A bimetallic catalyst and a method for preparing polyether polyols using the same.

Abstract

This invention discloses a bimetallic catalyst and a method for preparing polyether polyols using the same, relating to the field of polyether polyol preparation technology. The invention involves adding ethylenediaminetetraacetic acid-crown ether covalent ligand to anhydrous ethanol, slowly adding potassium cobalt cyanide solution, stirring until homogeneous, then slowly adding a manganese-cobalt bimetallic catalyst precursor, stirring, centrifuging, washing, and vacuum drying to obtain a manganese-cobalt bimetallic catalyst. The manganese-cobalt bimetallic catalyst is then added to anhydrous ethanol, followed by the addition of zinc-nitrogen co-doped biochar, and ultrasonicated; stirred, centrifuged, washed with alkali, and vacuum dried to obtain the bimetallic catalyst. Propylene oxide is passed through a molecular sieve. The bimetallic catalyst, 1,4-butanediol, and polyglycerol are mixed homogeneously, and the mixture is gas-purified; propylene oxide is added, and when the pressure inside the reactor drops to half of the initial pressure, propylene oxide is added in batches to remove impurities, yielding the polyether polyol.

Description

Technical Field

[0001] This invention relates to the field of polyether polyol preparation technology, specifically a bimetallic catalyst and a method for preparing polyether polyols using the same. Background Technology

[0002] Polyether polyols, prepared by initiators and epoxides such as propylene oxide under the action of catalysts, are commonly used in the polyurethane industry as detergents, defoamers, demulsifiers, dispersants, wetting agents, excipients, emulsifiers, papermaking additives, and thermal insulation materials. The catalysts used in the preparation of polyether polyols typically fall into two categories: One type is the alkaline catalyst, such as potassium hydroxide. Alkaline catalysts are inexpensive and have mature processes; however, compared with bimetallic catalysts, on the one hand, alkaline catalysts catalyze side reactions, leading to isomerization and producing polyether polyols with high unsaturation; on the other hand, alkaline catalysts are difficult to catalyze high molecular weight polyethers and have a wide molecular weight distribution. Another type is bimetallic catalysts, such as zinc-cobalt bimetallic catalysts. On the one hand, bimetallic catalysts can significantly improve catalytic efficiency and shorten reaction time through synergistic effects. On the other hand, the polyether polyols produced by bimetallic catalysts have low unsaturation and narrow molecular weight distribution; however, they are prone to aggregation, have low catalytic stability, and have complex post-processing.

[0003] To address the aforementioned problems, this invention provides a bimetallic catalyst and a method for preparing polyether polyols using the same. Summary of the Invention

[0004] The purpose of this invention is to provide a bimetallic catalyst and a method for preparing polyether polyols using the same, so as to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: Step 1: Add ethylenediaminetetraacetic acid-crown ether covalent ligand to anhydrous ethanol, slowly add potassium cobalt cyanide solution, stir until homogeneous, then slowly add manganese-cobalt bimetallic catalyst precursor. Stir for 2.5-3.5 h at 55-65℃, centrifuge, wash, and vacuum dry to obtain manganese-cobalt bimetallic catalyst. Step 2: Add anhydrous ethanol to the manganese-cobalt bimetallic catalyst, then add zinc-nitrogen co-doped biochar, sonicate, stir, centrifuge, wash with alkali, and vacuum dry to obtain the bimetallic catalyst.

[0006] A more optimized method for preparing the ethylenediaminetetraacetic acid-crown ether covalent ligand is as follows: 4'-aminobenzo-15-crown-5 and ethylenediaminetetraacetic acid dianhydride are added to N,N-dimethylformamide and reacted at 60-70℃ for 11-13 h to obtain the ethylenediaminetetraacetic acid-crown ether covalent ligand.

[0007] A more optimized method for preparing the manganese-cobalt bimetallic catalyst precursor is as follows: manganese chloride is added to deionized water and stirred until homogeneous to obtain a manganese chloride solution; potassium cobalt cyanide is added to deionized water and stirred until homogeneous to obtain a potassium cobalt cyanide solution; ethylenediaminetetraacetic acid-crown ether covalent ligand is added to anhydrous ethanol, and manganese chloride solution is slowly added dropwise. The mixture is stirred at 55-65℃ for 2.5-3.5 h to obtain the manganese-cobalt bimetallic catalyst precursor.

[0008] A more optimized method for preparing zinc-nitrogen co-doped biochar is as follows: take zinc-doped biochar, heat it to 700-800℃ at a heating rate of 4-6℃ / min, calcine for 2.5-3.5h, cool it, adjust the pH value to 6-8 with hydrochloric acid solution, and dry it to obtain zinc-nitrogen co-doped biochar.

