Sustainable Aromatics: Synthesis and Hydrogenolysis of Lignin Monomer Compounds

Plant biomass is an ideal alternative source to address the increasing demand for oilderived chemicals. Lignin constitutes ca 35% of dry woody biomass and is produced as a non-commercial waste by-product from the Kraft Pulping industry. The polyphenolic chemical structures of lignin are built largely from guaiacolpropane subunits units linked through C-C and ether C-O bonds, which resist degradation of the woody biomass. Guaiacol represents around 40% of the phenolic monomers within digested lignin. We have investigated processes that might be commercially viable for the hydrodeoxygenation of poly–oxygenated aromatic compounds including guaiacol and vanillin, which could come from digested lignin. The use of mild, low energy conditions have been achieved efficiently using phenolic activation with cyanuric chloride; the subsequent hydrogenolysis reactions have been developed into a flow process that gives selective and high yielding formation of aromatic fine chemicals such as anisole, meta-methoxybenzyl alcohol and benzoic acid. Cyanuric chloride is a potentially cheaper and/or recyclable reagent for the activation/hydrogenolysis of lignin monomer compounds. A viable flow hydrogenolysis process has been developed for tri-substituted triazine compounds using a cascade continuous stirred tank reactor.