R. Berry

Kraft Pulp Bleaching Using In-situ Dimethyldioxirane: Mechanism and Reactivity of the Oxidants

Dimethyldioxirane (DMD) is a cyclic peroxide made by oxidizing acetone with the peroxymonosulfate (PMS) anion in water buffered at pH 7.5 using sodium bicarbonate. It has been shown that DMD generation can be achieved in-situ within a pulp suspension allowing very selective TCF bleaching of kraft pulp. This process involves simultaneous generation of DMD, reaction of PMS and DMD with residual lignin, and spontaneous decomposition of both oxidants. In this work, we have studied the effect of pH and the nature of the buffering agent on the efficiency of delignification of kraft pulp. We have found a positive linear relationship between delignification and pH in the range from 2 to 11 when using buffers other than bicarbonate. However, using bicarbonate gives a significant enhancement of delignification between pH 7 and 8. From this work, we have proposed that the H 2 CO 3 /HCO 3 - buffer improves the rate of DMD formation during DMD in-situ bleaching and possibly during DMD synthesis. A possible mechanism accounting for this improvement is proposed.