[0009] A more optimized method for preparing 4'-aminobenzo-15-crown-5 is as follows: benzo-15-crown-5 is added to chloroform and stirred until homogeneous. Acetic acid is then slowly added dropwise and stirred until homogeneous. Concentrated nitric acid and acetoxyxamic acid are then slowly added dropwise. The reaction is carried out at 20-25℃ for 17-19 hours. After removing impurities, the mixture is dried under vacuum to obtain 4'-nitrobenzo-15-crown-5. Anhydrous ethanol is added to deionized water and mixed until homogeneous to obtain a solvent. Nitrogen gas is introduced, and 4'-nitrobenzo-15-crown-5 is added to the solvent and stirred until homogeneous. The pH value is adjusted using citric acid-sodium citrate, and ascorbic acid is added and stirred until homogeneous. The reaction is carried out at 59-61℃ for 4-6 hours. The mixture is filtered, impurities are removed, and the mixture is dried under vacuum to obtain 4'-aminobenzo-15-crown-5.

[0010] A more optimized method for preparing zinc-doped biochar is as follows: Take straw, cut, crush, and sieve it. Add the straw powder to deionized water, stir evenly, and heat to 180-220℃ at a heating rate of 4-6℃ / min. React at 180-220℃ for 11-13 hours. Cool, filter, wash, and vacuum dry at 75-85℃. Sift to obtain hydrothermal char. Add zinc chloride and ammonium bicarbonate to the hydrothermal char, mix evenly, add deionized water, stir evenly, and evaporate to dryness at 90-100℃ to obtain zinc-doped biochar.

[0011] For optimal results, the pH value should be adjusted to 4-5.

[0012] For a more optimized method, take the bimetallic catalyst, 1,4-butanediol, and polyglycerol prepared above, mix them evenly, and then replace them with gas; take propylene oxide and pass it through a molecular sieve, add propylene oxide, and when the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 3-5 batches to remove impurities and obtain polyether polyol.

[0013] Compared with the prior art, the beneficial effects of the present invention are: Ethylenediaminetetraacetic acid (EDTA)-crown ether covalent ligands were prepared by reacting the primary amino group of 4'-aminobenzo-15-crown-5 with two highly reactive anhydride groups of EDTA dianhydride to form a diamide bond, resulting in a spatially stable EDTA-crown ether covalent ligand. In this ligand, EDTA multidentately chelates metal ions, while benzo-15-crown-5 selectively binds metal ions by adjusting the cavity size through ether bond rotation. The synergistic effect of these two ligands enhances the catalytic activity against metal ions and improves the stability of the catalytic system. On the one hand, the addition of ethylenediaminetetraacetic acid (EDTA)-crown ether covalent ligand as an organic ligand to the catalyst system improves the system's dispersibility, prevents catalyst particle agglomeration, and enhances system stability. On the other hand, the introduction of this sterically hindered organic ligand into the manganese-cobalt bimetallic catalyst occupies the space around the active sites of the manganese-cobalt bimetallic catalyst, which helps to restrict the diffusion direction of epoxide molecules, inhibit the disordered diffusion of epoxide molecules, and improve the binding efficiency with the active sites. Furthermore, it guides the epoxide to insert into the polymerization chain in a head-to-tail manner, inhibits the formation of reaction byproducts, reduces the unsaturation of the product, and yields a product with a narrow molecular weight distribution.

[0014] Manganese-cobalt bimetallic catalyst was prepared using manganese chloride as the manganese source, potassium cobalt cyanide as the cobalt source, and ethylenediaminetetraacetic acid-crown ether covalent ligand as the organic ligand. Manganese chloride and potassium cobalt cyanide underwent a coprecipitation reaction to generate a bimetallic complex with divalent manganese ions and trivalent cobalt ions as bimetallic active centers. Based on the design concept of "bimetallic synergistic mechanism", divalent manganese ions and trivalent cobalt ions were selected as the core metal ions of the bimetallic catalyst; on the one hand, divalent manganese ions belong to half-filled d-phase... 5 Electron layer, its d 5 The high spin state gives divalent manganese ions high symmetry and stable exchange energy, resulting in high stability. Furthermore, the divalent / trivalent redox reaction of manganese ions accelerates chain transfer, shortening the induction period of polyether polyols. On the other hand, trivalent cobalt ions carry three positive charges and have a high charge density. They coordinate with the oxygen atoms of epoxides, which have lone pairs of electrons, to form strong cobalt-oxygen coordination bonds, inhibiting epoxide isomerization and suppressing the formation of reaction byproducts, resulting in products with a narrow molecular weight distribution. The cyano bridge stabilizes the structure of the manganese-cobalt bimetallic catalyst, regulates electron distribution, improves the catalyst's catalytic performance, and enhances the synthesis rate and product quality of polyether polyols. Meanwhile, divalent manganese ions form a stable tetrahedral coordination structure, while trivalent cobalt ions form a rigid octahedral framework. Together, they form a stable three-dimensional cubic lattice, improving the stability of the bimetallic catalyst. The two also form a metal-metal interaction through cyano bridges. On the one hand, this enhances the Lewis acidity of divalent manganese ions, promoting the activation of propylene oxide. On the other hand, the cyano bridges, as a π-conjugated system, promote electron transfer between divalent manganese ions and trivalent cobalt ions, forming a stable network of active centers.

