A study on the structural features of the water-insoluble fraction (WIF) isolated from biomass slow steam pyrolysis liquids

•WIFs were isolated from pyrolysis liquids of biomass model components and A.donax.•WIF chemical features are different from those of the parent feedstocks.•WIFs from the cellulose and xylan pyrolysis liquids are similar to humins.•WIF from the lignin pyrolysis liquid is a mixture of oligomers (m/z 100-800).•WIF from the A. donax pyrolysis liquid is a mixture of lignin oligomers and humins.

This work focuses on the isolation and characterization of the water-insoluble fraction (WIF) of liquids obtained from biomass pyrolysis. This fraction, usually referred to as pyrolytic lignin, contributes significantly to the viscosity, reactivity and instability of the pyrolysis liquids. The WIF isolated from pyrolysis liquid produced by the slow steam-assisted pyrolysis of A. donax canes was compared to the WIFs isolated from pyrolysis liquids of model biomass single components (cellulose, xylan and lignin). The WIFs were characterized by gas chromatography-mass spectrometry, thermogravimetry, infrared spectroscopy and photoionization mass spectrometry coupled with an ion trap analyzer. Overall the data allowed to define the structure of the WIF most abundant components and to relate the WIF composition to the structure of the parent feedstock. Evidence for synergistic effects among the components was also found in real biomass suggesting that biomass acts differently than the sum of its main components.