Lignin Degradation in Oxygen Delignification Catalysed by [PMo7V5O40]8- Polyanion. Part I. Study on Wood Lignin

Abstract

Summary The behaviour of lignin in wood delignification by oxygen in acidic media in the presence of the molybdovanadophosphate heteropolyanion [PMO7V5O40]8−as studied using wet chemistry methods, solid and liquid state 13C NMR spectroscopy. Lignin is oxidised by [PMO7V5O40]8− almost completely to carbon dioxide, with a minor yield of intermediate low-molecular weight aromatic products. The analysis of the reaction products shows that the lignin acidolysis and homolysis involving the oxygen participation in oxidation take place. The residual lignin in the wood residue is more “condensed” and richer in guaiacyl structural units than that in the initial wood. The analysis of “condensed” structures issued from permanganate oxidation of residual lignins suggests that these are formed predominantly by acid-catalysed reactions. The use of an organic solvent, such as ethanol, in the pulping solution favours the oxidative delignification, protecting the lignin against competing reactions (condensation).