Date of Award
Doctor of Philosophy
Paper Engineering, Chemical Engineering and Imaging (to 2013)
The kraft lime cycle can be either replaced or supplemented by borate-based autocausticizing (total or partial autocausticizing, respectively). The borate-based autocausticizing uses sodium metaborate to produce sodium hydroxide in the two-step reaction performed in a recovery boiler and dissolving tank. In accordance with the borate-based autocausticizing chemistry, sodium metaborate is an additional chemical in both pulping and recovery. The studies of kraft pulping in the presence of sodium metaborate provide insight into the effect which sodium metaborate might have on the pulping process including the delignification rate, selectivity of lignin removal, and the properties of both pulp and black liquor.
Kraft pulping of birch, maple, and spruce with and without presence of sodium metaborate (kraft-borate and kraft pulping) was conducted at an increasing H-factor. The chemical and physical characterization of the resulting pulps and black liquors was conducted. Additionally, the properties of commercial slash pine black liquor were studied in the presence of different levels of sodium metaborate.
The studies showed that sodium metaborate, at the level corresponding to 10 to 52% level of autocausticizing, has a potential to increase the screened yield ofspruce kraft pulp. Also, at the level corresponding to 35% autocausticizing, sodium metaborate does not affect the delignification rate in birch, maple, and spruce pulping, and does not cause the pulp quality change.
The boiling point rise of black liquor increases in the presence of sodium metaborate, but at 35% autocausticizing, it is only about 2.5°C at 70% solids. It was proposed that lignin-borate complex might cause the boiling point rise to be less than expected as sodium metaborate is completely soluble in black liquor.
These studies were performed under the same conditions regarding the autocausticizing level and the pulping parameters as sulfidity, active alkali charge, temperature, and liquor-to-wood ratio. Future studies should include a variation of these conditions to evaluate their interaction and suggest the optimal conditions for pulping in the presence of sodium metaborate, which will provide both high level of borate-based autocausticizing and high pulp quality.
Bujanovic, Biljana M., "Effects of Sodium Metaborate on Kraft Pulping" (2003). Dissertations. 1212.