Sequential utilization of birch sawdust using a two-step hot water treatment

Abstract

AbstractIn this research study, birch sawdust (BSD) was sequentially treated in hot water to obtain liquid fractions containing C5 sugars/furfural or C6 sugars/5-hydroxymethyl furfural (HMF), and lignin containing solid fractions. In the first step, 76% of the hemicellulose was hydrolyzed using microwave irradiation to the liquid fraction as C5 sugars/oligosaccharides/furfural while most of the cellulose and lignin remained in a solid fraction. Increasing the temperature and time increased the furfural formation during the first step. The highest furfural yield, 39%, was obtained using 200 °C for 60 min. In the second step, higher temperatures were used to enhance the cellulose decomposition, which was observed as decreasing the crystallinity of the solid fraction and increasing the HMF content in the liquid fraction. The highest HMF yield, 17%, was obtained using 260 °C with a 30 min treatment time in the second step, whereas the first step was performed at 200 °C. After the sequential treatment, 32% of the sawdust remained in the solid state when the most efficient treatment conditions were applied (the first step at 200 °C, 20–60 min; the second step at 260 °C, 30 min). The solid fractions were found to contain mainly lignin/lignin degradation products. The study demonstrates the potential of sequential hot water treatment in the separation and utilization of all main components of wood.