Effect of process variables on the performance of electrochemical acidification of Kraft black liquor by electrodialysis with bipolar membrane

Lignin which is dissolved in the residual black liquor stream of Kraft pulping mills can be extracted and converted into a wide range of value-added bio-based products. To this end, design and development of an eco-efficient lignin extraction method is crucial. Electro-membrane technologies and particularly, electrodialysis with bipolar membrane (EDBM) is a promising and green avenue to acidify the black liquor and extract the lignin. Therefore, the aim of this study is to evaluate the performance of the EDBM acidification process in terms of current efficiency and energy consumption. The effect of main process variables such as operational temperature and black liquor chemical composition on the efficiency of the EDBM process have been evaluated. The experimental results demonstrated the substantial influence of these parameters on the EDBM current efficiency, energy consumption and fouling of the ion exchange membranes. Furthermore, it was indicated that promoting the hydrodynamics of the system could delay and mitigate the lignin self-aggregation and precipitation inside the EDBM stack. The highest current efficiency and, subsequently, the lowest energy consumption were achieved when the EDBM process was carried out at 55 °C with the black liquor solution containing 20 (wt.%) total dissolved solids.