An ECF sequence for the ALCELL® process including an ethanol-assisted ozone stage

An elemental chlorine-free (ECF) bleaching sequence was developed for the ALCELL® process. The sequence consists of an efficient washing stage with an ethanol-water mixture to further decrease the residual lignin content, a high-consistency ozone bleaching stage using a pH of 2, a 70% w/w ethanol solution for pulp impregnation, a hot ethanol-water extraction stage, and two chlorine dioxide stages for final brightening. This solvent-based bleaching process is compatible with a recently developed ethanol-based solvent pulping technology and shows very limited carbohydrate degradation. We found that the physical and optical properties of this ECF-bleached pulp are similar to or better than those of the corresponding ODED bleached pulp. The advantage over the ODED bleaching sequence is that the use of sodium hydroxide is eliminated or decreased to a level that will not affect the economics or environmental impact of an ethanol-water pulp mill that is operated without a high-capital-cost caustic recovery system. Application : the ozone-based ECF bleaching sequence naturally fits into the ALCELL® process.