Kinetics of oxygen delignification

The kinetics of the medium-consistency oxygen delignification of southern h ardwoods is characterized by an apparent high rate order with respect to th e kappa number. The observed kinetic behaviour can be explained in terms of a large number of parallel first-order reactions taking place simultaneous ly during the delignification process. The slow second phase on the kappa n umber vs time curve, which gives rise to the apparent high order, can be at tributed to the presence of difficult to remove lignin moieties. To achieve high levels of delignification and low final kappa numbers requires progre ssively more severe process conditions to remove refractory lignin moieties which adversely affect pulp selectivity. Thus, it may be necessary to deve lop techniques where the stubborn lignin is activated and converted to less refractory lignin fractions if high levels of delignification and low kapp a numbers are to be achieved while maintaining high pulp strength.