The Upgrading of Lignin-Derived Compounds: Case Studies on Model Compounds

Abstract

One of the strategies of interest in the upgrading of lignin isolated from various pretreatment processes, is its depolymerisation followed by selective up-grading to either chemical industry intermediates such as phenol and BTX’s or deoxygenation to fuel substitutes. Using a prototype of the aromatic methoxy linkage, i.e. Anisole (Methoxy benzene), the pyrolytic pathways in the presence and absence of a hydrogen donor solvent (Tetra-lin) have been studied under high temperatures and pressures close to or exceeding supercritical conditions for both components. At high tetralin to anisole ratios the condensible products are phenol and toluene in about 4:1 ratio. The homogenous reaction produces a wide slate of compounds including benzene, cresols and polymer in addition to phenol and toluene. Evidence is provided for a free radical initiation in both cases with the initiating step being the thermolysis of the methyl-oxygen linkage leading to methyl and phenoxy radicals. The propagation steps, however involve the phenoxymethyl radical which appears to be able to invert the oxygen aryl linkage in favour of the aryl carbon linkage through a long lived spiranic oxiran radical intermediate, thus explaining the benzaldehyde and benzyl alcohol production.