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Glycolysis of PET using Zn-Ni/Al catalysts obtained from hydrotalcites
Glicólisis de PET empleando catalizadores de Zn-Ni/Al obtenidos a partir de hidrotalcitas
DOI:
https://doi.org/10.15446/ing.investig.117669Keywords:
glycolysis, PET, hydrotalcites, mixed oxides, BHET (en)glicólisis, PET, hidrotalcitas, óxidos mixtos, BHET (es)
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This study investigates the catalytic glycolysis of post-consumer poly(ethylene terephthalate) (PET) using Zn-Al and Zn-Ni-Al mixed oxides derived from hydrotalcite-like precursors. The catalysts were synthesized by constant-pH coprecipitation and calcined at 500 °C to generate mixed oxide phases. Structural characterization by XRD revealed the collapse of the layered structure and the formation of ZnO domains together with spinel-type MAl2O4 phases (M = Zn, Ni, or mixed Ni–Zn). Nitrogen physisorption showed a strong composition-dependent evolution of the mesostructure, with the Ni0.44Zn0.22Al0.33 catalyst exhibiting the highest surface area (177 m2·g-1). Control experiments demonstrated that PET depolymerization does not occur in the absence of catalyst, that ZnO promotes polymer degradation but with low selectivity toward BHET, and that bulk NiO is essentially inactive. The best catalytic performance was obtained for Ni0.44Zn0.22Al0.33, reaching 96.4% PET depolymerization and 82.0% selectivity toward bis(2-hydroxyethyl) terephthalate (BHET). The recovered monomer was identified by FTIR spectroscopy, differential scanning calorimetry (DSC), and morphological analysis confirming the formation of crystalline BHET as the main reaction product. The results indicate that catalytic performance is governed by the structural integration of Zn and Ni within the mixed oxide matrix rather than by the simple coexistence of individual oxides. A mechanistic interpretation suggests that Zn-related Lewis acid sites activate the ester carbonyl groups of PET, while the incorporation of Ni into aluminate structures modifies the surface environment and improves site accessibility within the mesoporous framework, leading to enhanced depolymerization and selectivity.
En este trabajo se estudió la depolimerización catalítica de PET post-consumo mediante glicólisis con etilenglicol empleando óxidos mixtos Zn-Al y Zn-Ni-Al derivados de precursores tipo hidrotalcita. Los catalizadores se sintetizaron por coprecipitación a pH constante y posteriormente se calcinaron a 500 °C para generar las fases óxidas activas. La caracterización estructural por difracción de rayos X evidenció el colapso de la estructura laminar y la formación de dominios de ZnO junto con fases tipo espinela MAl2O4 (M = Zn, Ni o Ni–Zn). Los análisis texturales mostraron una fuerte dependencia de la mesoestructura con la composición, alcanzando el sólido Ni0.44Zn0.22Al0.33 el mayor desarrollo superficial (177 m2·g-1). Los experimentos de control demostraron que la depolimerización de PET no ocurre en ausencia de catalizador, que ZnO promueve la degradación del polímero, pero con baja selectividad hacia BHET, y que NiO es prácticamente inactivo bajo las condiciones de reacción. El mejor desempeño catalítico se obtuvo con el sólido Ni0.44Zn0.22Al0.33, que alcanzó 96.4% de depolimerización de PET y 82.0% de selectividad hacia bis(2-hidroxietil) tereftalato (BHET). El monómero recuperado fue identificado mediante FTIR, calorimetría diferencial de barrido (DSC) y análisis morfológico, confirmando la formación predominante de BHET cristalino. Los resultados indican que el desempeño catalítico está gobernado por la integración estructural de Zn y Ni en la matriz de óxido mixto y por el desarrollo mesoporoso del material. Un análisis mecanístico sugiere que los sitios ácidos de Lewis asociados al Zn activan los grupos carbonilo del PET, mientras que la incorporación de Ni en fases aluminato modifica el entorno superficial y favorece la accesibilidad de los sitios activos, mejorando la eficiencia y selectividad del proceso de glicólisis.
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