Characterization of water insoluble solids isolated from various biomass fast pyrolysis oils

A solid water insoluble material (WIS), commonly called pyrolytic lignin, can be isolated from biomass fast pyrolysis oils. Such material was isolated from the bio-oils produced from barley straw, barley hulls, switchgrass, soy straw and oak and then fully characterized. Analytical techniques employed in the characterization included elemental analysis, pyrolysis-GC/MS, Nuclear Magnetic Resonance Spectroscopy (NMR) and Gel Permeation Chromatography (GPC). The characterization showed that the materials were mostly but not entirely derived from the lignin fraction of the biomass; they were largely made up of aromatic rings, substituted with varying amounts of methoxy groups and linked by varying types of aliphatic linkers. The NMR identified different types of aliphatic linkers in the isolates, some previously reported and some newly proposed. GPC analysis showed that the dimers and trimers were the most common oligomeric size though units comprising a wide variety of molecular weights, some >1500 Da, were detected.