UN PROCEDIMIENTO PARA BLANQUEAR MATERIALES CELULËSICOS EN UN MEDIO ACUOSO

摘要

Cellulosic pulp, e.g. wood pulp, is bleached in an aqueous medium by treating it with a mixture of chlorine and chlorine dioxide containing 20-95% by weight of the dioxide, subjecting it to caustic extraction and again treating it with chlorine dioxide. The treatment with the mixture of chlorine and chlorine dioxide may be carried out at 0 DEG -35 DEG C. for 5-60 minutes. The pulp of consistency between 3 and 18% may then be subjected to a hot alkali extraction by treatment with sodium hydroxide in an amount of from 0.25 to 5% based on the weight of the dry pulp sufficient to give a pH of 11 or more for 5-180 minutes at 40 DEG -130 DEG C. The pulp having a consistency of from 5 to 15% may then be treated with 0.1-2% of chlorine dioxide based on the weight of the pulp at 30 DEG -90 DEG C. for 5-300 minutes. After the caustic extraction the pulp having a consistency of 5-15% may be treated with sodium or calcium hypochlorite in an amount sufficient to supply 0.1-4% available chlorine based on the weight of the pulp at 20 DEG -70 DEG C. for 5-180 minutes and then treated at a consistency of 5-35% with 0.05-4% of hydrogen peroxide based on the weight of the pulp for 5-300 minutes at 3-90 DEG C.