Pressurized hot water extraction (PHWE) of industrial hardwood waste dust: characterization of isolated materials

Pressurized hot water extraction (PHWE) is a green and effective method for lignocellulose fractionation. However, the utilization of ultrafine biomass, which is considered dust waste in industrial processes, was not well elucidated. Herein, the PHWE of ultrafine industrial hardwood dust with a particle size of 20-250 μm was investigated, and the dissolution effect was studied. To estimate the particle size effect, the PHWE of sawdust (250-1400 μm) was also performed. Obtained post-treated solids (PHWE solids) and hemicelluloses dissolved in liquid media (hydrolysates) were subjected to lignin and hemicellulose recovery using organic solvents, respectively. Comprehensive analysis revealed that the application of ultrafine dust was much more advantageous for the precipitation of dissolved hemicelluloses. For example, the highest amount of material precipitated from hydrolysates produced from dust and sawdust was about 70 and 40 wt% of total dissolved solids (TDS), respectively. Moreover, it was noted that particle size affected the composition of recovered precipitates. For instance, xylose content in the precipitates from dust-originated hydrolysate was 35% higher than that in material recovered from hydrolysate produced after PHWE of sawdust at similar conditions. The molar mass (Mw) of dust-originated extracts and their precipitates obtained using acetone as an anti-solvent was generally twice as high as that of materials obtained after PHWE of sawdust. The results of the study indicate that industrial hardwood dust could be a promising feedstock for hemicellulose recovery, and that the yield, properties, and composition of the recovered fractions could be adjusted by PHWE conditions applied.