Northwestern University researchers have developed a sustainable, inexpensive two-step process that can upcycle organic carbon waste; including lignin.
By processing waste through a microbe-driven biorefinery, the researchers turned lignin into carbon sources that could be used in high-value, plant-derived pharmaceuticals and antioxidant nutraceuticals as well as carbon-based nanoparticles for drug or chemical delivery.
The study was featured on the cover of the January issue of the journal ACS Sustainable Chemistry and Engineering.
“Lignin should have tremendous value, but it’s intrinsically regarded as waste,” said Northwestern’s Kimberly Gray, who led the research. “Lignin makes up 20-30% of biomass but 40% of the energy, which is a lot, but it’s difficult to tap this energy source. Nature made lignin so recalcitrant to processing that people haven’t figured out how to use it. Researchers have been trying to solve this problem for decades. Using an oil refinery as a template, we developed a biorefinery that takes in waste streams and produces high-value products.”
One of the most abundant organic polymers in the world, lignin is present in all vascular plants. Found between cell walls, lignin gives strong, sturdy plants — like trees — structural support. Without lignin, wood and bark would be too weak to support trees. And wooden houses and furniture would simply collapse.
But most industries that use plants — such as the paper manufacturing and brewing industries — strip out lignin, leaving behind cellulose, a type of sugar. Instead of making use of nature’s ultra-resistant material, industrial teams burn lignin as a cheap fuel.
When the researchers exposed lignin to the bio-based caustic chemical, however, lignin’s polymers broke apart in a way that preserved the aromatic rings. About 17% of the processed lignin turned into rings of carbon called flavonoids, an antioxidant-rich phytonutrient often found in supplements. Commonly used in medicinal chemistry, these rings could be used as plant-derived, sustainable precursors to inexpensive pharmaceuticals and supplements.
“It breaks apart the polymer bonds but selectively leaves the ring,” Gray said. “If you can preserve that ring, then you can make high-value materials. Chemists have developed catalysts that break apart the whole compound, and then they have to rebuild the ring. But we were able to break it selectively to preserve the valuable structures.”
The rest of the processed lignin (about 80%) became carbon-based nanoparticles, which could be used to encompass substances for targeted drug delivery in humans or targeted nutrient delivery in plants. The nanoparticles also could offer a sustainable, plant-derived alternative for sunscreens and cosmetics.