Progress in the development and optimization of polyoxometalate delignification systems

We have reported the use of polyoxometalates (POMs) as selective, regenerable delignification agents that are inherently thermodynamically stable, and self-buffering. The re-activation with oxygen is under conditions that mineralize the organic byproducts of the delignification process. Thus, the POMs provide the basis for a closed bleach plant wherein the consumable oxidant is oxygen and the primary byproducts are carbon dioxide and water. They have been shown to reduce the kappa levels of softwood kraft pulps from 30 to below 5 while retaining viscosity above 20. Recently we have concentrated on POMs that are more efficient in the uptake of electrons from the substrate pulps per mole of POM. We have also studied the determinants of rates of electron transfer from the substrates to the POMs. All of these must be optimized in order to achieve the full economic potential of POM-based delignification. This report will summarize progress along the multiple fronts that we are investigating including the possibilities of using POMs as a complement to high yield pulping and electrochemical bleaching using POMs as mediators.