Title
Biomimetic oxidation of lignin in pulp by simple inorganic complexes
Authors
XUE-FEI ZHOU

Received September 14, 2013
Published Volume 49 Issue 3-4 March-April
Keywords ammonium persulfate, copper acetate, cobalt acetate, eucalyptus kraft pulp, biomimetic oxidation, residual lignin

Abstract
In recent years, the growing concern about the fate of chlorinated organic compounds in the bleaching area determined a higher demand of new bleaching technologies. Several well-known systems, such as peroxydisulfate plus Cu(II), Co(II), Ag(l), Fe(II) and Mn(II), have been successfully applied in the oxidative degradation of phenols and lignin model compounds, providing a good example for oxidation of the lignin moiety of pulp. Model studies, however, do not reflect all the reactions that lignin might undergo as a macromolecule in the pulp matrix. To advance the understanding of delignification with simple inorganic complexes, eucalyptus (E. urophylla × E. grandis) pulp was subjected to catalytic delignification (Cat) with atmospheric dioxygen at 70 oC in a peroxydisulfate-acetate system, i.e. in CH3COOH-H2O medium containing (NH4)2S2O8 and Cu(CH3COO)2/Co(CH3COO)2, the latter being used as catalyst. The Cat-treatment was followed by alkaline extraction (Ep) under standard conditions. Lignins in the bleached pulps were isolated and analyzed by different techniques, including Elemental Analysis, FTIR, NMR and GPC. The transformation of lignin during the aerobic treatment of eucalyptus pulp with a simple inorganic mixture was investigated. A comparative analysis of residual lignins isolated from pulps in the catalytic bleaching sequences (CatEp) showed that lignin underwent changes that included a reduction in the content of PhOH groups, a demethylation, and an increase in carbonyl groups. The FTIR results indicated that the catalytic treatment of pulp led to the loss of aromaticity. The GPC studies showed lignin depolymerization.