Rapid and selective catalytic oxidation of hexenuronic acid and lignin in cellulosic fibers

Processes called pulping and bleaching are required for preparing industrial scale pure cellulose from biomass. Bleaching generally purifies the cellulose from components called hexenuronic acid (HexA) and lignin. Nevertheless, the oxidation reactions of these bleachable components generally consume stoichiometric volumes of oxidant and hours of retention time. The efficiency of the oxidants can be enhanced by catalysis. The present study focuses on increasing the selectivity of hypochlorous acid (HOCl) produced during chlorine dioxide bleaching toward oxidation of HexA and lignin with the help of a tertiary amine as a catalyst. A strong electrophile forms when HOCl reacts with tertiary amine, which further reacts selectively and efficiently with HexA and lignin. Catalytic oxidation experiments were conducted at broad range of pH, temperature, and oxidant dosage in conditions that are milder than used today in industry. Surprisingly, catalytic amounts of industrial tertiary amine were used, and the oxidation reactions took place in seconds. This study opens the door for future chemical pulp bleaching technologies with reduced oxidation time, less chemical consumption, and high chemical oxidation efficiency.