Delignification of eucalypt kraft pulp with manganese-substituted polyoxometalate assisted by fungal versatile peroxidase

Oxidation of the manganese-substituted polyoxometalate [SiW11MnII(H2O)O39]6− (SiW11MnII) to [SiW11MnIII(H2O)O39]5− (SiW11MnIII), one of the most selective polyoxometalates for the kraft pulp delignification, by versatile peroxidase (VP) was studied. First, SiW11MnII was demonstrated to be quickly oxidized by VP at room temperature in the presence of H2O2 (Km = 6.4 ± 0.7 mM and kcat = 47 ± 2 s−1). Second, the filtrate from eucalypt pulp delignification containing reduced polyoxometalate was treated with VP/H2O2, and 95–100% reoxidation was attained. In this way, it was possible to reuse the liquor from a first SiW11MnIII stage for further delignification, in a sequence constituted by two polyoxometalate stages, and a short intermediate step consisting of the addition of VP/H2O2 to the filtrate for SiW11MnII reoxidation. When the first ClO2 stage of a conventional bleaching sequence was substituted by the two-stage delignification with polyoxometalate (assisted by VP) a 50% saving in ClO2 was obtained for similar mechanical strength of the final pulp.