Currently available commercial (technical) lignins are typically severely degraded and condensed compared to native lignin. This makes such lignins hard to utilize for selective depolymerization to aromatic platform chemicals as well as for the synthesis of functionalized polymers with defined structures. This asks for new approaches to lignin valorization that involve lignin-first strategies that either depolymerize lignin during extraction or by isolating lignin that is less degraded and condensed. To enable the latter approach, we have been working on the efficient organosolv extraction of lignin under mild conditions. Utilizing relatively low temperatures (&lt;120°C), acidic alcohol/water mixtures as extraction solvent in a flow-through setup, we have demonstrated extraction efficiencies of over 90% with very high retention of the regular β-O-4 structure. A key to the success of this extraction was shown to be the selective incorporation of alcohols in the lignin structure under reaction conditions which increases the solubility of larger lignin fragments. It was shown that this incorporation already occurs in the lignin trapped in the solid lignocellulosic matrix. An issue with the efficient extraction of lignin utilizing butanol as solvent is it that also butoxylated carbohydrate monomers like butyl-xyloside are formed. These co-precipitate with lignin leading to impure lignin. Therefore, we developed an in-line biphasic purification methodology using a continuous centrifugal contact separator that allows to remove most carbohydrate impurities and additionally facilitates lignin precipitation. Overall, these isolated lignin with a relatively regular structure high in β-O-4 content allow for selective modification strategies to make all types of novel lignin materials with tuned properties or allow for more efficient selective depolymerization to specific phenolic compounds.

Highly efficient mild organosolv lignin extraction and purification in flow and the importance of benzylic alkoxylation

ACS Spring 2022

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