High Pressure Oxygen Delignification of Kraft Pulps I - Kinetics, 1995 Pulping Conference Proceedings

José Iribarne & Leland R. Schroeder

SUNY-ESF

Current operating practices and previous studies of oxygen delignification cover oxygen concentrations up to 0.012 mol/L in the aqueous, alkaline media. This range was increased almost ten times through the application of high oxygen pressure in the gas phase. The experimental results were generalized through models of the apparent kinetics of delignification and polysaccharide cleavage. Delignification kinetics could be modeled in two phases, each first-order on lignin content. One phase showed little dependence on alkali and oxygen while the other phase was close to first-order on both alkali and oxygen. The relative importance of the two phases depend on the operating conditions. Polysaccharide cleavage could be modeled in one phase, approximately 0.3-order on both alkali and oxygen. The models suggest that delignification selectivity can be maximized by low reaction temperatures, a short first stage at high oxygen pressure and high alkali concentration, and a second stage at low pressure and low alkali concentration. This strategy was shown to be beneficial in trial runs.