ARS | Publication request: Characterization of water insoluble solids isolated from various biomass fast pyrolysis oils

Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2010
Publication Date: December 21, 2010
Citation: Mullen, C.A., Boateng, A.A. 2011. Characterization of water insoluble solids isolated from various biomass fast pyrolysis oils. Journal of Analytical & Applied Pyrolysis. 90:197-203.

Interpretive Summary: Fast pyrolysis is a process of heating in the absence of oxygen that can produce a liquid product (bio-oil) from biomass like wood, grasses and agricultural residues (i.e. straws). Bio-oil is a liquid that has the potential to be refined into renewable gasoline and diesel fuels. Today these fuels are produced from crude oil in a petroleum refinery, but these refineries produce other products like chemicals. As we move to a more bio-based fuel supply, bio-fuel plants (bio-refineries) will also produce co-products such as chemicals and other bio-based materials. One potential source of such co-products is the solid water insoluble fraction of pyrolysis bio-oil which can be easily separated from the liquid product. However, these materials vary in composition depending on their source. We use a variety of analytical chemistry techniques to determine the composition of these materials derived from several sources including wood, grasses and straws. We found that the materials can vary significantly depending on what source material was used in the pyrolysis process. This information will be important to those considering producing non-fuel coproducts from pyrolysis bio-oils and those considering refining pyrolysis bio-oils.

Technical Abstract: A solid water insoluble material, 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, soystraw 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 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 composed of a wide variety of molecular weights, some > 1500 Da, were detected.