POLYOXOMETALATE DELIGNIFICATION - STUDY OF LIGNIN MODEL COMPOUNDS

The oxidation of four lignin model compounds (phenolic and non-phenoli c, with ol without an alpha-carbonyl group) with polyoxometalates was studied. It was found that the reactivity of nonphenolic lignin struct ures rewards polyoxometalates is negligible while the reaction with ph enolic lignin structures takes place readily. The kinetic study shows that the oxidation of vanillin with alpha-k(5) [SiV5+ W11O40] exhibits a first order reaction with respect to vanillin and a second order wi th respect to the polyoxometalates. The effect of pH was also studied. A reaction mechanism compatible to the observed experimental evidence was proposed. Further study explored the use of polyoxometalates in a catalytic amount during oxygen delignification, however the results w ere not successful because the re-oxidation of the reduced polyoxometa lates under the present conditions was not feasible.