Evaluation of chlorine dioxide as a supplementary pretreatment reagent for lignocellulosic biomass

Chlorine dioxide (ClO₂) is a bleaching reagent used in paper industry. Two different types of pretreatment methods were investigated incorporating ClO₂ as a secondary reagent: (a) alkaline followed by ClO₂ treatment; (b) dilute-sulfuric acid followed ClO₂ treatment. In these methods, ClO₂ treatment has shown little effect on delignification. Scheme-a has shown a significant improvement in enzymatic digestibility of glucan far above that treated by ammonia alone. On the contrary, dilute-acid followed by ClO₂ treatment has shown negative effect on the enzymatic hydrolysis. The main factors affecting the enzymatic hydrolysis are the changes of the chemical structure of lignin and its distribution on the biomass surface. ClO₂ treatment significantly increases the carboxylic acid content and reduces phenolic groups of lignin, affecting hydrophobicity of lignin and the H-bond induced association between the enzyme and lignin. This collectively led to reduction of unproductive binding of enzyme with lignin, consequently increasing the digestibility.