Kraft pulp bleaching using dimethyldioxirane: Stability of the oxidants

Dimethyldioxirane (DMD) is a cyclic peroxide made by oxidizing acetone with peroxymonosulfate (PMS) 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. The first part of this work is a kinetics study of the decomposition of PMS and DMD as a function of pH under conditions similar to those for in situ bleaching. The effect of chelation as well as the effect of transition metal ions on decomposition rate was also investigated. DMD is very sensitive to pH and its half-life is very short under alkaline conditions. The presence of any transition metal ion that can be involved in a one-electron transfer is detrimental to DMD stability. However, fast reaction of DMD with pulp almost counteracts the effect of metal ions.