Effect of wet storage on alkali-oxygen pulping of bagasse

Carbohydrate degradation is a serious problem in alkali-oxygen pulping due to the inherently oxidative reaction conditions. Hemicellulose and short-chain cellulose are particularly susceptible to degradation by oxidation, and thus have a great effect on the pulping yield, as well as the viscosity and crystallinity of resultant pulp in alkali-oxygen pulping. Removal of the low molecular weight substances by wet storage prior to alkali-oxygen pulping may increase the pulping yield and improve pulp properties, in addition to savings in pulping chemicals and energy. This paper investigated alkali-oxygen pulping of bagasse pretreated by wet storage, and results show that wet storage of bagasse had a significant effect on its alkali-oxygen pulping, in terms of pulping yield, pulp viscosity and crystallinity. The pH and time were found to be the two most important factors in wet storage on bagasse. Pulp crystallinity increased from 31.78% to 42.06% when the wet storage of bagasse was performed at pH 6.0 for 16 days. In addition, the screened pulp yield increased from 58 to 60%, and pulp viscosity increased from 650 to 700 mL/g. The improved pulping performance was attributed to increased pore volumes in bagasse due to dissolution of low molecular weight lignin and carbohydrates during wet storage, which in turn improved the selectivity of delignification in the alkali-oxygen pulping process.