Jussi Lahti

Kraft black liquor, side product of the kraft pulping process, is nowadays mainly burned to recover inorganic cooking chemicals and to produce energy. However, ligneous compounds and hydroxy acids, which are present in black liquor, would be valuable raw material for instance for renewable fuels and materials replacing oil based chemicals. In addition, the separation of lignin from black liquor would reduce the load of the recovery boiler and enable increasing of the capacity of a pulp mill.
Applicability of precipitation and ultrafiltration for separation of lignin from kraft black liquor has been studied since the 70’s. Nevertheless, commercial applications are still rare and knowledge of how to improve separation efficiency is still needed. This study produces novel information on the separation phenomena, which can be utilized in the fractionation of hydroxy acids and lignin from black liquor. In addition, the effect of process conditions and raw materials on separation phenomena and stability of polymeric membranes under extreme conditions prevailing in black liquor treatment are studied to evaluate feasibility on commercial membranes for this application. The results of this study give valuable contribution for the development of wood-based biorefineries.