[0015] In the preparation of bimetallic catalysts, on the one hand, the oxygen-containing functional groups on the surface of biochar interact with metal ions and ligands, which is conducive to the binding of active components in manganese-cobalt bimetallic catalysts and promotes the combination of biochar and manganese-cobalt bimetallic catalysts; on the other hand, the raw materials for the preparation of biochar are inexpensive, widely available, and environmentally friendly. Biochar has a high specific surface area and a porous structure, which is conducive to the adsorption of manganese-cobalt bimetallic catalysts, promotes the high dispersion of manganese-cobalt bimetallic catalysts, exposes more active sites for catalyzing polyether polyols, significantly improves catalytic stability, and increases reusability. Furthermore, nitrogen doping of biochar introduces nitrogen-containing functional groups, enhancing the adsorption capacity of biochar for polar manganese-cobalt bimetallic catalysts and improving the electron transfer efficiency of biochar. Zinc-doped biochar promotes electron transfer between divalent zinc ions and manganese-cobalt bimetallic catalysts through the conjugated network of biochar, improving the Lewis acidity of divalent manganese ions and trivalent cobalt ions, and enhancing their polarization ability on the carbon-oxygen bonds of epoxides.

[0016] Ammonium bicarbonate is added as a nitrogen source and is added together with zinc chloride when doping the biochar. During the subsequent heating process, it thermally decomposes to generate carbon dioxide and ammonia. On the one hand, the generated carbon dioxide expands and increases the porosity of the biochar, improving the dispersibility and adsorption of the biochar-supported manganese-cobalt bimetallic catalyst; on the other hand, the generated ammonia is used to dope the biochar with nitrogen. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The sources and types of substances involved in this invention are not particularly limited, and exemplary examples include: The product code for benzo-15-crown-5 is M06212, and it is supplied by Shanghai Myriel Biochemical Technology Co., Ltd. Acetoxyxamic acid, catalog number 1, is supplied by Shaanxi Xiangherui Fine Chemical Co., Ltd. The product code for ethylenediaminetetraacetic dianhydride is S44933-5g, and it is provided by Shanghai Yuanye Biotechnology Co., Ltd. N,N-dimethylformamide, product number 05, is supplied by Jinan Hongteng Weiye New Materials Co., Ltd. The potassium cobalt cyanide, catalog number S27437-25g, was supplied by Shanghai Yuanye Biotechnology Co., Ltd. The product code for polyglycerol is 10247, and it was provided by Xi'an Xinfengda Pharmaceutical Excipients Co., Ltd. The molecular sieve, catalog number MS-10010, was provided by Shanghai Zhenzhun Biotechnology Co., Ltd. Example 1: A bimetallic catalyst and a method for preparing polyether polyols using the same; Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.4g of benzo-15-crown-5 to 9mL of chloroform, stir well, slowly add 7mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 20℃ for 17h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 4 using citric acid-sodium citrate, add 3 g of ascorbic acid, stir well, react at 59℃ for 4 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 2.58 g of 4'-aminobenzo-15-crown-5 and 2.53 g of ethylenediaminetetraacetic acid dianhydride were added to 19 mL of N,N-dimethylformamide and reacted at 60 °C for 11 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand. Step 2: Preparation of manganese-cobalt bimetallic catalyst S1: Add 20g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 20g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of manganese chloride solution, and stir for 2.5h at 55℃ to obtain a manganese-cobalt bimetallic catalyst precursor; Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above, stir for 2.5h at 55℃, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst; Step 3: Preparation of Zinc-Nitrogen Co-doped Biochar S1: Take straw, cut, crush, and sieve. Add 0.5g of straw powder to 10mL of deionized water, stir evenly, and heat to 180℃ at a heating rate of 4℃ / min. React at 180℃ for 11h. Cool, filter, wash, and vacuum dry at 75℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char, add 3g of zinc chloride and 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 90℃ to obtain zinc-doped biochar; take the zinc-doped biochar obtained above, heat it to 700℃ at a heating rate of 4℃ / min, calcine for 2.5h, cool, adjust the pH value to 6 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar; Step 4: Preparation of bimetallic catalyst 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, followed by 1 g of zinc-nitrogen co-doped biochar. The mixture was sonicated for 25 min. The mixture was then stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain the bimetallic catalyst. Step 5: Preparation of polyether polyols S1: Take 0.75g of bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement twice under the conditions of pressure -0.05MPa and