Advanced NMR characterization of AquaSolv Omni (AqSO) biorefinery lignins/LCCs

Our recently reported AquaSolvOmni (AqSO) process shows great potential as a parameter-controlled biorefinery, which allows to tune the structure and properties of the products towards their optimal use in high-value applications. Herein, we report a comprehensive NMR (quantitative 13C, 31P, and 2D HSQC) structural characterization of AqSO lignins. The effect of the process severity (P-factor) and liquid-to-solid ratio (L/S) on the structure of the extracted lignins has been investigated and discussed. Low severities (P-factor in the range 400-600) and L/S = 1 led to the isolation of less degraded lignin with a higher β-O-4 content up to 34/100 Ar. Harsher processing conditions (P-factor = 1000-2500) yielded more condensed lignins with a high degree of condensation up to 66 at P-factor = 2000. New types of lignin moieties, such as alkyl-aryl and alkyl-alkyl chemical bonds together with novel furan oxygenated structures have been identified and quantified for the first time. In addition, the formation of LCCs bonds have been hypothesized at low severity and L/S. Based on the obtained data we were able to formulate a possible outlook of the occurring reactions during the hydrothermal treatment. Overall, such detailed structural information bridges the gap from process engineering to sustainable product development.