Studies on the Na Xylensulfonate Cooking and Peracetic Acid Bleaching by Adjustment of pH

Abstract

This work was undertaken in order to investigate the effect of pH at NaXS (Na Xylensulfonate) cooking and PA (peracetic acid) bleaching.After the NaXS cooking of beech chips, pH of the waste liquor showed about 4. When the waste liquor were used repeatedly at the next cooking, pH drops remarkably. Thus, pH of the cooking liquor become about 3 after 5 recyclings, and pulp are also degraded and lost.In order to avoid to decrease pulp yields and viscosity, the cooking liquor must be adjusted about pH 7 by NaOH. Beech chips that were cooked by NaXS contain much lignin. The elimination of lignin from NaXS pulps by washing is ineffective, because soluble lignin in waste liquor become insoluble solid. But, it removed easily by NaOH extraction, and K-value of NaXS pulp reduced.In PA bleaching of NaXS pulp, pulp are degraded at about pH 2 and viscosity goes down. At about pH 4, however, the degradation of pulp is slightly. It has been found from above results that pH of the cooking liquor and the bleach liquor is one of important factors to control pulp quality.