temperature 100℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in three batches at a pressure of 0.15MPa and a temperature of 130℃, with 679g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0019] Example 2: A bimetallic catalyst and a method for preparing polyether polyols using the same; Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.5g of benzo-15-crown-5 to 10mL of chloroform, stir well, slowly add 8mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 23℃ for 18h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 4.5 with citric acid-sodium citrate, add 3.5 g of ascorbic acid, stir well, react at 60℃ for 5 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 2.87 g of 4'-aminobenzo-15-crown-5 and 2.56 g of ethylenediaminetetraacetic acid dianhydride were added to 20 mL of N,N-dimethylformamide and reacted at 65 °C for 12 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand; Step 2: Preparation of manganese-cobalt bimetallic catalyst S1: Add 25g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 25g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of manganese chloride solution, and stir for 3h at 60℃ to obtain a manganese-cobalt bimetallic catalyst precursor; Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above, stir for 3h at 60℃, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst; Step 3: Preparation of Zinc-Nitrogen Co-doped Biochar S1: Take straw, cut, crush, and sieve. Add 1g of straw powder to 10mL of deionized water, stir evenly, and heat to 200℃ at a heating rate of 5℃ / min. React at 200℃ for 12h. Cool, filter, wash, and vacuum dry at 80℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char, add 3g of zinc chloride and 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 95℃ to obtain zinc-doped biochar; take the zinc-doped biochar obtained above, heat it to 750℃ at a heating rate of 5℃ / min, calcine for 3h, cool, adjust the pH value to 7 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar; Step 4: Preparation of bimetallic catalyst 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, followed by 1 g of zinc-nitrogen co-doped biochar. The mixture was sonicated for 30 min. The mixture was then stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain the bimetallic catalyst. Step 5: Preparation of polyether polyols S1: Take 0.75g of bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement three times under the conditions of pressure -0.05MPa and temperature 105℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 4 batches at a pressure of 0.15MPa and a temperature of 130℃, with 509.5g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0020] Example 3: A bimetallic catalyst and a method for preparing polyether polyols using the same; Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.6g of benzo-15-crown-5 to 11mL of chloroform, stir well, slowly add 9mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 25℃ for 19h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 5 with citric acid-sodium citrate, add 4 g of ascorbic acid, stir well, react at 61 °C for 6 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 3.15 g of 4'-aminobenzo-15-crown-5 and 2.59 g of ethylenediaminetetraacetic acid dianhydride were added to 21 mL of N,N-dimethylformamide and reacted at 70 °C for 13 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand; Step 2: Preparation of manganese-cobalt bimetallic catalyst S1: Add 30g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 30g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of manganese chloride solution, and stir for 3.5h at 65℃ to obtain a manganese-cobalt bimetallic catalyst precursor; Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above, stir for 3.5h at 65℃, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst; Step 3: Preparation of Zinc-Nitrogen Co-doped Biochar S1: Take straw, cut, crush, and sieve. Add 1.5g of straw powder to 10mL of deionized water, stir evenly, and heat to 220℃ at a heating rate of 6℃ / min. React at 220℃ for 13h. Cool, filter, wash, and vacuum dry at 85℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char, add 3g of zinc chloride and 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 100℃ to obtain zinc-doped biochar; take the zinc-doped biochar obtained above, heat it to 800℃ at a heating rate of 6℃ / min, calcine for 3.5h, cool, adjust the pH value to 8 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar; Step 4: Preparation of bimetallic catalyst 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, followed by 1 g of zinc-nitrogen co-doped biochar. The mixture was sonicated for 35 min. The mixture was then stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain the bimetallic catalyst. Step 5: Preparation of polyether polyols S1: Take 0.75g of bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement 4 times under the conditions of pressure -0.05MPa and temperature 110℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 5 batches at a pressure of 0.15MPa and a temperature of 130℃. Add 407.6g of propylene oxide in each batch. Remove impurities to obtain polyether polyol.

