Solid Lewis acid catalyst as well as preparation method and application thereof

Abstract

The invention discloses a solid Lewis acid catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing amino acid hydrochloride with Lewis acid metal halide to prepare ionic liquid or double salt; the method comprises the following steps: mixing an ionic liquid or double salt with a cyclic ester polymer, dispersing the ionic liquid or double salt in a cyclic ester polymer melt through a mechanical action at a temperature above the melting point temperature of the cyclic ester polymer, and carrying out self-polymerization crosslinking on the ionic liquid or double salt of a dispersed phase to form solid microspheres by utilizing continuous heating and high vacuum conditions; catalyzing cyclization depolymerization of the cyclic ester polymer by the solid microspheres to form a cyclic ester monomer; and removing the cyclic ester monomer generated in the reaction system through reduced pressure distillation to realize the separation of the solid microspheres and the polymer, and the solid microspheres are the solid Lewis acid catalyst. The solid Lewis acid catalyst provided by the invention is good in stability, still has relatively high catalytic efficiency under a relatively low specific surface area, can be recycled without regeneration treatment, does not reduce the catalytic efficiency, and is high in total recovery rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of the treatment or processing of macromolecular compounds and chemical or physical methods, such as the preparation technology of catalysts. More specifically, the present invention relates to a solid Lewis acid catalyst, its preparation method and application. Background Art

[0002] Currently, the cyclic ester monomers that can be mass-produced and applied mainly include: L-lactide, ε-caprolactone, glycolide and p-dioxanone. The cyclic ester polymers obtained by ring-opening polymerization of the above cyclic ester monomers have excellent degradability and biocompatibility, and show broad application prospects in many fields such as environmental protection packaging, textiles, agriculture, 3D printing, biomedicine and water treatment. Ring-opening depolymerization, as the reverse reaction of ring-opening polymerization, has double meanings: on the one hand, waste cyclic ester polymers can be chemically recycled into cyclic ester monomers through ring-opening depolymerization, and then the closed-loop cycle can be realized by repolymerization of the recycled monomers; on the other hand, oligomers obtained by esterification polycondensation of hydroxy acids can be synthesized into cyclic ester monomers through ring-opening depolymerization, and ring-opening depolymerization is also the key technology for synthesizing high-purity cyclic ester monomers.

[0003] Currently, the common catalysts used for the ring-opening depolymerization of cyclic ester polymers include metal salts and metal complexes of tin, magnesium, iron, zinc or titanium (Nature Sustainability, 2023, 6(8), 965-973). These catalysts are applicable to the depolymerization processes of various cyclic ester polymers, such as polylactic acid, polycaprolactone, polyglycolide and poly-p-dioxanone. However, in terms of depolymerization efficiency, selectivity and yield, these catalysts still need to be further optimized. Taking polylactic acid, the cyclic ester polymer with the largest current production capacity, as an example, stannous octanoate (Sn(Oct) 2 ) is used to catalyze the depolymerization of polylactic acid under reduced pressure conditions (400 Pa) at 250 °C. Although the crude lactide yield can reach 94%, the depolymerization product still contains nearly 30% of the racemization by-product - meso-lactide (Polymer Degradation And Stability, 2017, 141, 77-83). Zinc acetate (Zn(Oct) 2 ) is used to catalyze the ring-opening depolymerization of polylactic acid under reduced pressure conditions (600 Pa) at 200-210 °C, and the crude lactide yield is as high as 98%, but the depolymerization product still contains more than 10% of meso-lactide (ChemistrySelect, 2020, 5(46), 14759-14763). In addition, Zn(Oct) 2Catalytic depolymerization of polycaprolactone was carried out under reduced pressure (40 Pa) at 180 °C, and the yield of ε-caprolactone was 35% (Angewandte Chemie, e202420688). CN116393174A uses an amino acid metal chelate (zinc D-proline) to catalytically depolymerize and cyclize oligomers of polyglycolide under reduced pressure (300 Pa) at 260 °C, and the crude yield of glycolide is 41%. The issues of selectivity and yield in recovering monomers during the cyclode-polymerization of cyclic ester polymers urgently need to be resolved.

[0004] In 2023, Williams et al. applied thermogravimetric analysis to study the cyclode-polymerization of polylactic acid. A commercial tin(II) and alcohol catalyst system showed very high activity and selectivity. Catalytic cyclode-polymerization of polylactic acid was carried out under reduced pressure (5 Pa) at 160 °C, and the crude yield of lactide was 92%, with the meso-lactide content less than 1% (Journal of the American Chemical Society, 2023, 145(36), 19840 - 19848). CN119241492A reported that a kaolin-based catalyst prepared using a zinc precursor and a tin precursor was used for the cyclode-polymerization of oligomeric polylactic acid at 190 °C, and the crude yield of lactide was 90%, with the meso-lactide content being 1%. In 2023, Byers et al. used ZnCl 2 and an alcohol catalyst system to catalytically depolymerize polycaprolactone under reduced pressure (13 Pa) at 160 °C, and the yield of ε-caprolactone could reach 96% (Angewandte Chemie, 2023, 135(25), e202303762). In 2025, Zhang et al. used an organozinc and alcohol catalyst system to catalytically depolymerize polyglycolide under reduced pressure (30 Pa) at 230 °C, and the yield of glycolide could reach 94% (Polymer, 2025, 317, 127957). Although the above catalysts have good activity and selectivity for the cyclode-polymerization of cyclic ester polymers, there are still the following key problems: (1) The catalyst is prone to co-distillation with cyclic ester monomers under high-temperature and high-vacuum conditions, resulting in catalyst loss and contamination of the prepared cyclic ester monomers. (2) The catalyst is prone to deactivation during the reaction, and it needs to undergo complex regeneration treatment to restore its activity after deactivation, which not only increases the operating cost but also reduces the overall reaction efficiency. (3) After the reaction is completed, it is difficult to efficiently separate the components of the composite catalyst system (such as ZnCl 2 and alcohol substances), which not only leads to low catalyst recovery rate but also poses a severe challenge to its green and sustainable application. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or deficiencies and provide at least the advantages described hereinafter.

[0006] To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing a solid Lewis acid catalyst, comprising the following steps:

[0007] Step 1: Mix an amino acid hydrochloride with a Lewis acidic metal halide to prepare an ionic liquid (melting point ≤ 100 °C) or a double salt (melting point > 100 °C);

[0008] Step 2: Mix the ionic liquid or double salt with a cyclic ester polymer, and disperse the ionic liquid or double salt in the melt of the cyclic ester polymer through mechanical action above the melting point temperature of the cyclic ester polymer. By using continuous heating and high vacuum conditions, the ionic liquid or double salt in the dispersed phase self-polymerizes and crosslinks to form solid microspheres; while the ionic liquid or double salt is converted into solid microspheres, it can catalyze the ring depolymerization of the cyclic ester polymer to form cyclic ester monomers; finally, the cyclic ester monomers generated in the reaction system are removed by vacuum distillation to achieve the separation of the solid microspheres from the polymer, and the obtained solid microspheres are the solid Lewis acid catalyst.

