Southern pine oxygen delignified pulps produced in a Berty throughflow reactor: How to obtain the highest degree of delignification while maintaining pulp yield and quality

The kappa number, intrinsic viscosity, and yield of Southern Pine pulps were determined after oxygen delignification at different alkali concentrations, temperatures, oxygen pressures, and treatment time in a Berty throughflow reactor. It was found that the highest delignification-cellulose degradation selectivity is achieved at low alkali concentrations and temperatures of about 100°C or less. Oxygen pressure has little effect on selectivity. Carbohydrate yield loss is proportional to kappa number loss up to kappa reduction of 60%. At higher delignification, the carbohydrate yield loss increases more strongly than delignification. However, carbohydrate yield loss is linearly correlated with cellulose degradation at all degrees of delignification. Hexenuronic acids are not removed during conventional oxygen delignification. To increase delignification of softwood pulp beyond about 60%, oxygen system design should be changed so that alkali concentration and charge are decoupled, as is similarly done in modern cooking systems.