Combining Fractionation and High-Resolution Mass Spectrometry Approaches to Characterize a Bio-Oil From Flax Shive Pyrolysis.

In a context where environmental concerns and circular economy drive innovation, co-products from the flax industry emerge as valuable lignocellulosic feedstocks. Pyrolysis of these biomasses generates bio-oils with complex and highly oxygenated composition, which requires in-depth molecular characterization to optimize valorization processes. This study focuses on the molecular-level characterization of bio-oil derived from flax shives, a local co-product in Normandy. Size-exclusion chromatography (SEC) was used to fractionate the bio-oil into five distinct fractions based on apparent molecular size. The complete bio-oil and each SEC fraction were then analyzed by high-resolution mass spectrometry (Fourier-transform ion cyclotron resonance [FT-ICR MS] and Orbitrap MS) to identify and compare thousands of molecular formulae. A custom Python-based workflow was developed to align and annotate Orbitrap MS data using the FT-ICR MS dataset as a reference, allowing for rapid molecular formula assignment. Chemical class distribution, oxygen content, and Van Krevelen analysis revealed specific trends across fractions, indicating that SEC separation was influenced not only by molecular size but also by polarity and structural interactions. This approach offers a refined strategy for exploring the chemical complexity of lignocellulosic bio-oils and supports future efforts in their upgrading and application.