Delignification bleaching of chemically produced cellulose pulp - involves activation with nitrogen peroxide and high temp. alkali treatment

摘要

Cellulose pulp chemically produced from lignocellulosic materials is bleached by delignification by contacting the pulp, in an activation step in the presence of water, with a gaseous phase contg. NO2, oxygen gas being fed in such manner that the intermediate NO prod. is used to activate the pulp, the latter being then subjected to alkaline treatment. The activation step and the alkaline treatment are effected under severe conditions, i.e. at high temp. during activation, to obtain some degradation of the cellulose molecules and at 95-150, pref. 101-140, esp. 11-120 deg.C during alkaline treatment, the duration of treatment at the lowest temp. limit within these temp. ranges not exceeding 45,30 and 15 min respectively. The process does not involve use of chlorine and therefore does not produce toxic effluents. It is also more selective i.e. more lignin is eliminated while a high pulp viscosity is maintained Pulp yield and kappa index are also improved.