The Formation of Gaseous Products and its Relation to Pulp Bleaching During the Peracetic Acid Treatment

Abstract

When used in pulp bleaching, peracetic acid is consumed by two competitive pathways: oxidation of pulp and wasteful reactions such as decomposition. In this paper, the peracetic acid consumed in wasteful reactions is quantified by determining the gaseous products evolved. It is found that although carbon dioxide is formed under certain conditions, oxygen is the dominant product of the wasteful reactions. The oxygen formation is directly proportional to the consumption of oxidants (as peracetic acid and hydrogen peroxide) in the wasteful reactions with 2 moles of oxidant consumed per mole of oxygen formed. Therefore, the brightening efficiency during peracetic acid treatment can be characterized by correcting the measured peracetic acid consumption for decomposition. The peracetic acid brightening results for an oxygen delignified softwood kraft pulp are reported. It is found that a significant amount of peracetic acid is consumed by the wasteful reactions during the brightening. The effect of process parameters on the peracetic acid brightening efficiency is determined. It is shown for an oxygen delignified softwood kraft pulp that there is a unique relationship between pulp brightness gain and peracetic acid consumption due to the pulp oxidation irrespective of the brightening conditions.