High-efficiency chlorine dioxide delignification. Summary of progress, April 1--June 30, 1998

The authors have been pursuing strategies for improving the efficiency of utilization and environmental performance of ClO{sub 2} in the delignification of kraft pulps. These strategies combine a pretreatment followed by ClO{sub 2} treatment under conditions selected to result in high efficiency, and a suitably altered alkaline extraction stage. In addition, a series of experiments was completed in which the authors compared the response to conventional D(EO) delignification of conventional kraft pulps and pulps from a laboratory simulation of Ahlstrom`s Lo-Solids{reg_sign} extended delignification (modified) process. These experiments were conducted over a range of kappa numbers for both pulping processes, and at high and low kappa factors. The results showed that the modified pulps were slightly easier to bleach in the conventional process, an observation which parallels the corresponding observation made earlier, when the same pulps were bleached with the Rapid D{sub 0} short-retention process. In other experiments, two sets of hardwood pulps of varied unbleached kappa number were subjected to determinations of their hexeneuronic acid contents. Pulps representing both conventional batch and extended (RDH) kraft pulping processes were included. Residual lignin and effluent structural analyses by NMR and gel permeation chromatography are continuing to generate data for the development of structure-bleachability relationships. Analysis of this data is in progress