Practical Brightening for Low-pH Kraft Pulp Through In Situ Creation Of Peracetic Acid From Peracetate

ABSTRACT
Peracetic acid (PAA) has been demonstrated as an effective brightening oxidant for kraft pulp, however,
its application has been limited due to practical considerations of manufacturing and handling. Prior
studies have shown that peracetate/single oxygen chemistry has comparable performance to PAA at pH
levels from 5.5 to 9.5. Some kraft bleach plants use large quantities of chlorine dioxide, e.g., D-Eop-D,
and have a low final pH that would be well-suited for PAA brightening in the HD storage chest. The
ability to create PAA through converting peracetate (PAc) to PAA for the low pH environment in the HD
chest presents an opportunity to add an additional bleaching stage without the logistical challenges, capex
and safety hurdles associated with supplying PAA.
The ability to introduce an additional brightening stage to a short-sequence ClO2 bleach plant may have
significant benefits. Excessive residual ClO2 in the HD chest results in potentially problematic ClO2
carryover, excessive corrosion, brightness reversion, and excessive cost. Frequently, the marginal use of
large quantities of ClO2 delivers little benefit and can inhibit development of high brightness pulp.
This paper compares the brightening of post-bleached pulp with equilibrium PAA, PAA created from
acidified sodium peracetate (NaPAc), and sodium peracetate directly directly [HK1]added to the low pH
pulp. Sodium peracetate added directly to the pulp has the benefit of releasing reactive oxygen species
that can enhance its performance. 

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