Polyoxometalate Bleaching of Kraft Pulp: A Highly Selective Closed Mill Technology, 1995 Pulping Conference Proceedings

I. A. Weinstock, R. H. Atalla, R. S. Reiner, M. A. Moen and K. E. Hammel

USDA Forest Service

C. L. Hill

Emory University

C. J. Houtman

University of Wisconsin-Madison

A process for using polyoxometalate (POM) salts and oxygen in the commercial bleaching of chemical pulps is herein described. A clear advantage of polyoxometalates over oxygen alone, hydrogen peroxide or ozone is their inherently high oxidative selectivity for the residual lignin in softwood kraft pulps. Softwood kraft pulps delignified to low kappa numbers using POM salts possess papermaking properties comparable to those obtained using chlorine/chlorine dioxide and alkali. The goal of ongoing research and development efforts is to develop a highly selective, oxygen-based polyoxometalate delignification and bleaching technology compatible with mill closure. To this end, several Unit Operations are under development. These include: Bleaching, pulp washing, wash water recovery, removal of salt impurities, wet oxidation of dissolved organic compounds, and aerobic oxidation of spent polyoxometalate salts to their bleaching active forms.