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The effect on pulp yield and strength properties of extending the delignification in kraft pulping conditions by using a higher H-factor, increasing the alkali charge, or by addition of anthraquinone, was investigated. It was found that delignification could be extended by only 15% using a 27% increase in H-factor with 2% decrease in pulp yield. An 11% increase in effective alkali resulted in a 24% reduction in kappa number, but also with lower yield. Increasing the H-factor at higher alkali charge failed to reduce the kappa number any further. Addition of 0.1% anthraquinone at standard pulping conditions (1720 H-factor, 16% EA, 30% sulfidity) resulted in a 24% reduction in kappa number without an increase in alkali charge or H-factor and resulted in a 2% pulp yield increase. Lowering the kappa number from 30 to 22 by these methods of extended delignification did not affect the strength properties.
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Anthraquinone - A Simple Approach for Extended Delignification in Conventional Kraft Pulping, 1992 P