[0021] Comparative Example 1: Without the addition of ethylenediaminetetraacetic acid-crown ether covalent ligand, the rest is the same as in Example 2, and the specific operation is as follows: Step 1: Preparation of manganese-cobalt bimetallic catalyst S1: Add 25g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 25g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Take 50 mL of anhydrous ethanol and slowly add 50 mL of manganese chloride solution. Stir for 3 h at 60 °C to obtain a manganese-cobalt bimetallic catalyst precursor. Take 50 mL of anhydrous ethanol and slowly add 70 mL of potassium cobalt cyanide solution. Stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above. Stir for 3 h at 60 °C, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst. Step 2: Preparation of Zinc-Nitrogen Co-doped Biochar S1: Take straw, cut, crush, and sieve. Add 1g of straw powder to 10mL of deionized water, stir evenly, and heat to 200℃ at a heating rate of 5℃ / min. React at 200℃ for 12h. Cool, filter, wash, and vacuum dry at 80℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char, add 3g of zinc chloride and 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 95℃ to obtain zinc-doped biochar; take the zinc-doped biochar obtained above, heat it to 750℃ at a heating rate of 5℃ / min, calcine for 3h, cool, adjust the pH value to 7 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar; Step 3: Preparation of bimetallic catalysts 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, followed by 1 g of zinc-nitrogen co-doped biochar. The mixture was sonicated for 30 min. The mixture was then stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain the bimetallic catalyst. Step 4: Preparation of polyether polyols S1: Take 0.75g of bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement three times under the conditions of pressure -0.05MPa and temperature 105℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 4 batches at a pressure of 0.15MPa and a temperature of 130℃, with 509.5g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0022] Comparative Example 2: No manganese chloride was added; all other procedures were the same as in Example 2. The specific operations are as follows: Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.5g of benzo-15-crown-5 to 10mL of chloroform, stir well, slowly add 8mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 23℃ for 18h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 4.5 with citric acid-sodium citrate, add 3.5 g of ascorbic acid, stir well, react at 60℃ for 5 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 2.87 g of 4'-aminobenzo-15-crown-5 and 2.56 g of ethylenediaminetetraacetic acid dianhydride were added to 20 mL of N,N-dimethylformamide and reacted at 65 °C for 12 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand; Step 2: Preparation of cobalt metal catalyst S1: Take 50 mL of deionized water, stir well to obtain a solution; take 25 g of potassium cobalt cyanide, add it to 50 mL of deionized water, stir well to obtain a potassium cobalt cyanide solution; S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of solution, and stir for 3h at 60℃ to obtain a cobalt metal catalyst precursor; add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the cobalt metal catalyst precursor obtained above, stir for 3h at 60℃, centrifuge, wash, and vacuum dry to obtain a cobalt metal catalyst; Step 3: Preparation of Zinc-Nitrogen Co-doped Biochar S1: Take straw, cut, crush, and sieve. Add 1g of straw powder to 10mL of deionized water, stir evenly, and heat to 200℃ at a heating rate of 5℃ / min. React at 200℃ for 12h. Cool, filter, wash, and vacuum dry at 80℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char, add 3g of zinc chloride and 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 95℃ to obtain zinc-doped biochar; take the zinc-doped biochar obtained above, heat it to 750℃ at a heating rate of 5℃ / min, calcine for 3h, cool, adjust the pH value to 7 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar; Step 4: Preparation of cobalt metal catalyst supported on zinc-nitrogen co-doped biochar 0.2 g of cobalt metal catalyst was added to 20 mL of anhydrous ethanol, and then 1 g of zinc-nitrogen co-doped biochar was added. The mixture was sonicated for 30 min. The mixture was stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain the cobalt metal catalyst supported on zinc-nitrogen co-doped biochar. Step 5: Preparation of polyether polyols S1: Take 0.75g of zinc-nitrogen co-doped biochar supported cobalt metal catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement three times under the conditions of pressure -0.05MPa and temperature 105℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 4 batches at a pressure of 0.15MPa and a temperature of 130℃, with 509.5g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0023] Comparative Example 3: Zinc chloride was not added; all other procedures were the same as in Example 2. The specific operations are as follows: Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.5g of benzo-15-crown-5 to 10mL of chloroform, stir well, slowly add 8mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 23℃ for 18h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 4.5 with citric acid-sodium citrate, add 3.5 g of ascorbic acid, stir well, react at 60℃ for 5 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 2.87 g of 4'-aminobenzo-15-crown-5 and 2.56 g of ethylenediaminetetraacetic acid dianhydride were added to 20 mL of N,N-dimethylformamide and reacted at 65 °C for 12 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand; Step 