Process for a two stage peroxide bleaching of pulp
AssigneeAtochem
InventorBernard Dubreux
Life of this patent
Estimating the term…
Abstract
A two-stage hydrogen peroxide bleaching treatment of chemical pulp at a temperature of about 90.degree.-100.degree. C. comprising subjecting said pulp in a first stage to hydrogen peroxide and to at least about 3 grams/1 of bath of a metal ion sequestering agent selected from nitrogen containing sequestering agents or agents derived from polyphosphoric or polyphosphonic acids at a pH of 8.5 to 9.5 so that hydrogen peroxide of about 0.3 to 2.5 wt. % relative to dry pulp weight is consumed, and subjecting said pulp in a second stage to hydrogen peroxide and to at least about 3.times.10.sup.-3 gram-atoms per 100 grams of dry pulp of magnesium in the form of magnesium hydroxide and a pH of at least about 11 so that about 2 to 5 weight % of hydrogen peroxide per weight of dry pulp is consumed during the two stages.
Claims9
A two-stage hydrogen peroxide bleaching treatment of chemical pulp at a temperature of about 90.degree.-100.degree. C. comprising:
- a. subjecting said pulp in a first bleaching stage to hydrogen peroxide and at least about 3 grams/l of bath of a metal ion sequestering agent selected from nitrogen containing sequestering agents or derived from polyphosphoric or polyphosphonic acids at a pH of about 8.5 to 9.5 so that hydrogen peroxide of about 0.3 to 2.5 wt. % relative to dry pulp weight is consumed;
- and
- b. subjecting said pulp in a second bleaching stage to hydrogen peroxide and to at least about 3.times.10.sup.-3 gram-atoms per 100 grams of dry pulp of magnesium in the form of magnesium hydroxide and a pH of at least about 11 so that additional hydrogen peroxide is consumed in said second stage and about 2 to 5 weight % of hydrogen peroxide per weight of dry pulp is consumed during the two stages and wherein said magnesium is present only in said second stages.
Dependencies are inferred from the claim text.