Multi-purpose production with valorization of wood vinegar and briquette fuels from wood sawdust by hydrothermal process

Abstract

Low conversion efficiency and simplex derived product with low added value of biomass waste resource have become prevalent challenges. A novel route for the preparation of hydrothermal wood vinegar (HWV) and briquette fuels by hydrothermal treatment process from wood sawdust (WS) has been developed. The interactive effect of the hydrothermal temperature and the ratio of WS to deionized water on the yield of HWV was studied by response surface methodology, and the results indicate that hydrothermal temperature played the dominant role during the treatment process. The yield of HWV decreases from 70.6% to 68.8% when the treatment temperature increases from 200 °C to 230 °C, and then increases to 72.4% at 260 °C. The chemical constituents in HWV were formed by the hydrolysis and conversion of hemicelluloses before 200 °C, and celluloses and lignins at 200–260 °C. The size of WS particles became smaller after the hydrothermal treatment at 200–260 °C and abundant functional groups are retained on the surface of hydrochar. However, there is nearly no obvious change in the functional groups on the surface of the briquetted hydrochar with increasing temperature. Hydrogen bonds between celluloses and lignins acted as binder are responsible for the high tensile strength of the briquetted hydrochar. The energy density (24.6 GJ/m3) of the hydrochar briquette prepared at 230 °C (24.6 GJ/m3) is significantly higher than that prepared from WS (18.6 GJ/m3). The energy density of the hydrochar briquette was further improved to 26.4 GJ/m3 by carbonization process at 400 °C. Lignin played the bonding role between carbon particles in carbonized briquette.