Organosolv processing of Sitka Spruce sawdust: Large scale preparation of native-like lignin and ligninOX for valorisation

Abstract

Sitka Spruce (SiS) dominates wood production in Scotland and represents an important source of wood in the UK. A systematic analysis of the lignin obtained from SiS sawdust using methano-, ethano-, butano- and isobutano-solv pretreatments was carried out. Detailed analysis of the resulting lignin using a range of methods (GPC, 31P after phosphitylation and HSQC NMR) and assessment of solvent costs enabled a comparison of the 4 pretreatment methods. The high quality of the lignin obtained reflects its stabilisation through alcohol incorporation at the α-position of the β-O-4 units. Scale up of the butanosolv pretreatment led to the controlled synthesis of a selectively oxidised form of the lignin (SiS ligninOX) on a relatively large scale. Additional insights into the detailed structure of ligninOX are presented. It is argued that this interesting, modified biopolymer may have significant potential for lignin valorisation.