Lignin is regarded as a promising raw material for the production of biobased products, such as chemicals, materials and fuels, and will most probably be a key component in future lignocellulosic biorefineries.

This thesis examines the lignin extraction process in a kraft pulp mill, the technologies that are available for this purpose, and the impact made on the mill. Several different kraft lignin extraction processes and technologies are currently available and are basically linear: chemicals are brought from outside the mill and introduced into the process and the mill balance. Depending on their origin, the addition of these chemicals will affect the mill to a lesser or greater degree, both economically and environmentally. A conceivable way of reducing the impact made on the mill´s balance would be the in-house production of the chemicals used, sulphuric acid and CO₂, which takes a more sustainable circular approach.

The results obtained show that utilisation of existing process streams in the mill as a source of chemicals could be a way of not only reducing these impacts but also making lignin extraction more sustainable. Internal production of sulphuric acid is possible and could generate a substantial amount for use as replacement of the fresh sulphuric acid needed for the lignin extraction process; CO₂ is available in large quantities in the mill and could be captured and used for lignin extraction.