ion molar amount is 1% of the polymer repeating unit molar amount), and place it in a vacuum distillation apparatus (glass reaction flask, gram scale); first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 1.5 hours, no fraction distilled off, collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 47.5 g of colorless and transparent purified monomer. Gas chromatography analysis showed a purity of 99.9% and a monomer yield of 95.0%. The obtained purified monomer was used for ring-opening polymerization (using stannous octoate as a catalyst, bulk polymerization at 120℃) to obtain PPDO with an intrinsic viscosity of 2.4 dL / g.

[0028] Example 2 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1: Catalyst Preparation: Catalysts with different EG to CaO molar ratios were prepared (EG fixed at 62 g, 1.0 mol): Example 2a: CaO 2.8 g (0.05 mol, molar ratio 20:1); Example 2b: CaO 5.6 g (0.1 mol, molar ratio 10:1); Example 2c: 28 g CaO (0.5 mol, molar ratio 2:1); Example 2d: CaO 56 g (1.0 mol, molar ratio 1:1); Preparation method was the same as in Example 1 (140℃, 4 hours), and an orange-red mixture was obtained in both cases; Step 2, same as in Example 1; Step 3: Same as Example 1; The product purification results of Example 2 are shown in Table 2. It can be seen that the catalysts prepared by EG and CaO in a molar ratio range of 1:1 to 20:1 can effectively catalyze depolymerization. The purity after recovery and purification is not less than 99.5%, and the intrinsic viscosity of PPDO prepared from the recovered monomers is higher than 1.8 dL / g.

[0029] Table 2 Example 3 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 62 g (1.0 mol) of EG and 14 g (0.25 mol, molar ratio 4:1) of KOH to a reaction flask, heat to 160℃ under normal pressure, stir and react for 2 hours, continuously separating the generated water until no water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 0.9 dL / g), add the above catalyst (potassium ion molar amount is 1% of the molar amount of the polymer repeating unit), and place it in a vacuum distillation apparatus; first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 2.0 kPa with a water ring vacuum pump, raise the temperature to 180℃, stir the reaction, and continuously distill off the PDO monomer generated by depolymerization, condense and collect; after the reaction has been going on for 4.0 hours, no fraction distilled off, and collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 46.0 g of colorless and transparent purified monomer. Gas chromatography analysis showed a purity of 99.6% and a monomer yield of 92.0%. The obtained purified monomer was used for ring-opening polymerization (using stannous octoate as a catalyst, bulk polymerization at 120℃) to obtain PPDO with an intrinsic viscosity of 1.9 dL / g.

[0030] Example 4 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst Preparation: Add 62 g (1.0 mol) of EG, 7 g (0.125 mol) of CaO and 7 g (0.125 mol of KOH, 0.25 mol of total metal ions, molar ratio of EG to total metal ions 4:1) to a reaction flask, heat to 140℃ under normal pressure, stir and react for 4 hours, continuously separating the generated water until no more water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization Reaction: Take 50 g of waste PPDO (intrinsic viscosity 1.1 dL / g), add the above catalyst (total metal ion molar amount is 0.5% of the molar amount of polymer repeating unit), and place in a vacuum distillation apparatus; first, melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 120℃, and stir the reaction. The PDO monomers generated by depolymerization are continuously distilled off and collected by condensation; after the reaction proceeds for 0.5 hours, no fraction is distilled off, and the crude distillate is collected; the yield of the crude distillate is 99.4%; the results are as follows by gas chromatography (normalization method). Figure 2 As shown in Table 3, the crude distillate is p-dioxanone monomer with a purity of 99.6%; Step 3: Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃) to obtain 49.5 g of colorless and transparent refined monomer. Figure 3 As shown in Table 4, the purity of the monomer was 99.9% by gas chromatography, and the yield of the purified monomer was 99.0%. The obtained purified monomer was used for ring-opening polymerization (bulk polymerization at 120℃ using stannous octoate as catalyst) to obtain PPDO with an intrinsic viscosity of 2.5 dL / g.

