High Temperature Peroxide Bleaching of Mechanical Pulps, 1996 Pulping Conference Proceedings

Roy Hill, Patricia Hill, Joellen Huey and Lucien Plumet - Solvay Interox

Over the last few years, pulp mill closure issues have spurred a rash of research activity in the area of metal control and peroxide bleaching, particularly for kraft pulp. Brightnesses in excess of 90% ISO have been achieved on both softwood and hardwood pulps using pressurized peroxide stages with temperatures in excess of 100°C and retention times as short as two hours. Little or no work, however, has been performed on mechanical pulps with pressurized high temperature systems. The results of a study which explored the effect of bleach temperatures up to 120°C on mechanical pulp brightening with hydrogen peroxide are discussed. Maximum brightness responses at retention times between 30 minutes and four hours were observed at temperatures between 60°C and 90°C. Temperatures in excess of 100°C did not increase the brightness response and did not appreciably reduce the required retention time. Furthermore, the bleaching reaction was relatively difficult to control and quite often resulted in alkaline darkening.