Effect of sulfuric acid pretreatment on the efficiency of hydrogen peroxide bleaching

In hypochlorite-hydrogen peroxide bleaching (HP) process and oxygen delignification-pressurized hydrogen peroxide bleaching (OPo) process of soda-AQ wheat straw pulp, the effect of sulfuric acid pretreatment (A) before hydrogen peroxide bleaching was studied. The results showed that pretreatment with sulfuric acid would remarkably improve the efficiency of hydrogen peroxide bleaching. The end brightness, followed the OAP(O) and HAP bleaching sequences, increased about 15%ISO units and 3%ISO units compared to that of the bleached pulp without sulfuric acid pretreatment. In addtion, the sulfuric acid pretreatment stage did not have visible negative influence on the viscosity of the bleached pulp, and it decreased the kappa number and increased the brightness of the post-treated pulp. The optimized sulfuric acid pretreatment conditions for the OAP(O) bleaching process were as follows: 70 degrees C of temperature, 30 minutes of reaction time, 5% of pulp consistency, and 3.0-3.5 of initial pH value. For the following P-O stage, the higher brightness and viscosity of the bleached pulp were, obtained at 30 minutes of reaction time with pressure under the given bleaching conditions. The highest final brightness under these pretreatment conditions got up to 82.71%ISO. However, for the HAP bleaching process, the best sulfuric acid pretreatment conditions were: 40 degrees C of temperature, 4% of pulp consistency, 3.0 of initial pH value, and one minute of reaction time.