[0031] Table 3 Peak sequence Component name Retention time [min] Peak height [pA] Peak area [pA*s] area[%] content[%] 1 impurities 0.613 11.92 70.54 0.0011 0.0011 2 impurities 0.767 7.74 35.96 0.0006 0.0006 3 impurities 0.858 13.97 89.52 0.0014 0.0014 4 impurities 1.079 9.11 72.22 0.0011 0.0011 5 impurities 1.264 12.47 54.98 0.0009 0.0009 6 impurities 1.473 51.9 245.52 0.0038 0.0038 7 impurities 1.979 16.14 89.08 0.0014 0.0014 8 impurities 2.074 18 163.2 0.0025 0.0025 9 impurities 3.136 2.99 40.89 0.0006 0.0006 10 impurities 3.638 500.72 19085.86 0.2971 0.2971 11 impurities 5.602 124.17 4737.63 0.0737 0.0737 12 impurities 7.812 36.73 1271.11 0.0198 0.0198 13 impurities 10.221 4.93 128.95 0.002 0.002 14 impurities 11.012 11.45 434.63 0.0068 0.0068 15 monomer 13.051 65839.01 6398613.8 99.5872 99.5872 --- total ------- 66661.25 6425133.91 100 100 Table 4 Peak sequence Component name Retention time [min] Peak height [pA] Peak area [pA*s] area[%] content[%] 1 impurities 0.538 3.2 8.87 0.0002 0.0002 2 impurities 1.1 1.88 7.89 0.0001 0.0001 3 impurities 1.525 29.86 114.84 0.002 0.002 4 impurities 1.965 6.52 62.54 0.0011 0.0011 5 impurities 3.928 3.18 80.89 0.0014 0.0014 6 impurities 5.605 1.86 31.23 0.0005 0.0005 7 impurities 6.188 3.05 53.14 0.0009 0.0009 8 impurities 11.482 4.94 110.51 0.0019 0.0019 9 monomer 12.87 65788.93 5766896.43 99.9919 99.9919 --- total ------- 65843.42 5767366.34 100 100 Example 5 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: 76 g (1.0 mol) of 1,2-PDO and 14 g (0.25 mol, molar ratio 4:1) of CaO were added to a reaction flask. The mixture was heated to 140°C under normal pressure and stirred for 3 hours. During the reaction, the generated water was continuously separated until no water was distilled off, and the resulting mixture was the catalyst. Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 0.6 dL / g), add the above catalyst (calcium ion molar amount is 1% of the molar amount of the polymer repeating unit), and place it in a vacuum distillation apparatus; first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 15 kPa using a vacuum compressor, raise the temperature to 180℃, and stir the reaction. The PDO monomer generated by depolymerization is continuously distilled off and collected by condensation; after the reaction has proceeded for 6.0 hours, no fraction is distilled off, and the crude distillate is collected; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 45.2 g of colorless and transparent purified monomer. Gas chromatography analysis showed a purity of 99.5% and a monomer yield of 90.4%. The obtained purified monomer was used for ring-opening polymerization (using stannous octoate as a catalyst, bulk polymerization at 120℃) to obtain PPDO with an intrinsic viscosity of 1.9 dL / g.

[0032] Example 6 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst Preparation: Add 62 g (1.0 mol) of EG, 7 g (0.125 mol) of CaO and 5 g (0.125 mol, total metal ions 0.25 mol, molar ratio 4:1) of NaOH to a reaction flask, reduce the system pressure to 10 kPa, raise the temperature to 70℃, stir the reaction for 3 hours, continuously separate the generated water until no water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 1.3 dL / g), add the above catalyst (total metal ion molar amount is 0.2% of the molar amount of polymer repeating unit), and place it in a vacuum distillation apparatus; first, melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa with a rotary vane vacuum pump, raise the temperature to 130℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 1.0 hour, no fraction distilled off, and collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 49.0 g of colorless and transparent purified monomer. Gas chromatography analysis showed a purity of 99.9% and a monomer yield of 98.0%. The obtained purified monomer was used for ring-opening polymerization (using stannous octoate as a catalyst, bulk polymerization at 120℃) to obtain PPDO with an intrinsic viscosity of 2.1 dL / g.

