Lignin holds the key for maximizing value extraction from lignocellulosic biomass. This is currently hindered by the application of fractionation methods that significantly alter the lignin structure to give highly recalcitrant materials. For this reason, it can be highly beneficial to use less-severe fractionation conditions that allow for efficient extraction of lignin with retention of the β-aryl ether (β-O-4) content. Here, we present a detailed study on mild alcohol-based organosolv fractionation with the aim of understanding how to achieve a balance between efficiency of lignin extraction and the structure of the resulting lignin polymers, using walnut shells as model biomass. Monitoring different extraction conditions reveals how the structure of the extracted lignin changes depending on the extraction conditions in terms of molecular weight, alcohol incorporation, and H/G/S ratios. Moving from ethanol to n-pentanol, it was revealed that, in particular, alcohol incorporation at the benzylic α-position of β-aryl ether units not only plays a key role in protecting the β-O-4 linking motif but more importantly increases the solubility of larger lignin fragments under extraction conditions. This study shows that α-substitution already occurs prior to extraction and is essential for reaching improved extraction efficiencies. Furthermore, αsubstitution with not only bulky secondary alcohols and tertiary alcohols but also chloride was revealed for the first time and the latter could be involved in facilitating α-alkoxylation. Overall, this study demonstrates how by tuning the fractionation setup and conditions, the resulting lignin characteristics can be influenced and potentially tailored to suit downstream demands.

Pyrolytic lignin is the collective name of the lignin-derived fraction of pyrolysis liquids. Conversion of this fraction to biobased chemicals is considered an attractive valorization route. Here we report experimental studies on the ozonation of a pine-derived pyrolytic lignin dissolved in methanol (33 wt %). Results show a high reactivity of ozone, and a molecular weight reduction of up to 40% was obtained under mild conditions (0 °C, atmospheric pressure) without the need for catalysts. Detailed analysis of the product mixtures (GC/MS-FID, HPLC, GPC, NMR) showed the presence of low molecular weight (di)­acids and esters, along with larger highly oxygenated aliphatics. A reaction network is proposed including the heterolytic cleavage of aromatic rings, followed by secondary reactions. The observations were supported by experimental studies using representative pyrolytic lignin model compounds and a biosynthetic lignin oligomer, which aided further elucidation on the reactivity trends for different chemical functionalities. Accordingly, the presence of hydroxy and methoxy substituents on the aromatic rings is shown to be the main reason for the high reactivity of pyrolytic lignin upon ozone exposure.

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Lignocellulosic biomass is a key feedstock for the sustainable production of biofuels, biobased chemicals and performance materials. Biomass can be efficiently converted into pyrolysis liquids (also known as bio-oils) by...

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