Characterization of pellets produced from extracted sawdust: Effect of cooling conditions and binder addition on composition, mechanical and thermochemical properties

Abstract

Hot-water extraction (HWE) is a biomass processing method that offers an excellent possibility to generate multiple value-added products. In this study, the pellets were produced from the original spruce sawdust and the sawdust after HWE. Two different arrangements to separate the extracted sawdust from the liquid phase (extract) were applied, namely a rapid solid-liquid separation at high temperature and a slow cooling of extracted sawdust along with the extract. Furthermore, the extracted sawdust was also used several times as an adsorbent to purify the extract from the HWE. The effect of binders (kraft lignin and corn starch) on the pellet properties was also evaluated. Fuel properties, mechanical characteristics and chemical composition of produced pellets were analyzed. The HWE improves the mechanical and energy properties by increasing the pellet's length (2–9% increase), particle and energy density (24% and 31% increase correspondingly) in comparison with the untreated sawdust pellets. Additionally, the pellets from the treated sawdust indicated reduced water absorption capacity and improved strength and durability characteristics compared to the untreated ones. The HWE modifies the lignocellulosic matrix of feedstock resulting in more significant modifications than in the case of binder added to the untreated sawdust. The method of residual sawdust separation from the extract had a pronounced effect on the pellet's characteristics, namely a slow cooling of extracted sawdust in mixture with liquid fraction resulted in a smaller amount of hemicelluloses and monosaccharides in the sawdust and more intensive release (up to 70%) of ash forming elements to the liquid phase.