Basic Engineering Design Data for Ozone/Solvent Bleaching of Alcell Derived Pulp, 1996 International Pulp Bleaching Conference Proceedings

X. Zhang, Y. Ni, A.R.P. van Heiningen

University of New Brunswick

The ALCELL ® process is an ethanol-based auto-catalyzed solvent pulping technology which is being developed by Repap Enterprises Inc. We have found that the impregnation of unbleached pulp with an acidic ethanol solution significantly improves the lignin to carbohydrate selectivity during ozone bleaching. Since this solvent based ozone bleaching technology is completely compatible with the ALCELL ® process, a study was undertaken to determine the optimum operating conditions for this novel technology (called Z,). It was found that the ozone delignification efficiency is not influenced by the temperature in the Zn stage for pulp impregnated with a 70% ethanol-water solution acidified to pH = 2 with H2 SO4 . The delignification efficiency is high up to about 1% (on o.d. pulp) ozone consumed, while the efficiency becomes low at ozone consumptions larger than 2%. For example at an ozone consumption of 1% the kappa no. decreases from 27 to about 12, while a kappa reduction of only 6 units is achieved by the next 1% O3 consumption. On the other hand, the lignin-carbohydrate selectivity of the Zn stage improves significantly when the temperature is lowered from 25 to 10°C. Thus, when pulp is delignified from a kappa no. of 27 to 5, the viscosity decreases from 23 cP to 17.5 cP at 25 °C, while a 20 cP, 5 kappa pulp is obtained at 10°C. Temperatures below 10°C only further improve the selectivity by a small amount. Based on these findings it is concluded that + 10°C is the optimum temperature for the Zn stage. Other process parameters, such as residence time, reactor loading, counter-current integration of the filtrate, are also studied.