[0009] Preferably, in Step 1, the structural general formula of the amino acid hydrochloride is AA·HCl, where AA is an amino acid, and the amino acid is at least one of glycine (Gly), L-lysine (L-Lys), DL-lysine (DL-Lys), L-arginine (L-Arg), L-histidine (L-His), L-glutamic acid (L-Glu), L-alanine (L-Ala), D-alanine (D-Ala), L-phenylalanine (L-Phe), D-tryptophan D-tryptophan hydrochloride (D-Trp), L-tryptophan (L-Trp), L-threonine (L-Thr), L-leucine (L-Leu), L-isoleucine (L-Ile);

[0010] The structural general formula of the Lewis acidic metal halide is MX n , where M is one of Sn, Mg, Fe, Zn, Ti, X is one of Cl or Br, and n is an integer greater than or equal to 1;

[0011] The structural general formula of the ionic liquid or double salt is AA·HCl-xMX n , where x is the molar ratio of the Lewis acidic metal halide to the amino acid hydrochloride, and its value is 0.2 to 3.0; the ionic liquid or double salt is glycine chloro / bromo metalate (Gly·HCl-xMX n ), L-lysine chloro / bromo metalate (L-Lys·HCl-xMX n ), DL-lysine chloro / bromo metalate (DL-Lys·HCl-xMX n ), L-arginine chloro / bromo metalate (L-Arg·HCl-xMX n) L-Histidine chloride / bromide metalate (L-His·HCl-xMX n ) L-Glutamic acid chloride / bromide metalate (L-Glu·HCl-xMX n ) L-Alanine chloride / bromide metalate (L-Ala·HCl-xMX n ) D-Alanine chloride / bromide metalate (D-Ala·HCl-xMX n ) L-Phenylalanine chloride / bromide metalate (L-Phe·HCl-xMX n ) D-Tryptophan chloride / bromide metalate (D-Trp·HCl-xMX n ) L-Tryptophan chloride / bromide metalate (L-Trp·HCl-xMX n ) L-Threonine chloride / bromide metalate (L-Thr·HCl-xMX n ) L-Leucine chloride / bromide metalate (L-Leu·HCl-xMX n ) L-Isoleucine chloride / bromide metalate (L-Ile·HCl-xMX n ) and one of the following:

[0012] Preferably, in the first step, the amino acid hydrochloride is mixed with the Lewis acidic metal halide and stirred at 80 - 170 °C for 5 - 18 hours.

[0013] Preferably, in the second step, the cyclic ester polymer includes: polylactic acid, polycaprolactone, poly(p-dioxanone), polyglycolide; and the corresponding cyclic ester monomers are lactide, ε-caprolactone, p-dioxanone, and glycolide.

[0014] Preferably, in the second step, the mass ratio of the ionic liquid or double salt to the cyclic ester polymer is 1:0.5 - 1:3, the heating temperature is 180 - 260 °C, the high vacuum condition is ≤1 kPa, and the preparation time is 0.5 - 14 h.

[0015] Preferably, the mechanical action for dispersing the ionic liquid or double salt in the molten cyclic ester polymer by mechanical action is one of high-speed mixer stirring, emulsifier emulsification, and high-speed mixer stirring combined with ultrasonic dispersion.

[0016] Preferably, in the second step, the yield of the solid microspheres relative to the ionic liquid or double salt is ≥75%.

[0017] A solid Lewis acid catalyst is prepared by the preparation method of the above solid Lewis acid catalyst; the prepared solid microspheres are solid spheres, and the average diameter of the solid microspheres is 1-36 μm; the tin content of the solid microspheres is 20-40 wt%, the magnesium content is 7-16 wt%, the iron content is 10-20 wt%, the titanium content is 9-15 wt% or the zinc content is 10-25 wt%, the solid microspheres show weak acidity, and the total acid amount is 6-45 μmol / g.

[0018] Preferably, the solid Lewis acid catalyst is applied to catalyze the ring-opening depolymerization of cyclic ester polymers to prepare cyclic ester monomers, and the cyclic ester polymers used are the same as or different from the cyclic ester polymers used in the preparation of the solid Lewis acid catalyst; the mass ratio of the solid Lewis acid catalyst to the cyclic ester polymer is 1:5-1:1000, the reaction temperature is 130-260 °C, the reaction pressure is ≤1 kPa, the reaction time is 0.5-20 h, and the yield of the cyclic ester monomer obtained by vacuum reaction distillation is ≥90%.

[0019] Preferably, after one ring-opening depolymerization reaction is completed, the solid Lewis acid catalyst can be directly recycled without any treatment, and the catalytic efficiency retention rate is ≥94% after 30 cycles of use.

[0020] The present invention has at least the following beneficial effects:

[0021] 1. Since the catalyst provided by the present invention has good stability, still has high catalytic efficiency at a low specific surface area, can be recycled without regeneration treatment and the catalytic efficiency will not decrease, the total recovery rate in the whole depolymerization process is high, there is no loss of the catalyst, and thus it has better economic cost and greenness, which is beneficial to improving the product competitiveness.

[0022] 2. Since the catalyst provided by the present invention is non-volatile, the cyclic ester monomers obtained by ring-opening depolymerization are free from metal ion pollution, which makes the subsequent monomer purification steps simple, the purified monomer yield is high, and the monomer purity is high, reducing the subsequent industrial purification cost.

[0023] 3. Since the preparation method of the catalyst provided by the present invention is simple, it can be automatically separated from the distillation product, and the raw materials are cheap and easy to obtain, so it can be prepared on a large scale and is suitable for industrial production.