[0033] Example 7 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 62 g (1.0 mol) of EG and 6.0 g (0.25 mol, molar ratio 4:1) of LiOH to a reaction flask, heat to 160℃ under normal pressure, stir and react for 3 hours, continuously separating the generated water until no water distills out, and obtain a pale yellow mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 1.6 dL / g), add the above catalyst (lithium ion molar amount is 5% of the molar amount of the polymer repeating unit), and place it in a vacuum distillation apparatus; first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa with a rotary vane vacuum pump, raise the temperature to 140℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 0.5 hours, no fraction distilled off, collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 44.0 g of colorless and transparent purified monomer. The purity was 99.8% by gas chromatography analysis, and the purified monomer yield was 88.0%.

[0034] Example 8 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 106 g (1.0 mol) of DEG and 18.5 g (0.25 mol, molar ratio 4:1) of Ca(OH)2 to a reaction flask, reduce the system pressure to 0.1 kPa, stir the reaction at room temperature for 12 hours, continuously separate the generated water until no water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 1.0 dL / g), add the above catalyst (calcium ion molar amount is 1% of the molar amount of the polymer repeating unit), and place it in a vacuum distillation apparatus; first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa with a rotary vane vacuum pump, raise the temperature to 140℃, stir the reaction, and continuously distill off the PDO monomer generated by depolymerization, condense and collect; after the reaction has proceeded for 2.0 hours, no fraction distilled off, and collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 46.5 g of colorless and transparent purified monomer. The purity was 99.7% by gas chromatography analysis, and the purified monomer yield was 93.0%.

[0035] Example 9 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 90 g (1.0 mol) of 1,4-BDO and 10 g (0.25 mol, molar ratio 4:1) of MgO to a reaction flask, heat to 180℃ under normal pressure, stir and react for 8 hours, continuously separating the generated water until no water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 0.4 dL / g), add the above catalyst (the molar amount of magnesium ions is 5% of the molar amount of the repeating unit of the polymer), and place it in a vacuum distillation apparatus; first, melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa with a rotary vane vacuum pump, raise the temperature to 180℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 3.0 hours, no fraction distilled off, and collect the crude distillate; Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 42.5 g of colorless and transparent purified monomer. The purity was 99.5% by gas chromatography analysis, and the purified monomer yield was 85.0%.

[0036] Example 10 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst preparation: Add 92 g (1.0 mol) of Gly and 14 g (0.25 mol, molar ratio 4:1) of KOH to a reaction flask, reduce the system pressure to 30 kPa, raise the temperature to 120℃, stir the reaction for 12 hours, continuously separate the generated water until no water is distilled off, and obtain the mixture, which is the catalyst; Step 2, Depolymerization reaction: Take 50 g of waste PPDO (intrinsic viscosity 0.5 dL / g), add the above catalyst (potassium ion molar amount is 1% of the molar amount of the polymer repeating unit), and place it in a vacuum distillation apparatus; first melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 1 kPa with a rotary vane vacuum pump, raise the temperature to 150℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 2.6 hours, no fraction distilled off, and collect the crude distillate; Step 3, Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃) to obtain 45.0 g of colorless and transparent purified monomer. The purity was 99.5% by gas chromatography analysis, and the purified monomer yield was 90.0%.

[0037] Example 11 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst Preparation: Prepare the catalyst according to Step 1 of Example 4; Step 2, Kilogram-scale depolymerization: In a 5 L stainless steel batch reactor, 2 kg of waste PPDO (19.6 mol repeating units) was taken, and the above catalyst (total metal ion molar amount is 1% of the polymer repeating unit molar amount) was added. The mixture was first melted and stirred at 120°C under a nitrogen atmosphere for 0.5 hours, then the pressure was reduced to 0.1 kPa using a rotary vane vacuum pump, and the temperature was raised to 120°C. The reaction was stirred, and the PDO monomers generated by depolymerization were continuously distilled off and collected by condensation. After the reaction proceeded for 2.0 hours, no more distillate was distilled off, and the crude distillate was collected. Step 3: Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃). Gas chromatography analysis showed that the purity was 99.9% and the purified monomer yield was 97.0%.

