Exploring Cellulose Fast Pyrolysis Secondary Reactions Through Reactive Molecular Dynamics and Direct Insertion Probe Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

Although extensive literature exists on the depolymerization, fragmentation, and dehydration reactions occurring during cellulose pyrolysis, little is known about the secondary reactions involving dehydrated and fragmented oligomeric molecules that lead to the formation of highly modified oligomeric products in bio-oils and char. These secondary reactions are of significant practical importance. The highly dehydrated and modified dimers and trimers present in bio-oils are believed to act as coke precursors during hydrotreatment, while the larger oligomeric products contribute to char formation during pyrolysis. To bridge this knowledge gap, this study employs molecular dynamics simulations using the reactive force field (ReaxFF) to investigate the secondary reactions of dehydrated cellulose oligomers and the mechanisms driving heavy fraction formation. Postsimulation analysis identified over 400 reactions, proposed multiple reaction networks, and revealed key intermediates. To validate the modeling strategy, theoretical predictions were compared with experimental data obtained via direct insertion probe Fourier transform ion cyclotron resonance mass spectrometry (DIP FT-ICR MS) in the 87–1000 Da mass range. Probability distribution functions and molecular weight distribution analysis showed a 77% overlap between ReaxFF predictions and DIP FT-ICR MS data, confirming the reliability of the modeling strategy in forecasting fast pyrolysis behavior. Further validation was achieved through a van Krevelen diagram, which demonstrated that char fragments derived from ReaxFF simulations closely aligned with experimental data for cellulose char obtained at 400 °C. By integrating computational and experimental approaches, this study provides new insights into the secondary reactions of cellulose oligomers, highlights the role of key intermediates and water removal in these processes, and offers new opportunities for advancing selective biomass conversion technologies.