Stable carbon isotope analysis of wood hydropyrolysis residues: A potential indicator for the extent of cross-linking between lignin and polysaccharides

Hydropyrolysis (hypy) as a fast means for preparing lignin concentrates for stable carbon isotope analysis was evaluated by performing hypy at different temperatures (200–500 °C) on Klason lignin concentrates, cellulose, and wood samples followed by bulk stable carbon isotope analysis of the solid residues. The δ 13 C values of cellulose, Klason lignin and their hypy residues revealed that hypy does not produce isotopic fractionation throughout the temperature range explored. The δ 13 C of hypy residues from cellulose-Klason lignin physical mixtures obtained at 500 °C were in the value range of the corresponding Klason lignin indicating that cellulose decomposed completely and that no major structural rearrangements, which could lead to carbon cross-linking between these two moieties are produced by hypy. The hypy residues obtained from wood samples at 500 °C were consistently depleted in 13 C by 0.8‰ and enriched by 1.6‰ relative to the original wood and Klason lignin, respectively. This finding results from polysaccharide derivatives remaining in the wood residue, with a percentage of polysaccharide derived carbon 1.9 and 3.7 times higher than expected at 300 and 350 °C, respectively. It is concluded that the results presented here provide an indicator of the extent of cross-linking between lignin and polysaccharides (hemicellulose) in the native wood forming lignin–carbohydrate complexes.