Methodologies for bio-oil characterization from biomass pyrolysis: A review focused on GC-MS

Residual biomass pyrolysis offers a promising route for the production of bio-oil, which can be further processed into various green value-added fuels and chemicals. However, the complex composition of bio-oil requires thorough physicochemical characterization to optimize conversion processes and improve biomass-to-liquid technologies. This review provides a comprehensive appraisal of the influence of operating conditions, particularly biomass components, on the composition of bio-oil produced by pyrolysis, addresses physicochemical characterization methods, focusing on Gas Chromatography-Mass Spectrometry (GC-MS) for chemical analysis. Various analytical methods were reviewed, revealing differences in sample preparation, injection conditions, temperature programs, heating rates, chromatographic column dimensions, and stationary phases. The variety in methods difficult data comparison and highlights the need for standardized methodologies. While some approaches yield well-defined chromatograms with effective separation of bio-oil components, further assessments of repeatability and reproducibility are essential - both across laboratories using identical samples and within laboratories using varying samples. After compound identification, quantification using either GC-MS or GC-FID (GC with Flame Ionization Detection) with appropriate standards is recommended to enhance the reliability and validity of the results. Additionally, because GC-MS primarily identifies semi-volatile and volatile compounds, complementary techniques are necessary for a more comprehensive analysis. This review provides crucial insights into the existing methodologies and compiles a database of frequently identified compounds by GC-MS, aiming to support tool to the development of standardized methodologies for the accurate and comprehensive characterization of pyrolysis-derived bio-oils.