Why is this important/Goals:

An additional step using oxygen is widely used for lignin removal before the bleaching sequence during the production of semi- and fully-bleached kraft pulps. Since introduced in industrial pulp mills this process has reduced the cost, improved yield and environmental performance, compared to traditional chlorine bleaching. This project aims to provide fundamental understanding of the behavior of oxygen delignification systems, in more detail about the kinetics and mass transport. For an adequate prediction of the rate equations of lignin reduction and carbohydrate degradation both reaction kinetics and mass transport resistance must be considered, currently this field is largely unexplored.

Methods we use:

Reaction and extraction of lignin from the fiber wall under conditions relevant to oxygen delignification will be performed in laboratory conditions. The parameters that will be varied are time, temperature, pressure and caustic concentrations.  Studies to identify the structural features (size, covalent bonds, structure) of lignin that enhance reactivity towards standard and extended oxygen delignification of standard kraft softwood pulp andhigh kappa pulps and have a positive impact on mass transfer rate will be studied with NMR and SEC. Some structural analysis of cellulose will also be done (SEC). In the later stages of the project modeling will be done in combination with industrial application.

Expected results and scientific impact:

In this project the impact of mass transfer rates on the oxygen delignification efficiency and in more detail the extraction of lignin out of the fiber wall is addressed. This knowledge is expected to result in further improvements and enable the development of resource efficiency in the processes of the bio-based industry.