Pressurized hot water flow-through extraction of birch sawdust - Effects of sawdust density and sawdust size

Birch sawdust was extracted using a pressurized hot water (PHW) flow-through system, with the aim of recovering polymeric, water- soluble xylans. The extraction temperature was 180 degrees C for 60 min with a constant water flow through the extraction vessel. The sawdust was packed in the extraction vessel with densities in the range of 0.2 - 0.7 kg/l. Higher packing densities of birch sawdust gave higher concentration of extract. Higher sawdust densities had also lower liquid to wood ratios during extractions. The highest extract concentration peak was achieved with 0.5 kg/l density of birch sawdust. At the beginning of the higher density extractions, more xylans and lignin were extracted than lower densities. Birch sawdust with three different particle sizes was also extracted under the same conditions. The amounts of extracted xylans were higher for the smallest particle size. Higher sawdust densities decreased the difference in the extraction yield between different particle sizes of sawdust.