Hardwood delignification: investigating kraft cooking of pin chips vs standard chips

The project will be performed within the national research and educational program Resource Smart Processes that gathers the main industrial and academic actors within the Swedish forest industry and provides a strong collaborative environment with close connection to as well industry as state-of-the-art research infrastructure. As a master-thesis student in this program you will also participate in the networking and scientific events (workshops, conferences, project meetings) and collaborate closely both with the industrial and academic partners involved.

This project is together with: Chalmers, Södra


Pulp mills provide raw materials for several applications, many times competing with or replacing fossil-based products. The versatility of the products they offer puts them in a strategic position when considering the transition towards a bio-based economy.  Thus, a good understanding of the pulping process, specially kraft pulping, is essential to ensure the future development of the sector. In that sense, investigating how different process parameters affect pulp quality and the composition of the side streams is highly pertinent. One important parameter to be considered is the wood chip size[1] . The ideal chip dimensions depend on the wood species and on the characteristics of the chipper, but most processes work with 20-30 mm of length, 15-30 mm of width and 2-8 mm of thickness[2] [3]. However, when the wood logs are being cut, part of the wood will inevitably be turned into smaller pieces (called pin chips) and sawdust. These fine fractions are undesired, as they overcook in the kraft digester, leading to higher consumption of pulping chemicals and lignin condensation[1] [3]. Not surprisingly, the amount of fines added to the system during pulping is well controlled in the mills. Another solution is to pulp these fractions separately, but usually the final pulp quality is inferior to the one achieved with standard chips. Therefore, improving the understanding of how pin chips behave during pulping can lead to fine tuning of the kraft process, increasing the final yield and pulp uniformity.

Purpose and aim:

The aim is investigating the differences between batch kraft cooking of standard chips and pin chips, for the purpose of expanding the understanding of kraft pulping of pin chips, which can deliver new insights towards a more resource-efficient process. This project will be part of BioInnovation’s Resource Smart Processes, as a complementary piece to the PhD project Improved uniformity of the fibers liberated in the kraft pulp digester and will receive full support from Södra and the Resource Smart Processes network. As such, it also aims at building a strong network in which the master student will interact with members of the program for the future development and competence provision.


Pin chips and standard chips of different wood species (focus on birch and aspen) will be sampled on site at the pulp mill (Södra Cell Mörrum). They will be subjected to kraft cooking considering experiments using constant composition (high liquor to wood ratio) and also industrial conditions (e.g., liquor:wood = 4). Afterwards, samples of the pulps and black liquor fractions will be collected, including separation of different portions of black liquor[4] and the composition of each sample will be analyzed. In addition to evaluating the rate of delignification during pulping, the composition of pulps and black liquor will be determined and structural differences between the dissolved wood components (specially lignin) will be   analyzed for selected samples.


The applicants should preferably have a background in chemical engineering, wood chemistry and process technology with a collaborative approach. The project can be performed in pair.

Project start:

January 2024

Contact details:

Supervisor: Carolina Marion de Godoy godoy@chalmers.se

Industry supervisor: Fredrik Wernersson Brodin, fredrik.wernerssonbrodin@sodra.com

Examiner: Merima Hasani, merima.hasani@chalmers.se