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

摘要

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 ℃ (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 ℃, 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 ℃), hydrogenation of unsaturated C_(18) fatty acids toward fully saturated compounds was observed.