On the Dissolved Organic Material in the Closed-Cycle Bleaching: Molar Mass Distributions in the TCF Bleaching Filtrates, 2001 Pulping Conference Proceedings

J. Fiskari--This investigation studied the consequences of a partial closure of the liquid circulations in a TCF bleaching sequence. A series of experiments was performed with an oxygen-delignified hardwood kraft sample from a Finnish pulp mill. The bleaching filtrates were recycled in order to simulate the liquid circulations of a partially closed bleach plant. The conditions (chemical charges, retention times, temperatures) were similar to those of an actual mill. The filtrates were analysed for COD and relative molar mass distributions of the dissolved organic material. The results show that the COD levels of the filtrates increased significantly when the filtrates were recycled. It was found that the molar mass distributions of the dissolved organic material varied greatly depending on their origin. The ozone stage filtrates had significantly lower relative molar mass distribution than the hydrogen peroxide stage filtrates. As a result of recycling, the differences between the filtrates became less pronounced, as expected.