[0024] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a scanning electron microscope image of the solid microspheres prepared in step two of Example 1;

[0026] Figure 2 Double-beam scanning electron microscope images of the solid microspheres prepared in Step 2 of Example 1 and their cross-sections;

[0027] Figure 3 Ammonia-temperature-programmed chemical adsorption and desorption diagram of the solid microspheres prepared in Step 2 of Example 1. The test results show that the solid microspheres exhibit weak acidity;

[0028] Figure 4 Pyridine-infrared spectrum of the solid microspheres prepared in Step 2 of Example 1;

[0029] Figure 5 Gas chromatogram of the crude lactide (prepared as a 10% CH 2 Cl 2 solution) prepared by the first ring-opening depolymerization of poly(lactic acid) of the solid microspheres prepared in Step 2 of Example 1;

[0030] Figure 6 Gas chromatogram of the crude ε-caprolactone (prepared as a 10% CH 2 Cl 2 solution) prepared by the ring-opening depolymerization of polycaprolactone of the solid microspheres prepared in Step 2 of Example 2;

[0031] Figure 7 Gas chromatogram of the crude monomer of 1,4-dioxan-2-one (prepared as a 10% CH 2 Cl 2 solution) prepared by the ring-opening depolymerization of poly(1,4-dioxan-2-one) of the solid microspheres prepared in Step 2 of Example 3. Detailed implementation mode

[0032] The present invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0033] It should be understood that the terms such as "having", "comprising" and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0034] Catalysts with high catalytic activity and selectivity are prepared and screened by simple synchronous pyrolysis and vacuum distillation. The morphology of the solid Lewis acid catalyst is observed by scanning electron microscopy and double-beam scanning electron microscopy. The acidity of the catalyst is determined by ammonia-temperature-programmed chemical adsorption and desorption tests. The total acid amount value of the catalyst is determined by pyridine-infrared tests. The yield of the crude cyclic ester monomer obtained by ring-opening depolymerization is calculated by the mass change in the collection bottle before and after the reaction. The content of the recycled cyclic ester monomer is determined by nuclear magnetic resonance hydrogen spectroscopy combined with gas chromatography.

[0035] Example 1

[0036] Step 1: Add 5.0 g of Gly·HCl (45 mmol) and 8.5 g of SnCl 2 (45 mmol) into a 100 mL round-bottom flask, and heat and stir at 100 °C in an oil bath for 10 h to obtain Gly·HCl-1.0SnCl 2 .

[0037] Step 2: Add 5.0 g of Gly·HCl-1.0SnCl 2 and 5.0 g of polylactic acid into a 100 mL three-necked round-bottom flask, and react under reduced pressure (180 Pa) at 200 °C using a high-speed stirrer. After reacting for 6 h, after the polylactic acid is catalytically ring-opening depolymerized and distilled off, solid microspheres formed by self-polymerization cross-linking of Gly·HCl-1.0SnCl 2 are obtained. By weighing and calculating, the yield of the solid microspheres is 78.5%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 20 μm, the tin content is 35.6 wt%, and the solid microspheres show weak acidity by ammonia-temperature-programmed chemical adsorption and desorption tests, and the total acid amount is 8 μmol / g by pyridine-infrared tests.

[0038] The scanning electron microscope image of the solid microspheres prepared in Step 2 of this example is as Figure 1 shown, Figure 1 showing that the morphology of the solid microspheres is spherical.

[0039] As Figure 2 shown, this figure shows that the solid microspheres are solid spheres.

[0040] As Figure 3 shown, the test results show that the solid microspheres show weak acidity.

[0041] As Figure 4 shown, the test results show that the solid microspheres have both Bronsted acidity (B) and Lewis acidity (L), and the total acid amount is 8 μmol / g.

[0042] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst, add 0.05 g of solid microspheres and 5.0 g of polylactic acid into a 100 mL three-necked round-bottom flask (the three mouths of the round-bottom flask are used as the feeding port, the connecting mechanical stirring port and the reaction distillation port respectively), and react under reduced pressure (200 Pa) at 200 °C using a high-speed stirrer. After reacting for 2 h, weigh and calculate that the yield of the crude lactide ring-opening depolymerization obtained by reaction distillation is 99.5%. As Figure 5 shown, the L-lactide content is 99.3% and the meso-lactide content is 0.6% calculated by gas chromatography characterization normalization method, indicating that the solid Lewis acid catalyst prepared in Step 2 has high catalytic activity and good selectivity.

[0043] The solid catalyst in the reaction flask after the first ring-opening depolymerization above was not treated at all, and 5.0 g of polylactic acid was directly added again to continue catalytic ring-opening depolymerization. After reacting for 2 h, the reaction was stopped. The yield of crude lactide was 99.5%, and the content of L-lactide was 99.2%.

[0044] The solid catalyst in the reaction flask after the second ring-opening depolymerization above was still not treated at all. 5.0 g of polylactic acid was added again to continue catalytic ring-opening depolymerization. After reacting for 2 h, the reaction was stopped. The yield of crude lactide was 100.0%, and the content of L-lactide was 99.1%. After cycling 30 times like this, the reaction was stopped. The average yield of crude lactide was 99.6%, and the average content of L-lactide was 99.1%. The content of metallic tin in the recovered crude lactide each time was <1 ppm (lower than the detection limit).

[0045] Under the same reaction conditions, the yield of cyclic ester monomer in the first ring-opening depolymerization was 99.5%, and the yield of cyclic ester monomer in the 30th ring-opening depolymerization was 95.0%. The retention rate of catalytic efficiency during the recycling of the catalyst was calculated by (the yield of cyclic ester monomer in the 30th ring-opening depolymerization / the yield of cyclic ester monomer in the first ring-opening depolymerization) * 100% to be 95.5%.

[0046] Example 2

[0047] Step 1: Add 5.0 g of Gly·HCl (45 mmol) and 1.7 g of SnCl 2 (9 mmol) to a 100 mL round-bottom flask, and heat and stir in an oil bath at 120 °C for 8 h to prepare Gly·HCl-0.2SnCl 2 .

[0048] Step 2: Add 5.0 g of Gly·HCl-0.2SnCl 2 and 2.5 g of polylactic acid to a 100 mL three-necked round-bottom flask, and react under reduced pressure (200 Pa) at 190 °C by a high-speed stirrer. After reacting for 8 h, after the polylactic acid was catalytically ring-opening depolymerized and distilled off, Gly·HCl-0.2SnCl 2 self-polymerized and cross-linked to form solid microspheres. After weighing and calculating, the yield of the solid microspheres was 77.3%. The prepared solid microspheres were solid spheres, the average diameter of the microspheres was about 25 μm, the tin content was 32.1 wt%, and the solid microspheres showed weak acidity by ammonia-programmed temperature chemical adsorption and desorption tests, and the total acid amount was 10 μmol / g by pyridine-infrared tests.

[0049] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.10 g of the solid microspheres and 5.0 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (230 Pa) at 220 °C by a high-speed stirrer. After reacting for 20 h, weigh and calculate that the crude ε-caprolactone ring-opening depolymerization yield obtained by reaction distillation is 94.7%. As Figure 6 shown, the ε-caprolactone content calculated by the normalization method of gas chromatography characterization is 93.6%, and the ε-caprolactone cyclic dimer content is 5.6%.

[0050] Example 3

[0051] Step 1: Add 5.0 g of Gly·HCl (45 mmol) and 2.6 g of SnCl 2 (14 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 110 °C for 13 h to prepare Gly·HCl-0.3SnCl 2 .

