Comparative life cycle assessment of kraft lignin valorisation pathways: from pulp mill co-product to aviation fuel and bioadhesive.

This thesis evaluates two different pathways for the valorisation of kraft lignin from a pulp mill: the production of sustainable aviation fuel (SAF) and a lignin–isolated soy protein bioadhesive (LISP). The study was conducted using an attributional Life Cycle Assessment approach, implemented in Activity Browser and supported by ecoinvent background datasets. In the first stage, a kraft pulp production process with lignin extraction was modelled. Dry-mass allocation was applied to distribute the environmental impacts among pulp, lignin, and the other material co-products. The allocated lignin was then used as the input for the two valorisation pathways.The SAF pathway was modelled based on data from the ABC-Salt process and compared with fossil kerosene. Several scenarios were also developed by varying the electricity source used for hydrogen production, including grid, photovoltaic, and wind electricity.The LISP pathway was modelled using inventory data from the literature for the production of 1 kg of bioadhesive and was compared with conventional adhesive resins, including urea-formaldehyde, phenolic, and melamine-formaldehyde resins. The results show that all SAF scenarios have a lower climate change impact than fossil kerosene, with the lowest value achieved in the scenario using wind electricity. For LISP, the climate change impact was estimated at 2.8 kg CO₂-eq/kg, mainly due to steam consumption and the use of soybean meal as a proxy for isolated soy protein. LISP has a higher impact than urea-formaldehyde resin, but a lower impact than phenolic and melamine-formaldehyde resins. Finally, the results were reassessed from the pulp mill perspective, using 1 kg of available lignin as a common basis. From this perspective, SAF appears to be the most robust pathway for reducing climate change impacts, whereas the benefits of LISP strongly depend on the conventional resin selected as the reference product. The study has several limitations, including the use of proxy datasets, geographical inconsistencies in the background data, and the primary focus on the climate change indicator. Moreover, the comparison between adhesive systems was conducted on a mass basis and does not fully account for differences in performance, application dosage, or curing conditions.