Lignin is the most abundant aromatic biopolymer on Earth and the only renewable source of aromatic chemicals. Yet, conversion of lignin to valuable products has shown little commercial viability. We investigate an environmentally benign and economically competitive method of obtaining high-value lignin products, including low molecular weight aromatics and carbon-based nanoparticles, by coupling lignin solubilization and depolymerization to a microbial electrolysis cell (MEC) that uses a model wastewater as a source of carbon. The application of this work is an integrated biorefinery that can treat food industry wastewaters with high organic contents and convert lignin wastes to high value products. Organosolv lignin isolated from corn stover was processed at room temperature and atmospheric pressure with the cathodic effluent of an MEC, which is characterized by high pH and high salt content. This method of lignin valorization is in line with the principles of green chemistry by re-inventing waste as a resource, producing valuable chemicals and materials through mild conditions and minimal waste, and using renewable feedstocks. Products were characterized and quantified with a variety of analytical techniques including: UV-vis spectroscopy, high resolution LC-MS, NMR, nanoparticle tracking analysis and SEM. Our analysis shows nearly 100 % lignin solubilization using a pH 10.8, 179 mmol L<sup>-1</sup> phosphate buffer, which mimics the properties of the cathode effluent. The product mixture was, on average, 35 % phenolic and 10 % flavonoid, specifically tricin and antiarone-F. Vanillin, <i>p</i>-coumaric acid and ferulic acid were also identified. Following the neutralization of the solubilized lignin, we are able to close mass balance with an oligomeric fraction that we and others have characterized as lignin nanoparticles (LNPs). The LNPs are spherical ranging from 70 nm to 500 nm in diameter. These results show a greater concentration of low molecular weight aromatic products than previously reported, including the production of flavonoids, which have applications in pharmaceuticals or nutritional supplements. This method of lignin conversion also produces a second, high-yielding product stream – nanoparticles, which have potential applications in the cosmetic, medical, and agricultural industry. This integrated biorefinery can provide one of many paths to a post fossil-fuel society.

Transforming lignin into high value products through green processing

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.