[0052] Step 2: Add 5.0 g of Gly·HCl-0.3SnCl 2 and 3.5 g of polylactic acid into a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (240 Pa) at 180 °C by a high-speed stirrer. After reacting for 9 h, after the polylactic acid is catalytically ring-opening depolymerized and distilled off, Gly·HCl-0.3SnCl 2 self-polymerizes and crosslinks to form solid microspheres. After weighing and calculating, the solid microsphere yield is 75.1%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 27 μm, the tin content is 34.2 wt%, and the solid microspheres show weak acidity by ammonia-temperature-programmed chemical adsorption and desorption test, and the total acid amount is 7 μmol / g by pyridine-infrared test.

[0053] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.10 g of the solid microspheres and 1.0 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (600 Pa) at 130 °C by a high-speed stirrer. After reacting for 11 h, weigh and calculate that the crude p-dioxanone ring-opening depolymerization yield obtained by reaction distillation is 94.7%. As Figure 7 shown, the p-dioxanone content calculated by the normalization method of gas chromatography characterization is 99.7%.

[0054] Example 4

[0055] Step 1: Add 5.0 g of L-Lys·HCl (27 mmol) and 1.0 g of MgCl 2 (11 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 90 °C for 9 h to prepare L-Lys·HCl-0.4MgCl2 。

[0056] Step 2: Add 5.0 g of L-Lys·HCl - 0.4MgCl 2 and 4.0 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction through an emulsifier under reduced pressure (350 Pa) at 200 °C. After reacting for 14 h, after the polycaprolactone is catalytically ring-depolymerized and distilled off, L-Lys·HCl - 0.4MgCl 2 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 80.4%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 2 μm, the magnesium content is 7.6 wt%, the solid microspheres show weak acidity, and the total acid amount is 15 μmol / g.

[0057] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.10 g of solid microspheres and 5.0 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction through an emulsifier under reduced pressure (400 Pa) at 260 °C. After reacting for 10 h, by weighing and calculating, the yield of the crude ε-caprolactone obtained by reaction distillation is 95.1%.

[0058] Example 5

[0059] Step 1: Add 5.0 g of DL-Lys·HCl (27 mmol) and 2.6 g of FeCl 3 (16 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 130 °C for 5 h to prepare DL-Lys·HCl - 0.6FeCl 3 。

[0060] Step 2: Add 5.0 g of DL-Lys·HCl - 0.6FeCl 3 and 4.5 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction through an emulsifier under reduced pressure (120 Pa) at 210 °C. After reacting for 13 h, after the polycaprolactone is catalytically ring-depolymerized and distilled off, DL-Lys·HCl - 0.6FeCl 3 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 82.1%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 1 μm, the iron content is 9.6 wt%, the solid microspheres show weak acidity, and the total acid amount is 18 μmol / g.

[0061] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.05 g of the solid microspheres and 5.0 g of polylactic acid oligomer (prepared by polycondensation of L-lactic acid, with a molecular weight of 2.3 kDa) into a 100 mL three-necked round-bottom flask, and carry out the reaction in an emulsifier under reduced pressure conditions (500 Pa) at 210 °C. After reacting for 7 h, the yield of crude lactide is 100.0%, and the L-lactide content is 99.4%.

[0062] Example 6

[0063] Step 1: Add 5.0 g of L-Arg·HCl (24 mmol) and 2.6 g of ZnCl 2 (19 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 130 °C for 5 h to prepare L-Arg·HCl-0.8ZnCl 2 .

[0064] Step 2: Add 5.0 g of L-Arg·HCl-0.8ZnCl 2 and 6.5 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction in an emulsifier under reduced pressure conditions (90 Pa) at 220 °C. After reacting for 11 h, after the polycaprolactone is catalytically cyclized and depolymerized and distilled off, L-Arg·HCl-0.8ZnCl 2 self-polymerizes and crosslinks to form solid microspheres. After weighing and calculating, the yield of the solid microspheres is 81.0%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 3 μm, the zinc content is 15.7 wt%, the solid microspheres show weak acidity, and the total acid amount is 20 μmol / g.

[0065] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 2.0 g of poly-p-dioxanone into a 100 mL three-necked round-bottom flask, and carry out the reaction in an emulsifier under reduced pressure conditions (650 Pa) at 140 °C. After reacting for 12 h, weigh and calculate that the yield of the crude poly-p-dioxanone obtained by reaction distillation is 95.2%.

[0066] Example 7

[0067] Step 1: Add 5.0 g of L-His·HCl (26 mmol) and 2.4 g of MgBr 2 (13 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 140 °C for 15 h to prepare L-His·HCl-0.5MgBr 2 .

[0068] Step 2: Add 5.0 g of L-His·HCl-0.5MgBr 27.5 g of poly(p-dioxanone) was added to a 100 mL three-necked round-bottom flask, and the reaction was carried out by a high-speed stirrer + ultrasound under reduced pressure (250 Pa) at 190 °C. After 4 h of reaction, poly(p-dioxanone) was catalytically depolymerized and removed by distillation, and L-His·HCl-0.5MgBr 2 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 75.6%. The prepared solid microspheres were solid spheres, the average diameter of the microspheres was about 26 μm, the magnesium content was 8.4 wt%, the solid microspheres showed weak acidity, and the total acid amount was 18 μmol / g.

[0069] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 3.0 g of poly(p-dioxanone) were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out by a high-speed stirrer + ultrasound under reduced pressure (150 Pa) at 150 °C. After 2 h of reaction, by weighing and calculating, the yield of the crude p-dioxanone obtained by reaction distillation was 90.3%.

[0070] Example 8

[0071] Step 1: 5.0 g of L-Glu·HCl (27 mmol) and 3.7 g of ZnCl 2 (27 mmol) were added to a 100 mL round-bottom flask, and heated and stirred in an oil bath at 150 °C for 14 h to prepare L-Glu·HCl-1.0ZnCl 2 .

[0072] Step 2: 5.0 g of L-Glu·HCl-1.0ZnCl 2 and 10 g of poly(p-dioxanone) were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out by a high-speed stirrer + ultrasound under reduced pressure (140 Pa) at 200 °C. After 3 h of reaction, poly(p-dioxanone) was catalytically depolymerized and removed by distillation, and L-Glu·HCl-1.0ZnCl 2 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 76.2%. The prepared solid microspheres were solid spheres, the average diameter of the microspheres was about 27 μm, the zinc content was 16.4 wt%, the solid microspheres showed weak acidity, and the total acid amount was 13 μmol / g.

[0073] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 4.0 g of recycled waste polylactic acid (this polylactic acid sample was taken from a disposable polylactic acid straw used in the cafeteria of Sichuan University and was prepared after washing, drying, and dissolution-precipitation treatment) into a 100 mL three-necked round-bottom flask. React under reduced pressure (550 Pa) at 180 °C using a high-speed stirrer + ultrasound. After 18 h of reaction, the crude lactide yield is 96.5%, and the L-lactide content is 98.8%.

