Development of stable redox complexes to mediate delignification of kraft pulp by laccase

The use of laccase and mediators to delignify and bleach kraft pulp is now well documented. Several nitrogen-containing aromatic compounds have been shown to mediate the oxidation of lignin by laccase. In order to apply this technology in the kraft pulp industry, development of cost-effective mediators and laccases are of prime importance. Our electrochemical studies on the interaction between laccase, mediator and lignin indicate that effective mediators must behave like true catalysts, i.e. they must be reversibly reduced by lignin so that the mediator will be continuously regenerated and made available for further cycles of oxidation by laccase. We report on the use of transition metal complexes in combination with laccase to mediate catalytic delignification of kraft pulps. Due to their redox properties and stability, these metal complexes can be recycled many times for pulp delignification.