| 摘要 |
Lignin is removed from fibrous material by contact with ClO2 or precursor thereof (e.g. NaClO3 or NaClO2), peracetic, performic or perpropionic acid at a pH of 2.5-4.0, and terminating the reaction before the residual lignin content is reduced below 2% wt. Substantial removal of carbohydrate does not occur. The reaction may be conducted at 40-70 DEG C. The ClO2 may be used as a saturated aq. solution. When peracetic acid is used sodium acetate or NH4+ may be present. Before delignification the raw fibrous material may be subjected to laceration, extraction, mild alkaline pretreatment e.g. with NaOH and a squeezing pretreatment between surfaces moving at different speeds. This squeezing may be followed by washing. The delignified material may be contacted with an additional amount of one of the above compounds. The delignified material can be defibrered e.g. under mild alkaline conditions. The fibrous material may be wood, straw, grass, pulp, bast, flax, pulp board, waste paper or newsprint. |