[0074] Example 9

[0075] Step 1: Add 5.0 g of L-Ala·HCl (40 mmol) and 4.5 g of FeCl 3 (28 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 160 °C for 15 h to prepare L-Ala·HCl-0.7FeCl 3 .

[0076] Step 2: Add 5.0 g of L-Ala·HCl-0.7FeCl 3 and 12.5 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask. React under reduced pressure (400 Pa) at 190 °C using a high-speed stirrer + ultrasound. After 12 h of reaction, after poly(p-dioxanone) is catalytically depolymerized and distilled off, L-Ala·HCl-0.7FeCl 3 self-polymerizes and crosslinks to form solid microspheres. After weighing and calculating, the solid microsphere yield is 78.9%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 22 μm, the iron content is 11.3 wt%, the solid microspheres show weak acidity, and the total acid amount is 22 μmol / g.

[0077] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 5.0 g of polyglycolide into a 100 mL three-necked round-bottom flask. React under reduced pressure (330 Pa) at 230 °C using a high-speed stirrer + ultrasound. After 8 h of reaction, weigh and calculate that the crude glycolide yield obtained by reaction distillation is 92.5%.

[0078] Example 10

[0079] Step 1: Add 5.0 g of L-Phe·HCl (25 mmol) and 0.7 g of TiCl 4 (4 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 130 °C for 10 h to prepare L-Phe·HCl-0.2TiCl 4 .

[0080] Step 2: Add 5.0 g of L-Phe·HCl-0.2TiCl4 10.5 g of polylactic acid was added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (220 Pa) at 180 °C. After 11 h of reaction, the polylactic acid was catalytically ring-opening depolymerized and removed by distillation. Then, L-Phe·HCl-0.2TiCl 4 self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 76.3%. The prepared solid microspheres were solid spheres, with an average diameter of about 30 μm, a titanium content of 9.2 wt%, the solid microspheres showed weak acidity, and the total acid amount was 7 μmol / g.

[0081] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 1.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (210 Pa) at 210 °C. After 1 h of reaction, the yield of crude lactide was 90.9%, and the L-lactide content was 98.9%.

[0082] Example 11

[0083] Step 1: 5.0 g of D-Trp·HCl (21 mmol) and 4.3 g of SnCl 2 (23 mmol) were added to a 100 mL round-bottom flask, and the mixture was heated and stirred in an oil bath at 140 °C for 5 h to prepare D-Trp·HCl-1.1SnCl 2 .

[0084] Step 2: 5.0 g of D-Trp·HCl-1.1SnCl 2 and 5.5 g of poly(p-dioxanone) were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using an emulsifier under reduced pressure (430 Pa) at 180 °C. After 14 h of reaction, the poly(p-dioxanone) was catalytically ring-opening depolymerized and removed by distillation. Then, D-Trp·HCl-1.1SnCl 2 self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 75.3%. The prepared solid microspheres were solid spheres, with an average diameter of about 28 μm, a tin content of 33.4 wt%, the solid microspheres showed weak acidity, and the total acid amount was 38 μmol / g.

[0085] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 2.0 g of polyglycolide were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using an emulsifier under reduced pressure (460 Pa) at 240 °C. After 5 h of reaction, the yield of the crude glycolide obtained by weighing and calculating the reaction distillation was 90.5%.

[0086] Example 12

[0087] Step 1: Add 5.0 g of L-Trp·HCl (21 mmol) and 7.1 g of TiCl 4 (37 mmol) into a 100 mL round-bottom flask, and heat and stir at 150 °C in an oil bath for 6 h to prepare L-Trp·HCl-1.8TiCl 4 .

[0088] Step 2: Add 5.0 g of L-Trp·HCl-1.8TiCl 4 and 9.0 g of polylactic acid into a 100 mL three-necked round-bottom flask, and react under reduced pressure (270 Pa) at 190 °C using a high-speed stirrer. After reacting for 12 h, after the polylactic acid is catalytically ring-opening depolymerized and distilled off, L-Trp·HCl-1.8TiCl 4 self-polymerizes and cross-links to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 77.2%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 29 μm, the titanium content is 14.5 wt%, the solid microspheres show weak acidity, and the acid amount is 16 μmol / g.

[0089] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 3.0 g of polylactic acid into a 100 mL three-necked round-bottom flask, and react under reduced pressure (20 Pa) at 220 °C using a high-speed stirrer. After reacting for 0.5 h, the crude lactide yield is 93.6%, and the L-lactide content is 98.2%.

[0090] Example 13

[0091] Step 1: Add 5.0 g of L-Thr·HCl (32 mmol) and 2.2 g of ZnCl 2 (16 mmol) into a 100 mL round-bottom flask, and heat and stir at 160 °C in an oil bath for 7 h to prepare L-Thr·HCl-0.5ZnCl 2 .

[0092] Step 2: Add 5.0 g of L-Thr·HCl-0.5ZnCl 2 and 13.5 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask, and react under reduced pressure (650 Pa) at 190 °C using an emulsifier. After reacting for 13 h, after the poly(p-dioxanone) is catalytically ring-opening depolymerized and distilled off, L-Thr·HCl-0.5ZnCl 2 self-polymerizes and cross-links to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 76.1%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 27 μm, the zinc content is 20.9 wt%, the solid microspheres show weak acidity, and the total acid amount is 13 μmol / g.

[0093] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 4.0 g of polycaprolactone into a 100 mL three-necked round-bottom flask, and carry out the reaction with an emulsifier under reduced pressure (6 Pa) at 230 °C. After reacting for 4 h, weigh and calculate that the yield of the crude ε-caprolactone obtained by reaction distillation is 91.1%.

[0094] Example 14

[0095] Step 1: Add 5.0 g of L-Leu·HCl (30 mmol) and 16.4 g of TiCl 4 (86 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 170 °C for 8 h to prepare L-Leu·HCl-2.9TiCl 4 .

[0096] Step 2: Add 5.0 g of L-Leu·HCl-2.9TiCl 4 and 14.5 g of polylactic acid into a 100 mL three-necked round-bottom flask, and carry out the reaction with a high-speed stirrer under reduced pressure (310 Pa) at 200 °C. After reacting for 10 h, after the polylactic acid is catalytically ring-opening depolymerized and distilled off, L-Leu·HCl-2.9TiCl 4 self-polymerizes and cross-links to form solid microspheres. After weighing and calculating, the yield of the solid microspheres is 75.4%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 34 μm, the titanium content is 14.9 wt%, the solid microspheres show weak acidity, and the total acid amount is 38 μmol / g.

[0097] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 5.0 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask, and carry out the reaction with a high-speed stirrer under reduced pressure (300 Pa) at 140 °C. After reacting for 8 h, the yield of the crude p-dioxanone is 97.3%.

[0098] Example 15

[0099] Step 1: Add 5.0 g of L-Ile·HCl (30 mmol) and 6.5 g of ZnCl 2 (68 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 150 °C for 9 h to prepare L-Ile·HCl-2.3ZnCl 2 .

