A New, Energy-Efficient Method for the Recovery of Lignin from Agriculturally Based, Unevaporated Black Liquor Streams

M.C. Thies, B.S. Lynn
Clemson University,
United States

Keywords: lignin, black liquor, recovery, grass, bioproduct


Techno-economic analysis of a lignocellulosic biorefinery indicates that co-products can greatly facilitate their economic viability; however, the inefficiencies inherent in lignin recovery have impeded progress. We have discovered (and filed a provisional patent application on) a new method for recovering lignins from the products of alkaline pretreatment. The proposed technique allows recovery of the lignins directly from the dilute, acidified black-liquor stream, replaces the energy-intensive evaporation step, and recovers the lignin in high (>90%) yield. In brief, the discovered process creates a novel phase separation, concentrating the impurities in the spent black liquor and recovering the lignin in its own unique phase. Thus, all washing and filtration steps are eliminated. One negative of the new lignin-recovery process is that the lignin is recovered in relatively low purity (~85%). Fortunately, we have discovered that our patented ALPHA process (10,053,482) can reduce the ash and sugars content of the recovered lignin down to 0.1-0.2% in a single liquid--liquid equilibrium stage. We propose that ultraclean lignins (<100 ppm metals) can be achieved in <5 stages. A significant positive of our new process is that the recovery of lignin from agriculturally derived and unevaporated black liquors, such as those from corn stover, wheat straw, and other grasses, can be applied at a scale commensurate with the resources available to start-up companies in the rapidly emerging sustainable packaging and biomaterials industry.