2: Preparation of manganese-cobalt bimetallic catalyst S1: Add 25g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 25g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of manganese chloride solution, and stir for 3h at 60℃ to obtain a manganese-cobalt bimetallic catalyst precursor; Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above, stir for 3h at 60℃, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst; Step 3: Preparation of nitrogen-doped biochar S1: Take straw, cut, crush, and sieve. Add 1g of straw powder to 10mL of deionized water, stir evenly, and heat to 200℃ at a heating rate of 5℃ / min. React at 200℃ for 12h. Cool, filter, wash, and vacuum dry at 80℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char and add 1.35g of ammonium bicarbonate, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 95℃; heat to 750℃ at a heating rate of 5℃ / min, calcine for 3h, cool, adjust the pH value to 7 with 0.1mol / L hydrochloric acid solution, and dry to obtain nitrogen-doped biochar. Step 4: Preparation of nitrogen-doped biochar-supported manganese-cobalt bimetallic catalyst 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, and then 1 g of nitrogen-doped biochar was added. The mixture was sonicated for 30 min. The mixture was stirred for 12 h at 60 °C, centrifuged, washed with alkali, and dried under vacuum to obtain nitrogen-doped biochar-supported manganese-cobalt bimetallic catalyst. Step 5: Preparation of polyether polyols S1: Take 0.75g of nitrogen-doped biochar-supported manganese-cobalt bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement three times under the conditions of pressure -0.05MPa and temperature 105℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 4 batches at a pressure of 0.15MPa and a temperature of 130℃, with 509.5g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0024] Comparative Example 4: Ammonium bicarbonate was not added; all other procedures were the same as in Example 2. The specific operations are as follows: Step 1: Preparation of ethylenediaminetetraacetic acid-crown ether covalent ligand S1: Add 0.5g of benzo-15-crown-5 to 10mL of chloroform, stir well, slowly add 8mL of acetic acid, and stir well at 0℃; then slowly add 0.3mL of concentrated nitric acid and 1.5mL of acetoxyxamic acid, and react at 23℃ for 18h. Remove impurities, dry under vacuum to obtain 4'-nitrobenzo-15-crown-5. S2: Add 20 mL of anhydrous ethanol to 20 mL of deionized water and mix well to obtain a solvent; purge with nitrogen gas, add the 4'-nitrobenzo-15-crown-5 obtained above to 40 mL of the solvent, stir well, adjust the pH value to 4.5 with citric acid-sodium citrate, add 3.5 g of ascorbic acid, stir well, react at 60℃ for 5 h, filter, remove impurities, and vacuum dry to obtain 4'-aminobenzo-15-crown-5; S3: 2.87 g of 4'-aminobenzo-15-crown-5 and 2.56 g of ethylenediaminetetraacetic acid dianhydride were added to 20 mL of N,N-dimethylformamide and reacted at 65 °C for 12 h to obtain ethylenediaminetetraacetic acid-crown ether covalent ligand; Step 2: Preparation of manganese-cobalt bimetallic catalyst S1: Add 25g of manganese chloride to 50mL of deionized water and stir well to obtain a manganese chloride solution; add 25g of potassium cobalt cyanide to 50mL of deionized water and stir well to obtain a potassium cobalt cyanide solution. S2: Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 50mL of manganese chloride solution, and stir for 3h at 60℃ to obtain a manganese-cobalt bimetallic catalyst precursor; Add 3g of ethylenediaminetetraacetic acid-crown ether covalent ligand to 50mL of anhydrous ethanol, slowly add 70mL of potassium cobalt cyanide solution, stir until homogeneous, then slowly add the manganese-cobalt bimetallic catalyst precursor obtained above, stir for 3h at 60℃, centrifuge, wash, and vacuum dry to obtain a manganese-cobalt bimetallic catalyst; Step 3: Preparation of zinc-doped biochar S1: Take straw, cut, crush, and sieve. Add 1g of straw powder to 10mL of deionized water, stir evenly, and heat to 200℃ at a heating rate of 5℃ / min. React at 200℃ for 12h. Cool, filter, wash, and vacuum dry at 80℃. Sift to obtain hydrothermal carbon. S2: Take 1g of hydrothermal char and add 3g of zinc chloride, mix well, add 10mL of deionized water, stir well, and evaporate to dryness at 95℃; heat to 750℃ at a heating rate of 5℃ / min, calcine for 3h, cool, adjust the pH value to 7 with 0.1mol / L hydrochloric acid solution, and dry to obtain zinc-doped biochar. Step 4: Preparation of zinc-doped biochar-supported manganese-cobalt bimetallic catalyst 0.2 g of manganese-cobalt bimetallic catalyst was added to 20 mL of anhydrous ethanol, and then 1 g of zinc-doped biochar was added. The mixture was sonicated for 30 min. The mixture was stirred at 60 °C for 12 h, centrifuged, washed with alkali, and vacuum dried to obtain zinc-doped biochar-supported manganese-cobalt bimetallic catalyst. Step 5: Preparation of polyether polyols S1: Take 0.75g of zinc-doped biochar-supported manganese-cobalt bimetallic catalyst, 300g of 1,4-butanediol, and 300g of polyglycerol, mix them evenly, and perform gas replacement three times under the conditions of pressure -0.05MPa and temperature 105℃. S2: Take 2098g of propylene oxide and pass it through a molecular sieve. Add 60g of propylene oxide at a temperature of 130℃. When the pressure inside the reactor drops to half of the initial pressure, add propylene oxide in 4 batches at a pressure of 0.15MPa and a temperature of 130℃, with 509.5g of propylene oxide added in each batch. Remove impurities to obtain polyether polyol.

