Hexenuronic acid removal from unbleached kraft eucalyptus pulp by peroxymonosulfuric acid

The use of peroxymonosulphuric (Ps) acid to remove hexenuronic acid (HexA) present in unbleached eucalyptus kraft pulps was evaluated here. HexA is formed during pulping and is held responsible for reagent consumption during bleaching. Laboratory experiments, using oxygen predelignified eucalyptus kraft pulps (kappa number around 9), treated at 20-110degreesC and 0.2-1.0%Ps, were conducted here. Experimental results show that Ps effectively removed both HexA and lignin, even under mild conditions. Selectivity towards HexA increased at higher temperature and lower Ps loads. However, at lower temperatures and higher Ps concentrations, cellulose was also attacked. As a result of Ps pre-treatment, ClO2 savings in pulp bleaching in the range 40-79% were determined here. Moreover, all Ps pretreated pulps yielded higher brightness than untreated pulps. Furthermore, lower AOX emissions occurred as a result of lower ClO2 loads. However, moderate Ps pre-treatment conditions were necessary to obtain a bleached pulp with acceptable mechanical properties. Results reported here show that HexA removal by Ps offers an interesting option for industrial implementation, both from an economic and environmental point of view.