Secondary reactions of lignin-derived primary tar components

Secondary reactions of lignin-derived primary tar components were studied with a closed ampoule reactor under the conditions of N-2/600 degrees C/40-120 s. The tar fractions from Japanese cedar milled wood lignin and model compounds were characterized with the GPC, H-1 NMR and GC/MS analyses. Changes in the tar composition indicated the following pathways; unsaturated side-chain (>C=C<) and phenolic aromatic ring, both of which are the major structures of the primary tar fraction, are the most reactive structure and would be converted to the condensation products; Then, the side-chains are cracked to form the low MW aromatics with saturated alkyl groups or -H: decarbonylation of the aldehyde groups and change in the substitution pattern of the aromatic ring also occur along with this cracking reaction; the guaiacyl (4-hydroxy-3-methoxyphenyl)-type aromatic ring in the primary tar fraction is converted to the catechol-, o-cresol- and phenol-type aromatic rings. Although the pure catechol-type compounds were stable, these compounds became reactive in the presence of the guaiacol-type compounds. Radical chain reaction through the H-abstraction from the phenolic hydroxyl groups would activate the catechol-type compounds. (C) 2008 Elsevier B.V. All rights reserved.