Application of peroxymonosulfuric acid as a modification of the totally chlorine-free bleaching of acacia wood prehydrolysis-kraft pulp

Abstract

The totally chlorine-free (TCF) bleaching process avoids the generation of organochlorine substances. In this study, the application of peroxymonosulfuric acid (H₂SO₅: P_sa) to TCF bleaching was proposed as a modification of the bleaching process of hardwood prehydrolysis-kraft pulp. Acacia mearnsii pulps were treated by oxygen bleaching, followed by P_sa treatment, ozone bleaching, alkali extraction, and finally, hydrogen peroxide bleaching. The P_sa treatment was conducted with 10 % pulp consistency at pH 3 and 70 °C. The use of P_sa increased the removal of hexenuronic acid from the pulp and improved pulp brightness. After the final hydrogen peroxide bleaching, pulp brightness increased to 86.0 % ISO with a 0.6 % P_sa dosage. The P_sa treatment showed better selectivity, i.e., kappa number decrement per unit of viscosity, compared with ozone bleaching. A dosage of 0.2 % P_sa afforded a 3.4 kappa number decrement with a 10.9 cP viscosity loss, while ozone treatment with a dosage of 0.5 % resulted in a 2.6 kappa number decrement with a 12.5 cP viscosity loss. The results showed that the P_sa treatment can enhance pulp quality in terms of brightness and reduce ozone consumption, which improves the TCF bleaching process.