Ultrasound-Assisted Sequential Extraction for Lignocellulose Pyrolysis Bio-oil Fractionation. Part II: Comparative Application

Building upon the novel ultrasound-assisted sequential extraction (UASE) method introduced in Part I, the second paper delves deeper into the fractionation and analysis of bio-oils produced from lignocellulosic pyrolysis. The current study exploits advanced analytical techniques such as GPC-UV-DAD and negative-ion Electrospray Ionization (ESI) coupled with ultrahigh-resolution mass spectrometry, 21 T FT-ICR MS, to facilitate a detailed comparative analysis of various bio-oil samples produced from lignocellulosic pyrolysis. The results highlight significant differences in composition, molecular weight distribution, and oxygen content as a function of process conditions, which demonstrate the efficacy of the UASE method to distinguish different types of bio-oils. A sample generated by reactive catalytic fast pyrolysis (RCFP) reveals a composition that has potential for fuel production, evident by its low oxygen-to-carbon ratio and high concentration of non- to moderately polar fractions. Interestingly, the most polar fraction obtained by the UASE method has a GPC elution behavior consistent with lignin standards, indicating that the method unravels “undesired” pyrolysis byproducts and recalcitrant species. The characterization workflow presented confirms the potential of the RCFP process for fuel production and advances our understanding of bio-oil molecular composition. The insights gained are pivotal for advancing bio-oil processing techniques and standardizing quality assessment, especially for industrial applications, thereby continuing the advancement of bio-oil research established in the first paper of this two-part paper series.