Comprehensive characterization of vacuum residue and tall oil co-pyrolysis: Impact of heating methods on synergistic effects

Gradually transitioning from fossil fuels to renewable energy sources by modifying the existing refinery infrastructure is essential to reduce the risks of abrupt industrial changes and achieve net-zero emissions by 2050. To investigate the chemical interactions between vacuum residue (VR) and tall oil (TO) during co-pyrolysis, this study employed an integrated multi-analytical approach combining pyrolyzate identification and quantification, petroleomic approach via ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for heavy oil characterization, and high-temperature electron spin resonance (ESR) spectroscopy for in-situ radical measurements. Two heating regimes (slow and rapid heating) were investigated under conditions mimicking delayed coker units to evaluate the feasibility of utilizing TO as a sustainable co-feedstock. The results revealed that the heating rate significantly dictated the reaction pathway. Rapid heating increased light oil yields by approximately 10% compared to slow heating, primarily by promoting volatilization and suppressing secondary reactions. Conversely, slow heating favored radical recombination and char-forming reactions. ESR measurements showed that the VR/TO blend exhibited a lower spin concentration but a higher g -value than pure VR, suggesting that TO actively influenced radical chemistry. The spin concentration increased with heating temperature, indicating an increase in the radical population during pyrolysis. Furthermore, the petroleomic approach provides insights on VR and heavy oil composition after pyrolysis. By linking radical dynamics with detailed compositional transitions across varying thermal regimes, this study provides critical insights into the influence of biomass-derived intermediates on the thermal conversion of heavy petroleum residues, offering a technical roadmap for refinery-based co-processing.