11.1 Introduction Lignin accounts for 20–30 % by weight of lignocellulosic biomass , and is a promis-ing renewable resource for the production of aromatic chemicals and bio-fuels [ 1 ]. It is composed of phenylpropane units containing three different aromatic ring sub-stitution patterns: p -hydroxyphenyl (H), guaiacyl (4-hydroxy-3-methoxyphenyl , G) and syringyl (3,5-dimethoxy-4-hydroxyphenyl , S) [ 1 ]. Softwoods contain a greater proportion of G units and smaller amounts of the H type, whereas hardwood s con-sist of G and S units while herbaceous species contain G, S and H units [ 1 ]. These monomers are linked together through ether (C–O) and condensed (C–C) bonds. Accordingly, lignin pyrolysis proceeds heterogeneously, depending on the plant species . This is in contrast to the pyrolysis of cellulose, a homogeneous polymer of D-glucose units connected via β-1 → 4 linkages . In this chapter, molecular mechanisms involved in lignin pyrolysis are discussed with the focus being primarily on G-lignin after the brief analysis of the devolatil-ization temperature of lignin and the product compositions. Although many papers have reported theoretical investigations of specifi c pyrolysis reactions of lignins, this chapter concentrates on the results of experimental investigations conducted by the author's research group.
Kawamoto, H. (2016). Molecular Mechanisms in the Thermochemical Conversion of Lignins into Bio-Oil/Chemicals and Biofuels (pp. 321–353). https://doi.org/10.1007/978-981-10-1965-4_11