Pretreatment of lignocellulosic biomass by Sodium Chlorite

Alkaline reagents have been used for pretreatment of lingocellulosic biomass to improve its enzymatic digestibility. In alkaline pretreatments, majority of carbohydrates is retained while removing large fraction of lignin. The enhancement of digestibility is caused primarily by delignification. Retention of hemicellulose after pretreatment provides a significant economic benefit since it eliminates the need of detoxifying hemicellulose sugars. Sodium chlorite is commonly used for bleaching of pulp in paper making. It is normally applied in combination with acetic acid for delignification. The primary objective of this study is to assess the technical feasibility of a pretreatment method based on sodium chlorite. For this purpose, three different feedstocks with varying degree recalcitrance were used: corn stover, Miscanthus, and Pine. Pretreatment experiments were carried out in batch reactors applying the conditions of: 60 - 90 °C, 6 - 24 hr treatment time, 1-10% (w/v) sodium chlorite, and 10-15% solids. Pretreated samples were analyzed for solid composition. Results indicate that sodium chlorite is highly effective in delignification showing 60-90% of delignification, with retention of 90-95% of glucan and 65-75% of xylan. The treated samples were subjected to enzymatic saccharification using Novozymes C-Tec 2 at 5-15 FPU/g-glucan. The observed hydrolysis yields were found to be in the range of 50-90% for glucan and 40-70% for xylan depending on the feedstock and treatment conditions. The data were analyzed to determine the optimum treatment conditions. Selected samples were further investigated by XRD, FTIR and SEM in an attempt to correlate physical properties with the enzymatic reaction.