[0025] experiment: The degree of unsaturation of the polyether polyols prepared in Examples 1-3 and Comparative Examples 1-4 was determined. The procedure was performed in accordance with GB / T12008.6-2010 "Plastic Polyether Polyols - Part 6: Determination of Unsaturation", using the low-volume reagent method. The data obtained from the above experiment are shown in Table 1 below: Table 1

[0026] Conclusion: Based on the analysis of the above experimental data, the polyether polyols prepared in Examples 1-3 of this invention have low unsaturation, indicating that the prepared polyether polyols produce fewer byproducts and have a low degree of isomerization, and the bimetallic catalyst has good catalytic performance. In contrast, the polyether polyols prepared in Comparative Examples 1-3 have high unsaturation, indicating that the prepared polyether polyols produce more byproducts and have a high degree of isomerization, and the bimetallic catalyst has poor catalytic performance.

[0027] Comparative analysis of Comparative Example 1 (without ethylenediaminetetraacetic acid-crown ether covalent ligand) and Example 2 shows that the preparation of the ethylenediaminetetraacetic acid-crown ether covalent ligand involves the reaction of the primary amino group of 4'-aminobenzo-15-crown-5 and the two highly reactive anhydride groups of ethylenediaminetetraacetic acid dianhydride to form a diamide bond, resulting in a spatially stable ethylenediaminetetraacetic acid-crown ether covalent ligand. In this ligand, ethylenediaminetetraacetic acid multidentately chelates metal ions, while benzo-15-crown-5 selectively binds metal ions by adjusting the cavity size through ether bond rotation. The synergistic effect of these two chelates metal ions, improving the catalytic activity of metal ions and the stability of the catalytic system. On the one hand, the addition of ethylenediaminetetraacetic acid (EDTA)-crown ether covalent ligand as an organic ligand to the catalyst system improves the system's dispersibility, prevents catalyst particle agglomeration, and enhances system stability. On the other hand, the introduction of this sterically hindered organic ligand into the manganese-cobalt bimetallic catalyst occupies the space around the active sites of the manganese-cobalt bimetallic catalyst, which helps to restrict the diffusion direction of epoxide molecules, inhibit the disordered diffusion of epoxide molecules, and improve the binding efficiency with the active sites. Furthermore, it guides the epoxide to insert into the polymerization chain in a head-to-tail manner, inhibits the formation of reaction byproducts, reduces the unsaturation of the product, and yields a product with a narrow molecular weight distribution.

[0028] Comparative analysis of Comparative Example 2 (without manganese chloride) and Example 2 shows that, in preparing a manganese-cobalt bimetallic catalyst, manganese chloride is used as the manganese source, potassium cobalt cyanide is used as the cobalt source, and ethylenediaminetetraacetic acid-crown ether covalent ligand is used as the organic ligand. Manganese chloride and potassium cobalt cyanide undergo a coprecipitation reaction to generate a bimetallic complex with divalent manganese ions and trivalent cobalt ions as bimetallic active centers. Divalent manganese ions belong to the half-full d-type ion group. 5 Electron layer, its d 5The high spin state gives divalent manganese ions high symmetry and stable exchange energy, resulting in high stability. Furthermore, the divalent / trivalent redox reaction of manganese ions accelerates chain transfer, shortening the induction period of polyether polyols. Simultaneously, divalent manganese ions form a stable tetrahedral coordination structure, while trivalent cobalt ions form a rigid octahedral framework. Together, they form a stable three-dimensional cubic lattice, improving the stability of the bimetallic catalyst. Through cyano bridges, they form metal-metal interactions, enhancing the Lewis acidity of divalent manganese ions and promoting the activation of propylene oxide. On the other hand, the cyano bridges, as a π-conjugated system, promote electron transfer between divalent manganese ions and trivalent cobalt ions, forming a stable network of active centers.

[0029] Comparative analysis of Comparative Example 3 (without zinc chloride) and Example 2 shows that, in preparing a bimetallic catalyst, zinc-doped biochar promotes electron transfer between divalent zinc ions and the manganese-cobalt bimetallic catalyst through the conjugated network of biochar, thereby improving the Lewis acidity of divalent manganese ions and trivalent cobalt ions and enhancing their polarization ability on the carbon-oxygen bonds of epoxides.

