The effect of anthraquinone and anthrahydroquinone penetration on delignification in the soda pulping of Norway spruce

The extent of anthraquinone (AQ) penetration into handcut Norway spruce chips as a function of cooking time was examined through the combined use of 14 C-label-led AQ and various wood sectioning techniques. The results indicated that in the initial stage of the cook, the AQ was deposited mainly at or near the chip surfaces in contrast to the alkali which penetrated to the chip core. With increasing cooking time, free and/ or combined AQ concentration at the transverse surface of the chips first decreased then increased both in this region and in the chip interior. This non-uniform distribution of AQ and alkali within the chips during the initial stage of pulping was also manifest by the Kappa number which increased significantly in proceeding from chip exterior to core. A substantial reduction in Kappa number without sacrifice in yield was achieved by impregnating the chips with an alkaline solution of anthrahydroquinone prior to pulping with alkali as compared with AQ addition in the conventional manner. Subsequent experimentation led to the conclusion that the improved performance of AQ in this case was probably attributable to its more efficient use as a delignification "catalyst" as a result of its being dispersed throughout chips in its reduced form from the outset of pulping. Contribution No. 166 from the Empire State Paper Research Institute, State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210. The results of the investigation reported herein have served to re-emphasize the importance of AQ being in its reduced (AHQ) form as a prerequisite for exerting a beneficial effect on delignification. It was further shown that the benefits of AQ with respect to Kappa number reduction at a given yield can be enhanced if a practical way of pre-penetrating the chips with AHQ prior to pulping could be found. There is, moreover, a likelihood that further gains in Kappa number reduction can be achieved through refinement of the pre-soaking and pulping procedures used in the present study.