Utilisation of additives in oxygen delignification of hardwood kraft pulp

Oxygen delignification is widely applied in pulping and bleaching plants to meet stringent environmental regulations in different countries. The degree of oxygen delignification is often below 50%. One way to increase the delignification degree is to install capital-intensive two-stage, or multi-stage oxygen delignification systems. This study, however, selected the alternative of using additives to enhance the delignification degree. Surfactants, chelating agent DTPA (diethylenetriamine pentaacetate), peroxide bleaching activator TAEB (tetraacetylethylene diamine), oxone (potassium peroxymonosulfate), KAQ (alkaline solution of disodium salt of 1,4-dihydro-9,10-dihydroxy anthracene), AQ (anthraquinone) and urea were tested to assess their effects on the oxygen delignification of a hardwood kraft pulp. Whereas surfactants DTPA and TAED improved the delignification, KAQ and oxone decreased the delignification degree. AQ and urea, on the other hand, maintained the delignification degree. A mill trial using one of the surfactants (the non-ionic surfactant S) confirmed the laboratory results in terms of the gain in delignification degree and the preservation of pulp strength.