COMPARATIVE STUDY OF HEMICELLULOSES EXTRACTION FROM BEECH AND OAK WOOD

Beech and oak wood chips were treated with dilute oxalic acid (0.0825 %), hot water and water solution of green liquor (3 % Na2O charge on ODW) at elevated temperature in order to extract a part of hemicelluloses. The extractions were performed at 160 degrees C, H-factor was changed in the range from 0 to 850 hrs. Dissolution rate of wood components was highest in case of extraction with dilute oxalic acid followed by extraction with hot water and green liquor solution. The extraction rate of oak chips was higher than of beech chips by all agents. The total content of monosugars in the hydrolysed extract of dilute oxalic acid was 7.6 % on ODW for beech and for oak 5.5 % on ODW, in hot water extract 6.5 % on ODW for beech and 4.1 % on ODW for oak, in green liquor extract was 2.8 % on ODW for beech and 2 % on ODW for oak, at 10 % wood weight loss. The xylose content in hydrolysed beech wood extracts represents about 79 % from the total monosugars content in all extracts, while in hydrolysed oak wood extracts only 49 %. Glucose content in hydrolysed extracts was in the range 0.165 % to 0.58 % on ODW; it was higher in dilute oxalic acid and hot water extracts. Lignin content in extracts was 0.8 to 3.8 % on ODW; it was higher for oak wood. Insoluble solids content was in the range 0.42 to 1.8 % on ODW; it was higher for oak wood and the highest content was in green liquor extracts. The beech wood is more suitable for pre-extraction of hemicelluloses prior to pulping than oak wood because the extracts contain more hemicelluloses.