Disassembly of lignin and chemical recovery in supercritical water and p-cresol mixture Studies on lignin model compounds Kazuhide Okuda, Satoshi Ohara, Mitsuo Umetsu, Seiichi Takami, Tadafumi Adschiri * Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Received 25 June 2004; received in revised form 20 March 2007; accepted 20 March 2007 Available online 30 May 2007 Abstract The aim of the study was to gain insight into the role of the each unit of lignin in the formation of products. Glycerol, guaiacol, the mixture of glycerol and guaiacol (Gly&Gua), and guaiacylglycerol-b-guaiacyl ether (GGGE) were used as lignin model compounds to study fragmentation of lignin in an excess of water and p-cresol at 400 °C. The products have been analyzed employing gas chromatog- raphy (GC)–mass spectrometer (MS) and gas chromatography-frame ionization detector for qualitative and quantitative analysis. GC– MS analysis indicated that phenol, o-cresol, methyl-anisole, di-methyl-phenol, ethyl-methyl-phenol, 2-(hydroxy-benzyl)-4-methyl-phenol (BMP) and 2-(2-hydroxy-5-methyl-benzyl)-4-methyl-phenol were formed. The products were similar to the products by the fragmenta- tion of lignin. The products, except o-cresol, were primarily derived from glycerol and/or guaiacol. We also found that the amount of BMP derived from GGGE, which has glycerol unit and guaiacol unit in its structure, is much more than that derived from Gly&Gua. The increase of the BMP yield by reaction with GGGE compared with (glycerol and/or guaiacol) indicates that guaiacylglycerol unit with linkage of Gly&Gua plays an important role in the formation of BMP and also it is suggested that the BMP formation from GGGE has pathways other than that from Gly&Gua. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Lignin model compounds; Supercritical water and p-cresol mixture; GC–MS (FID); Chemical recovery; Formation pathway 1. Introduction Plant biomass has attracted resent interest as a potential substitute for petroleum. Various conversion processes are proposed that liquefy biomass to use as the alternative source of fuel (Mok and Antal, 1992; Ando et al., 2000; Sakaki et al., 1996; Antal et al., 2000; Sasaki et al., 1998, 2000). In addition to the use as a fuel, biomass is also a rich source of chemicals (Dorrestijn et al., 2000). Plant biomass consists of approximately 50 wt% cellulose, 30 wt% hemi- cellulose, and 20 wt% lignin. Lignin is a complex hetero- polymer of trans-p-coumaryl, coniferyl, and sinapyl alcohols (Lin and Dence, 1992; Adler, 1977; Nakano, 1992) and is a potential source of aromatic chemicals. Freudenberg (1939); reported the production of vanillin from lignin by an alkali-nitrobenzene method (Nakano, 1992). One of the authors (Saisu et al., 2003) also demon- strated the conversion of organosolv lignin, which is a soluble component of lignin in organic solvents, into chem- icals in a water–phenol (2.5:0.75 g) mixture at 400 °C. However, prolonged reaction time can result in uncon- trolled polymerization during the decomposition process, leading to low conversion/selectivity and the formation of char. We found that an increase in the ratio of phenol, which presumably serves as a capping agent for reactive intermediate products to prevent unfavorable polymeriza- tion, decreased the formation of char (Okuda et al., 2004a,b). Recently, we have succeeded in the complete dis- solution of lignin in a water-p-cresol (1.8:2.5 g) mixture at 400 °C without formation of char. We also successfully converted lignin into chemicals with low molecular weight 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.03.062 * Corresponding author. Tel.: +81 222175629; fax: +81 222175631. E-mail address: ajiri@tagen.tohoku.ac.jp (T. Adschiri). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 1846–1852