Abstract
In order to economize natural resources and to save energy costs of pulp mills, many chemical additives were attempted to gain more pulp amount and/or promote delignification in the alkali pulping processes. For example, sodium hydrosulfite and sodium borohydride (as reducing agent), polysulfide and quinone compounds (as oxidizing agent) were examined as pulping aid. Many reports explain that some of them increase pulp yield by preventing the “peeling” reaction and/or accelerate delignification by fragmenting the lignin macromolecule into smaller alkali-soluble structures.
Among these additives, only the quinone compounds, such as anthraquinone (AQ) and disodium salt of 1, 4-dihydro-9, 10-dihydroxy anthracene (SAQ®), and polysulfide (PS) have been commercialized for their excellent economical performance. Many pulp mills are practicing kraft pulping with the quinone additives. And some of mill's experiences of PS pulping with the quinone additive had been reported.
In this report, at first, history of the kraft pulping with the quinone additives and PS pulping are described. Then the method of PS pulping with the quinone additive is reviewed as means of increasing pulp yields and also as a method of lowering kappa number for the purpose of decreasing the amount of chlorinated organic compounds (AOX) from the bleach plant. Finally, several producing methods of polysulfide are introduced.
