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 have previously demonstrated an integrated biorefinery approach  to obtain 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. We’ve determined that 10 -15% of the products are in the form of low molecular weight aromatics (2-4% as monomer and 8-11% as dimers/oligomers) and 85-90% of the products are in the form of nanoparticles (spherical, size 50-550 nm). We now investigate how the structure of the starting lignin affects the two product streams – focusing primarily on ß-O-4 linkage abundance modified by different extraction methods and varying S/G ratios with different biomass sources. Lignin is isolated from corn stover, a hardwood and softwood via organosolv, Björkman, and Klason processing and analyzed with SEM, UV-vis, FTIR, and NMR for structural composition. The extracted lignin is processed at room temperature and atmospheric pressure with the cathodic effluent of an MEC, which is characterized by high pH and high salt content. The low molecular weight aromatics are characterized though LCMS and the nanoparticles are characterized by microscopy, nanoparticle tracking analysis, and zeta potential.  By studying the relationship between the structure of the lignin and composition of products we elucidate the mechanism of product formation and gain insights into the tunability of the conversion chemistry. For example, we see higher flavonoid yields are associated with the harsh extraction conditions of the Klason process, providing insight into the secondary reactions among depolymerization products. 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.

Effects of lignin source and extraction on green depolymerization processing:  Product composition and yields

ACS Spring 2022

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