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CN-121695950-B - Composite catalyst for alcoholysis of PET waste bottle and preparation method thereof

CN121695950BCN 121695950 BCN121695950 BCN 121695950BCN-121695950-B

Abstract

The invention belongs to the technical field of high polymer material recovery and catalytic chemistry, and discloses a composite catalyst for PET waste bottle alcoholysis and a preparation method thereof. The composite catalyst is based on bionic enzyme engineering and dynamic covalent chemical strategies and comprises three parts of a binuclear metal cluster active center, a limited-area microenvironment shell layer and a dynamic covalent network skeleton, wherein the binuclear metal cluster is constructed by zinc/cobalt/manganese ions and a tridentate ligand C 9 H 8 N 2 O 4 , the shell layer is a functional polymer derived from polydopamine, and the skeleton is formed by crosslinking aromatic and aliphatic monomers through boric acid ester bonds. The invention solves the problem of performance attenuation caused by instability of active centers of the existing enzyme-like catalyst in industrial cyclic application. The catalyst not only has the enzyme-like catalytic characteristics of high activity and high selectivity, but also realizes the autonomous repair after damage through a built-in multiple dynamic chemical mechanism, and provides a novel catalytic material with both performance and durability for the efficient and sustainable chemical recovery of PET waste bottles.

Inventors

  • ZHANG FEIPENG
  • ZHANG JIAHONG
  • CHEN QINGMIN
  • XU ZHONG

Assignees

  • 福建省百川资源再生科技股份有限公司

Dates

Publication Date
20260508
Application Date
20260212

Claims (6)

  1. 1. A composite catalyst for the alcoholysis of PET waste bottles, characterized in that it comprises: Catalytically active sites composed of binuclear metal clusters: a confined microenvironment shell layer constructed around the catalytic active center: And a dynamic covalent network backbone extending through and covalently crosslinked with the domain-limited microenvironment shell layer; The binuclear metal cluster is formed by connecting two adjacent transition metal ions through a bridging ligand, wherein the transition metal ions are selected from any one or two of zinc, cobalt and manganese, the bridging ligand is a tridentate organic ligand with a molecular formula of C 9 H 8 N 2 O 4 , and the three organic ligands are respectively coordinated with the two metal ions through two carboxylic acid oxygen atoms and form a secondary coordination bond through imidazole nitrogen atoms; The limiting-domain microenvironment shell is a polydopamine derived shell, the surface of the limiting-domain microenvironment shell is rich in phenolic hydroxyl groups and quinoid structures, and can form hydrogen bonds with reaction intermediates to promote the oriented arrangement of PET chain segments near a catalytic active center, and the limiting-domain microenvironment shell is wrapped on the periphery of a binuclear metal cluster through the coordination effect of catechol groups and metal ions and pi-pi stacking effect to form a compact shell with the thickness of 2-5 nm; the dynamic covalent network skeleton is formed by alternately connecting 1,3, 5-tri (4-hydroxyphenyl) benzene and 1, 6-hexanediol through boric acid ester bonds, and a three-dimensional network is formed through phenylboric acid crosslinking.
  2. 2. The composite catalyst for the alcoholysis of PET waste bottles according to claim 1, characterized in that the loading density of the binuclear metal clusters is 0.8-1.2 clusters per square nanometer, the pore size distribution of the domain-limited microenvironment shell layer is concentrated at 0.6-0.9nm, and the crosslinking density of the dynamic covalent network skeleton is 4.5×10 19 -6.0×10 19 crosslinking points per cubic centimeter.
  3. 3. The composite catalyst for the alcoholysis of PET waste bottles according to claim 1, characterized in that the boric acid ester bonds in the dynamic covalent network skeleton can be reversibly broken and recombined in the presence of trace amounts of water or alcohol, and the catalyst is endowed with micro-component migration capability and macro-deformation adaptability.
  4. 4. The composite catalyst for the alcoholysis of PET waste bottles according to claim 1, characterized in that the domain-limited microenvironment shell is partially carbonized after heat treatment to form a conductive carbon layer that retains residual phenolic hydroxyl groups and enhances the electronic coupling with the catalytically active centers.
  5. 5. A method for preparing the composite catalyst for the alcoholysis of PET waste bottles as claimed in any one of claims 1 to 4, comprising the following steps: Step 1, synthesizing a binuclear metal cluster precursor, namely dissolving transition metal salt and a tridentate organic ligand C 9 H 8 N 2 O 4 in the molar ratio of 1:1 in absolute ethyl alcohol, stirring and reacting under the protection of nitrogen, cooling, filtering, washing and vacuum drying; Step 2, constructing a limited-domain microenvironment shell layer, namely dispersing the binuclear metal cluster precursor in water, adding a dopamine hydrochloride solution, adjusting the pH value to 8.5+/-0.5, stirring, reacting, and centrifugally washing to be neutral; step 3, growing a dynamic covalent network skeleton in situ, namely dispersing the obtained core-shell structure intermediate in N, N-dimethylformamide, sequentially adding 1,3, 5-tri (4-hydroxyphenyl) benzene, 1, 6-hexanediol and phenylboric acid, wherein the molar ratio is 1:1.2:3, adding triethylamine for catalysis, reacting under a nitrogen atmosphere, centrifuging, washing and drying.
  6. 6. The method for preparing a composite catalyst for the alcoholysis of PET waste bottles as claimed in claim 5, further comprising a heat treatment step after the 3 rd step, wherein the obtained composite catalyst is placed in a nitrogen atmosphere, heated to 200+ -10 ℃ at 2+ -0.5 ℃ per min, and naturally cooled after 2-3 hours of heat preservation.

