Molecular Characterization of Polarity-Based Fractions of Bamboo Tar: Implications for Upgrading Challenges

Bamboo tar, produced from bamboo pyrolysis, is a promising renewable feedstock for fuels, chemicals, and carbon materials. However, its complex chemical composition—particularly the presence of highly oxygenated polar compounds—poses significant challenges for efficient upgrading and high-value utilization. In this study, five distinct polarity fractions of bamboo tar were separated by column chromatography and investigated using gas chromatography–mass spectrometry (GC–MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results revealed that the moisture content and oxygen content of bamboo tar were 15.70% and 28.43%, respectively. Besides, the yields of non/weakly polar fractions (F-I, F-II, F-III) and polar fractions (F-IV and F-V) were 8.16% and 35.82%, respectively. GC–MS analysis of the non/weakly polar fractions revealed phenolics (24.08%), furans (15.99%), and methoxyphenols (13.10%) as the predominant volatile compounds, which hold promise for applications in biofuels, biochemicals, and biobased materials. FT-ICR MS analysis of the polar fractions uncovered a dominance of O4–O6 class compounds, primarily polycyclic aromatic structures enriched with oxygen-containing functional groups, concentrated in the lignin-derived region of van Krevelen diagrams (0 ≤ O/C ≤ 0.6, 0.5 ≤ H/C ≤ 2.0). The high abundance of polyoxygenated aromatic compounds with labile oxygen-containing substituents is identified as the structural basis for the thermal instability, coking propensity, and upgrading challenges of bamboo tar. These findings provide theoretical guidance for the efficient processing of fractions with different polarities from bamboo tar and other lignin-derived pyrolysis oils.