[0038] Example 12 A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers includes the following steps: Step 1, Catalyst Preparation: Prepare the catalyst according to Step 1 of Example 4; Step 2, initial depolymerization: Same as Step 2 in Example 4; the residual liquid phase (containing catalyst and a small amount of unconverted polymer) is reserved for future use; Step 3, Recycling: Add 50 g of waste PPDO (from the same batch of defective products) directly to the above residual liquid phase again, and depolymerize under the same conditions. Repeat this operation and record the reaction time and monomer yield each time. Results: After 30 catalyst cycles, the time for a single depolymerization reaction gradually increased from 0.5 hours in the first cycle to approximately 1.0 hour in the 30th cycle (efficiency decreased by half), but the purified monomer yield in the 30th cycle still reached 98.5% with a purity of 99.8%. The total purified monomer yield from 30 depolymerization cycles (total collected monomers / total polymer input) was 98.8%. The intrinsic viscosity of PPDO obtained from the polymerization of the recycled purified monomers from 30 cycles was ≥1.8 dL / g. This example demonstrates that the catalyst exhibits excellent recyclability when using substandard products with extremely low impurity content as raw materials.

[0039] Comparative Example 1 (without catalyst) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g) to a vacuum distillation apparatus; first, melt and stir at 120℃ under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160℃, stir the reaction, and continuously distill off the PDO monomers generated by depolymerization, condense and collect; after the reaction has proceeded for 8.0 hours, no more fractions are distilled off, and the crude distillate is collected; Step 2, Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃), with a refined monomer yield of only 12.6%.

[0040] Comparative Example 2 (EG added alone) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g) and 1.2 g of EG to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160°C, stir the reaction, and the viscosity of the reaction liquid will slowly decrease. After the depolymerization reaction for 6.0 hours, collect the crude distillate. Step 2, Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 31.2% and a purity of 98.5%.

[0041] Comparative Example 3 (CaO added alone) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g) and 0.28 g (5.0 mmol) of CaO to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160°C, and stir the reaction. The reaction solution always maintains high viscosity, making stirring difficult, and local discoloration occurs. Collect the crude distillate after 6.0 hours of depolymerization reaction. Step 2, Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 65.8% and a purity of 99.2%. The refined monomer was used for ring-opening polymerization (bulk polymerization at 120℃ using stannous octoate as catalyst) to obtain PPDO with an intrinsic viscosity of 1.4 dL / g.

[0042] Comparative Example 4 (KOH added alone) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g) and 0.28 g (5.0 mmol) of KOH to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160°C, and stir the reaction. The viscosity of the reaction liquid slowly decreases but remains at a high level, making stirring difficult, and local discoloration occurs. Collect the crude distillate after 6.0 hours of depolymerization reaction. Step 2, Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 71.1% and a purity of 99.5%. The refined monomer was used for ring-opening polymerization (bulk polymerization at 120℃ using stannous octoate as catalyst) to obtain PPDO with an intrinsic viscosity of 1.6 dL / g.

[0043] Comparative Example 5 (Stene octoate catalysis) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g) and 0.25 g of stannous octoate (approximately 0.5 wt%) to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160°C, and stir the reaction. After 1.5 hours of reaction, the yield of crude distillate is 98.5%, but significant self-polymerization occurs during storage of the crude distillate, resulting in substantial purification losses. Step 2, Product Refining: The collected crude distillate was refined by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 82.0% and a purity of 99.8%.

[0044] Comparative Example 6 (Direct addition of EG and CaO) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.4 dL / g), 1.2 g of EG, and 0.28 g of CaO to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, raise the temperature to 160°C, and stir the reaction. The viscosity of the reaction liquid slowly decreases, and the depolymerization reaction lasts for 1.5 hours. The yield of the crude distillate is only 38.0%, and the purity is 99.4%. Continue depolymerization until the total reaction time is 6.0 hours, and collect the crude distillate. Step 2, Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 93.8% and a purity of 99.6%.

