Abstract
MnO2 can potentially suppress the degradation of carbohydrates in oxygen delignification, because MnO2 catalyzes the decomposition of H2O2 to H2O and O2 and possibly that of organic peroxides to alcohols and O2 without the formation of any active oxygen species, which degrade carbohydrates. The addition of MnO2 actually suppressed the degradation of a carbohydrate model compound, methyl β-D-glucopyranoside, when reacted with active oxygen species generated from reactions between a phenolic lignin model compound, vanillyl alcohol, and O2 under oxygen delignification conditions. However, the addition of MnO2 did not have any meaningful effect when hardwood unbleached kraft pulp was oxygen-delignified. The addition surprisingly had a deleterious effect on pulp viscosity when MnO2 was generated in situ in pulp fibers. This deleterious effect would result from a phenomenon whereby the oxidation of Mn2+ to MnO2 was not complete in the in situ generation and Mn3+-related species, along others, were generated. In contrast, substitution of the latter half of oxygen delignification with a MnO2 oxidation stage at a pH of 2 substantially suppressed the degradation of carbohydrates, compared to the common oxygen delignification without substitution.
https://ror.org/057zh3y96 
