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 o f kraft pulp. This process involves simultaneous generation of DMD, re action of PMS and DMD with residual lignin, and spontaneous decomposit ion 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 conditio ns 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 ve ry short under alkaline conditions. The presence of any transition met al ion that can be involved in a one-electron transfer is detrimental to DMD stability. However, fast reaction of DMD with pulp almost count eracts the effect of metal ions.