Översikt
Datum:
Startar 28 april 2026, 10:00Slutar 28 april 2026, 15:00Plats:
Lecture hall HB3, Hörsalsvägen 10, Chalmers.Opponent:
Professor Christine Chirat, Université Grenoble Alpes, France.Avhandling
Läs avhandlingen (Öppnas i ny flik)
Kraft pulping accounts for most of the global paper pulp production. Nevertheless, the detailed mechanisms that govern delignification during this process are still not fully understood. Hence, this work investigated impregnation and kraft cooking of hardwoods, aiming to strengthen our knowledge regarding the rates and uniformity of lignin removal within wood chips, particularly considering the influence of specific morphological features.
The experiments included wood chips of alder, aspen, beech, and birch, and their behavior was examined from two perspectives: changes in global and local chemical composition, and changes in wood microstructure. The latter was evaluated in-situ via synchrotron X-ray tomography. Additionally, a multiscale model describing the delignification of birch chips during kraft cooking was developed.
The results revealed that the concentration and distribution of alkali within the chips after impregnation have major impact on delignification and are strongly affected by wood chip porosity. Furthermore, structural analysis during impregnation showed that vessels provide the main path for liquor penetration and distribution among adjacent cells. No substantial changes in cell wall thickness due to alkaline swelling were observed.
When comparing hardwood species, lignin removal was significantly faster in aspen. Delignification uniformity also increased with chip porosity and was shown to improve when utilizing low cooking temperatures (e.g., 145 °C) or impregnation liquors with high alkali concentrations. Differences in ray cells among the hardwoods had no clear impact on local rates of lignin removal. In terms of microstructural changes, delignification led to increased chip porosity and a minor decrease in cell wall thickness.
Finally, the proposed modeling approach has potential to be used for investigating the defibration point of wood chips. According to it, lignin removal from the cell walls appears to be limited by reaction kinetics and diffusion of lignin fragments, whereas the overall delignification behavior at the chip scale is heavily influenced by the balance between alkali transport and consumption.
The experiments included wood chips of alder, aspen, beech, and birch, and their behavior was examined from two perspectives: changes in global and local chemical composition, and changes in wood microstructure. The latter was evaluated in-situ via synchrotron X-ray tomography. Additionally, a multiscale model describing the delignification of birch chips during kraft cooking was developed.
The results revealed that the concentration and distribution of alkali within the chips after impregnation have major impact on delignification and are strongly affected by wood chip porosity. Furthermore, structural analysis during impregnation showed that vessels provide the main path for liquor penetration and distribution among adjacent cells. No substantial changes in cell wall thickness due to alkaline swelling were observed.
When comparing hardwood species, lignin removal was significantly faster in aspen. Delignification uniformity also increased with chip porosity and was shown to improve when utilizing low cooking temperatures (e.g., 145 °C) or impregnation liquors with high alkali concentrations. Differences in ray cells among the hardwoods had no clear impact on local rates of lignin removal. In terms of microstructural changes, delignification led to increased chip porosity and a minor decrease in cell wall thickness.
Finally, the proposed modeling approach has potential to be used for investigating the defibration point of wood chips. According to it, lignin removal from the cell walls appears to be limited by reaction kinetics and diffusion of lignin fragments, whereas the overall delignification behavior at the chip scale is heavily influenced by the balance between alkali transport and consumption.
Carolina Marion de Godoy
- Doktorand, Kemiteknik, Kemi och kemiteknik