Method of producing pulp using single-stage cooking with formic acid and washing with performic acid
AssigneeChempolis Oy
InventorsPasi Rousu, Paivi Rousu, Esa Rousu
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Abstract
The invention relates to a method of producing pulp with a high brightness using single-stage cooking with formic acid, washing with performic acid and bleaching with oxidizing bleaching chemicals. In performic acid washing, the rapid formation and rapid reactions of performic acid (HCOOOH) are utilitized for modification of residual lignin. The method of the invention provides an ISO brightness exceeding 90% without a chlorine chemicals. The method can be applied to both herbaceous plants and wood.
Claims15
A method based on single-stage formic acid cooking for producing pulp with a high brightness, the method comprising the stages of:
- (a) dignifying cellulose raw material in single-stage cooking with formic acid, possibly together with other organic acids, at a temperature of 105-135.degree. C.,
- (b) removing cooking liquor from the delignified pulp and washing the pulp with formic acid using a multiple-stage washing sequence,
- (c) removing the formic acid and possibly other organic acids from the washed pulp, and
- (d) bleaching the pulp by using oxidizing bleaching chemicals, wherein the last formic acid washing stage in the multiple-stage washing sequence of stage (b) comprises washing the pulp, free from cooking liquor and in a medium or high consistency state, with formic acid containing performic acid produced in situ and possibly other peracids.
Dependencies are inferred from the claim text.