Application of catalytic hydropyrolysis for the rapid preparation of lignin concentrates from wood Laura E. Beramendi-Orosco a , Miguel Castro-Dı ´ az a , Colin E. Snape a , Christopher H. Vane b , David J. Large a, * a Nottingham Fuel and Energy Centre, School of Chemical, Environmental and Mining Engineering (Scheme), University of Nottingham, University Park, Nottingham NG7 2RD, UK b British Geological Survey, Keyworth, Nottingham NG12 5GG, UK Received 7 January 2003; accepted 22 July 2003 (returned to author for revision 5 May 2003) Abstract 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 13 C 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 13 C 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 b-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 13 C NMR. At 350  C, the residual cellulose accounts for ca. 30% of the lignin concentrate obtained from hypy. # 2003 Elsevier Ltd. All rights reserved. 1. Introduction Lignin and its phenolic derivatives are an important source of palaeoenvironmental data (Huang et al., 1999; Orem et al., 1997; van Bergen and Poole, 2002). Since it is an aromatic polymer with a complex three-dimensional network comprising phenyl-propane units (Sarkanen and Ludwig, 1971), it is possible to isolate lignin either as an insoluble residue or by dissolving it (Schubert, 1965). Amongst the wet chemical methods (Table 1), Klason lignin is considered as the standard method for measur- ing lignin content. To prepare Klason lignin, wood is treated with sulfuric acid to hydrolyse polysaccharides to water-soluble sugars to recover lignin as an insoluble residue (Adams, 1965; Obst and Kirk, 1988). Although this method is considered to be a good quantitative technique for determining the lignin content of wood, it does modify the structure of lignin by condensation reactions and by adding a considerable amount of HSO  4 groups (Fengel and Wegener, 1983; Obst and Kirk, 1988). The most appropriate, least altered, lignin prepara- tion for chemical and biological studies is Milled Wood Lignin (MWL), also known as Bjo¨rkman lignin. How- ever, aqueous p-dioxane extraction of finely milled wood gives lignin in low yields ( < 20% of total lignin). The method is also time consuming, taking several days to complete and leaves a crude MWL that contains up 0146-6380/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2003.07.001 Organic Geochemistry 35 (2004) 61–72 www.elsevier.com/locate/orggeochem * Corresponding author. Tel.: +44-115-9514114; fax: +44- 115-9514115. E-mail address: david.large@nottingham.ac.uk (D.J. Large).