Description

Composite catalyst for alcoholysis of PET waste bottle and preparation method thereof Technical Field The invention belongs to the technical field of high polymer material recovery and catalytic chemistry, and relates to a composite catalyst for PET waste bottle alcoholysis and a preparation method thereof. Background Polyethylene terephthalate (PET) is one of the thermoplastic polyesters with the greatest global yield, and efficient chemical recycling of waste bottles has become a key element in achieving plastic recycling economy. Among the numerous depolymerization routes, the alcoholysis process is of great interest because of its relatively mild reaction conditions and because the product can be used directly for repolymerization, where the choice and performance of the catalyst directly determine the economics and sustainability of the process. In recent years, in order to improve the catalytic efficiency and selectivity, researchers widely refer to the engineering concept of bionic enzymes to develop a series of composite catalytic systems with enzyme-like catalytic characteristics, and the materials generally construct a finite field microenvironment on a molecular scale by simulating an active pocket structure of natural enzymes, so that the oriented activation and fracture of PET chain segments are realized. The catalyst often combines a metal active center and an organic ligand or a functional polymer matrix, and builds a reversible cross-linked network by means of a dynamic covalent chemical strategy, so that not only is a certain structural flexibility provided for the material, but also the possibility is provided for realizing dynamic regulation and control of catalytic sites. The composite catalyst reported in the prior art is mostly loaded on a porous carrier (such as MOFs, mesoporous silica or functionalized polymer) by adopting transition metal complexes such as zinc, cobalt, manganese and the like, or a catalytic unit is embedded into a self-assembled frame through dynamic covalent bonds such as Schiff base, borate and the like. In the initial reaction stage, the design does obviously improve the catalytic activity and alcoholysis selectivity, and partial system can realize complete depolymerization of PET waste bottles even at lower temperature. Although the dynamic covalent bond gives the material a macroscopic repairable appearance, the metal active center on the microscopic level is still extremely easy to be irreversibly deactivated due to disturbance of coordination environment, on one hand, trace sulfur-containing, nitrogen-containing or carboxylic acid impurities in the reaction system can be strongly adsorbed on metal sites to cause active center poisoning, on the other hand, under thermodynamic driving, highly dispersed nanoscale metal clusters or monoatomic sites tend to undergo Ostwald ripening to cause sintering aggregation, thereby losing the catalytic advantage brought by high specific surface area, and the dynamic network can be locally dissociated in repeated swelling-shrinkage or acid-base fluctuation, so that part of catalytic components are lost to liquid phase in the form of ions or complexes to cause permanent activity attenuation. Disclosure of Invention In order to achieve the aim of the invention, the invention provides a composite catalyst for the alcoholysis of PET waste bottles and a preparation method thereof. The composite catalyst is based on a bionic enzyme engineering principle and a dynamic covalent chemical strategy, a multilevel structure system with a quasi-enzyme catalytic activity pocket and built-in self-repairing capability is constructed, and in-situ regeneration and functional recovery of an active site can be realized through a dynamic reconstruction mechanism of a molecular layer after the composite catalyst is subjected to metal active center poisoning, sintering or component loss and other damages, so that the structural stability and the service life of the composite catalyst under an industrial cycle working condition are remarkably improved while the high catalytic efficiency and the selectivity are maintained. The composite catalyst comprises three core structural units, namely (1) a catalytic active center formed by binuclear metal clusters, (2) a limited-domain microenvironment shell layer constructed around the catalytic active center, and (3) a dynamic covalent network framework penetrating through the limited-domain microenvironment shell layer and being covalently crosslinked with the limited-domain microenvironment shell layer. The binuclear metal cluster is formed by connecting two adjacent transition metal ions through a bridging ligand, wherein the transition metal ions are selected from any one or two of zinc, cobalt and manganese, the bridging ligand is a tridentate organic ligand containing two carboxylic acid groups and an imidazole ring, the molecular structural formula is C 9H8N2O4, the structural formula is HOOC-C 4H2 -I