Lignin release during oxygen delignification – kinetics, structure and potential
Time: Fri 2026-01-23 10.00
Location: F3 Lindstedtvägen 26
Language: English
Subject area: Fibre and Polymer Science
Doctoral student: Jenny Sjöström , Fiber- och polymerteknologi
Opponent: Professor Christine Chirat, Grenoble INP – Pagora, UGA, Frankrike
Supervisor: Docent Olena Sevastyanova, Wallenberg Wood Science Center, Träkemi och massateknologi; Professor Gunnar Henriksson, Wallenberg Wood Science Center, Träkemi och massateknologi; Professor Tomas Vikström, Fiberprocesser; Doktor Claudia Esteves,
QC 20251216
Abstract
Oxygen delignification is a critical stage in modern kraft pulp production, enabling significant reductions in chlorine-based bleaching chemicals and environmental emissions while maintaining fiber quality. The process remains limited by challenges in efficiency and selectivity, governed jointly by chemical reactions and mass transport constraints. This thesis investigates the interplay between these mechanisms and explores the properties and valorisation potential of oxidized lignin (oxlignin) extracted from oxygen-stage wash liquors. Experimental results demonstrate that lignin removal during oxygen delignification is driven by a combination of rapid early-stage oxidative reactions and diffusion-controlled leaching. High oxygen pressure and sufficient alkalinity promote lignin depolymerization and oxidation, improving selectivity, while insufficient chemical conditions lead to lignin redeposition and cellulose degradation. Upstream factors such as brownstock washing efficiency and storage conditions significantly influenced lignin leaching and pulp quality, highlighting the importance of integrated process control. Oxlignin, isolated from industrial filtrates, differed markedly from conventional kraft lignin, exhibiting higher carboxylic acid content, improved water solubility, and a narrower molecular weight distribution. These properties suggest potential applications as dispersants or additives in biopolymer formulations. Ultrafiltration proved to be a viable approach for fractionating oxlignin. By connecting process optimization with resource valorisation, this work contributes to more sustainable kraft pulp production and supports the development of new lignin-based value streams in future biorefineries.