Kraft Delignification: Recent Findings Regarding the Impact of Non-Reacting Ions in the, 2011 PEERS Conference

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The present paper reports and discusses results from recent studies and ongoing research aimed at obtaining further insights into the factors that determine the course of kraft delignification. Much of the knowledge we have about kraft delignification comes from trials in the laboratory. However, differences in cooking liquor composition between laboratory trials and industrial cooks may lead to misinterpretations of results. In industrial situations, the cooking liquors have high ionic strengths (predominantly due to high concentrations of different sodium salts) and in the laboratory this may be compensated for by the addition of sodium salts e.g. NaCl. Results presented highlight that various anions affect delignification to different degrees and that the choice of anions for a reference series can have a considerable impact on the interpretation of results. Another example that shows the importance of the composition of the cooking liquor is that the addition of carbonate to the white liquor used in laboratory cooks increases the rate of delignification of birch and aspen. The effect of carbonate is concluded to be due to the precipitation of calcium carbonate, since free calcium ions counteract the solubilization of lignin.