Pulp Pretreatments for Improved Selectivity and Extended Oxygen Delignification, 2003 Fall Technical Conference

Pulp pretreatments prior to oxygen delignification are known to improve pulp selectivity during oxygen delignification. The techniques investigated were pretreatment of the pulp using DTPA (Q), pretreatment by washing the pulp with acid (A), and acid washing the pulp with a small amount of ClO2 present (AD).

The three pretreatment techniques investigated were compared to control experiments. Each of the four delignification conditions was investigated in both a stainless steel reactor and in glass to test the hypothesis that metals are leached from the stainless steel reactor and influence the results. All of the experiments were performed in quadruplicate with and without H2O2 reinforcement in the oxygen stage. Response variables were the kappa number, intrinsic viscosity, degree of delignification, and the selectivity coefficient (α). The effectiveness of the various conditions on the response variables was determined using the student t-test.

The results of the experimental investigation showed that all of the pretreatment techniques improved the selectivity of oxygen delignification. Use of the AD pretreatment stage led to additional delignification compared to the no pretreatment case and also when compared to the Q- and A-stage pretreatment techniques. Lastly the use of H2O2 to reinforce an oxygen stage resulted in an improvement in the level of delignification but a loss in selectivity. This was true for all of the cases evaluated except for the oxygen stage with AD pretreatment where no difference was detected in delignification when the reaction was conducted in stainless steel. DTPA was extremely effective in controlling metals and no drop in selectivity was observed even for the case of using H2O2 reinforced oxygen delignification.