Application of catalytic hydropyrolysis for the rapid preparation of lignin concentrates from wood

The use of hydropyrolysis (hypy) is described as a potentially rapid procedure for obtaining lignin-enriched residues from wood for either simply estimating lignin content or for performing stable isotope ratio measurements. Hypy was carried out on samples of oak wood and, as reference materials, Klason lignin and pure cellulose over the temperature range of 200–500 °C. The composition of the residues were assessed by solid-state 13C NMR. At 300 and 350 °C, the extents of conversion achieved for cellulose was 88 and 95% respectively, indicating that highly lignin-enriched residues should be obtained for wood samples. This was confirmed by solid-state 13C NMR which also indicated that any remaining cellulose had aromatised to a significant extent. In addition, hypy caused quite extensive demethylation of methoxyl functionalities and cleavage of the characteristic β-O-4 ether lignin linkage. Finally, correcting the 300 and 350 °C hypy residues for residual cellulose gave estimates of the lignin content for oak wood in close agreement with those obtained by the Klason method and by solid-state 13C NMR. At 350 °C, the residual cellulose accounts for ca. 30% of the lignin concentrate obtained from hypy.