Basket cases IV: higher yield with Paprilox[TM] polysulfide-AQ pulping of hardwoods.

Application: Kraft mills may be able to apply the polysulfide-AQ pulping method discussed here to obtain a higher yield of pulp from wood.

Pulp yield from wood is a hallmark of all pulping processes, and any practical means to increase it is advantageous. Poly-sulfide pulping is such an option in kraft mills, but only a handful of PS mills exist because of the high cost of converting kraft white liquor to polysulfide orange liquor using special catalysts and clarified feed liquor.

The Paprilox[TM] polysulfide liquor-generating process, a simpler and cheaper option, can be applied in a mill's causticizers, and uses existing lime mud plus Mn[O.sub.2] particles to catalyze the liquor oxidation. In 1998, mill-scale liquor-making trials of this process were run at the Espanola, Ontario, mill of Eddy Forest Products Ltd. (now part of Domtar Inc.) in Canada. Late in 1999, the Paprilox[TM] system began converting half of the mill's white liquor to orange liquor, and the batch kraft hardwood pulp production line was changed to polysulfide-anthraquinone (PS-AQ) pulping.

To measure the yield gain with PS-AQ pulping of birch in the mill, we used triple hanging baskets, thereby obtaining direct mass in/mass out data. We based the comparison on two different chip furnishes--pure white birch reference chips, and run-of-the-mill birch chips. PS-AQ pulping had a yield advantage of 1.6% to 1.8% over kraft at 15 kappa number. In pilot-plant experiments using the same chip furnishes and the mill made pulping liquors, the PS-AQ yield advantage was at least 1.4%. The unbleached basket pulps from the two processes were essentially alike in physical properties. We found no differences in the mill-bleached pulps, nor any change in fine papermaking in the mill.

This paper was originally presented at the TAPPI 2001 Pulping Conference. It was named as the 2001 David Wetherhorn Award winner and the 2001 Pulping Conference High Impact Paper.

MacLeod, Radiotis, and Uloth are with Paprican, Pointe-Claire, Quebec, and Prince George, British Columbia, Canada; Munro is with Domtar Inc., Espanola, Ontario, Canada, and Tench was with Kvaerner Chemetics Inc., Vancouver, British Columbia, Canada; contact MacLeod by email at [e-mail].