[0100] Step 2: Add 5.0 g of L-Ile·HCl-2.3ZnCl 211.5 g of polycaprolactone was added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (240 Pa) at 230 °C. After 9 h of reaction, after polycaprolactone was catalytically ring-depolymerized and removed by distillation, L-Ile·HCl-2.3ZnCl 2 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 80.4%. The prepared solid microspheres were solid spheres, the average diameter of the microspheres was about 2 μm, the zinc content was 18.1 wt%, the solid microspheres showed weak acidity, and the total acid amount was 19 μmol / g.

[0101] The solid microspheres prepared in the second step were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 6.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (400 Pa) at 230 °C. After 4 h of reaction, by weighing and calculating, the yield of the crude lactide obtained by reaction distillation was 94.2%, and the L-lactide content was 99.1%.

[0102] Example 16

[0103] Step 1: Add 5.0 g of D-Ala·HCl (40 mmol) and 3.4 g of MgCl 2 (36 mmol) to a 100 mL round-bottom flask, and heat and stir in an oil bath at 170 °C for 16 h to prepare D-Ala·HCl-0.9MgCl 2 .

[0104] Step 2: Add 5.0 g of D-Ala·HCl-0.9MgCl 2 and 15 g of polylactic acid to a 100 mL three-necked round-bottom flask, and carry out the reaction using a high-speed stirrer + ultrasound under reduced pressure (290 Pa) at 200 °C. After 10 h of reaction, after polylactic acid was catalytically ring-depolymerized and removed by distillation, D-Ala·HCl-0.9MgCl 2 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 75.2%. The prepared solid microspheres were solid spheres, the average diameter of the microspheres was about 17 μm, the magnesium content was 13.8 wt%, the solid microspheres showed weak acidity, and the total acid amount was 14 μmol / g.

[0105] The solid microspheres prepared in the second step were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 6.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer + ultrasound under reduced pressure (50 Pa) at 190 °C. After 3 h of reaction, the yield of the crude lactide was 93.6%, and the L-lactide content was 99.3%.

[0106] Example 17

[0107] Step 1. Add 5.0 g of L-Lys·HCl (27 mmol) and 5.0 g of MgBr 2 (27 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 80 °C for 17 h to prepare L-Lys·HCl-1.0MgBr 2 .

[0108] Step 2. Add 5.0 g of L-Lys·HCl-1.0MgBr 2 and 3.0 g of polyglycolide into a 100 mL three-necked round-bottom flask, and react under reduced pressure (300 Pa) at 230 °C using a high-speed stirrer. After reacting for 7 h, after the polyglycolide is catalytically ring-depolymerized and distilled off, L-Lys·HCl-1.0MgBr 2 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 79.7%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 30 μm, the magnesium content is 10.4 wt%, the solid microspheres show weak acidity, and the total acid amount is 35 μmol / g.

[0109] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 7.0 g of polycaprolactone oligomer (prepared by polycondensation of 6-hydroxyhexanoic acid, molecular weight 3.1 kDa) into a 100 mL three-necked round-bottom flask, and react under reduced pressure (140 Pa) at 220 °C using a high-speed stirrer. After reacting for 16 h, by weighing and calculating, the yield of the crude ε-caprolactone obtained by reaction distillation is 91.7%.

[0110] Example 18

[0111] Step 1. Add 5.0 g of DL-Lys·HCl (27 mmol) and 6.1 g of SnCl 2 (32 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 90 °C for 10 h to prepare DL-Lys·HCl-1.2SnCl 2 .

[0112] Step 2. Add 5.0 g of DL-Lys·HCl-1.2SnCl 2 and 6.0 g of polyglycolide into a 100 mL three-necked round-bottom flask, and react under reduced pressure (260 Pa) at 240 °C using an emulsifier. After reacting for 5 h, after the polyglycolide is catalytically ring-depolymerized and distilled off, DL-Lys·HCl-1.2SnCl 2 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 80.8%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 32 μm, the tin content is 30.1 wt%, the solid microspheres show weak acidity, and the acid amount is 26 μmol / g.

[0113] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 8.0 g of polylactic acid into a 100 mL three-necked round-bottom flask, and react under reduced pressure (270 Pa) at 200 °C using an emulsifier. After 9 h of reaction, the crude lactide yield is 99.4%, and the L-lactide content is 98.6%.

[0114] Example 19

[0115] Step 1: Add 5.0 g of L-Arg·HCl (24 mmol) and 3.2 g of MgCl 2 (34 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 100 °C for 11 h to prepare L-Arg·HCl-1.4MgCl 2 .

[0116] Step 2: Add 5.0 g of L-Arg·HCl-1.4MgCl 2 and 7.0 g of polyglycolide into a 100 mL three-necked round-bottom flask, and react under reduced pressure (130 Pa) at 250 °C using an emulsifier. After 2 h of reaction, after the polyglycolide is catalytically cyclized and depolymerized and distilled off, L-Arg·HCl-1.4MgCl 2 self-polymerizes and crosslinks to form solid microspheres. After weighing and calculation, the solid microsphere yield is 78.2%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 31 μm, the magnesium content is 14.9 wt%, the solid microspheres show weak acidity, and the total acid amount is 15 μmol / g.

[0117] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of the solid microspheres and 9.0 g of polyglycolide into a 100 mL three-necked round-bottom flask, and react under reduced pressure (200 Pa) at 240 °C using an emulsifier. After 6 h of reaction, weigh and calculate that the crude glycolide yield obtained by reaction distillation is 90.4%.

[0118] Example 20

[0119] Step 1: Add 5.0 g of L-His·HCl (26 mmol) and 1.5 g of FeCl 3 (9 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 110 °C for 12 h to prepare L-His·HCl-0.4FeCl 3 .

[0120] Step 2: Add 5.0 g of L-His·HCl-0.4FeCl 38.0 g of polylactic acid was added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using an emulsifier under reduced pressure (180 Pa) at 200 °C. After 6 h of reaction, the polylactic acid was catalytically cyclodegraded and removed by distillation. Then, L-His·HCl-0.4FeCl 3 self-polymerized and crosslinked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 83.1%. The prepared solid microspheres were solid spheres, with an average diameter of about 32 μm, an iron content of 11.5 wt%, the solid microspheres showed weak acidity, and the total acid amount was 14 μmol / g.

[0121] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 10.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using an emulsifier under reduced pressure (10 Pa) at 220 °C. After 4 h of reaction, the yield of crude lactide was 91.3%, and the L-lactide content was 98.8%.

[0122] Example 21

[0123] Step 1: 5.0 g of L-Glu·HCl (27 mmol) and 1.0 g of ZnCl 2 (7 mmol) were added to a 100 mL round-bottom flask, and the mixture was heated and stirred in an oil bath at 120 °C for 13 h to prepare L-Glu·HCl-0.3ZnCl 2 .

