A clean high-concentration chlorine dioxide bleaching process at room temperature facilitating the rapid degradation of lignin and its kinetic

Abstract

Elemental Chlorine-Free (ECF) bleaching is a globally prevalent pulping technology that primarily utilizes chlorine dioxide (ClO₂) as a bleaching agent. However, the chlorination side reactions during ECF bleaching lead to the formation of chlorinated adsorbable organic halides (AOX), which are difficult to degrade and pose a potential threat to the ecological environment. This study presents a novel high-concentration ClO₂ pulping bleaching technology at room temperature, which effectively suppresses the chlorination side reactions through the strong oxidizing properties of high-concentration ClO₂, thereby achieving both bleaching and a reduction in AOX generation. The results indicate that high concentrations of ClO₂ efficiently removed residual lignin from the pulp, promoted the cleavage of lignin ether bonds, and had no adverse impact on the strength or crystalline structure of the cellulose. The amount of AOX was effectively controlled to 0.41 kg/t pulp. Kinetic analysis demonstrated that the degradation of lignin in this bleaching system follows first-order reaction kinetics, with an activation energy of 1310.78 J/mol. Approximately 95 % recovery of the ClO₂ solution was achieved through a four-step reabsorption method. This technology advances the development of pulping and bleaching techniques and provides theoretical guidance for the innovation of cleaner pulping and papermaking technologies.