In-digester reduction of organic sulfur compounds in kraft pulping

This experimental research examines the relationship between the formation of organic sulfur compounds and delignification during kraft wood pulping. A phase transition point (PTP) was discovered below and above which the for mation of total organic sulfur compounds, with respect to delignification, changes significantly. The PTP occurs at approximately pulp kappa number 35 for softwoods and 20 for hardwoods. The PTP is directly related to the pha se transition in kraft delignification from bulk to residual delignificatio n. Significant in-digester odor reduction can be achieved using phase trans ition cooking (PTC), i.e. limiting delignification to the bulk delignificat ion phase or the PTP. It was also discovered that anthraquinone (AQ) as a c atalytic additive can reduce organic sulfur compound formation during kraft pulping. The reduction of sulfur compound formation is linearly proportion al to the square root of the level of AQ addition (in percent). A 40% in-di gester reduction in total reduced sulfur (TRS) formation can be achieved by using PTC and AQ in kraft pulping. (C) 2001 Elsevier Science Ltd. All righ ts reserved.