How to improve the lignin removal selectivity of pulp during the process of removing lignin by high density oxygen

摘要

Unbleached pulp is combined with an aqueous alkaline solution while in a state of low consistency (9) to distribute a first amount of alkaline material substantially uniformly throughout the pulp. The consistency of the pulp is then increased (12) to above about 18%, and the high consistency alkali containing pulp is then treated with oxygen (21) to effect delignification (20). Additional alkali may be applied onto the high consistency pulp prior to oxygen delignification to provide a total amount of between 0.8 and 7% by weight of oven dry pulp. The invention contemplates the use of one or more wash presses (7,30) for reducing the overall amounts of alkaline material utilized in the process. High strength, low lignin pulps (25) are subsequently formed which may be further bleached to high brightness with reduced amounts of chemicals by following the methods of the invention. IMAGE