Closed-Mill Delignification by Design Using Polyoxometalates, 1999 Environmental Conference Proceedings

C.J. Houtman, R.H. Atalla & I.A. Weinstock

USDA Forest Service

Forest Products Laboratory

R.S. Reiner, S.E. Reichel & M.J. Birchmeier

Department of Chemical Engineering University of Wisconsin-Madison

C.E. Sullivan

W.L. Gore and Associates

Polyoxometalates (POMs) are a class of delignification agents that promise to provide the basis for a new closed-mill bleaching technology. The results presented here are based on the use of Na6SiV2W10O40, which is effective in reducing the Kappa number of softwood Kraft pulp from 30 to below 10 with minimal loss in viscosity. A critical part of a viable POM process is the elimination of the organic lignin and carbohydrate-derived fragments dissolved during the delignification. To simulate a closed process, a series of pulp samples were delignified with the same POM liquor. Before each pulp sample was treated, the liquor was oxidized to regenerate the POM and remove a large portion of the organic material dissolved during the previous delignification step. By collecting and reusing the wash water during this set of experiments, we showed that a steady-state carbon load will be achieved and that the proposed industrial process is feasible. The rate of the wet oxidation of organic material was similar to the rate observed for acetate oxidation.