Revealing the key role of structural cross-link between lignin and polysaccharides during fast pyrolysis of lignocellulose.

Lignin-carbohydrate complex (LCC) is the native existing form of major components in lignocellulose. In this study, the structural cross-link between lignin and polysaccharides in lignocellulose was quantitatively estimated with carboxymethylation-separation (CM-Sep) method, and its influence on lignocellulose pyrolysis was systematically investigated. The cross-linked lignin was found to positively correlate with the production of small molecules and furan derivatives while negatively affecting the generation of anhydrous sugars. Content of small molecules was increased by 97% while that of anhydrous sugars was decreased by 47% in pyrolytic products with levoglucosan yield lowered by 54 wt% in the existence of cross-linked lignin. Furthermore, the impact of cross-linked lignin was revealed to be significantly distinguished from free lignin. Impeded glycosidic end formation and boosted glycosyl ring scission as well as lignin fragmentation were responsible for the distinction. Excellent correlations between structural cross-link and lignocellulose pyrolytome could facilitate product prediction and process design.