The oxidation of manganese-substituted polyoxometalate [SiW11MnII(H2O)O39]6- (SiW11MnII) to active in selective kraft pulp delignification specie [SiW11MnIII(H2O)O39]5- (SiW11MnIII) by versatile peroxidase (VP) was studied. Releasing upon lignin oxidation SiW11MnII was quickly oxidized by VP even at room temperature in the presence of H2O2 (Km= 6.4±0.7 mM and kcat= 47±2 s-1). This allowed 95-100% reoxidation of reduced polyoxometalate with VP/H2O2 in the filtrate from eucalypt pulp delignification. In this way, it was possible to reuse the liquor from a SiW11MnIII/O2 stage for further delignification, in a sequence constituted by two polyoxometalate stages, with a short intermediate step consisting of the addition of VP/H2O2 to the filtrate for SiW11MnII reoxidation. When the first D stage of a conventional DEDED bleaching sequence was substituted by the two-stage delignification with polyoxometalate (POM) assisted by VP (POM-VP-POM), a 50% saving in ClO2 consumption was obtained for similar mechanical strength of the final pulp (89%ISO brightness).

This study has been supported by the EU project BIORENEW (NMP2-CT-2006-026456) and the Spanish projects AGL2008-00709 and BIO2008-01533. We thank ENCE (Pontevedra, Spain) for pulp samples. G. M. and F. J. R.-D. thank the Spanish MICINN for a FPI fellowship and a Ramon y Cajal contract, respectively.

Peer reviewed