A new environmentally benign technology for transforming wood pulp into paper. Engineering polyoxometalates as catalysts for multiple processes

A new environmentally benign technology, based on the use of polyoxometalate (POM) salts and oxygen, is being developed to bleach wood pulps for use in the manufacture of paper. Details of POM chemistry relating to the unit operations of an effluent-free bleaching process are reported. These include anaerobic delignification of wood pulp, aerobic reoxidation of reduced POMs for their cyclic reuse and POM catalyzed and initiated aerobic mineralization (wet oxidation) of lignin fragments removed from pulp during bleaching. The results of bleaching trials using a series of isostructural POM complexes of the Keggin family are reported. Key structural components of the POMs are varied to determine the effects of these changes on POM performance. Homogeneous reactions of lignin-model compounds with select POMs are used to help interpret kinetic data obtained in the heterogeneous reaction of POM solutions with pulp fibers. Finally, new directions in catalyst design that promise to expand the potential of the technology are discussed.