Characterization of Birch Wood Pyrolysis Oils by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Insights into Thermochemical Conversion

A laboratory-scale reactor was used to produce pyrolysis oils from Finnish silver birch hardwood (Betula pendula). The resulting wood distillates were characterized by ultrahigh-resolution (12 T) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled with negative-ion electrospray ionization (ESI). Two different pyrolysis temperatures were tested: 300 and 380 degrees C (the resulting oil samples were named as Oil-300 and Oil-380, respectively). The detected species were sorted on the basis of heteroatom class, carbon number, and double bond equivalent (DBE). About 1200 and 1400 unique compounds were identified from the ESI FT-ICR spectra of Oil-300 and Oil-380, respectively. These were mainly oxygen-containing compounds (O-x heteroatom classes, with x = 2-14), comprising up to 90% of all identified compounds. The compounds in the O-2, O-3, and O-4 classes comprised of different fatty acids, hydroxy/epoxy fatty acids, and diacids. The compounds in the O-5-O-8 classes comprised of mainly lignin degradation products and phenolic extractives. The compounds in the O-9-O-14 classes comprised of both low- and high-DBE compounds. Upon increasing the temperature from 300 to 380 degrees C, many compounds showed an overall decrease in their DBE and carbon number. The distribution of fatty acids in Oil-300 qualitatively matches the known lipid-derived fatty acid composition of silver birch. At a higher pyrolysis temperature (380 degrees C), hydrogenation of unsaturated C-18 fatty acids toward fully saturated compounds was observed.