[0124] Step 2: 5.0 g of L-Glu·HCl-0.3ZnCl 2 and 8.5 g of polycaprolactone were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (350 Pa) at 250 °C. After 1 h of reaction, the polycaprolactone was catalytically cyclodegraded and removed by distillation. Then, L-Glu·HCl-0.3ZnCl 2 self-polymerized and crosslinked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 82.6%. The prepared solid microspheres were solid spheres, with an average diameter of about 2 μm, a zinc content of 11.1 wt%, the solid microspheres showed weak acidity, and the total acid amount was 13 μmol / g.

[0125] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.01 g of the solid microspheres and 5.0 g of polycaprolactone were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (140 Pa) at 210 °C. After 15 h of reaction, the yield of the crude ε-caprolactone obtained by weighing and calculating the reaction distillation was 94.6%.

[0126] Example 22

[0127] Step 1. Add 5.0 g of L-Ala·HCl (40 mmol) and 0.7 g of MgCl 2 (7 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 130 °C for 12 h to prepare L-Ala·HCl-0.2MgCl 2 .

[0128] Step 2. Add 5.0 g of L-Ala·HCl-0.2MgCl 2 and 9.5 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask, and react under reduced pressure (190 Pa) at 180 °C using an emulsifier. After reacting for 7 h, after the poly(p-dioxanone) is catalytically ring-opening depolymerized and distilled off, L-Ala·HCl-0.2MgCl 2 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 81.3%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 28 μm, the magnesium content is 7.6 wt%, the solid microspheres show weak acidity, and the total acid amount is 9 μmol / g.

[0129] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.01 g of solid microspheres and 3.0 g of poly(p-dioxanone) into a 100 mL three-necked round-bottom flask, and react under reduced pressure (15 Pa) at 140 °C using a high-speed stirrer + ultrasound. After reacting for 1 h, by weighing and calculating, the yield of the crude p-dioxanone obtained by reaction and distillation is 91.6%.

[0130] Example 23

[0131] Step 1. Add 5.0 g of D-Ala·HCl (40 mmol) and 14.7 g of MgBr 2 (80 mmol) into a 100 mL round-bottom flask, and heat and stir in an oil bath at 140 °C for 11 h to prepare D-Ala·HCl-2.0MgBr 2 .

[0132] Step 2. Add 5.0 g of D-Ala·HCl-2.0MgBr 2 and 10 g of poly(glycolide) into a 100 mL three-necked round-bottom flask, and react under reduced pressure (130 Pa) at 250 °C using a high-speed stirrer + ultrasound. After reacting for 0.5 h, after the poly(glycolide) is catalytically ring-opening depolymerized and distilled off, D-Ala·HCl-2.0MgBr 2 self-polymerizes and crosslinks to form solid microspheres. By weighing and calculating, the yield of the solid microspheres is 75.4%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 27 μm, the magnesium content is 16.0 wt%, the solid microspheres show weak acidity, and the total acid amount is 42 μmol / g.

[0133] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.5 g of the solid microspheres and 5.0 g of polyglycolide to a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (180 Pa) at 250 °C by a high-speed stirrer + ultrasound. After reacting for 5 h, weigh and calculate that the yield of the crude glycolide obtained by reaction distillation is 92.9%.

[0134] Example 24

[0135] Step 1: Add 5.0 g of L-Lys·HCl (27 mmol) and 0.7 g of ZnCl 2 (5 mmol) to a 100 mL round-bottom flask, and heat and stir in an oil bath at 150 °C for 7 h to prepare L-Lys·HCl-0.2ZnCl 2 .

[0136] Step 2: Add 5.0 g of L-Lys·HCl-0.2ZnCl 2 and 11.0 g of polylactic acid to a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (100 Pa) at 190 °C by an emulsifier. After reacting for 4 h, after the polylactic acid is catalytically ring-opening depolymerized and distilled off, L-Lys·HCl-0.2ZnCl 2 self-polymerizes and crosslinks to form solid microspheres. After weighing and calculating, the yield of the solid microspheres is 75.8%. The prepared solid microspheres are solid spheres, the average diameter of the microspheres is about 36 μm, the zinc content is 12.6 wt%, the solid microspheres show weak acidity, and the total acid amount is 18 μmol / g.

[0137] Collect the solid microspheres prepared in Step 2 as a solid Lewis acid catalyst. Add 0.1 g of the solid microspheres and 5.0 g of polylactic acid to a 100 mL three-necked round-bottom flask, and carry out the reaction under reduced pressure (350 Pa) at 210 °C by an emulsifier. After reacting for 13 h, the yield of the crude lactide is 91.3%, and the L-lactide content is 99.4%.

[0138] Example 25

[0139] Step 1: Add 5.0 g of DL-Lys·HCl (27 mmol) and 6.4 g of MgCl 2 (67 mmol) to a 100 mL round-bottom flask, and heat and stir in an oil bath at 160 °C for 8 h to prepare DL-Lys·HCl-2.5MgCl 2 .

[0140] Step 2: Add 5.0 g of DL-Lys·HCl-2.5MgCl 212.5 g of polycaprolactone was added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (200 Pa) at 260 °C. After 11 h of reaction, polycaprolactone was catalytically depolymerized by ring-opening and removed by distillation. Then, DL-Lys·HCl-2.5MgCl 2 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 82.2%. The prepared solid microspheres were solid spheres, with an average diameter of about 4 μm, a magnesium content of 14.5 wt%, the solid microspheres showed weak acidity, and the total acid amount was 20 μmol / g.

[0141] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.05 g of solid microspheres and 5.0 g of polycaprolactone were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (450 Pa) at 260 °C. After 14 h of reaction, by weighing and calculating, the yield of the crude ε-caprolactone obtained by reaction distillation was 93.5%.

[0142] Example 26

[0143] Step 1: 5.0 g of L-Arg·HCl (24 mmol) and 11.7 g of FeCl 3 (72 mmol) were added to a 100 mL round-bottom flask, and the mixture was heated and stirred in an oil bath at 170 °C for 6 h to prepare L-Arg·HCl-3.0FeCl 3 .

[0144] Step 2: 5.0 g of L-Arg·HCl-3.0FeCl 3 and 15.0 g of poly(p-dioxanone) were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using an emulsifier under reduced pressure (120 Pa) at 190 °C. After 5 h of reaction, poly(p-dioxanone) was catalytically depolymerized by ring-opening and removed by distillation. Then, L-Arg·HCl-3.0FeCl 3 Self-polymerized and cross-linked to form solid microspheres. By weighing and calculating, the yield of the solid microspheres was 76.7%. The prepared solid microspheres were solid spheres, with an average diameter of about 18 μm, an iron content of 19.8 wt%, the solid microspheres showed weak acidity, and the total acid amount was 45 μmol / g.

