Molecular composition of oxygenated compounds in fast pyrolysis bio-oil and its supercritical fluid extracts

• A three-step supercritical CO2 extraction was developed for selective fractionation of bio-oil.
• Different compound classes were enriched in different fractions, facilitating the following analysis.
• ESI FT-ICR MS was used to characterize oxygenated compounds in bio-oil at molecular level.

A three-step supercritical CO2 extraction was used for selective fractionation of fast pyrolysis bio-oil. Oxygen-containing compounds in bio-oil and its fractions were characterized using infrared spectroscopy (IR), 1H nuclear magnetic resonance spectroscopy (NMR), gas chromatography–mass spectrometry (GC–MS) and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). With appropriate optimization of extraction parameters, lipids, hemicellulose, lignin and condensed aromatics were found enriched in three different fractions. The molecular composition and compound classes were identified by combined analytical techniques, and the selectivity of the fractionation was proved. The compound-type-specific fractionation also facilitated the following characterization and provided insights into the chemical composition of bio-oil. Results indicated that CO2 supercritical fluid extraction was potential for bio-oil preprocessing.