A major shortcoming of kraft pulping, the predominant chemical pulping process worldwide, is the significantly higher amount of residual lignin in the produced pulps. Though lignin condensation reactions are one of the main challenges in removing this residual lignin from kraft pulps, there has been limited focus on devising techniques to minimize these reactions. This study aims to develop a novel method to reduce the occurrence of lignin condensation reactions during pulping, resulting in faster and more selective delignification and higher pulping yield, and verify earlier patent claims by Jiang et al. To accomplish this goal, a specific phenolic compound (2,4-Xylenol) was utilized as an additive in the pulping process. We investigated the role of this novel cooking additive in kraft pulping using a state-of-the-art laboratory batch digester and mill-environment (unscreened) wood chips. The impact of the H-factor, the amount of additives, and the timing of additive dosage have been investigated. The preliminary results showed that the additive effectively increased the delignification and selectivity of the pulps with a yield gain of up to 1.6 units (3.7% increase) with a moderate dose of 0.5 wt.% based on bone-dry weight of wood chips. This increased selectivity has potential industrial impacts in terms of additional pulp production, lower cooking chemicals consumption, energy savings, and so on. In our future work, we will analyze the structural features of the isolated lignins using advanced tools such as NMR and GPC to gain insights into the reaction mechanism.