[0030] Comparative analysis of Comparative Example 4 (without ammonium bicarbonate) and Example 2 shows that adding ammonium bicarbonate as a nitrogen source, along with zinc chloride during zinc doping of biochar, results in thermal decomposition to generate carbon dioxide and ammonia during subsequent heating. On one hand, the generated carbon dioxide expands and increases the porosity of the biochar, improving the dispersibility and adsorption of the manganese-cobalt bimetallic catalyst supported on the biochar. On the other hand, the generated ammonia allows for nitrogen doping of the biochar, introducing nitrogen-containing functional groups and enhancing the adsorption capacity of the biochar for the polar manganese-cobalt bimetallic catalyst, thereby improving the electron transfer efficiency of the biochar.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A bimetallic catalyst characterized by: The preparation method of the bimetallic catalyst includes the following steps: Step 1: Add ethylenediaminetetraacetic acid-crown ether covalent ligand to anhydrous ethanol, slowly add potassium cobalt cyanide solution, stir until homogeneous, then slowly add catalyst precursor, stir for 2.5-3.5 h at 55-65℃, centrifuge, wash, and vacuum dry to obtain manganese-cobalt bimetallic catalyst; Step 2: Add anhydrous ethanol to the manganese-cobalt bimetallic catalyst, then add zinc-nitrogen co-doped biochar, sonicate, stir, centrifuge, wash with alkali, and vacuum dry to obtain the bimetallic catalyst; The preparation method of the ethylenediaminetetraacetic acid-crown ether covalent ligand is as follows: 4'-aminobenzo-15-crown-5 and ethylenediaminetetraacetic acid dianhydride are added to N,N-dimethylformamide and reacted at a temperature of 60-70℃ for 11-13 h to obtain the ethylenediaminetetraacetic acid-crown ether covalent ligand; The catalyst precursor is prepared as follows: manganese chloride is added to deionized water and stirred until homogeneous to obtain a manganese chloride solution; potassium cobalt cyanide is added to deionized water and stirred until homogeneous to obtain a potassium cobalt cyanide solution; ethylenediaminetetraacetic acid-crown ether covalent ligand is added to anhydrous ethanol, and manganese chloride solution is slowly added dropwise. The mixture is stirred for 2.5-3.5 h at a temperature of 55-65℃ to obtain the catalyst precursor. The preparation method of the zinc-nitrogen co-doped biochar is as follows: Take straw, cut, crush, and sieve it. Add the straw powder to deionized water, stir evenly, and heat to 180-220℃ at a heating rate of 4-6℃ / min. React at 180-220℃ for 11-13 hours. Cool, filter, wash, and vacuum dry at 75-85℃. Sift to obtain hydrothermal carbon. Add zinc chloride and ammonium bicarbonate to the hydrothermal carbon, mix evenly, add deionized water, stir evenly, and evaporate to dryness at 90-100℃ to obtain zinc-doped biochar. Heat the zinc-doped biochar to 700-800℃ at a heating rate of 4-6℃ / min, calcine for 2.5-3.5 hours, cool, adjust the pH value to 6-8 with hydrochloric acid solution, and dry to obtain zinc-nitrogen co-doped biochar.

2. The bimetallic catalyst of claim 1, wherein: The preparation method of 4'-aminobenzo-15-crown-5 is as follows: benzo-15-crown-5 is added to chloroform and stirred evenly. Acetic acid is slowly added dropwise and stirred evenly. Concentrated nitric acid and acetoxyxamic acid are then slowly added dropwise. The reaction is carried out at 20-25℃ for 17-19 hours. After removing impurities, the mixture is dried under vacuum to obtain 4'-nitrobenzo-15-crown-5. Anhydrous ethanol is added to deionized water and mixed evenly to obtain a solvent. Nitrogen gas is introduced, and 4'-nitrobenzo-15-crown-5 is added to the solvent and stirred evenly. The pH value is adjusted using citric acid-sodium citrate, and ascorbic acid is added and stirred evenly. The reaction is carried out at 59-61℃ for 4-6 hours. The mixture is filtered, impurities are removed, and the mixture is dried under vacuum to obtain 4'-aminobenzo-15-crown-5.

3. The bimetallic catalyst according to claim 2, characterized in that: The pH value was adjusted to 4-5 using citric acid-sodium citrate.

4. A method for preparing a polyether polyol, characterized in that: Includes the following steps: Take the bimetallic catalyst described in claim 1, 1,4-butanediol, and polyglycerol, mix them evenly, and then replace them with gas. Take propylene oxide and pass it through a molecular sieve. Add propylene oxide and wait until the pressure inside the reactor drops to half of the initial pressure. Add propylene oxide in 3-5 batches to remove impurities and obtain polyether polyol.

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