[0145] The solid microspheres prepared in Step 2 were collected as a solid Lewis acid catalyst. 0.1 g of solid microspheres and 1.0 g of poly(p-dioxanone) were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out using a high-speed stirrer under reduced pressure (5 Pa) at 160 °C. After 0.5 h of reaction, by weighing and calculating, the yield of the crude p-dioxanone obtained by reaction distillation was 91.6%.

[0146] Comparative Example 1

[0147] Using SnCl2 As a solid Lewis acid catalyst, 0.05 g of SnCl 2 and 5.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out with a high-speed stirrer under reduced pressure (200 Pa) at 200 °C. After 2 h of reaction, the yield of crude lactide was 21.3%, the L-lactide content was 88.2%, and the metal tin content in the crude lactide was 57 ppm.

[0148] Comparative Example 2

[0149] Using Sn(Oct) 2 As an acid catalyst, 0.05 g of Sn(Oct) 2 and 5.0 g of polylactic acid were added to a 100 mL three-necked round-bottom flask, and the reaction was carried out with a high-speed stirrer under reduced pressure (200 Pa) at 200 °C. After 2 h of reaction, the yield of crude lactide was 79.8%, the L-lactide content was 82.1%, and the metal tin content in the crude lactide was 21 ppm.

[0150] The equipment quantities and processing scales described herein are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be apparent to those skilled in the art.

[0151] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated examples described herein.

Claims

1. A method for preparing a solid Lewis acid catalyst, characterized in that: The following steps are involved: Step 1: mixing amino acid hydrochloride with Lewis acidic metal halide to prepare an ionic liquid or a double salt; Step 2: Mix the ionic liquid or the complex salt with the cyclic ester polymer, disperse the ionic liquid or the complex salt in the cyclic ester polymer melt by mechanical action at a temperature above the melting point of the cyclic ester polymer, and use continuous heating and high vacuum conditions to make the ionic liquid or the complex salt in the dispersed phase self-polymerize and cross-link to form solid microspheres; while converting the ionic liquid or the complex salt into solid microspheres, it can catalyze the cyclization and depolymerization of the cyclic ester polymer to form cyclic ester monomers; finally, remove the cyclic ester monomers generated in the reaction system by reduced pressure distillation to separate the solid microspheres from the polymer, and the obtained solid microspheres are solid Lewis acid catalysts.

2. The method for preparing a solid Lewis acid catalyst as claimed in claim 1, wherein In the step 1, the general structural formula of the amino acid hydrochloride is AA·HCl, wherein AA is an amino acid, and the amino acid is at least one of glycine, L-lysine, DL-lysine, L-arginine, L-histidine, L-glutamic acid, L-alanine, D-alanine, L-phenylalanine, D-tryptophan, L-tryptophan, L-threonine, L-leucine, and L-isoleucine; The general structural formula of Lewis acidic metal halides is MX n , wherein M is one of Sn, Mg, Fe, Zn, and Ti, X is one of Cl or Br, and n is an integer greater than or equal to 1; The general structural formula of ionic liquid or double salt is AA·HCl-xMX n , x is the molar ratio of the Lewis acidic metal halide to the amino acid hydrochloride, and its value is 0.2-3.0; the ionic liquid or the double salt is one of glycine chloride / bromide metalate, L-lysine chloride / bromide metalate, DL-lysine chloride / bromide metalate, L-arginine chloride / bromide metalate, L-histidine chloride / bromide metalate, L-glutamic acid chloride / bromide metalate, L-alanine chloride / bromide metalate, D-alanine chloride / bromide metalate, L-phenylalanine chloride / bromide metalate, D-tryptophan chloride / bromide metalate, L-tryptophan chloride / bromide metalate, L-threonine chloride / bromide metalate, L-leucine chloride / bromide metalate, and L-isoleucine chloride / bromide metalate.

3. The method for preparing a solid Lewis acid catalyst as claimed in claim 1, wherein In the step 1, the amino acid hydrochloride is mixed with the Lewis acid metal halide and stirred at 80 to 170° C. for 5 to 18 hours.

4. The method for preparing a solid Lewis acid catalyst as claimed in claim 1, wherein In the step 2, the cyclic ester polymer includes: one of polylactic acid, polycaprolactone, polydioxanone, and polyglycolide; the corresponding cyclic ester monomers are lactide, ε-caprolactone, polydioxanone, and glycolide.

5. The method for preparing a solid Lewis acid catalyst according to claim 1, wherein In the step 2, the mass ratio of the ionic liquid or the double salt to the cyclic ester polymer is 1:0.5 to 1:3, the heating temperature is 180 to 260° C., the high vacuum condition is ≤1 kPa, and the preparation time is 0.5 to 14 hours.

6. The method for preparing a solid Lewis acid catalyst according to claim 1, wherein In the step 2, the mechanical action for achieving the dispersion of the ionic liquid or the complex salt in the cyclic ester polymer melt is one of stirring with a high-speed stirrer, emulsifying with an emulsifier, and stirring with a high-speed stirrer combined with ultrasonic dispersion.

7. The method for preparing a solid Lewis acid catalyst according to claim 1, wherein In the step 2, the yield of the solid microspheres relative to the ionic liquid or the double salt is ≥75%.

8. A solid Lewis acid catalyst, characterized in that The solid Lewis acid catalyst is prepared by the preparation method of the solid Lewis acid catalyst according to any one of claims 1 to 7; the prepared solid microspheres are solid spheres, and the average diameter of the solid microspheres is 1 to 36 μm; the solid microspheres contain 20 to 40 wt% tin, 7 to 16 wt% magnesium, 10 to 20 wt% iron, 9 to 15 wt% titanium or 10 to 25 wt% zinc, and the solid microspheres show weak acidity, with a total acid content of 6 to 45 μmol / g.

9. Use of the solid Lewis acid catalyst as claimed in claim 8, characterized in that: The solid Lewis acid catalyst is used for catalyzing the cyclodepolymerization of a cyclic ester polymer to prepare a cyclic ester monomer. The cyclic ester polymer is the same as or different from the cyclic ester polymer used to prepare the solid Lewis acid catalyst. The mass ratio of the solid Lewis acid catalyst to the cyclic ester polymer is 1:5 to 1:1000, the reaction temperature is 130 to 260° C., the reaction pressure is ≤1 kPa, the reaction time is 0.5 to 20 h, and the yield of the cyclic ester monomer obtained by reduced pressure reaction distillation is ≥90%.

10. Use of the solid Lewis acid catalyst as claimed in claim 9, characterized in that: After the solid Lewis acid catalyst has finished one cyclization and depolymerization reaction, the solid Lewis acid catalyst can be directly recycled without any treatment, and the catalytic efficiency retention rate is ≥94% when it is recycled for 30 times.

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