Impact Of Dissolved Matter In The Oxygen Delignification Stage, 2016 Pulping, Engineering, Environmental, Recycling, Sustainability (PEERS) Conference Proceedings

The presence of dissolved matter in the pulp suspension to the oxygen delignification stage, mainly dissolved lignin, is normally considered to affect the delignification rate negatively due to the competing reactions between the fiber bound lignin and the lignin dissolved in the filtrate. Recirculated oxidized filtrate from the post-O2 washing is considered to be less harmful to the delignification efficiency than unoxidized dissolved matter originating from the cooking stage. In order to develop a better understanding of the mechanisms of the dissolved matter’s reactions and impact on the oxygen stage performance, laboratory oxygen delignification experiments with varying levels of unoxidized and oxidized dissolved matter were conducted.  

The results showed that unoxidized dissolved matter had a negative impact on the delignification in the oxygen stage whereas oxidized dissolved matter actually had a positive effect. The delignification efficiency of the laboratory experiments thus depends on both the amount of dissolved matter and its origin. The pulp viscosity decreased with increasing dissolved matter content irrespective of the origin, i.e. unoxidized or oxidized. At higher COD levels however, the viscosity drop was larger for the unoxidized dissolved matter. In terms of selectivity, the oxidized filtrate had a similar impact as additional NaOH charge. Both types of filtrates consumed hydroxide and the final pH decreased with increasing dissolved matter content. The final pH was significantly lower for the unoxidized filtrate at higher COD levels.

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