Patent ID: 6156156
Filing Date: 2000-12-05
Classification: D21C

Abstract:
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.