Increasing oxygen delignification efficiency of oriental spruce kraft pulps

Increasing Oxygen Delignification Efficiency of Oriental Spruce Kraft Pulps Oxygen delignification can be considered as an intermediate stage between kraft pulping and bleaching process for lignin removal. But its delignification effectiveness is limited to about 50 % after which a severe loss of pulp strength occurs. In this study, for improving the efficiency of oxygen delignification, three alternative trials were examined; 1- Activation of kraft pulp prior to oxygen delignification using some oxidative agents such as nitric acid, peracedic acid and chlorine 2- Enhancing of lignin removal and viscosity stability with peroxide and sodium perborate addition into oxygen delignification media, 3- Improving the selectivity of oxygen delignification with sugar based polymer addition. The kraft pulps which used at these experiments were produced from oriental spruce wood in laboratory-scale Chlorine was determined as the most effective activator for pretreatment but it is not suitable for environmental friendly bleaching process. Peracedic acid and nitric acid pretreatment of the pulps assisted oxygen delignification stage by reducing the kappa number while retaining pulp viscosity. In addition to this, peroxide and sodium perborate addition into oxygen delignification reaction media increased the delignification degree and brightness. For the best delignification selectivity, peroxide and sodium perborate dosages were optimized as 1 % and 0.5 % respectively. Also to obtain selective lignin removal, plum gum was used as radical scavenger. So pulp viscosity increased from 793 cm3/g to 852 cm3/g in same oxygen delignification conditions with only 2 % gum addition to alkaline reaction media. But gum addition affected the brightness negatively. Consequently, combining of these three options could be considered for improving the efficiency of oxygen delignification. For example, kraft pulp can be treated with suitable activator, than oxygen delignification can be reinforced with perborate addition. At the same time, sugar based polymer can be added to oxygen delignification liquor. So more strong reaction conditions such as addition of higher alkali charge can be realized.Key Words: Oxygen Delignification, Activation, Selectivity, Sugar Based Polymer, Nitric acid, Peracedic acid, Chlorine, Peroxide, Sodium perborate X