Mechanism of acid-oxidation synergistic effects on lignin-carbohydrate complex degradation and adsorbable organic...

Addressing the environmental challenge of bleaching effluent toxicity is crucial for green development in the pulp and paper industry. While high-temperature chlorine dioxide (D_ht) bleaching enhances delignification, its mechanistic impact on lignin-carbohydrate complexes (LCC)-the primary precursors of adsorbable organic halogens (AOX)-remains unexplored, limiting source control of chlorinated pollutants. This study employs an integrated experimental and computational approach to systematically investigate, for the first time, the degradation pathways of LCC during D_ht bleaching (90 °C, 1.5% ClO₂ charge, pH 3.0, 120 min, 10% pulp consistency) and establishes their direct correlation with AOX formation, providing a mechanistic solution for pollutant source control. The results demonstrate that D_ht efficiently deconstructs LCC networks via acid-oxidation synergy, cleaving phenyl glycosidic/ester bonds and preferentially degrading syringyl unit, which subsequently undergo ring-opening to carboxylic acids. Molecular weight analysis indicates heterogeneous degradation, evidenced by increased polydispersity and reduced LCC formation. Quantum chemical calculations reveal the spontaneous dissociation of phenyl glycosidic bonds at high temperature and electrophilic attack by ClO₂ on methoxy sites. Crucially, the D_ht effectively enhances delignification while simultaneously reducing AOX formation, as it accelerates lignin degradation and minimizes the generation of chlorinated intermediates. This elucidated mechanism provides a critical theoretical foundation for developing efficient, low-pollution bleaching technologies, advancing the industry toward cleaner production.