Production of carbonaceous microspheres from wood sawdust by a novel hydrothermal carbonization and extraction method

Abstract

Here we present the production of monodispersed carbonaceous microspheres directly from wood sawdust by a novel hydrothermal method, combining hydrothermal carbonization and hydrothermal extraction. This is the first time to obtain high-quality carbonaceous microspheres from crude biomass except carbohydrates, the morphology of which is quite different from the hydrochar obtained from woody biomass by traditional hydrothermal carbonization processes. Carbonaceous microspheres obtained from two wood sawdust samples have uniform spherical morphologies and yields as high as ≥16%, with sizes ranging from 0.1 to 6.9 μm. The analysis of yields and functional groups on the surface indicates that these carbonaceous microspheres were formed from the extraction of hydrochar, and it forecasts that this novel hydrothermal method will be effective with different wood feedstocks. Based on the evidence of morphology, yield, elemental composition, and functional groups, an initial mechanism was proposed to explain the production of carbonaceous microspheres from wood sawdust. During the hydrothermal treatment, a liquid-phase precursor formed first from the carbonization of wood sawdust and extraction of hydrochar, together with some decarboxylation reactions, and then carbonaceous microspheres appeared from this precursor and grew during the cooling process. This research opened a new door for the application of wood sawdust, and extended the sources of carbonaceous microspheres greatly.