High-pressure oxygen delignification of kraft pulps. Part I: kinetics

Abstract

Previous studies of oxygen delignification cover oxygen concentrations up to 0.012 mole/L in the aqueous alkaline media. This range was increased eight times through the application of very high oxygen pressure in the gas phase. The experimental results were generalized through apparent kinetics models. Delignification could be modeled in two phases, each first order on lignin content. One phase showed little dependence on alkali and oxygen. The relative importance of the two phases depends on the operating conditions. Polysaccharide cleavage could be modeled in one phase, 0.3- and 0.4-order on alkali and oxygen concentration, respectively. Application : the use of high pressure could potentially improve the selectivity of alkaline oxygen stages, enabling higher delignification while maintaining pulp strength.