Sustainable bleaching of Eucalyptus sp. kraft pulp with hypochlorous acid, ozone and hydrogen peroxide
Estefania Isaza Ferro, Kyösti Ruuttunen, Jordan Perrin, Tapani Vuorinen
Abstract
Eucalyptus sp. is the most important planted crop for the production of chemical pulp. This pulp is mostly bleached with chlorine dioxide, which produces hypochlorous acid in situ when reacting with lignin. However, applying hypochlorus acid directly is not practiced, even though it contributes significantly to the bleaching reactions. Therefore, this article presents hypochlorous acid as the main bleaching chemical for oxygen delignified Eucalyptus sp. kraft pulp. The results showed that hypochlorous acid solely decreased the kappa number of the pulp more efficiently than chlorine dioxide did, without increasing the content of adsorbable organic halogens (AOX) in the effluent. The bleaching sequence with hypochlorous acid, ozone and hydrogen peroxide produced fully bleached pulps, with low organically bound halogens (OX) and aerobically digestible effluents. The bleached pulps and digested effluents complied with international standards for the pulp industry. The hypochlorous acid bleaching sequence is appealing because it is short, uses mild conditions and requires less or similar energy to produce the bleaching chemicals than comparable ECF bleaching sequences from literature.