Scale-up and Optimization of Membrane Processes for Kraft Black Liquor Fractionation

Improving lignocellulosic biorefineries is a crucial step in transitioning from a fossil-based economy to a bio-based one. These biorefineries convert lignocellulosic biomass feedstocks into value-added products such as biofuels, biopower, biochemicals, and biomaterials, while also recovering valuable components from underutilized process streams. Pulp and paper mills are lignocellulosic biorefineries that have several process streams from which valuable components could be recovered. One of these streams is kraft black liquor (KBL) is a side stream of the kraft pulping process, the most widely used pulping method worldwide. KBL is usually evaporated and burned to obtain energy. However, implementing membrane processes within the pulp mill could recover lignin and decrease the energy consumption of the evaporators. This presentation examines the scale-up and optimization of membrane processes for kraft black liquor (KBL) fractionation, starting from the first industrial application at Metsäliiton, Finland, in 1975. This initial work utilized polymeric ultrafiltration membranes for the concentration and fractionation of KBL. Recent developments have focused on ceramic ultrafiltration membranes to fractionate lignin in KBL, combined with polymeric and ceramic nanofiltration membranes to concentrate low-molecular-weight lignin. Furthermore, the different concepts for lignin recovery within a pulp and paper mill will be considered in a techno-economical evaluation. Finally, the presentation investigates the application of response surface methodology to optimize membrane cleaning in the nanofiltration of KBL, aiming to improve efficiency and reduce the impact of fouling in these advanced membrane systems. Overall, the presentation will provide a comprehensive overview on the development and status of this application.