[0045] Comparative Example 7 (Direct addition of EG, KOH, and CaO) Step 1: Add 50 g of waste PPDO (intrinsic viscosity 1.1 dL / g) and 0.62 g (10.0 mmol) of EG, 0.07 g (1.25 mmol) of CaO, and 0.07 g (1.25 mmol, total metal ions 2.5 mmol, molar ratio of EG to total metal ions 4:1) to a vacuum distillation apparatus; first, melt and stir at 120°C under nitrogen atmosphere for 0.5 hours, then reduce the pressure to 0.1 kPa using a rotary vane vacuum pump, stir the reaction at 120°C, and collect the crude distillate after 2.0 hours of depolymerization reaction. The viscosity of the reaction liquid decreases slowly during the melting and stirring stage under nitrogen atmosphere and no longer decreases during the depolymerization reaction stage. Step 2, Product purification: The collected crude distillate was purified by vacuum distillation (0.1 kPa, 70℃), with a monomer yield of 44.9% and a purity of 99.6%.

[0046] Draw a process flow diagram of the present invention, such as... Figure 1 As shown.

[0047] The results of Examples 1 to 12 and Comparative Examples 1 to 7 are shown in Table 5.

[0048] Table 5 #Note: In Example 11, a kilogram-scale experiment was conducted using a batch reactor; all other examples were conducted at the gram level. Note: In Example 12, the catalyst was recycled 30 times, while in other examples it was recycled only once. *Note: In Comparative Example 5, the yield of the crude distillate was 98.5%, and the yield after purification decreased to 82.0%. The yield after purification is used in the table to reflect the purification loss. Note: Yield and purity of crude distillate.

[0049] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for catalytically depolymerizing waste poly(p-dioxanone) to recover monomers, characterized in that, Includes the following steps: Step 1, Catalyst Preparation: The metal compound is mixed with a polyol, stirred and reacted, while the water generated during the reaction is removed to obtain the catalyst; wherein the metal compound includes one or more of the following: alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides, and alkaline earth metal hydroxides. The specific conditions for the stirring reaction include: (1) Under normal pressure, the reaction temperature is 100~180℃ and the reaction time is 1~8 hours; Or, (2) Under reduced pressure conditions, the reduced pressure working pressure is 0.1~30 kPa, the reaction temperature is 10~120℃, and the reaction time is 2~12 hours; Step 2, Depolymerization reaction: Waste polydioxanone and catalyst are added to the reactor, and the temperature is raised to 120~180℃ under reduced pressure to carry out the depolymerization reaction. The polydioxanone monomer generated during the reaction is continuously distilled off by reduced pressure distillation, and collected by condensation to obtain crude distillate. Step 3, Product Refining: The collected crude distillate is refined by vacuum distillation to obtain polymer-grade p-dioxanone monomer.

2. The method for recovering monomers from catalytic waste poly(p-dioxanone) by depolymerization as described in claim 1, characterized in that, In step one, the polyol is a diol and / or a triol.

3. The method for recovering monomers from the catalytic depolymerization of waste poly(p-dioxanone) as described in claim 2, characterized in that, The polyols include one or more of the following: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, glycerol, and trimethylolpropane.

4. The method for recovering monomers from catalytic waste poly(p-dioxanone) by depolymerization as described in claim 1, characterized in that, In step one, the molar ratio of the metal compound to the polyol is 1:(1~25).

5. The method for recovering monomers from the catalytic depolymerization of waste poly(p-dioxanone) as described in claim 1, characterized in that, The alkali metal is one or more of lithium, sodium, and potassium.

6. The method for recovering monomers from catalytic waste poly(p-dioxanone) by depolymerization as described in claim 1, characterized in that, The alkaline earth metal is one or both of magnesium and calcium.

7. The method for recovering monomers from the catalytic depolymerization of waste poly(p-dioxanone) as described in claim 1, characterized in that, In step two, the amount of catalyst used, expressed as the molar amount of metal ions, is 0.2% to 5% of the molar amount of the waste polydioxanone repeating unit.

8. The method for recovering monomers from catalytic waste poly(p-dioxanone) as described in claim 1, characterized in that, In step two, the pressure under the decompression condition is 0.1~30 kPa.

9. The method for recovering monomers from catalytic waste poly(p-dioxanone) by depolymerization as described in claim 1, characterized in that, In step three, the pressure of vacuum distillation is 0.05~1 kPa.

10. The method for recovering monomers from the catalytic depolymerization of waste poly(p-dioxane) as described in claim 1, characterized in that, In step three, the temperature for vacuum distillation is 60~80℃.

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