Method for bleaching mechanical pulp with hydrogen peroxide and an alkaline earth metal carbonate
AssigneeQueen's University at Kingston
InventorsJeffrey K. -S. Wan, M. Catherine Depew
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Abstract
A method for bleaching unbleached softwood or hardwood pulps using hydrogen peroxide without added alkali for activation is described. The aqueous hydrogen peroxide solution contains an alkaline earth metal carbonate, preferably magnesium carbonate and can be used at elevated temperatures. Bleached hardwood or softwood mechanical pulps with high brightness, low yellowness (b*) and reduced reversion properties are produced.
Claims24
A method for bleaching a wood pulp containing lignin, comprising the steps of:
- mixing wood pulp with aqueous H2O2 and alkaline earth metal carbonate to form a suspension, wherein said suspension has a H2O2 concentration of at least 4% and an alkaline earth metal carbonate concentration of at least 6% by weight of said pulp, and
- allowing bleaching of said pulp in said suspension to take place at a temperature of at least 15° C., wherein pH of said suspension remains in a range of 6 to 8 during said bleaching;
- wherein said suspension does not contain added sodium hydroxide.
A method of reducing brightness reversion and yellowness (b*) of a wood pulp containing lignin, comprising the steps of:
- mixing wood pulp with aqueous H2O2 and alkaline earth metal carbonate to form a suspension, wherein said suspension has a H2O2 concentration of at least 4% and an alkaline earth metal carbonate concentration of at least 6% by weight of said pulp, and
- allowing bleaching of said pulp in said suspension to take place at a temperature of at least 15° C., wherein pH of said suspension remains in a range of 6 to 8 during said bleaching, so that yellowness b* is reduced to below 8.
Dependencies are inferred from the claim text.