Pressurized hot water extraction of Norway spruce hemicelluloses using a flow-through system

Norway spruce saw meal was extracted with pressurized hot water at 120–240°C using a flow-through system. Only small amounts of hemicelluloses were extracted at 120–160°C, but dissolution was significantly enhanced when higher extraction temperatures were applied. All hemicelluloses but only 15% of lignin were removed from wood at 220°C, and even less lignin was extracted at lower temperatures. Partial degradation of cellulose seemed to take place only at 240°C. Of the total amount of extracted hemicelluloses, 4–22% was hydrolyzed to monosaccharides. Although the average molar masses of extracted hemicelluloses decreased with increasing extraction temperature, even at 240°C the extracted carbohydrates occurred, on average, as polysaccharides. Polysaccharides with an average molar mass of 31 kDa were obtained at 170°C. The molecular-mass characteristics and yield of carbohydrates depend on the extraction temperature, which should be chosen based on the end use of the isolated hemicelluloses.