AN ECF SEQUENCE FOR THE ALCELL(R) PROCESS INCLUDING AN ETHANOL-ASSISTED OZONE STAGE

An elemental chlorin-free (ECF) bleaching a sequence was developed for the ALCELL(R) process. The sequence consists of an efficient washing stage with an ethanol-water mixture to further decrease the residual l ignin content, a high-consistency ozone bleaching stage using a pH of 2, a 70% w/w ethanol solution for pulp impregnation, a hot ethanol-wat er extraction stage, and two chlorine dioxide stages for final brighte ning. This solvent-based bleaching process is compatible with a recent ly developed ethanol-based solvent pulping technology and shows very l imited carbohydrate degradation. We found that the physical and optica l properties of the ECF-bleached pulp are similar to or better than th ose of the corresponding ODED bleached pulp. The advantage over the OD ED bleaching sequence is that the use of sodium hydroxide is eliminate d to decreased to a level that will be affect the economics or environ mental impact of an ethanol-water pulp mill that is operated without a high-capital-cost caustic recovery system.