Desarrollo de un método Fenton en condiciones moderadas de reacción para la despolimerización oxidativa de lignina Kraft.
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Date
2025
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Universidad de Concepción
Abstract
La valorización de la lignina Kraft mediante procesos de despolimerización ha sido identificada como una estrategia clave para el avance hacia una bioeconomía sostenible. No obstante, los métodos tradicionales presentan limitaciones significativas: los procesos térmicos y catalíticos suelen requerir condiciones severas (elevada temperatura, presión y costos), mientras que los procesos biológicos se caracterizan por su baja velocidad de reacción. En este contexto, los procesos de oxidación avanzada (AOPs) han sido propuestos como alternativas promisorias, debido a su capacidad para generar especies reactivas capaces de romper estructuras recalcitrantes como la lignina. Entre estos, la reacción de Fenton (basada en la activación del peróxido de hidrógeno en presencia de hierro) destaca por su eficiencia en la generación de radical hidroxilo (•OH). Sin embargo, su aplicación convencional requiere la incorporación de agentes reductores o catalizadores adicionales para mantener el ciclo redox del hierro, lo que limita su escalabilidad.
En el presente trabajo se desarrolló un proceso de despolimerización tipo Fenton bajo condiciones moderadas (bajas concentraciones de Fe(III) y H₂O₂, temperatura ambiente y presión atmosférica), aprovechando la capacidad dual de la lignina Kraft para quelar y reducir Fe(III) a Fe(II), permitiendo así la generación continua de radical hidroxilo sin necesidad de aditivos externos. Las condiciones del proceso fueron optimizadas mediante un diseño experimental circunscrito central compuesto, identificándose como óptimas 0,4 mg·L⁻¹ de Fe(III) y 68 mg·L⁻¹ de H₂O₂, lo que resultó en una reducción del 49 % en el peso molecular promedio (Mw), con una disminución del índice de dispersidad (Ð) de 3,12 a 2,52 según análisis por GPC.
Los análisis complementarios mediante FT-IR, SEM, ángulo de contacto, RMN y pirólisis evidenciaron modificaciones estructurales y morfológicas consistentes con una despolimerización de tipo oxidativo. Adicionalmente, el análisis por GC-MS permitió identificar cuatro productos principales. Estos hallazgos contribuyen a una comprensión más profunda del mecanismo de despolimerización de la lignina y evidencian el doble rol funcional de esta biomolécula como agente quelante y reductor, habilitando un proceso autoactivado, sin catalizadores externos, y potencialmente cíclico. En conjunto, se propone una ruta sostenible y de bajo impacto energético para la valorización de la lignina Kraft, con aplicaciones potenciales en la producción de compuestos aromáticos de valor agregado.
The valorization of Kraft lignin through depolymerization processes has been identified as a key strategy for advancing a sustainable bioeconomy. Nevertheless, conventional methods exhibit significant limitations: thermal and catalytic approaches typically require harsh conditions (high temperature, pressure, and cost), whereas biological processes are characterized by slow reaction rates. Within this context, advanced oxidation processes (AOPs) have been proposed as promising alternatives due to their ability to generate reactive species capable of degrading recalcitrant structures such as lignin. Among these, the Fenton reaction—based on the activation of hydrogen peroxide in the presence of iron—has demonstrated high efficiency in generating hydroxyl radical (•OH). However, its conventional implementation necessitates the addition of reductants or external catalysts to sustain the iron redox cycle, thereby limiting scalability. In the present study, a Tipo Fenton depolymerization process was developed under mild conditions (low concentrations of Fe(III) and H₂O₂, room temperature, and atmospheric pressure), leveraging the dual functionality of Kraft lignin to chelate and reduce Fe(III) to Fe(II), thus enabling continuous hydroxyl radical generation without external additives. Process conditions were optimized using a central circumscribed composited experimental design, identifying 0.4 mg·L⁻¹ of Fe(III) and 68 mg·L⁻¹ of H₂O₂ as optimal, resulting in a 49 % reduction in weight-average molecular weight (Mw) and a decrease in dispersity (Ð) from 3.12 to 2.52, as determined by GPC. Complementary analyses by FT-IR, SEM, contact angle, NMR, and pyrolysis revealed structural and morphological changes consistent with oxidative depolymerization. Furthermore, GC-MS analysis identified four major products. These findings provide deeper insight into the depolymerization mechanism of lignin and underscore its dual role as both a chelating and reducing agent, enabling a self-activated, catalyst-free, and potentially cyclic process. Overall, a sustainable and low-energy pathway for Kraft lignin valorization is proposed, with promising applications in the production of value-added aromatic compounds.
The valorization of Kraft lignin through depolymerization processes has been identified as a key strategy for advancing a sustainable bioeconomy. Nevertheless, conventional methods exhibit significant limitations: thermal and catalytic approaches typically require harsh conditions (high temperature, pressure, and cost), whereas biological processes are characterized by slow reaction rates. Within this context, advanced oxidation processes (AOPs) have been proposed as promising alternatives due to their ability to generate reactive species capable of degrading recalcitrant structures such as lignin. Among these, the Fenton reaction—based on the activation of hydrogen peroxide in the presence of iron—has demonstrated high efficiency in generating hydroxyl radical (•OH). However, its conventional implementation necessitates the addition of reductants or external catalysts to sustain the iron redox cycle, thereby limiting scalability. In the present study, a Tipo Fenton depolymerization process was developed under mild conditions (low concentrations of Fe(III) and H₂O₂, room temperature, and atmospheric pressure), leveraging the dual functionality of Kraft lignin to chelate and reduce Fe(III) to Fe(II), thus enabling continuous hydroxyl radical generation without external additives. Process conditions were optimized using a central circumscribed composited experimental design, identifying 0.4 mg·L⁻¹ of Fe(III) and 68 mg·L⁻¹ of H₂O₂ as optimal, resulting in a 49 % reduction in weight-average molecular weight (Mw) and a decrease in dispersity (Ð) from 3.12 to 2.52, as determined by GPC. Complementary analyses by FT-IR, SEM, contact angle, NMR, and pyrolysis revealed structural and morphological changes consistent with oxidative depolymerization. Furthermore, GC-MS analysis identified four major products. These findings provide deeper insight into the depolymerization mechanism of lignin and underscore its dual role as both a chelating and reducing agent, enabling a self-activated, catalyst-free, and potentially cyclic process. Overall, a sustainable and low-energy pathway for Kraft lignin valorization is proposed, with promising applications in the production of value-added aromatic compounds.
Description
Tesis presentada para optar al grado de Doctor/a en Ciencias y Tecnología Analítica.
Keywords
Lignina, Oxidación, Reciclaje